vr4 pistons compression test

oggy · Post by **oggy** » Sat May 30, 2009 3:30 pm

g'day all!

just a quick question, for those of you running vr4 pistons with SOHC head. what compression test results (warm) are you getting?

cheers :beer

docile · Post by **docile** » Mon Jun 01, 2009 1:04 pm

I remember reading compression goes down to 6.8 or something like that so I think you should be getting 120psi or therabouts on a fresh build.

oggy · Post by **oggy** » Tue Jun 02, 2009 8:17 am

cool. i knew that they comp ratio went pretty low but i didn't know that low! 20psi here i come :pimp

mines got 115psi in all 4.

cheers! :D

redzone · Post by **redzone** » Tue Jun 02, 2009 5:26 pm

it goes to 6.8 with a 2.4 head, 7.5 with a 2.0 jet valve type head, havnt measured a T head yet. somewhere around 120 ish would be good i'd say for a 2.0 head.

orange car with VR4 type JE's and 2.4 head had 100psi comp on a fresh motor, and hasnt changed in 4 years. starts fine, power comes on at 3000 rpm :)

quest · Post by **quest** » Wed Jun 03, 2009 10:01 pm

shouldn't camshaft choice be mentioned ? or no difference to comp test readings ?

redzone · Post by **redzone** » Thu Jun 04, 2009 6:48 am

yes it will make a difference but its pretty rare for people over here to change cams..

thrash · Post by **thrash** » Thu Jun 04, 2009 10:26 am

camshaft will only make a difference to the number that the gauge reads.. but all cylinders being roughly the same reading is the more important thing isn't it?

docile · Post by **docile** » Thu Jun 04, 2009 1:43 pm

quest wrote:shouldn't camshaft choice be mentioned ? or no difference to comp test readings ?

Yes, intake closing degree. A more accurate test is a leak down test rather then comp test.

I should mention a cr of 6.8 will always make less power then the same motor with a cr of 8.5 so if you can avoid it, please do so.

quest · Post by **quest** » Thu Jun 04, 2009 10:03 pm

yes, but they're comparing compression gauge readings, relative to compression ratio. A longer duration cam will lower/skew that.

pretty rare for people over here to change cams..

From reading here, u seem to have at least 2 excellent low priced proven regrids from Wade & Camtech. Why would one who pursues performance, go as deep as pistons but stick with the stock cam ? that is odd.

redzone · Post by **redzone** » Thu Jun 04, 2009 10:27 pm

usually pistons are a necessity, cams are a power thing, usually not done until you start really throwing money at em :)

iXNAY · Post by **iXNAY** » Fri Jun 05, 2009 5:06 am

cams are easy to change at any time really

JD_Stazza_Brendan · Post by **JD_Stazza_Brendan** » Fri Jun 05, 2009 6:57 am

quest wrote:Why would one who pursues performance, go as deep as pistons but stick with the stock cam ? that is odd.

Usually anything above 15psi will kill our stock pistons due to bad ring land design.

quest · Post by **quest** » Sat Jun 06, 2009 4:54 am

a good reasonable priced cam seem like a very wise addition for such a minimal cash outlay. You won't have to run as much boost to make the same power with a cam.
With boost built up in the intake, that "restriction" heating things up, surely not doing those ring lands any favours

oggy · Post by **oggy** » Sat Jun 06, 2009 8:38 am

reason i went to forged vr4 pistons is because at 18psi my cast hypertec pistons didn't really like it too much...... ended up being able to pull chunks of ring lands out of 1 piston and the other had a few cracks in the lands. 7,500km old motor too!

i do also have a ported head, i think with some combustion chamber smoothing, and roller rockers with a billet cam from RPW. :) which would affect readings, but i was mainly after a vague indication.

i was mainly doing the comp test to see if cylinders were even, but i was a little worried when comp came out so low. but not now :D

OLD FART · Post by **OLD FART** » Sat Jun 06, 2009 9:03 am

My ported & polished & cc'd head now resideing in sunny downtown Rocky had 50.4 cc chambers before it was recoed and a skim to ensure a true surface .You can do the math if you have the negative volume of the pistons +the hg volume

Austarion

vr4 pistons compression test

vr4 pistons compression test

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