Horsepower versus gas mileage ...where to stop

[Roothawg]

Been pondering this for a while.
Gonna rebuild the 283 that is in the 36. It is a good little motor but she is tired.

I was just wondering at what point does a guy start losing gas mileage when installing performance parts?

This 283 has power pack heads which you all know has dinky valves. In theory I think if I reduce the amount of resistance for the exhaust to exit, increase the ability to scavenge the cylinders, increase the lift to a slightly larger cam, shouldn't this increase the gas mileage while increasing the performance?

I know it takes more power to turn over a high compression engine but we are talking about an 8.5:1 motor.. tops.

There seems to be a fine line there.....where should a guy stop?

[Roothawg]

BTW, I have a set of 1.94/1.50 slated for the overhaul.

[Paul]

As we all know,

with the internal combustion engine,

the ONLY way to make power is to consume fuel,

you must convert one form of energy (stored) to another (thermal).

the more fuel you burn,

the more energy (power) you produce.

period.

My daily driver gets about 10 mpg.

my hotrod gets maybe 8,

both I hope are relatively efficient converters. http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif

Paul

[Roothawg]

This 283 averages around 16-18 now, but it is pretty lame.

[draggin'GTO]

I would keep the power pack heads with the 1.72/1.50 valve sizes. The higher velocity air flow from the smaller ports and valves will increase throttle response and require less throttle opening to get the car moving thereby enhancing fuel mileage. Big ports will kill the velocity and there goes your gas mileage as well as low and mid-range power and throttle response. The power pack heads should give you 9.5:1 compression.

Once you put the bigger 1.94/1.50 heads on your 283 you pretty much end up making a higher RPM powerband engine out of it (even with a smallish cam), similar to the 302 Z-28 engines. Those engines ran great, but you had to twist them to make 'em run hard and of course fuel mileage was not their strong suit. Plus the lower 8.5:1 compression ratio of the bigger combustion chamber 1.94 heads will also contribute to a loss in effiency (gas mileage).

I would give the power pack heads a chance, combined with some small-tube headers and a free-flowing exhaust with 2 or 2-1/4" pipes to keep up the exhaust gas flow velocity.

----- Bart -----

[Roothawg]

Very interesting........keep talking ya'll.

[Fat Hack]

Check out my 305 post in the Tech-O-Matic...those figures were obtained in a hefty four door Malibu with a well-used 305 using bolt-on parts. The key is to make it as EFFICIENT as possible. An efficient engine makes power using less fuel than an inefficient one does. The parts break-down is included in that post so I won't run through it again here. A 283 oughtta provide similar numbers with the same equipment, although the 305 has the benefit of the 350 engine's 3.48 inch stroke to aid low rpm grunt.

[choprods]

Honestly I think the most common mistake on a 283 is OVERCARBING IT.Best 283 I built had '59 two barrell heads and WCFB[small] carb and 350 horse 327hyd cam/nothing else........ran hard and clicked off 20 MPG regularly....if there is a lessen here I'd say its SMALL COMBUSTION CHAMBERS/small ports =low end response,and also larger combution chambers[lower compression] and large runners= knocks all the wind out of 283 until you cross 4000 RPM.In other words you can easily end up with an engine that only revs freely when in NEUTRAL- and when pulling a load its a deadass with no tourque on low end.Kinda like what that guy-"Fueling" who makes the heads for big blocks that have tiny combustion chambers.......discovered http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Revhead]

There's more to it than just more fuel = more power. There's efficiency. The c5 vette makes 350hp net and gets in the 20s for mileage, where my stock C3 gets about 12mpg and rougly makes 300 net hp. I'm no engine designer, but I can imagine that better flow and smoother paths would help mileage by keeping the fuel well atomized all the way to the combustion chamber and having a more complete burn. You could have the same amount of fuel being put into two engines and one make more power because the fuel is used better. Also I would think that evacuating the exhaust out and filling the chamber with a cleaner mix would get you more power, but I guess in that case it just wouldn't suck in as much fuel so there would be a loss in mileage.

[fab32]

Keep in mind that a more powerful engine doesn't have to work as hard to make the same power. You may be able to run a lower rear ratio with a more powerful engine and experience an increase in milaage.

Frank

[Paul]

Revhead,

absolutely.

efficiency is key.

tune for the power band you need.

with the small motor, if put together right

should get you a good snappy little mileage maker.

especialy in a lighter car with the right gearing.

..'course some of us go the other way and build for as much grunt as we can tolerate.

the motor in my hot rod for instance has the 2.19/ 1.88 valves

with somewhere in the neighborhood of a 1000 CFM in carburation

with 2" primaries and 3" exhaust.

and some might even think This is conservative!

it's all relative..

Paul

[Machinos]

Keep in mind that the C5 is aerodynamic as hell and has .50 OD http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif

I think the main thing is low-end torque. Torque is what you need to overcome wind and rolling resistance on the highway, and if you can do it at low throttle you're not using much gas.

Second thing is wind resistance. A couple weeks ago I was driving a work truck with an open-sided trailer on it. It went from a full tank to half a tank from the start of the drive to the finish. Next day I was driving the same truck, but pulling a very tall, enclosed, roofless flat fronted trailer. The exact same drive took 3/4 of a tank!

I know it's not really the "thing" here, but my car goal is to have a great cruiser with vintage style and unique, VERY efficient power. I don't want a 12-second car, I more want one with 350hp an 23mpg at 75mph http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

[Rainer]

hmm I'm running my roadster with a 355 hp sbc - 18.5 mpg (2.56 ratio) - and high 12's on the quater - not a bad mix - f*%§k all the C5 http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif -

[Unkl Ian]

[ QUOTE ]
if I reduce the amount of resistance for the exhaust to exit, increase the ability to scavenge the cylinders, increase the lift to a slightly larger cam, shouldn't this increase the gas mileage while increasing the performance?


[/ QUOTE ] There needs to be a balance between intake and exhaust flow.By increasing the exhaust flow you can over scavange the cylinder,reducing power.

[Hot Rod To Hell]

406 SBC, 11.6:1, 825 race demon carb, custom 1-3/4" hdrs, 3"duals with flowmaster delta mufflers, 3100 lb car, th400/4000 rpm stall, 4.11 9", 30" tall tires. High 10's @ 126-ish, 12-13 MPG when daily driving, 3-4 mpg when hot rodding !:o

[InPrimer]

the other factors that affects mileage is gear artio, trans and body shape,also the ultimate killer speed

[Roothawg]

Now to further confuse things...valve overlap.
If I have a cam with say more valve overlap will this increase or decreas mileage?

Also isn't the stock CC size on a powerpack around 58?
Just wondering what kinda compression ratio I will have if I zero deck the block and run a flat top piston?

Now, should I run a Hypereutectic piston or forged? Hypers don't change dimensions as much but with the new pistons thesilicon content is different from the pistons in the old days. I would think less reciprocating weight equals more mileage....right?

[FWilliams]

gas mileage?GAS MILEAGE?!!, Jesus i leave on a couple week trip and come back to talk of gas milage concerns, God almighty the next thing you will want is a HAMB store on every corner where you can get your lastest fashion trend ; and a fucking espresso http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

[Fat Hack]

More valve overlap bleeds off compression at lower rpms. It's common on old-school cams ground for high horsepower applications...NOT the best way to go for mileage!

A good forged piston will do the job for you, as will a CAST piston...but less reciprocating weight DOES lend itself to faster revs and increased efficiency.

Anything you can do to reduce weight, friction, blow-by or thermal loss will increase power and mileage as efficiency is increased. To this end, things like gapless rings and engine coatings can give you an extra measure of efficiency and they are becoming more and more commonplace every day.

Aluminum rods, lighter pistons, a lighter flywheel, crank counterweight mods...all these things reduce the rotating mass and help race engines to spin up faster and deliver more horsepower. The Big 3 also experimented with lightened (weakened!) engine designs in the late 70s and early 80s in an effort to squeeze more mileage out of their older V8 staples. The 267/301 Pontiacs were an example of this thinking taken to an extreme! They're light, but also weak. Using race parts such as aluminum rods and quality aftermarket pistons will get the weight down without giving up strength.

As for thermal loss, things like aluminum heads and headers contribute to this. It's really a trade-off, however. Popular opinion says that iron heads hold heat better and increase efficiency, but that doesn't offset the more aggressive ports and valve found in aftermarket aluminum heads which run cooler, but also resist detonation more. You have to decide what you're looking for in an engine. Your iron heads will work great on a mild street performer with modest (below 10:1) compression and will promote efficiency. Header wraps became popular in the 80s as guys tried to experiment with reducing thermal loss yet still gaining the performance advantage of tubular headers.

[Roothawg]

Fred is it wrong to wanna Von Hamb shirt?

[Paul]

[ QUOTE ]
gas mileage?GAS MILEAGE?!!, Jesus i leave on a couple week trip and come back to talk of gas milage concerns, God almighty the next thing you will want is a HAMB store on every corner where you can get your lastest fashion trend ; and a fucking espresso

[/ QUOTE ]

hahahaha!

[Roothawg]

Actually, I desire a car that gets 4 mpg........ http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

BTW, that's what ya get for leaving........ http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif

[modernbeat]

Root, you know that to produce power, you will have to burn gas and air at a 1:14 ratio.

The more air and gas, the more power. Rev higher, bigger valves opening to larger bores and strokes, and more carburetion to feed the bigger, higher revving engine will all increase power and gas consumption.

To increase power WITHOUT increasing consumption, you have to make sure that you aren’t mixing your gas and air at a higher ratio than necessary, and that you’re getting the full burn of what you do mix. On that note, tuning your port size, valve size, and runner length to the power band you want to run in, optimizing your ignition, containing thermal loss, and improving the efficiency of your carburetors (and accelerator pumps) all give more power (or more usable power) without reducing mileage. Most of these also add to the longevity of the engine, reduce emissions, and make it easier to drive.

My recommendations would be to keep the intake track relatively short, keep the cross-section of the runners from the plenum to the valve the same size, and as small as possible to increase air speed through the runner. This will give you great throttle response and make it fun to drive. Another tip, keep the torque peak and horsepower peak as far apart as possible. For a driver car, as opposed to a race car, you’ll want to be able to achieve torque quickly and have a long rev range to build power instead of having to rev very high to achieve enough power to get off the line.

[Roothawg]

All very good points.........Thanks.
Here is what I was thinking.
283 which will hopefully clean up at .030"
Forged pistons , as light as possible, with flat tops
stock guts mainly.
Small cam with a lift approx. .460ish.
duration .....260 degrees.
stock powerpack heads or 1.94/1.50 depending on the shape after teardown.
A dual plane aluminum performer intake with a 600 cfm Holley or Edelbrock carb
MSD drop in distributor.
TH-350 with a 3.36 rear end since that is what's in it now.
Prolly have a 29" tall tire or so.

How is this combo?

[stealthcruiser]

we don't need no stinkin' gas mileage!
time and distance is what it's all about!

[Roothawg]

I have a car for that purpose........ http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Fat Hack]

Sounds like a great combo, Root! I'd go with the Holley 600 vacuum secondaries carb on the Edelbrock Performer intake with short insulator/spacer under the carb. Check out the TRW #274 cam, it's a replacement cam for stock 350 and 400 small blocks and it really works great in a mild small block with fewer cubes.

A good set of headers and a basic 3-angle valve job with a recurved distributor should make you pretty happy all around...good mileage AND a broad torque curve. Your gearing sounds perfect for a mild small block like this, and you can tweak it a pinch with tire selection.

[Roothawg]

I was thinking of the 260H possibly....Too much?

[Fat Hack]

You mean a Comp Cams 260H?

I had a 270H in a 305 and it was a dud. Most of those bargain basement Comp Cams grinds are square pattern cams...even LAWNMOWER engines use dual pattern cams! Go with a better cam, like the TRW one I mentioned, or a mild Crane hydraulic grind...you'll be glad you did!

[Roothawg]

Gimme a set of specs on something you like.....
I read a lot of good things about the CC 260H.
I have an old Engle solid that loves 265's and 283 but you have to live with the ticking.....and setting the valves.

I think it was a .440" lift and a 255 degrees roughly.

[Fat Hack]

Here's what I recommend:

Crane grind # H-260-2

Hydraulic street/strip performance cam

Duration @ .050" = 204/216
Advertised Duration = 260/272
Lobe seperation = 112
Gross Lift = .427/.454

Compares to the Comp Cams 260H, but with a dual pattern grind...oughtta be stout in a 283!

[Roothawg]

I have an old cam in there from the 80's now. I think it was a retro cam grind for the 300 hp 327. It thumps pretty good.

[choprods]

Dont know exact spec on 350 hp 327 cam Root but it was IDEAL......also try a 500 CFM carb first to compare it with the 600 plus you guys mentioned.I think the WCFB'swere 400 450 CFM[smaller venturi faster air speed at launh[assumimg street use]......[Mine was in a 2970 lb 39 chevy 2drsed/Manual trans-W -3:73 rear]

[Deuce Roadster]

http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif


I have a .060 over 283 in my 40 Ford coupe. I use the '097' Duntov camshaft. RPM range is 1800 to 6200. 287 advertised (both I & E), 228 I and 230 E at .050, 110 separaton and 106 centerline. The main drawback is it is a solid lifter camshaft http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif. It is somewhat lumpy......

Old late 50's aluminum Weiand intake and a 500 Edelbrock.

http://photo.starblvd.net/~DeuceRoadster/2-4-2.jpg

As we all know, a 40 Ford is as aerodynamic as a barn door. It weighs 2975 lbs. and has a 3.78 ratio rear end. I get 16 - 17 mpg at 60 - 65 MPH.

I believe that a lot of folks gear their cars TOO high and lug the engine.........


.

[Roothawg]

That sounds like a nice setup on your 40. My 36 weighs in at around 2750 I think.

[Deuce Roadster]

[ QUOTE ]
That sounds like a nice setup on your 40. My 36 weighs in at around 2750 I think.

[/ QUOTE ]


Thanks.........it runs and pulls pretty hard....for a 292 cubic inch engine.......

I weighed it a at a government scale that was fresh calibrated. Spare tire, a few tools and a half tank of gasoline. I believe a 36 is a little lighter.

http://photo.starblvd.net/~DeuceRoadster/2-4-1.jpg

I use a 66 Chevy Nova V8 PVC system to help it also.



http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[FWilliams]

Root- touchet' PS dont toss out that 260h just yet

modernbeat- great words on the subject, 60s style also

fathack- man i would love to see your data on dual pattern vs single pattern cams. i have seen you post more than once that single pattern cams are junk, and dont even belong in a lawn mower, i dont think any body here is building lawn mowers any way , unless its for there minis.

After various dyno tests on cams, we found that the dual pattern only showed a difference on engines with very restricted exhaust systems, cats and cat back systems especially, and then it was very slight. I totally agree that there are situations where dual patterns may be the way to go, but they are not the holy grail, and in fact I was having lunch with a friend who works R AND D for a major cam company while he was in town, and he was telling me the emphasis is now leaning back to single pattern cams due to the strides in flow technology on after market cylinder heads. So as this is a topic that comes up in my shop a lot, we would love to see some of your numbers supporting your claims on the downfall of the single pattern cam. if the file is large and you dont want to tie up space on ryans board feel free to send it to my e- mail address or i could send you my fax number.

thanks RACEFAB

[Crosley]

I dont know what mpg my Dodge gets. Speed-O does not function.

[Fat Hack]

Racefab, I don't have any hard-core dyno test results to prove that single pattern cams are less effective than dual pattern cams...but in my own personal experience, dual pattern cams DO work better. I've used both, and ALWAYS had better results with a dual pattern.

Single pattern cams are good because they can be made available to the masses for less money and they are BOUND to out-perform a stock cam, so the customer isn't likely to complain.

However, even OEM cams are dual pattern grinds. Believe me, after working at Ford for a few years, I can assure you that if there is a way to shave a few pennies off of each vehicle, the Big 3 will do it....but even they don't run single pattern cams! (At least they didn't used to...don't know about today!).

It just makes sense to me that you can't treat the intake and exhaust side of a camshaft the same way...there are different characteristics and physics involved, and to gain the optimum advantage from a performance cam grind, I believe that you NEED to engineer different specs for each valve in a given cylinder. Crane and other companies have done their homework and having used their cams several times, I am convinced that they know what they're doing.

Even Competition Cams now offers dual pattern grinds, but the core of their market are still their catch-all single pattern grinds. Better than a stock cam? Maybe. But the best bang for the buck? I doubt it...I think it's worth the extra few bucks to buy a cam with a little more thought put into it. If you use the same specs on both lobes, you HAVE to compromise ONE of them. Not so with a dual pattern.

The other thing that irks me is when some cheap-o cam companies make cams with the exact same specs (square pattern, usually!) and offer it for EVERY engine application! Most of the time, they take what works okay on a 350 Chevy, and then grind cams for small block Mopars, Fords, Pontiacs, etc to the same specs! We're talking about different engine designs with different heads, intakes, valves, etc....how can they honestly expect us to think that ONE spec will work equally well in EVERY engine under the sun?

Look at the better cams offered by the leading manufacturers, and check out the specs on OEM cams. You'll find that they are not only dual pattern grinds, but that each application will have camshafts ground specifically for THAT application...rather than just slapping one set of specs on everything!

That's my thinking on the subject...and from what I have personally experienced with both single and dual pattern cams...I feel confident saying that I believe in the concept of specifically designed dual pattern cams, and that they are worth spending a few extra dollars on, since the camshaft dictates how an engine will run and is such a vital part of the overall combination. Buy a universal carb if you want to save a few dollars...you can always tune it to your engine later...but don't settle for a "probably good enough" cam!

[Fat Hack]

I understand what you're saying, Racefab...but most of us run factory heads and exhaust systems, so I firmly believe that dual pattern cams are a better choice in such applications.

Ford engines are notoriously restricted on the exhaust port side, and they SCREAM for a dual pattern grind! I think any vehicle employing OEM heads and an exhaust system with mufflers would do better with a dual pattern cam than with a single pattern. In the world of dual purpose vehicles, it just makes sense.

On the dyno, I'm sure that the difference between two similar cams, one a single pattern and the other a dual pattern, would be small...but as the old saying goes, "You don't race a dyno...or drive it to work on Monday!". A chassis dyno might offer a better chance at measuring the differences between the two schools of thought, and I would be eager to see how that worked out on cars with street/strip potential, but equipped to go down the road. (Mufflers, non-race trannies, street gears, etc).

You make valid points, but I'll stand by my claim that dual pattern cams HAVE to be better for the typical street/strip vehicle.

[Roothawg]

Now remember boys, we're talking ghas mileage along with performance.

[Fat Hack]

Exactly, Root...you asked about performance AND gas mileage in a street engine with iron heads that will undoubtedly run an exhaust system. That's what I offered my recommendation for, and I still think it'd be better for ya.

How much better? Impossible to say, but since your engine will see FAR more part throttle cruising, stop and go driving and idling around than it will wide open throttle running, it's just smarter to go with a cam engineered to take those variables into consideration.

Your 260H will work well, I'm sure...but if your looking to wring out maximum streetable power AND the best economy, then I think a dual pattern grind will help you reach that goal a little more effectively.

No ill will towards Racefab, I'm positive that he knows more about making top end power on drag engines than I do...but all of my experience comes from building and tuning engines that had to perform in everyday driving in addition to making passes down the local strips on weekends! Just wanted to offer you the benefits of what I've learned. I tried a 270H and a TRW cam in the same engine and vehicle, and the stock replacement 350 cam ran BETTER at the strip and delivered more mileage on the street in that 305. True, my car was "compromised" with 3.31 gearing, an auto tranny, and an exhaust system...but the dual pattern grind did better there!

[cornfieldrodder]

Root,
IMHO the bigger valves are extra weight and will lower charge velocity. The 283 has a rod to stroke ratio of around 1.9:1 and not much space to fill. With a stroke of only 3.00" and all that piston dwell time, I'd go for max torque at 3000 rpm and let it run out of breath at 5500 or less. A set of modern high swirl heads with 9.5: compression should work with pump gas well if you don't lug the thing. I'd also go with a 390 cfm carb to get the best throttle response and easiest tuning. The small carb will limit the top end power, but you've got a car for that.
Just some of my thoughts.

[burger]

Root- I ran both a 390 and a 600 cfm Holley 4160 on my 289, and the 390 ran much better.. crisper and noticeably easier on gas. (Keep in mind the 289 has a stock cam).



Ed

PS. I'd recommend a Weiand Stealth over an Edelbrock Performer. Never played with thier Chevy stuff, but the SBF Stealth is WAY nicer than the Performer. Plus, it goes Idle-6800 instead of Idle-4500, which is nice for a dual purpose vehicle.

PPS. The 283 in my coupe has an Isky Z-25 cam -- 240 duration @ .050, .480 lift. I haven't fired it up yet but I'd wage money that it's going to be one mean performer. 462 casting heads w/ 1.94/1.50 valves, FeO2 helped me with the porting, trip intake w/ 48's, ram horn manifolds (I'm thinking about getting something more free flowing).