Based on some recent discussions I thought I would provide an update on some developements with my car.

Where to start….?

Last year I learned a lot about the limitations of the S4 engine and fuel system with respect to supercharging which helped direct my winter engine rebuild.
This is nothing new here but detonation is the largest factor causing failure in forced induction engines and those are the areas I specifically addressed.

The fuel system is maybe good to about 10psi of boost. It’s not the fuel flow that is the limitation but the HP of the pump to deliver the fuel at elevated pressures. Using the stock ECU you are limited to the size of fuel injector and still maintain drivability. So, on my car (and in my sc kits) I run 30# injectors at a lower than stock fuel pressure. When the boost comes on it raises the fuel pressure, in proportion to boost, and provides adequate fueling for the added HP. This is where the stock pump has its limitations. As the pressure rises the volumetric efficiency of the pump falls off sharply. I played around with a Kenny Bell “Boost a Pump” which increases the voltage to the pump (HP) under boost but it turned out to be a big guessing game whether or not it was set right and delivering the required fuel. I definitely ran out of fuel way upstairs and experienced detonation on a number of occasions. To remedy this problem I now run two of the high performance Bosch fuel pumps in series (one feeds into the next one) which will give me the fuel flow of the higher flow pump at two times the pressure capability. We have tested a similar setup to over 170psi in a stock 928 S4 fuel system. One pump “maybe” would have done the job but I didn’t want to take that chance. The other concern was with fuel distribution at the fuel rails. I pushed out the head gasket at #4, twice. The first time I attributed it to a weak rotten gasket but the second time made me wonder if the detonation I was experiencing was most severe at cylinder #4. Now I feed the fuel rails in the front and the back and exit each rail between the middle injectors which should eliminate the possibility of starving the number 4 injector, which is farthest from where the fuel comes into the rails.

Another problem I experienced when running higher boost is that the boost comes on very quickly and you get what is called “Tip In Detonation”. This is more prevalent with positive displacement blowers because the boost can come on quickly at any RPM whereas with centrifugal blowers it is more of a problem at higher rpm. I could actually feel the power fall off, just for a moment, between shifts and knew I had a lean condition. We confirmed this with the data logger feature on the LM1 wide band unit. I still have this situation today so I have to slowly roll into the throttle between shifts and when getting into the throttle from higher rpm. I believe what is happening is when you flip open the throttle the pressure sitting behind it rushes into the intake and the fuel system can’t feed it quickly enough. The fuel injectors are most likely firing like they should but you have to wait for the fuel pressure to get up high enough to get enough fuel though the injector. On a gauge it looks like the fuel pressure is instantly there but I think if you data logged the pressure vs boost you will find it lags just a bit. I have a fix in the works to dampen the rate of boost rise that I believe will fix this problem. The automatic cars don’t have as much of a problem because the throttle plate is wide open between shifts, although the auto’s could face the same situation when they initially stomp the pedal down and see the instant boost. With a centrifugal set to run 8psi max boost this has not been a problem and the lean spot is not measurable. When my car makes 8psi boost at 4000 rpm is when I started seeing problems.

On one of the cars we installed EGT’s at each cylinder exhaust port and had some very interesting things that we witnessed with these gauges. The number one thing was how dirty injectors affected the cylinder temps or better yet how injector cleaner additive slowly cleaned them. When the EGT’s were first installed there was quite a variation between cylinders. Initially we thought we would have to mix and match injectors or modify the manifold passages but after the car ran for a while with the injector cleaner all the cylinders eventually equaled out with respect to temps. On this particular car the fuel rails were modified as mentioned above so it is not known for certain that the stock setup would be inadequate.

As for the setup on my car right now, I did a complete engine rebuild over the winter. I am running GT cams, lowered compression to 8.7:1, ceramic coated the tops of the pistons, Cometic MLS head gaskets, modified fuel system as stated above, 13psi boost, air/water intercooler, Ott X-Pipe, 87 resonators, Bullet rear mufflers, custom machined cylinder support rings, and performance chips. I just recently changed the chips because they give a higher idle speed and also raised the rev limiter to 6800RPM (I was constantly hitting it). I have no idea what else the chips do for the performance other than after changing the chips my air/fuel ratio has dropped from 11.5:1 down to the low 10’s under WOT which is way too rich. I’m going to get a set of GT chips and give those a try because as far as I know, they just raise the rev limit and idle speed. We are working on custom burning our own chips but that is most likely months away yet.

In the works, we are building three 6.1 liter stroker motors with 9:1 Mahle forged pistons, Carillo rods and Moldex cranks. I will most likely have to switch to the Paxton Novi 2000 supercharger because I believe this engine will be beyond the 800HP limit of the Vortech T trim unit I use now. Why are we doing this??? Just in case the adrenalin rush wears off from driving at 600-700HP ;>)

I’m thinking about putting my car on the dyno this weekend to see where it is at but I only have 400 miles on it so I’m debating on waiting another week or so.

Anyway, it is nice to get back behind the wheel of my rocket ship.

 

Murph............new breather system..........new fuel distribution system............Looks good. How extensive ae the fuel rail modifications? brazing required?

 

Sounds like good stuff in the works...

I look forward to your new dyno numbers.

The engine looks great, BTW. Very clean!

 

Gretch, the fuel rail mod was simple. I added the same dampener as in the front in place of the stock regulator. I then braised the AN-6 fittings to the rails and ran them to a "T".

BTW, I bought my wife an 87 BLK BLK AT with 38K miles. I will be testing a low output SC kit (4-5 psi) that will literally take 3-4 hours to install and cost less than $5K, if it works like I am planning. I hopfully will do this within the next 2 weeks.

 

Where are the cylinder support rings Tim? At the top of the bore, or down a bit? Can you machine some more, or do you need the specific block to be at the machine shop?

On the fuel rails, are you going in striaght to each end of the rails, and then OUT THROUGH the fuel pressure regulators?

As I have discussed with you, I *THINK* that I can just go into one end of eachof the rails, go out the front into ONE or TWO pressure regs, back to the tank, all -10AN, since I will have sequential injection, but do we think there still may be a pressure difference between, say, the first injector by the fuel entrance and the last one by the exit? Mike S. has always suggested actually increasing the volume of the rails themselves, thereby creating more fuel and less pressure drop because of this added volume.

That breather system - is that part of your kit?

I assume that blue pump on the driver's side behind the rad is the second bosch pump?

Thanks for your info Tim.

 

The machining of the cylinders is difficult to do. When we had the sleeves made we made 7 sets to cut down on the cost. There were several machining procedures and heat treating processes that were done to the steel rings. Right now there are too many other things going on but perhaps this winter we could entertain doing it again for someone else.

The breather system is a prototype. The jury is still out on how effective it is.

I feed the rails from the front and the back. The exit is in the middle of each rail. You can see in the pic the one on the passenger side.

The blue thing behind the radiator is the fuel filter. Both pumps are mounted in the back.

Here is a pic of the block.

 

The new 928 looks awesome!

The model you hired for that pics looks pretty good to.

Don't you have some other pics of her with the super shark?

Back to work before I get in trouble on multiple levels.

 

hacker...did you see any engine photos in this thread. I must have gotten sidetracked. Just kidding. I wish I had the knowledge and/or the you know whats to do something like this. It is fun reading up on what you extremist are up to.

 

perry - I just take pictures and bring beer, screem like a little girl when Tim goes WOT in 2nd......
I was lucky enough to have the same mechanic as Tim, years ago when he first bought it. The rest is history.

Thanks to Tim's 2nd 928, and the model in the pic that also knows my girlfriend. I'm now hearing "when do I get my own 928?"

 

Tim thanks for the update!!

 

Tim, thanks for sharing ... and your wife is lovely, especially alongside that gorgeous car.

 

This is great stuff Tim!
How many hours/miles did you need to run before the injector cleaner did its work? And what did you use? Techron?
Don't take the following as advice. I'm seeking understanding. Isn't this the exact same issue - albeit less - you have with a normally-asperated system and the reason why the vacuum-activated dampers/regulator provide a pressure bump during the transient fuel demand caused by the throttle plate opening quickly? When you mash on the throttle, the electronics widen the fuel pulse, more fuel is delivered by the injectors, the fuel pressure in the plenum volume of the rails lowers suddenly, and the fuel system has to 'catch-up.'

Might this be partially solvable with more volume in the plenum (i.e. fatter fuel rails that hold more fuel) thereby increasing the capacitance of the fuel system for transient pressure demands?

 

Put two fuel pumps in parallel, which is what the 911 turbo guys do.

re: persisting to use the stock ECU I'm impressed that you have been able to produce serious power numbers, but the stock ECU was never meant to support those numbers, nor forced air. Kludging fuel pressures and voltages is not the most optimum and controllable way to get fuel to the motor - that's what the injectors and ECU are suppose to do.

For the costs that you are going to put into the blower and engine pieces, wouldn't it be better to go with an aftermarket EFI setup rather than rely on the stock ECU to 'pretend' it's still a stock motor? I am using a very simple efi setup on my n/a car, it was cheap and easy to use, it's proven and runs anything - including monster turbo motors. No affiliation to the company, but check it out: www.sdsefi.com

 

Tim


Thanks for the update on your fine rocketship, that is one cool machine

And dont worry i've not forgoten about you and the kit


Stuart

GT UK

 

Murph,

What kind of performance numbers are you expecting from the low boost model you will put on your wifes car???