So 3 months after the original engine blew and its almost there.

So far I have a new 454 HO crate engine with an LS6 intake manifold. I was going to use the old quadrajet but I need a square bore, and I might as well get a better carb anyway.

My question is which carb? I know this has been asked alot and I have read a bunch of the old posts. I had been thinking about a 800 or 750 Edelbrock performer. After reading a few posts I am not sure.

Things to consider: I am not sure if any carbs are too tall butt I want to keep my original 71 BB hood, thats why I got the LS6 intake. This is a street car. Not a daily driver but almost. Fast is fun. Gas prices are high. I know a few of those are almost directly contradictory, still they are considerations.

THANX
TED

 

800

 

is the 800cfm Edelbrock big enough or should I get an even bigger Demon or Holley? Does anyone have any experience with the Performers? I read one post that said they do not maintain flow around corners and in severe braking.

THANX
TED

 

MINIMUM of an 850 Dual Feed mechanical secondaries. My choice would be bigger!

 

you can figure out mathematically how much carb you need

formula is (engine c.i. / 2) / 1728 * Max RPM

so (454/2) / 1728 * 6000 RPM = 788 CFM

 

The LS6 intake is basically similar to the L72, L88, and ZL1. unfortunately it will not clear a stock hood. A very good all around and tough to beat dual-plane intake for solid lifter engines from 4000 to whatever, 7g`s +. Marginal with a hydraulic cam because performance really takes effect with this intake where the hydraulics stop, namely over 5500. A OEM style 780 Holley with divorced choke and vacumm secondaries is a good choice. Dont over carb the engine or all you will get is problems. 850`s are for extreme HP, L88`s, LS7`s and ZL1`s at 550+ hp

 

Urban legend!! Check with Lars for the real facts.....

 

I always heard on here that the LS6 intake would fit under a bb hood. I know a Torker II will fit as I ran that combo for a coupla years under a stock 74 hood.

I run a Holley 850 that's tuned with an O2 sensor. It runs great. Even on a mild 454, don't run less than an 800 cfm in a Holley or BG.

 

Has anyone had problems with Edelbrock carbs? I think I will go with the 800cfm performer unless I get a good reason to go with somehting else.

THANX
TED

And from my understanding, the LS6 intake is the only manifold ever made that will clear the hood on a BB with square ports. It has a low profile. It came stock in a handful of 71 LS6s I think. However, I am no expert and my knowledge comes from reading other's posts.

 

What facts am I to look for? There were a few LS6`s in 1971 Vettes and there could be a lowrise manifold besides the tall dual-plane that could fit under the stock hood. If so, extremely rare.

 

That's a fair question. How about

- Real life, hands on tuning of the carbs referenced in this thread
- Real life, hands on evaluations "" ""
- Real life, hands on comparisons - side by side and substitution

I hope that answers your question. I hung around with guys like Lars in the 60's and early 70's - wizards!! I learned a lot from them, and I have done a lot with a lot of cars over the years, but when you got real serious issues, you gotta get in touch with the wizard. In this house, that would be Lars.

 

KING -
Your engine combo will run great with either a 750 or an 850 on it. My personal preference would be an 850. People with Over-Carbo-Phobia will tell you 750 (or 390, or something...)

Here are some facts from recent personal experience - I've tuned and installed literally hundreds of carbs, so I'm not pulling this out my rear:

- Pulled a well-tuned Speed Demon 750 (mechanical) off of a stock 427 and installed a Speed Demon 850 (mechanical). Results: Noticeable improvement in off-idle feel, throttle response and top-end power.

- Installed the 750 Speed Demon (which flows a bit more than 750) from the 427 on a stock 350 after removing a stock 750 Q-Jet. Results: Significant improvement in throttle feel, low-end torque, and WOT power.

- Pulled a 650 Speed Demon off of a built 355 and installed a 750 Speed Demon. Results: Massive improvement in power and throttle feel throughout the rpm range.

- Pulled a 650 Edelbrock Performer carb off of a stock 350 and installed the 650 Speed Demon (which flows more than 650). Results: So much of an improvement in throttle response and power that even a girl was able to tell the difference.

- Pulled an 850 Holley HP (mechanical) off of a small block 406 and installed a 1050 Dominator. Results: Reduced 1/4-mile times by .2 second.

Question I get asked a lot: Have you ever installed a carb that was too big, resulting in off-idle and low-rpm problems. Answer: No. I've never been able to get a "too big" carb to perform badly or poorly at any rpm. Every case of problems that I have seen associated with a carb that's "too big" (stumbles, rich mixture, poor torque) have been tuning problems with the engine not associated with the size of the carb, and the problems have been fixed by correctly tuning the carb & ignition - without changing the size of the carb.

If it were me, I'd go for an 850 on a big block. No question about it. Keep the rpm up and keep the engine in its power range before you hammer it. You'll have a great time. The 750 will run well, and is a safe bet. But a well set up 850 will take it...

Here's a 1050 cfm carb on one of our small blocks. Street driven and runs mid-10's:
http://forums.corvetteforum.com/pho...php?photo=29692

 

Lars,
What would be the best way to have you set up a new Demon; Buy it and send it to you or send you the money and have you buy it?

 

LARS a big block needs a 1100cfm minumum and my 327 needs a 350cfm!! What you talking about?

 

As big as you know how to tune. 850 minimum.Even a dominator could make that rock with the proper tuning.

 

The LS-6 manifold with a Holley will definitely fit under a stock big block hood. Use Lars advice for size.

 

I dont know the gentleman. I`m sure he`s good if you say so. However I would invite you to look over my "My Corvette Photos" and then click on this site and review it closely, http://www.nitroalley.net Some real NHRA history can be found here. Bench racing is not allowed in my house, only performance qualifies.

 

Any way you can measure the height of the stock setup and then mock up the new one on the LS-6 manifold? The Holley web site gives data on all the manifolds (as does Edelbrock, I think) to include height at front and rear... If you carefully take measurements of your stock manifold and the LS-6 manifold you should be able to answer your question about clearing the hood. As for carbs, get one from Lars!