Don Terrill’s Speed-Talk

Does any of you have any experience using a P&G or similar engine displacement gauge? Are they accurate, hard to use,etc.? I have heard you can check the same engine three different times and get three different readings. Any info will be appreciated.

You can check 3 times and get three different readings but if you do the correction the right way you will read within about 1%. I've also been told that if it reads big it IS big!

If the engine is cold when using it they give pretty close numbers. If the engine is hot/warm and the temp correction is used it throws them off and they can read several percent (or more) low. I've never seen one read high anytime.

Rick

Agree with the above....very close when motor is cold..
when hot have to do the math for the temp.
The ones I have been around are always with in 2ci.

The big deal IMO is you have to watch out for them Hi TQ mini staters..
some times it will blow the piece right out the top of tube. You will have
a learning curve on using it...I would tell you to kinda hold you hand over the tube
so nothing flys out and would not be a bad idea to order extras,,I have seen a newbe
run one and they spent 15 min. looking for the ring that flew out...lol

overtime wrote:Does any of you have any experience using a P&G or similar engine displacement gauge? Are they accurate, hard to use,etc.? I have heard you can check the same engine three different times and get three different readings. Any info will be appreciated.

Using the P&G, in the right hands, will hit the cubic inch with in a half a cubic inch every time. doesn't matter what starter is used. the critical thing are: all plugs removed, rockers for cylinder beeing tested removed,tube properly lubed, and temp of the air in bore only, thermometer can not touch any metal.

Sam is correct. I have done hundreds of NASCAR and DIRT cylinder volume checks. The temps are critical as well as the sealing of the tube in the spark plug adapter. You also need to remove the tube every time you test because leaving it in the head only heats up the metal adapter thus heating the air entering the measuring column and you don't want that or engine reads big.

My tech usually included checking compression on the same cylinder with a Katech Whistler so the actual compression was calculated on what that cylinder was. If the numbers came out bad on either test race had option to pull cylinder heads for mechanical measuring.

Roughly 200+ tests I only had 3-4 guys tear down for confirmation and all of them were correct with the mechanical testing. As I recall, one was Freddie Querry, Mike Garvey, Wayne Willard and Scott Bloomquist. The carbon in the combustion chamber in each case was responsible for the reduced size in chamber kicking it out on the Whistler.

Thanks for the info. I'm about to inherit one of these instruments. Sounds as if they will work as intended if you take time to use them properly.