Hot Rods Tunnel Ram over carbed

Okay,
350 Mexican block, brand new (20 miles on engine) Thumper style cam: 290 cam. Hydaulic 194/150 cast heads and electronic distributor. 5 speed Tremec NV3500 manual and 411 gears.
Engine has a Edelbrock street tunnel ram and two Holley 600 CFM street 4160s (the polished newer ones). Timing is 28 all in,

I choked the jets down to 58s and the nozzles to 28s. She is a little better but still stumbles on hard acceleration. Idle is great and responsive and once the dead spot clears ( 1800 -2200) she takes off like a batoutta hell and breaks the tires. Plugs are black on the rim and grey ashen and clean in the center.

Can anyone tell me the actual jet and squirter numbers for the stock 450 CFM Holley 4 barrels?

My idea is to choke these things out as low as I can before giving up and putting out the cash for two new 450s at 600 a piece!!!!!.

 

Might want to get a better understanding of how carbs work, and what changing jets does, before you get carried away making changes like that.

Work on the accelerator pumps, and getting the car to not apply load to the engine until it's past that dead spot.

 

Your not over jetted. You got too much intake for the engine. In other words your mismatched intake and carbs have resulted in a engine that too souped up to run properly.

 

I have seen many a glass 32 Fords with really mild crate blocks and the Speedway tunnel ram set up (same manifold as I have but with twin 450s or even 390s. I have these 600s and don't want to separate teh cash from my wallet. Numbers. Anyone have numbers?

 

The difference between different size carbs, is how much air they flow. That's what you need to make smaller. Jetting won't do that.

 

Squirrel, I have adjusted/moved the pump cams to the positions available to no avail. The car smells rich and the plugs have black on the skirts. She is, with no question,. running rich.

 

DUH?

 

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I thought that at first as well, expect that there are tons of this particular ram at every show with tamer engines than mine. I may hafta just go out and buy the damn carbs. I just figured for thirty bucks and twenty minutes time, it may be worth switching the jets and squirters.

 

;

Interesting; so educate me, seriously, as I am confused. I thought that the issue with a tunnel ram is filing the plenum since it is so large. I am not really not being a wise ass, but how would less cfm coming in supply that plenum volume?

Secondly, when I have run the car with cleaners off up and down the street, she actually pulls a little harder?

 

The info your seeking won't do you much good , the venturis in your 600's is bigger than the 450's , you must maintain and air/ fuel ratio. Have you ridden with any of the other tunnel ram guys ? Most likely most are suffering the same predicament as you . FWIW , you might try adding some timing , get into 34°-38° , depending on your compression . I would opine that you don't have the engine needed for that induction system .If you slip the clutch to get air flowing , then you won't have as much bog ,( that's what high stall converter s do...buying different carbs won't necessarily help your situation. Go back to the larger shooters ,that will " band and" the " hole" that occurs in your fuel/ air mix when you slam the throttle , the low speed mix the engine was running on falls out of suspension when you open the throttle blades , this leaves you w/ a momentary hole or lean spot in the manifold until the air speed increases enough to pull fuel from the main Jets , the large shooters help to cover that hole . Do you understand ?

 

TE="Old wolf, post: 13250557, member: 49396"]DUH?[/QUOTE]

Yeah, great response. Tool

 

You just are not keeping a steady vacuum thru the intake and the air fuel mix is changing as well as volumetric efficiency. Your carbs & intake are too big or your engine is too small.

 

Agreed. It's a really hard pill to swallow. A friend suggests that unless I do more with the heads, I am lucky to have what I got (drivable and reasonably reliable). I was just hoping that maybe a half hour of work and a few bucks might garner me a little better pedal . I have learned to feather and mind the bald spot . Thanks for the timing tip, I will def give it a go.

 

You might try making a pair of restrictor plates. and capping off the back secondary of the carbs. Make it run and idle on the primary of both carbs. the extra shot of fuel from both primarys at once might help with the bog.

 

To give you some understanding of what's happening....a carb works by having air flowing through the venturi (restriction) creating a low pressure area, and atmospheric air pressure then pushes fuel through the jets, into the nozzle in the venturi. If the air flow through the venturi is too slow (because the venturi is too large for the size of engine and RPM at the time) then there won't be enough pressure drop to let any fuel flow.

The fuel smell in the exhaust is probably from a lean misfire. When the engine is running rich, it will get a little bit of raw fuel out the exhaust, but also a lot of partly burned fuel (carbon monoxide) which you can't smell.

Try going richer on the jets, perhaps 2 to 4 numbers higher than stock. Play with the pump cams as well as the squirters. But the main thing is to either get the RPM up before going wide open, or get smaller carbs so the air flow speed is high enough to get fuel flowing right away, and get rid of that lean stumble.

 

Okay, so choking the cfm will actually be better as it will create more vaccuum , correct . SO in theory, my cleaners on should work better, right?

 

I won't pretend to know the answer to make your combination work, but the "Thumper" type cams have been called fairground, or poser, cams.

I'd think you need more cam, more rear gear and more time above 3000 RPM. I'd also hope the 28 degrees of all in timing mentioned above is a misprint. 28 * sounds more like total timing for a flathead. Good luck with it!
-Dave

edit: a good dose compression won't hurt a thing as long as you've got the fuel to support it too.

 

More timing advance should help, for sure!

 

He should be running the carbs 1:1 now , I believe they're vac sec so the sec. are closed until he gets some rpm up any way.......

 

Can make a difference. ^^^
Had similar probs w/2 AFB's
Either one would have fed my 327cu.

 

I've always thought that qjets would make excellent tunnel ram carbs .....

 

Did you ever siphon gas? the smaller the hose the easier it is to siphon gas. the larger the hose the harder to get it started. As air flows thru the carb it siphons gas thru the jets and out the venture. the smaller the passage that air flows thru the better and steadier the velocity is.

 

Tunnel rams aren’t for low engine speeds... don’t drive it like a pussy!

 

Thanks Squirrel!
I will give it a go as I actually have a set of 35s and the original 63 jets I pulled (can't hurt to try). I fear I will prob do what I should have from the beginning, which is buy twin 450s as everyone else has had success with.

 

Lastly, several things I have read suggest blocking off the center of the top plate of the ram so each carb has a direct run to the front and back cylinders. There is even a supposed company making them this way now Have you heard of this?

 

There was one guy on our tbucket forum that bought one of those , for what he had in it he coulda' put a blower on , anyway , he said it ran great , he sold the car shortly after , never heard anymore about it . I have 2x450 Holley's on mine , I still have a slight bog if I'm below 1500 rpm I've worked with them for 15 years , tried 2x390 , 2x600 2x450 , I like the 450 the best ( more responsive in normal driving) I have an acquaintance who loves his 600's , we both have stroker small blocks , cams , heads are similar , compression within 1/2 a point , I get a bit better mileage , that's about it ........

 

I can drive through town at 1200 rpm in 4th gear , not exactly high r.p.m.

 

Like most fellas suggested.......you need MORE timing. (total & initial) Limit it to about 40*....have it all in by 1500-2000rpm. 20* initial ain't too much...so long as the starter is up to it when warm. Snotty camshafts AND tunnel rams need lotsa initial timing.
Do a test. Warm engine....then wing the carb linkage and hear how its slow to catch up. ....now turn the timing up about 10* and the idle speed goes up AND...it revs up quicker. (re-adjust curb idle after you add in more initial)
May need to go with a locked distributor. Use plastic tie wraps and hold the weights in the distrib all the way out (like full advance) and maybe rig up an ignition interrupter switch. Where you can spin the engine up with the starter and flip the switch and turns on the ignition. Hard to explain on the net. It gives the engine a 'head start' and then turns the ignition on. Your problem is timing not too big carbs. IMHO
6sally6

 

just use a vacuum gauge time to max vacuum to start with on 91 octane,those crate engines don't have much compression.

 

You could also try putting the carbs back to factory spec's and switching to a progressive throttle linkage instead of 1:1 and see if that helps. Another 8-10 degrees of timing definitely wouldn't hurt anything either. JMO
Oh, the factory jetting on a 450 is 58 jets, 31 squirters, and 8.5 PV, with a 1.5 inch throttle bore, in regards to your original question.