#1  
Old 08-04-2020, 08:53 PM
mike76 mike76 is offline
Senior Chief
 
Join Date: Oct 2011
Location: Cleveland,Ohio
Posts: 300
Default Rhoads V-max and compression test

I heard some time ago that doing a compression check using regular Rhoads lifters will not give accurate readings. Don't know if this is so. I am installing a set of the V-max lifters and am wondering if they will skew my readings. Thx, Mike

  #2  
Old 08-05-2020, 02:06 AM
Will Will is offline
Ultimate Warrior
 
Join Date: Dec 1999
Location: Pugetopolis
Posts: 5,297
Default

Rhoads will of course bleed down a lot more than regular lifters at cranking RPMs, thus shortening the cam duration and increasing cranking compression numbers as compared to regular lifters.

So, in that sense they will skew the pressure numbers higher. But usually a compression test is done to compare the cylinders to each other in order to find a problem. If you have a blown gasket or burned valve or broken ring, you're still going to see numbers that are lower in the affected cylinder(s) as compared to the others.

__________________
----------------------------
'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 350/4-speed Black on Black, mix & match.
  #3  
Old 08-05-2020, 07:21 AM
Cliff R's Avatar
Cliff R Cliff R is offline
Ultimate Warrior
 
Join Date: Nov 2000
Location: Mount Vernon, Ohio 43050
Posts: 17,972
Default

You are likely to get more accurate readings using Rhoads lifters than many of they hydraulic lifters out there currently being sold for these engines.

Rhoads lifters are designed to provide a very precise and controlled leak path past the plungers. Instead of leaking down in 120 seconds, for example, they may be close to 20 seconds. As mentioned this will reduce duration slightly and readings would be a little higher than a slower bleed lifter. With the V-Max variety if you are setting them with a feeler gauge between the valve tip and rocker arm with the plungers bottomed out the leak down potential would be very close and make readings even more accurate.

If you want to get your feelings hurt test some of these hydraulic lifters currently on the market. Many are all over the map for plunger to body tolerances and leak down rates. Was just having this discussion a couple of days ago with a very experienced engine builder who REFUSES to use Morel HR lifters for this reason, and they are supposed to be USA made parts. Imagine where the "offshore" stuff is at?........

__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran!
https://cliffshighperformance.com/
73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -4. The time now is 08:03 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017