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SBC 383. Blow by

General engine tech -- Drag Racing to Circle Track

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73c34me
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SBC 383. Blow by

Post by 73c34me »

Greetings- been chasing my tail- leading to a possible conclusion of needing a hone and new rings refresh. Motor sat for 8 years, oiled and indoor storage. It had approximately 1500 miles on it at this point. During storage I ported the heads (3rd time) had them cut .025” and the machine shop installed new valve seals. years later after a frame off restoration- the motor smoked a lot and used oil. I then had the victor jr. cut on the China rail ends to fit appropriate. Better but It still smoked so I changed the intake gaskets and it improved.- but not completely cured;still smoked etc. NextI installed a PCV and catch can, gained an improvement, Catch can would collect nearly a cup in a 150 miles. Next I improved the baffling in the valve cover installed new plugs. More improvement, but not smoke free. Recently I resealed the intake rocker studs w/ Indian head shellac snot. I thought I was golden. A couple of short drives and the spark plugs were looking decent. Yesterday I drove the car 2 hours- it started puffing smoke out the tail pipes at stoplights. I pulled the plugs and they are oily- but significantly better than I have had. Not long ago I did a compression test and it was 230 lbs. so it seemed healthy. I haven’t done a leak down test. Are the low cost leak down testers accurate enough? The car runs really strong and dangerous with the Cooper 275-60/15 street tires. Options. More pcv work? Leak down test? Vacuum pump? Or new spark plugs every 150 miles or approximately every other month... thnx

Note- I have the pcv on the passenger side cover if this matters. I couldn’t find anything to verify this or prove it wrong.
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Re: SBC 383. Blow by

Post by pdq67 »

Were the rings installed right?

Just asking is all, maybe one or two were put in upside down?

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Re: SBC 383. Blow by

Post by 73c34me »

Good question. I don’t know. I had a professional race ship assemble the short block.
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Re: SBC 383. Blow by

Post by lefty o »

did it smoke prior to valve seals being messed with?
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Re: SBC 383. Blow by

Post by 73c34me »

No. Smoking began after another round of porting, heads milled and a few years of storage. A diff ENT shop installed the valve seals the 2nd time. I did remove a valve spring and visually didn’t see anything of concern. I could not wiggle the valve with my fingers.
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Re: SBC 383. Blow by

Post by prairiehotrodder »

take a spark plug out, put the piston down and shine a light or a bore-scope in there and have a look. I had a motor wash down the cylinders with a junk used carb that i shouldn't have bought. The cylinder walls and rings turned blackish and it needed rebuilt.
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Re: SBC 383. Blow by

Post by Schurkey »

73c34me wrote: Sat Sep 26, 2020 7:16 pm Yesterday I drove the car 2 hours- it started puffing smoke out the tail pipes at stoplights. I pulled the plugs and they are oily- but significantly better than I have had.
I'd be looking at the valve guides/valve stem seals before I ripped the engine out for rings and hone.

Given the amount of "resealing" done, perhaps a smoke machine is needed to verify intake manifold fitment.
73c34me wrote: Sat Sep 26, 2020 7:16 pmNot long ago I did a compression test and it was 230 lbs. so it seemed healthy.
That's "beyond" healthy. I've never seen a cranking compression reading that high in my life. Consider testing the compression tester gauge for accuracy. I connect mine to "shop air" a couple times a year to verify that the compression testers and the gauge on the compressor regulator all agree within reasonable limits--about 5 psi is good enough for me. I have one compression tester that reads 10 psi low, that one is marked so I can mentally adjust the indicated reading a bit higher.

Given cranking compression that high, any chance you've got detonation problems that are causing ring-seal issues?
73c34me wrote: Sat Sep 26, 2020 7:16 pmI haven’t done a leak down test. Are the low cost leak down testers accurate enough?
Define "Low cost leakdown tester".

I have two. First one is a Snap-On single-gauge unit I bought new in the late 1980s. MT324, I think. Mine had a reputation for being extremely sensitive, but cleaning out the internal orifice seems to have brought it back in line. My newer one is claimed to be made to FAA ("aircraft") specs for bore sizes smaller than 5"; and has a "Master Orifice" that allows me to test the tester and recalibrate my expectations. VERY recommended. It normally ships with an 18mm spark plug hole adapter, they shipped mine with a 14mm adapter at my request. Or buy several sizes of plug adapters depending on your needs.
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Note that the "Master Orifice" is a Continental-Teledyne requirement, calibrated to their engines. For the purposes of high-performance engines, the concept is valid but the actual orifice used could be smaller. Continental allows more leakage than I'm comfortable with on automotive engines.

ANY leakdown tester not having a Master Orifice needs to be used on several "known-good" engines similar to the one you actually want to test, so that you learn how that individual tester reacts. The indicated leakage has as much to do with the internal orifice as it does with the actual cylinder leakage. You need to know how YOUR leakdown tester works on good engines before you can determine what's "bad".

I've heard of folks fabricating their own "Master Orifice" using brass fittings or brass stock for easy machining, and a Holley jet as the actual orifice--but I've forgotten what size jet is recommended. #89, perhaps?
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Re: SBC 383. Blow by

Post by 73c34me »

thnx for the replies. I feel better just sharing my frustration.
Next- I will get a bore scope and look into the cylinders.
I appreciate the feedback on leakdown gages, I am not surprised.
I will post up a couple pics of the cylinder walls, if I can take them during the inspection.

One more thing, I remembered after the post. Just before i disassembled the car, in 2006. Carb tuning- fire it up, forgot to reinstall the power valve. Gas was just dumping into the plenum. Ran it for a minute or less. I have an MSD system so I hoped the multiple sparks ignited it. Perhaps washed the cylinders down?
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Re: SBC 383. Blow by

Post by BobbyB »

My new 347 ford used some oil, sounds very much like your experience. As a test, I eliminated the PCV for 2,000 miles. My oil consumption problem went away with the PCV elimination. I sent my oil off for analysis to Blackstone and asked them to look for any trouble with the oil from not having PCV. The results should come soon. Many say a PCV is a requirement, other disagree.

For me, I am satisfied that the PCV was my oiling problem. I am VERY glad, not to be yanking my new engine to look for problems that hopefully don’t exist. If my oil analysis comes back good, I will probably leave things alone. I can be happy changing my oil more frequently and not having PCV.

What would you do if you were 95% sure that all the oil going into you combustion chambers was getting there through the PCV system? Good luck with it!
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Re: SBC 383. Blow by

Post by ptuomov »

In my opinion, if the bore walls have a normal amount of oil during the test, the leakdown tester mostly tests the piston ring gap width. If you test a new engine and then later a worn engine, you can compute from the new and worn engine leakdown numbers how much the ring gap has grown. This in turn allows you to estimate how much the rings and the bore walls have worn. Does the leakdown tester test anything else?

The ring seal can be tested with a blowby meter on a dyno. I’ve got one from performance trends and it’s worked well so far. The maximum blowby happens at peak torque rpm, if the engine combo makes overall sense. If the blowby starts picking up at high rpms and exceeding the peak torque rpm level, I interpret that as ring flutter that is caused by too wide rings for the stroke and rpm.

Knock sensors tell you if the engine knocks. With a blowby meter hooked up, it will show you if the blowby is caused by knocks causing the rings to flutter and lose their seal. It’s a good combo of sensors to monitor, luckily my car has knock sensors from factory.

If the engine doesn’t knock or record excessive blowby, my guess would be that the short block is fine. For what it’s worth.
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Re: SBC 383. Blow by

Post by 73c34me »

Appreciate all the feedback. This site is a wonderful resource. I think I will add an oil analysis and smoke/ leak detection to the early on diagnosis steps. The Dyno blow by test sounds awesome.
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Re: SBC 383. Blow by

Post by Schurkey »

ptuomov wrote: Sun Sep 27, 2020 11:01 am In my opinion, if the bore walls have a normal amount of oil during the test, the leakdown tester mostly tests the piston ring gap width. If you test a new engine and then later a worn engine, you can compute from the new and worn engine leakdown numbers how much the ring gap has grown. This in turn allows you to estimate how much the rings and the bore walls have worn. Does the leakdown tester test anything else?

The ring seal can be tested with a blowby meter on a dyno. I’ve got one from performance trends and it’s worked well so far. The maximum blowby happens at peak torque rpm, if the engine combo makes overall sense. If the blowby starts picking up at high rpms and exceeding the peak torque rpm level, I interpret that as ring flutter that is caused by too wide rings for the stroke and rpm.

Knock sensors tell you if the engine knocks. With a blowby meter hooked up, it will show you if the blowby is caused by knocks causing the rings to flutter and lose their seal. It’s a good combo of sensors to monitor, luckily my car has knock sensors from factory.

If the engine doesn’t knock or record excessive blowby, my guess would be that the short block is fine. For what it’s worth.
Rings don't seal on scored cylinders. Broken rings don't seal well at all. Air noise out the throttle body verifies leakage at the intake valve. Air noise at the tailpipe verifies exhaust valve leakage. Air leakage into the next cylinder verifies head gasket leak. Bubbles in the radiator verify head gasket leak, or cracked castings. So, yes, you're seeing more than just ring gap...but in some cases you don't know what until you disassemble for inspection.

Thanks for the rest of that. Makes sense logically, and I hadn't thought enough about it.
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Re: SBC 383. Blow by

Post by DCal »

This doesn't add up to me. My race motors were only 240 cranking, my street car has 185 psi . Pump all the cylinders and if one is low, squirt some oil in there and if it get a higher reading the rings are gone away. You mentioned that also. The part that is confusing is that if the rings are wiped out how are you getting that 230 number? Unless there really is that much oil in those cylinders.
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Re: SBC 383. Blow by

Post by ptuomov »

Schurkey wrote: Sun Sep 27, 2020 6:00 pm Rings don't seal on scored cylinders. Broken rings don't seal well at all. Air noise out the throttle body verifies leakage at the intake valve. Air noise at the tailpipe verifies exhaust valve leakage. Air leakage into the next cylinder verifies head gasket leak. Bubbles in the radiator verify head gasket leak, or cracked castings. So, yes, you're seeing more than just ring gap...but in some cases you don't know what until you disassemble for inspection.
I agree with all that. Pressurizing the system will reveal all sorts of things.

In terms of the short block, yes, if something is literally broken then it’s probably not broken in all cylinders. So uneven leakdown numbers will tell you there’s a problem. A friend had some chunks missing from the ring land in a way that wasn’t visible in a boroscope screen and leakdown tester detected that.
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Re: SBC 383. Blow by

Post by F-BIRD'88 »

If this engine was subjected to detonation say from excessive compression ratio for the fuel octane and running conditions, the detonation damages the piston ring lands
If the ring lands are damaged blow by will be excessive and honing and new rings will not fix it.
The cranking compression seems pretty high for a pump gas engine.
If the piston ring lands are now distorted and damaged from detonation the only fix is replacing the pistons .
What is the real compression ratio.
A flat top piston 383 with 64 cc heads and O deck can have excessive compression and suffer detonation on typical premimun unleaded pump gas.
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