PercentSevenC

Sterling, using your formula, and using 100% as my VE (probably way optimistic, but I really have no idea) and using an 8000 RPM ceiling (in reality I don't take it above 7500 due to the 3mm steel apex seals), I got ~426 CFM for my large streetported 4-port 13B. What this tells me is that a 45 DCOE with 36mm venturis (~440 CFM, according to various sources) would be plenty big enough for my engine. Now, loads of others have said that that is too small, and that you want at least a 48mm throttle size. Your own modded Nikkis also flow more than 440 CFM if I recall correctly. What is your opinion on this? If I do need more, is it a good idea to use larger than a 36mm venturi with the 45mm throttle size? Robert doesn't seem to think so. How does all this change when forced induction is added to the mix?

Sterling

I don't. In this thread I'm calculating the maximum size the carburetor needs to be to satisfy the engine at it's maximum intake capacity to illustrate that people who think a 600CFM Holley on a 12a are very much mistaken.
As far as 2bbl carbs, IMO they are for the track, or for unstreetable blow-through applications where the pedal is either in the idle position, or mashed to the floor.

Well for one thing, there's this bizarre discrepancy regarding the actual cfm rating for 2bbl carbs as compared to 4bbl carbs. Typically, 4 bbl carbs are flow tested at a pressure drop of 1.5" mercury while 2bbls are tested at 3". I don't know why they are measured under different conditions.
I did find an equation to convert 2bbl flow to it's 4bbl counterpart, though;
cfm of 2bbl carb divided by 1.414 = it's cfm on the 4bbl "scale".
The Sterling flows 465 cfm as tested by Rx7Carl. We worked on numerous venturi shapes and booster configurations until we met what we needed for the theoretical maximum. Honestly, we took it farther because we knew that there is no denying that there is a large chunk of the performance market out there that is relatively ignorant about these things, and the fact is "numbers" sell products like these. It was actually quite a triumph for the both of us, more than most realize, because any moron could just hog out the venturis .5-1 mm and bring the total cfm up 20+ more. We succeeded in matching our closest similar competing product (RBs Holley 465) in flow without sacrificing signal to the main circuit, so that low end wouldn't suffer as a result.
Everyone from the Yaw school knew the flow didn't need to be that high.

purple82

Just FYI,

Most folks have heard that doubling the speed of a car quadruples the wind resistance. And some folks are familiar with the Bernoulli equation where P (pressure) is proportional to V^2 (velocity squared), P~V^2. The 1.414 number comes from the same physical phenomenon.

The 1.414 is the square root of 2. If you compare two tests where one doubles the pressure of the test, velocity ratio (and therefore flow rate) of the flow goes up by the square root of 2 because of the relationship between pressure and velocity. If the second test was 3 times the pressure drop, the flow would go up by 1.732.

It's ideal, and the actual multiplier will be somewhat less than 1.414, but it'll work.

PercentSevenC

Interesting. So in reality, a 45 DCOE with 36mm venturis actually flows about the same as a stock Nikki. Well, now I have to rethink my plans.

Edit: I saw this looking up information on Webers just now. I lol'd.

warwickben

iTrader: (1)

omg lol

orion84gsl

iTrader: (5)

Awesome 16 bbl setup. A little excessive but nice. I tried telling... someone, I don't remember who, that his Holley 650 was too big for his SP(I think) 13B. I told him he might be getting tons of air, but his velocity wouldn't be optimal, he said he had the right velocity. I really should have asked him how he knew that, considering he had no way of measuring it. I hope this info is going to make it's way to the website Sterling.

Hyper4mance2k

iTrader: (40)

It's easy. it means that anything that has mass moving at the speed of light squared is nolonger mass, but energy. energy=mass times the speed of light squared

so any mass moving at 89,875,517,873,681,764 meters per second is energy.



back to carbs. With a 45 dcoe on a stock ported gslse engine i went from 136.5 @6450 rwhp to 139.0 @6450 rwhp by changing from 38mm chokes to 40mm chokes. nothing else was changed.