Howard

Anyone have advice on maximum igniton advance on a 993 based race engine? Here are the specifics:

Carrillo/Andial rods
12.5:1 CR, Motorsport injectors, J&E pistons, normally run 112 octane leaded fuel. Custom throttle bodies with slide valve injection. Autronic engine/fuel management, GE 100 cams ( Jerry Woods) running Autronic CDI direct fire with 6 MSD coils, crank fired. Currently making 319 rwhp.
I checked the ignition map and the ignition is currently at 27 degrees at 80 %load at 7500 rpm. can I safely go just a tad more with the advance?
Thanks in advance ( no pun intended)

Steve Weiner-Rennsport Systems

Howard:

I would not go beyond 27 deg at that load setting.

You don't get any more power with that CR, and it will detonate no matter what gas you have,....BTDT.

Geoffrey

You can find the maximum timing your engine requires by using a load bearing engine or chassis dyno. This is THE ONLY WAY to determine timing unless you are using real time cylinder pressure analysis. Find a Dyno Dynamics or Dynapack chassis dyno and use the features of the dyno to hold the engine at a specific RPM and load site and adjust the timing until you have peak torque. Use the LEAST amount of timing the engine requires to obtain peak torque at that site and move on to the next site and repeat the test. You will find that you can run more timing after peak torque occurs which on your engine combination should be at 5750. I agree with Steve that 27-28 degrees is the most you can run at peak torque. However, you will want to optimize timing everywhere in the map to improve drivability and throttle response. This is particularly important at low VE% areas.

Autronic is by far the easiest system to tune and if done correctly, with your combination, you should see approximately 290ft/lbs and 342rwhp. I have tuned an identically configured engine as yours with individual throttle bodies and straight exhaust. I was able to get 270rw torque from 3500-6600 with a peak of 292tq torque. This produced a peak rwhp of 342 at 6900rpm. This equates to about 404fwhp or RSR sprint engine. This was using a factory style inductive ignition. You will likely find improvements by using the Autronics R500 CDI unit which is excellent and should be able to best my numbers.

If you are running the green colored PMNA injectors (Bosch 0280150803) they are 37lb/hr injectors and you will need close to 65psi of fuel statically set to be under 85% duty cycle. A better injector for your application is a Bosch 0280150400 which is 44lb/hr and run factory 3.8bar (55psi) of fuel pressure. Alternatively you can use the orange 994TT injector (can't remember part number) but these are sturated injectors, not peak and hold so you give up some injector performance.

If you would like an opinion on your map, you can email it to me.

Howard

Thanks to both of you for your help and valuable information.


Howard

Geoffrey

I would also retest you engine on a different dyno. The Dynojet HP and Torque curves will be skewed from what they actually are. This is because it only measures the torque required to accelerate a known mass (the roller). It always shows high, and always shows more HP and Torque than the engine is actually producing. The Dynajet has really outlived its usefulness for providing meaningful information for EFI tuning. If you want to do comparison runs (one exhaust vs another), it is a good device that will give you repeatable results. Beyond that, you need to step up to newer dyno technology to properly understand how your engine is running.

m42racer

What is the optimum CR on these Heads? Why does the higher CR not make any more torque? Surely the CR limit would be based upon the Piston design and the amount of Ignition lead, with the fuel type and acceptable Cylinder Heads temps factored in. Would not the use of CDI allow a higher CR to be used? I was also under the impression, that when the problem with the 993 RSR Cylinder Head Chamber/Seat/Port problem was found, that 110HP/Litre was achieved. I do not know what the problem was, but I do know that PMSNA was unaware of it, but when shown and told of it, decided not to offer the upgrade as it was not authorized by Motorsport AG.

dwightp

Howard:

I have a similar setup. The cam's and exhaust are probably the biggest difference. Slidevalve and ign details second. I'm running a Motec and did some road tuning with the ign. What I did is pick a certain throttle and rpm region to change ign timing slightly advanced or retarded. (Running alpha-N) I could definitely feel a difference when I was in the delta regime. I shared my findings with Steve and he pretty much expressed the same advice as he posted here. I'm staying out of that neverland of more than 27deg advance. I think I max at 26deg. I yield to his vast experience. It is a fxn of many parameters as you know. I hope to get some time on another dyno (dynopak) to tweek it in further. FWIW, I agree with Geoffrey too when he states that the dynojet quickly looses value as a EFI tuning tool after a few hours on it. I only wish I could rent a dynopak for several days. Finding one is difficult enough (at least for me) in this area. Finding one who will let you (car owner) do the tuning, is more difficult.

Care to share your Torque and Hp curves? I'm interested in seeing the characteristics.

Howard

I'm making some more changes, cam advancement, exhaust, etc. In the next few weeks I plan to schedule a dyno tuning session with Geoffrey and Ben ( EFI U) . At that time I'll forward the results to you for comparison.
The problem I have currently is that the peak HP was still ascending when we reached the REV limit at 7400. I need to bring the peak torque and HP closer to the operating range during a race. ( 6700-7300 or so.)