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.

 

VD?

 

 

With barometric stability velocity attraction correction dynamics.

 

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

 

I dunno, you made it, so...

 

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

 

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.

 

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.

 

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.

 

/\ 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

 

 

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.

 

 

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