Healthy Compression For Rb26dett ?

[legend01]

So I bought an R32 gtr can't help myself ,the gtst is just to dangerous on the streets way to much power even on low boost for a 2 wheel drive so its going back to stock to be sold of .

Now I ve started playing with the gtr just pulled it down to check the health of the engine and did a search to try and find a healthy compression ratio for an rb26 but it ranges from 80psi to 160 psi and all say engine is fine , well damn thats alot of differance .For the most part the cars stock at one stage I'd say it had an aftermarket boost controller on it but it still has the restrictor on the factory boost control line ,oil pressure is good no water leaks so atm its looking good .

Had one problem with it when I reved it to 8000rpm it blew the dipstick part way out which didn't look good but you could rev it to 6000rpm with no problems so had a bit of a check and found someone had cable tied an electrical junction to the hose that ran to the pvc valve and flatened the hose .well hoping thats the problem havn't had a chance to check that yet as pulled the starter motor out (major operation just doing that )because it sounded a bit iffie, rather fix it now than latter on the side of the road.

So if anyone has any info on any of this please feel free to comment and I'm gonna try and leave it standard though I don't much like my chances already thinking turbos ,Damn my need to fiddle

Cheers Peter

[siddr20]

shouldnt compression be consistant across all cylinders?

[legend01]

thats not my compression ratio thats what they varied from in the posts i searched and that was many posts just to find what was considered a healthy compression level

[wolverine]

hi pete

i would think around 140-150psi would be healthy.

[GTR1993]

generally don't look at the actual number, because it can vary between testers and motors, look at variation between cylinders, closer to each other the better, around 15% is probably still ok, but not much more.

I think the manual says its around 160 for a stock 26 and gives a tolerance.

For example my RB26 is rebuilt and it seems its used lower comp pistons (i dont know why you want this but i didnt build the motor bought like this) but was 120-125 across all cylinders. Also blowing a dip stick out isnt a good sign and PCV isnt working at full throttle only light cruise...

[legend01]

Gday Andrew

Yeah was thinking along those line's myself, got no 6 cylinder on the gauge b4 I pulled the starter motor on a slow crank it read 150psi by slow crank I mean like a flat battery and that was with all plug's removed so thought that was good for a start .the service book says to cold crank at about 300rpm which I was nowhere near so keen to see what the other 5 come up with

Hi Alex

The book does give a compression ratio but thats on new engine ,I want the get a rule of thumb on an engine thats done quite a few k's so that why i searched the threads but as I posted some said there engine was good with 80psi and others 100 or 125 ,differnt people had differing ranges all the way to 160 psi which is close to new

People build a low compression engine from new as it allows the to screw more boost into them, a good example are the rb30de blocks with the rb25 or 26 heads on the there comp ratio is only about 7.25 or something like that allows massive boost.The PVC valve is not what I was talking about whether it works on high or low rev's but the vacuum hose leading to it was cable tied so tight it wasn't allowing it to recirculate engine fumes so my resaining was it was building up back pressure in the engine block and that pressure needs a release hence pressure pushing out the dip stick well thats what im hoping thanks for your imput its food for thought

Cheers Peter

[djr81]

Well 80 psi is dead or atleast in cardiac arrest.

A good motor should give you a figure or 150psi or better.

[GTR1993]

Oh i knew why people reduce compression ratio, but these days with good fuel and good tuning there should really be no need

I agree that 80 is really too low, what did yours come up as?

[legend01]

I still have to do the, test pulled the starter motor because it sounded sus and wasn't turning engine quick enough so will do complete test when I get it back

[alexk]

don't worry about the gauge reading so much because who knows when pressure gauges get calibrated and if calibrated properly (should be done against a reference manometer). If the results are consistent then you should be ok.

[legend01]

Did compression test today came up good I think

1.....165psi

2.....150psi

3.....160psi

4.....165psi

5.....160psi

6.....150psi

[GTRsean]

125PSI min in the manual.

160 normal

171 new

no more than 14 psi difference between highest and lowest readings.

Quoting from service manual.

Cams, thottle open or not and crnking speed all make a difference as well as cold or hot.(should be done at operating temp).

[benm]

Can't help yourself can you, even when it's working fine you still have to muck about with things

[wolverine]

i'd say you bought a sack of shit.

if you want to park it in my garage to get rid of it i'd be happy to help you out...

[legend01]

I know I know can't help myself its bad ,I was just gonna check the plugs and it snowballed,compression, starter motor, I had to hurry up and put it back together, was thinking of pulling the head of and porting it or maybe even a rebuild with forgies I gotta learn to leave things alone DAMN!!!!!!!

[legend01]

which one the red one or the white one