jeff jackson

Fellows... I certainly didn't mean to come of as a "naysayer", with regards to turbocharging a 928. I personally owned a 1995 3000GT VR4, and know first hand the pleasures of boost. Sorry, if I came accross as a "doubting Thomas", just that I've heard the staggering costs associated with engine rebuilds after timing belt failures, and can only tell you that "leaning out" under boost, or moderate detonation, would be equally, if not more disasterous. I am not however saying this "won't work" or "you'll be sorry", or any such nonesense. I firmly believe, given the right engineering, and safeguards, it CAN be done...just not easy. I will now "butt out" and watch/read the progress of this effort with keen interest.

Imo000

No need to worry.....it already HAS been done for years and it's fairly easy to boost. The 928 engine is way over built and it can take boost really well.

Ketchmi

There are more than a few of us running over 500rwhp on basically stock 5.0L 32 valve engines with CS. At that point traction with street tires is a joke below 60mph. I'm sure the turbo guys can do the same thing if not more but how much more is needed? Why put down the CS design when it does everything the turbo does to the limits of adhesion and common sense? I have daily driven CS cars running 2 years without any problems. All it takes is some common sense to keep the engine from leaning out or pre detonating. The same goes for turbos BTW!

If you are worried about how fat the dyno sheet is in midrange, check your tire size. With 500rwhp on a CS and an auto car you have to baby it past 60mph to have any traction at all with 295/35/18" rears! Turbos may be better at midrange which means you just have to baby it all the more to try to hook up.

Boost is boost. Be it from a TS, a CS or a single or twin turbo. They all do the same things, they all are proven to work (to a limited degree) on basically stock 928's. Most will provide more power than their users need on the street. Some people have found what doesn't work by trial and error and have needed to rebuild their engines. That's normal. I don't care if the single or twin turbo is mounted on the roof, does it work? The whole idea of the rear mounted turbo has my attention. Will I build one? I have no plans but the day is young...who knows what tomorrow may bring. I have built CS cars that work and really enjoy them. I may build a TS car just to experience the difference and see what it's limits are.

I appreciate the effort to find new and fun ways to enjoy our 928's. I also will not try to drag another style through the mud just because I believe in a different style.

porshhhh951

I never said turbo was cheep. I just said it was the best at making hp and tq with powerband in relation to higher boost levels.

I believe the roots blower to be about the best street application for FI if you arent going to run much boost because of the instant tq and insane powerband you get with the roots blower. Its simply the best if you arent looking for peak #'s.

Hell my friends 32v roots blown cobra makes 402rwhp with a homemade catback exhaust system.lol.

Once he changes the pulley and chip with CAI he will be 450rwhp with 15-16psi or so. Thats pretty impressive

porshhhh951

agreed! mostly deffentely. They all have their place

atb

ketchmi wrote:

Well I will. All of I've got to say to that is AMB. All Motor Baby. When you're ready to get serious about motor building Dave and are done playing with those hair dryers, let me know. Cubes dude. 6.5L's worth. In a Porsche wrapper. That's where its at.

hacker-pschorr

You get my vote for the post of the month - well said

Ketchmi

Yo Adam, all I'm gonna' say is if I ever get enough time and money at the same time....7.3L on oh say 30psi!!!! (I'll let you all wonder if it will be CS or Twin Turbo)

But that will just be a shop mule to test frame rigidity, rear suspension shear points and to see how far I can throw a CV axle.

BTW, just spec'd tires for the 6.1L supercharged widebody we are building. How about some 355/25/19's? They take 13" wide wheels and will be necessary for the horsepower the 6.1 will push. The 335/30/18's on GT2 12" wheels just weren't enough.

jeff jackson

Ketchmi...
If your car is "putting down over 500 rwhp"...I am curious to know, have you ever taken it to the dragstrip ??? I am just wondeing what a 3300# car, so tuned it can hardly keep traction, at under 60mph...would actually ET in the 1/4 mile,.... (with slicks of course)...even 8 inchers. I for one, am ready to see numbers, BESIDES dyno numbers... I am not trying to flame you, or get flamed in return. I just would like to see, "real world, representative numbers"...I can equate to these "dyno" numbers... I keep seeing in the 400+ rwhp category. Because...a Camaro, Firebird, Dart, Demon or Stang....laying down these kind of HP / torque figures...would be turning ETs in the mid to low 11s or better.And ALL these cars are at least as heavy as the OEM shark. I know...these cars are "geared" to rev faster, and therefore pull harder, through the 1/4 mile than the shark, BUT...if traction is "virtually non-existant" at WOT... at less than 60 mph, on a 928 with the centrifugal supercharger...even WITH" 295/35/18" rear tires, I would think that with some traction, (Read SLICKS)....even narrow ones... the 928 ought to be one formidible 1/4 miler... also...as the "superchargers" response to throttle input is virtually "instantaneous"...as opposed to the turbos needing to "spool", you would "think" that one of these 400+ bhp "supercharged" behemoths...would be putting down documented numbers in this region. Or am I missing something here ???Are these Dyno HP and torque numbers more sales oriented, than real world performance claims.??? Let the flames fly. This post is all in good fun, and quest for better understanding.

hacker-pschorr

jeff, no flames – See the post made by Gretch in the IC thread - quite a few of the CS crowd have given up on Rennlist and I doubt they will ever return. They are driven by determination to make their 928's the best they possibly can. In return, if the end result is wanted by others, it will sell.

When Tim Murphy posted his first dyno chart, a well known supplier called him a liar right off the bat. Said he must be using nitrous, engine wasn’t stock etc…For such a small community, there sure are a lot of backstabbers around here.

Funny how the best seller of boosted 928 kits is the quietest of the bunch on the list. All the chest pounding in the world will not sell kits. Making a damn good product will. Word of mouth sells more kits than a few bragable numbers on a web forum. The first customer I ever met of Tim’s outside of the GB group has never posted on this site, I doubt he ever will either. Everything performance related about 928’s is not on Rennlist. In fact, if it were not for Tim Murphy and myself, Todd and Jim’s cars would never make these pages, ever.

Sorry for the rant, Gretch’s post got to me.

jeff jackson

OK, my friend...thats precisely the kind of info, I am seeking. I amnot interested in "braggable" claims, but if somebody has "documented" data...BESIDES dyno data...which I hope everyone knows is "corrected" for a number of variables..., and in no way should be interpreted for anything, other than baseline, vs. "tuned" HP and torque, and the net improvements after tuning.

FlyingDog

Yes, most are 9.3 or 9.4 which is lower compression than factory turbos from SAAB and Audi.

Ketchmi

Well Jeff, the car was built by me for a customer. I don't exactly have the ability to run it at the dragstrip at will. Being winter in Utah doesn't help either. It also weighs in at well over 3600# with the supercharger and aux. coolers I have added to allow it to run in 100 degree heat with the a/c cranked and not overheat. It has a total of 5 fans to cool everything and also has an upgraded stereo w/subwoofer. It's no lightweight. I am worried about the drivetrain already without putting slicks on it. I believe it's near the limit for a stock auto transmission and rear axles without going to slicks. With slicks I believe it would start scattering pieces.

The CS boost is linear with rpm, not instantaneous like a twin screw. The turbo lies somewhere inbetween. But you being an authority on these things would already know that.

With the CS the 89' auto will not spin from a dead stop in a straight line until you hit about 7psi which is usually about halfway through the intersection. That is when they start to spin. When it shifts to second the tach stays at redline and the tires try to catch up...usually in a cloud of smoke.

If the turbo designers get things properly built, they will encounter traction problems earlier than this car. If they want to put slicks on their cars and go for it I have a lot of used, new and upgraded parts to sell them...

928's are not set up suspension wise for launching with high horsepower and running down the quarter mile. It would detract from the reason they were built. If the suspension were optimized as well at the gearing, they would be comparable to the dart, camaro, mustang drag cars you are referring to. There is as much of a science to drag racing as there is to road racing. Weight transfer has a lot to do with traction in high horsepower cars, not just slicks. Do some research and see what you can find out about 1/4 mile drag cars and suspension setups. You will see why a 928 doesn't make a good drag car even with high horsepower. I have no doubt that this 89' will be in the 12's even at this altitude. (4400'). A properly prepped drag car with the same horsepower would probably be in the 10's.

I'm proud of the car I built as I hope John, Andy, Tim, Imo, Tony, Darien, Mark, Dave and everyone else that has built one of these toys are. We are in the middle of building another one this winter that will waste the 89' without even breathing hard but it will have a lot of parts upgraded to be able to handle the power. It still will not be set up to run the quarter mile. Join the club and show us what you can do.

Jim R.

Jeff,

I have an "undocumented" old G-tech which I turned 3.96 sec 0-60 with. Traction is a major issue with 295-30-18's. I feel the centrifugal makes launching the 5 speed car easier than a car with higher low end torque. Much easier on the clutch, trans, CV's etc. I have not run a 1/4 yet due to the local enforcement/revenue generators and the need for a long safe space to run and launch 0-130 or so. It is now in the 20's here, so no drag runs. Trust me, the suddenly "inferior" CS setup is not lacking for performance. Anyone making significant boost with any system will be limited more by traction more than by the source of boost.

I plan on heading to NJ this spring for a 1/4 mile day at the strip (LI Motorsports Park is permanently closed). Anyone else interested? A northeast drag day perhaps? Turbo vs TS vs CS. Could be a lot of fun.

Jim

heinrich