View Full Version : 292 get best mileage


simplyMyself
05-06-2008, 09:33 PM
I am looking to keep my 292 inline Chevy with my 65 pickup, but I would like to try and get better mileage out of it. These are my considerations that are more simple.


3.50-4.10 rear
5 speed transmissionMy next consideration is to put in a MPI or TBI system to tune in better mileage. I have the original single barrel that is being rebuilt right now and was wondering if any thought it would be worth just keeping that, but I am leaning towards a MPI system down the road.

Does anyone have any better ideas?

scottybaccus
05-06-2008, 10:27 PM
The biggest issue is weight. With limited torque, you will have your foot deeper in it to get rolling. On the hiway, you may be fine, but stop & go will kill ya.

You didn't say what your target is. Even a light weight truck is doing well to get 20 mpg hiway. What have you seen so far?

old dirt tracker
05-06-2008, 10:34 PM
your fighting a losing battle trying to get mileage from a 292. that said the bigest bang for your buck is a higher gear rear end.

simplyMyself
05-06-2008, 11:02 PM
The biggest issue is weight. With limited torque, you will have your foot deeper in it to get rolling. On the hiway, you may be fine, but stop & go will kill ya.

You didn't say what your target is. Even a light weight truck is doing well to get 20 mpg hiway. What have you seen so far?
I am shooting for about 20mpg if I can with my C10. I am leaning closer to 4.10 and hoping to shoot around 1900rpm.

MPI will be the last thing tackled, with first shot towards the new rear gear. I am thinking of a T5 from a S10.

scottybaccus
05-06-2008, 11:08 PM
I think you're bringing a knife to a gun fight. If you ever abuse that T5 in such a heavy truck, you'll be on the expensive end of a bad deal.
Even with EFI, that's not much motor. If you really want good driveability and mileage, think bigger. A 283 with efi and a 700r4 would be a step in the right direction. The best available would probably be to dig up a 4.8 LS1 from a late model truck. You could probably find one with a matching 5 speed that would be better suited than the T5.

63Biscuit
05-07-2008, 01:53 PM
I wondered how posts it would take before someone tried to convert you to a V8! Keep 'em in a row!

Have you consider other possibilities? These could be taller rear tires (although it'll hose your speedo) or improved aerodynamics (OK, weird when applied to a truck, but include a slight lowering of the front end, skinnier front tires, or even a subtle chin spoiler). Hell, I remember C10s have HUGE side view mirrors...you could replace them with something off a modern pickup.

belair
05-07-2008, 02:01 PM
A truck is a heavy brick. Scotty is on the money. F.I. and gears would help, but the laws of physics are unrelenting taskmasters.

simplyMyself
05-07-2008, 02:11 PM
I have lived the V8 life all of mine and have chucked a inline once upon a time. This time, the I6 will stay, but I want to do the best I can with it. It is partially taste and heck, if I did what everyone else did, I would be just like everyone else. I have spent my whole life not being like everyone else, with exception to the engines (still yet to get a 327 at some point). I know I could get a newer engine and slide it in with all the EFI ready to go, but now what would the fun be to getting a bit creative.

Now if anyone has a suggestion that keeps me in my 292, please spread the gospel, but for the V8's, thank you very much for considering the bigger badder, but for once I think I need to keep the 292.

Halfton65
05-07-2008, 02:23 PM
My 292 is getting 10-12 with a Rochester 1 bbl. If you can find a Holley Economaster for the 292 you'll be golden. There was one on my truck for 20+ years(8 of those years sitting)-zero maintenance and it got 16+ mpg.

I really miss that carb :(

cwatson1953
05-07-2008, 02:24 PM
i've got a 292 in my '53 chevy sedan. can't tell you much about my mileage cause its yet to see that much of the road.
but it will be my daily. i've talked to and seen guys running 292s in full bodied/heavy cars that claim they can get 20 on the highway. maybe true, stop and go traffic is different....and a truck may be a different story.

i know one thing, and this is straight from Tom Langdon's mouth,...that stock 1 bbl ain't enough. you'll get better performance and possibly gas mileage out of a SMALL 4bbl.
Tom told to me that the 292s fuction way better with a carb(s) as close to 400cfm as possible. he recomended a holley 390, i went with a carter AFB 500.
that stock 1bbl i THINK is onlt about 200cfm.
OR a 2x1 set-up.
i know i'm not gonna get the greatest MPG ever, my 292 has a mild cam, headers, and a single 4 bbl, but i don't think it will be all that bad.

raven
05-07-2008, 02:25 PM
Keep the 292.
The 283 backed up with a 700r4 will still need a steep gear to be efficient.
The 292 has enough torque since it's a long-stroke motor.
Go with a 390 cfm four barrel carb and headers to breathe along with a good ignition and you have a good, durable combination.
Remember, to direct your attention to increased efficiency. That means breathability and accurate, strong spark along with an efficient air/fuel mixture.
Find out where your modified combination starts to climb up on the cam and set your gearing to run there for most driving applications. Put a 5 speed behind it, too.
r

FiddyFour
05-07-2008, 02:28 PM
wow
i hope louver dude sees this post... he's got a 250 six in his 53 chevy and with a 200r4 he was getting close to 26mpg with it... no reason NOT to expect numbers above 20mpg for a 292

cwatson1953
05-07-2008, 02:31 PM
wow
i hope louver dude sees this post... he's got a 250 six in his 53 chevy and with a 200r4 he was getting close to 26mpg with it... no reason NOT to expect numbers above 20mpg for a 292

26! thats badass!
i gotta scrap this TH350...

58Fridge100
05-07-2008, 03:03 PM
I think it's a cool idea.

I say stick with it--
http://67-72chevytrucks.com/vboard/showthread.php?t=276823



For any others that are interested in hearing why MPI doesn't work on a Chevy 6, follow along. These 6 cylinders all have an intake port design called "siamese", where cyls 1&2 share a runner, as do 3&4 and 5&6. This goes right into the head, so the two intake valves are effectively side by side, drawing on the same runner. So what's the big deal? The valves are open an equal amount of time, so no problem, right? Well, no, because of the firing order which is 1-5-3-6-2-4. Obviously, any fuel injected (even at the port) can only really enter the cylinder when the valve is open. And any fuel injection system will have the injectors open up to 80% of the available time (when wide open). But, the valves are really only about 25% of the time, so the fuel just puddles on the backside of the valve. In SB chevys, this is no problem, because when the valve does eventually open, the fuel enters the cylinder, just as intended.

Okay, lets look at that firing order again (1-5-3-6-2-4). Notice how the space (and thus the time) is not equal between 1 and 2 (and also 5 and 6)? 1 fires, then 3 other cylinders fire, then 2 fires, then 1 other cylinder fires. What this means in terms of fuel is that #2 gets 2/3 of the fuel, and #1 gets 1/3 of the fuel. Not exactly an ideal mixture.

This doesn't happen with a carb, because all air contains fuel, so the cylinder breathes when it wants, and gets the same air/fuel mixture.

In my case, I was stumped by why #1 and #6 were always lean, and #2 and #5 were always rich (leading to bad stumbling at times).

Should have thought about this earlier, but then one day I discovered this link: http://www.starchak.ca/efi/siamese.htm
which explains the whole thing with far more mathematics than I want to get into here. They even propose a few solutions, but I would chalk them up as impractical.

Anyway, fed up with the MPI (and not yet knowing the explanation of why it didn't work), I switched the throttle body over to a GM TBI (real cheap and reliable, these things). Well, that cleaned the problem up right away, and had some side benefits: easier installation, less wiring ratsnest, cheaper, looks more like stock (if that matters to you).

I'm kind of thinking (but never tried) that a dual TBI on a dual 4bbl manifold would be the ultimate because it would cut down the runner length for the fuel and it would make the manifold more symmetrical for more even air/fuel distribution.

Old wolf
05-07-2008, 04:10 PM
We have some trucks with 292s they will out pull v8s but use lots of fuel mainty due to 456 gears. Our 64 3/4 ton wrecker gets 23 mpg with a 81 250 intergrated head with a 1 bbl rochester and 390 gears with285 75 r 16 tires. I was thinking of putting an intergrated head on a 292 they have a stainless steel plate type gasket between the intake and exhaust that superheats the gas after it leaves the carb.If you polished and cced the combustion chambers i dont think the compression ratio would be a problem.:cool:OlsWolf

wvenfield
05-07-2008, 04:19 PM
An efiecient carb, better breathing exhaust, gears and more efficient tranny will likely gain you a little.

Then the question is, is the cost above worth the gains. Not to piss anyone off, but I don't believe 26.

Gemini EFI
05-07-2008, 04:25 PM
I think it's a cool idea.

I say stick with it--
http://67-72chevytrucks.com/vboard/showthread.php?t=276823
Agreed! The TBI will make the problem go away on most street engines. If you make a lot of power requiring serious amounts of fuel delivery the problem comes back. My blown and TBI injected truck makes 460 H.P. and does not have the problem. Harry Sternemann's 800 H.P street driven 9 second '38 Chevy does. That's because of the volume of fuel required. My truck weighs 3400 lbs.Holley 4 barrel TBI, Clifford headers, .512 lift, MSD. 12 lbs. boost. 3.55 rear, 700R4,12.70 on street tires. Gets 16 MPG the way I drive it (hard).
I can guarantee going to a 283 would be a step backwards in torque.
Gemini EFI

BlackCherryImpala
05-07-2008, 04:31 PM
I've always passed on the integrated head 250's even when I have found them at reasonable prices because I've heard guys say they are problematic, cracking and so forth. Have you witnessed any problems? If no, I'll certainly reconsider one when I find one on the cheap. Thanks for the info. I like the mileage your 64 is getting. BlackCherry

We have some trucks with 292s they will out pull v8s but use lots of fuel mainty due to 456 gears. Our 64 3/4 ton wrecker gets 23 mpg with a 81 250 intergrated head with a 1 bbl rochester and 390 gears with285 75 r 16 tires. I was thinking of putting an intergrated head on a 292 they have a stainless steel plate type gasket between the intake and exhaust that superheats the gas after it leaves the carb.If you polished and cced the combustion chambers i dont think the compression ratio would be a problem.:cool:OlsWolf

Old wolf
05-07-2008, 05:00 PM
There are two types of intergrated heads one has a 2 bbl carb and dual pipes. The one we use has a 1 bbl carb and a single 2 3/4 pipe with a 3 bolt flange this type doesent seem to crack like the 2 bbl ones do. Also electronic ignition will help.:cool:OldWolf

fordorford
05-07-2008, 05:14 PM
The 292 is inherently a gas hog. The 250 will run circles around it, mileage wise. It is a real stump-puller, but it loves gasoline.

oldsman71
05-07-2008, 05:30 PM
higher gears might make better use of the 292 in stock form. I had one in a 65 chevy pu we put 3:08 in it. it ran better than the 3:90 did! good luck. cjc

scottybaccus
05-07-2008, 09:09 PM
fuel economy is simple math. First CIDxRPM/3456 is theoretical volumetric efficiency of 100%. The best street engines are lucky to find 85%. That is just a frame of reference. Now take a 40 year old inline 6 and the awkward intake and exhaust paths they used and you can imagine that they manage maybe 65-70% ve.
Now take into account that it takes about one half pound of fuel per HP per hour in a gasoline engine. Can't change that, it's just a fact based on the BTU output of gasoline.
Now consider parrasitic losses. Maybe 10-15% through a good transmission and rear gear, more if it's unusually deep for pulling. Then add in the wind resistance of a 6' wide brick that stands 6' high and catches air in the wheel wells, under the chin, on the tailgate, mirrors and even the rear bumper.
All this rolls up to 2 factors. How fast do you drive and how quickly to you accelerate to get there? Say you can achieve 26 mpg at 1850 rpm, that may be at 35 mph or 65 mph, depending on all of these parasites. Now, do you achieve 60 mph in 3 seconds or 13? It takes each vehicle a given HP to accelerate in a certain time frame and then another given HP to maintain that speed. A 2007 vette can pull near 30 mpg at 70 due to the right final drive ratios and tremendous aerodynamics. Put that exact powertrain in a '62 Chevy truck and I seriously doubt you see half that.
I love inline motors. I just don't think you will see good mileage with such a stacked deck. Anyone claiming 26 mpg, I doubt they are in metro freeway conditions or sustained 70 mph.
imho

dutchtreat
05-07-2008, 09:37 PM
Here is my 2 cents on the subject.
Start with a the later model T-5 trans and use one of the TBI intake setups that Chev put on the 305 Truck engines on a Clifford or Offy 4 barrel intake with the adapter to take the TBI unit. Then go with a set of headers and 2.5" exhaust-Clifford made a dual exhaust header setup. If you go single exhaust go start at 2.5" and open it up to 3"
There is a place in Arizona that does TBI systems and they can make it work for you. This should get you 20MPG if you keep your foot out of it on the road. I built a 1969 Ford 1 ton van and with a rebuilt 302 (I rebuit it) got 18MPG Highway (city was 13 to 14mpg) with a C-4 (that means no over drive) and a Holley 4 barrel setup with the RV power valve.
A 292 with it's larger stroke will get better mileage than a 250 as TQ is what gets you going and if you use a Vac. gauge to drive off city driving will be good too.
Good Luck
Dutch

simplyMyself
05-07-2008, 09:43 PM
There are some seriously great responses from the group. I know I am looking for something that could quite a reach, but considering the issue with the MPI, That is one area that will need to be reconsidered completely.:o

It appears that at least a 4 hole carb is likely the next spot to look at and from what it looks like, a 390-400cfm. Possibly a TBI if I want to screw with electronics that much. :rolleyes:

Gearing and a 5-speed will be the next place to review.:cool:

[Next question - Edelbrock or Holley?]:confused:

willowbilly3
05-07-2008, 09:49 PM
All the 292s I was ever around were thirsty critters, it'll never see 20 mpg unless you can coast off the continental divide with a strong tailwind. If you want an economical (chevy) six then get a 250. It has respectable power and is much more efficient, or better yet put a 300 Ford in it.

58Fridge100
05-07-2008, 10:31 PM
I don't realistically think that there is any secret to the difference between a 250 and a 292.
For one thing, the 250 was far more likely to be found in a much lighter vehicle straight from the General.

Another thing to consider is, of course- is the low static CR (with a cam that matches) you are working with, and the anemic single bbl carburetor. This motor can't be very efficient in stock form, and has to possess a really short diesel-like powerband...
Being asked to pull around a 4 to 5,000 lb vehicle with a long legged three speed manual transmission-- of course it will be very thirsty. It's being asked to perform outside of it's tiny little sweet spot for the majority of it's operating period.

The great thing about the 292 is that it's a stroker, so it HAS to be an ideal straight six to pull that truck around. It just needs a larger powerband, and like everyone else says- some extra gears w/overdrive.

I'm not so sure that headers/ large diameter exhaust is something that's required. In fact, with a respectable "RV" type cam, a little smaller exhaust will help the efficiency of the motor through improved exhaust scavenging..

willowbilly3
05-08-2008, 01:38 AM
I don't realistically think that there is any secret to the difference between a 250 and a 292.
For one thing, the 250 was far more likely to be found in a much lighter vehicle straight from the General.

Another thing to consider is, of course- is the low static CR (with a cam that matches) you are working with, and the anemic single bbl carburetor. This motor can't be very efficient in stock form, and has to possess a really short diesel-like powerband...
Being asked to pull around a 4 to 5,000 lb vehicle with a long legged three speed manual transmission-- of course it will be very thirsty. It's being asked to perform outside of it's tiny little sweet spot for the majority of it's operating period.

The great thing about the 292 is that it's a stroker, so it HAS to be an ideal straight six to pull that truck around. It just needs a larger powerband, and like everyone else says- some extra gears w/overdrive.

I'm not so sure that headers/ large diameter exhaust is something that's required. In fact, with a respectable "RV" type cam, a little smaller exhaust will help the efficiency of the motor through improved exhaust scavenging..

My comparison is based on similiar model 1/2 ton pickups of the day and there was a big difference in milage between identically equipped, basic 4 speed, 2wd longbed trucks in stock form. The 292 has a well earned rep as a guzzler.

simplyMyself
05-08-2008, 09:23 AM
My comparison is based on similiar model 1/2 ton pickups of the day and there was a big difference in milage between identically equipped, basic 4 speed, 2wd longbed trucks in stock form. The 292 has a well earned rep as a guzzler.

Let me ask this question... was the 292's that you drove stock setup or were they altered with work done to try and to make them more fuel efficient? Or, did these 292's you drove just written off as gas guzzlers and nothing more than that? What were their carb, trans, rear setup?

I ask these questions because I have heard from people that have their vehicles dialed in and are getting an average around 18 mpg. This isn't going to be driven hard, I can put in a 327 and get what I need from that if I wanted to do that, or better yet, a late model chevy engine, though I would much prefer a 327 if I wanted to do that. I am looking for those tricks that may help me push me closer to the edge of efficiency. The first will be to do without the 1-bbl and get towards a 4-bbl that can get a better tune-ability. Most of this can be done without breaking the bank, but if someone had experience that showed that putting the funds in the right spot, I would consider it, again depending on what I see there.

I thank you for your input, willybill.

I appreciate all the feedback I have received thus far, guys.:cool:

cwatson1953
05-08-2008, 09:57 AM
Let me ask this question... was the 292's that you drove stock setup or were they altered with work done to try and to make them more fuel efficient? Or, did these 292's you drove just written off as gas guzzlers and nothing more than that? What were their carb, trans, rear setup?

I ask these questions because I have heard from people that have their vehicles dialed in and are getting an average around 18 mpg. This isn't going to be driven hard, I can put in a 327 and get what I need from that if I wanted to do that, or better yet, a late model chevy engine, though I would much prefer a 327 if I wanted to do that. I am looking for those tricks that may help me push me closer to the edge of efficiency. The first will be to do without the 1-bbl and get towards a 4-bbl that can get a better tune-ability. Most of this can be done without breaking the bank, but if someone had experience that showed that putting the funds in the right spot, I would consider it, again depending on what I see there.

I thank you for your input, willybill.

I appreciate all the feedback I have received thus far, guys.:cool:


and on a side note....when i changed out my intake and exhaust for the headers and AFB... i have NO problems with it "lagging" from a stop....it's a toquey ass motor...it will move...AND with the headers and 4bbl....it sounds GREAT! of course...the lack of finished exhuast mufflers help that too:D...actually a little too loud at rev...but really good at idle:D

good luck and keep us posted.

nexxussian
05-08-2008, 10:13 AM
FWIW I have always heard the 292 was thirstier than the 250 (disproportionately).

Having said that, a better intake and exhaust has to help. Even if it's a hommade split exhaust w/ dual pipes that should be better. But if you can find a set of SMALL tube headers, that could help too.

I have wanted to try the Offy Dual Port 360 on a straight 6 for a while (w/ heat for the primary charge).

I would reccomend an Edelbrock (500) at this point (for what you are trying to do).

Gears (trans or rear) are a great idea, be carefull not to get the total drive ratio too tall, or you'll be lugging the engine and in power enrichment all the time. A slightly taller set of tires would help (radials, and if you change the gear or trans you are gonna have to recal the speedo anyway) and run them as high a pressure as you can stand (within the manufacturers inflation limits). Synthetic grease in the wheel bearings helps (a little, but it's cheap and easy). Make sure your brakes are not dragging.

Aero mods as previously recommended, lower it (if it's not already).

Then there is the inside of the engine. More compression would help. With that drastic a change (intake and exhaust, especilaly if you up the compression) you will probably want a different grind on the cam.

A set of the port lumps might help help as well but you should probably ask that on the Inliners (http://inliners.org) forum (search 'Lump Port Heads').

There is a book by Leo Santucci that's worth having if you plan on doing much to the engine.

Keep us posted.

nexxussian
05-08-2008, 10:18 AM
Oh yeah, a Toneau cover for the bed not only looks cool, but it can help economy too (or at least it did for the Mythbusters:confused:).

34Hupmobile
05-08-2008, 10:50 AM
You absolutely can get decent mileage with a 292. I get 20 mpg around town with my foot in it and 25+ on the highway at 70mph. Like others have said, make it breath. I've got Stovebolt headers, a Holley 390 cfm carb, Clifford intake with heater and HEI ignition. Not integrated but a propane head for higher compression. Power is transferred via a 200R4 tranny to a Jag rear with 3.53 gears. I run a 235/15 tire on the rear. It can be done! Don't listen to the naysayers. My car has enough torque to pull a house off its foundation and enough get up and go to blow away most V8s.

BillBallingerSr
05-08-2008, 11:01 AM
The '80s trucks had a good trans for mileage, the Turbo 200. It is a tough trans, I think the six was 250, but we used to pull a weigh wagon/auger around with a 1/2 ton like it was a toy. It had better grunt in the field than a 305 easily and the mileage was about 18-20. They made the trans with the Chevy and BOP patterns, so you will need to look close. I liked the Turbo 200 better than the 700. It just seemed to be geared better for a six and running in the muck.

Sixes are really nice with an automatic trans and a lockup OD, the torque multiplication gets you underway well, and they are just mice. My son has a '94 F150 with a 300/5-speed OD with 3.55s, and you really are shifting a lot, but at least he gets 20 mpg out of it on the highway, around town though be doesn't want to brag on it. We drove one with an auto and a taller gear and it was really in its element. Stop and go in traffic gets tiring too with the 5 speed.

58Fridge100
05-08-2008, 11:07 AM
The 292 has a well earned rep as a guzzler.


In stock configuration(valvetrain/carb/intake/exhaust)-- which is was what I was pointing out in my post.

Otherwise- the 292 has got to be a great choice for a heavy vehicle due to it's undersquare bore/stroke and few extra cubic inches.

63Biscuit
05-08-2008, 11:15 AM
[Next question - Edelbrock or Holley?]:confused:

Fro carb choice, I think it comes down to preference. I've got an Edelbrock 600 on mine, and it ran fine right outta the box - still monkeying with it to get best overall power and drivability. Side note: I intend to put a cam and 307 Chevy pistons in it at some point, which lead to buy the bigger carb.

From posts on Inliners, definitely go with an Offy intake. The Clifford might make more power, but the Offy is more drivable.

Also...highly recommend HEI. HEI dizzys are pretty cheap even brand new ($150 or so off eBay)...used ones off of Chevy sixes can be damn near free. The switch from points to HEI made a big difference on my 292.

SteadyT
05-08-2008, 11:36 AM
[quote=willowbilly3;2796330]All the 292s I was ever around were thirsty critters, [quote]

Me too. Except it was a 66 Chevy Light Dumptruck that I put a Fleetside Bed on it :D(4.88's at least - that truck whined like a dog everywhere). I probably got 4 miles to the gallon with the 4 speed.

I could see the 292 being a great motor with some taller gears. It had enough torque with the gears I had to mow down 4" trees and clear property all day long.

willowbilly3
05-09-2008, 07:51 AM
I admit I have no experience with anything but the stock 1/2 ton pickups of the 60s-70s. I did run a repair shop and also worked at a GMC dealership breifly so I got a lot of feedback from the owners on milage.
Do stay away from the integrated head, those are junk. A 194 head will yeild the highest compression I believe.
As with any straight six, the smallish one barrel carb is a huge restriction to breathing. I also know the 300 really wakes up with some moderate head clean up so I would assume this pricipal would apply to a 292 also.

simplyMyself
05-09-2008, 09:01 AM
I thank you very much for your responses! Alot of this is confirmation I was thinking the right direction. The great thing is I have gotten a few more specifics I didn't have before:

Carb 4bbl with around 400cfm
Clifford or Offy, but the Offy is more drivable.
Exhaust should be opened up a bit, about 2-1/2" into a 3" if staying single exhaust.
5spd transmission - best found from a 90 or earlier chevy truck (last year for the 292)
after the transmission is placed spec a gear that will not make the truck to sluggish.If I go for a TBI use a TBI from a Chevy and get the adapter plate for the 4bbl intake. Use the electronics from the donor vehicle.

MPI does not work with the 292 because of the issue with the cylinder timing.

I will post pics of my PU once I have it completed and will let you know what I have gotten with mileage after each piece has been applied. I do think that moving from the 1bbl to a 4bbl will be the first biggest improvement.

Thanks guys!

nexxussian
05-09-2008, 09:16 AM
MPI does not work with the 292 because of the issue with the cylinder timing.

:confused: Splain please.:confused:

simplyMyself
05-09-2008, 09:30 AM
I think it's a cool idea.

I say stick with it--
http://67-72chevytrucks.com/vboard/showthread.php?t=276823

For any others that are interested in hearing why MPI doesn't work on a Chevy 6, follow along. These 6 cylinders all have an intake port design called "siamese", where cyls 1&2 share a runner, as do 3&4 and 5&6. This goes right into the head, so the two intake valves are effectively side by side, drawing on the same runner. So what's the big deal? The valves are open an equal amount of time, so no problem, right? Well, no, because of the firing order which is 1-5-3-6-2-4. Obviously, any fuel injected (even at the port) can only really enter the cylinder when the valve is open. And any fuel injection system will have the injectors open up to 80% of the available time (when wide open). But, the valves are really only about 25% of the time, so the fuel just puddles on the backside of the valve. In SB chevys, this is no problem, because when the valve does eventually open, the fuel enters the cylinder, just as intended.

Okay, lets look at that firing order again (1-5-3-6-2-4). Notice how the space (and thus the time) is not equal between 1 and 2 (and also 5 and 6)? 1 fires, then 3 other cylinders fire, then 2 fires, then 1 other cylinder fires. What this means in terms of fuel is that #2 gets 2/3 of the fuel, and #1 gets 1/3 of the fuel. Not exactly an ideal mixture.

This doesn't happen with a carb, because all air contains fuel, so the cylinder breathes when it wants, and gets the same air/fuel mixture.

In my case, I was stumped by why #1 and #6 were always lean, and #2 and #5 were always rich (leading to bad stumbling at times).

Should have thought about this earlier, but then one day I discovered this link: http://www.starchak.ca/efi/siamese.htm
which explains the whole thing with far more mathematics than I want to get into here. They even propose a few solutions, but I would chalk them up as impractical.

Anyway, fed up with the MPI (and not yet knowing the explanation of why it didn't work), I switched the throttle body over to a GM TBI (real cheap and reliable, these things). Well, that cleaned the problem up right away, and had some side benefits: easier installation, less wiring ratsnest, cheaper, looks more like stock (if that matters to you).

I'm kind of thinking (but never tried) that a dual TBI on a dual 4bbl manifold would be the ultimate because it would cut down the runner length for the fuel and it would make the manifold more symmetrical for more even air/fuel distribution.

:confused: Splain please.:confused:

This was posted earlier in the thread. From what I know it makes sense. I had not considered the Siamese when thinking of the MPI, though if I put my head towards it, I am sure I could come up with a working solution. This would require quite a bit of programming , testing and tuning however.

plym_46
05-09-2008, 09:43 AM
Some other 6 experience. I have a 46 Plymouth, stock it got 16/17 mpg with is 6.0 to 1 compression ration 218 single 1bbl carb. Swapped in a 30 over 230 engine from a 56. took ,050 off the head/block added a fenton intake, dual carbs (same as stock Carter B1B's) advance the timing a bit. opened the exhaust from 1 3/4 to 2 1/2 id. with a dynomax turbo flow muffler. 225 75 rear tires. with a 1 to 1 top gear and 4.10 to 1 rear it now gets 19/20.

Breathing and compression and taller tires equaled 2 to 3 mpg 56 miles per tank.

And on a small truck;

Back in the first fuel crises I had a 73 Datsun Pickup. 1.8 liter 4 speed. It got about 22 mph. I added the dual carb intake and shaved head from a 510 sedan, headers into single exhaust 2 in id with a dumpster resonator from a buick dual set up. swapped the c 78 14 tires for d 78 15's. Took off the big west coast mirrors, added a chin spoiler made of coroplast. blocked off all the grille except the area directly infront of the radiator, made plexiglass covers for the head light area. Put a fibreglass camper top on the bed with a Kamm back type spoiler on the trailing end. And then lowered the truck by 2 inches.

Result was 27 mph highway driving 65 miles per tank.

nexxussian
05-09-2008, 09:47 AM
Yeah, I forgot what board I was on. There is a fairly detailed thread on the Inliners forum where a guy did put MPI on a 292 (with lump ports and the whole bit). I keep trying to post links to threads on Inliners here and they never work (goes everywhere but where it needs to). IIRC he put two injectors per port with each at an angle (I don't remember how much). Still working from memory, he had it wired and programmed to fire as two batches of 3 injectors each. He said before (when he tried it as one batch of 6) that #1 would indeed hog the fuel from #2, at low speed. Claimed the effect diminished by 1500 or so.

I mis read your statement as it being a physical imposibility to put MPI on a 292. My mistake, I appologise. Thank you for clairifying.

cwatson1953
05-09-2008, 09:51 AM
I thank you very much for your responses! Alot of this is confirmation I was thinking the right direction. The great thing is I have gotten a few more specifics I didn't have before:

Carb 4bbl with around 400cfm
Clifford or Offy, but the Offy is more drivable.
Exhaust should be opened up a bit, about 2-1/2" into a 3" if staying single exhaust.
5spd transmission - best found from a 90 or earlier chevy truck (last year for the 292)
after the transmission is placed spec a gear that will not make the truck to sluggish.If I go for a TBI use a TBI from a Chevy and get the adapter plate for the 4bbl intake. Use the electronics from the donor vehicle.

MPI does not work with the 292 because of the issue with the cylinder timing.

I will post pics of my PU once I have it completed and will let you know what I have gotten with mileage after each piece has been applied. I do think that moving from the 1bbl to a 4bbl will be the first biggest improvement.

Thanks guys!


i went with the Offy intake after finding out (exactly what you said) that clifford is good, but more geared around "racing" and bigger HP.
the Offy is what i would recomend for a daily.

as for the carb...the Carter AFB i picked up, had some issues with it at first. rebuilt it. easiest carb ever! edle is just about the same!
for me at least, they're both easiest to work with over Holley, but i know everyone has their thing.

simplyMyself
05-09-2008, 09:59 AM
Yeah, I forgot what board I was on. There is a fairly detailed thread on the Inliners forum where a guy did put MPI on a 292 (with lump ports and the whole bit). I keep trying to post links to threads on Inliners here and they never work (goes everywhere but where it needs to). IIRC he put two injectors per port with each at an angle (I don't remember how much). Still working from memory, he had it wired and programmed to fire as two batches of 3 injectors each. He said before (when he tried it as one batch of 6) that #1 would indeed hog the fuel from #2, at low speed. Claimed the effect diminished by 1500 or so.

I mis read your statement as it being a physical imposibility to put MPI on a 292. My mistake, I appologise. Thank you for clairifying.

NP, man! I have been all over inliners looking for good solutions and came in with pretty good idea. I have been a V8 guy my whole life, but I just couldn't throw out the 292 on the truck. I can see it doing some good for a while yet. That said, I have been lucky to find some good open minders here.

Again, Thanks ya'll!

63ChevyII
05-14-2008, 02:33 PM
This is my plan for a 292 I was going to put in my 63 Chevy II. I may need to replace the 350 in my 66 c-10. Since putting the 292 in the truck will be much easier, it may end up in the c-10 and the II may end up with a small v8.

I already have:

T5 (wc camaro tranny w/ s-10 tailhousing)
offy intake
stovebolt headers
390 cfm holley
cam - 264-H 264 duration 214 @ .050" .498" lift 110 lobe center

I need:
head from 194 L6 (bump up compression, I have one, it needs to be rebuilt)
3.08 rear (currently has 4.10)

The truck is lowered and doesn't have the big mirrors anymore.
The truck is a daily driver. I hope the gas mileage won't be too horrible.

http://63chevyii.com/photos/galleries/misc/myfleet/images/66C-10_profile_edit.JPG

nexxussian
05-14-2008, 03:22 PM
Carefull with the gears there 63C2. I don't know what OD you have in your T-5 but with the one in my A (.68) a 3.70 w/ 28 inch tall tires is a bit too steep on the freeway (lugging in 5th). I have a somewhat cammed up V8, so the 292 will likely be happy crusing at a lower RPM, but 3.08 W/ OD sounds kinda tall (ie 3.08X.75= 2.31 final). Not saying it won't work, but it won't help economy any if you gear it to be in or right at the power enrichment point for manifold vacuum at cruise (it's the problem I'm having currently).

Slick lookin' truck BTW.

simplyMyself
05-14-2008, 03:37 PM
Carefull with the gears there 63C2. I don't know what OD you have in your T-5 but with the one in my A (.68) a 3.70 w/ 28 inch tall tires is a bit too steep on the freeway (lugging in 5th). I have a somewhat cammed up V8, so the 292 will likely be happy crusing at a lower RPM, but 3.08 W/ OD sounds kinda tall (ie 3.08X.75= 2.31 final). Not saying it won't work, but it won't help economy any if you gear it to be in or right at the power enrichment point for manifold vacuum at cruise (it's the problem I'm having currently).

Slick lookin' truck BTW.
I will agree, I have heard that keeping it around 4.10 with the T5 actually is going to be better with the mileage. Maybe even down to 3.9. Any lower and you may end up sucking down the fuel in OD.

63ChevyII
05-14-2008, 03:48 PM
thanks for the heads up on the rear end ratio. I'll see how it goes with the 4.10s

Twisted6
05-14-2008, 06:37 PM
63ChevyII
you may also want to think about lump porting that head to improve the air flow It will also help the over all performance.

Bodacious
05-14-2008, 09:05 PM
Although I've built hundreds of engines over the years for fun and/or profit, I certainly don't consider myself an engine guru. I can't quote fancy engine theory chapter and verse. What I do know how to do however is research and homework for the project at hand. An ongoing project/daily driver for going on five years now is an electronically managed SBC. It's an LT1 in a 3400# car that's been bored and stroked to 388 cid. It has a lightweight rotating ass'y, fully ported heads and intake, internal coatings for heat retention-rejection and low friction, a 10" 3000 stall lock-up converter, 4L60E trans., 3.07 gears, underdrive ATI damper, effecient exhaust, etc. Short story, although in a body that cuts a much smaller profile than a pick-up, it is capable of nearly 29 mpg on the highway and I know there's still more there. It also makes 400 HP and 450 lb-ft of torque at the rear wheels. I feel very sure that a 292 in a heavier vehicle is fully capable of similar mileage, depending upon how deep you want to go as a starting point. You'd obviously want to concentrate on maximizing flow velocity, quench and other things that optimize combustion efficiency and also well tuned fuel and ignition systems. Sequential fire injection would be your best starting point. A torque engine such as your 292 should be an excellent start for your vehicle. I worked on quite a few of these years ago and since have always been quite impressed by them.
There's lots of good advice in this thread that should get you thinking.

old dirt tracker
05-15-2008, 12:52 AM
34hupmobile has the answer with his real world combo. did you figure his final gear ratio. right at 2.50.

63ChevyII
05-15-2008, 10:35 AM
63ChevyII
you may also want to think about lump porting that head to improve the air flow It will also help the over all performance.


Hey Twisted6,

I have been thinking about that for a while, esp after spending some time on the phone with you and looking at your website.

For now I think I am going to run it with the stock 292 head and as time and money allows, get the 194 head rebuilt and possibly add some lump ports. What is the approx cost on this?

I haven't touched the engine since Nov or so. I picked up another harmonic balancer and a distributor for it. Hopefully that takes care of the problems I am having with the engine. (http://www.jalopyjournal.com/forum/showthread.php?t=207053)

Twisted6
05-16-2008, 06:51 AM
I sent you a PM in regaurds to that.

63Biscuit
06-02-2008, 10:17 PM
FWIW - I've been driving the Biscayne as a daily for the last week...that means a good deal of stop-and-go and surface street driving; although I've discovered that the motor is strong enough to allow me 2nd gear starts. When traffic opens up, 65MPH = 2500RPM so I'm not exactly lugging the motor...and since I still really really like the sound of the secondaries opening up, there's the occasional WOT test. You know...just to check. But, I digress...

I filled it up today and I'm getting just a hair better than 17 to the gallon. I could probably lean out the carb a touch, and if I avoid the loud pedal a bit, I oughta be able to touch 20.

63Biscuit
07-24-2008, 08:52 AM
Update: we took the Biscayne on a ~250 mile road trip - me, the spousal unit, her sister and fiance, and two kids, plus requisite kid-gear and entertainment. Fairly steady 60-65 MPH, and we got just shy of 20MPG...with the 4/65 air conditioning going the whole way out.