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08-02-2017, 09:09 PM | #1 |
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Trying to figure out if I have a High Compression Head
Hi All,
I have a 1930 Coupe with a fairly fresh engine. It was apparently "really" gone thru. Ungortunatly I did not get the paperwork re. this work when I got the car last summer. And it's not available - I checked. My question is: How can I tell if it's got a High Compression Head - will a simple compression test tell me? What should the "stock" compression be on a fresh engine w. a OEM head? TIA ... again Chris Union, ME |
08-02-2017, 09:45 PM | #2 |
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Location: Redondo Beach, CA
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Re: Trying to figure out if I have a High Compression Head
Fresh, stock engine ~ 65psig. Hi Compression... Higher. Depends on the ratio.
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08-02-2017, 10:15 PM | #3 |
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Re: Trying to figure out if I have a High Compression Head
I have a similar issue. I have no history on a great engine in a coupe i bought. The owner got it from his dad and can only remember years ago he helped put a "rebuilt" engine in the car. It does have a police head with the large "d" on it toward the front half of the head. 94 psi in all four cylinders. Wish i knew where it came from and if they still do engines. This one is great, but no idea what is inside it.
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08-02-2017, 10:18 PM | #4 | |
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Re: Trying to figure out if I have a High Compression Head
Quote:
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08-03-2017, 04:16 PM | #5 |
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Re: Trying to figure out if I have a High Compression Head
Do a compression check. Take the average value you get and divide by 15. That will give you a close approximation of your compression ratio. Stock heads have a 4.2 compression ratio.
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08-03-2017, 04:33 PM | #6 |
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Re: Trying to figure out if I have a High Compression Head
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Terry |
08-03-2017, 07:01 PM | #7 |
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Re: Trying to figure out if I have a High Compression Head
Using Terry's formula I get 88.2 lbs. for my engine. Using Al in NY i get 6.7 compression ratio. Somethings wrong here... Snyder said that head is 6.0:1 I'm getting 100 lbs. in all 4 holes.
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08-03-2017, 07:34 PM | #8 |
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Re: Trying to figure out if I have a High Compression Head
i get 67 on my stock head. no idea how fresh. I think stock can be up into the 80s. over that high comp in various state of wear.
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08-03-2017, 07:54 PM | #9 | |
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Re: Trying to figure out if I have a High Compression Head
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08-03-2017, 08:08 PM | #10 |
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Re: Trying to figure out if I have a High Compression Head
Also, should compression be done on a cold, warm or hot engine?
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08-03-2017, 09:47 PM | #11 |
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Re: Trying to figure out if I have a High Compression Head
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08-03-2017, 11:16 PM | #12 |
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Re: Trying to figure out if I have a High Compression Head
I always do them cold because when your engine wont run you wont be able to warm it up. So at that time you will be comparing apples to apples. also I always hear people say do the test with throttle open but I see no difference on the gauge.
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08-03-2017, 11:33 PM | #13 |
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Re: Trying to figure out if I have a High Compression Head
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08-04-2017, 12:09 AM | #14 |
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Location: Camarillo, CA and Pine Grove, CA
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Re: Trying to figure out if I have a High Compression Head
Sadly my compression tester is too small for my head. I guess I'll have to break the porcelain out of an old spark plug to test it.
I'm off the 405 in the SF Valley.
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1921 Runabout 1930 Tudor Early 1930 AA Speed costs money. How fast do you want to go? |
08-04-2017, 12:45 AM | #15 | |
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Re: Trying to figure out if I have a High Compression Head
Quote:
http://www.snydersantiqueauto.com/spark-plug-adapters My Snap-On compression tester has the Model A size included. |
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08-04-2017, 01:09 AM | #16 | |
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Re: Trying to figure out if I have a High Compression Head
Quote:
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1921 Runabout 1930 Tudor Early 1930 AA Speed costs money. How fast do you want to go? |
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08-04-2017, 07:57 AM | #17 |
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Re: Trying to figure out if I have a High Compression Head
Yep, it never made a difference for me either.
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08-04-2017, 10:56 AM | #18 | |
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Re: Trying to figure out if I have a High Compression Head
Quote:
But the one from Snyder's is threaded for a 14mm plug and my compression tester screws right in. Unless you have a el cheapo gauge with just a rubber tip, then that is a moot point. |
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08-04-2017, 02:07 PM | #19 |
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Re: Trying to figure out if I have a High Compression Head
I have been using my rubber tipped El Cheapo for over 50 years.
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1921 Runabout 1930 Tudor Early 1930 AA Speed costs money. How fast do you want to go? |
08-04-2017, 04:18 PM | #20 |
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Re: Trying to figure out if I have a High Compression Head
I used one of the o-ringed ends that comes with the cheap kits. had to hold it with two hand and have a helper run the starter.
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