Team Chevelle banner
1 - 14 of 14 Posts

·
Registered
Joined
·
406 Posts
Discussion Starter · #1 ·
I am building a 496 Big Block. 454 .60 over stroker = 496 for my 71 Chevelle SS 454. I am running 049 ported and polished heads with bigger 2.19 / 1.88 valves. Solid roller cam @.50 248/252 660 lift. 10.2.1 compression. RPM range 2200 to 6200. 2800 stall. I have been told a 850 double pumper to a 750 double pumper. This will be driver on the street 95 percent and 5 at the track. I will be mashing on it hard but not over 6500rpms. I think either on may work if jetted correctly. I want the correct size and dont want to get caught up in just going bigger. Thanks John
 

·
Registered
Joined
·
7,729 Posts
I would either go with a 950 hp or a 850 dp.

The 950 actually only flow 830 cfm so either will be pretty close.
Edit: I deal with AED they are pretty helpful if you have any tech issues.
Dave
 

·
Registered
Joined
·
707 Posts
A full service speed shop with a dyno would really be the best route. But. I have a 427 at around 500hp. I went from a 750 dp holley to a 850 demon and picked up 6mph on the top end of the 1/4. Cheap way would be to barrow a few carbs if possible. Or see what others use on basically the same motor in similar climates. But 750 does sound rather small for your motor considering I run an 850.

The main reason I suggest a shop is that the cfm number on carbs is useless. Some companies use 1.5hg (air pressure basically) and some use 3.0. The numbers are mostly to sound good. There are many factors that make a difference such as style boosters. Some carbs use big venturies and small butterflies to help with streetability and part throttle. That being the usual obstacle of the big blades on the dominators. So to take 3 750s or 850s from different companies would get different results.
 

·
Registered
Joined
·
14,338 Posts
850 w/o question.
 

·
Registered
Joined
·
237 Posts
I am running 9:1 on my 496 and just had the dyno done last weekend. My 850 demon had to be jetted three different times however we were able to get it running OK for the normal hot days in Florida. When it turns cold however I will either have to buy a 800 or have the air bleeds re-drilled. They had a 750 double pumper there and we tried that out for the heck of it and all though the 750 ran good, the motor ran better with the 850.

Don't waste your money on anything until you get the motor dyno'd. Check in your area and find one that has different carbs on hand to test out for your set up... trust me you will be MUCH happier with the outcome of your motor.

PS AED carbs according to the machine shop that did my dyno said that they are the best!!
 

·
Premium Member
Joined
·
1,499 Posts
Your 496 is basiclly an air pump. So much CFM will flow through an air pump depending what RPM you are at and how efficient the amount of air will flow. If your engine is 92% V.E. at 6500 RPM. It will flow 860CFM. You will need 900CFM carb to get the full power. A tri power setup will work very nice. It will give you smooth but strong throttle response at low end.
And all the CFM when you gun that 496.
 

·
Registered
Joined
·
1,346 Posts
These formulas always calculate carb sizes much smaller than whats typically recommended on this site and in magazines. Why the disconnect?
 

·
Administrator
Joined
·
17,201 Posts
These formulas always calculate carb sizes much smaller than whats typically recommended on this site and in magazines. Why the disconnect?
I suspect that the V/E is being mis-represented by the user input.
Kinda like cam selection where bigger isn't always better and frequently the wrong cam gets selected.
 

·
Registered
Joined
·
406 Posts
Discussion Starter · #12 ·
Re: How do you determine carb size for a 600hp 496?

Well, from the responses, I am still confused. I plan to drive on the street 95 percent of the time and 5 percent at the track. I am like everyone else and want the best of both worlds but realize I may no get it with out having a street carb and track carb. Still looking for input. John :confused:
 

·
Registered
Joined
·
445 Posts
Re: How do you determine carb size for a 600hp 496?

not sure which brand is your preference, but Holley has a Q&A on their website that will select a few different carb styles and give you cfm as well, it's easy to use. BG has a spec chart that list some parameters of a motor and will list carbs for you. My motor is a 454, .30 over, 10:1, eddy oval heads, 240/246 @.50, air gap, and is also a street car, I'm using a 850 mighty demon annular boosters (i called the BG tech line, and that's what was suggested) and this carb works very,very well. As mentioned above i think an 850 would do the job, Holley Hp, or Mighty demon.
 

·
Registered
Joined
·
7,577 Posts
I feel your frustration man. I learned that sometimes the manufacturer's tech act like salesmen a little, and tend to stay away from them. I was looking at the graph that was produced when I plugged your numbers in, and you could probably get by with a 750 or an 850, ultimately depending on what your engine's actual VE is. Then there are probably a thousand other factors to consider, like jet sizes and other mechanical parts as well as environmental factors too.

Hey, get an 800. It is right in the middle, right? :p
 
1 - 14 of 14 Posts
Top