Lemming

Ok, thought that I would finally start a new thread so that we would no longer muddle up Carl's thread on his street SC kit.

Went to the dyno today to get my dyno certification. If you remember from the other thread, I had hoped for 300 rwhp on my race car to put me in the right place for my new class (NASA GTS4). My previous dyno on a Mustang dyno had the car at 307 rwhp. This was going to be a problem as NASA requires certifications have to be done on a dynojet, so add 10% to the Mustang numbers.

So, off the the dynojet today and low and behold I ended up with 309 rwhp at 6600 rpms. Great for my race classification but why 10% down from the last dyno.

Changes to the car since that dyno:

1. Pulled the supertrapp muffler (with 20+ discs) and added a Dynomax turbo shorty muffler. Why, I was sick of the awful noise made by the supertrapp. This muffler may be a bit more restrictive.

2. Added an MSD ignition and Magnecor 8.5 wires. I wanted something with an adjustable rev limiter since the current chip is at over 7,000 rpms. Plus, upgrading the ignition couldn't hurt on an FI application.

3. Put on a new IC and BOV that is documented in the other thread.

So, why didn't I make 330+ on the dynojet? Not sure but one thing that was different was that I only made 5 lbs of boost at 6600 rpms, where I was making 6 lbs of boost before. Not sure why this would be. I did not measure the SC pulley that Carl sent me with the rebuild, am wondering if I got the larger pulley?

I did not have issues with slippage with the new knurled pulley, so that is a big plus!!!! You will notice an oscillation in the boost graph below, that only occurred when we were using the port directly above the throttle body to measure boost, when we took it from the intake manifold, it was very linear. As for the image below, we limited the rpms to 6400.

As you can see, the car is running rich in the middle of the rpm range. We tried everything to dial it out but could not without dramatically affecting with low or high rpm A/F.

dillon410021

I would love to see some more videos of your new toy!

Jfrahm

Nice. I have the knurled pulley handy and it measures 2.36" vs. 2.25" for my old Stage 2 pulley. I do not think there is a Stage 2 knurled pulley.

-Joel.

Lemming

Interesting, the spare that I have is 2.301.

Carl Fausett

Pulley sizes:

2.25 = first generation Stage 2 pulleys
2.30 = first generation Stage 1 pulleys
2.35 = second generation Stage 1 pulleys

The 2nd generation Stage 2 pulley has not been shipped yet, it will be shipped with the Stage 2 crankshaft pulley. Shipping date expected to be late May.

There is about a 1 psi boost drop from the First Gen Stage 1 pulley to the 2nd Gen Stage 1 pulley. That is the result of the slightly larger size to combat the belt slip that was being reported from the racers in the field. The larger pulley has more belt contact (increased tractive force) and lower loads (spinning the supercharger slower).

It will provide the longest service intervals for those Stage 1 owners that just want to enjoy their 968 SC on the street.

The New Stage 2 kit will be much more agressive for you racers. By increasing the crank pulley size, I can increase the supercharger speed a LOT and still have zero belt slip. There will be an increase of several psi with this new Stage 2 setup. Rule-of-thumb: 1 psi = 20 HP.

Carl Fausett

That was the goal of the new pulley. Not designed for max boost, designed for zero slip and longest service intervals. It will be good to hear how the belt looks after a race.

Lemming

Well, that explains the decrease in boost. Can't wait to get my hands on the new stage 2 pulleys. I hope to build boost sooner and then bleed off power at the top to stay in class. I could see this being done by either bleeding boost (at 5 lbs) or through engine management.

Carl Fausett

Nice AFR numbers under boost. I like to see 12:1 for safety. You started to go north of that at 6400 rpm, watch that. Thats where the detonation will occur, max boost, max load, max cylinder pressures and temps.

Carl Fausett

I have a nice analog Boost Limiter here if you want to bleed off any overboost:
http://www.928motorsports.com/parts/...mitervalve.php

Lemming

I was on the dyno for a good bit on Saturday as we tried to get the AFR set. We had a tough time with the trough that you see around 4,750 rpms. We ended having to dial out most of the rising rate and tip in point. I had the same issue on the last sets of dynos as well. I'm seriously thinking of going stand alone on this car so that I can tune it properly. Biggest issue is $$$$$$$$$$$$.

And yes, once the stage II crank and SC pulleys are out, you can send me a boost limiter!

Lemming

Carl,

What do you think the max boost will be for the stock 968 engine in good condition? That is, what can we boost to before breaking things. Assume that this is on a car running an intercooler.

Carl Fausett

The boost is not what harms headgaskets - its the detonation. If you can fuel the boost correctly, then I dont see a problem running 10 or 12 psi of boost.

I too have seen that rich drop in the A/F ratio of the 968 in the midrange, and was unable to tune it out. This is in the area just before the Variocam acts, so I ran my 968 with and without the Variocam active to see if that changed things and it did not.

I am working now with a fuel pump voltage modulator on a Mercedes Benz SC kit I am developing, and if it works it could be an alternative to the FMU. The problem is the MBenz is a dead-head fuel system and the 968 is a full-return fuel system.

The other solution is an aftermarket Engine Management System, like the Electromotive that we sell.
That also would allow you to tune-to-boost at every point in the curve.

Lemming

We did manage to dial out out the rich condition at midrange, but then it was too lean down low and up top. When you do get the midrange correct, you pick up 12 hp or better from 4-5.5K rpms! I agree with needing to make adjustments and am working on a stand alone system. Will give more details when they are ironed out.

nick_968

If you run 12 psi on a 16v 968 you will be knocking on the door of 400hp, at least you would be with a turbo. At this power you will need a good intercooler or at least that you can verify is actually keeping intake charge under control. You will also be approaching the limit of the factory fuel pump and the rods. You may want to think about reducing compression with a thicker head gasket if you dont uprate/ modify the engine internals.

Lemming

Just for kicks, here is the SC dyno followed by a previous dyno of my engine without SC. This was done a few years back on the same dyno. It is interesting to me that the torque numbers have not increased that dramatically (25 ft lbs), but what has changed is the shape of the tq curve and when the car makes max tq (5500 vs 4250 rpms).