[Jay S]

Yikes! That is some violent pinging for a 160 compression test! It was coming on strong then wham....Compression numbers are the same as Sam’s combo.

Not sure why you mentioned eventually needing lighter springs? It’s sounds to me like the timing is coming in way to fast really suddenly, almost like you have a wore out bushing in the distributer and it is unbinding itself all of a sudden.

[TAQuest]

Originally Posted by Johnny99

I'm thinking that TAQuest may be right though of course I hope not. Here is a video of the issue https://youtu.be/aUujtuc-_jg.

Cranking compression I get this

1. 150
2. 160
3. 160
4. 160
5. 160
6. 150
7. 160
8. 160

Temperature driving around at about 30 mph is 180. In garage doing the timing check about 200. It's' about 75 out today. Colder BKR7E plugs installed

The distributor is a stock cast iron unit out of a 66 GTO with stock springs and weights. I did have to replace the can on it and it's got a B1 on it now that I limited to 14 total but the vac advance is not hooked up right now.

To test the max advance I pulled 1 spring off of the weights and total mechanical advance was right around 24 bring timing total to 30 though I never hit that with the 2 springs installed. I suppose ultimately this distributor will need lighter springs but that is the least of my issues

• 500 (idle in park with no vac adv) 6 btc
• 1000 10 btc
• 1500 14 btc
• 2000 15 btc
• 2500 15 btc
• 3000 18 btc

I drained the tank to about 5 gallons and added a can of VP Octanium. There was no access to racing fuel yesterday. Based on the above I would find it hard to believe the high octane would make a difference though since the total advance in the car now seems pretty mild .

Yup. Had the same thing once that's how I figured it might not be detonation.
428 in a car that had been beat to death racing.
Worse spark knock I ever heard. Couldn't get it to quit. Tore the engine down and the land between the rings was busted out and it had been rattling to beat the band. Put the issue in my memory and a piston land in my tool box top drawer for future reference. Nice to have some experiences to draw on for trouble shooting.

[PunchT37]

Originally Posted by Johnny99

I'm thinking that TAQuest may be right though of course I hope not. Here is a video of the issue https://youtu.be/aUujtuc-_jg.

Cranking compression I get this

1. 150
2. 160
3. 160
4. 160
5. 160
6. 150
7. 160
8. 160

Temperature driving around at about 30 mph is 180. In garage doing the timing check about 200. It's' about 75 out today. Colder BKR7E plugs installed

The distributor is a stock cast iron unit out of a 66 GTO with stock springs and weights. I did have to replace the can on it and it's got a B1 on it now that I limited to 14 total but the vac advance is not hooked up right now.

To test the max advance I pulled 1 spring off of the weights and total mechanical advance was right around 24 bring timing total to 30 though I never hit that with the 2 springs installed. I suppose ultimately this distributor will need lighter springs but that is the least of my issues

• 500 (idle in park with no vac adv) 6 btc
• 1000 10 btc
• 1500 14 btc
• 2000 15 btc
• 2500 15 btc
• 3000 18 btc

I drained the tank to about 5 gallons and added a can of VP Octanium. There was no access to racing fuel yesterday. Based on the above I would find it hard to believe the high octane would make a difference though since the total advance in the car now seems pretty mild .

I might try a second compression gage and verify your numbers.

[Jay S]

I think I was reading your tach wrong, I thought it was start at 3k. But all that mayhem is happening at 2k? That does not appear to be a timing or timing curve related problem. I can see why your frustrated. That does sound like it could have something inside the engine getting hot and causing the problem. It would be nice to know what the afr was doing when your problem is occurring before you got to deep into things.

[Johnny99]

The lighter springs comment was for the future, the curve seems off . Least if my problems now though.

Wouldn’t mind getting an afr gauge. Just a big expense now, I’ve got to have it towed to the shop to get the bungs welded in. By the end of the day that’ll be a $600 bill. Don’t think it’s really going to help me with this now though


Sent from my iPhone using Tapatalk

[Johnny99]

I’ll try a second gauge for comparison purposes


Sent from my iPhone using Tapatalk

[Jay S]

FWIW, It is always less frustrating to start high on octane and work down than low and work up. Use the best gas you have available, C12., 110LL av gas, or something like this.

https://www.summitracing.com/parts/mef-100032/

[Johnny99]

Compression test is similar with another gauge.

I had used a bottle of octanium with the full tank. Maybe that brought octane to 95 from the advertised 93. I added another bottle after draining the tank to 5 gallons. That had to bring it up to the high 90s if not 100. Octane won’t cure this

The car idles great with no smoke and revs to 3k in park with no noise. Could the piston lands still be broken?

I’m moving forward based on the idea that the cam being to small and dynamic compression being to high

I’ve got to change the cam either now or later if there is internal engine damage. What to use?

I do want to keep the power brakes so need at least 13” of vacuum . I can do solid or hydraulic I really don’t want to go roller. And I’d like a nice idle, growl more than lumpy.





Sent from my iPhone using Tapatalk

[Jay S]

I had an engine once that we did a CT on and thought it should run on pump gas with some booster. We started low and kept adding booster, it would ping when it was sitting their idling. Went to town a bunch of times for more additive. We eventually gave up and drained the gas out and put race gas in it. Then went 10.80s @ 121 in a 3500lb car with race gas. I would highly suggest you find were your threshold is for octane so you can eliminate as many questions as you can.

[PunchT37]

Double check your ICL.

[moontower69]

My money is still on cam install.

There's just no way that cam is installed properly - no way given your reasonable compression and build parameters that your engine is a veritable KNOCK machine unless cam is off.

[adynes]

Don't remember if anyone suggested earlier, but it would be a good idea to verify the timing marks on the damper against tdc using a piston-stop, to make sure the outer ring hasn't slipped.

[PunchT37]

Originally Posted by adynes

Don't remember if anyone suggested earlier, but it would be a good idea to verify the timing marks on the damper against tdc using a piston-stop, to make sure the outer ring hasn't slipped.

Good catch.

[steve25]

Yup that would be a good thing to confirm.

Once you find a TDC 36 degrees will be 2 1/8" around on the Balancer .

[TAQuest]

Originally Posted by Johnny99

Compression test is similar with another gauge.


I’m moving forward based on the idea that the cam being to small and dynamic compression being to high

You have already proven that theory wrong with your compression tests.

[TAQuest]

Harmonic balancer aside. Just retard the distributor as far as you can and have it run. Then check for spark knock. Should eliminate a lot of possibilities. You should definitely be able to get rid of the 'spark knock' by retarding the timing. If not then it's something else.

[Johnny99]

Originally Posted by TAQuest

You have already proven that theory wrong with your compression tests.

Not according to Cliff and a few other folks. They all knew my cranking compression before immediately saying the cam is to small.

I've gone back as far as 4btc with no difference, well maybe the knocking kicked in closer to 2500 that way.

I'm not making any claims that I know what the issue is. The best I can do is test what I logically think it could be and after that listen to others recommendations and test against those.

I've checked TDC and the balancer mark multiple times using a Vac/Pressure gauge. Everytime it reads dead on. This was while installing the cam. I just ordered a hard stop to check and verify tdc that way as well.

Next I'll follow Stan Weiss's suggestion from another thread:
OK, Pull the valve cover so you can see the valves for number 1. Rotate the crank until the mark on the balance lines up with timing mark. Make sure that this is the overlap TDC where both valves are open. If the intake valve is open more than the exhaust valve, the cam is installed to far advanced.

After that I'll pull the timing cover off and check the timing marks as well as the cam install. That'll take a few days as I just ordered a cam degree kit and I should see it Friday. And I'm sure it'll take a bit for me to learn how to use it.

I'll take it from there when the time comes.

If the cam is off I'll correct it and possibly button it back up to test.

I might just correct it to learn the process and NOT button it back up.

Might make more sense pull off the intake and radiator and change the cam, though I'm not sure which cam to look at yet.

Hoping it's not internal, such as the piston ring landings. The only thing I think I can do now is follow through with testing,be open to all suggestions and recommendations and learn somethings in the process.

[TAQuest]

Originally Posted by Johnny99

Not according to Cliff and a few other folks. They all knew my cranking compression before immediately saying the cam is to small.

.

Right! They always say that.
Ridiculous to say it with your compression test.
They must not believe it.
Either way, twist that distributor to retard the timing so it will just run.
Check for spark knock. If you have the sound it's not spark knock.
Doesn't that sound easy?

[pastry_chef]

Originally Posted by Johnny99

a few other folks. They all knew my cranking compression before immediately saying the cam is to small.

Others?

160 psi is too damn low to cause an issue running premium gas provided timing and fuel ratio are correct.
With that low number it is very probable your cam is installed retarded and *that* could be the issue.

Originally Posted by Johnny99

If the intake valve is open more than the exhaust valve, the cam is installed to far advanced.[/COLOR][/I]

Good idea but I disagree with the numbers. I don't have those exact lobes on file but assuming 109 intake centerline, 119 exhaust centerline (114 LSA advanced 5) the intake valve lift will be about .084, the exhaust valve lift will be about .069 at TDC with 1.5 ratio rockers.

[Jay S]

Originally Posted by pastry_chef

Others?

160 psi is too damn low to cause an issue running premium gas provided timing and fuel ratio are correct.
With that low number it is very probable your cam is installed retarded and *that* could be the issue.



Good idea but I disagree with the numbers. I don't have those exact lobes on file but assuming 109 intake centerline, 119 exhaust centerline (114 LSA advanced 5) the intake valve lift will be about .084, the exhaust valve lift will be about .069 at TDC with 1.5 ratio rockers.

I agree with Pastry here.

That cam that the first compression check was taken on was 296/304 and a 106 lsa, 104 Icl. The Intake closing would be 72* ABDC. It is an old ultra dyne profile, it is probably closer to 74* actual at .009 valve lift out at the valve.

The 2802 at .006 tappet lift or .009 out at the valve is is about 284-286 total duration at .006. It shuts the intake valve and 71*-72* ABDC.

If you plug those ICL numbers into this calculator:

http://www.wallaceracing.com/dynamic-cr.php

They have nearly the same pumping compression, AND the actual compression tests were nearly identical. 160 is about right on the lunati cam, it is to low on the summit, it should be closer to 180.

That is becuase that Lunati cam has 88* of overlap. The summit has 63*. Overlap pummels compression tests. They should NOT be the same on a CT test. The Wallace dynamic compression calculator always runs 30-40 lbs low on pumping pressure on most Pontiac engines that have around 60 degrees of overlap. Because it only looks at the intake closing event on cam specs. Chances are the cam is retarded to much and heating up the air charge. Far more likely this cam is currently retarded than it is advanced. Rarely have I seen a cam installed dot to dot need to be retarded, they almost always need some advance.

The 2802 cam should work in the combo. Good chance it is retarded to much and causing temp spikes on the intake charge.