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Old 10-10-2011, 07:07 PM
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new sbc blowby

I have a fresh 383 stroker in my roadster and after tuning and general cam breakin with a couple of short drives iam getting some blowby with and without the pvc. i know i should get some until its broke in, but it seems a little excessive to me. i pulled the plugs and they look even and pretty good telling me no broke rings. could timing effect blowby, iam running 76cc heads on 8cc dome pistons with a compression ratio of about 10.5 on 93 octane. does anybody think race gas or 100 octane avfuel would help. total timing is only 32 advance. thanks agian........

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Old 10-11-2011, 12:03 AM
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On many new builds, guys put it together, throw it in, crank it up, break it in then drive it. A week later they go back to adjust the valves then look in the covers and see water mixed with oil and right away go into panic mode thinking it`s got a blown head gasket, but that`s not the case. Since parts are new, they have to seat up plus get used to constant hot and cold usage. During this time, there`s alot more condensation going on inside the engine than normal and it comes out with the blowby making it look like it`s excessive. This is why the watery looking oil is in the top of the valve cover, as after it`s shut down, the condensation rises to the highest point in the engine which is the valve covers. Take your rod for a ride and get it up to normal speed, then when you know a stop sign is coming up but still a ways off, let off the gas and down shift a gear, and let the gears slow the vehicle down, when it gets low as it can go and it`s no longer slowing the vehicle down, go down another gear. Repeat this several times then you can be assured the rings are broke in. Also I`ll ask what oil are you using and what oil did you use during the cam break in period?
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Old 10-11-2011, 04:55 AM
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Quote:
Originally Posted by stegman
I have a fresh 383 stroker in my roadster and after tuning and general cam breakin with a couple of short drives iam getting some blowby with and without the pvc. i know i should get some until its broke in, but it seems a little excessive to me. i pulled the plugs and they look even and pretty good telling me no broke rings. could timing effect blowby, iam running 76cc heads on 8cc dome pistons with a compression ratio of about 10.5 on 93 octane. does anybody think race gas or 100 octane avfuel would help. total timing is only 32 advance. thanks agian........
Do a leak down test at TDC to see if there are ring seal issues, If your block was not plate honed it will be hard to get the rings to seal.
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Old 10-11-2011, 05:12 AM
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Goes w/o saying besides having round cylinders, the cylinder finish must match the ring material for them to break in the best, or in some cases- at all. Moly breaks in quickly, plain cast iron takes a bit longer all the way out to chrome faced rings that can take a good while to break in.

Octane will not have any real effect on blowby, just be sure there's no detonation- and w/those timing figures and 93 octane there shouldn't be detonation unless the cam has a way-short intake closing point. I don't want to get sidetracked w/timing, but unless you have fast burn chambers the max power total timing will probably be found to be closer to 36. Aluminum heads will usually tolerate a bit more timing (more doesn't always mean better), but given the 10.5:1 CR, let the signs of detonation be your guide.
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Old 10-11-2011, 06:50 AM
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thx again, iam runnung zinc have shelf 10w40, going to run it up and down the open hwy tonight. i may do a leak down as well, but all the plugs look good and even. could i have to much oil in it? i have a 6 qt. pan and filled it to the proper dipstick mark or should i try running 5 qts. just a idea...........thx again...........
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Old 10-11-2011, 07:17 AM
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Quote:
Originally Posted by stegman
thx again, iam runnung zinc have shelf 10w40, going to run it up and down the open hwy tonight. i may do a leak down as well, but all the plugs look good and even. could i have to much oil in it? i have a 6 qt. pan and filled it to the proper dipstick mark or should i try running 5 qts. just a idea...........thx again...........
My thoughts on a deep sump pan is to use the same amount as before in order to lower the oil away from the crank and rods. Using more oil will extend the oil change interval a bit, and the oil takes longer to reach operating temp, but less windage losses and reducing air entrainment is the real benefit to me.

When you do your ring break in procedure, don't forget to slow down using engine braking as you cycle the engine through different speeds/loads. I avoid WOT runs for about 1000 miles, but other guys run them hard from the get-go and report no probs.
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Old 10-11-2011, 03:08 PM
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Can you define this blowby?

Some is normal, excessive is not. Excessive would be like a freight train under full load coming out the breathers, normal would be like a lit cigarette inside the valve cover.

Keep in mind it needs time to seat the rings, I've seen some real smokers that calmed right down once it was broken in after 1000 miles...usually because of a coarse ring hone etc.

Sounds like you haven't even broken the engine in yet, relax and give it time. In a good thousand miles is when you need to worry about it...if the plugs look OK it might just require patience.
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Old 10-11-2011, 04:31 PM
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Quote:
Originally Posted by stegman
thx again, iam runnung zinc have shelf 10w40, going to run it up and down the open hwy tonight. i may do a leak down as well, but all the plugs look good and even. could i have to much oil in it? i have a 6 qt. pan and filled it to the proper dipstick mark or should i try running 5 qts. just a idea...........thx again...........
The plugs are not a good indication of what is causing the blow by. The issue that is letting pressure is getting into the crank case will not necessarily let oil up past the rings. I had 2 busted pistons and was not buring oil and the plugs were fine.

As the others have said, drive it a little more before you panic. If it doesnt go away a compression and leak down test are in order.
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Old 10-11-2011, 07:00 PM
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Thx again guys, i let it get hot and did a little tuning and drove it with the braking technique, worked great with a 5 speed. The pan leak wasnt as bad as it was at yesterday, but still leaking. runs and starts good, so time to drive it a little. just a little paranode had a 355 that spin a rod bearing with about 1500 miles. good news is the 383 with 3 twos and a 5 speed is a blast. can you say neck snapper??? thx i hope i can help........
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Old 10-16-2011, 12:21 PM
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thx for all the good advice, i ran it up and down the highway a couple of time and its still blowing oil excessively. so i did a comp test and 2 of the cyclinders show about 90 psi max, i then squirted a couple of drops of oil in the spark plug hole and it came up a bit. also blew air in and could hear a little air in the bottom of the case. should i pull the motor and see if the rings are broke or wait for them to break in???
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Old 10-16-2011, 12:37 PM
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Quote:
Originally Posted by stegman
thx for all the good advice, i ran it up and down the highway a couple of time and its still blowing oil excessively. so i did a comp test and 2 of the cyclinders show about 90 psi max, i then squirted a couple of drops of oil in the spark plug hole and it came up a bit. also blew air in and could hear a little air in the bottom of the case. should i pull the motor and see if the rings are broke or wait for them to break in???
I would do a leak down test at TDC to find out whats going on if your block was machine corrcectly the rings should be seated by now!!

I have seen circle track engines that were not prepared correctly and after 3 years or running they still had rags wrapped around the breathers because of blowby issues.
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Old 10-16-2011, 05:39 PM
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Are the low holes next to each other? What do the plugs look like from the low holes? Besides the chance of bad ring seal, you might have inverted rings in the bad holes.

Was a torque plate hone done on this engine? What type rings were used- moly or plain cast iron, or ? Normal width rings or 1/16"/metric? Low tension oil rings or standard?
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Old 10-16-2011, 08:37 PM
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Moly rings, i resorted to tearing it down and the bores and top of the pistons look good. ill push the pistons out tomorrow. thx again........
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Old 10-16-2011, 11:00 PM
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Here is a pic of some cylinders that had poor ring seal and blowby issues,

[IMG][/IMG]
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Old 10-17-2011, 02:41 AM
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Quote:
Originally Posted by stegman
Moly rings, i resorted to tearing it down and the bores and top of the pistons look good. ill push the pistons out tomorrow. thx again........
In case there was a ring installed upside down, be careful to pay attention to the pip marks or chamfers that show which way is "up". Most times these can be seen w/o removing the rings from the pistons but the pistons do need to be out of the block.

There's a slight chance that a ring could have broken and still not tore up the bore. And the bore/hone job can look OK and still not be good- it sometimes takes a close look to see the 'high and low' spots that are witness to a bore that isn't round.
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