MarkRobinson

"Very easy to install, not all the heat a Turbo adds, many proven systems being run etc"

An in-engine-compartment turbo/s, yes, but not mine. My engine runs cooler than stock with all the airbox stuff out of the way & the turbo stuffed way down yonder. I could call it the "down-under" turbo kit.

Mark

JEC_31

Please, not another turbo vs SC thread...

But for the record I'm also in favor of the best electronic fuel-air-spark control available. When you think about it, control is just as important as the hard parts - because without it your hard parts end up looking like this:
http://forums.probetalk.com/showthread.php?t=1701176545


rixter: if you haven't yet, read Corky Bell's books Supercharged and Maximum Boost.

Tony

Rixter, Take a drive in a 400plus RWHP car first, then decide about the 500+ number. You wil be amazed what the car feels like at just 400. I was....even more so at 450. Cant imagine over 500. Im sure DR will be giving a few test flights in June if you havent gotten one already.

Im kind of doing the same thing you are. But i modified my stock pistons and will just end up with a low CR S4, 5.0 L enigne. Re-ring..Re seal and toss it back together and be done with it. Probably run appx 12psi...that should get me close 500rwhp as 10psi has me at 450 now. I was going to stroke this motor as well ,but i honeslty thought it would be a bit of overkill in the TQ department.

Tom. M

I hate to say it on a boosted application, but a thicker head gasket will work wonders for your CR calculations. I'm sure Cometic makes a 2mm thick head gasket designed for boosted applications. You might be able to bring the CR down to 10:1 with just this....but of course..a better way is to either custom mill the piston crowns as Tony did..or get slightly shorter rods.....

It's only money..

later,
Tom
89GT

MarkRobinson

Good Point (Tom), & cheap too (by comparison).

JEC_31

Working wonders on paper calculations is one thing, wreaking havoc on Porsche's excellent quench & squish dynamics is another.

Every point of comprssion lost is both a chunk of power and a percentage of efficiency lost. The power can be made up with more boost of course but the efficiency and is irrecoverable. You end up with a motor that's a slow thirsty dog when off-boost.

This leads back to my point about fine tuning control of fuel-air-spark. With that you are safer even without the crutch of low compression.

A lot of work has been done lately with dished pistons to lower compression yet maintain good squish & quench. Just not for our cars...

MarkRobinson

Supra's have almost identical-looking combustion chambers to the 928, with even sharper angles on top of the pistons for the dish/fly-cut valve reliefs: no issues at all. You can take a Lexus SC300 6 cylinder, put a cometric HG on it & run 30psi to make nearly 600rwhp/tq on a stock engine, no detonation with proper ignition tables. I wouldn't hesistate to do this on a 928 if I knew the pistons were stronger.

www.boostlogic.com

Mark

JEC_31

That's the key! Proper control.

The Toyota inline-6 engine is naturally harmonically balanced, and the thick iron block holds up to much abuse. Those are wonderful engines.

However the visual simularity of the combustion chambers you note makes me wonder just how much we can get away with on a 928.

Rixter, try the headgasket trick and make me eat my words!
After all it is cheap.
But I wouldn't try it with CIS...

hacker-pschorr

Parts for three engines were ordered and assembled.

Here are details on these engines:
https://rennlist.com/forums/928-forum/166901-i-would-like-to-share-my-supercharged-928-project-car.html

Rixter - Sending you a PM about some other details you may be interested in.

FBIII

Dropping compression by adding a thicker head gasket typically doesn't work. What it usually does is make an engine detonate worse because you are ruining the squish characteristics. Engines tend to detonate less if you run the piston very close to the squish area of the cylinder head. http://www.speedomotive.com/Building%20Tips.htm

Tom. M

I think the key here is that the Supra engine and controls were designed for boost...and many just up the boost.. with stock forged internals...and get away with it. If you look..most of the normally aspirated Supras..will have higher CR than the turbo versions..... same goes for other turbo/na models..my Volvo 850 R has 8.5 to 1 with forged internals....wereas the NA 850 has 10:1 and non forged internals..

For the 928 we are in uncharted territory. No factory 928 turbo motors....so we are working at a disadavantage already. The stock computers (S4) are not sufficient for controlling the fuel and timing on a boosted motor...so..we have to live with piggyback solutions...ie Begi...or SMT etc. Sure one can go with an aftermarket EFI system...(I know Louie is..and Thurston almost has his DTA system working for his S4)..but they both have spent lots of time and money doing the full conversion...not easy to say the least..

I have hopes that the Sharktuner will help in this realm. But for now..it cannot control ignition (sounds like he is working on it).

In my case I am using 24 lb inj..(30's were too much for 5psi) and the SMT to control the fuel and ign for now..(only drawback is I can only really control fuel under WOT)...as well as a Greddy Protech B turbo controller to control how the turbo behaves...(I have yet to play with this aspect..)

With my CR pretty well sitting at 10:1..(GT motor)..I have to be careful....Those with S4 motors have a little built in safety courtesy of the factory ( CR range 10:1 - 0.6 spec....most end up around 9:5 or less..)...

Either way..it's a lot of fun

Proper control is correct..but we need all the safety factors including a lower CR to help.

Later,
Tom
89GT

P.S. The other rear turbo motor is going to be around (9:1 CR..with custom forged pistons etc.....) to handle more boost than what I am running..

Lance J

i will be Converting Efi from Cis but i have full control of my timing. and Rixter there is and easier to pick-up your engine speed than just mounting a trigger wheel. the little green wire on your Dizzy can pick up engine speed. Any will i have 20psi. 30lb d-jet hose style injectors. all i need is l-jet fuel rails anyone? the injectors are off an 80's 300zx and are low ohms one of the many swaps i've learn to keep my budget down to stick with l-jet fuel rails

bd0nalds0n

When I swapped to GT heads, I used a Cometic gasket that was 0.074" instead of the stock 0.045". Based on the back-of-the-envelope calculations with the engineer at Cometic, this should've reduced my CR by around half a point.

I used to have knock during tip-in, and I don't anymore. I haven't dynoed the car so I don't know how my car stacks up against all the other TS SC'd cars, but any knock/detonation problem went away, it wasn't exaggerated.