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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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Re: SBC 383. Blow by

Post by 73c34me »

Aluminum heads. I ran 93/94 octane with a boost, 180-190 coolant temps and did not lug the engine. Perhaps that compression ratio can’t be done. Track time would have had race gas.

I will start with a camera inspection and see if I can borrow a decent leakdown tester.
F-BIRD'88
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Re: SBC 383. Blow by

Post by F-BIRD'88 »

A compression ratio of 10.5:1 will be a lot more reliable on your 93/94 pump fuel. There is no free lunch.
73c34me
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Re: SBC 383. Blow by

Post by 73c34me »

Update. I drove the car approximately 100 miles the other day. No changes from before, which facilitated my original post. I drained the catch can after the drive. I got about a teaspoon of oil. I could not see tail pipe smoke, but am sure there would be some. My original post- i drained nearly a cup of oil from the catch can after a 125 mile drive, so a big reduction. I have ordered an oil analysis kit and will use a bore scope soon. But currently- the car runs really strong and good...
C.A.R.E.
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Re: SBC 383. Blow by

Post by C.A.R.E. »

While you inspecting things with the Bore scope check the pushrod relief in the heads. When the last head work was done it may have been ported to thin and be cracked from the port to the pushrod relief. It'll pull oil thru the crack. Especially high vacuum ( idle & coasting with the throttle closed. ASK Me how I know !
73c34me
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Re: SBC 383. Blow by

Post by 73c34me »

Good advice! I have wondered if i am pulling oil from a crack. A couple areas were getting a little thin during the porting phase... the porter was stubborn! I am the guilty party.
73c34me
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Re: SBC 383. Blow by

Post by 73c34me »

Update. Flipped the breather and PCV around; pcv on driver side. Replaced the hose to catch can w/ clear reinforced hose. I can see an oil trail flowing up the hose to the catch can.
Also, layed painters paper (thin)over valve cover (pcv) hole. When running it does not suck into the cover. It pushes away slightly.
Also. Sprayed some carb cleaner in the same hole on engine idle. It did not pickup rpm. Duplicated this test using acetylene- again no change in rpm.
Blackstone oil analysis kit arrived in mail. Will sample and send off in a day or two.
Will get a borescope on my next session.
Schurkey
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Re: SBC 383. Blow by

Post by Schurkey »

73c34me wrote: Wed Oct 21, 2020 5:28 pm Update. Flipped the breather and PCV around; pcv on driver side. Replaced the hose to catch can w/ clear reinforced hose. I can see an oil trail flowing up the hose to the catch can.
Excessive blow-by, or insufficient baffling. Maybe both.
73c34me wrote: Wed Oct 21, 2020 5:28 pm layed painters paper (thin)over valve cover (pcv) hole. When running it does not suck into the cover. It pushes away slightly.
Confirmation of excessive blowby; assuming all is well with the PCV valve and intake vacuum.
73c34me wrote: Wed Oct 21, 2020 5:28 pmAlso. Sprayed some carb cleaner in the same hole on engine idle. It did not pickup rpm. Duplicated this test using acetylene- again no change in rpm.
Not surprising, since the excess blow-by would push the carb cleaner or acetylene right back out the hole.
73c34me
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Re: SBC 383. Blow by

Post by 73c34me »

Removed the carb today, looked down the intake runners. I can see where the bottom edge of the fel-pro 1205 gasket has raised up to where the printo-seal is visable. Also, oil is present on the floor of the intake. I have dimpled the floor with the tip of a 3/16th drill bit. Most of those divots have oil in them. Pretty sure i am going to need a corrective cut on the intake manifold face; block cut .020” & heads milled .025”. Whrn i pull the manifold i will inspect with a borescope.
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