Crate motor carb size

[Dirtmod13]

Maybe brad can chime in on this one. Was wondering what size carbs work best for the 604 crate. I know back in the street car days most people bolted on the biggest carb they could find and it hurt performance. But that was for drive ability issues also. So is a 750 too big for a 350 with 400 horse?

[Matt49]

Maybe brad can chime in on this one. Was wondering what size carbs work best for the 604 crate. I know back in the street car days most people bolted on the biggest carb they could find and it hurt performance. But that was for drive ability issues also. So is a 750 too big for a 350 with 400 horse?

I would also somewhat defer to Brad but my opinion (and this shared by John at JDR) is this:
650 works better on small, stop and go tracks
750 works better on big momentum tracks

[50j]

JDR has other choices too.

[brad hibbard]

in a short answer i agree with John at JDR
but we can enter into the discussion further

lets start with basic carb explanation

when we say "big" carb we are refering to the venturi size and in the crate world "big" equates to 750
when we say "small" carb it would be a 650

big carbs accelerate slow but make good HP in the upper RPM band
big carbs tend to have a flat spot or hesitation on restarts and corner exit

small carbs accelerate quickly but flatten out on the power curve early
small carbs can create wheel spin on slick tracks during restarts and corner exit

with the price of quality built carbs being what it is ---its not feasible for most teams to own two different carbs for changing track sizes and conditions
thats why over 5 years ago we came out with the 700 carb-----its a good blend of low end response and top end power

1 thing to remember is that a 604 does not race well if its not accelerating
engines with "big" carbs tend to run more gear to get the car to accelerate-----speed is created with less gear when the rpm is limited

hope that helps
Brad

https://www.race-1.com