Is a Holley 800cfm too big?
Thread Starter
Burning Brakes
Joined: Jun 2000
Posts: 892
Likes: 0
From: GA
Is a Holley 800cfm too big?
My friend has a new never installed Holley 800cfm for $300. I have a 600cfm now on my 355 4spd. It seems to bog when getting off the line but this could be b/c I don't have it tuned correctly...
Do you think the 800 will be too much carb?
My engine is putting out 375-385 HP with 400 lb ft.... not sure if that information is needed.
Do you think the 800 will be too much carb?
My engine is putting out 375-385 HP with 400 lb ft.... not sure if that information is needed.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Mr.Gearhead
My friend has a new never installed Holley 800cfm for $300. I have a 600cfm now on my 355 4spd. It seems to bog when getting off the line but this could be b/c I don't have it tuned correctly...
Do you think the 800 will be too much carb?
My engine is putting out 375-385 HP with 400 lb ft.... not sure if that information is needed.
Do you think the 800 will be too much carb?
My engine is putting out 375-385 HP with 400 lb ft.... not sure if that information is needed.
I would go about 750 double pumper but then again I am a fan of double pumpers.
Thread Starter
Burning Brakes
Joined: Jun 2000
Posts: 892
Likes: 0
From: GA
I didn't know that about intakes... I always thought the carb was determined by horsepower needs... I checked some carb "calculators" and they recommend around a 600 cfm. This is the one true area that I have never tried to play around... I just though it would be easy to buy one for the car instead of jetting and such... My intake is an Edelbrock Performer... I wanted to be able to clear my stock hood without any issue. From your pics... I see you did the same... 
So a 750 Vac Sec double fits the bill? Can you tell me what the true difference between a double and single will do for me... THANKS.
So a 750 Vac Sec double fits the bill? Can you tell me what the true difference between a double and single will do for me... THANKS.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
you know i have a speed demon 750 vac sec carburetor and thats probably comparable to a holley 800 cfm. My speed demon works great its not too big for my 355/350 hp engine and i have a performer intake also
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Advanced
Joined: Aug 2005
Posts: 50
Likes: 0
From: Michigan
Tech Contributor
Joined: Aug 1999
Posts: 14,384
Likes: 6,408
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by kb2fzq
Here we go with my "too much carb?" thing again... 
Lars, please enter here....
Lars, please enter here....
Originally Posted by Mr.Gearhead
So a 750 Vac Sec double fits the bill? Can you tell me what the true difference between a double and single will do for me... THANKS.
If you're looking for a bolt-on carb that will not require any tuning or jet changing, a used 800 is probably not the best idea. Any carb will require setup and tinkering, so you're just as well off working with what you have.
The 800 can be made to run fine on your car, but it's bigger than you need. If you're going to spend $300, don't spend it on a compromise - save up another $150 and get a nice, new, correctly-sized carb for your application. This, by the way, will still need to be tuned... I run 750 mechanical sec carbs on the engines I set up. Many people have very good luck (and performance) with 650s. Bob's 750 vac sec carb (it's a BG Speed Demon) runs really well on his car and pulls very strong.
Last edited by lars; Dec 13, 2005 at 01:26 PM.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I mentioned there is sometimes a need to tune the carb for the intake. Let me roughly explain this.
If you are using the 600 the velocity of the air through the venturi will be high. If the intake is low rise the air/fuel mixture will have to take the turn into the runners at high speed. The gas particles don't want to make this high speed turn so they continue past the ports and hit/bounce off the intake floor and this is fuel seperation.
'The same carb would benefit from a spacer to let the mixture have a chance of making the bend.
Put a 800 on the same intake and the velocity is slower and this will allow the mixture to make the turn into the passages. This carb would NOT benefit from a carb spacer.
Now put the 600 back on a high rise intake, one with more time/distance for the mixture to slow down and make the turn without fuel seperation.
On the mustang with a 355 I like to run a 750 double pumper. I find there is not guessing if the secondaries are opening/ when this is happen and you control when and how they open.
I also like the 4 corner idle.
Properly tuned they are a very responsive carb.
I run two 850 double pumpers, 4 corner idle on my 460. Great on gas and never the slightest hesitation when pushed.
If you are using the 600 the velocity of the air through the venturi will be high. If the intake is low rise the air/fuel mixture will have to take the turn into the runners at high speed. The gas particles don't want to make this high speed turn so they continue past the ports and hit/bounce off the intake floor and this is fuel seperation.
'The same carb would benefit from a spacer to let the mixture have a chance of making the bend.
Put a 800 on the same intake and the velocity is slower and this will allow the mixture to make the turn into the passages. This carb would NOT benefit from a carb spacer.
Now put the 600 back on a high rise intake, one with more time/distance for the mixture to slow down and make the turn without fuel seperation.
On the mustang with a 355 I like to run a 750 double pumper. I find there is not guessing if the secondaries are opening/ when this is happen and you control when and how they open.
I also like the 4 corner idle.
Properly tuned they are a very responsive carb.
I run two 850 double pumpers, 4 corner idle on my 460. Great on gas and never the slightest hesitation when pushed.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by lars
... I run 750 mechanical sec carbs on the engines I set up. Many people have very good luck (and performance) with 650s. Bob's 750 vac sec carb (it's a BG Speed Demon) runs really well on his car and pulls very strong.
Couldn't use a full 800 cfm on its best day. You'll have more snap with the 600 
Race Director
Joined: Jan 2000
Posts: 13,024
Likes: 2,266
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Once again..I'm with Lars here.
I love big carbs, but the 800's I've used before always were sort of a morphodite sorta deal. They were much "fatter" throughout the entire curve and were trickier to get set right. They were great on a typical high 10 sec small block high compression (13.00) race car type deal. With a little work they were fine, but you have to have some experience with them to get it perfect.
Something like the old basic 4779 Holley 750 DP is about the most universal carb out there. It will run well on anything with little effort.
JIM
I love big carbs, but the 800's I've used before always were sort of a morphodite sorta deal. They were much "fatter" throughout the entire curve and were trickier to get set right. They were great on a typical high 10 sec small block high compression (13.00) race car type deal. With a little work they were fine, but you have to have some experience with them to get it perfect.
Something like the old basic 4779 Holley 750 DP is about the most universal carb out there. It will run well on anything with little effort.
JIM
