Good afternoon Forum Chums,
I am soliciting your input as to what I should be seeing in terms of compression on my model T…… I am on the road and I don’t have any of my manuals with me…… I plan to do the compression test when I get home in a couple of days……. I’d love to hear your thoughts on what I should have in terms of what’s good?
what’s OK?……and what is a problem!….. As always, appreciate your help and many thanks!
Cheers!
Compression
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Flyingpiper59
Topic author - Posts: 140
- Joined: Wed Jul 20, 2022 6:02 pm
- First Name: Edwin
- Last Name: Douglas
- * REQUIRED* Type and Year of Model Ts owned: 27 Tudor
- Location: Millport, PA
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J1MGOLDEN
- Posts: 1233
- Joined: Sun Jan 06, 2019 5:39 pm
- First Name: James
- Last Name: Golden
- * REQUIRED* Type and Year of Model Ts owned: 1926 Model T Roadster
- Location: Bowie, MD
Re: Compression
The formula is Sea Level air pressure (about 14.5) times the compression ratio, which is close to 4.
That equals 58 psi.
A Model T engine will start and run with only 40 psi, with very little power.
50 to 60 psi is good to excellent, unless you have Domed Pistons or a High Compression Head.
You can only have one or the other, but the Domed Pistons should give 60 to 75 psi.
The High Compression Heads can give you 90 to 120 psi.
That equals 58 psi.
A Model T engine will start and run with only 40 psi, with very little power.
50 to 60 psi is good to excellent, unless you have Domed Pistons or a High Compression Head.
You can only have one or the other, but the Domed Pistons should give 60 to 75 psi.
The High Compression Heads can give you 90 to 120 psi.
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speedytinc
- Posts: 4729
- Joined: Fri Feb 12, 2021 12:24 pm
- First Name: john
- Last Name: karvaly
- * REQUIRED* Type and Year of Model Ts owned: 14/15 wide track roadster. 23 touring, 27 roadster pickup, 20ish rajo touring
- Location: orange, ca
- Board Member Since: 2020
Re: Compression
A fresh motor should be 60# consistent. I had an old motor that ran ok with 50#. I would be unhappy with less.
I was surprised to see some folks running with 40# & happy.
I was surprised to see some folks running with 40# & happy.
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Art M
- Posts: 964
- Joined: Wed Jun 19, 2019 12:57 pm
- First Name: Art
- Last Name: Mirtes
- * REQUIRED* Type and Year of Model Ts owned: 1923 Touring
- Location: Huron, Ohio
- Board Member Since: 2016
Re: Compression
At 40 psi. the car will run fairly well, but a little slow starting At 60 psi the engine performs much better. This is what I experienced. A valve grind got it to 50. New rings brought it to 62. Standard head. 23 touring car
Art Mirtes
Art Mirtes
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Flyingpiper59
Topic author - Posts: 140
- Joined: Wed Jul 20, 2022 6:02 pm
- First Name: Edwin
- Last Name: Douglas
- * REQUIRED* Type and Year of Model Ts owned: 27 Tudor
- Location: Millport, PA
Re: Compression
Thank y’all