1990 Corvette, aftermarket chip, 160 thermo Bosch match flow injectors, otherwise stock. Primary use autocross, frequent 2nd gear redline, Fuel Chevron 92, Oil Mobil One. Pretty basic. Engine has 127K miles on it. Replacing the O2 sensors, and having the timing checked before this weekends Pro Solo at El Toro. Is there a safe (no risk of detonation or other bad things) timing advance that would add a little performance. I understand 4 degrees positive is max? don't know if that is true.

Thoughts are welcome.

 

6* BTDC is the stock setting, but I bump it up to 8 degrees.

 

i think i recall seeing some ware that you can go up to 11 deg but like all engines it is a case by case deal. i will look and see if i can find a article about the lt4 esc and or using a resistor off of the knock sensor, thus the esc pulls less timing giving more power but still being reasonably safe

 

Not sure 11 would do any good. EST will pull most of the advance as the first sign of detonation.

 

im back it was a 4.3 caprice module post # 10
http://forums.corvetteforum.com/c4-t...-question.html

 

the resistor i mentioned earlier pg 53
http://books.google.com/books?id=1Ti...page&q&f=false

i know you did not ask about knock or detonation but building a little extra power with advancing the timing is easy and free hp until things go awry via detonation hopefully with the 4.3 module you will still have your safety blanket with out being choked by a overly sensitive esc

 

I am running 6* and I spray a 75hp shot of N2O, so far not detonation.

 

Like Vader said you can bump the base timing from 6 to 8 BTDC. Running 92 octane you should be just fine.

 

If you want performance timing, why don't you do it right by getting it dyno tuned? Why play all those tricks? Sure, crank up the timing but do realize that means everything gets that increase whether it needs it or not. If not, detonation results. If it needs more, you can't give it any more. That is the old school trick they used to do. I am not in favor of doing it across the board.

If you get detonation, 2 things to consider. Sure, the ECM will pull out timing and protect the engine

1. You lose the power anyways
2. Until the detonation stops, some damage could be done. What is the cumulative effect?

If you want to do something, why not do it right the first time?

 

Safer to get it done thru the ECM. Better too. That way you can bump up timing and fuel at one point and not the other. All this does is fool this and that.

 

These are indpendant systams that work togather. I wouldent so much say your fooling anything but giving the system a better cleaner signal to base its adjustments off of. All you are doing is exploiting a already usefull feature you have as is but to a more refined degre. The stock module seems to find more false knock thus pulling timing when it is not warrented, expecialy after headers have been installed

 

Dunno why but we hooked up a MSD unit to the KS area and got the same results, give or take. Did a run, see the counts the ECM got. Do another run, see the counts the MSD one gave and they were pretty consistent. Same hole, same dyno.

You can hook up an LT4 KS to an LT1. Supposedly it doesn't detect false knock. Somehow, I think it is less sensitive. I think they did that with the L98 too. Don't know. Never got into that. They have also talked about wrapping it with teflon tape to reduce the sensitivity. Somehow, I am not confident about that. As to the headers giving false knock, could they be hitting on something? If you make it less sensitive, what happens when there is real knock and it doesn't pick it up until it becomes more severe? I would think that isn't good.

People have reported that they got false knock from bad valvetrain, headers knocking around, loose exhaust, etc, etc. Before I desensitize anything, I want to know what is the cause. If all failed, MAYBE. Too many people jump to the simple cheap solution and find out that it cost them something in the long run. IMO, the best thing is to get a good tuner to do a dyno tune. That will enable you to push the edge within the safety of the system as designed. If you are still getting knock, find out what is causing it instead of simply desensitizing the sensor or "refining" it like you call it. I could break your leg and give you enough morphine that you won't feel a thing. Doesn't mean your leg isn't broken or needs to be fixed.

 

I don't race mine but I installed the Bosch III's and it ran ok. Got a good tune...way better!! The Bosch type III's don't seem to run right in the L98 without tuning.

 

If it runs better after you install injectors, you probably have an issue with your old injectors. I would say it is wise to have them checked every 3 or 4 years or 50K.

Curious. Why would that be? If you a tune, it changes the equation. How is the Bosch III different from Multecs in that respect? Could the atomization of the fuel make that much of a difference?

 

My Multec's were trash, it barely ran with them so I got the set of Bosch's. That got it running and I drove it that way for almost a year. Recently installed RR's, headers, catback Magnaflow, 180 stat. I decided to have it tuned and even with the base tune before final touch-ups it runs so much better.

According to my tuner, the Bosch's are designed to work with the newer engines so essentially the atomization is different. My car was running dangerously lean when I first started datalogging.

 

I wouldn't bump it up at all untill you know what the timing tables are like on the custom chip you have. They could very well have all the advance wrote into them leaving you no room for safe adjustment of the bass timing.

Do you have any ALDL tools?

 

RR, headers and exhaust all will help it breathe better. So I would suspect it is making it lean with stock timing. If the Multecs are trashed, anything in good working order will make it run better. I think the Boschs have finer atomization so it burns better and is a little leaner or a more complete burn.

 

When I switched to Bosch 3's on my 1990; I found I was running lean also...about 144-146 BLM. ..bumped up fuel pressure to 50 psi and it dropped to about 136 BLM....since the 1990's are a Speed Density system; I relocated the Mat sensor and mounted it to the rad shroud and now am running about 131 BLM. The spark plugs now look better for colour and it runs fine.
Bill

 

i cant speak for data logging; but after i replaced the multecs with bosch III in my 90 l98 my car is harder to start. I replaced the fuel pump and injectors and have to prime the system before i crank the car or it will crank for 4-5 seconds. With the original multecs the car could sit for weeks and I could hit the key and it would start right up. The idle is smoother and I did increase the timing to 8 also which helped the car from bogging at low speeds. So overall I am happy and just adjusted my starting procedure. hopefully get a tune this summer after I replace the cats.

 

I do the same start-up procedure for the exact same reason.