I know it probably has been beat to death a billion and a half times but can't find it. I am looking to hear from anyone with a high horsepower car with turbos. Is there any difference in hp levels with stock oem upper plenum than a high rise like crawford, APS, or spacers. I have a crawford but want a stock polished one to clean up the engine bay. Thanks- James

 

Someone is selling a polished Crawford plenum in the classifieds, you might check that. Best of both worlds right there.

Oh and if you want to sell your Crawford, I'll take it as long as it's the newer version, not the modified stock ones they used to sell.

 

What do you care more about, power or a clean looking engine bay. I believe you made that decision when you bought the Crawford piece, no?

Polish the crawford?

 

It is the old ugly version, the modified stock piece. I would like to clean up the engine bay if the crawford doesn't make any power over stock on high boosted cars.

 

Any other insight on this topic?

 

You pick up roughly 10% more airflow with a spacer. I've done flow bench testing with both the angled and straight spacer. Both gave the same results and did a good job of balancing the flow front to rear over stock.

If you sand down the casting on the inside of the upper and lower plenum you can get another 5% to 8% increase in airflow.

The only way to really take advantage of the increased airflow is with forced induction.

I estimate a stock plenum with spacers and interior sanding would equate to most after market plenums, but haven't looked at their airflow numbers.