Detonation in my 59AB engine

[qmdv]

Lets start with what I know about the engine: My dad bought it 50 or so years ago. 59AB, bored to 3 5/16, 4" crank, Offenhauser 375 heads and 2 97's. It sat for many years and I went through it. Cylinder walls rough so I went 30 over and put it in a 32 Hi Boy roadster. Unfortunately I did not check head volume while engine was opened up.

Now for the problem at hand. I put 87 non Ethanol gas in it and it rattled terrible. Drained the gas and put in some 100LL aviation fuel. Man it ran great and sounded great. So I drained out that gas and put in some 91 non eth gas and if I really get into it in high gear I get just a little detonation.

So what are my choices? I can just drive conservatively but now and then I like to put my foot in it. Maybe bight the bullet and get new heads.

[Phil Gillespie]

Originally Posted by qmdv

Lets start with what I know about the engine: My dad bought it 50 or so years ago. 59AB, bored to 3 5/16, 4" crank, Offenhauser 375 heads and 2 97's. It sat for many years and I went through it. Cylinder walls rough so I went 30 over and put it in a 32 Hi Boy roadster. Unfortunately I did not check head volume while engine was opened up.

Now for the problem at hand. I put 87 non Ethanol gas in it and it rattled terrible. Drained the gas and put in some 100LL aviation fuel. Man it ran great and sounded great. So I drained out that gas and put in some 91 non eth gas and if I really get into it in high gear I get just a little detonation.

So what are my choices? I can just drive conservatively but now and then I like to put my foot in it. Maybe bight the bullet and get new heads.

.
I should first establish your piston to head clearance. Then go from there aiming for 40 to 50 thou clearance. You may be able to work existing heads to suit your set up. And also maybe establish your cc volume at combuston space as some deads are 64 cc and others at 75cc another area for you to work with. Dont continue driving as from experience detonation can screw up your engine big time. I have been there .
All the best Phil

[Step-down]

I’m no expert so with that I’m assuming the distributor advance is correct you may back off the distributor brake .

[qmdv]

Originally Posted by Step-down

I’m no expert so with that I’m assuming the distributor advance is correct you may back off the distributor brake .

Has a crab ignition. Runs like a wildcat on aviation fuel. Has any body had any luck with octane boost? In the old days you could get Chevron White Pump Custom Supreme

[tubman]

Once you find out what's going on, let us now what you have. I wouldn't think that it would be possible to have that much compression with normal parts and assembly.

[Brian]

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i had the same problem with an engine a while back. It had 165 lbs compression at cranking speed and would detonate badly. I modified the advance curve of the crab distributor by using the advance assembly out of an earlier model distributor. I find the crab distributors advance too much, too soon. The earlier dissy's have a slower advance curve and finish at 18 degrees, engine much happier with this set-up. I had a coupla threads on here whilst I was trying to sort all this out

[Brian]

This is information that lawrie sent me when I was chasing my detonation issue.
Sorry, it's probably too small to read....if one of you clever guys sends me your email, I could email it to you in order you can work your magic?

[Ol' Ron]

Yes, I had a similar problem with a 294ci engine/L-100. Just retarded the timing (8BA) runs great on 81 dct gas now.
Gramps

[Pete]

Listen to Ron. Just try retarding the spark a little.
For Saturday night drags at the drive-in go back to advanced and av gas.
Just the smell of av gas exhaust will scare the competetion half to death.....LOL

[qmdv]

Originally Posted by Ol' Ron

Yes, I had a similar problem with a 294ci engine/L-100. Just retarded the timing (8BA) runs great on 81 dct gas now.
Gramps

Pulled a head this morning. 56 cc's and domed pistons. I am wondering if the dome is about the same as the relief and the gasket. If so I calculate about 10.9 to 1 compression ratio. Do you think that retarding the spark will do the trick?

[Ol' Ron]

If your gona start modifying an engine you have to be able to tune it fuel and ignition are the magic that wins races. Using aluminum balls you cam make from foil about 1/2 in dia. Just drop the head back on the block put a few bolts back in and tighten them down with your fingers. rotate the engine a couple of times then remove the squached alum balls and measure them any ball with less than .945" thickness should be grond down, I use a Dremmel with a round berr going around the places where it tight. I would guess it around the outside of the bore, but don't know what pistons you have.
This goes pretty fast because your not remving much material. After you do a few dozen of then it will become second nature. I also made a red doming tool, because I' basically lazey
Gramps

[Bored&Stroked]

I think Ole' Ron meant .045 thickness on the aluminum ball.

Question: Do you have a TDC pointer on the crank? If not, you should make one such that you can actually figure out how much advance you're running. You can use a 'dial back' timing light to figure out have many degrees of advance you have total - this will help. On a street engine I usually run 22 - 24 degrees total advance.

Also, post a picture of your combustion chambers - is hard to imagine that they are only 56 CCs, unless the heads have been milled quite a bit and would probably be fly-cut for valve clearance.

You can figure out the CC's of the piston crown with a little math.

[35fordtn]

My 37 with 375 iffy heads rattles like hell unless I run octane booster. I retarded the timing and it fixed it but killed the bottom end power. I would up putting in a set of 68 series weights from a 37-40 distributor and narrowing the advance slot on the shaft to limit overall advance and it’s been fine on 87 fuel ever since. Some of the crab distributors put out 26 degrees of advance and I have it dialed down to 19degrees

[Ol' Ron]

I'll have to start readding my post as I do have allot of red lines, from mist spelt words do to stupidity or bas eyesight. I think my spell checker is Illliterat. I;ve never been able to get that much compression in any of my engines. But I don't build any 300 cubic inch ones either.
Gramps

[Mart]

Would I be over simplifying it to say just back the timing off a bit? You might need to use a better grade of fuel, but only what is commonly available at the pumps. What am I missing here?
Mart.

[Desoto291Hemi]

I’m with the others,,,try the timing .
If it didn’t rattle before,,,,why would it start after boring it an extra.030 ?
And the extra bore shouldn’t really affect the cylinder head clearance that much .
10.9 CR sounds kind of high to me,,,,,check your dimensions and calculations.
Pete and old Ron,,,,and the others know a ton more than I do,,,listen to them .

Tommy

[B-O-B]

Pete said:
"For Saturday night drags at the drive-in go back to advanced and av gas.
Just the smell of av gas exhaust will scare the competition half to death.....LOL"
And the price will scare you!!! the rest of the way. !!!

[Pete]

Originally Posted by B-O-B

Pete said:
"For Saturday night drags at the drive-in go back to advanced and av gas.
Just the smell of av gas exhaust will scare the competition half to death.....LOL"
And the price will scare you!!! the rest of the way. !!!

Consider this. Locally, gas is roughly 6 bucks a gallon right now.
Alcohol is roughly 70 bucks a barrel. (1.27 a gallon) But you need roughly 3 times as much alcohol for proper mixture. 1.27 x 3 = 3.81.
Looks to me like burning straight alcohol is a fairly good bargain for a flathead Ford engine running Stromberg carbs. They can be converted to alcohol with nothing more than a few drills.
As a side effect of converting to alcohol with no other mods, you gain about 10% hp. You will need to replace the rubber hose at the fuel pump with a neoprene one but you should have done that for gas anyway.

Oh, I forgot to mention, the exhaust from alcohol smells even better than that from av-gas....

[Brian]

Both Michael and myself have told you what to do to the distributor....

[qmdv]

Originally Posted by Desoto291Hemi

I’m with the others,,,try the timing .
If it didn’t rattle before,,,,why would it start after boring it an extra.030 ?
And the extra bore shouldn’t really affect the cylinder head clearance that much .
10.9 CR sounds kind of high to me,,,,,check your dimensions and calculations.
Pete and old Ron,,,,and the others know a ton more than I do,,,listen to them .

Tommy

This engine was built when 100 octane was available at the pump. My dad bought it it 1976 well after it was retired. I pulled it apart and saw that it was worn 3 5/16 so took it out to .030. It then sat for many years and I ended up with it. Put it in a highboy several years ago and took it around the block a few times with 91 non eth but never really put my foot in it. So now the car is pretty much done it it has a small rattle if you get into it.
If you think my 10.9 to 1 is off, it may be. Help me calc the comp ratio. 3 5/16 plus .030 bore. 4" stroke. Domed pistons .125 dome height. .070 gasket thickness. And the outer edge of piston flush with deck at top dead center. Combustion chamber is 58cc's on my last check. I do not know volume of the relief.