AO

According to my spreadsheet, the stock crank pulley (yes, 6-rib alternator position) is 5.13 inches. This is considerably narrower of the Keel pulley and the Murf pulley.

No the bolt patterns are not the same. 1.7 an 2.0 are the same. I think the 2.2 and 2.4 are the same - somewhere I have the specs.

Not trying to get an apples to apples per se, but more of an idea of what is capable.

The GT and S4 (I think the GTS too) do not any overlap on the valve timing. Not sure about the Mustangs, but I don't think they do either. If that is the case then is should be a pretty close comparison becasue you're comparing manifold pressures - not flow. (I think... probably wrong though.)

blown 87

resistance to flow is what gives you pressure.
I have seen on Corvettes that with the same cams, and blower, just doing head work will lower the boost, but the car has more power.

Tony

The 2 inch will hit hard, trust me! I got mine to hook up but im pretty sure i became intlet restricetd as the boost dropped of pretty quick after it hit. You shouldnt have any probs with Drs dual intake and the belt wrap you have. I ended up putting the next bigger one on..apppx 8-9 psi.

Vlocity

Andrew,

Where did you get these?

Are they 6 rib or 8 ?

Ken

Cosmo Kramer

I think someone wants to win a dyno shootout against Murf!

Seriously if you can get a belt to grip that little pulley your car is going to be such a beast! Against some opinions, I am using a Gatorback belt on my Vortech and I find it grips better and is less prone to glazing over then the Gates.

hans14914

1.7L - 2.2L use the same bolt pattern. The 2.4 and larger use a different discharge outlet and the case is slightly larger.

dprantl

The Keel lower pulley is either 5" or 5.125", much smaller than the Murf one, so it seems to be the same or almost the same size as DR's. Anyway, 5.13" lower / 2" upper * 6700RPM = 17186 blower RPM. AFAIK the MX Autorotor design limit is 15000 RPM. If you don't exceed 6k RPM, you will be ~400RPM above the limit, which is probably ok, but 2000RPM over and I think bad things may start to happen. Also, if you exceed the design limit too much, you probably won't be making any more power since the efficiency of the blower will drop off rapidly and it will heat the air a lot more. So... if you limit yourself to 6k RPM you will be losing HP anyway.

And Greg said it right, boost psi is completely dependent on engine displacement, design and intake volume and design. I run 25psi of boost on my SAAB, not the same as running 8.5psi on the GT.

Also, if you do frag the S/C, the engine could ingest some crap and toast some cylinders. Don't get me wrong, I am all for upping boost, but I wouldn't want to see your car down.

Dan
'91 928GT S/C 475hp/460lb.ft

AO

They are 6-rib. Got them from Kenne Bell. Called them and they had them in stock. Go figure.

Nope... don't want to win at the dyno... Just on the street! He can have the peak number. I want to win the drag race. Of course, he could always pull out the 5-speed.

I kinda figured I wasn't on solid ground with that assessment. Oh well.

I believe max RPM on the SCer is 18,000 RPM. With the 2" pulley, at 6,800 RPM, I'll be spinning it at 17,850. Don't jinx me.

hacker-pschorr

Or take his skirt off and re-tune Rachel's car........ (inside joke)

Looks like a nice and long over-due upgrade. We need to start working on the annual spring GTG.
Maybe this year Rudy can remember to come along.

We need to find someone to bring a car up for another build, that's always fun. Then again, might be time to tinker with the 79.

928mac

Good luck with this Andrew.
It is always nice when a project comes together without a hitch.

hans14914

Andrew,

From my understanding on these units, the ultimate enemy is heat, not speed (rotational speed ultimately translates friction in the bearings into heat, and then into the oil and then the plastic couplers, seals... etc). I would think that if the heat was kept in check, you should have no problem spinning the unit faster. If you go back and look, the original autorotors used the engine oiling system to pump fluid through the gear housing. This was later changed to a sealed system and beleive the recommended RPM range was reduced at this time. Perhaps installing a temp probe in the dipstick tube and logging would be a good way to determine if the 2" is a safe upgrade.

I have never seen it done, but a hot-oil scavange pump used on remote turbo installs and an external oil cooler may be the cheap way to get a 1.7 to put down some very impressive numbers.

Good luck with the project and be sure to share whatever data you can. I for one am very interested.

Thanks,
Hans

dprantl

http://www.hi-flow.com/HP7Super.htm

Dan
'91 928GT S/C 475hp/460lb.ft

AO

Yep... heat buildup is a concern. I think I may look at putting in an oil filter sandwich to provide the Scer with engine oil. It should be easy enough to do. As for monitoring temp, I could probably put a thermocouple on the top of the dipstick and get a good enough idea as to heat differences between the 2 pulley sizes.

Thanks for that link... I knew I had seen it before.

Vlocity

As for heat buildup, you could probably just shoot the front of the case with a pyrometer and get a good comparison.

I put my car away with it down on boost, there probably is a small leak either in the mating between the blower and the manifold or the manifold to the head. The worse case scenario is that the unit is finally showing some wear after several years of heavy track use. Do any of you know where these can be rebuilt or what is involved?

Thanks,

Ken

AO

I think Kenne Bell is one of the few places that can/will rebuild these units. I would give them a call.