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Title:Free HP for CPI

Author:Sparky

Intake Manifold Tuning Valve (IMTV) modification.

After doing exhaust mods I was surprised at the drop-off in power above 4500. In data-logging my runs I noticed the IMTV shuts back off at 4650. Why would Chevy do this? I'm assuming so the trans would go ahead and upshift, but don't really know. First, I just grounded the relay and it picked up a full tenth in the quarter mile. I looked at MAP voltage at idle and it increased .1 volt when open (I was worried it would increase it more than that and dump fuel). I then pulled the upper intake, sawed out the bar below the valve and sawed off the IMTV flapper. MAP voltage increased another tenth at idle, but no ill effect. Gained, on average, .18 sec. in 1/4 mile. It actually picked up my 60' time (stock doesn't turn on 'til 3000 rpm's) also.

DISCLAIMERS & ADDL. INFO.

1) My Blazer already had a higher stall converter and 4.10 gears.

2) It is a 92 with 4L60 (700r4). I do not know the results with a 4L60E.

3) I had the stock y-pipe with a 2.5 inch Flowmaster dumping down in front of the rear axle. It has since had full-length Heddman headers and dual Flowmasters. I feel the increase even more now (I think).

I highly recommend going to the track to test. Make 2 passes and then ground or jumper the relay and make 2 more passes. I believe the results will be well worth the time and expense to test. Besides, who doesn't like going to the track? If it picks up you can feel safe to perform cutting mods. Good luck!