Carl Fausett

We have just completed our re-design of our Stage II supercharger kit for the 968.

The design objectives for our Stage I kit, introduced 3/9/2009 were as follows:
a) low boost (and no special head gaskets)
b) use the stock injectors and ECU (no chip needed)
c) keep the Air Conditioning
d) ease of installation
e) low cost

The design objectives for this Stage II kit, are different, and are:
a) maximum performance
b) track-ready belt drive system

as it just so happens, we were able to again retain the air conditioner, although that was not directly a design goal.

another sub-goal was to provide an easy upgrade for owners of our Stage I kit or our first Stage II kit should they want to upgrade to this newer version.

As discussed on the Stage I kit forum, the Stage II kit is an ADVANCED kit. Not the simple bolt-on and drive of the Stage I kit. The Stage II kit does require modifications to the 968 fuel delivery systems to fuel the greater amounts of boost that this kit provides.

There are a number of ways that can be accomplished. You could go with large injectors, an FMU, and fight the IAC (Idle Air Controller) to get an idle that works. We chose to remove the IAC and the FMU, and instead use a modern engine management system to control all igntion and injector events.

The Tec-GT system we installed recognizes boost pressure in the manifold, and adjusts the fuel and ignition timing as needed for maximum output yet safety for the motor. The stock engine management systems cannot do that.

This provided the least tuning headaches and the greatest flexibility for the customer, because now he can continue to build on this platform if he wishes (agressive camshafts, etc) and he will be able to adjust his tune to any modification easily.

We did discover that the 40 lb/hour injectors that the customer had were adequate for this installation because he had fitted a 1:1 rising rate fuel pressure regulator. Conversely, a person could use 50 lb/hr injectors and the stock regulator with the TecGT system and also get a good tune. Electromotive does make an adapter that allows use of the stock IAC with the TecGT EMS, but as this is a track car, we chose to remove the IAC altogether. The Tec-GT also was able to use the stock throttle position sensor, the stock knock sensor, and the stock crank reference sensor, among others. This simplified the installation for us.

We did actually achieve 297 RWHP on a couple runs, but we had the ignition timing very finely tweaked to do that. That equates to 349.41 HP at the crank.
But with the timing so edgy, we thought one batch of bad gas could endanger the motor. We backed out a couple degrees of advance to add a margin of safety for the customer, and arrived at the numbers below.

The dyno we were using is a eddy-current dyno type, known for lower numbers compared to inertial drum (Dyno-jet) dyno's.

Our goal was durability and safety for the customer - he tracks this 968 - so we knew it would be pushed hard and long during road races. We ran the car under load in a numbers of gears at many different rpm ranges and throttle positions for more than two hours. We arrived at an extremely reliable installation with a tune that is exceptionally safe for this engine.

I hope you will also agree with me that the installation is clean and uncluttered.

mtnspeed

Would you put this on a car that doubles as a weekend cruiser and DE track day car? I guess what I am saying is, "would one expect to have consistent tweaking to keep in running well?"

Eric_Oz_S2

Carl,

What boost are you running? Has the engine been decompressed? Does the 110 octane fuel allow you to run such comparatively high AFRs of around 12?

Carl Fausett

Yes, as we have it installed here, absolutely. It will not require continuous tweaking and fiddling. The tune is very stable with the Electromotive Engine Management System. Frankly, this tune is more stable than the Stage I kit because we got rid of the old (1992) computer with its slow processor and the IAC. Both are very limiting. Now it is stable and reliable.

The Stage I kit uses the stock ECU in order to hit a price point. This one does not. So the idle on the Stage I kit will actually do more hunting than this one. But off idle, the Stage I kit does very well, even with the stock ECU.

Carl Fausett

On this carwe saw only 5.8 pounds of boost.... actually less than we saw on the Stage I kit on a stock 968.

Now, before anybody gets excited, realize that PSI measured at the boost gauge is not a measure of supercharger output. It is a measure of engine restriction. And, as restrictions are removed, HP will go up and the PSI at the boost gauge will go down. Those are good things.

In this case, this 968 is a track car, and had a free flowing exhaust system without catalytic converters. We are spinning the supercharger impeller several thousand more rpm than in the Stage I kit and I can assure you the CFM it puts out is higher. But, because this engine is breathing better than a Stage I install with stock exhaust, the pressures are lower.

This engine has stock camshafts, and we left the Variocam running normally. No changes.

As to "comparatively high AFR" I cant answer because I do not know what you are comparing it to. Maximum power is produced at 12.5:1 A/F with gasoline, and we typically go richer than that for the cooling effect of the additional fuel and the safety it adds. Low to mid 11:1's is common.

If you think 11.9:1 is high, then its because of the aluminum heads (which helps prevent pre-igntition and detonation well compared to steel/iron heads; and the quality of the combustion chamber shape. The shape of the combustion chamber has a lot to do with how even and uninterrupted the burn and the flame propogation is.

We never logged a knock event on this engine, although we had A/F ratio's as high as 13:1 while we were tuning. Of course, the fuel was worked out first before we started adding ignition timing back in. We never run aggressive timing on an engine until we know full well that we have the A/F ratio fully controlled in every cell of the map.

Each cell of the tuning map corresponds to about 200 rpm.

BTW: someone is going to ask what the boost gauge would say on a Stage II kit with a stock exhaust. My guess would be about 8 psi. Remember there is more than boost pressure involved. Actually an increase in PSI isnt even our goal in supercharging. OuR goal is an increase in air MASS. Air DENSITY.

The Raptor we use has a high adiabatic efficiency - the quality of a compressor to pressurize the air without heating it. Because, after all, hot air is less dense than cold air. So, because the charge air coming from the Raptor is so cool (relative to other brands/types) we can get more HP from a motor with less pressure/PSI. Or to put it another way, a supercharger with lower adiabatic efficiency will have to work harder and make more pressure to equal our performance levels, because they are producing hotter (less dense) air.

Eric_Oz_S2

The graph title says AFR = 11.9 (which is what my comment was based on), but I just realised the actual is more like 11.4:1. My reference to high AFRs is through discussion with tuners that recommend around 11:1 to 11.5:1 max for a high compression engine that has been supercharged.

I plan to eventually delete my Cat and put in a better flowing exhaust header. It will be interesting to see the difference in "boost" pressure and power.

Sorry for all the questions - I'm always keen to see how others go about these supercharger installs and what sort of results they get out of them.

Carl Fausett

Don't be sorry for all the questions - they are good questions!

Yes that AFR graph is almost entirely between 11.4 and 11.6 AFR. The graph reports 11.9 as the "average" because of the initial tip in at 3,000 rpm (the early bump in the AFR graph). I should have mentioned that before. The actual in use was 11.5 AFR, not 11.9.

nick_968

How much is that ally cover on the cam tower, I can't see it listed on the site?

mtnspeed

Thanks for the feedback Carl. When can we expect you to put a price point up on your website. I am assuming it is different from the current Stage II?

Carl Fausett

I did design this drive system around the easy to get Gates double-sided belt, so that our customers can more easily get spare and replacement belts when they want to. I wanted to avoid a custom belt or an imported-and-trimmed belt if I could.

The NAPA part number for this belt is 25-D060674

This belt worked very well, and is reasonably priced.

Carl Fausett

I hope to have the new Stage II kit up and on our website this week. Yes, because of the crank pulley and other new parts, the price will be higher.

I intend to list it two ways: the Stage II kit only; and the Stage II kit with matching ElectromotiveTec-S kit with instructions (complete). I'm listing the Stage II kit only option for those customers that want to use Haltech, Motronic, Mega-squirt or whatever.

Carl Fausett

It is an accesory to our electromotive kits for the 928. Here is the link.
The price is per pair of distributor covers, obviously you only need one.

http://www.928motorsports.com/parts/...tor_covers.php

Lemming

Carl,

Do you have a dyno sheet with the correct scaling on the y-axis? The one shown above seems strange, as the torque and HP curves should intersect at 5252 rpms?

wpb968

Any plans to do a dyno run on pump gas? Will the AFR be different on pump gas?

Thanks,
Steve

Carl Fausett

The lines would intersect at 5252 if the chart was HP to Torque. But, I posted HP to AFR and those lines will never intersect. I have called the dyno and they are emailing over a HP/Torque chart for me to post that will be more "normal". Good catch. I'll put it up as soon as it gets here.

Steve, To run pump 91 octane you would take some boost out (larger drive pulley), and back off the timing and you'd be fine.