Detonation Blues

joevette57 · 04-07-2003, 07:07 PM

I recently purchased a 66 Coupe. The car has a 427/390 engine, but the engine has been built by a previous owner. Originally it had a solid lifter cam, but the shop I bought the car from installed a milder hydraulic cam for better drivabilty.
However they also told me that when they removed the heads, the engine has pop-up pistons. (I don't know much about engine internals except for how to maintain them. But I guess this means the engine has higher than normal compression for a 390hp car).
Using 93 gas I am getting detonation under any kind of acceleration. I haven't checked the timing yet. (timing light took ill, need to buy another.)
As I see it, I have only a few choices....
1. mix racing fuel with the pump gas. (hard to find around here)
2. Octane booster (do they work???)
3. possibly adjust timing (will this work)

I'm afraid to drive the car until I resolve the problem, any advice would be welcome.
Thanks
Joe

VETDRMS · 04-07-2003, 08:11 PM

Retarding the timing will work, but it can also make it run hotter and you'll loose some "oomph*. The larger higher duration cam could possibly ran with less or no detonation due to the greater overlap bleading off some clyinder pressure. You can mix race gas, but that is a hassle for sure.

You can retard the timing, then get some octane boost and bring it up in 2 degree increments until you hear detonation, then back it off and you should be ok. There are people here who know a lot more than me and I'm sure they will have some good advice soon. :yesnod:
Hope that helps a little. :cheers:

Vetterodder · 04-07-2003, 09:43 PM

Your first step should be to check it's timing with a light, total as well as initial. Without knowing where the timing is at, there's no way to know if there is another problem or not. L36's had a hydraulic cam and a 10.25 compression ratio than the solid lifter L72's 11:1. Most guys with L36's aren't having problems with 93 octane but the higher compression L78/L71/L72 owners sometimes need a little help.

joevette57 · 04-07-2003, 10:34 PM

I'm going to get a new timing light (or borrow one) this weekend and check. Piston's aren't stock though so compression might still be a factor.

LD85 · 04-07-2003, 10:50 PM

VETDRMS was'nt you car in the vette or corvette fever mag just recently?

VETDRMS · 04-07-2003, 11:31 PM

Quote:

VETDRMS was'nt you car in the vette or corvette fever mag just recently?

Yes, the may issue of CF on page 56 and 60. I spent some time discussing the subject of custom wheels and tires with little to no modification with John Pfanstiel, and he offered to use a couple photos of my car with the article. An article like this would of helped a lot when I was initially looking for wheels that would fit, as no suppliers had a clue. :smash: I have had excellent results with the new setup. To say the least I was flattered and
excited to see the product of many long weekend nights and hard work find its way into a publication. :yesnod: :cheers:
I'm currently building a rather snotty 406, and hopefully I'll have it finished in the next month or two. I will be documenting the whole process, and will post a "series" in the C3 section once I get started this week.

Sorry for hijacking the thread! :conehead

Let us know how the timing turns out! :cheers:

[Modified by VETDRMS, 8:32 PM 4/7/2003]

Chuck Harmon · 04-11-2003, 01:47 AM

Beautiful Car! I would suggest running a tank of race gas and see how it runs. If this takes care of all your problems except for causing incredibly rapid tire wear you may need to consider a longer duration cam or perhaps a piston change. Depending on the number of miles you drive, adding a few gallons of race gas to each tank may bring the greatest happiness.

Chuck

joevette57 · 04-11-2003, 06:45 AM

I found someplace reasonable to purchase racing gas (110 octane). He's familiar with the car I bought and said two gallons to every ten of 93 should do it.
I'm still going to check the timing Saturday to make sure it's right. But if a few gallons per tank will work, I'm OK with that.

marky mark · 04-22-2003, 03:47 PM

THE STOCK L-36 PISTON DID HAVE A SLIGHT DOME SO MAYBE THEY JUST PUT THE TRW2300'S IN THERE OR MAYBE A CAST VERSION OF THE SAME PISTON. ASSUMING YOU STILL HAVE THE CLOSED CHAMBER HEADS AND THEY USED FEL-PRO HEAD GASKET #10171 WITH A .041 HEIGHT AND A ZERO DECK HEIGHT YOU ARE PROBABLY IN THE 9.7:1 COMPRESSION RANGE. THAT IS ON THE EDGE FOR DETONATION WITH CAST IRON HEADS. I WOULD TRY ADJUSTING THE TIMING (RETARDING) LIKE THE ABOVE POST STATED BUT DO IT WITHOUT THE RACE GAS TO GET A GOOD BASELINE. HOPEFULLY IT WILL WORK OUT FOR YOU.