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what size carbs for tunnelram

20K views 14 replies 11 participants last post by  Rick_L  
#1 ·
hi im currently building a 350 sb for my 56 truck its got cast steel heads im ussing a tunnelram but im unsure of what carbs i should use ive got brand new 600cfm carbs but some say its to big any suggestions and is it difficult to tune
 
#2 ·
Traditionally the tunnel ram setup uses 600 CFM carbs like the ones you have. IF you are building the car for the street, this setup will look cool, but will hinder performance do to the flow capibility of the SBC. That being said I have seen many over the years that work well enough to be a fun car to drive.
 
#3 ·
Which camshaft, heads, ignition and gears really will help determine the answer. Without knowing your combo, I would put the smallest carbs you can get... even if you end up with 2 500 cfm Edelbrocks, that's 1000 cfm of flow, and that's probably too much.

Traditionally the tunnel ram will work the best at the high end of your RPM range, and will give up power/driveability at the low RPM's. IF you don't have a decent cam and fairly low gears, the tunnel ram would be better used for a boat anchor.
 
#6 ·
The problem with a tunnel ram is not so much "over carbing" it, but with the big plenum under the carbs, and the fact you have two carbs, you'll have little airflow velocity at low engine speeds. So a small carb with small venturis to keep the airspeed up through the carb makes sense for driveability.

Summit sells a tunnel ram/carb kit with two 390 cfm Holleys. It's a good setup to make your tunnel ram behave better at low speeds. Two of the smallest Edelbrocks would be an equivalent choice.
 
#7 ·
A stock chev two four intake use,s two 490 cfm carter wcfb,s that is 980 cfm. many stock350,s used a 850 quadrajet. So i am of the opinion ifyou have added a cam and hedders to your 350 and use progressive linkage two 600 cfm carbs will be ok.A small block chev can use more cfm per cubic inch than most other engines. Randall
 
#9 ·
Two 600's "could" be too much but they can be dealt with. The engine is only going to take as much air as it needs. That said if you're using Edelbrocks , in my opinion, they can be dealt with even easier. By dropping the acc. pump linkage to the bottom hole , you'll be shortening the throw.(less fuel) Then make your ordinary adjustments. If it's just too rich where you can't dial it out then pick up 2 of the Edelbrock step up spring kits. These kits have 5 differant size sets of springs in differant colors so you can't screw them up. On either side of the top of the carb you'll find a torx screw. Undo one at a time and turn the cover off to the side while at the same time "catching " the rod coming up. Once you do that you'll find a spring in there that you take out and compare to the kit that you bought.You can probably get away with dropping 2 sizes or maybe even 3 in each carb. Just make sure that the springs match before you install them. Button it up and start the adjusting again. Take it out and lay into it to clean it out. Once you get back, check for richness and if it's still too rich then drop another spring size and take it out again. Just remember that turning the adjustment screws in on the right side of the carb, leans it out by cutting fuel supply. Alittle rich is good but too lean is not. Good luck
 
#10 ·
if you dont have the cam and heads plus intake i would go with 2 450s for street:tu
 
#13 ·
If you already have the carbs, run them. Even if they are not ideal they will still work.
A tunnel ram supposedly makes your engine act like it has bigger heads.
Your peak torque is usually unchanged with the "wrong" carb, but horsepower may suffer.
I tested a Pontiac 400 with a quadrajet, 750 holley vac sec, 650 holley d.p., 850 holley d.p., and a carter of unknown size. They acted different, but all worked well.
 
#14 ·
we have tried MANY different combinations with track testing to back up our seat-of-the-pants "street dyno" and the best we saw was a tunnel ram with a single holly 850 on top. It went 2/10th's faster in the eighth mile with the single 4 bbl over the dual 600's. That was on a 468 motor in a 69 chevelle.