Dual Quad Question

[scorpion1110]

Hi guys:

I have a question. I am building a 283 for my '55 2-door wagon. I will be running an edelbrock 2-four intake. My question is to break in. I don't want to fiddle with setting up the carbs when I initially fire the motor and run it to break in. Can I close off one of the carb openings with a steel plate and break the motor in off of just one carb? Then once broken in, set up the dual quad intake?

The alternative is to fire it up with a single 4 intake, break it in and then switch intakes on the car. Thats a bit of a nuisance. Try-Five friend says close off the openings and use 2 four manifold, Machine Shop says switch intakes.

Thoughts guys?

thanks!

Scorp

[Rick_L]

No need to block off one of the carb mounting flanges. Just don't hook up the linkage to one of them.

[WagonCrazy]

I have no experience with a dual carb setup, so I'm asking a newbie kind of theory/question here:
Running 1 carb (on a manifold designed for 2 with the other one capped off) means the fuel source is closer to either the front 4 cylinders, or the back 4 cylinders.
Does that affect equal distribution of fuel as each intake valve sucks the air/fuel mixture in? And does that unequal distribution mean one set of the 4 cylinders runs a bit leaner than the other 4 because its farther away?
And would that screw things up when breaking in an engine?
Just thinking it through without having any practical experience here...
Would hate to see you blow your engine up due to lean situation on some cylinders.
Common sense tells me to switch to the single carb manifold for the break in period, because it's sitting dead center over the middle of the engine...so maybe air/fuel distribution is more equal to all cylinders?

Call me right or wrong here guys...who's got the answers?

[Bihili]

Many years ago one of the Hot Rod magazines did a comparison of one carburetor vs two carburetors.
I don't remember all the details but the bottom line was overall one carburetor out performed the two carburetors.
If you break in your engine with a single carburetor and single carburetor manifold then you will establish a baseline for a comparison when you switch to two carburetors.
Personally I think you will have problems with two fours on a 283 engine.
Look at the Wallace Racing calculators page.

http://www.wallaceracing.com/intakecfm.php


(http://www.wallaceracing.com/intakecfm.php)

[scorpion1110]

Thanks for the feedback.

I think that I can break it in with the two fours. They need to run 1:1 not progressive and the carbs may need to have different metering rods installed. Still checking.

The Factory offered dual quads in the late 50's Vettes and the 57 Chevy (I think) and these were on 283s so I believe the 283 with the 2x4s will be ok. Its a nearly stock build though with a 10/10 under crank and 30 over flattop pistons. All ARP hardware and the other internals are high end. The heads are Powerpak with milled bosses, screw in studs and guide plates with stainless valves, hardened seats and new guides and viton seals. Also running roller rockers. The lifters are hydraulic and I have a moderate lift Erson cam.

Had forgotten, but when I fired up the 302 in my 69Z after that build, I was running a Smokey SY1 crossram and a single quad 850 CFM carb. That was a finicky set up but we fired her, got her to 2000 RPMs and let her Stella in. Motor ran fine.

Just older now and worry more :)

S

[BamaNomad]

That should be a strong running 283+ regardless of the manifold/carbs used... :) Personally, I've never been a fan of multiple carbs as (for me) *looks* aren't everything. Obviously with multiple carbs you do have some 'wow' factor at the local cruise ins, but for reliability, ease of tuning, etc.. not to mention gas mileage... the properly sized single carb is the best answer. For your setup, unless you are charging around at 6000+ rpms regularly, 600-7-- cfm is all you need. The fifties/sixties 283s that ran dual carbs ran with wcfb carbs that probably pushed 400-450 cfm of mixture.

If you are determined to do it, I'd break it in with a 'known good' single four carb (600 cfm holley would be a good choice, or an AFB..?). As someone posted, when you get a couple thousand miles on it and change to the dual carb manifold, you''ll have a good feel for the difference in performance... :)

[scorpion1110]

I am still checking on jets and metering rods but I expect that I will need to lower the overall CFM. I am running two 500CFM Edelbrocks 1:1 linkage. I also talked to a good friend who is our local "Chip Foose" and he said he would be happy to handle the break in and tune if I wish.

I agree the single quad is the best approach, and may try that, as the motor hasn't gone in yet.

I don't think I can run a single quad on the two four manifold with one carb down due to the intake runners as mentioned above.

Here are a few pics of the build so far:

7683

7684

Thanks, S

[markm]

When I installed the tunnel ram on my 396 in my 55 I first tried to run two Holley 450s. I could not get them to idle. To eliminate intake leaks from my list I installed a motor lift plate over rear carb opening and reinstalled my 780 on front. It ran fine like that, so I installed each 450 and dialed them in separately, reinstalled them as a pair, gave up . installed two model 1850 vac. secondary 600s and its ran fine ever since.

[NickP]

But he doesn't have Holley carbs nor a tunnel ram. Totally different animal and, it's a SBC.

[chevynut]

But he doesn't have Holley carbs nor a tunnel ram. Totally different animal and, it's a SBC.

LOL! :D

[NickP]

Thanks for the feedback.

I think that I can break it in with the two fours. They need to run 1:1 not progressive and the carbs may need to have different metering rods installed. Still checking.

The Factory offered dual quads in the late 50's Vettes and the 57 Chevy (I think) and these were on 283s so I believe the 283 with the 2x4s will be ok. Its a nearly stock build though with a 10/10 under crank and 30 over flattop pistons. All ARP hardware and the other internals are high end. The heads are Powerpak with milled bosses, screw in studs and guide plates with stainless valves, hardened seats and new guides and viton seals. Also running roller rockers. The lifters are hydraulic and I have a moderate lift Erson cam.

Had forgotten, but when I fired up the 302 in my 69Z after that build, I was running a Smokey SY1 crossram and a single quad 850 CFM carb. That was a finicky set up but we fired her, got her to 2000 RPMs and let her Stella in. Motor ran fine.

Just older now and worry more :)

S

What exact manifold is in question?

[markm]

But he doesn't have Holley carbs nor a tunnel ram. Totally different animal and, it's a SBC.

The point I was trying to make was answer his question about running one carb when setup called for two.

[scorpion1110]

Hi-

The manifold is an Offenhauser 360 low rise dual quad. Manufacture date 1988. I don't recall a casting number.