Carl Fausett

This low boost kit should not really impact engine longevity in any way. In fact, there are those that argue that mild boost is easier on the rods than no boost at all (cushioning the piston to a stop at the top as it changes direction).

Of course, high boost requires you consider your head gasket, and I am aware that the 968 has a reputation about head gaskets.

I have almost finished the development of an improved head gasket for the 968... this will be a Graphite Composite Steel; head gasket similar to that which we pioneered for the Porsche 928 for use in NA and boosted applications.

You can read about it here: http://www.928motorsports.com/parts/...el_gaskets.php

They have done very weel for us and have held 12-14 psi so far on the 928 wwithout a failure.

I do not have them in my possesion yet - the engineering was finished about 3 weeks ago and I expect the first units soon.

Jfrahm

The serpentine belt should last a long time and frankly I would not care if I had to change it at 5000 mile intervals. I expect it will last 30K if not allowed to get loose and slip. Who cares? It's a belt. The car is fast now.

-Joel.

edz968s

The belt stretches in the first 100 miles or sdo and on the non a/c install, I can only get 8mm of stretch before changing as I run out of adjustment with the amount of travel the alternator can move. but they are cheap

Lemming

When you say "run out of adjustment", is that a function of your make-shift adjuster, or does the alternator hit something limiting travel?

I've not played with this yet, as my belt has not yet come in.

edz968s

It`s the amount of travel I can get with the adjuster and the chassis rail being in the way, plus the travel of the alternator, before it goes up to high and into negative adjustment.

On a more pressing note, I have just returned from the Rolling road session and disappointingly, the Stage 2 kit I have fitted, achieved 230 RWHP and 236 ft/lbs of tourque, I believe it should make around 280 RWHP.
Are you able to measure the diameter of your drive pulley to see how it compares with mine, sure I got the wrong/bigger size, thats if you also have the Stage 2 kit.

Lemming

Do you know what kind of rwhp you had before the install? 230 is low, I'm pushing that in NA form on a dynojet (200 on a Mustang dyno). Is the 230 figure corrected for temperature, pressure, and altitude?

I have the stage 1, Carl thought it best to start with that kit given that it will be flogged on the race track. My pulley has a diameter of 59 mm.

edz968s

I would guess around 200+. There where guys on the day with n/a 968`s ranging from 190-213 rwhp. Air temp 81F, 29.82 in-Hg, humidity 34%.
I was expecting around 280 as per the results from carl`s fiqures.
The stage 2 has larger flow injectors, that won`t work with my kit over fuelling and a smaller pulley for increased boost @ 6-7 psi, I believe. Thats what has me thinking the pulley is to large. I`ll have to strip it later and measure the diameter. Your`s 59mm on the inner belt run.
Cheers

Lemming

59 mm is the inner belt run diameter.

Lemming

Is it possible that your belt was slipping?

Jfrahm

Hmm, my pulley is also 59mm. Strange. My setup is supposed to be a stage 2.

I am seeing 5-6psi but I am at 1500m of altitude.

If your belt is slipping you see boost drop off sharply at high RPMs.

Lemming

I thought that only difference between the kits were the size of the injectors?

Jfrahm

I do not know offhand.

I thought the description of the stage 2 was injectors and a little more boost (which I suppose means a pulley change.)

https://rennlist.com/forums/7070422-post367.html

Maybe the difference in the pulley sizes is very small.

"Taking our 968 Stage 1 kit Up a Notch! Where our Stage 1 kit took the stock injectors just as far as they could go, this kit provides a new set of 4 3rd generation (improved) injectors and brings in a little more boost. "

I could try to dyno my car but it would be hard to get meaningful numbers. I am at altitude, and it's hot and generally not a good time of year to make power.

-Joel.

Lemming

That's what corrected dyno data is for, it corrects for temperature, altitude, and barametric pressure. I've dynoed in the heat of summer (95o and high humidity) and in the dead of winter 55o and the corrected numbers were almost identical. As you might expect, actual uncorrected numbers were higher in the winter.

Jfrahm

Sure but I find dyno results inconsistent enough to make corrected numbers even more blasphemous. Also there would be no way to correct for timing pullout due to the weather. With my old Saab I had to pull a few pounds of boost off for the really hot weeks of summer.

I suppose if I get numbers with and without the blower in play that'd tell us something, but lots might be left on the table due to loss of spark advance.

I never should have romped on the car when I had it in WI at 20 degrees F and nearly at sea level. I'll never get that kind of power up here at a Mile High.

-Joel.

Carl Fausett

I am certain Chris is experiencing a belt slippage problem.

As I mentioned in my email to Chris this morning:

In addition, although we supply larger injectors with the Stage 2 kit, Chris has not been able to use them because it runs too rich when he tried to do so. Further indication that he is not moving enough air.

His install is a little non-standard because of the lack of the AC idler. My best guess is that the belt tensioner that he has fitted is allowing much too much slip.