wwinton

After quite a few mods and most recently a Scivision MAF and chip, I decided to have my car dynoed, especially to check air/fuels, as I have never had them done. The good news is that A/F's are spot on, but HP was only 198.0, I have always thought my car was a little slower than a couple of my friends 951's, there's done 230HP on the dyno, and always thought it was the AFM(the porsche dealer even thought it was faulty), but after fitting the MAF the car feels exactly the same, not even any better response.
I have done the usual mods, removed the insides from the Cat, 3" cat back exhaust, 38mm Tial Wastegate, MBC bypassing the cycling valve, 3 bar FPR.
Yesterday at the dyno I had the boost maxed at 15.5psi.
I have checked and double checked for vacuum leaks, I also get a couple of flat spots as I accelerate after hitting boost.
Any Ideas?

Chris Prack

I would check for excessive voltage drop on the battery to engine/chassis ground. I had a car that had low numbers and found it had 980mv voltage drop on the ground. Cleaned the ground points and replace the battery cables and the power jumped back up where is should have been.

This problem is more common that people know. I have two 951's recently that have had excessive drop that improved after cleaning.

wwinton

Thanks, that is a good place to start as our RHD cars have the battery in the back, an earth problem could easily happen.

special tool

You need to run the car in 4th gear also.
Your chart says 4th, but it is obviously not.

wwinton

Yes is was 4th gear, I did get him to do a run in 3rd as well, we got 208HP.

special tool

So you shut the car off at 4600 rpm?
Because that is about what 159 Kilometers per hour equates to in 4th gear with a turbo transaxle.

wwinton

I wasn't in the car, but it sounded like redline to me. I will try to get some more readouts from them and have a good look.

special tool

I think you are misinterpreting me.
In the above chart, either it is 3rd gear, or the speedo calibration is WAAAY off.
Not maybe.

Either way, maybe there is an explanation here.

xsboost90

mine with same mods at alittle less boost was 219.9rwhp on a dynojet- stock chips/3'' exhaust/ tial 38/ mbc @12psi. I would say yeah it maybe down slightly.

xsboost90

wait thats in KPH not MPH- difference?

philcav7

He is in Australia. They don't have miles there, they have Kilometers

159KPH is like 98MPH

Lorax

Forgive me for ignorance... but what is the point of having someone else drive your car on the dyno?

wwinton

With all the safety rules around now, I was not even let into the bay where they do the dyno, all I could do was stand and watch from a roped off area.
I just went back to the shop, they printed out every readout they could for me, except RPM readings, they don't log them, they just run the car flat until the HP tapers off, I was there, the car was revving its **** off!

Lorax

That sucks! Time to find a more laid back shop lol. i guess it's no big deal i was just wondering.

Bri Bro

Torque and RPM cross at 5250 RPM so the max RPM on the chart was around 6K, had to be a third gear run since you were below 100MPH.