Jim R.

Yeah, yeah. Have fun,

Jim

dprantl

Ha ha! That's what you say now.

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

Courtshark

At 10:1 compression, 7 psi of boost goes a very long way. Far enough for me, anyway!

AO

I take it then, you've never tried crack.

Courtshark

I take it then, that you have! . The closest I have come to crack is Ledo's pizza here in Maryland. We're fairly certain there is crack in the sauce. it's impossible to stop eating it until it's all gone.

I know what a lot of boost feels like, and how it can be intoxicating. I also know what a lot of boost poorly delivered can do to an engine and transmission. I have blown up both using 25 psi of boost (@ 9:1) in my learning experience. Had a ton of fun in the process, of course. But at 10:1, 7 psi should be plenty, and provide a nice linear power curve, too. I'd say 10 psi max is safe before you have to start reinforcing head gaskets, upgrading fuel pumps, using a rising rate fuel pressure regulator, water injection, etc.

Lizard928

You can run way more than 10psi on stock gaskets. Over 500rwhp the fuel system needs mods, and the list goes up.

dprantl

If a '91 9000T 2.3l can do 23psi and get ~130hp/liter (mine has been doing this for years), the 928 should have the same kinds of stress on the heads with a 5.0l at 650hp (which is ~550rwhp with 15% drivetrain loss and probably around 12psi). Bigger injectors, 044 fuel pump and Sharktuning and you are done.

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

Cosmo Kramer

Watching your videos earlier in the thread Mike, man your boost in 4th gear makes me jealous, way better then a centrifugal system for sure. Glad to see it is working good for you!

Courtshark

My brother had a similarly equipped 92 9000T; that thing was a handful! Torque steer galore. Nonetheless, I'm trying to go slightly conservative on my boost configuration. Definitely not going over 10 psi! Things simply break faster with more boost. I want something that will be a ton of fun but also somewhat reliable and that will not chew through transmissions and clutches.

Tom. M

One thing to keep in mind with the rear turbo setup is that an electronic boost controller can be really effective in tailoring the boost to where you want it. I had one on my GT when I was running the original rear turbo setup and unfortunately didn't play with it as much as I should have...

Like Mike said..check in with JT to see what he can put together for you... he is always "around"...just not here on rennlist etc..

dragonflyjones

I have boost spool envy of Mike's car too!!!! My 62/67 comes on way slower than his! His responds like a twin turbo under the hood! I don't even make full boost until 3000 rpms. His is probably in the 2000 range.

dragonflyjones

Agreed! I've run as high as 9 psi.......on accident before.
Now at 8.5psi, my 30# injectors are at 85% duty cycle. That's pretty much maxed out. I also am running the 044 pump and removed the FMU. The fmu definitely helps fueling without having to go to larger injectors, but tuning around it is a nightmare! I finally pulled mine. I'm currently installing Meth Injection, and plan on wicking up the timing a bit. I pulled about 4 degrees out of my previous tune (at 6psi) to tune for the 8.5psi I'm currently running. If I can get the power I'm looking for (500whp/tq) with timing, I'll stay here at 8.5 psi.
My car was on jacks this weekend, and my wife asked will I EVER be done tinkering with THIS car? My reply.....................probably not. Once you're not afraid of a certain boost level anymore, it loses it's addition power! The way I see it, I'm still way ahead as far as cost goes. Considering I was looking at a 996TT to modify.
DFJ

IcemanG17

do not forget there is much more to the formula than PEAK power on a dyno......if you run low compression plus high boost (like a Supra) you end up with a dyno queen.....with no power down low, horrible turbo lag and torque and hp rising at 45' angles together on your dyno chart....this car would be horrible to drive on the street or racetrack.....

The strength of 928's is its wide powerband....a nice low boost turbo that comes in early, is about perfect.....no loss of bottom end, with more midrange and top end...

dragonflyjones

I agree 100%! I just wish I had boost right off idle like a twin screw with the midrange and top end of the turbo! Wait a second, hasn't Mike Vance been talking about a set-up with these kinds of characteristics?!?

Imo000

My dyno graph is like that. Like a table top. The belt was old and loose so the boost fell off at the end but that is another story.