Valve Seat Pressure For Rb20/25/26

[Cubes]

Hi ppls,

I've had my valve springs replaced and was told with the standard RB25 N/A valve springs I had seat pressure of 10pounds across the board.

After the valve springs were replaced this jumped to 35-40pouinds (was vague).

Would any one know what the factory seat pressure is supposed to be for the RB20DET, RB25DET or even Rb26DETT?

He was quite happy with the seat pressure its now at.

What do you all think? Whats considered 'good' or 'over the top' seat pressure for an RB DOHC head?

Thanks ppls.

[Adriano]

Doesnt sound right, 10 pound iassuame, not psi, just doing a toyota turbo head, and it has 35pound which is too low for turbis, hoping to get up to 55lb with performance springs.(10lb is about 4kg)

[Cubes]

I'd say it was 10 pound. It was valve floating with anything more than 4500rpmish and 10pounds of boost.

Hrmm so now its 35pound and possibly still not enough. :S

He was a little vague when I spoke to him though. He said its much better 35 to 40 pounds. Not psi like I repeated.

Any idea what RB25DET's std or Rb26DET std run?

[Adriano]

I'd say it was 10 pound. It was valve floating with anything more than 4500rpmish and 10pounds of boost.

Hrmm so now its 35pound and possibly still not enough. :S

He was a little vague when I spoke to him though. He said its much better 35 to 40 pounds. Not psi like I repeated.

Any idea what RB25DET's std or Rb26DET std run?

It could be, but the head shop(the one sydneykid uses) siad 35lb wasn't enough, at 10lb, boost pressure would be holding the valve open(assuming the valve it 1sq inch), nothing to close it, but im no expert, sounds like we have a mix up in measurements. The head shop also said that hydrauloic lifters need more spring pressure as they have to move the weight of the lifter.

[Cubes]

Ahh well I'll find out. :S

Thanks.

I went with SK's oil feed recommendation of blocking off the rear and dropping a 1.5mm up front. See how we go.

[Cubes]

In the manual the GTR springs are supposed to see 24kg (52.9pounds) at installation load which is the spring length compressed to 35mm. Not sure if installation load represents seat pressure? :S

Ahh well as the saying goes. The poor/tight man pays twice. lol

I dropped a set of GTR springs in my RB25 head; the gtr springs are slightly taller than the gtst springs so they should provide more seat pressure than when sitting in a GTR head.

Hopefully all is good, if not I'll be paying twice. lol

Should have simply dropped a set of performance springs in they only cost $280 odd.

[Adriano]

In the manual the GTR springs are supposed to see 24kg (52.9pounds) at installation load which is the spring length compressed to 35mm. Not sure if installation load represents seat pressure? :S

Ahh well as the saying goes. The poor/tight man pays twice. lol

I dropped a set of GTR springs in my RB25 head; the gtr springs are slightly taller than the gtst springs so they should provide more seat pressure than when sitting in a GTR head.

Hopefully all is good, if not I'll be paying twice. lol

Should have simply dropped a set of performance springs in they only cost $280 odd.

Yep, installation load is seat pressure, i would just make sure that its not going to coil bind at full lift.

[Cubes]

I had them check that; no bind.

Quite a few others have ran with GTR springs and they haven't had issues so I was fairly certian I wouldn't either.

Sky30 ran tomei 260 9mm cams without bind.

This is bugging me... It can't have 35-40lbs of seat pressure if anything it must have equal to or slightly greater than what a gtr runs.

That being ~52lbs.

I'll give them a buzz tomorrow and ask how they check the seat pressure and quiz as to why it may be lowish. They feel that 35 to 40pounds what ever that means is perfectly fine for DOHC turbo.

Makes me wonder if they check valve seat pressure while installed (if thats possible) or if they simply measure valve spring pressure at possibly suspected installation load.

[Cubes]

Gave them a buzz.

What they did was measure from the seat to the top of the shim??? and then throw the spring on the spring compressor and check the load required to compress the spring to that value. So sounds all a little dodgy but ahh well you get that. :S

He said GTR's generally get a little less than 35lbs. So I suspect they are not using the 35mm compressed value but rather a slightly higher value which is why they are getting a lesser lbs value. So using the same measurement.. 10pounds with the std springs and 35pounds after.

If all that makes sense.

Ahh well bugger it; see how it goes.

Thanks Adriano.

[mr_rbman]

mmmmmmmm, interesting. I remember when i had my head checked and bolted to the block that he said i had about 35 pounds of seat pressure and that was with the na springs!

[Cubes]

Was that with them shimmed up ash?

[mr_rbman]

i can't remember to be honest, i think so!

[CEF11E]

joys!

I have been looking into this a bit as i gather the bits for my 25/30 combination.

I am using a series 1 R33 RB25DE head. I have just pulled out 1 intake and 1 exhaust valve to find they have different length and thickness springs.

both are VERY stiff but i will have to have them measured for seat pressure the measurement I have for base of seat to top of retainer is 37.5mm and the retainer is a few mm thick so i will have them compressed to say 34mm and see what the pressure is.

Are GTR springs different lengths? its a budget build I am doing and don't really want to run much over 1bar ever so the factory items might do the job. I will post my findings once i get them over to someone with a guage

[Cubes]

Ahh I was under the impression you went with the R32 RB25DE head.

Yes the R33's run 2 different length springs; they are a tad more than the r32 springs from Performance springs in QLD.

The factory springs may very well do the job with the r33's. The problem witht he R32's is that the springs they use in the R32 Rb25DE head are the same as they are in the RB20DET head. While they are fine controlling a smaller valve with the rb20; once you shove more weight behind from the rb25's head them they struggle. :S

Let us know the seat pressure just for my own curiosity. If need be shim them up a touch to get around 50-55 pounds.

[CEF11E]

Thanks Cubes,

will do

[1400r]

the boss ordered some high rated springs form highoctane might be worth contacting them to see what they suggest

was a waste as the boss went 26 and the motors just sitting in the workshop sleeping