Compression ratio from compression test?

From famous pros to weekend warriors, our friendly members will help answer your tech questions.
User avatar
TurboDiverArt
Posts:18
Joined:Mon Sep 10, 2007 9:16 pm
Compression ratio from compression test?

Postby TurboDiverArt » Thu Sep 13, 2007 10:59 pm

Hi All,

I have what I think is a relatively simple question. Although I know not too accurate, I’m trying to get an idea of the compression in my engine. I just bought the car turnkey and have not really done much with it other than take it to the track a few times. I know the engine was originally built to run on methanol so it’s got some compression in it. I did a compression test on the engine while hot. The numbers across all cylinders were between 220 and 230 PSI. Can anyone give me an idea of what the effective compression ratio is?

Thanks,
Art.
Art Paltz
230" Undercover, 468ci stock block, 7.840@170.14

greenracing
Posts:782
Joined:Thu Mar 02, 2006 12:50 pm
Location:NE Ohio

Postby greenracing » Tue Sep 18, 2007 8:45 am

Since C/R is based solely on volume calculations, and the compression test numbers you get are based on how well things are sealed up, I don't think that you can reliably convert from one to the other.

User avatar
SLICK VIC
Posts:1652
Joined:Mon Mar 27, 2006 12:39 am
Location:Washington State
Contact:

Postby SLICK VIC » Wed Sep 19, 2007 12:41 am

You would need to know the specs on the motor.
cylinder head cc, piston dome cc, deck ht,
gasket thicknes & diameter, bore, stroke..etc.etc..

So if you ever tear the motor down and find the info
listed above use this link below to figure your C/R

http://www.fuelinjectionenterprises.com/compression.htm

Vic
http://www.vicmillerracing.com/
SMOLDERY SMOKEY BURNOUTS TO YOU ALL

User avatar
TurboDiverArt
Posts:18
Joined:Mon Sep 10, 2007 9:16 pm

Postby TurboDiverArt » Wed Sep 19, 2007 5:52 am

Since C/R is based solely on volume calculations, and the compression test numbers you get are based on how well things are sealed up, I don't think that you can reliably convert from one to the other.
I definitely agree you there. I just want to try and get a general idea if possible. The engine's running great so there's no real reason to tear it down.

Art.
Art Paltz
230" Undercover, 468ci stock block, 7.840@170.14

greenracing
Posts:782
Joined:Thu Mar 02, 2006 12:50 pm
Location:NE Ohio

Postby greenracing » Wed Sep 19, 2007 8:10 am

The engine's running great
Then the CR must be 'just right' 8)

User avatar
pro70z28
Posts:11682
Joined:Fri Feb 24, 2006 12:17 pm

Postby pro70z28 » Wed Sep 19, 2007 8:13 am

can you find out who built the engine? Follow the paper trail backwards.
15th Annual DRAGLIST Nationals Sometime in 2020. Somewhere in the USA.

User avatar
stimpy
Posts:1129
Joined:Sun Jul 23, 2006 12:33 am
Location:MP 127 on I-80

Postby stimpy » Wed Sep 19, 2007 7:46 pm

you could do it the nascar way and pump the motor or fill the cylinder up with a fluid to measure the volume at tdc and bdc , but the hard part is getting all the fluid out it would be a guesstamite .
the Groom that went Vroom At DLN IV

User avatar
Eric David Bru
Posts:505
Joined:Thu Sep 07, 2006 1:32 pm
Location:The Skunk Works
Contact:

Postby Eric David Bru » Wed Sep 19, 2007 10:17 pm

you could do it the nascar way and pump the motor or fill the cylinder up with a fluid to measure the volume at tdc and bdc , but the hard part is getting all the fluid out it would be a guesstamite .
Are you sure that isn't CID not compression ratio?

EDB
Outlaw Eric :cool:

User avatar
jim sanders
Posts:8740
Joined:Fri Feb 24, 2006 8:54 am
Location:St.Louis Mo.
Contact:

Postby jim sanders » Wed Sep 19, 2007 11:16 pm

The engine's running great
Then the CR must be 'just right' 8)
I'M WITH Mr.Green.. run it unti;ll you take it apart.
GOOD TO GO !!
Uncle Curt Wasson album
[url=http://www.glowfoto.com/users2/gatorgumbo][img]http://www.glowfoto.com/siteimages/linktogallery.gif[/img][/url]

User avatar
stimpy
Posts:1129
Joined:Sun Jul 23, 2006 12:33 am
Location:MP 127 on I-80

Postby stimpy » Wed Sep 19, 2007 11:18 pm

compare the volume at tdc vs the volume at bdc should give you the ratio and yes its a way of checking cid too but you use total volume .
the Groom that went Vroom At DLN IV


Return to “Tech Questions”

Who is online

Users browsing this forum: No registered users and 11 guests

cron