Building A Forged Rb25

[marksuxass]

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.

Just read this for difference in characteristics

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

a smaller search and you may find more info.

as for his budget, he hasnt actually stated one has he? so its just another one of your assumptions? i know for a fact he was looking for tomei pistons but couldnt find any that were a std 86mm (we work in the same workshop)

Have you actually built an engine yourself with tomei pistons? or have you delt with them personally? or is your budget 'too tight?'

[N1GTR]

Guys why bother?

This "build" is so budget. Put new stock pistons in and be done with it

[R31Nismoid]

Characteristics? I want hard specifications. Not some marketing mumbo jumbo.

There is hardly an iota of specifications. Doesn't even tell you how heavy the piston is for gods sake.

I've had 3 motors (2 26's, one 25) with the apparently inferior pistons - Not one has made any noise on start up.

All motors have made 350rwkw+ without a problem, 15,000-20,000kms and compression is fine. Good enough for me, and good enough for the vast majority of users here and around the world.

My budgets generally are not tight, I just refuse to waste money on exotic brand name Jap stuff that offers no discernible advantage over another product local or US etc other than to lighten my wallet unnecessarily.

[femno]

Guys why bother?

This "build" is so budget. Put new stock pistons in and be done with it

Not even.

Just buy a second hand 25 and slap it in. It will be better than your hand built 25 anyday. Genuine Nissan built ftw.

You cant just be a noob and build a RB by 'specs'. You gotta know the tricks.

Although I guess it is cool to say you built your own forged 25 for an awesome 300hp. Not really actually. Its a complete waste of time.

[XxNinjaxX]

lol, i didnt mean to start a shit fight. but for me this build is far from pointless, the budget is very tight arse, yes i admit that but the amount i can learn from building a motor myself is far from "pointless" to me and who's to say the second hand "low km" motor isnt just going to shit its self in another 10,20>30,000km's? and put me back to square one? sure it may not happen but i'd prefer to have the reassurance that the motor under my bonnet is built by me so i know everythings right with it.

[R31Nismoid]

That's the point Femno was making

Who's to say because you built it, that it wont fall apart in 10k --> 30k kms?

The fact you want next to no power, have a ridiculously tight budget - its really not making any sense at all.

The 2nd hand motor makes more and more sense with each post you make

[r33_racer]

Regardless of anything. He can do whatever he wants. If he wants to waste a build to learn from it then kudos to him. However I would just do it as std recondition so you can follow the manual. Unless you know better, then go for gold.

[Harey]

lol, i didnt mean to start a shit fight. but for me this build is far from pointless, the budget is very tight arse, yes i admit that but the amount i can learn from building a motor myself is far from "pointless" to me and who's to say the second hand "low km" motor isnt just going to shit its self in another 10,20>30,000km's? and put me back to square one? sure it may not happen but i'd prefer to have the reassurance that the motor under my bonnet is built by me so i know everythings right with it.

I cant find the other thread at the moment which has all the people who have built custom engines and only had them last 10-30,000kms. I would put more faith in a second hand factory engine then a custom built engine at your power levels. The ultimate would be a factory rebuild I think.

[Rolls]

I cant find the other thread at the moment which has all the people who have built custom engines and only had them last 10-30,000kms. I would put more faith in a second hand factory engine then a custom built engine at your power levels. The ultimate would be a factory rebuild I think.

Agreed, see my thread where I asked how long motors last and who's had a motor grenade before 5,000kms, there was a reasonable number of people, something around 10-20% and I HIGHLY doubt that that many second hand motors grenade.

[STATUS]

dude, go the import wreckers fit a Neo engine and be done with it, for your wishes a std neo engine will be happy for about the life of your ownership. building an engine is a waste of time, the neo head will allow nice cams without the big expense of springs and so forth

will save you a fortune...

[marksuxass]

One of the reasons ive gone with tomei pistons, is cause ive taken my time to really research thousands of forum threads, not only on skyaus but others worldwide.

What i found is people who have had engine rebuilds (with the said cheaper pistons) have had them fail within 30,000kms of a rebuild, and thats from being built in fairly reputable workshops all over the world (also stated on a thread on skyaus).

This is due to various reasons, one of them being pistons slap (even if it cant be heard with the naked ear) and it eventually turning your bores from being circular to more oval in shape. This is caused by the piston rocking on its pin as it goes up and down the cylinder (when cold). Have also found out its to do with the metal expansion rate being too large in some of these said pistons. Having a larger piston to bore clearance is what the manufacturer has put in place to try compensate this. Thats fine once the engine is at normal operating temp, but very disasterous when the engine is still cold.

I actually had this happen to a friend of mine. He had a fresh set of (not going to name the pistons) put into is rb26. After 10,000kms piston slap became audible. 15,000kms later ridiculous amounts of blowby. He had his engine builder (fairly repitable workshop here in perth that i will not name) who actually built his engine in the first place strip it down. What he found was excessive wear on the thrust faces of his bores due to piston slap. The engine builder then stated to him that most of the cheaper pistons will do this due to thermal expansion rates of the cheaper styled pistons, and also said it was not the first case of this happening. He also recommended tomei pistons to him and explained the benefits of them too him, so they where indeed fitted.

80,000kms after a set of tomei pistons and a brand new n1 block (block was totaled by previous pistons) and the car hasnt missed a beat. That is also another prime reason i chose tomei pistons. Im not goin to preach to anyone anymore. What im trying to say is do your homework before you get stuck into your build, it will save you a load of money even if it costs a little more!

[zebra]

GIVE IT A REST!

[Rolls]

80,000kms after a set of tomei pistons and a brand new n1 block (block was totaled by previous pistons) and the car hasnt missed a beat. That is also another prime reason i chose tomei pistons. Im not goin to preach to anyone anymore. What im trying to say is do your homework before you get stuck into your build, it will save you a load of money even if it costs a little more!

If no one can post the expansion rates of the tomei pistons and compare them to other reputable brands then I don't think anyone is going to take this that seriously, if you can't hear the piston slap there is no way in hell they are going to fail due to it in 30,000kms

not to mention there are plenty of audible slapping pistons that last >100,000kms

ive heard of lots of failed builds but none due to piston slap.

[zebra]

If CP's, JE, Mahles, Ross, Probe etc etc were so bad, would they be used in 1000+hp Prostock motors, 1000+hp blown street motors etc etc?

I cant say i have seen an engine fail due to a bit of slap when stone cold...if they were slapping when warm then the machinist/engien builder has f**ked it not the piston.

[marksuxass]

If CP's, JE, Mahles, Ross, Probe etc etc were so bad, would they be used in 1000+hp Prostock motors, 1000+hp blown street motors etc etc?

I cant say i have seen an engine fail due to a bit of slap when stone cold...if they were slapping when warm then the machinist/engien builder has f**ked it not the piston.

But would you have 1000hp blown street engine racking up the kms as a daily driver? And of course your gonna want things looser in a 1000hp motor! Like you said i think its about time we gave it a rest and go back on topic perhaps?

[marksuxass]

ohh and by the way, im not saying there 'soo bad'. Im just stating would i would choose due to research. each to their own!

[Harey]

then the machinist/engien builder has f**ked it not the piston.

+1

Remember that is just one engine builders advice. Whats to say he didnt setup the engine with the Tomei pistons differently and blame the cheaper pistons??

At least have a chat to a few other engine builders and get their opinions.

But if you have already decided and willing to go against everyone here then just do it.

[marksuxass]

+1

Remember that is just one engine builders advice. Whats to say he didnt setup the engine with the Tomei pistons differently and blame the cheaper pistons??

At least have a chat to a few other engine builders and get their opinions.

But if you have already decided and willing to go against everyone here then just do it.

Thats what im trying to get at here. Tomei states to setup the engine differently to suit these pistons, so of course its been setup differently.

Thats just one engine builders advice that has been dealt with personally. The list would be too long of other reports stated on other forums. But yeah like you said im not going against anyone. This is just my opinion on this.

[STATUS]

One of the reasons ive gone with tomei pistons, is cause ive taken my time to really research thousands of forum threads, not only on skyaus but others worldwide.

What i found is people who have had engine rebuilds (with the said cheaper pistons) have had them fail within 30,000kms of a rebuild, and thats from being built in fairly reputable workshops all over the world (also stated on a thread on skyaus).

This is due to various reasons, one of them being pistons slap (even if it cant be heard with the naked ear) and it eventually turning your bores from being circular to more oval in shape. This is caused by the piston rocking on its pin as it goes up and down the cylinder (when cold). Have also found out its to do with the metal expansion rate being too large in some of these said pistons. Having a larger piston to bore clearance is what the manufacturer has put in place to try compensate this. Thats fine once the engine is at normal operating temp, but very disasterous when the engine is still cold.

I actually had this happen to a friend of mine. He had a fresh set of (not going to name the pistons) put into is rb26. After 10,000kms piston slap became audible. 15,000kms later ridiculous amounts of blowby. He had his engine builder (fairly repitable workshop here in perth that i will not name) who actually built his engine in the first place strip it down. What he found was excessive wear on the thrust faces of his bores due to piston slap. The engine builder then stated to him that most of the cheaper pistons will do this due to thermal expansion rates of the cheaper styled pistons, and also said it was not the first case of this happening. He also recommended tomei pistons to him and explained the benefits of them too him, so they where indeed fitted.

80,000kms after a set of tomei pistons and a brand new n1 block (block was totaled by previous pistons) and the car hasnt missed a beat. That is also another prime reason i chose tomei pistons. Im not goin to preach to anyone anymore. What im trying to say is do your homework before you get stuck into your build, it will save you a load of money even if it costs a little more!

Not sure but i think they are made by cosworth, and yes they are generally better (i have run greddy pistons in about 7 engines (SR's and RB's) now) than the run of the mill probe, mahle, CP, JE etc but the reason they are generally better is they come out of the box with killer ring sets better crown profiles and base stock but as for life there is not much in it if it is built properly.... we get the same life out of JE's (our most used brand)... wear on the thrust side and audible slap @ 10,000km was a builder issue not a piston issue.

The greddy pistons (again i think cosworth due to very odd ring sizes) are generally quieter and run finer tolerances as the base stock is better but @ up to triple the price you could do another engine for what you saved... I use them only on high end builds and my own stuff.

[marksuxass]

Not sure but i think they are made by cosworth, and yes they are generally better (i have run greddy pistons in about 7 engines (SR's and RB's) now) than the run of the mill probe, mahle, CP, JE etc but the reason they are generally better is they come out of the box with killer ring sets better crown profiles and base stock but as for life there is not much in it if it is built properly.... we get the same life out of JE's (our most used brand)... wear on the thrust side and audible slap @ 10,000km was a builder issue not a piston issue.

The greddy pistons (again i think cosworth due to very odd ring sizes) are generally quieter and run finer tolerances as the base stock is better but @ up to triple the price you could do another engine for what you saved... I use them only on high end builds and my own stuff.

Tomei's are made in there own warehouse as with all there items, they too have very wierd rings, there quite alot smaller?