Carb selection for BB (part II)
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 905
Likes: 1
From: New Bern NC
Carb selection for BB (part II)
I received an email from a high performance carb place that is recommending a really big carb. Here is the email:
Your carb selection will depend on how far over the 425 hp range you are.
400- 425 hp I recommend a modified 750 cab. when you begin to exceed the 425
hp We go to the 950HP carb. I know a lot of guys use 850 carbs. But we try
to stay away from those carbs for any type of street use. The venturi wall
is so straight that it has a weak booster signal. The 950 is an incredibly
quicker responding carb. These would be my recommendations. The 750 is $495
Brand new and custom calibrated for your motor. The 950 is $595 same thing.
You will need to provide the engine specifications. I know these prices are
higher than you see in the auctions. Those carbs are stock calibrations.
What I am offering you is completely different. The throttle response, fuel
consumption, and overall performance is night and day. I hope this helps you
and doesn't confuse you.
Jim
I like the idea of looking at a huge carb, the size of a breadbox. Is that an overkill? Does his recommendation about staying away from 800 cfm carbs make sense? My 454 is rated at 425hp. I do plan on increasing HP as much as my budget can handle.
Thanks,
Your carb selection will depend on how far over the 425 hp range you are.
400- 425 hp I recommend a modified 750 cab. when you begin to exceed the 425
hp We go to the 950HP carb. I know a lot of guys use 850 carbs. But we try
to stay away from those carbs for any type of street use. The venturi wall
is so straight that it has a weak booster signal. The 950 is an incredibly
quicker responding carb. These would be my recommendations. The 750 is $495
Brand new and custom calibrated for your motor. The 950 is $595 same thing.
You will need to provide the engine specifications. I know these prices are
higher than you see in the auctions. Those carbs are stock calibrations.
What I am offering you is completely different. The throttle response, fuel
consumption, and overall performance is night and day. I hope this helps you
and doesn't confuse you.
Jim
I like the idea of looking at a huge carb, the size of a breadbox. Is that an overkill? Does his recommendation about staying away from 800 cfm carbs make sense? My 454 is rated at 425hp. I do plan on increasing HP as much as my budget can handle.
Thanks,
Racer
Joined: Dec 2001
Posts: 498
Likes: 0
Re: Carb selection for BB (tworottiedogs)
If you have an LS5 your factory raiting is 365HP. The LS6 was 425HP. Let me know what you are thinking about for cam, compression, heads, intake, exhaust, and carb, and I will run it through Desktop Dyno for you.
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 905
Likes: 1
From: New Bern NC
Re: Carb selection for BB (compuvette)
It is a newer 454HO GM crate motor. Rectangular port heads, LS6 intake, Hedman headers, roller cam (don't know the specs but can fine them) and HEI ignition.
Racer
Joined: Dec 2001
Posts: 498
Likes: 0
Re: Carb selection for BB (tworottiedogs)
With a 780 Holley and guessing on the cam (I used a Comp. Cams 258XE Hyd. Roller) it comes out to 440HP@5000RPM and 595LB@2000RPM. Man, look at that torque!!! If you go with the 950, you get 450HP with no change in torque. If you get the exact specs on the cam, post them and I will re-run the numbers.
Drifting
Joined: Jul 2001
Posts: 1,418
Likes: 1
Re: Carb selection for BB (tworottiedogs)
That is a pretty small cam in that motor.I would run a out of the box Holley 4779 "750" or a out of the box 4781"850 because of the dual plane manifold if you plan on stepping the power up later with a cam
[Modified by mountainmotor, 3:11 PM 12/25/2001]
[Modified by mountainmotor, 3:11 PM 12/25/2001]
Racer
Joined: Dec 2001
Posts: 498
Likes: 0
Re: Carb selection for BB (mountainmotor)
Yea, I just guessed because it is a factory 454 roller cam. It would defenetly run better with a bigger cam. But look at that torque number! The curve on Desktop Dyno is long and fat! That thing would be murder on tires!
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 905
Likes: 1
From: New Bern NC
Re: Carb selection for BB (compuvette)
here are the cam specs:
This steel roller is for the 502 and 454 H.O. engines. (Must use distributor gear P/N 10456413.) The duration at .050" tappet lift (intake/exhaust) is 211/230; and maximum lift with 1.7:1 rocker ratio (intake/exhaust) is 510/540. Valve lash is zero/zero and lobe centerline is 112 degrees.
This steel roller is for the 502 and 454 H.O. engines. (Must use distributor gear P/N 10456413.) The duration at .050" tappet lift (intake/exhaust) is 211/230; and maximum lift with 1.7:1 rocker ratio (intake/exhaust) is 510/540. Valve lash is zero/zero and lobe centerline is 112 degrees.
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Racer
Joined: Dec 2001
Posts: 498
Likes: 0
Re: Carb selection for BB (tworottiedogs)
With your real cam specs it is looking like this:
780cfm
490HP@5000
580LB@2500
850cfm
495@5000
582@2500
950cfm
498@5000
582@2500
Remember, these numbers can be off by at least 10%. But it sould at least give you an idea. Man, I bet that thing is fast!
780cfm
490HP@5000
580LB@2500
850cfm
495@5000
582@2500
950cfm
498@5000
582@2500
Remember, these numbers can be off by at least 10%. But it sould at least give you an idea. Man, I bet that thing is fast!
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 905
Likes: 1
From: New Bern NC
Re: Carb selection for BB (compuvette)
That is NUTS !!! I don't know if it is fast. It hasn't left the driveway yet. :mad
Does that program show recommended updates. Does it go as far as selecting a better intake if there is one? Looks like there is not much of a difference with carb selection.
Thanks
Does that program show recommended updates. Does it go as far as selecting a better intake if there is one? Looks like there is not much of a difference with carb selection.
Thanks
Drifting
Joined: Jul 2001
Posts: 1,418
Likes: 1
Re: Carb selection for BB (tworottiedogs)
Yeah the bottom end torque is overkill.Get a larger cam so the car will move off the line and run up top better. That intake can be modded for a little better top end performance.What gears do you have?You are close to have a very fast car with 3 mods :cool:
edited to ask that when you get it running will you get a sound byte of those Moroso Spiral Flow's ?
[Modified by mountainmotor, 5:31 PM 12/26/2001]
edited to ask that when you get it running will you get a sound byte of those Moroso Spiral Flow's ?
[Modified by mountainmotor, 5:31 PM 12/26/2001]
