1963 Corvair Engine detonation

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edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

I rebuilt the engine 2 years ago, so I know the engine is free of any debris. I have the oil temp sensor in the hollow bolt holding the oil filter. I never checked the internal flow of the oil cooler. Are there tiny passages that could be blocked? I notice the detonation only at higher temps. Why is it running so hot? Should I change spark plugs?

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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

Has it done this since it was rebuilt? Lean fuel mixture can cause heating. what size are the primary jets?
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edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

yes, it has done it since it was rebuilt. I bought a carb rebuild kit from Clarks and told them I had a 63 with powerglide and the 102 HP engine. I don't know for sure which in one they gave me. I assume #49 as in chart on page 59 of Clarks catalogue. I have the mixture screws unscrewed about 3 1/2 turns. If the car has 2 carbs, they are both primary? Only 4 carbs have 2 primary and 2 secondary right? Should I order a #51 jet ? That is what Clarks use in their rebuilt carbs according to their catalogue p59.

joelsplace
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Re: 1963 Corvair Engine detonation

Post by joelsplace »

3 1/2 turns out is abnormal. 1 1/2 is more normal. You may have a vacuum leak. Main jets will be different depending on how far above sea level you normally drive.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

Mixture screws effect idle mixture, not driving mixture. The mixture screws should generally not be out more that 2 turns from seated . #49 jets are stock. Your engine is certainly not "stock" with 180 PSI compression. With today gas I always run #52 jets in a stock powerglide 102. I am not sure what I would do with a 180 PSI compression 102. I might well be inclined to take the engine apart and change the head and or cylinder base gasket thicknesses to get the engine back closer to a stock compression. If there is nothing else wrong causing this issue such as vacuum leaks, incorrect distributor (or faulty) and or vacuum advance, badly out of balance carbs or something similar, the only way to fix this detonation issue might be to lower compression.

You say you rebuilt the engine? Why did you configure it to deliver such a high compression? Why did you not specify what jet size in the carbs? What camshaft did you install? Are the cylinders stock or oversized? Is the distributor the correct one for a 102? Is the vacuum advance the correct one for a 102? What is the static ignition timing at idle (600-800) RPM? Are you sure the carbs balanced at idle? (I much prefer using a Unison carb synchronizer over a vacuum gauge...makes it very easy with zero guesswork).
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
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flat6_musik
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Re: 1963 Corvair Engine detonation

Post by flat6_musik »

Detonation can grenade your motor. I'm not even a fan of vacuum advance, and if mine, the first thing I would do is disconnect it. I would also carefully go over the intake system, crossover pipe/PCV....and ensure that there are no leaks. You might even want to try a couple different carb setups just to put your mind at ease that that's not the culprit.

With a lot of compression like that, you're going to have to get a little creative (like jet the carbs a bit richer or add water injection). But you absolutely don't want to drive around with a pinging engine. You could crack a piston or ring.

edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

I question the engine compression value of 180psi because, I cranked it over about 7-8 times and the gauge just gets pumped up. How may times should l I turn it over before I take the gauge reading?
I can order a #52 jet and try that on both carbs.
Cam has same lift as original but slightly longer duration, pistons are 0.020" oversize. Distributor is original.

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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

when doing a compression test the needle will jump every time that piston come up on compression. The pulses will raise the gauge each time until the pulses no longer raise the gauge. the peak on each pulse will be about the same at this point. This is the reading you want. usually take 5-8 strokes or so. You must also hold the throttle wide open during the process. What is your timing set at? Manual says 13 degrees BTDC at idle with vacuum advance disconnected and line plugged. I would not want to be set higher than that at least until you fix it where it will not detonate. Lower timing settings will help reduce detonation chance. I would be backing off the timing below 13 if it pings there to see how I could effect it.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
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Located in Snellville, Georgia

edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

The carbs are using a #51 jet. How do you know if the car is running too lean? The idle mixture screw is turned out 3 turns so it is running rich on idle.
Should I buy a #52 or #53 and try it? Trying to figure out how to reduce engine temp. It doesn't detonated until it gets around 215F.

joelsplace
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Re: 1963 Corvair Engine detonation

Post by joelsplace »

Put a clean spark plug in it and run it until it starts detonation. Shut off the engine and pull out the plug. Post a picture here.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

From your description your engine has way too high a compression ratio. It is very possible you must reduce compression to stop detonation.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
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Located in Snellville, Georgia

Wagon Master
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Re: 1963 Corvair Engine detonation

Post by Wagon Master »

edherba wrote:
Mon Sep 07, 2020 5:52 pm
The carbs are using a #51 jet. How do you know if the car is running too lean? Should I buy a #52 or #53 and try it? Trying to figure out how to reduce engine temp. It doesn't detonated until it gets around 215F.
Did the jet change from #49 to #51 have any effect on the detonation? That would at least tell you you're going in the right direction. How to know if the engine is running lean, you have to "Read" the spark plugs. You want dry with a slight tan color. Many Chilton manuals have pictures of various conditions.

edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

So I too a break from the Corvair for 6 weeks or so. I redid the compression test (engine was sitting for 6 weeks). The values are as follow:
cyl 1 -180psi
cyl 2- 160psi
cyl 3- 170psi
cyl 4- 180psi
cyl 5- 195psi (I noticed oil puddling in the cylinder since car was sitting tilted towards cyl 5)
cyl 6- 180psi

So the test was done cold and cyl 5 had oil puddling in it from sitting for 6 weeks, therefore the higher value. I cranked the engine 11 times for each cylinder until the compression value remained steady. See youtube video for cyl #1.
https://www.youtube.com/watch?v=bjAr9vgmg80

Will there be a big difference if I do the test on a warm engine? If 180 psi is high and I am getting detonation, would octane booster do anything? I run 94 octane always.

I checked the spark plugs and they have carbon deposits around the base near the threads. So it doesn't seem to be running lean (car runs hot around 255F).

My plan is to redo the compression test on a warm engine. If values are still high, then do I need to reduce compression with thicker head gaskets? That's a job I would rather avoid, but if it's the only option, I'll do it.

The carb has 51 jets but I bought 52s and 53s incase I wanted to try that.

Any suggestions are appreciated

Thanks

joelsplace
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Re: 1963 Corvair Engine detonation

Post by joelsplace »

Those numbers are really high but compression testers are notoriously inaccurate in my experience.
Reducing the compression with head or base gaskets is a catch 22. It moves the piston away from the head which reduces squish and makes detonation more likely so you have to really lower it. The best option is to open up the combustion chamber with a grinder, and match all the volumes. Better yet get the pistons about .035" from the squish area and add a Singh groove. That way you can get high compression with the more power and efficiency that brings as well as detonation resistance.
By the way 255 is really cool for a Corvair engine.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

If the head gasket seat step was machined heavily during head rebuild and the removed material was not compensated for with thicker head gaskets higher compression would result which would influence tendency for detonation and increase engine loading (has to work harder to make all that compression) and operating temp as well. If 15 thousandths of an inch is removed from the head gasket seat of the head then to go back stock 15 thousandths thicker head and base gasket total thickness should be used. If much or all of the head gasket seat step in the head is machined off, the material removed could be 20-30 thousandths or more, which should certainly be compensated for.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

joelsplace wrote:
Sat Oct 10, 2020 8:29 pm
By the way 255 is really cool for a Corvair engine.
Read again Joel, that 255 is oil temp so it is running pretty hot as well.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

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