Quick ques about Forge Pistons

B

BabyGodzillaGTi-R

Member
Hey guys i'm looking for a set of forge pistons and were looking at this brand.
ACL. http://www.aclperformance.com.au/NissanSR20DETForgedPistons.htm

Then there was this remark that made me slightly concerned.
What does it really mean?
"(Note : Piston does not have oil squirter reliefs for GTiR motors) "

Can i still run this pistons or it's just that i won't take full advantage of our oil squirters?

Another brand i was thinking off is JE and CP pistons which are available in Malaysia. Are they reasonable pistons to consider?
But then again would i have the same issues like the above quote in regards to the ACL pistons?

Or end of the day it doesn't really matter or stick to stock pistons.
End of the day i just want reliability.

Another question is regarding piston to bore clearance.
I heard we need to run much more clearance compared to normal cast pistons.
If i recall roughly, 0.01 - 0.03mm for OEM cast pistons vs 0.0889mm or 0.0035inch as recommended by CP.

What i'm wondering if this would not be too good for the engine in the long run in terms of reliability? I'm no engine builder but there must be a reason for OEM specs to prefer cast and for HKS to build their pistons to allow lesser expansion so that they don't require to run more piston to bore clearance.
Btw i did read the high and low silicon content in forge piston article in the sticky. Good read.
Just leave more questions....

So what' s your opinion guys?
Need a quick decision b4 i take the plunge.
 
gtir_pimp

gtir_pimp

New Member
why are you thinking of taking the plunge? is your engine in need of a rebuild, are you going for big bhp or is the engine ok and you got money to burn?!
 
B

BabyGodzillaGTi-R

Member
long term reliability and of course still have the hardware to cope to run more boost.
I understand we need forge this and h beam that.
but just nice to understand the fundamentals before taking the plunge and buying things that are not necessary just to achieve a bulletproof 350bhp on wheel engine.
Just planning to build up my spare engine that's all.
End of the day i want responsive power, not a lag monster.

I've tried running 1.5 bar with a GT2871R on 300zx 87mm cast pistons. Unfortunately it eventually blew the ringland area for piston 3.
I think it was doing around 320bhp on wheels.

So yeah guys anyone have a better understanding and can shed more light about piston to bore clearance when choosing a forge piston and this quote,
"(Note : Piston does not have oil squirter reliefs for GTiR motors) "
?

I'm tempted to get the ACL pistons.
 
GTIR-LOZ

GTIR-LOZ

New Member
the pistons will come with the required tolerences, i believe its to do with the fact they are made from stronger materials so expand less than the oem ones,

you may have to have the reliefs for the squirters cut into the skirts, if the skirt is not short enough to not hit the squirters
 
J

jpward

Guest
GTIR-LOZ said:
the pistons will come with the required tolerences, i believe its to do with the fact they are made from stronger materials so expand less than the oem ones,

you may have to have the reliefs for the squirters cut into the skirts, if the skirt is not short enough to not hit the squirters
Click to expand...
Just to add to this the reason why less clearance is due to more Silicone in the material which when heated expands less compared to cast or other forged pistons such as the JE weisco etc

This will with stand a little more abuse but when they get damaged they are more likely to fail in a big way as their more brittle.

Personally I looked in to this when I was requiring some and found for the extra cost of buying them it simply was not worth it I used a set of Je's which came with a spec sheet for all the info a machine shop would need for the final bore/hone ;-)

Get on to Eric in LA he has 3 different sizes on the shelf of JE, weisco and CP and all should have the oil squirter cut out and nice oil gallery.

Ebay Ericsproformanceparts.

:thumbsup:
 
fubar andy

fubar andy

Moderator & N/W Rep
Staff member
From the FAQ's:

Its to do with the various metals used 2618 and 4032 and the different ways in which these work and react in different applications and how this in turn affects your clearance, niose, performance and wear...

4032 - is a low silicon piston. These are more for street applications. Low silicon pistons expand less and so can run tight clearances as with the likes of HKS. However the 4032 piston can become brittle under extreme stress and crack. If the 4032 starts to crack it continues and causes mass failiure.

2618 - is a zero silicon piston. There are more for higher power/pressure applications. Zero silicon pistons expand more and so require greater piston to wall clearance like the JE and CP for example. This can make them a little more noisy on cold start up. However they will handle greater pressures. In the unlikely case where a 2618 piston were to develop a crack it would lead to a lower point of stress and stop. The piston would still work fine..
Click to expand...
 
P

pulsarboby

Guest
from my own experiences ive found cp to be the best pistons to use! weve built a few engines now and never had a problem with them using cp's. not saying that hks etc arent also good but think the cp jobbies are
good value for money
come with spec sheet for bore clearances etc
no need to cut skirts for oil squirters
good expansion rates for anything running around the 450 mark

the main thing that can cause probs is insufficient end gaps on the rings. take your time to get this right as its very important and a lot of people overlook it and just get engine bored to spec without worrying about ring gaps.
also the bigger you go with piston size and the more you up the boost will mean you are generating more heat therefore its even more important that the gaps are ample.
but it explains all this info on spec sheet when you purchase the pistons
 
B

BabyGodzillaGTi-R

Member
Thanks mates, more or less reconfirm my understanding.

Hey pulsarboby,
so if i was to order CP pistons i can just order a normal SR20 set right?
I don't need to request for GTi-R specific pistons right? Is there such thing as a GTi-R specific CP pistons to begin with?
So i should stick to stock 86mm pistons too to be on the safe side? Always suspect the boring process is never accurate enough when performed by the machine shop.

I wonder if anyone have personally used ACL pistons? Would have asked the Oz forums but they've been down for ages.

Oh yeah does anyone know off hand how thick is the OEM paper head gasket?
I'm planning to order the ACL metal head gasket kit until i realised it's 1.0mm thick, when i noticed that HKS and Tomei normally specify 1.2mm.
So was abit concerned if it would affect the Compression Ratio completely?
Or it still should be ok? Feel free to shoot your opinions.

Cheers.
 
gtirx2

gtirx2

Member
Always remember that whatever sr20 pistons you go for(unless gtir specific if you can get them?) you should knock around 0.2 i think it is off the overal compression ratio,as the gti-r head is different.
The standard gtir headgasket is 1.2mm and again i think roughly every 0.1mm thicker you go with the headgasket is around -0.1 off the compression ratio.
 
P

pulsarboby

Guest
i thought stock head gasket was 1.4mm which compressed to 1.2mm:?

yes if your bores are good then just hone them out and go with the 86mm kit with 8.5:1 comp ratio pistons which will give you best response on anything upto 400bhp

dont know about acl pistons or gaskets as ive never used them
 
gtirx2

gtirx2

Member
pulsarboby said:
i thought stock head gasket was 1.4mm which compressed to 1.2mm:?

yes if your bores are good then just hone them out and go with the 86mm kit with 8.5:1 comp ratio pistons which will give you best response on anything upto 400bhp

dont know about acl pistons or gaskets as ive never used them
Click to expand...
You maybe right about the headgasket,but i always thought it was 1.2mm.
I am going to have to have a measure now just to put my mind to rest:lol:
Either way when fitted i am pretty sure it ment to be 1.2mm so if you are rebuilding you engine and not skimming the head or block you are best of aimming for a 1.2mm gasket to keep your cam timing as close as possible to stock.
 
P

pulsarboby

Guest
i could also be wrong there rich as im not donning my superbob cape at the moment:lol:
ive got one in workshops thats new (h/g that is) so il put a vernier on it tomorrow to see but i seem to remember it being 1.4 uncompressed
 
gtirx2

gtirx2

Member
pulsarboby said:
i could also be wrong there rich as im not donning my superbob cape at the moment:lol:
ive got one in workshops thats new (h/g that is) so il put a vernier on it tomorrow to see but i seem to remember it being 1.4 uncompressed
Click to expand...
Yep think you are right mate,i just measured one not Nissan but a Blueprint one and got 1.3mm on the outside of the gasket and 1.4mm on the fire rings and between the cylinders.
Have you got an old used gasket kicking about you could measure just to check that it is 1.2mm compressed?
 
B

BabyGodzillaGTi-R

Member
http://www.aclperformance.com.au/NissanSR20DETMLSGaskets.htm

ACL gaskets for the GTi-R.

But i do notice something about ACL gaskets they come only in 1.0mm and 1.6mm for the SR20....
While Tomei, HKS and Cometic are normally 1.2mm and 1.8mm.
Unless they calculate their compression ratios differently or they are measured differently.

Personally what's your opinion of stock gaskets?
I heard apparently they sealed better and the reason they are made of paper is so that it acts like a fuse and prevents the engine from getting damaged if something goes wrong.
 
B

BabyGodzillaGTi-R

Member
Oh yeah i forgotten to check this out too.
Any idea which aftermarket pistons out there have their skirts coated?
Are CP normally coated?

I also notice that the low silicon content pistons tend to be coated while the zero silicon content are not coated.
Another brand someone suggested to be are Supertech pistons. Apparently they are coated and have low silicon content. So they don't expand too much.

Just curious to date what are the pistons u guys have used and have no issues with the oil squirters?
I assume the pistons that are ok are

HKS, CP, Tomei, Jun,

how about JE, Wiseco or any other brands u guys have used, feel free to list them down.
thanks.
 
Last edited:
J

jpward

Guest
BabyGodzillaGTi-R said:
Did some research. Interesting to know how critical are those piston skirt reliefs.
http://forums.nicoclub.com/zerothread?id=293975&postid=0

They can break oil squirters.
Click to expand...
They are fairly important alright! and if you think about modifying a cheap SR20DE set to give you relief's dont forget the balance of the piston will then be out meaning it will rock more in the cyclinder wearing the skirt and rings faster.

Better to get pistons made for the job to start with! ;-) ;-)
 
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