: Timing and Octane....I searched.



msta293412
03-03-08, 08:28 AM
I know the 2001 sts (obd2) was rated at 300hp WITH 87 octane....and several sources here say that if you run 93 the pcm advances spark timing to compensate....this is something I have experienced, definetley better throttle response if nothing else. My question is , if I run race fuel, or say 100 octane, maybe mix it with an 1/8 tank 93, will the pcm further increase spark timing to compensate, thus creating a little more horsepower? Pleas forgive if already covered somewhere, I did search.........Thanks to anybody willing to respond.

C&C
03-03-08, 11:21 AM
No, it doesn't work that way. What the ECM does is retard the timing if it detects detonation from the knock sensor. The timing adjustment can only go so far (this set by the program) so it will go to its highest specification when no knock is observed. In fact you may get that extra-performance by just going to a mid grade gasoline, say 89 octane. Anything beyond what would cause knock is wasting money.

Ranger
03-03-08, 11:48 AM
:yeah:

dwight.j.carter
03-03-08, 12:24 PM
I use 89 and mine drives like a raped ape lol.

BlackCaddy87
03-03-08, 01:01 PM
What about using 100 octane with a chip??? My car is rated for premium anyway, then the chip advanced the timing even more. She will sometimes knock when i go out of town and put 91 in it, I guess I'm lucky we have 93 here

Submariner409
03-03-08, 01:34 PM
A higher octane rating, in and of itself, does not generate more horsepower. It slows combustion flame travel which allows the use of higher compression and other mechanical modifications (which do not exist for a N*), which requires timing adjustment.

msta293412
03-03-08, 07:46 PM
Actually , BlackCaddy87. Sounds like YOU would benefit from the 100 octane not me. I have limitations, what submariner sais, makes sense....You on the other hand can further advance the timing(manually) so to speak....I think......:-)

Murphyg
03-03-08, 10:00 PM
Ya...Big difference between an 01 and a 95.
Definetally benefit that way.

BlackCaddy87
03-04-08, 02:31 AM
Well I'm going to Tulsa this weekend and running the 1/4 so we'll see what happens...looking for low 14's

Murphyg
03-04-08, 02:53 AM
Well I'm going to Tulsa this weekend and running the 1/4 so we'll see what happens...looking for low 14's

Get someone to video it. Can post it right on the site here. Would be very cool to see.

What we was getting at though...is the fact that the 01 STS that msta owns is not chip compatible as your 95.
Sure both may be N#s. But still totally different animals. Very very much different things have been done with the Cadillac N# in 6 years. Very very much has been done with Cadillac in general in 6 years.

If by chance there is someone there in Tulsa with a stock CTS-V....see if you can sit beside that and get it on video. Or any 99 or newer stock N# for that matter. Would be nice to see what youve done with the 95.

BlackCaddy87
03-04-08, 08:51 AM
http://www.hotrod.com/techarticles/engine/fuel_octane_rating_comparison/index.html

I found that a long time ago...I know the northstar is a different engine but this engine matches the northstar's compression.

It states that no matter what kind of octane you use there is still a limit on how far you can go with your timing.

They also claim to gain horsepower by using higher octane even with stock timing.

CaddyCruisin420
03-05-08, 04:08 AM
if i run 87 octane in my 95 concourse, will it knock? Is it even worth cheaping out on the lesser octane? I heard you end up getting lower MPG, so why not just get the 91octane (no 93 in cali) and enjoy the better performance and MPG? i just would like to know which octane better benefits cost and performance effectiveness.

Submariner409
03-05-08, 08:59 AM
Caddy, I believe that your 95 will be OK with 87 octane as the knock sensor will adjust the timing for the best curve with the gas used. That said, your economy and cost effectiveness can only be determined by your own location and driving habits. City, hills, rapid acceleration = poor gas mileage. Country, flat road, easy on the pedal = good to exceptional gas mileage. Whether you run 87 or 91 won't make much difference, if any, in the observed gas mileage under your conditions.

BlackCaddy, Compression varies all over the place from engine to engine. Just because one V8 has a 9.75:1 ratio and another has 10.5:1 has absolutely no bearing on HP output. Regardless of CR and octane, once you get past a total advance (vacuum + static + mechanical/electronic) of about 38 degrees BTDC, further advance introduces the real possibility of detonation regardless of octane, because the piston is still traveling up in the bore as the flame kernel is initiated. Some large, high HP engines will run satisfactorily in the midrange under light load with up to 42-44 degrees advance, but vacuum or electronic retard must come in fairly rapidly upon acceleration or you run the risk of holing a piston. CR isn't everything, but it's an important part of the whole formula.......This is a pretty sketchy explanation, because maximum output engine power is a very thin tightrope: one mistake in one of several factors = disaster.

Ranger
03-05-08, 12:03 PM
if i run 87 octane in my 95 concourse, will it knock? Is it even worth cheaping out on the lesser octane? I heard you end up getting lower MPG, so why not just get the 91octane (no 93 in cali) and enjoy the better performance and MPG? i just would like to know which octane better benefits cost and performance effectiveness.
Try it and see. You might be surprised. I ran 87 in my '97 for 3 years. Never noticed any difference in performance or mileage.

dwight.j.carter
03-05-08, 02:06 PM
I lost a mile or two when I went down to 89 from 91 but I think it's because our 89 is ethanol blend.