Rb26 Std Head Gasket Thickness

[nsta]

Im getting my head gasket replaced, and going for a tomei item over factory. Im wanting to buy the headgasket now - and need to know the right size to go for, and if its worthwhile getting a very thick gasket and changing compression at all - power goal in mind is 300rwkw or slightly over with a gt-ss setup.

tomei headgaskets are as follows:

1.0 mm. 87.0 mm bore. 8.7 compression ratio

1.2 mm. 87.0 mm bore. 8.5 compression ratio

1.5 mm. 87.0 mm bore. 8.3 compression ratio

1.8 mm. 87.0 mm bore. 8.1 compression ratio

then the same as all above in 88mm bore

for my power delivery in mind which gasket should i go for, car is driven on the street and wanting to be tuned for 300rwkw or more with hks twin gt-ss setup (very similar to n1 turbos) - response is key, so i was thinking higer comp would help?

Also the guy who rebuilt my motor said that forged pistons were used, would i need to find out the right bore size (if its been changed at all) before going ahead and buying my gasket?

thanks.

Edited December 28, 2007 by nsta

[sh@un]

Err, dood- the 1.0 and 1.2mm gaskets won't give the same comp ratio.

Go the 1.0mm head gasket. On 98 octane fuel with an aftermarket ECU and a full exhaust (separated wastegate dumps if possible) the GT-SS's will still be able to make max power and you'll still have the best transient response and fuel economy possible.

[nsta]

cheers mate - so having the highest compression ratio possible wont be a problem when aiming for 300-330rwkw max? that would really help, as i would like to keep it responsive, but would i tbe reliable, or would it be better to o slighter thicker, and run more boost?

mmm....now im wanting to know what cause the headgasket to go in the first place.....what would generally be the cause?, the head not being machined properly???....the car had done a head recon 10,000kms ago...

Edited December 28, 2007 by nsta

[sh@un]

mate, there are drag GT-Rs that run 9's using unleaded fuel on engines with over 9.0:1 comp ratios.

run the 1.0 gasket and GT-SS's with a good ECU (a D-Jetro Apexi PFC would be the ducks guts) and you'll be blown away with how tractable and economical it is.

[STATUS]

or go the 1.2mm if you need to skim the head. On advice from ABE (nomura-ken BLITZ R34 engineer) for our setup mid 300rwkw RB26 1.2mm is best comprimise.

[nsta]

Is it safe to be using 1mm headgaskets?, if head needs to be skimmed and i fit a 1.2mm gasket, would that mean id have the same comp ratio as if i were to use a 1mm gasket on a non-skimmed head?sort of?.

[sh@un]

no

standard gasket thickness is 0.9mm- the only thing you will need is cam gears to dial in the cam timing

just do it

[Beer Baron]

if it were my choice I'd go the 1.2mm. and I did.

[nsta]

Thanks mate, im still deciding which one to go for - another quick question, ive been searching the forums on this one.

While the head is open, im thinking of replacing the cams to some Tomei Poncams for the rb26dett, these ones here...

TOMEI PONCAM Camshaft Type B Kit -143035

(Camshafts)

PONCAM Intake and exhaust camshafts. 260 degree, 9.15mm lift intake and exhaust camshafts.

These seemed to work well on the rb26dett - are these a direct fit for the 26's, as i was thinking why not do these while the head is open....would this be a good mod for low down response and better power all round - as im planning on going the twin gt-ss route soon enough - and will the stock studs be fine, or would it pay to get some tomei studs for the cams aswell...or is this going overboard?), and will they be fine with factory ecu, or run extremely rich???

I was too thinking 1.2mm thick gasket, my bore size is most likely 88mm (got wiseco pistons so most likely bored out).....what would the compression be in my case beer baron...and why did you choose 1.2?

thanks in advise all!

Edited December 29, 2007 by nsta

[nsta]

anyone else think 1.2mm would be the go - dont know whether or not cams would be ideal as well since its all open, are they direct fitment?

[Abo Bob]

I doubt you have 88mm bores yet. That's a second major rebore. For some reason I don't understand people seem to skip a size over when rebuilding and go straight to 87mm. 88mm is 4 sizes over. I only went 87 on my RB25 because I couldn't find 86.5mm pistons. They are available these days however.

Those cams will be a great match for the GT-SS's. Keep the CR as high as you dare. I'd go the 1mm but 1.2mm wont kill you.

[Adriano]

If you are fitting froged pistons, i would build the bottom end first, and get the head serviced, then measure everything up and calculate the comp ratio and squish using the different head gaskets, any good engine shop will be able to do this.

[nsta]

Thanks guys, like i said, ill have to open up to see what the bore size is first, bottom end was rebuilt with forged pistons already, and i dont have any $$$ to get anything else fitted to the bottom end right now, unless its easy to get to while the head is open - i see people running gt-ss turbo setup on stock internal gtr's with no issues either way.

What's the std bore size on the rb26dett?, and from the receipts ive seen from the previous rebuild, there was a rebore that took place. When the head has been rebored, does that mean the compression goes up or down?, even when using the stock gasket?

P.s theres varied opinions on headgaskets, some say 1mm and have more compression, others say 1.2mm.....which would be a safe bet with my 300-350rwkw target?for the street, mountain sprints....and reiability being key, as is response.

The tomei kits come with an oil restrictor gallery orifice...what is this exactly?and is this something the bottom end needs to be opened for? It comes with new gaskets for inlet/exh manifolds aswell....i was thinking if i should replace these manifold studs aswell with oem nissan maybe?

Sorry for all the questions guys, the head may be getting pulled out within the next few days and i would appreciate as much info as possible.

So tomei 9.15mm lift cams are direct bolt up, and will just work?, do i need to adjust them at all???

Thanks.

[nsta]

Just an update - ill be doing the headwork removal tommorow:)

[nsta]

Mm...still deciding on what comp ratio i should go for on my rb26 motor....are cams easy to install - id like to do them as the engine is already open for it......do i need anything else to install the cams, as im after the tomei 260 9.15mm lift like alot of others here use...

[Abo Bob]

86mm standard bore size.

It's not the head that gets rebored, it's the block - the cylinders.

All else being the same, an overbore will increase the CR as you are sweeping a bigger volume into basically the same size combustion chamber.

There are many different opinions on what CR you should use. It seems to me that the old school way to get power out of engines was to drop the CR and shove lots of boost in. These days people want better response so they tend to go for higher CR with the result being that you have to be more careful with your tune and perhaps keep the boost a little lower. RB26's start at 8.5:1 and RB25's at 9:1. I dropped my RB25 to 8.75:1 and the response is stock like. It has been at times difficult to tune but not impossible and any decent tuner should be able to deal with it.

You will see GTR's with big turbos sometimes dropping the CR to 8.2:1 or even occasionally 8:1 but these are usually big power cars, not the sort of thing you are after. That said, the Gibson GTR way back in the day apparently ran 9.4:1 and big boost from smallish turbos and ran ok. Maybe it was the datalogging and such that kept it alive. I don't know.

If stock engined GTR's can happily bolt in GT-SS's and run 300awkw then your rebuilt one should have no issues at the same CR. I also don't think that CR should be a problem at 350awkw given appropriately sized turbos.

One last thing; I've been told as a very general rule of thumb, if you drop the CR 0.2 then you need an extra 0.1 bar of boost to make the same power. I think that's how it went.

Oh, cams, yes those cams will bolt straight in. They are Tomei Poncams Type B. Cam gears wouldn't hurt but I don't think you'll be crying without them.

[nsta]

Thanks abobob:) much appreciated! - just a few questions, would it be ok to get a 87mm headgasket(as 86 is rear with aftermarket stuff) if my bore size is still stock 86mm?.....

Now i know the bore size from stock, im thinking of going 1.2mm headgasket....if my cylinders have been bored to 87mm (i think i have some wiseco istons in there already, will find out tommorow), will 1.2mm gasket make me reasonably close to stock compression anyhow, maybe even higher, as long as its safe im happy, asnd yes 300-350awkw on smaller gtss turbos are the plan, response is a must:)

thanks - the cams i want are the tomei straight bolt on ones, if i do get cam gears aswell, do i need a tune, as i have no $$$ for that right now, and only enough to buy the cams and gears and have them fitted to factory ecu and very little mods....

thanks.

[STATUS]

Thanks abobob:) much appreciated! - just a few questions, would it be ok to get a 87mm headgasket(as 86 is rear with aftermarket stuff) if my bore size is still stock 86mm?.....

Yes

[Beer Baron]

you do not need the head off the engine to fit cams. they are easy to fit at any time. just take of the cam covers, cams caps and bolt them in. the hard part is checking all the valve clearances and shiming up if they are not spot on. but there is no need to do it whilst your head is off.

I would not bother with the cams if you are running stock ecu and stock turbos. waste of time imo. get some cam gears first, and have them adjusted on the dyno (cost maybe $200 in dyno time). then down the track buy and fit cams when you do the turbos.

[nsta]

Thanks guys, head is off, and big problem, it looks like whoever rebuilt the motor last done it all wrong!, the pistons appear to be hitting the head, and that was confirmed once i showed the reconditioners the head, the block may need to be taken out, but maybe not if the pistons can be removed and re-shimmed to clear the gap.....

What's the best idea from here people?the cylinders have been bored out, dnno how much too though as i didn't have a vernia dial at the time, but i could see the sleeving....

I hear the stock rb26 headgasket is 0.9mm in size?, if my cylinder have been bored out, and the head gets machined, would 1mm headgasket thickness still be ok?or would i be pushing it....

Have alot of work still to do, here i was thinking im all done!...