What Is Healthy Compression For 4K?

[Kirill]

Hey guys just did compression test on a warm engine with all plugs out and gas pedal to the floor, results as follows:

 

1. 190 psi, or 13 bar

2. 180 psi, or 12.5 bar

3. 195 psi, or 13.5 bar

4. 190 psi, or 13 bar

 

Are these a little high? I remembr doing the same test on old charade and getting 140s

[Banjo]

Hi Kirill,

A 4K with 100K+ klms usually gives 150 - 160 PSI. As long as the readings are reasonably close together, then all is well. Yours are a bit high, so maybe the head has been shaved at some time. You can usually pick up whether the head has been shaved, by the depth of the "dipple" in the head, behind the dizzy, where the the head surface meets the block. The other possibility is that the 4K has been bored & O/S pistons fitted at some time. That will also increase the compression.

 

Cheers Banjo

[ke70dave]

High? noone complains abotu compression results being high!

 

Essentially if they are all within about 5-10% of each other and above 150ish the engine is doing well. The big thing is them all being close together though.

 

Do you know the history of the engine? perhaps it has slightly higher compression than a standard engine.

 

edit: and Banjo beat me

Edited August 21, 2013 by ke70dave

[Kirill]

Yeah I know that they all should be close and i guess they are apart from cylinder 2. The history of the car is as follows; My mates grandmother got it brand new in 1978 from Don Rogers (dodgy car dealer back in the day). Then she proceeded to own it until last year when she gave up get licence at age of 90. Then my mate took over for a year, having done zero maintenance.

 

I had a GSXR 1000 with hi comp JE pistons that I tested and that got 190. Did it with the same gauge. Maybe over time the spring in the gage got weak. The car has 235000 on the dial. I doubt an old lade would of gotten the motor rebuild and head shaved LOL

[Banjo]

Hi Kirill,

Dave's right about the 5% -10% max variation. Your max variation is 15 PSI between lowest & highest, which is about a worstcase 7-8% variation. Spot on ! I'd say your engine is pretty healthy, compression wise, which means rings, & valve seats are all pretty good.

 

I picked up a second hand 4K a couple of years ago, as part of a 5 speed G/Box & 4K combo, and the guy couldn't be bothered seperating them. I was only really after the 5 speed G/Box, which was out of a KE70. I got both for the cost of a the gearbox. When I did get to use the 4K recently, I was astounded how good it was. Taking the head off to do a general decoke, I found the engine had been fully reconditioned not that long ago.

 

Sometimes, you can be very lucky.

 

Cheers Banjo

[Banjo]

That's a remarkable result for a 4K with 235,000 klms on the dial. I guess your mates grandmother, didn't leave rubber at the lights !

[ke70dave]

The other thing is the accuracy of your compression tester. One of those $30 super cheap auto jobs are probably +/-10% at best anyway.

 

If you get 160/155/165/60......that is when you worry!

[Kirill]

Hi Kirill,

Dave's right about the 5% -10% max variation. Your max variation is 15 PSI between lowest & highest, which is about a worstcase 7-8% variation. Spot on ! I'd say your engine is pretty healthy, compression wise, which means rings, & valve seats are all pretty good.

 

I picked up a second hand 4K a couple of years ago, as part of a 5 speed G/Box & 4K combo, and the guy couldn't be bothered seperating them. I was only really after the 5 speed G/Box, which was out of a KE70. I got both for the cost of a the gearbox. When I did get to use the 4K recently, I was astounded how good it was. Taking the head off to do a general decoke, I found the engine had been fully reconditioned not that long ago.

 

Sometimes, you can be very lucky.

 

Cheers Banjo

Whoa, yeah you got lucky there mate! I once got an N12 pulsar (worst car in the world in retrospect) of some Aboriginals on my street. I just wanted parts off it for my clunky N12. Towed it home, open the bonnet and this thing had extractors, new alternator, new water pump and recond head! I was canibalising that car all through my uni degree and dint spend one cent on spare parts for about 4 years :P :P

[Banjo]

Love it Kirill ! That's better than finding $ 100 under the back seat !

 

Cheers Banjo