Tomei Pistons

[NYTSKY]

I just found some Tomei pistons that i might purchase,but before i do i would like to ask some questions:

Its for an RB25DET

These are the specs of the pistons:

Bore: 87.0mm (Will this be big enough? Allowing for the bore to be honed.Or will i need to go 20thou over?)

Pin Dia: 21mm

Recess: Nil

Ring: Standard(I think this means they are not Titanium coated.But are still Tomei rings.)

CHEERS

[Simon-S14]

bore size will depend a lot on the condition of your block. have you pulled the motor apart yet? your engine builder will be able to recommend which one to go for.

[NYTSKY]

bore size will depend a lot on the condition of your block. have you pulled the motor apart yet? your engine builder will be able to recommend which one to go for.

The motor is not apart yet.

I could only see that the seller only had the 87mm pistons,so i was wondering if this would be big enough,allowing for the bores to be honed.

Stock bore in a RB25DET is 86.5mm isnt it?

So having the 87mm pistons would allow for .5mm to be cleaned up.

or is this a too small of a margin to go off.

[legend01]

stock bore is 86mm .... 87mm is 40thou oversize

[NYTSKY]

stock bore is 86mm .... 87mm is 40thou oversize

Thats awesome.40thou is heaps i cant see why my builder would want to hone more than that.Motor is in great condition.

[NYTSKY]

$1364.48 for Tomei pistons.Is this a good price??

[BLN215]

Thats awesome.40thou is heaps i cant see why my builder would want to hone more than that.Motor is in great condition.

It'll depend on the condition of your bores as to how much will need to be bored/honed out of it.You'd be best to have the engine pulled down and inspected and/or machined before you shell out $1300+ for a set of pistons that you dont know if you'll need.

Just the way i'd do it

[NYTSKY]

It'll depend on the condition of your bores as to how much will need to be bored/honed out of it.You'd be best to have the engine pulled down and inspected and/or machined before you shell out $1300+ for a set of pistons that you dont know if you'll need.

Just the way i'd do it

Well i want to buy the pistons anyway.I should think 40thou over for the pistons should leave plenty of room for honing.

[BLN215]

Well i want to buy the pistons anyway.I should think 40thou over for the pistons should leave plenty of room for honing.

Your choice mate but you never know the condition of your bores till its pulled down and fully inspected.

[NYTSKY]

Fingers crossed then.As i will be picking these pistons up from Japan next week when im over there.There is no going back if i need them bigger.

[blind_elk]

40 thou is not a "hone". It is a major re-bore. You should really only consider that option if one or more of your bores has some serious damage.

[NYTSKY]

The seller only sells the pistons in 87mm.So i think that the 40thou over will cover me incase of poor bores.If my bores are in good condiiton,would an engine builder charge more for the bores to get...Bored?

[BLN215]

The seller only sells the pistons in 87mm.So i think that the 40thou over will cover me incase of poor bores.If my bores are in good condiiton,would an engine builder charge more for the bores to get...Bored?

If your bores are in good condition then you'll be using an oversize bore you dont need too and wasting perfectly good metal that could be needed down the track.You may only need a 20thou over bore so your using 2 overbores when you dont need too leaving you with less life in the engine block/sleves.

But if your determined to get them go for it,just remember were only trying to help you out here.

Edited December 29, 2007 by BLN215

[NYTSKY]

What comp ratio am i after 8.5:1 or 9.0:1??

[Beer Baron]

always go for the smallest oversize possible. far better to pull down the engine first, inspect. then buy pistons to suit your new bore size. if there is nothing really wrong with the motor you should be going for 86.5mm bore. .5mm oversize.

[Simon-S14]

how much boost you planning on running? 9.0:1 is stock CR and i personally would choose this to keep the off boost driveability. If your planning on running big boost then the 8.5's may be better

[NYTSKY]

Ill be running about 20psi through a GT3067(not all day ofcoarse) with a Tomei 1.2mm head gasket.

So i think i might keep the stock 9.0:1

[NYTSKY]

always go for the smallest oversize possible. far better to pull down the engine first, inspect. then buy pistons to suit your new bore size. if there is nothing really wrong with the motor you should be going for 86.5mm bore. .5mm oversize.

In that case i think it would be a better idea to get the pistons in Oz then.

[fEkuaR]

In that case i think it would be a better idea to get the pistons in Oz then.

Definately a better idea. Your engine would be absolutely stuffed if you NEEDED 40thou oversized pistons. Also if you dont go large oversize now you will be able to use the block again if need be in future re-builds. A block can only be taken so far out.

[NYTSKY]

OK ive been looking at new valves, how is 1mm oversize better or worse in terms of performance?