Juha,

Any updates, dyno results, thoughts on engine bay air flow pattern?

Geo.

 

The 993 has been sitting in my garage for the past couple of weeks. I've been too busy with work and trying to give as much time to our little daughter as I can. We also had the last race of the season last weekend.

But finally I dynoed the car today and got 10hp and 10Nm less than with the water/air intercooler.
There is a very good explanation for this; there is a loss of pressure accross the GT2RS cores. With the TPC cooler I saw 0,55bar boost and with the current setup I am only seeing 0,35bar.

Now I just need to compensate that by getting a smaller pulley to the SC.
Who sells these pulleys? And what size should I go with?

 

Pulley Boys - go the 2.4".
I see about 8psi with the charge cooler.
I saw up to 13psi without the charge cooler. Bum dyno felt a lot more powerful and a lot more wheel spin.

http://www.pulleyboys.com/store/prod...2&cat=9&page=1

 

Thanks man! I ordered a 2.4" pulley from them.
I also called Tom @ TPC, he was very helpfull as usual. He said the 2.4" is smallest he'd fit because if it was any smaller, the belt would start slipping and the SC would running too high revs.
He also told me to buy the pulley from pulleyboys.

 

Juha.... would you rec. getting the tpc without the intercooler and go with the GT2 or just go with what comes with tpc

 

For a street only car, i would get the tpc cooler. But if the car sees any track time, definately the gt2 coolers!

 

Hi Juha, thanks for the upates!

As the saying goes to finish first, first you have to finish....I think you've now got rock solid performance from an IAT perspective.

Although boost pressure in itself will be somewhat reduced through lower IAT's (lower temp = less pressure) I am mildly shocked to see a full 0.2 Bar difference!

Let's hope the 2.4 pulley doesn't push the charger too much out of its efficiency range and produce loads of heat which would mean going round in circles. Can be tested quick enough in real life, alternatively TPC might have compressor maps available??

Using a single RS core, instead of the seried pair will of course drastically cut pressure drop, IAT stability then becomes the big questionmark. As the ultimate solution, do you feel there would be enough room to reposition the 2 cores in parallel with different end tanks?

Love the thought, engineering and sharing data that goes into your project!

Cheers,

Harald

 

Thanks a million.... How's your new daughter? Best thing in the world!

 

The pressure drop is not down to the design of the cores, it is more likely to be caused by running the cores in series (end to end) with the resulting turbulence caused by the gap between the cores in the centre of the intercooler assembly. Much better to run the cores in parallel, lower overall PD & more efficient heat dissipation.

I would thus be reluctant to run a smaller pulley, all you will do is use more power to drive the supercharger, generate a lot more intake heat and overload the intercooler further.....

 

Colin, you have a good point!
However, since the supercharger I am using is a "positive displacement" type of charger, the amount of air blown in is directly proportional to the revolutions of the superharger. Therefore by raising the SC rpm (and staying within the limits of the chargerefficiency range), I will be getting more air into the engine at the same engine RPM. And we all know that more air+more fuel = more power.
Of course the SC robs more power the faster you spin it and the blown air gets hotter, especially when there is turbulence in between the two cores as you suggested. But all in all, I would think that raising the SC rpm a little would help. The cores are VERY efficient so I don't think heat will become an issue. It is more up to the capabilites of the SC itself and of course the engine is the other limiting factor.
I don't think there will be much more HP high, because in the higher rpm's the SC gets on the cams and there heads just don't flow well enough to get more power. But I am very certain that I can get a lot more torque down below...

Pulley should be here on Tuesday so let's see what happens next week...

 

You will see a lot more heat on the gen4 M90 unit.
Any smaller than 2.4" you see a large increase in heat generation and very little increase in power. It just gets very inefficient at this stage.
I found this data in a pdf online from a magazine that did a back to back test and measure between the gen3 m90 and some other sc make. They measured various pulley sizes and recorded the data in the article. It was a very good read - I'll see if I can find it for you.
The finding was that the eaton unit was pretty inefficient and made a lot of heat. The other test unit was far more efficient and generated less heat, with less crank power, and made more power.

When I switched from 2.6" to 2.4" I noticed a lot more heat from the sc unit. At this time I installed the meth kit and the current setup injects 50/50 water meth before the throttle body, and I have noticed that the cooling effect is pretty good.

Would meth injection work in your racing application ?
You are going to have a bitch of a time getting the old pulley off. It was hammer and screw driver for about 2 hours for me. But it came off. You may want to invest in the tool that will remove it with ease. I think pulleyboys has one of their site.

 

Found the article.
Have a read - http://www.kennebell.net/KBWebsite/T...NFORCEMENT.pdf

 

I also talked to the guys at Magnusen. We calculated that with the tpc supplied crank and working with the 2.4" pulley the sc would be just below its max recommedned rpm operating speed.

 

Yeah, that's what Tom (from TPC) told me as well.

Thanks for the link to the article, definately a good read!

 

Juha,
Can I suggest that you do the maths on the charge density in respect of the trade off between intake temperature, charge pressure and supercharger power consumption? We've played around with similar supercharged 964 engines on Motec for some years now and the maths never lies - we always find gains running the IAT cooler by reducing the boost, especially in acceleration terms. The secondary factor is that you can also run more ignition timing with less boost, resulting in reduced EGT (and as a result = lower CHT).