[Donovan]

I'm learning about square bores and the various features available on the modern versions.

I'm too slow for my own good. Where might I go to learn how to pick the right features for me?

for those that are curious the specs would be like this

6500rpm peak
345 cfm headflow
Muncie wide ratio M20
Something like 500+hp gross
Street driven but not a daily driver.
Curb weigh around 3200

So far I'm leaning toward no more than 800cfm
Vacuum secondaries
Electric choke
Annual boosters


Vanity-wise I do find the Demon series attractive. Not sure if getting an ultra all aluminum type unit would be worth the expense.

I don't think I need a DP, corner idle adjustments or billet anything but really don't have experience.

[ta man]

I'd suggest a carb mechanical secondary for a stick car.A good old style 850 Holley dbl pumper with a electric choke.If you can go without a choke a Holley 950 hp would work great.

[rexs73gto]

With the weight & being a stick I'd go with a 750 HP double pumper with mech. secondaries , that way you'll have all the cfm you need plus you will have the 4 corner idle adj. plus as you learn & grow it has adjustable air bleeds. But right out of the box it's a great carb & will give you all you need. It doesn't come with a choke so it will be a little finicky to idle at first but mine would start & go with out any problems. Tis is a good carb for you & as you learn about it you can add or subtract as you need.

[lust4speed]

I have always preferred vacuum secondaries on both my auto and stick street cars. The vacuum carbs can be larger without incurring any bog should the throttle be fed a little too quickly. A converter car will have less problems with mechanical secondaries, and I've never really understood the consensus for sticks being better off with mechanical secondaries.

Through the years I've had a stock Quadrajet, 800 Holley MS, 2-4 AFB's, 850 vacuum secondary Holley, and finally an 850 Edelbrock Quadrajet on the 4-speed street car. Favorite of all of them was the 850 vacuum secondary Holley that was an ebay purchase and was a new take-off from a 572 Chevy crate BB engine. From idle to redline, the carb just felt good.

As a side note, I ran it on the drag car for awhile before borrowing a friends 950cfm Quickfuel MS carb. The 850 had a little better 60' and was only a little off in MPH on the top end.

[ponyakr]

I'm not a Holley expert by any means. But I recently read where a guy, over on the GTO forum, did some dyno testing with several carbs, including an 800 Q-jet. He had a mild 400 engine. Of all the carbs he tested, the SS-680-VS Quick Fuel, made more power than the Q-jet and most of the Holley type carbs he tried.

http://www.gtoforum.com/f12/opinion-...tml#post624025

http://www.gtoforum.com/f12/opinion-...tml#post624121

This was a vac sec carb. You'd need a larger size. They come in 735, 780, and 880cfm.
These SS series carbs also come in mech sec models, if you prefer. But I'm guessing that the SS-880-VS will give you all the gas you need. In fact, for strictly street driving, the 780 might be better. And they have elec choke.

But they ain't cheap--$500 +

http://www.quickfueltechnology.com/c...condary-1.html

http://www.amazon.com/Quick-Fuel-Tec.../dp/B003M96BHW

http://www.summitracing.com/parts/qft-ss-880-vs

[rexs73gto]

I only recommend the Holley HP 750 because he asked for a Holley carb. Myself I run a tricked out Q-jet on my car. I have a 462 with E-heads & a RAIV blueprint cam, SRP lightweight forged pistons, a performer RPM intake, Eagle forged H-beam rods, an Eagle crank, dbl. roller timing chian & gears, Melling M54F 80 lbs oil Pump with a 60 lbs. spring, it a 4 spd, M-22 , with 3:73 to 1 rear gears. OH, & RA round port exhaust manifolds. I have an elect. choke on the carb & I get ok mileage 15-16 on the hwy. It's best time so far is 11:70's. But I like the Q-jet & if he would have asked about that , that is what I would have recommend for him to run for any CARB. There just trouble free. At least for me.

[Skip Fix]

Hard to beat a 850 DP right out of the box. I think the one on my pump gas motor in the 78 I ended up one click leaner on the jetting.

[ta man]

What is the displacement?345 cfm heads and 6500 rpm is going to need a big carb!

[stickboy]

I only have a BG carb because I bought it for $150. It is an mech sec annular "850". I have gone back and forth between down leg and annular boosters and I can tell you the annular drives WAY better on the street. The both ET about the same at the strip. Depending on the cam size and your goals for the car, I'd be looking at an 850 minimum. It will not be starved for airflow even with the annular boosters.

[Donovan]

fun talk! and I just saw I somehow ended up typing annual instead of annular! hahaha

Cam is a somewhat big HR- 227 and 243 with .630 lift
113 lobe separation

Displacement is 6.2 liters
Intake is a dual plane!

[Donovan]

TA Man - any downsides to the 950 otherwise?

Rex - I'm with you, learn as I go! I like that...

Lust4speed - what you are saying seems to feed my hunch. It sounds like there is a bit more balance. 850 huh... good example man, interesting on the 950.

Ponyakr - Whoa.... interesting details on that post. I was wondering about the QF carbs but didn't have a good impression. That's helpful info! And I agree I'd like to find one used, dang!

Skip - Thanks! What is the double pumper feature good for? reducing bog when kicking the throttle open?

Stickboy - it feels like the reason you see mostly mechanical secondaries on annular is because the superior atomization makes the mech sec work well! Sound true to your experience? Also sounds like because the annulars take up so much room you need a bigger carb to flow around them?

[NO67GTO]

I have a 850 annular demon on my 455 auto street car and love it. Never any problems in 10 years.

[ta man]

No issues with mine properly setup.Even though it is a 950hp its around 800 cfm for actual cfm.I've tested some quite a few carbs on my engine mainly 750 dl pumpers and a couple speed demonI've rebuilt for friends and they aren't even close for throttle response.

[Skip Fix]

Double pumper has mechanical secondaries not vacuum so has a secondary accelerator pump when they open.

Know a couple of other guys using a "950" also. Basically a 750 body w/ 850 throttle blade size.