Thread: Witch Carburator choose?

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Hi
I have a little 350 small block chevy. The only modification I made is a

Camshaft with lift:477/480 and duration@50: 224/231.
Valve spring that fit with my cam
make 3 angle valve seat and 2 angle on valve
I got a pair or 882 heads
aluminium intake
for the rest it is almost stock
I have no high stall torque converter
3 speed automatic th-350
run on manifold for the moment but I plan to have it

Now, somebody told me that it will be better if I put a vacuum secondary, but I've got in mind to put a holley 4150 650cfm mechanical secondary double pumper

Is it good or bad ??
Any Carb suggestion ??
Thanks at advance guys!!

You will want to run a stall converter with it--2400 would be about right. Otherwise, you will be shifting into neutral every time you pull up to a stop sign. As for the carburetor, I think you would be happier with the way a vacuum secondary Holley would perform with your automatic transmission. Double pumpers are a better choice for a car with a manual transmission because the clutch can allow you to raise the rpm immediately. If you use a double pumper with an automatic, and you stomp on the accelerator, you will have a great big bog because with all that fuel you don't have the rpm to use it. Vacuum secondaries open more slowly as the engines rpm increases. IMO, a 600 cfm vacuum secondary carb would be a good choice for your combination.

I concur with rumrumm, re; vacuum secondaries. I'd go with a 600CFM on this head. (Others may disagree and you'll want to hear them out as well!)

Holley Part #: 0-1850C is a 600cfm with vacuum secondaries as is the Edelbrock 1406 – both have electric chokes. The Edelbrock carbs tend to be rich out of the box and unless you’re prepared to re-jet/re-meter, I’d go with the Holley.

The 882 head is not the best performance head around but if you've already had them machined then I would use them. The problem with the 882 is it’s an open chamber smog head 72 to 76 cc. It may have 1.94 intakes, but some had 1.72 intakes. All had the 1.50 exhaust valves.

With 1.94 intakes they flow about 195CFM at .400 lift, 212CFM at .500, however, the small exhaust vales only allows 135CFM at .500. With your cam you will have a bit of a lumpy idle, but should still pull at least 16 inches of vacuum (minimum for good idle on the 1850 Holley).

Good Luck,
Glenn

What year gears do you plan to run?

I predict you will be very disappointed with your build. With 76cc heads, your static compression ratio is somewhere around 8.3:1 and will not work well with more cam.

The cam you have chosen closes the intake valve later than a stock cam, which would be a better choice for 8.3 SCR. The longer duration cam will lower the dynamic compression ratio into the toilet, along with cylinder pressure.

I'm pretty sure your vehicle will be slower than it was with stock parts.

To answer the question of carburetion, the rule of thumb is to use a vacuum secondaries carb if you are using a torque converter that stalls at less than 3000 rpm's. Over 3000 rpm's, you can use a double pumper to advantage.

i have some nice used caster flat tops if a low buck build and some new forged flat tops that will bump the thump up to

The more I thought about my previous post the more I questioned it and then Techinspector confirmed my doubt – the heads and cam are just not going to work well together.

It appears that you have already procured some 882 heads. While I hate to “spend twice”, I would encourage you to put your 882 heads and intake manifold on Craigslist or E-bay and procure some Vortec heads. The Vortecs have a 62-64cc chamber which will increase your compression 1 full point over the anemic 76cc of the 882's. Have a machine shop relieve the heads to accommodate the increased lift (stock Vortec is good for .420). That will make a huge difference and respond well with the cam you’ve selected, a Performer RPM manifold, and any of the vacuum carbs described above.

well i have and would use the pbm heads not the gm vortec heads lite casting that love to crack but that up to you. if you like spending good money on junk casting that flow good but need abit of machine work. you will need another intake to fit the gm vortec heads

Another affordable head choice would be the 68cc S/R Torquer heads from World Products. They would work nicely with your cam and boost your compression to a more efficient level.