Hank,

I discussed this very topic at length with a retired university prof that taught automotive engineering and did a lot of turbo work in the 70's, the direction was the effect is minor and not worth the headache of a diffuser.

I still wasn't convinced though until I happened to stop at RCTS the local high end tuner shop for high dollar stuff (>$150,000)cars. On the floor was a plastic BMW intake off of a factory supercharged M3 (6?)that had split from too much boost.... well not only didn't it have a diffuser - it had huge tapered trumpets inside the manifold pointing directly at the throttle body!

BWM has been building inlines for a long time so I took my clue from them and deleted the diffuser. So far no ill effects.

Perhaps over the winter I'll pull the turbo manifold and install 6 thermocouple wells so I can measure the EGT's which will tell whats going on.

Well hind sight is 100% perhaps putting it horizontal would be better for clearance. I was trying hard to not have anything hanging over the valve cover.

I'm considering moving the master cylinder and brake booster under the floor to clean up the firewall if this comes to pass, it will open up a lot of possibilities where to locate the TB. Maybe even redo the plenum so its a tapered upside down U and mount the TB outboard of the engine... all just random thoughts right now...

Thanks for the feedback though.

Last edited by efi-diy; 09/03/09 02:54 AM.
51 GMC 4.2 turbo
Can't solved today's problems using the same technology/thinking that created them