Cranking pressure 130? - Team Camaro Tech
Engine General Engine Discussion.

 
LinkBack Thread Tools Display Modes
post #1 of 13 (permalink) Old Apr 30th, 04, 02:16 PM Thread Starter
 
Join Date: Aug 2001
Posts: 409
Post

I just did a compression test on my 383 and its only at about 130-135 on all cylinders. This doesnt seeem right at all with my compression ratio. Maybe my starter is not fast enough? What rpm should I be cranking the engine over to get an accurate reading? I figured my engine should have atleast 180 pounds or so.
nitrous383 is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old Apr 30th, 04, 02:30 PM
Team Member
John
 
JohnZ's Avatar
 
Join Date: Sep 2000
Location: Washington, Michigan USA
Posts: 7,728
Post

Is it warm and do you have the throttle blocked wide open while cranking? Getting 4 or 5 compression strokes before taking the reading? [img]graemlins/thumbsup.gif[/img]

JohnZ
CRG
JohnZ is offline  
post #3 of 13 (permalink) Old Apr 30th, 04, 02:39 PM
Senior Tech
Matt Jones
 
Join Date: Jan 2002
Location: Renton, WA USA
Posts: 2,765
Post

You know, what I learned about that is that it's relative. If you had 180 before and now you have 130, then you may worry.

For example, I did my pressure test on my 412, and it read 265PSI ! I bought a new gauge, and it was down to a normal 220PSI.

So, I would borrow another gauge and see what it says.

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
Silver69Camaro is offline  
 
post #4 of 13 (permalink) Old Apr 30th, 04, 04:18 PM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
Post

Your cam will have a big impact on static compression readings as well. And ditto on blocking the throttle open.

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
dnult is offline  
post #5 of 13 (permalink) Old May 1st, 04, 12:23 PM
Senior Tech
Eric
 
Join Date: Dec 2000
Location: Kentwood, MI
Posts: 8,097
Post

Mine reeads right around 215-220 psi but that is with my gauge. Unless a gauge is bad, it should be fairly close to reality . . .

E85 racer and E85 carb builder

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
Eric68 is offline  
post #6 of 13 (permalink) Old May 1st, 04, 01:27 PM Thread Starter
 
Join Date: Aug 2001
Posts: 409
Post

Well, thats what I thought. I figured mine should be atleast 180, so 130 doesnt seem right at all. I can only think of a few things that are causing this.
1) The gauge is bad (though unlikely its a new MAC)

2) I installed my cam off by a tooth or two and retarded the cam timing

3) My timing chain is toast and the stretch has retarded the cam timing a bunch. How much would it have to be off to make a 60 psi difference in cranking pressure?

I will be checking again with the carb wide open and a different gauge asap.
nitrous383 is offline  
post #7 of 13 (permalink) Old May 1st, 04, 01:54 PM
Senior Tech
Matt Jones
 
Join Date: Jan 2002
Location: Renton, WA USA
Posts: 2,765
Post

The timing chain would have to be pretty far off. When I installed my cam, I wanted to see how the cranking compression changes as I advance and retard the cam. What I found was that moving the cam 4* either way changed the compression by 10-15PSI. Not a whole lot.

If that were the case, you'd have to be off by 20* or so.

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
Silver69Camaro is offline  
post #8 of 13 (permalink) Old May 1st, 04, 03:24 PM
Senior Tech
 
Join Date: Feb 2001
Location: Concord Cal. USA
Posts: 2,664
Post

It ran 114 in the quarter, right? There can't be a whole lot wrong unless the performance has deterated since then.
oger is offline  
post #9 of 13 (permalink) Old May 1st, 04, 05:28 PM
Senior Tech
Joe
 
Join Date: Jan 2001
Location: Benicia CA
Posts: 1,281
Angry

Mike, you have mail

Joe G

69 Coupe; ZZ430; TKO600; 3.55 posi; 13" Baer 4 wheel discs; 17" Billet Specialties wheels; Hotchkis/Koni rear; Ride Tech front; Classic AutoAir AC and power windows cuz I'm old and lazy!
Joe G is offline  
post #10 of 13 (permalink) Old May 2nd, 04, 08:21 AM
Senior Tech
 
Join Date: Feb 2001
Location: Concord Cal. USA
Posts: 2,664
Post

Thanks Joe
oger is offline  
post #11 of 13 (permalink) Old Nov 23rd, 04, 09:06 PM Thread Starter
 
Join Date: Aug 2001
Posts: 409
Angry

I finally did another compression test with a brand new gauge, I also changed my method. I wired the carb to full throttle, pulled the plugs and hooked up a battery charger. It spun much better than last time and I got 198-200psi on all cylinders, that sounds better than 130. I was amazed there wasnt more than 2psi difference between all cylinders, which is great.
nitrous383 is offline  
post #12 of 13 (permalink) Old Nov 24th, 04, 03:03 AM
Senior Tech
Eric
 
Join Date: Dec 2000
Location: Kentwood, MI
Posts: 8,097
Post

Thanks for the update. Having the engine throttled when doing thetest is most likely what made the numbers low. 2 psi is pretty consistent.

E85 racer and E85 carb builder

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
Eric68 is offline  
post #13 of 13 (permalink) Old Nov 25th, 04, 04:36 PM
Senior Tech
 
Join Date: Jan 2001
Location: skiatook, ok
Posts: 3,692
Post

200 psi sounds about right. My 388 has 1 point less compression and the same cam, and cranks 185psi.

"This is not a cheerocracy...I make the cheercisions around here"
travis is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome