Hi all,
Used a compression tester of a friend to check the compression of my engine and did all the steps as mentioned except for fully depressing the accelerator pedal to open the throttle. My compression numbers are shown below;



I have heard that you need to fully open the throttle when Doing a test. How much could the numbers above change between a closed throttle and an open throttle test

 

Do the test again and find out

 

In theory they might increase a little. In practice it's tough to say how much without testing on your setup.

 

+1 difference is probably not going to be very big

 

Thank you for the replies. Will redo the test soon and compare the results

 

Re-do the compression test. You're supposed to test at wide open throttle, and with the engine warmed up to operating temperature. Compression numbers will be lower at closed throttle.

FWIW, I own an RCT5.x rotary compression tester, and I've tested my 13BT at closed & wide open throttle - I saw about a 8~10 psi improvement (higher) compression readings at WOT.

 

It absolutely matters and changes the results. With the throttle plate closed your asking the engine to pull and overcome the vacuum presented by not allowing air past the throttle plate, this slows things down. Typical we see an increase of .4 kgf/cm2 with throttle WOT vs closed. Everything has to work harder, your RPMS will also struggle more.

 

If your goal is to prove that the engine is good you have already proven to have even compression and at around 100psi it's not "low" compression.
By testing again you will get a more accurate number that will be higher, but if you just wanted to verify your engine is good you've already done that.