detonation - solution
April 15th, 2010, 02:45 PM
#1
Registered User
Thread Starter
Join Date: Jun 2009
Location: Coto de Caza CA
Posts: 34
detonation - solution
just thought I'd throw this out for your thoughts ... moderately built 455 with Edlebrock heads and flat top pistons ... just about 10.5 to 1 compression, 200# tested compression ... cannot run on this California gas, 91, without rattling ... I have disconnected the vacume advance line and retarded it to about 31 total ... it has been suggested that we take it back down to about 9.9 to 1 to be comfortable for every day street driving ... has anyone else had this issue? Solved it? your suggestions greatly appreciated ... Bob Lynch blynch@fusioncmg.com
April 15th, 2010, 02:58 PM
#2
Ben
Join Date: Mar 2009
Location: Snohomish, WA
Posts: 1,823
How often do you drive?
buy a few bottles of Kemco 130 octane supreme- and put one in with a full tank of gas. And forget your problem.
This is not the cheap parts store crap- it has TEL in it (LEAD) and its very expensive- but will give you real high octane leaded gas.
I know quite a few guys riding that thin line of detonation w/ high compression engines and they all run this stuff. Lucky for them they don't put too many miles on their cars- ususally to and from the race track and sunday cruises to the burger stand.
Other options... Thicker head gasket? Change the heads?
If it were me i would try to avoid changing pistons.
buy a few bottles of Kemco 130 octane supreme- and put one in with a full tank of gas. And forget your problem.
This is not the cheap parts store crap- it has TEL in it (LEAD) and its very expensive- but will give you real high octane leaded gas.
I know quite a few guys riding that thin line of detonation w/ high compression engines and they all run this stuff. Lucky for them they don't put too many miles on their cars- ususally to and from the race track and sunday cruises to the burger stand.
Other options... Thicker head gasket? Change the heads?
If it were me i would try to avoid changing pistons.
April 15th, 2010, 03:01 PM
#3
Ben
Join Date: Mar 2009
Location: Snohomish, WA
Posts: 1,823
April 19th, 2010, 11:03 AM
#4
Registered User
Join Date: Mar 2008
Location: Massillon, Ohio
Posts: 198
I had a detonation problem with my 455. stock 68' Toto 455, 230/230 comp cam.
I had to disconnect the vacuum advance and retard the timing, I also put the heviest advance springs on the HEI, this reduced the rattling but did not cure it. What I found was that the Demon 750 was screwed up and the engine was running very lean. I rebuilt a 68' Q-Jet back to stock Oldsmobile spec's and put it on this spring. I had to add vacuum advance, go to lighter springs and advance the base timing and I still don't have a hint of detonation. I didn't know this but a lean miss can make your plugs look like the motor is running rich. I would swap out the carb and see if it fixes the problem.
I had to disconnect the vacuum advance and retard the timing, I also put the heviest advance springs on the HEI, this reduced the rattling but did not cure it. What I found was that the Demon 750 was screwed up and the engine was running very lean. I rebuilt a 68' Q-Jet back to stock Oldsmobile spec's and put it on this spring. I had to add vacuum advance, go to lighter springs and advance the base timing and I still don't have a hint of detonation. I didn't know this but a lean miss can make your plugs look like the motor is running rich. I would swap out the carb and see if it fixes the problem.
April 21st, 2010, 07:30 PM
#6
I had the same problem with one of my cars. I started with the carb and made sure it was not running lean. (Increased jet size by 2, put in a softer spring for the power piston - that helped) I did not want to retard the timing because it definitely affected performance. I changed the plugs and put in a colder heat range (45 down to 43). That made a big difference but still did not eliminate it completely. Octane boost was my answer. I still have the issue if I do not add the octane boost. My next step will be to swap out cams and put in one that bleeds off more cylinder pressure than the one I have in there now.
April 21st, 2010, 08:56 PM
#7
Registered User
Join Date: Nov 2009
Location: Lewisville, TX
Posts: 141
I too have an issue with detonation. Luckily for me, premium gas (or premium mixed with mid-grade) cures the problem completely. I have since adjusted my timing (it was 6 degrees advanced) and have noticed no power changes, but it knocks less when I try to run regular gas. I think I'll be able to get away with mid-grade without any premium. I'll have to try next fill-up.
I personally do not know just what to do from here to try to do away with the detonation. The owners manual clearly indicates I can use gas that is 87 or 91 octane. My I recently adjusted the air/fuel mixture on my carburetor to the optimal setting, and thats all I can think of off hand to do. Car is 100% stock and designed to run on unleaded fuel.
I do plan on doing some engine work when I get this car into secondary status and no longer a daily driver. Mild cam, new timing set(351C versus 351M...while off topic, I should mention that the 351M timing is retarded from factory), and a higher volume oil pump(dang 351M doesn't have very good oil pressure. Most don't. My solution was thicker oil and Lucas 100% petroleum additive. Boy, this will be a great time to find another Olds for cheap ($2K?).
--Ryan
I personally do not know just what to do from here to try to do away with the detonation. The owners manual clearly indicates I can use gas that is 87 or 91 octane. My I recently adjusted the air/fuel mixture on my carburetor to the optimal setting, and thats all I can think of off hand to do. Car is 100% stock and designed to run on unleaded fuel.
I do plan on doing some engine work when I get this car into secondary status and no longer a daily driver. Mild cam, new timing set(351C versus 351M...while off topic, I should mention that the 351M timing is retarded from factory), and a higher volume oil pump(dang 351M doesn't have very good oil pressure. Most don't. My solution was thicker oil and Lucas 100% petroleum additive. Boy, this will be a great time to find another Olds for cheap ($2K?).
--Ryan
Thread
Thread Starter
Forum
Replies
Last Post
82 Grocery Getter
Small Blocks
22
May 10th, 2009 09:57 AM
