Question for other Supercharger users

I finished installing my Whipple supercharger about a month ago but due to waiting for other parts to show up (mostly Kooks headers & H pipe) and waiting for the snow to melt I just today got to test drive it. I must say I'm in love but I have some questions.

First, the boost/vacuum gauge. At an idle and putting around the gauge reads around 22 of vacuum. Is this correct? I have never driven a boosted vehicle so I have no idea what it should read. When I jump on it I hear a beautiful whine and the gauge jumps to about 10lbs of boost. This I am sure is correct I just am not sure of the vacuum reading.

Second, when I come to a stop from any speed and put the clutch in the idle seems to hang around 1300-1500 for about 5 seconds or more before it slowly drops to 800-900 where it should be. Is this what your car does? I hate how it doesn't drop to 800-900 right away. It reminds me of when I tried the BBK throttle body. When I installed it I had a very similar problem with the throttle body so I took it off and went back to stock.

I purchases my Whipple kit from Lethal Performance and it came with a custom SCT tune from Dave Lund. I am not sure if a custom tune from my local tune shop can fix this or if it's something due to a vacuum leak. I am not convinced it's a vacuum leak because the idle does eventually drop to 800-900 and idles fine once there. I would think if it was a vacuum leak it would never drop to 800-900 rpm.

Maybe I should change the throttle body to a accufab or ford racing one before I get it dyno/tuned? I did use throttle body cleaner my stock unit when I was installing the supercharger to try and clean it up some.

Any input would be much appreciated

Thanks for the vacuum info. I am going to get a Ford Racing TB and have it custom tuned and see what happens.

ct07gt said:

See if Lethal Performance can get you a tune that gets rid of the hanging idle. I would imagine that they would be able to do that for free since you just spent a lot of money with them, they should just be able to update the tune. It might be worth trying before you buy a new TB.

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I am sure Lethal & Dave Lund can help with a new tune but I was going to have it done on the dyno anyway to see my numbers and to make sure its tuned exactly to the mods I have. Dez Racing is the place I go and he is "heard of" all over as one of the best tuners out there. I also wanted to get the FFRP TB this spring anyway, I was just going to use the Dave Lund tune to get me to the shop. Now that the idle needs tweaking, I figure Ill just get the TB and have it tuned now as opposed to later. I am very happy to hear, based on the replies I'm getting, that its most likely a tune issue and not a vacuum leak or something the like. Thanks for your reply

PHILJBRO said:

I also installed a Whipple SC in my 2008 GT and purchased it from your same source. However, they had me send off my computer to CA to get it tuned. My vacuum at idle is 21 inches and my boost goes to 6-7. My idle RPM is about 800 and after a little kicking it, it returns to 800 right away.

The only other mod I added is an oil separater in the PVC line. I get about a teaspoon of oil monthly; depending on how ofter I kick it.

I did not install the intercooler, however. For my purpose, it didn't seem necessary.

Hope this helps, PHILJBRO

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Hi, I didn't have to send out my computer because I already had an SCT tuner for which they could just send me a tune via email and I also planned to bring my car to to get custom dyno tune anyway. Not just that, I have long tubes and since long tubes are illegal in California they could not write me a tune for them. I have recently gotten my car tuned and it now runs absolutely beautiful. I am netting 455 rwhp @ 11.9 lbs of boost