460 Compression Specifications

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Oct 29, 2011 | 05:10 PM

RabidJade

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460 Compression Specifications

I searched the internet and the forums and was unable to find an answer.

What is the compression supposed to be in the 86' 460ci cylinders? I tested mine today with all eight cylinders and got readings between 125lbs to 145lbs.

Oct 29, 2011 | 05:58 PM

85e150

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I'm finding 130 as a common number. The difference between cylinders is a big deal. You are over the 10% difference by a little bit.

Did you do the test dry, and follow it with the oil in the cylinder test?

It's probably good enough to run for light to medium duty.

Oct 29, 2011 | 07:32 PM

RabidJade

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The test was done dry and I didn't know about an oil test. Main reason for the test was to find out why she was running lean while the carb jets are obviously over sized and to see if the engine was worth putting more money into.

Oct 29, 2011 | 09:44 PM

85e150

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Check for vacuum leaks at the carb base and intake gasket area.

The cylinder pressure isn't going to make it lean or rich, only the air/fuel ratio which is decided at the carb, and can be influenced by a vacuum leak downstream.

Nov 1, 2011 | 01:46 PM

85lebaront2

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From: Exmore, VA

One place to check is the canister purge line, it crosses in front of the carb and turns down at over a 90 degree angle. The bend is famous for collapsing and leaking. I've had to fix mine a couple of times.

Nov 1, 2011 | 09:29 PM

RabidJade

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Quote:

Originally Posted by 85lebaront2

It has a Weiand Stealth intake and a Road Demon 750 carb on it. All the emissions stuff has been removed for the most part.

Nov 1, 2011 | 11:03 PM

85e150

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Quote:

Originally Posted by RabidJade

.............for the most part.

Well, check those parts that are still there for a vacuum leak.....

You could still have vacuum leaks around the carb and intake manifold gaskets.

Was this carb tuned for the engine, rejetted or otherwise fiddled with? Did it ever run right? Is this a new problem?

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Nov 1, 2011 | 11:26 PM

RabidJade

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Quote:

Originally Posted by 85e150six4mtod

Carb was never tuned for anything, I rejetted it several times and the truck always ran lean. There is no leak between the carb and the intake as I checked the vacumm and it is around 15-17 on the raceways I checked. The carb is almost maxed out on jets with no change in the lean condition (90pri/96sec if I recall) but the truck starts and runs fine aside from feeling gutless for being a big block, my 4.0 jeep could out tow it right now.

However this thread is just about compression for each cynlinder and I think I have a thread somewhere going on about the jetting/lean nightmere I was dealing with until I gave up when the truck got parked a couple of months back.