hacker-pschorr

Here is the latest dyno from Todd’s 928. Few details to go over.

• 5 Liter – stock crank and rods, stock S4 heads, 85/86 camshafts, cometic head gasket
• Heads are 100% stock, 1989 vintage, no porting with stock valves & springs
• Autronic engine management system – This is a sequential injection system that allows for separate maps for each cylinder for both timing and fuel. It’s a MAP based system, no MAF
• Procharger Supercharger – with a custom (built by Todd) air / air intercooler – Max boost 30psi
• 944 Turbo pistons – The advantage to these pistons is they are forged. The downside is they are physically shorter than 928 pistons. This means they do not come up all the way in the bore like a stock piston would. This messes up the squish area of the combustion chamber. Not ideal since this can promote detonation.
  Why is he using them? This is a test motor he wanted to use for setting up and tuning Autronic. No sense is risking an exotic all custom motor with a new EFI system. Not to mention these are OEM Alusil pistons that have a proven track record under boost.
• Compression ratio with these pistons is 7.6:1
• Stock exhaust manifolds with an X-pipe and stainless exhaust of his design
• Eight oxygen sensors, one for each cylinder
• Intake manifold is stock except for a spacer on one side.
• Stock radiator with aluminum side tanks
• Stock 4-speed transmission with 2.54 final drive. A gear vendor overdrive unit is installed between the engine and transmission. This essentially gives him seven forward gears.
• In this run the flappy valve is disabled, set to the closed position.

Todd is experiencing ignition misses all over the place right now. Without the eight O2 sensors this would be a very difficult issue to track down.
Looking at the logs for the O2 sensors , one or two cylinders would go 100% lean for a split second, then back to normal. This indicates the spark is being blown out. This is happening from very low in the power curve all the way to redline.
Looking at the logs of all eight O2 sensors, this dyno is the result of only 5-6 cylinders firing.
As for the cause of the problem? Most likely his dwell time is too low. The next dyno session we are planning on using an oscilloscope on the coil which should allow Todd to dial in the dwell time better.
It is possible the ignition system has met its match.
Todd is planning on going coil over spark plug down the road anyway. If this problem becomes too big of a PIA he'll jump to that setup sooner then he originally planned.

Bottom line: there is quite a bit of power still left on the table with this configuration and boost level, once the ignition is fixed.

Todd’s next motor will “fix” the squish area with taller pistons and one compression point higher. Boost will remain the same.
With a "proper" squish area, in theory he will be able to add more timing and gain additional power across the board.

Once the ignitions issue is dialed out the flappy will be brought back into the equation. With Autronic he can set the flappy to open / close at any point. This adds another level to tuning the motor.

Bottom line is: 675hp / 614 lbft of torque at the rear wheels with an ignition miss and the flappy closed

Click here to see the thread on his eight O2 sensor setup:
https://rennlist.com/forums/928-forum/402332-using-8-o2-sensor-on-a-928-todd-s-garage.html

Click here to see details on his air / air IC:
https://rennlist.com/forums/928-forum/444296-todd-s-new-air-to-air-intercooler.html

Hope I covered everything, here is the chart:

Rick Carter

IIRC this info is from Lag/Sway.

The total cylinder volume is 619.7 cc's, add the S4 piston chamber volume of 75.3cc's to this creates a total volume of 695 cc's.
Divide this by the S4 piston chamber volume of 75.3 cc's yields an S4 static
C/R of 9.23:1.

The32V S chamber volume is 64.2cc not including head gasket. The S4 measured in at 67cc's. (25.4 piston/41.6 head) Add 8.3cc's for the head gasket gives a total chamber volume for the 32v S of 72.5cc's. Take the 619.7 cc's cylinder volume and add the 32v S piston chamber volume of 72.5cc's yields a total volume of 692.2 cc's. Divide this by the 32v S piston chamber volume of 72.5 yields a 32v S static C/R of 9.55:1.

A little better then the S4, well within the bounds of the 10:1 +/- .4 factory spec, but still pretty far from the touted 10:1 max spec.

Now, check out S4 heads on a 32V S block: 41.6 cc head + 8cc piston + 8.3cc head gasket = 57.9cc total chamber volume. Add the 619.7 cc cylinder volume for a total of 677.6 cc's, divided by 57.9 = 11.70:1 static C/R.

For you forced induction fans, 32v S heads on an S4 block: 56.2 head + 25.4 piston + 8.3 head gasket = 89.9 cc's. Add the 619.7 cc cylinder volume for a total of 709.6 cc's, divided by 89.9 = 7.89:1 static C/R. Not much throttle response there. This may be the way I go next as I have an extra 85 engine and can put S4 pistons in it.

Abby Normal

What piston rods did he use for this build?

SeanR

Holy cow. Over 700 at the crank........ by a mile.

Jim R.

Damn, impressive stuff!

Hey Todd...

Interesting stuff finding the limits on the stock parts, ignition, etc. A bit more compression, COP ignition.............

Jim

AO

To my knowledge, all internals are stock except for the pistons.

If we use the convention of 18% drivetrain loss for an auto that yields 823 CRANK Horsepower!

You and I aren't even close... although we may want to think about lowering the compression a bit to avoid detonation.

928autobahndreamer

Time to add this to the HP thread that the 4 banger crowd started.

Imo000

Nice number. That machine is starting to become very complex.




I wouldn't do that!

IcemanG17

NICE.....at a 20% loss thats 843hp....DAMM On basically a stock internal engine.....wow......it sounds high (cause it is) but its only 168.6 HP per Liter...which isn't bad for a turbo engine....the Supra-Evo crowd are well over 300hp/L

Was this on pump gas..93 octane???

Imo000

Hp/ litre is what the 4cyl crowd like to beat on. To put over +800hp through and engine is what matters and not how much HP/L you get.

Warren928

That is a nice hp show, sounds like the compression ratio would be a problem at or near idle. Once the boost goes up the problem goes away?

hacker-pschorr

He's not done yet
There are still a few more runs in store.
Step one is fix the ignition, then the flappy, then start playing around with methanol injection.

Once everything is all figured out, the new motor goes in with the piston height fixed and possibly larger displacement. I would imagine this new engine will also receive headers (Todd has been designing his own) and some head work.

This is still a development tune. There is some room to move up with timing with the current configuration. With the ignition acting the way it is, no sense in doing so right now.

100% pump gas, 93 octane.

There are no problmes at idle or anywhere on the map. Autronic is an amazing EFI, his car idles so smooth he likes to show off by balancing a nickle on the intake while the engine is running.
He spent more time fine tuning the idle map then most people spend tuning their entire motor. Todd's goal it to make this car run like a stock production car, only with a ton of HP.

I've ridden in this car more time then I can count (he offered to let me drive once, I ran and hid behind the garage.....). It's so smooth and docile you would think it's a 100% stock 928. Even when he nails the gas it's like a stock 928 except everything is happening really really fast!!

I told him we need to do the Lexus commercial with a dozen or so martini's stacked up on the motor while it's on the dyno

Carl Fausett

Knowing Todd, thats an under-statement.

Crazy man from Green Bay with Tools! Hats' off to Todd!

Fabio421

Do you have specs or pics of the A/A intercooler setup? Is it front mounted or in the wings?

hacker-pschorr

Second link above the dyno sheet