Steve40th396

I am sure this was discussed many years ago. TPIs made an air foil for our throttle bodys. Debate is whether it made any real gains. TPIs has a great reputation and I am not digging on them.
But, It was said that the top of the air foil was blocking a majority of the air that goes into the top of the throttle bodys cavity which then allows fresh air to go to valve covers, on LT1s at least. This could cause blow by due to lack of air getting in there, decreasing the effect of the PCV system..
Anyone ever have this issue?
Now there are many air foils out there.

Injuneer

Dyno test of TPIS air foil:

Drivetrain Modifications #4

Doesn't address the PCV air flow, but I don’t remember anyone raising the issue back then. Not worth much… almost seems within the tolerances if two dyno pulls.

Injuneer

This site was the basic reference for modifications “ back in the day”.

WS6.COM LT1 Trans Am

Steve40th396

Thnx. I saw a couple references to people having issues with blowby after using it. I am thinking it was the brand they used. I am sure TPIs would have seen issues with it considering how many they sold over the years.
I took it off the throttle body I am going to use. It was blocking the upper passage quite a bit.

Injuneer

That air stream (or lack thereof) from the side of the throttle body to the passenger side valve cover would not cause blowby. If blocked it would allow blowby to accumulate in the crankcase, reducing the effectiveness of the PCV system. If you already had excessive piston ring blowby, pressure could build in the crankcase, and that would typically cause backflow of vapor into the throttle body (and the typical oil buildup that accompanies it). That would probably get past the shielding of the passage by the air foil, since it wouldn’t seem to be a tight seal.

Personally, I would avoid the add-on air foil. If you really need to improve air flow to support modifications, just get a larger throttle body with the “streamline” machined into the body. I bought my Formula brand new in 1994. I fell for all the “miracle” HP enhancements - air foil, underdrive pulleys, AFPR, etc.. Eventually realized they caused more problems than benefits.

Steve40th396

^ Yes, I fell for all the little tricks when I bought my LT1 Corvette in 96..
But, with the 396 in it now, the AS&M has never been "right". It has the IAC passageway fixed in the back, but it always had minor idle issues. I now have the 52mm TPIs bored oem one I am going to try.. Its a mild 396 built by MorePerformance years ago. Not many miles on it..

Chimera96

OP, your stock, bored, TB would have the IAC hole in front. 1/8". The aftermarket TB's don't and often have idle issues because IAC counts are slammed.

You "may" find your 396 (assume a H/C build) with the stock bored TB will have higher than stock (30-35) IAC counts if you have scan ability to read IAC counts. Drilling the stock 1/8" hole 1/64" larger will lower the IAC counts if needed. You "may" also need to drill 1-3/64 larger than stock but take baby steps and test each size as 1/64" makes a big difference

Steve40th396

I was looking at two other throttle bodys I have on hand. One is the OEM that came off of the same year, 1993 corvette I have. It has a 11/64 hole already in it. The other one, from a 92 has a 3/16 hole. Both are twin 48mm. Interesting. The 93 came off a stock looking wrecked Corvette.
i do know the t body I have on the car is drilled to 11/64
i do have tts datamaster data logs for my 93 Corvette, couple months old. This laptop I have on work/travel doesnt allow tts to work.
So, if someone was able to view them, they could see my IAC counts now, I am sure.
i wont be able to till I get back in July.

Injuneer

If the logs are in .csv format I can review, but if you had a report in that format you could probably read it.

Long time since I’ve seen something from Datamaster.

Steve40th396

All my logs are in uni files. I finally found some hidden on my laptop.. And I was able to get a working copy of datamaster to work on the windows 11 laptop here.
My IAC is hovering around 65 to 75. This is rough because I have nothing where it is idling solid for a while. I need to re log when I get back home.

Chimera96

IIRC IAC counts peg at 160 so at 65-75 you still have some room but when turning the wheel, AC on (more load on engine) it would likely max out causing idle issues in those conditions. 32 is the target at idle (30-35)

regarding the air foil. My stock TB bored to 52 has one. IDK what brand but its been on for bout 25 years now. I don't have a blowby, or PCV issue and pass CA smog which is relentless. Even with a 400 RWHP 383 H/C motor.

Steve40th396

thnx.