Thread: Dual quad induction Question

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Hey guys I'm having no luck in the chevy small block room with my question. so here it is as it should apply to any motor.

I'm wanting my next project to sport a dual 4BBl set up on a Edelbrock Pro II tunnel ram to be exact. The problem is I got a 350 and its stock right now. teh carbs I purchased for the build up are 2 Holley 450 cfm carbs. (Ebay $150.00 for both) ok so I got 900CFM or carb, thats way way too much for a small block. Now for the question, What alterations (cheapest perferably) can I do to make the small block consume that much air. whats the cheapest way to go about it and still have the thing run and be reliable. I'm good at building motors its the altering I need help with.

Thanks Ford guys...

Mike...

Originally posted by Gyva


I'm wanting my next project to sport a dual 4BBl set up on a Edelbrock Pro II tunnel ram to be exact. The problem is I got a 350 and its stock right now.
Thanks Ford guys...

Mike...

I don't think ''dual quad tunnel ram'' and ''cheap'' ... work in the same sentence. ''Dual quads w/tunnel ram'' is not the optimum street use set up either. Sure it can be done, but there are better more street friendly systems out there.

lol "it can be done" ok, I won't use the word cheap but let say $5000 and we'll say $10,000 both are niether cheap but $5000 is the cheaper of the 2. many people say it can be done but no one lets me in on the componets that need to be altered. More stroke? more spark? more cam? more compression, more What? the only thing I don't want to change is motor size its a 350.


Mike

I'm working on a .30 over 302 with a pair of Holley 390's on a 289 tunnel ram intake, for 50% strip fun and 50% ricer intimidation around town. I should be firing it up in a couple of weeks; if I get any bright ideas I'll let you know.

Thanks for the reply Was II if you could give me a rundown on your engine specs that would be great.... what alterations did you do to make it swallow the extra CFM's of airflow...



Mike...

Don't know if it'll swallow it all, yet. I severely doubt it will at street level.

.030 over 302 block (306)
Hi-Po 1966 289 heads (10.5:1)
Weiand 289 tunnel ram intake
Holley 390's, (sync'd, not progressive)
Full-length Hedman headers (not shorties) with 2 1/2" cutouts for the track
No cats

I don't expect it to run smoothly, even when it's tuned. I expect it to idle around 1100 and sound like the end of the world. The Wow Factor is the thing, here; this is not a trailer queen, nor is it a commuter vehicle. This is about sheer intimidation and "What the HELL is that guy thinking?"

"Dano78" has dual 450's on a tunnel-rammed 302. You might want to PM him. He also has a thread on here about tuning dual quads. Do a search under Tunnel Ram or his user name.

My understanding is that stroking my current setup to 347 will increase its sense of humor with regards to the duals / tunnel ram setup. I intend on building out to 347 next year, but first things first. There's rice to eat.

"WOW a 300 thousandths OVERBORE.. must be pumpin' lotsa H2O huh!!!"


did you mean to say O2 as H2O would be water????



Anyways if someone has a workin dual 4BBL setup I'd love a rundown of your engine specs. Or if someone could tell me thats great as well thanks


Mike...

Typo. My bad.

"........... ''Dual quads w/tunnel ram'' is not the optimum street use set up either. Sure it can be done, but there are better more street friendly systems out there............" pro70z28 is absolutely correct. Chances are your motors will make more power and be a lot more fun to drive with a well matched single 4 bbl and appropriate manifold.

Tunnel ram manifolds were/are basically a race only piece designed to operate in a narrow high RPM range and tend to fall on their face when operated outside that range . Low RPM throttle response, idle quality and torque are also generally adversely affected when operated outside the RPM range these manifolds are designed for. Lets face it the only reason the only reason to run on of these manifolds on the street is either the "WOW FACTOR" or you have a VERY serious street racer (were talking an almost all out race engine with high compression, lots of cam, head work, a stick or very high stall converter, and deep gears).

That being said this is what I've found that may help you live with these on the street.

Manifold: Several years ago when the tunnel rams started showing up on the street (anybody remember the 80's and the start of PRO-Street?) some of the manufactures started making street tunnel rams. The basic design change was that the runners were smaller than the race pieces which helped with throttle response and helped keep the fuel suspended in the air stream. If you have a choice go with the manifold with the smallest runners available.

Carbs: Go conservative and use a carb with vacuum secondaries (or an AFB type carb with a secondary air valve). The 450's you have should be fine as long as their vacuum secondary. The secondarys will only open on demand and only as far as required (chances are with your stock 350 they will never fully open). The smaller the primaries are the better the throttle response will be.

Iginition: You will need the best you can find. Something like an MSD to help keep the plugs from fouling at low RPM might be a good investment.

Gears: Go with as deep of rear end ratio as you can live with. This will help make up for a lack of bottom end torque and put the engine RPM range closer to where it needs to be for these manifolds to work and will help make up for a lack of bottom end torque. If you running an automatic, start looking for a hi-stall converter. It will help pulling away from a stop light without embarrassing yourself.

Plan on doing A LOT of tunning to get the most out of these manifolds on the street. Chances due to a poor low RPM vacume signal you will need to play with power valves (or step rod springs if dealing with an AFB), jetting, secondary opening rates, and timing to get it to the point where it is livable.

Good luck to both of you.

February 05 CHEVY HIGH PERFORMANCE

383 ( 350 block 400 crank 3.75 stroke
e-tec heads
vortec dual quad intake
dual 500 cfm edelbrocks
lunati roller rockers
hei petronix street-strip distributor.
edelbrock performer hydraulic flat tappet cam 420/442 lift
445 torque
370 horse

buy this issue, go to chevyhighperformance.com and i think if you really want you can buy back issues or they might even post this story

good luck

Mike P I value your reply and now am getting the picture of what I need to do to get this thing to run half way decent on the roadway off the strip. I will order a MSD dist. and ignition box. I'm going to try stock heads but I'm going to get beefy valve springs to run a bigger cam, and since I have a friend in the machine buisness I'll get then ported to flow max air. roller rockers will also be installed. I'll also install a 400 crank to get some more cubic inches out of it. pistons will be dome top to up the compression a little, not to much I still want to run pump gas. I'll set the idle a little high and cross my fingers.



another question.... would crome molly rings be a good idea with a mild dome top piston? I would assume higher compression motors run hotter so I would not want to burn up regular rings.

as for what compression is desired I dont know anyone tell me what higher compression could still be ran on pump gas?

thanks....

Your elevation where you live and the design of your head's combustion chambers will dictate how high up in compression you can go before needing exotic fuels. If you're close to sea level 10 or 10.5:1 is really pushing the bill. The fella I bought my Tunnel Ram from was running 12 or 13:1 on his Ford 302. My 289 is right about 9:1 as I slapped the ram on an engine that wasn't idellically set up for it. But it seems to work pretty well as it is.

And let me repeat this....... Mike P is dead on right. You will need LOTS of patients and plan on having the hood up 90% of the time dialing it in. I was persistant too about putting on a tunnel ram (mostly for the wow factor) but it does have some cajones, certianly not on the bottom end, like it use to, but that was to be expected.

Ported stock heads may not actually be enough, but nevertheless, will definately help. Definately recommend a higher stall converter. I'm running a stock stall now, but getting it to idle in "drive" decently is proving to be almost impossible.

When I was looking into Rams, I was led to believe from the elder crowd, that running vacuum sceondary carbs on a Tunnel Ram was a no-no because Tunnel Ram's create a vacuum signal is so weak and inaccurate. I was told to use manual secondaries, even though I have seen other setups with vac secondary carbs. Just food for thought.

And another thing, you're only running 900cfm when your foot is completely burried in the throttle. So like what was said before, disabling the secondaries (if you're afraid of overfueling) may or may not be a bad idea. However if you jet it to operate in the lower rpm ranges (street use) you may easily run lean when you do "mash it."

Update:

The dual 390 cfm Holleys seem like they'll work well on the 289 Weiand #1988 manifold. We put spark to it last night and it started right up and idled thunderously. It wasn't getting fuel from the pump, though (???) -- dribbling gas into the carbs it would idle for 5-10 seconds at a time and then die.

We're working on the fuel pump glitch but this sounds like it's going to be a runner once we get that dialed in.

Future advice for anyone who finds this thread a year from now using the SEARCH function: Definitely go with the smallest carbs you can find if you're going to run a small-block dual-quad tunnel ram.

Thanks for all your help, everyone!

Good flowing HEADS, I use trick flow twisted wedge, 4:11 or lower gears, if auto at least 3000 rpm stall and vac sec carbs, progressive linkage is probley better but I don't use it, I'm running 10.1 comp on 92 oct, I do use a MSD 6al, as far as working on/tuning the carbs all the time, well I set mine about 5000 miles ago and it's still running fine, even in parades (idleing in gear for hour or so) she don't load up.

Don't worry about about the 900 cfm, mine total 1000 cfm but thats the MAX the carbs CAN flow, I doubt I flow 800cfm at WOT @ 7000 rpm.

The gears make up for the torque loss, it won't come into the sweet powerband slot till 4000-4500rpm, from there to 7000 or so it will make ya .

Oh yeah, FORGET about gas mileage

I was wondering who owned that! Nice ride!