Building A Forged Rb25

[Rolls]

also if piston slap is the issue a rebuild will make it worse as almost all forged setups have some piston slap.

[marksuxass]

also if piston slap is the issue a rebuild will make it worse as almost all forged setups have some piston slap.

yeah thats why you go tomei, they dont slap

[zebra]

Only if the clearances are right.

[Rolls]

yeah thats why you go tomei, they dont slap

it has nothing to do with the brand it has everything to do with the fact they are forged and the clearances you use.

You can minimise slapping by running as tight clearances as possible but the only way to avoid it entirely is to use non forged pistons, so no they will still slap.

[R31Nismoid]

Can't say I've heard any "slap" on any of my motors when cold.

[zebra]

And pretty sure Tomei pistons are made by Cosworth...I know some of them were.

If you dont want piston slap run a long skirt piston and really tight clearances. might cost you a handful of horsepower but much better for a street engine.

[Rolls]

Can't say I've heard any "slap" on any of my motors when cold.

it will still be noisier as you have to run a larger clearance, can probably get it pretty quiet though.

Edited November 8, 2010 by Rolls

[marksuxass]

it has nothing to do with the brand it has everything to do with the fact they are forged and the clearances you use.

You can minimise slapping by running as tight clearances as possible but the only way to avoid it entirely is to use non forged pistons, so no they will still slap.

its everything to do with the brand, tomei use different forging process's and different blends of metals for there pistons, thats why you can set the piston to bore distance closer (as specified by tomei), and there not made by cosworth, ALOT of people that have visited the tomei workshop can back this up!

[Rolls]

Surely their expansion properties are not that much different? Does anyone have them, I'm curious.

I'm sure they vary a bit but surely you'll still need a larger clearance than stock pistons.

[marksuxass]

Surely their expansion properties are not that much different? Does anyone have them, I'm curious.

I'm sure they vary a bit but surely you'll still need a larger clearance than stock pistons.

i have some on the way, there were a few threads on gtr uk about them too, people where questioning about the piston to bore clearance, and found out it was due to how much the expand when heated, which is very minimal. There also the only piston manufacturer with cooling chanels just like the OEM rb26 and 2jz pistons

[Rolls]

Interesting, perhaps the cooling channels restrict the expansion.

[marksuxass]

Interesting, perhaps the cooling channels restrict the expansion.

thats a good point, i know you can get non cooling too, and even the non cooling pistons have no slap.....

http://www.tomei-p.co.jp/_2003web-catalogu...iston_rset.html

some silent reading for you

[R31Nismoid]

no doubt they are a good piston. but most motors, built tight... won't have a problem regardless of what brand.

motors with wiseco, cp, whatever. ive heard plenty and all of them you couldn't pick if you tried.

plenty of tried and proven pistons out there without having to blow $3000 on tomei cooling channel items when a decent set will set you back around 1200.

either way to suggest tomei cooling channel as an option in this thread is ridiculous.

[marksuxass]

no doubt they are a good piston. but most motors, built tight... won't have a problem regardless of what brand.

motors with wiseco, cp, whatever. ive heard plenty and all of them you couldn't pick if you tried.

plenty of tried and proven pistons out there without having to blow $3000 on tomei cooling channel items when a decent set will set you back around 1200.

either way to suggest tomei cooling channel as an option in this thread is ridiculous.

if you read properly i didnt suggest tomei cooling pistons to anyone, just comparing. all i am saying is most pistons will have different heat expansion rates, tomei is one brand with the smallest of these (both cooling and non cooling).

[R31Nismoid]

You said it was everything to do with the brand, which is not the case at all as I've said - plenty of OTHER brands can also achieve a "slap"less result when the motor is built right. Hell you could build a shit motor and have Tomei's slap as well, wouldnt be hard with some of the motors I've seen built around the place.

End of the day Tomei pistons do not magically achieve something that nobody else has in the realm of piston slap in a cold motor.

[marksuxass]

You said it was everything to do with the brand, which is not the case at all as I've said - plenty of OTHER brands can also achieve a "slap"less result when the motor is built right. Hell you could build a shit motor and have Tomei's slap as well, wouldnt be hard with some of the motors I've seen built around the place.

End of the day Tomei pistons do not magically achieve something that nobody else has in the realm of piston slap in a cold motor.

yeah and that was in regards to piston slap, you seem to think tomei pistons are way out of everyones budget, i picked up a set for a few hundred dollars more, so why not go the extra? also read up on other forums other then skyaus (in relation to piston slap) and see what you find, it may shock you.....

[r33_racer]

Must be a combination of design and perhaps a higher silicon content in their pistons inorder to achieve those tight clearances and reduced piston slap.

Do they have some kind of power rating on the pistons?

[marksuxass]

Must be a combination of design and perhaps a higher silicon content in their pistons inorder to achieve those tight clearances and reduced piston slap.

Do they have some kind of power rating on the pistons?

not too sure ive heard people say 1500hp?

[R31Nismoid]

Tomei “cooling channel” are over 3k landed (RRP)

Normal Tomei are around 1800 landed (RRP)

Wiseco or CP (as an example) that come in around 1k-1.2k landed (RRP)

Tell me then please - what exactly do you get for 50% more cost (Tomei standard issue vs Wiseco/CP)?

Just reduced piston slap because of slightly different composition? Come on… Hardly a deal breaker.

Looks to be nothing drastic either way – as I cannot find a detailed spec sheet which would have me believe it’s probably not a lot different to most other pistson on the market, that for which, you can find detailed spec sheets.

Tomei ones don’t magically support another 1000hp, are any less prone to failure or anything else.

If the only thing they can claim is reduce piston movement in the bore due to their composition, then that honestly is not a deal breaker at all when you can have a motor built tight enough these days that piston slap isn’t really an issue.

I'm all for buying the best parts, but you must be mindful of a budget - and this guy is working to a very tight budget. An extra $600 or so when its simply not required, doesn't help him at all.

[r33_racer]

Thats quite substantial if correct. Though I doubt they would handle said power at the recommended clearances. Arent they something like .0015" - .002" piston to bore?