HinZ Friend

I need to know how to "De-Tune" my husbands car. I can't afford $9.50 a gallon for 109 octane. I've had many opinions on how to do this but I need solid advice. I've been told to turn the distributor back a few degrees and ajust the MAF. But what if the engine was buit wiith higher than normal compression ratios? I guess what I''m asking is how do you de tune a Z

engine to run on pump gas without having to replace parts with stock components..

Thanks for any help.

Zweet

Aviation fuel is much cheaper and you can simply mix it 1/2 to 1/2 with unleaded. The "low lead" aviation fuel supposedly has a lot more lead than the stuff that used to run through our cars and might foul the plugs. You could always try varying the ratios.

Befriend and FBO (Fixed base operator/owner of airport)

Worth a try.

AVgas scented exhaust smells NICE too!! Too bad CO is lethal to inhale.

If your hubby has a lot invested in his engine or the CR is really high you might want to stick with the expensive stuff.

Forgot to add this earlier.

Vicky,

As I understand it,The high Compression ratio is what makes it need the 'spensive stuf. Rolling back the timing will detune the car, lowering the need for the highest octane, but probably not the point of successfully using pump gas-it will also absolutley kill your MPG I don't know how to lower the compression ratio without opening up the engine and swapping parts-meaning I don't think the car in its present and absolutley beautiful configuration could be made to run on pump gas.

Will

What is in the engine? Is this the V8Z or the 6 cylinder? Did he leave you with a list of mods done to it? Without more specific info we're just SWAGing.

Vicky,

You could have a 2mm headgasket put in. That will lower the compression some but you won't need to other parts. Basically the car would look exaxctly the same. You really need to have Rick and I hook up some stuff to it and see where the car is. I always thought the car ran a little lean.

By the way, it was great to see you this weekend! I never did get over to check out your new car.

Jim P

I was also wondering if a thicker head gasket would help but if it truly requires 109 octane I'm not sure if that would be enough to get it down to even premium gas. In other words, the compression ratio might go from something like 14:1 down to 12.5:1 which is still quite high.

I was also wondering if a thicker head gasket would help but if it truly requires 109 octane I'm not sure if that would be enough to get it down to even premium gas. In other words, the compression ratio might go from something like 14:1 down to 12.5:1 which is still quite high.

Mike,

That is exactly what I was thinking. If it turns out to be right (Jims suggestions to really spec out the performance would be the first thing to do) I figured moving the prettys to a stock block would be the best answer. Drop the engine with the front crossmember and raise the body to keep off that beautiful paint.

Will

Yeah, what kind of compression ratio are you running that requires 109 octane? We ran 14.75:1 in the race car, and got along with 110 octane just fine. For anything 11:1 or less, 104 should be fine...and I can get that from the pump for $5 a gallon here.

And when Premium is running $3.75, there is a certian 'what the hell factor' involved filling the car with 104 octane unleaded VP straight from the pump...

Thanks for the replys

So, as I understand (and I'm learning) running lean means not enough fuel/air? Running rich is to much fuel (of couse along with air mixture) for both senarios. Just about every Z I've owned has "run rich" according to mechanics. Nature of the Z beast.

J mortensen, Scott has a build sheet on his car but this car was done by a famous drag racinging mechanic here in Fla. (Big Daddy Don Garlits ring any bells). My husband wanted a strip car and that required severe internal mods for "any" car. Hence the trailering for anything over 100 miles.

I can't deal with a Z that I want to drive but can't due to mods. The car is pretty and all but sitting pretty in the garage does me no good. I want to go be with fellow Z friends at gatherings and shows.

Please keep all help comming. I have the tools and books to work on the car but not the strength to break bolts.

Thanks in advance.

Vicky

Yeah, what kind of compression ratio are you running that requires 109 octane? We ran 14.75:1 in the race car, and got along with 110 octane just fine. For anything 11:1 or less, 104 should be fine...and I can get that from the pump for $5 a gallon here.

And when Premium is running $3.75, there is a certian 'what the hell factor' involved filling the car with 104 octane unleaded VP straight from the pump...

Yes that's my point Tony, the car runs fine on 109 like your race car. Well I can't get 104 here in FLA for $5.00. We tried 104 and that still produced the same effect. Suggestions from gearheads said the octane was to low, so we tried 109 and she purrs like a kitten, no bog, no hesitation, etc.

Premium runs about $3.00+. The car bogs down on pump gas that's the whole point to this thread.

Please continue you input and help.

Vicky

I read this information here: http://suncoastzcarclub.homestead.com/club_carz_Moschettos.html

and while it is not particularly thorough, it sounds like the car should not be running anything too extreme in terms of compression. Flat top pistons, not domed, .040" oversize, shaved head. Doesn't say what head is being used. Do you know which head is on it?

What the website info did tell me is that most of the compression is in the head because the flat top pistons are not REALLY high compression pistons. So rather than getting a new shortblock like hls30.com suggested, a new head would be the way to mellow out your engine. Either the P79 or P90 heads should drop your compression down to the high 8 to 1 range, and at that compression you can probably run 87 octane.

I would expect compression for your engine to be in the 10 to 11:1 range. I think my own engine is at the high end of possible ratios for flat top pistons since I have an E31 head which has one of the smallest chambers. Mine is about 11:1, and my engine requires about 95 octane to keep from pinging. I trial and errored it out until I got the minimum octane that I could use with full timing advance and not ping.

If you bought one gallon of the 109 octane and mixed it with 5 gallons of 92 octane, that would net you 94.89 octane. That should be pretty close to getting it to run without pinging. If that didn't quite cut it you could go with a 4:1 ratio for 95.4 octane. The lower your octane the more power you can get from the gas, so you should always run as low octane fuel as you can with the appropriate amount of timing for max power and not ping. I believe Dan Baldwin proved this on the dyno way back when. Upped the octane and lost hp, tried to increase timing, lost more hp.

Anyway I hope that helps some. The more info you give us the more closely we can try to figure it out.