Jump to content
Sign in to follow this  
Zrush

How to De-Tune a Z

Recommended Posts

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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...

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites
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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

If it's bog and hesitation that is your problem and not pinging under load or light loads, then I might think the issue with pump-gas -v- race-gas may be more in formulation. Many of the competition fuels are formulated to 'older' specifications with specific gravity more suited to carburetted use. ALL pump gases now are formulated for fuel injection so they lack the light aromatics that make carburetted fuel work in those systems.

I had a smiilar problem here on the left coast when they went to reformulated gases in the early 90's. My high compression Corvair didn't necessarily ping, but it wouldn't cold start worth a damn, and stumbled and bucked like crazy unless I ran Chevron Gasoline in it. Come to find out talking with some engineers at Unocal in Brea, as well as some people at Chevron Technical Assistance that indeed the Chevron Premium I was finding ran so well still had the old formulation...and they told me a specific date that it would no longer be available. Right to the week they said, the car started stumbling on Chevron as well. I went to Union76 Racing fuel of the lowest octane I could get (I think it was 95) that was set up for carburetted race series, and the car would run like a top! I found that blending the race fuel by about 10-20% (depending on what brand I was pumping)was all I needed to make the car operate correctly with it's NOS Rochesters. And that was with 87 or 91 octane. I found with the stumbling and bucking and hesitation (which sounds like exactly what you are experiencing!) it was not so much Octane as formulation of the fuel. See if they have a lower octane race fuel that is specifically set up for carburetted racing series. I know the 104 I get at the pump (VP Racing Fuel) is set up for Fuel Injected Imports, and haven't really tried it in anything carburetted but my pit minibike, and occasionally the lawnmower if I'm getting a lot of pressure to cut the grass!

If you're not pinging, and it's more a drivability problem, I think you are going to need to search for proper formulation, rather than higher octane. The 109 Octane you are running may be formulated for a carburetted racing series, and that is why it runs so well, not necessarily the Octane.

Oh, and that's about highway robbery for that fuel! If you are buying it in a five gallon pail...and it's going to sound bad...buy it by the drum! Our driver Dave Richardson buys his Race Fuel by the drum, and gets it for about a DOLLAR LESS per gallon than what I can buy it for at the pump! We save because we have access to drums so we don't get tagged for the deposit. We sell the gas off to friends for a bit of a profit to defray the costs, but the more you buy, the cheaper it is, and that $9.50 a gallon is highway robbery!

You also have to be able to store a drum of fuel....it's not a 'garage in the house' commodity, needless to say. Shop around, you should be able to get a better price than that, and like JM says, mixing is a viable option to really decrease your costs. With 11 or 12:1 compression you probably only need octane in the low 90's, and if your setup is like my Vair, you may get away with mixing 20% race fuel to standard pump gas to get enough aromatics in the gas to clear out the stumbles caused by the syrup they sell at the pump these days.

Good Luck!

Share this post


Link to post
Share on other sites

Hi Vicky,

Good to see you Saturday.

Have you considered swapping engines?

Maybe someone out there would be interested.

They get a go fast, built by Big Daddy, and you get a good driver on pump gas.

My 2 cents.

Barrie

Share this post


Link to post
Share on other sites

Thanks for the many suggestions, keep them comming.

Anyway, I went to the strip and ran the car down to a half of tank of 109 octane. Now, should I go the the gas staion and get premium 95 or regular at 87.

If the car runs fine on half and half that will save some scratch.

Thanking all my Z Freinds in advance.

Vicky

PS she ran 7:00 et in the 1/8th. Remember this is me driving, a more experienced driver could more than likely get a lower trap time.

Share this post


Link to post
Share on other sites

1/2 and 1/2 with 87 should give you 98 octane. Figure 16 gallon tank so 1/2 tank = 8 gallons. 8*87 = 696 + 8*109 = 872. Add those two together and divide by the number of gallons, 1568/16 = 98.

That's enough for 12:1 compression in all likelihood. I still think you could get down to 95 or so and be OK, based on the info we have.

Share this post


Link to post
Share on other sites

No Math Please

I'm running up to the staiton now and get 87. The track is open until 2:30, so that gives mew time to test.

If it still bogs on the half and half mixture what do I do then?

Vicky

Share this post


Link to post
Share on other sites

Outlaw or other octane booster!

Will

Octane booster is Tolulene or Xylene or a mixture of both. You can buy a gallon from the hardware store (it's also used as paint thinner) for ~$12, or you can buy a 16 oz bottle for $8. Tolulene is 114 octane and Xylene is 118 octane. When the bottle says it raises octane one point, that actually means .1 so it will take 92 octane to 92.1 octane. You can do the math in oz as shown in my previous post to see what the actual effect is, and it's basically nil.

There are site's with homebrew octane booster recipes, and I think it's been talked about here before. If not it's come up a couple times on Hybrid Z if you want to learn more.

Share this post


Link to post
Share on other sites

As your know I ran the Z down to a half of tank of 109 and went and bought 95. Seems OK until you down shift for more hp.

What now, air mixture adjustment?

Bogging is so embarassing. Please help. Plus black smoke came from the tailpipe wereas with 109 she was Greenpeace clean.

Help

Vicky

Share this post


Link to post
Share on other sites

Put simply, that don't make no sense. I would suggest at this point that you take it to a mechanic who knows Z's. Bogging shouldn't have to do with octane. Pinging should have to do with octane. 109 octane is ridiculously high for what you have there. Since your Z still apparently runs stock FI, I doubt that the issue is the specific gravity of the fuel. I think it has some other problem with the FI that's causing your hesitation.

Share this post


Link to post
Share on other sites

What can I say that's what happened when i did that. Actually this Zrush is a pain in the AZZ. Honestly race fuel is expensive here but pump gas boggs down the car. You dow know what bogging down means yes? That was a term we used in the 70's for crappy prerformance. Gas/Fuel can make all the difference, for any hi-po car.

I would appreciate any help with makeing this Z a daily driver.

PS no one really told me the difference between running rich and running lean. Which is what we want for our Z cars.

Thanking anyone in advance for help.

Vicky

Share this post


Link to post
Share on other sites

What can I say that's what happened when i did that. Actually this Zrush is a pain in the AZZ. Honestly race fuel is expensive here but pump gas boggs down the car. You dow know what bogging down means yes? That was a term we used in the 70's for crappy prerformance. Gas/Fuel can make all the difference, for any hi-po car.

If you mixed 50/50 109 octane, I can't see any way possible that the formulation of the gas could make the car bog. It would have plenty of the aromatics that Tony D referred to at that point and the octane should be sufficient for 12:1 compression, which I don't think you have based on the info that was on that website I linked to. That's why I think you have some other problem going on.

I would appreciate any help with makeing this Z a daily driver.

You could put a stock head on the engine. That would pretty much return everything back to normal as far as the engine is concerned. Then you'd have to figure out what kind of mods were done to the fuel injection to make it work in the racey configuration. Do those two things and it should run on 87.

PS no one really told me the difference between running rich and running lean. Which is what we want for our Z cars.

At cruise you want stoichiometric ratio, which is 14.7:1 air to fuel. At WOT (wide open throttle) for NA you want about 12.8 to 13.4:1 for max power.

Share this post


Link to post
Share on other sites

Stoichiometric ratio (sp?) is 14.7parts air to one part fuel if memory serves me. (Modern engines can stretch the ratio due to design) Proper Stoich ratio gives us cars that run right and have the nice by-product producing lowest emmisions.

Rich = Change the ratio to more fuel per unit of air and it will foul the plugs. (Black soot on plugs/Black smoke from exhaust)

Lean= Change ratio to less fuel per unit of air and things will run hot. (Lean is very bad on a high compression engine) Going excessively lean can soften/melt pistons to the point of failure. Hot spots can lead to preignition or detonation. Normally fuel expands at a certain curve but when the mixture detonates the expansion becomes more of a jarring/slamming effect on the engine's parts. In race engines the parts are already loaded and the above average heat decreases their load carrying ability. Throw a few shocks to the system and something will break. Torsional vibration from detonation can trash a crank.

It is interesting that some people in the past used water injection as a means of curbing detonation during peak power. Some combat aircraft in WWII used it. They had a minutes supply of water but that was often all they needed to outrun the bad guys etc.

The beauty of EFI is that when it runs right the mixture is appropriate for the engine's demands. Modern engines have a sensor in the block which "hears" detonation and automatically retards the ignition timing ten degrees or so to keep from hurting anything. In our Z's we don't have this luxury.

Jmortensen knows what he's talking about. It might not hurt to have the FI system looked over. There is also a great book on modifying Bosch fuel injection. This book explains many testing procedures and how things work. If I had a 280 I wouldn't be without it.

http://www.amazon.com/Modify-Bosch-Injection-Motorbooks-Workshop/dp/0879385707

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.