Cars making no HP, idk what to do.

we need more info ? is there black dust all over the front timing cover , could be the belt slipping on the blower

you might need a new tuner also,the only thing i see that can hold you back is the injectors, but i would think you should have no problem breaking 300rwhp with that setup

If he was measuring backpressure and it got to 10psi, then you obviously found your problem. The back pressure should never ever exceed boost pressure on a supercharged car. That would be significant back pressure, even for a turbo car running 5psi. An efficient turbo would be around 1psi back pressure for each psi of boost. I only mention turbo engines because they SHOULD create backpressure because the impeller is driven by the exhaust gases.

Do you have cats or not? It is very possible you have clogged cats. If you are still running the stock H pipe, then you could see some very significant gains by switching it out. The stocker on my 97 had 6 cats. I gained .25s in the quarter by going to an offroad H.

Sounds like you need to listen to your tuner. If he measured backpressure at 10psi, then something is seriously not right.

sharkbait11 said:

Its a nPi 4.6. Everything internal is stock. I was deffinitaly expecting to see somewere around 300. Id be happy with 280.

The car put down 5 psi on the dyno. Like tuner put the gauge in and it hit 5. He also had a gauge measuring the exhaust backflow. But i dont think a midpipe would suck up that much HP.

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I see you're also running Bosch plugs... they aren't the 4 prong platinum plugs are they? I don't think that would be helping your cause. You may want to try some Motorcraft AGSF-22Cs (copper, 1 heat range colder than stock) and see if that helps.

By nPI, I'm assuming you mean it's a 96-98 motor? Injectors are not your problem since your A/F is 11... that's a bit on the rich side even for a blown car and you are probably leaving 20-30 HP on the table because of the mixture. Is your MAF calibrated for 30 pound injectors? Did he look to see if the MAF is pegging? My Saleen was doing something similar since the MAF got pegged and the EEC didn't know what to do at that point.

There is clearly something going on around 3750 RPM since the graphs start falling off... Typically, a centrifigal should be making more HP at higher RPM than at lower RPM. That graph looks more like a roots blower, not a centrifigal...

Well for one you have belt slip starting at 4200rpms but that is not causing your power loss bad enough. Those plugs are garbage change them. If your tuner told you to go 2 steps colder on your plugs with your set up then find a new tuner. Your biggest problem is your using a garbage powerdyne. It takes almost twice the hp to turn that thing compared to a vortech. Plus they are the most inefficient supercharger on the market. They are belt driven and not oil cooled. That is why you never see that blower being used.

TQ seems low too. I had a stock 4.6L with a mid pipe and catback and made 241RWHP and 284RWTQ...no tune either.

I'd get a second tuner to look at it.