Compression Tester Needed

renaissance man · #1 (**permalink**) 11-08-2001, 06:46 AM

Anyone have a Compression Tester that they would care to share this weekend? I'm not sure of my compression??? Think it's somewhere between 9.0 and 9.5 to 1.

I'll supply the beer!

Gregg(What's his name)? · #2 (**permalink**) 11-08-2001, 10:22 AM

Ren,

I saw you post at 0546 man your not in the AIr Force any more. sleep in and stuff.

Let me check I think I might have one. I'll let you know tonight. Hell it's been so long since I've used it I don't know if it made the move downh.

Gregg H

ERA600hp · #3 (**permalink**) 11-08-2001, 01:53 PM

I've got a compression tester!!

renaissance man · #4 (**permalink**) 11-08-2001, 02:00 PM

Then bring her down and have a homebrew!!!

Joe Z · #5 (**permalink**) 11-08-2001, 05:46 PM

Hey Ren-Man,

Thanks for having us over last weekend. Lena and I had alot of fun.

Sorry to bear bad news, but I don't believe that you can actually get your compression ratio from a compression test. I know because I've already tried it. The test will only tell you maximum cylinder pressure in PSI. Valve timing and other factors skew the test greatly. Compression ratio can be calculated by the pencil and paper method if you know the chamber size of your heads, thickness of your head gasket, your bore and stroke, and piston head design. I might even research the formula for a jar of your famous hot sauce..........ha ha ha

BTW, I think I have a compression tester around here also. I'll look around for it.

Thorin · #6 (**permalink**) 11-08-2001, 06:07 PM

If everybody else lets you down, give me a holla, I will bring mine down

David Lowell

jdeatsch · #7 (**permalink**) 11-08-2001, 06:14 PM

Dave,

While I'd love to 'bring my compression tester' or for that matter 'leakdown tester" over to help you out, it won't do much good.

We CAN measure the compression in each cylinder and that will tell us the condition of the top end of the engine generally.

We will have to have more information to give you the 'compression ratio' which is a function of the volume of the combustion chamber when the piston is at Top Dead Center.

Unfortunately we cannot do that without either the info on the engine when it was built OR tearing it down.

Suffice it to say, if the compression is good, and it runs well, then you're good to go methinks. Besides, with a Cobra, just how much POWER does one need? Is it EVER enough?

Jim (not an owner or builder YET, but soon)

anil · #8 (**permalink**) 11-09-2001, 12:11 AM

What they said.... compression <> compression ratio. However, the real question is WHY do you want to figure out your compression ratio?

BTW, I also have a compression tester if you still need one and I know where it is since I used it last week.

renaissance man · #9 (**permalink**) 11-09-2001, 11:22 AM

Only reasons that I want to know are:

1. Curiosity
2. What gas to use???? 87, 89, 93.....

I think it's either 9.3 : 1 or 9.5 : 1

If I had an accurate reading I could also get a Desktop Dyno reading for the engine.

BMMILLER · #10 (**permalink**) 11-09-2001, 11:53 AM

Dave:

Try this link. It is a calculator which might help.

Good luck,

Blair

http://www.ford-trucks.com/articles/...sion_Ratio.zip

anil · #11 (**permalink**) 11-09-2001, 12:50 PM

If it's either 9.3 to 1 or 9.5 to 1, and (assuming) you're using iron heads, then I highly recommend you stay with 93 octane. You should be able to get by with less, but as we all probably know, gas is not perfect and I don't think you'd appreciate the detonation, which you probably couldn't hear anyway.

Also, compression ratio alone will not tell you what fuel to use -- smoothness of surface and sharp points will cause hot-spots that may require higher octane fuel.

Besides, it's a Cobra -- how do you think it would look if you pull up at a gas station and reach for the 87-octane pump?!

-Neil.