Does anyone have a Z06 that can tell me how the car runs on 87 octane gas? I'm building a "poor man's" LS6 by porting and milling my LS1 heads and I'm trying to determine the optimum compression ratio with the '02 LS6 cam and intake. Does anyone have any advice? I supose the PCM would retard the timing to prevent the detonation but would that cost so much HP that I'd be better off with a lower compression ratio?

Thanks,

 

Someone had some dyno numbers awhile back, and there was a 10-15HP loss with lower octane fuel. I can't remember if it was 87 or 89 vs 93 octane.
That ain't much!

 

If you really want to operate "on the edge", you need to consider compression ratio and valve timing together, since it's really the "dynamic" compression ratio, and not the static compression ratio that determines when an engine will ping. Are you installing an aftermarket cam? Cams with more valve overlap allow (and actuallly require) more static compression because some of the pressure bleeds off during valve overlap. There are simulation programs that calculate dynamic compression ratio. You will want to determine what the max dynamic compression ratio you can run on 87 octane in an LS1 w/o detonation. I would never consider lowering the compression ratio (unless I was building a motor for forced induction), but that's just me. You are leaving HP on the table, which is essentially free HP, because compression does not cost you in fuel consumption. In fact, it actually inproves fuel economy. Is ten to fifteen cents per gallon really going to make that much difference?

One more thing, your motor will have nothing in common with the LS7 . Did you mean to post this in the C5 Z06 section ?

 

DCR has NOTHING to do with overlap. It's determine by the point that the inlet valve CLOSES.

Duke

 

I would try C5 Tech.

 

 

I've ran my Z on a 87 for about 300 miles - it ran fine.

 

Thanks everyone for your input! It sounds like I can't go wrong with the 64.5cc and 10.5:1.

 

There was a post here a while back about re-programming the computer to run on lower octane. Results as far as I remember were fine.

 

I really don't understand these posts. Let's say you go through a tank of gas in a week. At 20 cents savings per gallon and 17 gallons to fill up, you save $3.40 a fillup. That only works out to $176.80 over the course of a year. Even if you double it and say you fill up twice a week, the savings seems so miniscule. We do drive Corvettes, right?

 

You may not notice much difference in just putting around town, but you will when you stand on it. The PCM moniters the knock sensors and with lower octane fuel it will most likely knock and the PCM will pull power accordingly. The difference becomes clear when you place some demand on the engine.
It is not reccomended to run lower octane fuel in the LS6.

I had my car dyno'ed a few months ago to get a stock power reading. I run 91 octane which is the most we can get here in CA. The tuner told me he could hear the knock sensors cutting in even with 91 octane fuel...87 would certainly do worse, and, as someone else mentioned, it really doesn't save much $$ at all.

 

Does anyone know why someone would take a somewhat high perf engine and screw it up by trying to make it do something it clearly wasn't designed to do? Leave it alone and just drive the car!

 

DITTO-DITTO The book for all Z06s including the new 505 H/P,call for 91 octane--The car will run great with 91 octane

 

They just started selling 100 octane at the gas station by work. They got rid of 89. There is 87, 91, and 100......at every single pump!!!

I don't mind the 5.99 a gallon since I don't drive the car much, it deserves some good drink.

BTW...It's a the Alliance gas station on Los Angeles Avenue and First Street in Simi Valley, CA.

 

Even the "dynamic" compression ratio formula has plenty of flaws… Mainly the fact that you only get one ratio out of it and it doesn’t take into consideration when any other events take place or airflow/manifold type. I’ve been trying to figure out the same thing because I would like to build a high performance LT1 with high compression that can run on lower octane’s and also be somewhat more fuel efficient (to the figure of 18-20MPG city and at least 22MPG for highway).

I can’t seem to find any sites that actually list the maximum compressions for the rating so does anyone here know what they can go to or how to find out?

Yea it’s a pain in the a$$ trying to program a new spark curve for a lower octane rating. I just changed over from 89 to 87 for my new engine (custom built so I really didn’t know which would be the best). I would imagine that because 87 burns faster you probably don’t want full timing to come in till a later in the RPMs and probably want to reduce timing overall just a hair.

Make sure it isn’t 100 low lead because that will mess up your O2 sensor along with your cat. Also there is no reason for adding that kind of fuel in your car. Studies show every time that people LOSE performance by switching to a grade higher that what is recommended (if you think you are seeing an improvement then something is obviously wrong or the pump that you are getting it from isn’t telling the truth about their ratings. Of course this is for stock application and unless you do something major like port your heads, get headers, and a new cam, don’t think you are getting more out of a slower burning, higher octane)