Operation 'Not Performance Improved'

nickmckinney · Sep 29, 2011

Cam specs are dead on good for these heads and blower combo, without the blower these cams will make more bottom end torque NA than the stock cams even. As for comparing NPI to PI heads, the exhaust port of the NPI head is a serious choke point that really shows in boosted applications, I want to say a stock NPI exhaust port is done at 130-140CFM give or take. Longtubes show more power gains on NPI heads than PI heads for this reason.

6-7PSI is pretty low though, no chance on getting a bit more boost out of it? Can't these get into the 8-10PSI range?

sneaky98gt · Sep 29, 2011

nickmckinney said:
6-7PSI is pretty low though, no chance on getting a bit more boost out of it? Can't these get into the 8-10PSI range?

That was exactly what my tuner said as well. If I would have known a 3.3 wouldn't have gotten any more boost than this, I would have gotten a smaller pulley to start with. I was seeing 7.5 pounds with my old 3.48 pulley before the cams. I was thinking/hoping I'd see around 8 or so with the 3.3 pulley and cams, but apparently the cams are just moving the air that much better.

I'm going to the track on Sunday in some nice cool weather. Depending on what happens then, a smaller pulley might be ordered first thing Monday morning. We'll see.

Gearbanger 101 · Sep 29, 2011

For reference sake....I was running a custom 2.35" 8-rib blower pulley on my M90 with only a hint of slippage.

I bet you could get away with a 2.80"-2.90" pulley without much fuss. The '03-'04 Cobra guys were running them without slippage. Granted, they were running 8-rib drive systems, but they were also fighting through an intercooler brick as well. I bet you won't have near the restriction on the discharge side that the OE Eaton MP112 set up from the Cobra had.

As for your low end torque pick up….I’m 100% positive that it was due in full to the smaller blower pulley and not the cams. The smaller the pulley, the faster that blower comes on and the earlier the torque curve develops.

nickmckinney · Sep 29, 2011

Gearbanger 101 said:
As for your low end torque pick up….I’m 100% positive that it was due in full to the smaller blower pulley and not the cams. The smaller the pulley, the faster that blower comes on and the earlier the torque curve develops.

These cams are advanced 6 degrees over the stock ones, this advance picks up the torque bigtime even NA. Basically with the cam swap we are opening the intake valve a full 18 degrees earlier than the stock cams (and only closing it 6 degrees later), this is a trick to getting bottom end torque gains with bigger cams. Looking at it most all his cam duration gain happens on the front side. If the intake port was the restriction rather than the blower itself, we would put more duration on the backside.

The guy with the NPI NA record that I did the cams for found a low end torque gain of I believe it was 20ftlbs even though we went over 10 degrees bigger on his cam swap.

Either of these cam specs would destroy a stock PI motor the PTV would be so dramatic. These are tricks only NPI can do stock, a PI motor needs a notch in the piston.

Tim2002GT · Sep 30, 2011

I wouldn't worry too much about the numbers. Let the mph at the track speak for itself. When I put LT's on my car, the dyno didn't really show much difference at all, but I picked up a consistent 4-5 mph at the track with the nitrous. Picked up 2-3 on motor.

Dark04GT · Oct 1, 2011

Car sounds great will. My hitechs are jealous.

Mr. Rustypwnz · Oct 1, 2011

what were the numbers at the peak over the old pi's?

I say you need to port the heads, and a 3" pulley. the difference from the heads alone would be huge.

sneaky98gt · Oct 1, 2011

Dark04GT said:
Car sounds great will. My hitechs are jealous.

Thanks man!

Mr. Rustypwnz said:
what were the numbers at the peak over the old pi's?

I say you need to port the heads, and a 3" pulley. the difference from the heads alone would be huge.

Both dyno tunes were from 3500 rpm up. From 3500 to 5500ish, it made exactly 15 ft-lbs, across the board. From 5500ish up (to around 6000 on our dyno pulls), it made around 20 ft-lbs more. (Keep in mind both pulls were uncorrected, and the original tune having much better weather). I think it would make quite a bit more out past 6000 than the old PI cams. The torque curve at 6000 is much more flat now than it was with the PI cams. I'm shifting around 6100-6200 now, and it is definitely still pulling there. If I wasn't worried about valve float or the extra stress on the bottom end, I think it would be good on out to 6500.

I thought about heads for a little while, but decided against them on account of cost. Just not worth it. I'll have a Cobra before I touch the heads.

It desperately needs a smaller pulley, haha. It's about 55 degrees outside and dry right now, and it's making just a little over 7 pounds. My tuner said that more boost would be good for two reasons: 1) More oxygen coming in (duh), and 2) Being able to run more beneficial timing with the meth.

I'm going to the track tomorrow. Gonna have great weather (high of 62). So I'll hold off until then to comment on whether I'll actually get another pulley or not.

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