If I measure differential pressure over throttlebody at wot,how much is too much(ie when I need bigger tb)?

 

Measurements are done.Results:diff.pressure from air cleaner snorkel (after filters)to plenum ->2.4 kpa at wot.Vacuum at plenum at wot ~2kpa.So I think original 2x48mm tb is enough to my combo.

 

Ideal is zero of course. Sounds about right for what you are doing. However I'm chasing the 2+kpa in my setup and going with the monoblade.

 

Do you mean+2kPa over pressure or 2kPa vacuum?

 

When my motor starts out at the track under wide open throttle the KPA will read somewhere around 100 to say 101 kpa in the plenum. As the rpm's get up around 6200 rpm the kpa will drop to the 98-99 range. So that is what I meant by the 2+ kpa drop. Heck that could mean 5 or more horsepower I'm losing. In my quest for 500hp at the motor I can't have that.

 

Do you have ram air that makes over pressure?When I made pressure measurements, there was +6kPa at air intake duct at part throttle(3000 rpm,4rd gear, and ~95mph).At wot ~6500rpm and +140mph at third gear there was -2kPa vacuum.I made my mesurements with VERY accurate differential pressure transducer.
When I yesterday talked with local enginebuilder ,he was sure that there was benefit a bigger tb.He told that they found +40hp when they went from 52mm tb->monoblade at 377ci(de stroked 400ci) miniram Vette engine.He told that with 52mm tb there was ~3kPa vacuum at plenum.

 

If you have an LB9 you don't need a 52mm TB.

 

Current engine is 355(hotcam,stealthram,EQ vortecs,SLP tri-y's etc)

 

I'm just data logging the info off the computer and reading the KPA. Atmospheric pressure usually reads somewhere between 100 and 101 KPA. So if I'm dropping down to 98 to 99 KPA in the plenum I have a slight depression.

There is a local head porter called the Air Doctor who claims good horsepower gains on LT1 motors by going to a monoblade. I'm going to give it a go.