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#1
09-29-2014, 01:59 PM
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My 70 GTO 455 detonates. Help!
I bought this car a year or so ago and I am still going through it trying to figure out all its issues. The most pressing and annoying issue is the car detonates whenever it is under load. it has an edelbrock carb, Stock distributor with a pertronix (points eliminator), 45 spark plugs. I have disconnected the vacuum advance. I have retarded the initial timing to 6 degrees. I have put a gun on it. The advance is
7 degrees at 1000 RPM 11 degrees at 1500 RPM 14 degrees at 2000 RPM 15 degrees at 2500 RPM 16 degrees at 3000 RPM I have a 455 with 6X heads. I did not build the motor so I don't know everything about it. I would imagine the compression ratio is about 9.25 to 1. The motor runs cool at about 170 o 180 degrees. I have tried different combination of weights and springs and I can't seem to make the detonation go away. I am next going to next test the harmonic balancer to see if maybe that is off. I have a sneaking suspicion that the cam as installed wrong and it is trapping too much cylinder pressure. I tried to put a compression gauge on it but that broke! From what I can tell ... it is definitely under 150. Suggestions? Advice? |
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#2
09-29-2014, 02:08 PM
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How do the spark plugs look. The first thing that stands out at me is the Edelbrock carb. They have a tendency to run lean especially on a big motor like a 455. A lean condition under load can cause pinging.
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#3
09-29-2014, 02:15 PM
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Red flag is your carb...which e-carb??? 1406. I imagine???
__________________
1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... 
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#4
09-29-2014, 03:13 PM
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Red flag for me is whether it has 6X8 or 6x4 heads, The 6X4 heads will give you around 9.75:1. With a small cam it would be a pinger.
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http://www.machdevelopment.com/album...775/527566.htm |
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#5
09-29-2014, 03:24 PM
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I am thinking flat lobe
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#6
09-29-2014, 03:31 PM
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I would finish that compession test. A blown head gasket between two cylinders will cause that. Most commonly between 4-6 and 3-5. Its happened to me in the past and there was a thread here recently where that ended up being the problem.
__________________
'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports, 3" pypes, Hooker 1 3/4" headers, hydraulic roller, 10" Continental, 3.42 gears 11.5 @117.5mph 3900lbs  ([_|_] ##\|/##[_|_]) |
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#7
09-29-2014, 05:01 PM
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150 psi is not excessive, like what was posted those carbs are crap in terms of the needed jetting for so motor that size, that being said though do confirm TDC on the balancer!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#8
09-29-2014, 06:42 PM
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Wow. Thanks for all the info. I am not sure how to tell the difference between 6X8 or 6X4 heads. Regardless ... I am putting 93 octane ... should not be pinging like that.
I don't think the cam has a flat lobe ... doesn't sound it. I will put a vacuum gauge on it this weekend to see if their is a bad head gasket. The plugs look fine. They don't look like the car is running lean. I will get the number off the carb too. In my last car it did the same thing. Turned out the cam was installed wrong. I put in a stock ram air 3 cam and it ran MUCH better. I really don't want to do a cam swap on this. |
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#9
09-29-2014, 07:38 PM
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Here is where to look for the code
 And here is the link to the Wallace site that explains what it means http://www.wallaceracing.com/head1.htm I have the same problem with my TA engine- in my case definitely caused by too much compression for the cam that it came with.
__________________
1969 Lemans vert, matador red, 462 CI, 3.07 12-bolt posi 1974 455 TA, admiralty blue/red interior HPP "cover car" - sold "The best way to show a car is to drive it" |
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#10
09-29-2014, 08:38 PM
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Motor is backfiring not pinging, different problem, check firing order, vacuum leaks, spark plugs, if I was you i swap carbs. Also make sure your dist is getting full + ign. Power My 2©s
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#11
09-29-2014, 09:02 PM
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I chased a pinging problem with my Bandit for a month, tried everything. Turned out to be a blown head gasket between two cylinders. Hopefully, that's not it!
__________________
1965 TriPower GTO, 1967 GTO, 1969 GTO, 1969 Judge, 1972 GTO, 1977 Smokey and the Bandit, 1989 TA ProStreet, 1968 Firebird NHRA 10.90 racecar, 1963 Tempest S/Gas |
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#12
09-30-2014, 06:49 AM
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If it really is pinging with the timing set that low then not likely caused by C/R. Especially if cranking compression is only around 150. You really need to do a complete compression test with a good gauge to see what all the cylinders are doing.
__________________
1969 Lemans vert, matador red, 462 CI, 3.07 12-bolt posi 1974 455 TA, admiralty blue/red interior HPP "cover car" - sold "The best way to show a car is to drive it" |
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#13
09-30-2014, 07:13 AM
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Hook the vacuum advance back up, it is only in at light load, and improves engine efficiency for "normal" driving.
Pinging under heavy load is all in the total mechanical timing. If it's pinging with only 16 degrees total timing in it the engine has issues, or the mark on the balancer is WAY off where it should be.....Cliff
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#14
09-30-2014, 07:22 AM
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You need to do a compression test with all the plugs out
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#15
09-30-2014, 02:03 PM
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Thanks guys ... I got more testing to do. I will get back with more info.
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#16
09-30-2014, 08:22 PM
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Quote:
OR ... is it a bad combustion chamber design? |
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#17
09-30-2014, 08:26 PM
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Quote:
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#18
10-01-2014, 06:12 AM
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It's not a chamber issue with the Pinging as all 1968 and up D port heads have the same chamber!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#19
10-01-2014, 07:07 AM
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You haven't mentioned the cam- do you know what it is? Also except for the ping does the engine run smooth? Any significant oil usage or blow-by?
My TA 455 has 5C-4 heads so should have the same size chambers. And flat top pistons, so high compression (pumps 175-180 on all cylinders). I have documentation showing it has a CC XE268 cam and if you read through threads here the cam is not recommended for this combo due to the very short seat duration. But backing down the total timing to around 30 without vacuum advance does eliminate the ping under heavy load. You are saying your engine still pings backed all the way down to 16 deg total. Based on my experience that should not happen even with a poor cam selection. One more time- get CR readings on all cylinders to confirm the valve train is OK and a head gasket is not broken. I am having a hard time believing that A/F could cause that bad a pinging problem all by itself unless maybe it is way, way off. Still worth taking a look at due to the questionable e-carb though. FYI my other 455 has similar size chambers and C/R, also pumps 170-180, but absolutely no ping even with an aggressive timing curve. Biggest difference is the cam has much longer seat duration.
__________________
1969 Lemans vert, matador red, 462 CI, 3.07 12-bolt posi 1974 455 TA, admiralty blue/red interior HPP "cover car" - sold "The best way to show a car is to drive it" |
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#20
10-01-2014, 07:23 AM
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+2
The cam used is a BIG player with the 455 and those heads on pump gas. It will pound like SLEDGEHAMMERS with a Comp XE262 or 268 in it and "normal" timing fuel curves. I've had two 455's in here over 9 to 1 compression using that cam, and one used the HR version of it, XR276HR, and both pinged EVERYWHERE unless we pulled a ton of timing out of them, and ran like crap as well......FWIW.....Cliff
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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