# compression



## SIXT5GTO (Mar 9, 2010)

I have a little time and have been trying to get the GTO running right.
Well the things Pings like crazy any time a load is added.
I am running Shell 93. and have added 108 otc. boost, still pings
Ran a compession check everything looks good 179-181.
with a 180 it should be around 10.5-1, I dont think I should be having the problem I am having.
I will try some timing setting today, did retard the timing but still had the same problem.
Thanks for any help.


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## geeteeohguy (Feb 2, 2008)

Your car should indeed ping on pump gas. I have the same problem with my '65 GTO, and every other GTO I've driven with stock compression and pump gas. Completely normal with 10+ CR in these cars. I run 98-100 octane in mine and it doesn't ping. The commercial ocatne boosters are not effective and are a waste of money. You need to run race gas, av-gas, or a decent booster like TEL130, which I understand is no longer available. You can and should retard the timing, and knock out the total advance.....I'd back it down to 4 degrees intial, maybe 2 degrees, and install a good adjustable vacuum advance (not an Accel unit) and dial the total advance to about 30 degrees max. The real cure for your car is a set of dished pistons to lower the CR to 9:1 with your heads or a set of aluminum heads (72cc) that will run on pump gas at a 10 CR. I've had and driven these cars over 30 years, and I hate to say it, that's the reality. These cars in stock form NEED high octane....not just 3/10ths of a point that the "108" octane boost gives. You can google Toluene, etc, and get some other ideas. Lots of folks are adding it to their fuel and it works....(it's already in race gas and regular gas)....but it's $30 a gallon here. Heck, I ended up bolting a set of low compression heads on my '67 GTO so I could drive it without going completely broke!! Keep us posted!


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## ALKYGTO (Mar 29, 2010)

:agree 100%


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## Thumpin455 (Feb 17, 2010)

Where do you live in NC? I have friends in Hickory and all over South Carolina. I was stationed in Charleston for 5 years, been all over the Carolinas.

I agree with the commercial octane boosters being a waste of money. No doubt about it. In the mid 90s I had a 400 with 670 heads, it didnt rattle where you could hear it, but on 93 and boosters it flattened the upper rod bearings. That is what your engine will do eventually running the low octane gas. Retarding the timing will only help so much, and getting the coldest air possible, along with blocking all heat to the carb will help a bit too, but you are still limited with pump gas.

We had a discussion about Toluene this past week on another gearhead forum. It works to raise octane, but it is expensive, and it is also hard on the lines, fuel pumps (both electric and mechanical) and some parts of the carb. If you cant get anything else and you want to drive your car, it will work. Also checked on the legality of it, and so far nobody has found anything about not being able to add it to your fuel. Its VERY toxic and you need to handle it with care, dont breathe the fumes, and it is classified has hazardous, but so is paint and gasoline. 

It is also hard to get it to light, you need lots of heat. The Honda F1 team ran straight toluene for fuel but they had to run the fuel lines through the exhaust manifold to warm it up enough to get good ignition, that would be pricey in a street car, but it lights ok mixed with gasoline, its just a very high mix of it might cause issues. If you want to go this route it works, and you can drive your car.

You also have another option. One that is cheaper and is a bolt on a carb and you are done deal. I checked North Carolina http://e85prices.com/e85map.php and you have lots of E85 pumps there. The Star Mart, in Garner North-Carolina has it for $2.79. It depends on where you are, like if you live near Greenville you have to drive a while to get some, but if you are near Raleigh, Charlotte, or Hickory, you can get E85 easily. It is most often priced lower than pump 87, the stores that have it higher are gouging since they get it much cheaper than gasoline. Your car will run cooler, make more power, not ping at all, and it wont hurt the fuel system at all, provided the carb has been rebuilt since 1983. Some rubber parts from before 83 arent compatible with both ethanol and gas, but all the new kits have parts that are.

One temporary drawback to running ethanol is if you have run only gas with no ethanol added to it in the car, you will have a large amount of varnish and sludge built up in the tank and lines. Some of it might be plugging rust holes, but even if it isnt when you run ethanol through it all that varnish and crud will be loosened and clog your filter. After it is all out, you wont have a problem with it again, but it might cost you a couple cheap filters.

Going the E85 route is cheaper and easier than installing new heads, particularly since you have pistons with valve reliefs for the pre 67 heads, or changing your pistons to dished slugs. If you have to drive over 50 miles to get it, then it is just as much of a pain in the rear as running toluene or race gas, even if it is cheaper. 

If you have a Holley or a Qjet then it is relatively simple to get them to run on E85. I havent done a Carter/Edlebrock carb yet, but I have a couple I might try it on. I might do a 2 barrel for Tri Power in the near future, and they can be converted, I just havent done one yet.

If you have multiple pumps in your town, then it is very easy and cheaper to drive your 65 and enjoy more power and no overheating. I would be more than willing to convert a carb for you if you send a carb and a rebuild kit for it to me. I will test it on a similar engine (I have several) get the tune close and send it back. I dont charge for this at all, because I learn more about it each time I do it, and its fun as well as therapeutic for me. 

So your options are, Toluene, E85, lower compression with heads/pistons, or race gas.


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## SIXT5GTO (Mar 9, 2010)

Thank yopu for the information, here is a link to a page that tested the additives.
Toluene..my octane booster of choice - SportsCarForums.com
I found a timing sety up that has reduced the pinging but will have to see if I can get the idle right.
I will see how a few gallons of AV gas 100 LL works out with the reg fuel.
So My question is why, I have have other engines in the 10-1 range with out this problem is it the newer cars timing system or head desighn, I met a guy who ditched his ram air heads because he could not keep the car from pinging. and now has a set of edlebrock heads on the car.
I am in the most far south east as you can get in NC.
Thanks for the help


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## Thumpin455 (Feb 17, 2010)

Ah you are right near South of the Border in SC then. Been through there a bunch.

Things like chamber design/shape, bore size, quench, and what the head is made of impact the octane tolerance. Environmental factors also play a part, hot humid air is more prone to ping than cool dry air. Altitude affects octane requirement as well, a car in Denver needs less octane for everything else being the same than you do near sea level in the hot humid air. Iron heads ping worse than aluminum heads because aluminum dissipates the heat faster and has fewer hot spots in the chamber. Deposits left in your engine from running it on gasoline also cause it to ping. The carbon built up on the piston, valve and chambers creates hot spots that make the pinging worse.

My 70 GTO never pinged in Nebraska with 5C heads on the 455, but trying to run 89 octane in South Carolina resulted in it pining, overheating, and running like crap. Part of that was in Nebraska it was running 10% ethanol, in SC it was straight gas. The other part of it is the environmental factors, altitude was a big part of that. Your engine has compression too high for 10%, it wont make a difference with 10:1.

I just avoid all of that and run E85 that can handle over 15:1 and is far cheaper than race gas or AV gas. There is a pump in North Myrtle Beach and one in Jacksonville. No carbon build up, runs cooler, easy to convert, doesnt overheat, and its cheap. 

If your driving is limited you can run the AV gas, but octane boosters are worthless. The only place in Charleston that had gas for one of my 455s with almost 12:1 was Bouchillon Performance, it got old paying $6 for it back in 2001-2004. Does anyone sell race gas where you are? You arent going to be able to crutch it with pump gas, it just wont do it where you live.


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## Willshire (Jul 14, 2011)

I will be running 94 (withb 10% ethanol) in my 389. My static cr is about 10.1:1. I am going to run a 160* t-stat, i also run a dual energy cam with an intake closing of 63* abdc to bleed off compression. i had .051 thick gaskets on it and it ran pretty good on 91 octane with a 180* tstat. that was with 8* of initial timing. now with .039 gaskets i will probably have to run 6* or 4* of init timing. a drag race guy (2 time local champ) recommended synergyn 120+ octane booster/ cleaner. he says it works pretty good. gonna give it a try i havent had a chance to floor it yet cuz i'm still in the first 200 miles after rebuild.


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## pontiac (Mar 6, 2011)

new heads are not steel, but aluminum, that is the big difference. toluene is legal to put in gasoline, is no more toxic than gasoline but regards a lot of volume to be affective in raising the octane no. of gasoline. 20 gallon tank, need 2gals or more depending on what octane no. you want. It will not affect any materials in the old car systems, as gasoline with lead had a lot of toluene in it back then.


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## Willshire (Jul 14, 2011)

SIXT5GTO said:


> I have a little time and have been trying to get the GTO running right.
> Well the things Pings like crazy any time a load is added.
> I am running Shell 93. and have added 108 otc. boost, still pings
> Ran a compession check everything looks good 179-181.
> ...


What cam are you running? a cam with a later closing angle would help with the ping. It would also allow you to run more timing. I run a 275deh and it's pretty torky (from what little i have goosed it). Run a cooler tstat and see if you can get a cooler air charge (cold air tube to the breather)to ease the pinging pains. I take a lot of advice but, sometimes you just gotta learn by doing. And so far the later closing angle i get from the 275deh does not produce any audible ping so i am becoming a believer in dynamic compression ratio being the ratio required for decent hi test pump gas motoring.


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## geeteeohguy (Feb 2, 2008)

High compression (10:1) and over 389's and early 400's are much more prone to detonation than others due to the closed chamber "bathtub" shaped combustion chamber. Newer cars do have aluminum heads, which can get away with another point or two of compression, but need to, as they are not as thermally efficent as iron heads. The "open chamber" heads from '68 up are less detonation prone...


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## Thumpin455 (Feb 17, 2010)

geettohguy is right, the closed chamber heads require more octane. They also sometimes need more advance to make best power, provided the fuel can handle it. The 455 that had ported 670s on it liked 52 degrees total advance, if we backed it down to 40 it lost a full second in the quarter. That was running 110 Sunoco and VP red.

If you plan to run 10%, then dont buy the 10% already mixed and 89 octane. They mix some really poor gasoline with ethanol to only get 89 octane. The stuff they mix with 10% ethanol is in the mid to high 60 octane range. They can do that because the octane increase from alcohol is more than it you might think when you add it to gas, it isnt linear. You get a much greater octane increase than if you mixed 110 gas with 87 octane. You just might as well start out with some gas with a decent octane rating.

Mixing two gallons of E85 per tank of 93 should be close to what you need. If it still pings add a bit more. I havent had any problems with jetting to 15% ethanol, and adding it to 93 increases the octane enough to cover your 10:1. Right now it should be 83% ethanol, in winter it can drop to 70%, so how much you need to add changes with the months. If you have a 20 gallon tank and you put in 2 gallons of E85, you are just a bout 15% most of the year. At most it might need a bit more jet, but I havent needed to jet one with that little of ethanol.

Even if E85 is $4 a gallon, which it isnt anywhere I have seen, it is cheaper than using a $30 can of toluene, and it wont harm your carb and fuel system. Check the octane booster and see if it is methanol or isopropyl alcohol, both of those can be hard on fuel system parts too. Toluene works, but its pricey and can tear things up in fuel systems. So far E85 hasnt hurt anything in any of my vehicles. 

You can do what works for you, just giving you info.


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## 3rd1967gto (Jun 12, 2011)

Thumpin455 said:


> geettohguy is right, the closed chamber heads require more octane. They also sometimes need more advance to make best power, provided the fuel can handle it. The 455 that had ported 670s on it liked 52 degrees total advance, if we backed it down to 40 it lost a full second in the quarter. That was running 110 Sunoco and VP red.
> 
> If you plan to run 10%, then dont buy the 10% already mixed and 89 octane. They mix some really poor gasoline with ethanol to only get 89 octane. The stuff they mix with 10% ethanol is in the mid to high 60 octane range. They can do that because the octane increase from alcohol is more than it you might think when you add it to gas, it isnt linear. You get a much greater octane increase than if you mixed 110 gas with 87 octane. You just might as well start out with some gas with a decent octane rating.
> 
> ...


Thanks for all this info. E85 is available near me, (Liberty, SC). I have a 67 GTO with the 670 heads and forged pistons. Question; Should I use 93 octane with no ethanol and add the e85 to that or use 93 with ethanol and add e85? Both are options here. I have an aluminum radiator and just added a Robertshaw 160 thermostat. Runs about 165 on the highway but runs up when just idling. Hoping that the right combination will help with running cooler. Thanks!


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## Thumpin455 (Feb 17, 2010)

Try it both ways, but the octane will be higher if you add E85 to straight 93. If it works with a gallon or two of E85 and 93 with 10%, then that will probably be less expensive. To only get the octane to 93 they use only marginally better gas than they mix to get 89, and that isnt good stuff. If you use much more than two gallons of E85 to a tank you are going to need to rejet the carb. 

Doing what is called splash mixing like this, you will want to run the tank almost dry before filling up again, otherwise you dont know how much ethanol is in the gas, and since you are running enough compression to hurt the engine on pump gas, you want to have enough in there to work, but not too much so you need to put bigger jets in.

You could also get a carb for E85 and just run that all the time since its near you and readily available. I could do a Qjet for you, or another guy I know is working on Qjets in SC and he might be able to hook you up.

If the car has never had any ethanol run through it, there will be varnish, sludge, and other crap left by the gasoline. Ethanol will clean that out of the tank and lines, then deposit it in the fuel filter and carb. I have a 79 Formula that had been running only race gas since 1995, and I added a gallon of E85 to the tank. It had so much stuff in the tank it clogged the sock on the tank pick up. Didnt actually hurt anything, just plugged it with crud that gas left.

The way to get around that is add some 93 with 10% ethanol over time and drive the car, use a couple fuel filters ahead of the carb. It will clean it out slowly instead of all at once.


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## 3rd1967gto (Jun 12, 2011)

Thanks! The carb was just purchased from AMES Performance, so hopefully it has been rebuilt with updated gaskets, and internal parts to better handle ethanol. The tank was new and all the lines when the car was redone a few years back. (I just purchased it in June). The guy I bought it from told me he had always ran pump gas 93 octane and lived north west of Atlanta. Right now it has a mix of both straight 93 and some 93 with up to 10 percent ethanol. There is about 1/2 tank total. I have the timing set (initial) at 6 degrees before TDC, but not sure what is in the distrib/advance. It doesn't seem to ping to where I can hear it, but I haven't really driven it much or very hard either. I will sure try your advice, and thank you for your reply and sharing your knowledge. I wish Sunoco 260 was still available like it was with my first new 67!


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## Thumpin455 (Feb 17, 2010)

If its a Qjet the only thing it needs is an accelerator pump cup made since 83. I got a very old kit and the cup was no good with ethanol, every kit I have gotten since has been fine. If its a Holley it has been good to go for a long time fresh out of the box, same with Edelbrock/Carter carbs.


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