Compression Test

[morto86]

Hey im about to buy a RB20DET motor with a compression test of 230. Not sure if that's good. I thoight stock would be around the 160 mark

[Ben C34]

Sounds wrong. That's too high.

[Missileman]

150-160 psi would be excellent

[morto86]

Yeah I thought so. The bloke is going to re do it and send photos of the results

[R.3.2.G.T.R]

done cold or warmed up?

[Missileman]

On a warmed engine with all sparkplugs removed, with accelerator fully depressed and a charge on the battery capable of cranking the motor at 300rpm.

RB20DE/T/26DETT

New = 170psi

Low Limit = 128psi

Max cylinder difference 14psi

...from engine workshop manual.

Edited November 13, 2013 by Missileman

[Missileman]

probably a good idea to unplug the cas and pull the fuse on the fuel pump too

[morto86]

I just got the reply 210. Cold. Does this mean the head has been shaved previously

[StevenCJR31]

Doubt it would make that much difference

That figure seems very "optimistic" at best

[Ben C34]

I just got the reply 210. Cold. Does this mean the head has been shaved previously

No as the comp ratio doesnt effect the compression test. it just ensures the rings and valves are sealing as they should.

[Missileman]

I just got the reply 210. Cold. Does this mean the head has been shaved previously

That seems wrong, do name the person/ workshop who did the test.

[Ben C34]

Maybe it was meant to be 120. thats more realistic

[Josh080691]

210 :// my newly built 25/30 only has 168 across the board.

[MagicMikeZ32]

I am guessing the gauge is way out of spec

[StevenCJR31]

Maybe it was meant to be 120. thats more realistic

Better hope not

130 is rebuild time

[morto86]

Def 200 all round with snap on gauge and warmed engine. With researsh this proves the comp ratio therefor is 10:1. As for the knob who said the comp is not relayed to the ratio. Actually write out the equation.

[Ben C34]

Def 200 all round with snap on gauge and warmed engine. With researsh this proves the comp ratio therefor is 10:1. As for the knob who said the comp is not relayed to the ratio. Actually write out the equation.

Settle down. explain to me how an engine when built has a certain compression test result, then when worn had a lesser compression test result? Did it's comp ratio drop? can you run more boost cos it has less comp ratio? NO. explain how comp ratio effects the comp test results please

[Ben C34]

please provide link to your researsh

[GTR-N1]

Anyone try LiquiMoly Engine Detox to remove residues/deposits and then find comp test improvement? Might be worth a go!

[KiwiRS4T]

Settle down. explain to me how an engine when built has a certain compression test result, then when worn had a lesser compression test result? Did it's comp ratio drop? can you run more boost cos it has less comp ratio? NO. explain how comp ratio effects the comp test results please

Well personally I would have though it was obvious that the higher the compression ratio the higher the expected compression test result . The value of the compression test for measuring wear depends on knowing the original compression so as above if the stock factory figure was 170 psi then yes 130 psi indicates a lot of wear which can be confirmed with a leakdown test. My engine had 130 psi compression when built because of the choice of pistons (CR about 8:1) and leakdown test is within limits at 5%