Yikes! Compression!

Discussion in 'Engine Performance + Maintenance' started by L31MaxExpress, Feb 22, 2021.

  1. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Thought some of you gearheads would get a kick out of this. After adjusting the rockers again, leaving the plenum off, all the plugs out and getting a good hot battery connected to it, the new 383 is cranking at 220-225 psi in all 8. Going to revisit #5 valve adjustment because it was the only cylinder to read higher than 220 psi.

    On a side note the 383 is finally pretty much ready to drop-in for the 2nd time. Just have to install a new coolant temp sensor, new knock sensors, new oil pressure sending unit and mount the coil correctly. Then cleanup the wiring harness with new looming and a couple new connectors. Also having to rewire the OEM fuel injector connector, the EGR valve and swap back to a single coil with distributor. Going back with all the smog stuff this time around and basically OEM look and function....EGR will be flashed out of the tune except for a few hundred miles before the emissions test.

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  2. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Also feel like sharing this. Robbed a stock intake manifold of all the hardware. Had been running that intake a while back on the Tahoe, had put a solid 75K on that 305. Still had the EGR enabled in that tune. I had been using a bottle of GM Top Engine Clean prior to every 7,500 mile Mobil One oil change. Basically pulled the intake hat off, unplugged the MAF, cycled the key on, off, on, then started so that the PCM would fail the MAF. With the engine idling I slowly poured the top clean down the IAC opening in the throttle body. At approximatly 1/2 can, I would increase the pouring speed until the engine stalled out. Then waited a few hours. Reinstalled the TB hat, plugged the MAF in, cranked it up and took it on a spirited drive. What the intake looked like with the regular top clean. Plan to top clean the 383 the same way moving forward in the future.

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  3. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Also finally got around to pulling the heads off the old 350 in the middle of this Texas Blizzard we had. Still pretty clean considering the abuse I gave that poor engine. Needs some bottom end work but the block still seems solid and the bores practically new. Going to build it into a nice little street/strip engine for the 1980 Z28 I have.

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  4. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Before I topped the plenum also played around with the bore scope camera I picked up a few months ago. Heads and intake line up pretty good after porting, despite the heads having been milled 0.020" and the block deck having also been cut. The Felpro problem solver gasket does have a slight overhang that was out of my control because of GMs weirdly shaped casting in places but I am not going to trim on the gasket and risk the rubber delaminating off the metal core. First picture is from the spider injector hole in the manifold. The injector tip has a straight shot to the back of the valve. Great for atomization.

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    Last edited: Feb 22, 2021
  5. Schurkey

    Schurkey I'm Awesome

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    High cranking compression and no EGR? You better watch the knock sensors for activity!

    "I" would leave the EGR functional.
    [EDIT]Did the lifters have oil in them? Pumped-up properly? If the lifters were full of air, you'd get high cranking compression readings due to the shortened duration.[/EDIT]

    I've got a few of those compression testers--it would be worth connecting yours to "shop air" and seeing if the compression tester gauge reads the same as the gauge on your air pressure regulator. And--I learned this the hard way--the spark-plug threaded ends and crimps on those hoses is suspect. I threaded the hose into the head, and when I tried to un-screw it, the hose just turned on the metal piece. Took an hour and lots of harsh language to get the adapter back out of the head. I took the adapter and hose to a local hydraulic shop so they could re-crimp the assembly after cutting off 3/4 inch of the end of the hose.
     
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  6. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Rhoads V-Max lifters....They do not fully pump up until 4,000 rpm.

    Going to be tuning it and I start with a very conservative timing advance curve. I built it to use mainly E85 for fuel.
     
    Last edited: Feb 22, 2021
  7. Supercharged111

    Supercharged111 I'm Awesome

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    Tough to see, but this was my first practical use of the bore scope camera. I dropped an injector harness clip down an intake port and I prayed whatever hole it was that the valve was closed enough to have kept it in the runner.

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    Lucky me. I fished it out with a magnet.
     
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  8. yevgenievich

    yevgenievich Newbie

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    What camera are you using? I have an old one, it is about useless for anything.
     
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  9. L31MaxExpress

    L31MaxExpress I'm Awesome

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    I can get the model number but it is an Innova sold on the shelf at Oreilly auto parts. It is actually clearer in person. Taking a picture of the screen with my phone pixelated it. The lighting on it is adjustable.
     
  10. CrustyJunker

    CrustyJunker Tractor

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    Yeah, I built a 383 with 210 PSI cranking pressure on 93 octane. Thing can tractor-chug up a hill off the IAC at 450 RPM without stalling. It's comical.
     
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