Bob Lynch

looking for suggestions on 455 detonation issue ... have Edbrock heads and flat top pistons ... about 10.5 compression ... at operating temp, 200 plus or minus ... it just wants to rattle away ... even if i back the timing down to about 30 total ... still detonates ... one engine builder indicated that it should not exceed about 9.9 on California pump gas ... that means eng. mods ... has anyone else solved similar conditions? How? Bob Lynch

citcapp

Sound like you might have a cam issue causing to much pressure. I run 10.5 on my 455 with 91 Octane no problem

J-(Chicago)

Mix with race gas, and check timing with a different gun.

Bob Lynch

thx guys ... i want to try anything short of tearing it down ... if need be, oh well, I'll do it and reduce the pressure ... I was told that 10.5 would be fine with alloy heads and pump gas ... it has almost 2000 miles on it and I have not even run it hard for 1320 feet ... sad to build a nice motor and then not be able to get on it ... cylinder pressure measured 160 after one crank and 200 to 205 after three cranks ... temp at operating temp reads 200 range where coolent exits the motor back to radiator ... just thought it might make sense to check with the tech guys at Edlebrock ... maybe they have solved similar issues ... thanks to all who have input ... Bob

Bunser

Just curious, what is your highest octane pump gas in California? With most of our Sunoco stations being turned into PetroCanada stations, I think our highest pump gas is 95 octane in most parts of Canada.(My W31 had a few broken piston rings running our high test gas!!)

442scotty

Timing, timing, timing...what Dist. are you running ?...and is it matched to the engines specs?...I had the same problem...tried to run an Olds HEI from a newer wrecker...timing advanced to fast etc...got tired of playing with it and had one custom build by DUI...problem solved

matt69olds

I agree, you probably need the distributor advance curve reworked.

Bob Lynch

I love it that u guys are helping out ... I am new at forums ... they call our premium 91 octane ... I really do not know if it is true 91 ..

I have some kind of msd pro billet clone (HEI) ... cannot find a name on it or any kind of label ... I have tried the initial timing at 8, 10, 12 & 14 ... at 14 it is about 34 at 3000 rpm ... do u know how your curve looks? say at 800, 1200 1500 2000 2500 3000 3500 etc ...
I used to be pretty good in the 60s, a couple of knotches above the average shade tree knuckle buster, then about a 40 year layoff ... now trying to play catch up ... appreciate all the input/suggestions I can get ... thanks guys and don't forget Mother's Day tomorrow ... my mom is 98ys old and still tellin me what to do ... some things never change ... Bob

Bob Lynch

Hey Matt ... both of my parents were raised in Scott Cnty ... I was born in Indy ... been in Cal since the 50s except a 5 yr career deal in Chi ... thx for chiming in .. Bob

cutlassefi

Cam Specs? Gear? Cranking compression may be a little high but with aluminum heads it should be workable.

You need to tailor you spark curve as previously mentioned. Remember, once it starts to ping/detonate that changes things, i.e.,

Lets say it doesn't ping at 30 degrees but does when you get to 32. You can't just go back to 30, you've now created excess heat. You'd probably have to go back to 26 or so for it to be cool enough not to ping. See what I mean?

So somewhere in your advance curve it's too much and once it starts to ping it'll be that much harder to get it to stop. You might also want to try 4 corner cooling, a high flow pump and/or colder plugs. Those could help as well.

I have an EFI'd 350 SBO, My cranking psi is about 180, I run 89 octane with stock cast iron heads, no issues cuz I can tailor my spark curve accordingly.

Good luck!!
Mark

Bob Lynch

thanks Mark ... that makes sense ... I'll go through the rpm range sitting on the driveway with no load ... log the existing advance curve ... see what it looks like ... I could also get it to a dyno shop and work through the fuel mixture and spark curve to find the sweet spot at each rpm ... probably better than tearing it down first and reducing the compression ... tough to build a nice motor to go strong and then permanently de-tune it out of it's optimum performance ... Thx Mark & others ... Bob

Bob Lynch

ps ... forgot to add ... cam is 523 - 544 lift ... 050; 236 - 248 duration ... installed 2 deg. adv. ... gear is 342

cutlassefi

That's plenty of cam and gear for that compression, you've got other issues imo.