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Compression readings seem high.
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Bug53
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PostPosted: Sat Sep 18, 2021 6:12 pm    Post subject: Compression readings seem high. Reply with quote

Not that it would be a bad thing.
Last Spring when I purchased the car before yanking the engine I took compression readings to know if it was worthwhile.
I was told as part of the restore of the car a rebuilt engine was done approx. 8K miles previously.
In order (1,2,3,4) 1 got 140's with one close to 150 with the carb. not even propped open.
I'm in the process now of doing dual Kadrons so while I was there and the manifolds are off I did it again with unrestricted intakes.
Surprisingly I get 150,158,150,150.
Am I to assume this is really good for a stock build or think maybe my compression ratio may be up a bit.
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67rustavenger Premium Member
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PostPosted: Sat Sep 18, 2021 6:20 pm    Post subject: Re: Compression readings seem high. Reply with quote

As long as the weakest cylinder is within 10-15% of the other three. You're good to go!

You're good to go!
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Bug53
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PostPosted: Sat Sep 18, 2021 11:05 pm    Post subject: Re: Compression readings seem high. Reply with quote

67rustavenger wrote:
As long as the weakest cylinder is within 10-15% of the other three. You're good to go!

You're good to go!


150,158,150,150
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anthax
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PostPosted: Sun Sep 19, 2021 12:14 am    Post subject: Re: Compression readings seem high. Reply with quote

High comp = good and efficient burn of the mixture = more power and better mpg.
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Floating VW
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PostPosted: Sun Sep 19, 2021 8:21 am    Post subject: Re: Compression readings seem high. Reply with quote

150 psi is pretty good for an ACVW engine, but it's not freakishly high, by any means. Especially if good quality rings were used in the cylinders and the compression ratio has been bumped up a bit. My own machine hits 155 psi on the dot, but I use Total Seal rings and my CR is a little higher than stock, which I'm sure helps a lot.

I've done compression tests on Ford Coyote engines that cleared 180 psi pretty easily.
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Shane Tuttle
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PostPosted: Sun Sep 19, 2021 8:41 am    Post subject: Re: Compression readings seem high. Reply with quote

As those compressions look good, I would perform cylinder leakdown checks in the future. It's not much more work and it tells a more accurate story of what's going on.
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VW_Jimbo Premium Member
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PostPosted: Sun Sep 19, 2021 9:21 am    Post subject: Re: Compression readings seem high. Reply with quote

On a stock 1600 I would get right around 125psi for a health engine. That was a stock motor with stock compression and a stock camshaft. If a stock engine was hitting in the high 140s, I knew the rings were shot, due to the oil being splashed and thrown onto the cylinder walls, which would seal the ring gaps. 150 would make me start saving money. I have seen numbers as high as 175psi, but they left a blue colored smoke trail on hard acceleration!

So, in your case, what do you have? Do you know anything about the internal side of the engine? Combustion chamber cc’s would be the one to know, along with stroke and cylinder size.
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67rustavenger wrote:
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Starbucket
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PostPosted: Sun Sep 19, 2021 2:11 pm    Post subject: Re: Compression readings seem high. Reply with quote

A big bore kit without shims will raise the comp. ratio along with fly cut rebuilt heads, so if you could contact the seller and find out what was done it would help. If it runs good without pinging run it.
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Bug53
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PostPosted: Sun Sep 19, 2021 6:46 pm    Post subject: Re: Compression readings seem high. Reply with quote

Starbucket wrote:
A big bore kit without shims will raise the comp. ratio along with fly cut rebuilt heads, so if you could contact the seller and find out what was done it would help. If it runs good without pinging run it.


Runs strong.
Doesn’t use any oil.
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