thumpetto007

iTrader: (15)

Oh, so the very top end was killed by the "step" of a non portmatched IM.

I didn't realize it was that big of a difference. That's huge.

curly

iTrader: (25)

VD?

18psi

iTrader: (76)

thumpetto007

iTrader: (15)

With barometric stability velocity attraction correction dynamics.

thumpetto007

iTrader: (15)

Ok, there is no way that's the correct plot... I was looking back at the pre and post skunk 2 plots back on page 3, and neither one of them take a nose dive... something must have been wrong with that pull?

The only reason I care is SCIENCE

18psi

iTrader: (76)

I dunno, you made it, so...

Stealth97

iTrader: (5)

Nice gains, but looking at the throat of the square top, I thought it would be a smoother transition. I'd love to see a comparo between flat top and a 99 with the throat cutout and re-welded

thumpetto007

iTrader: (15)

There isn't enough wall thickness to take much material out of the "throat" It's hard to see from the pictures.

I purposely stayed "shallow" with the portmatching, because I wanted to minimize potential ill effects.

Madjak

Similar to a 3 angle cut on a valve, or a rear diffuser, the air can flow over around a 15 degree change in angle smoothly, but any more and it separates and start to form a turbulent zone. As long as there is a smooth transition that's not super radical you'll pick up 90% of the airflow gains from removing the step. You could port is better to get that last 10% but it's hardly worth it for a stock motor.

So step vs no step was a 2-5hp difference? Not bad actually considering the engine isn't limited by the throttle body and it's such a simple job to do. The same mod on an engine that needs more air, like a stroker or a ported head with big valve and the difference would be double that.

Lokiel

You've still got plenty of meat to take off - here's my efforts for comparison:



I wasn't game enough to take any more off between 12 and 2 but everywhere else I've still got plenty of material left.

18psi

iTrader: (76)

/\ that looks super smooth, good job.

I think ours turned out even better than the pictures show, somehow the pictures make it look more rough than it actually was. Overall it was a time consuming and messy job, but not hard at all.

and yeah he made sure to make the transition smooth. I was holding the thing down, OP was grinding

Savington

iTrader: (31)

emilio700

iTrader: (3)

Inspired by this we're going to include a same day A/B test between the matched squaretop and Skunk TB tomorrow while we're dynoing some prototype Supermiata cams. The ported IM was on Deviate when we made 300whp with the Rotrex.

18psi

iTrader: (76)

curly

iTrader: (25)

Yay! I was going to do this myself, but the engine is a few weeks away from being completed.

stevos555