I cannot run my car for fear of blowing the motor. Pinging/detonation is scaring me. Engine is a 1971 olds 350, .30 over. Block zero decked. #7 iron Heads milled and polished. Flat top pistons. 10.1:1 compression ratio(calculated). I have felpro head gaskets. Cam is a Comp XE268H. Plugs are AC Delco 45s. Stock Distributor with Pertronix installed under the cap - stock springs/weights. I tried re-curving but was not happy with the results. Stock coil. Timing is dialed down to 8 initial. 1000 miles since built. Pings so bad I can't drive it. Even on 93 octane it sounds like an army shaking spray paint cans. Suggestions?

 

Welcome Phil. When did this issue start?

 

Ever since the engine was completed. Never could get a good tune on it.

 

Did you build it yourself, or have someone else build it?

Have you tried higher octane levels?

What's your timing at 3,000 RPM?

Welcome to ClassicOlds.

- Eric

 

Machine shop (local race shop with BOP experince) assembled the bottom end I did the top end. Timing at 3k rpm is an unsteady 36 deg btdc.

 

Are you running 100 octane?

 

I calculate 10.4:1 at a minimum. What did the heads cc at?

 

Yeah. I would definitely increase octane first, so that you know it works well, and then work backward from there, first by decreasing octane.

- Eric

 

I'll have to check the build sheet. I think volume was 62 on the heads. I've tried octane booster with some reduction in pinging. I built this with every intention of running pump (93) octane. And before anyone asks. The flex plate bolts are tight. ; )

 

Also mounted, out of the box, a Jet stage 2 quad until I can get a Sparky rebuild.

 

Okay, check me on this, in case I screwed up, but with bore 4.087, stroke 3.385, head gasket 0.042, deck 0, piston volume 0, and CC volume 62, I get 11.24:1 static.

If I didn't screw up, there's your problem.

If the CC volume is 64, it's 11:1.

If the CC volume is 68, it's 10.4:1

What octane booster did you try? I've used Octane Supreme, which is genuine tetraethyl lead, and it definitely did the job.

- Eric

 

Build sheet verifies 64 cc on the heads. Where can I get octane supreme? I've bought the crap off the shelf at Walmart.

 

With that much compression, and that little cam........you need almost 110 octane to not detonate. If you are truly at 11.24:1 (which is what I get as well) your machine shop really failed if they were in charge of speccing out this build.

 

Yeah, if the CCs really are 64ccs, and you've really got an 11:1 static CR with a fairly mild cam, that'd do it.

So that leaves three reasonable possibilities:
1. Use octane booster all the time. Stuff's expensive.
2. Change your cam. May not give you the drivability characteristics you want.
3. Get another pair of heads and do them up with 68cc chambers.

For now, I'd try the Octane Supreme (I got mine from WildBillsCorvette), just so you can drive your car, but in the long run, doing some head work and then swapping your heads isn't a huge big deal, and should get you where you want to be.

What I would recommend doing is to put as close to a measured 5 gallons of 93 octane gas in your car as possible,
add Octane Supreme to bring the octane up to about 95 or 96 (the equivalent of old-time 100 octane), and go for a drive.
If it still pings after a little while, pull over and add another couple of ounces.
Drive more.
Repeat until it quiets down, and keep track of how much octane boost you're using, so that you can add the proportionate amount the next time you fill up (and also so you can confirm what you believe to be true about your compression ratio).

Another alternative is to buy 5 gallons of 110 octane race fuel (and, Man, that stuff ain't cheap either) and try that.
Carry a can of 93 octane in the trunk.
If it's good, add half a gallon of 93, and drive again.
Continue driving and adding 93 until it starts to ping, at which point you've got a good idea of the ratio of 93 to 110 that will work for you (when you add up the price of the 110, you will become physically ill).

Good luck!

- Eric

 

I wonder what the piston to wall clearance is......I am assuming those are Speed Pros.

 

You need to find out the exact piston used. A lot of the small block pistons are "flat tops".
Beyond that, is E85 an option for you in your area. Just a thought besides the other options given.

 

Bore is 4.088. Pistons are speed-pro forged WL2320F30.

 

If it is 11.24:1, that would have been very high for a street engine...even back in the 60s. Some hipo vettes, Hemi Mopars and a few others that were really designed for the track.


I had a 1970 455 Pontiac years ago that became a ping-o-matic when they eliminated the lead and dropped the octane. I used octanes boosters and played with the timing, and even bought an Edelbrock water injection system. I was always chasing my tail, and never confident I could just jump on it. How much booster do I need to take on a long road trip? I finally changed heads and eliminated the problem.

 

Any thoughts on #8 heads with existing cam? That would get me to 9.3:1 until I can convince wifey that aluminum heads and intake are in the budget.

 

I get less than 9.2:1 with 80cc #8 heads, but, yeah, that should be fine.

If you want to go a bit higher, you can mill the heads about .020" and get about 9.5:1, or about 0.040" and get about 10:1 (assuming that my memory is about right that roughly 0.005" milled = 1cc).
Depending on what you did with your valvetrain, milling 0.20"-0.025" would bring everything back to the height that it was with the factory 0.016" head gaskets, while going further would make it lower, increasing lifter preload (how much? It depends...)

So, yeah, #8 heads are fine, and will let you drive the car until you can hide enough money for a set of aluminum heads.

- Eric

 

Thank you, everyone, for your timely and gracious responses. Now to the sale forums to locate heads.

 

You need a set of #8 heads? I got some. PM me.

 

The #8 heads would be ideal, just grind the "lip" under all the exhaust valves. My pairs of #8's measured just under the 79 CC factory measurement.

 

Who degreed the cam???
Sounds like a timing issue.....
"Unsteady 36" could be a bad Dizzy too....
Did you break in the cam???

 

I degreed the cam - straight up. Cam was properly broken in.

 

I'd do the simple stuff first.... check the Dizzy for loose parts. Check the lash on the valves too. Run it for a but then shut it off. Roll it to TDC on number one and check the lash..... then follow the firing order and check each one. It would be really odd for someone to have messed up that bad. BTW, when you rotate the motor to TDC on number one, check the rotor placement and make sure its on number one.

 

What was "straight up" in regard to ICL?

 

Where are you going with this?

We've already established that he built the engine for a 10:1 compression ratio but actually has 11:1.
It runs fine otherwise.
It is highly unlikely that the distributor would be pointing to the wrong cylinder on a running engine.

- Eric

 

He said that he did the top end. My point is that rotating assemblies go up and down. If he put the heads on himself and dialed in the cam "straight up" (which I assume that he means at 0 with no advance or retard) and he is absolutely sure that he has dialed the cam in correctly and broken the cam in correctly, (Not that a cam has ever gone flat on break-in ) there could likely be some elusive timing issue.

I'm not trying to say that you are wrong or trying to compete with your knowledge and experience. You are clearly more experienced than I. However, sometimes its the little things that mess up and isn't always what may be obvious. I'm sorry if I have offended you. This is not a challenge, just my humble opinion.

 

He absolutely needs to rectify the excessive amount of compression ratio per camshaft specs/pump gas scenario before he does anything else. He simply has too much compression which is causing his issues.

Maybe there are other problems as well, but he will continue to detonate the living hell out of this engine if he does not lower the compression, or use a much higher octane fuel.

Not being confrontational with you, just letting you know your advice is null and void until he gets this major issue fixed first.

 

Phil, I have almost the identical build as you. Same piston, cam, head combo. I have to go look up the numbers but I think my heads cc'd 67 or 68. I calculated the compression same as your original statement of 10.1 to 1. It took some tuning with the dizzy and springs but mine runs great now with no pinging. I too am wondering about the unsteady 36 degree timing. I had to use lighter springs to get the timing in quicker. My cam was advanced4 degrees.

 

Guys, we already established he is over 11:1 compression.

Sampson, did you zero deck your block as well? Just curious, could you do a compression test on yours and tell us what you have for cranking compression? And that goes for Phil as well.....I'd be curious to see what the readings are.

 

[QUOTE=

Not being confrontational with you, just letting you know your advice is null and void until he gets this major issue fixed first.[/QUOTE]

I respectfully disagree.....

Telling me my advice is null and void is rude....

Try again.....

 

It's okay, I'm not trying to compete either. I'm just saying that he has a known serious problem that is consistent with his symptoms, and I'm concerned about sending him in too many directions, when he needs to put a set of #8 heads on there.
It is certainly true that bad cam timing can possibly cause this sort of thing, but he's already got a great reason for it, and has no reason to suspect anything else.

That is not to say that I think that he shouldn't check what you suggest - he should - but he shouldn't allow that to distract him from the greater issue.

- Eric

 

Sorry I missed that he confirmed 64 cc'd on the heads. Again, mine cc'd 68.

11:1 is too much.

 

I applaud your debate skills. You are a gentleman and scholar.
Again, who cc'd the heads? What heads were on it before the Machinist decked the block?

He should check his work. He should not waste a set of head gaskets et al until he has. That's where I am coming from. You can't establish the true problem until you have eliminated all other possibilities. I wouldn't tear into that fresh engine until I could confidently say I did everything right. JMHO

 

Thank you.


I was taking him at his word that those numbers were checked and well established, but your perspective is also reasonable - On the Internet, nothing is a given, and people say a lot of things that are not completely accurate.

He's definitely got enough advice from all of us to figure it out now, regardless.

- Eric

 

Exactly.....

Bravo!!!

 

Point taken. However, he has stated his heads were milled. I do know that these heads were around 68-69ccs from the factory, which doesn't mean much after valve jobs and such.

So, assuming he has a zero decked block with flat top pistons, a .039 head gasket, and 68cc heads (assuming the heads were just slightly resurfaced and the valve job sunk the valves slightly) I still come up with 10.44:1 compression.

I agree, if the timing is an issue, that will definitely play havoc with a motor that already has too much compression for pump gas and that cam. However, if he truly is at that compression (10.44:1), he should be able to cruise at light (very light) throttle without pinging if the tune is good on that motor.

If the heads really did cc at 64 or 62......can we say that I was right and that your comments are null and void until he lowers compression?

 

Looking for validation??? Okay. I'll bite....

My comment is null and void and you are correct, this was an exercise in futility, I should keep my mouth shut and speak only when spoken too.....