Old & New

Lagavulin

I'm guessing it could happen at any RPM.

However, regardless of what the fuel pressure is, your air/fuel gauge will tell you what the mixture is, which is really all one needs to know.

For example, if you are at cruise and your air/fuel gauge is showing 'red', then you have a problem since the mixture is too lean. Worse yet, if at WOT and your air/fuel gauge is showing 'red', back out immediately as the mixture is way too lean. Bumping up the fuel pressure should solve both issues, although I've never come across the above scenario.

However, if at cruise and your air/fuel is showing 'yellow', then you're good to go as your are right around stoich which is good. If at WOT and your air/fuel gauge shows all 'yellow', back out immediately as the mixture is too lean since you do not want to be at stoich at WOT.

Likewise, if at cruise your air/fuel is showing 'green', then your mixture is too rich for the computer to compensate; the computer is programmed to operate your car at at stoich under cruise conditions. So what do you do? Lower the fuel pressure enough so that the computer is able to make it's corrections to maintain stoich. You know you have it right when at cruise, the air/fuel is showing 'yellow'.

What I'm trying to say is that as long as you obey your air/fuel gauge and adjust your fuel pressure accordingly, you won't have to worry about the fuel pressure being 'too low', thus running lean where one can detonate. That is why we run the air/fuel gauge, and why I bought a wide band O2 sensor.

Tim Murphy

Lag is right on. We actually run the fuel pressure very close to where the computer cannot compensate enough to keep from running rich. You could lower the fuel pressure way down from the 32 psi and the car will run just fine although you might loose a little throttle response. I like to run the car right on the rich edge because it is just safer for what we are doing.

Here is a picture of a gauge setup to tell us exactly what is going on. This car runs 42lb injectors and 18psi boost.


Alright, what happened to the picture. I'll try again in another post.

Tim Murphy

Here is another shot at the picture:

Old & New

Sweet!

What's that gauge where the clock used to be, fuel pressure?

Tim Murphy

What you see are 2 quad EGT gauges, fuel pressure (white), boost/vac, AFR, and the box is for the wide band oxygen sensor. We are waiting for the remote display to be released for the wide band and then the box will go away.

Also getting added to this car is the G-Tech Competition and Perfect Power SMT-6. The SMT will primarily be used to modify the timing with repect to boost. We will be able to datalog every function (except the egt's) with a laptop, including the G-Tech. Then we will play with the timing and see where it generates the best power.

Gretch

WOW, do I want the EGTs...........now that you have them installed, is there much variation between the cylinders? Tell us what you have discovered!!!!!!!!!!!!!!!!!!!

Tim Murphy

Actually, I have the same EGT's for my car and I may not even install them. It is really hard to study the gauges when you are driving because the car is so blazingly fast but they all appear to read exactly the same temps. We are going to mount a video camera in the car so we can play it back in slow motion just to verify them. I should also mention that the fuel system is pretty modified on this car to support this level of HP. What is the most surprising is after all the instruments were added, nothing was changed because it all worked perfect. 14.7:1 cruising and 12.2:1 WOT. It is actually amazing that we got this to work right out of the gate. We were afraid to hammer on the car before all the gauges were installed but now that the AFR and EGT is confirmed it is "hammer away".

Here is some eye candy:

Gretch

Tim I like what you did with the breather system, Is that a breather hose on the blower? please explain. I like the strut from the block to the bracket too.

Is this install a newer version of your kit? Interesting air intake approach too, why did you modify from the air box style? what happened to the fan install? are there two fan sets straddling the blower, or only one on the drivers side? Enquiring minds want to know.....

Tim Murphy

This is a good friend of mine's car. He is a master fabricator and has put many many many hours into this car. He is also the one who makes most of my fabricated parts for me. The strut is his version of my aluminum top bracket. The reason the blower has the line going to the crank breather assembly is because the oil return from the blower is connected to the oil pan, below the oil level. We found that it was generating a slight pressure in the blower and we wanted to make sure the oil would drain without restriction so he added the vent.

Tony

WOW..i think you could have made that intercooler about..eh..1/4" bigger!
Looks great!

John..

My hot wire is sized and calibrated for the HP I am running, in other words I do not run out of hot wire signal at full load, I think it runs to about 5 or 5.2 volts. The same could be done with the S4. You could install a differently calibrated hot wire for the power you are making and then intercept the voltage signal from the hot wire and condition it for sending back to the LH. Problem is in that ignition is tied into this equation on the modern Motronics, so you have to watch what the computer is doing with the MAF voltage as it relates to ignition advance. If you retard anywhere, it should be at or around torque peak. I have the luxury of pressure retard on the mechanical distributor, so this is quite easy and is actually a function of manifold pressure, not just an on or off deal.

The only thing I don't like about cranking the fuel pressure up too high is the injector can lock open. I think mine cap out at 65-70 psig on boost and they run 50 or so psig at atmospheric and about 40 at idle under vacuum. As I have heard these injectors should not be pushed much past 80 psig or you can start to have issues.

The devil is in the detials...if you can find a way to gain control of the entire fuel curve you are much better off than just having control over the limits of operation, i.e. idle and WOT.

BC

I will be doing a Coil-near-plug configuration (Ls1 Vette parts) with my DTA efi - Do you think there is enough room under the intercooler for some coils near each cylinder, or during fabrication, do you think I should find another place for them?

Lagavulin

Good info John.

One the driver side it won't be a problem, but you may run into space limitations on the passenger side since the intercooler and all it's plumbing takes up quite a bit of space.

SteveM928

Depending on the particular EGT gauge(s) used, there may be more or less lag time in the readings they show. You might be able to get a better idea of what's really going on if you check them with the car on a dyno that allows for the engine to be run under a steady state full throttle load. Either that or you could just keep your foot to the floor until things stabilize at top speed on the road.