my77stang

are those rhodes lifters noisy?

67mustang302

Roller cam and most overhead cam performance engines can manage to pull 90% VE or more if they're well built(good heads, induction etc), but yeah, less than 100% for sure which means a smaller carb than it would need with a higher VE. That's why it's still shocking how many people are putting 750cfm or larger carbs onstreet 289/302s. If a Cup car can pull 105-110% VE(possibly more)with a carb that's 20% "too small", then it's hard to see why someone could think that smaller(or rather properly sized) carbs are "too small" to make power on street engines.

fast66

Hey 67mustang, don't give away all our secrets. It what can give us the edge at the track!

falconfixer

Another apect is airflow velocity. The cars operate at higher speeds = more ram air/inlet pressure which is conducive to better high RPM performance.

At idle/ low speeds/launch - a one bbl is 'best'. As you increase RPMs and increase flow requirements a 2bbl and then a 4 bbl (and then a six pack...) is 'best'.

So i ask - what is your RPM range 'goal'? High speed oval or stoplight launch? It could change the recommended CFM carb (but really only slightly - i.e. half a size smaller or half a size larger... since we don't have 'custom' sizes or true variable venturi carbs).

My advice? When in doubt pick the smaller carb for the application. Just don't go down more than 100cfm than common/recommended application would dictate.

67coupe

Here is another thought to the whole restrictor mess. When they were allowed to build special engines for restrictor plate races they used larger ports on the restricted engines than on the unrestricted.

67mustang302

I think the most amazing thing is that even with restrictor plates and small carbs, they can still find all that power somewhere in the combination. And yeah, carb sizing is gonna depend on the application, which gets right back to why people stick large carbs on street cars, when for 90% of the driving a street car sees, the smaller carb is better. Certainly most street cars are a tradeoff of some top end power for some bottom end power, mileage, drivability, throttle responseetc, but it would seem the Nextel guys have proven that lots of top end can still be had from a restricive induction system, so on a street car there's no need to go huge to get power. I wonder what their manifold vacuum is at peak power. Certainly there is a difference with a restrictor plate engine too in the heads, cam etc, but again, it would seem they've proven that it can be worked around to still find power

And yeah, I guess I shouldn't be giving away all the secrets....want the Bushes Baked Beans recipe?

Starfury

VERY noisy Sounds like a solid lifter setup with a lot of valve lash. What happens is thatas the lifters collapse, the valves drop into the seats making a loud tap. Definitely not for everyone, but I'm very happy with the performance. I switched from a Comp CamsXE268H that was barely streetable with 3.25:1 gearing and would lean misfire at 1500rpm's, to a Magnum 280H with rhoads lifters that has great bottom end and runs all the way to 6200.

If you don't mind thevalve clatter, they're well worth the price.