Forged pistons

[dav 0]

Quick question,

do forged pistons require running in?

 

Thanks

Dav

[Blue_Joe 0]

No.............................................

 

But the piston rings you put on them do!

[dav 0]

Thanks

Just the same as you would any nornal rings?

[GazzaG60 0]

and the block needs to be honed before you fit otherwise they wont bed in.

 

softly softly wont help bedding in either. gotta force those rings out.

 

a forged piston usually contains more elasticity than a cast one and so makes it more able to handle pressures and poorer tuning. it may end up burning more oil thogh as the block usually has to be bored with some clearence for the expansion of the piston meaning it make smoke cold.

[Blue_Joe 0]

And you'll get a bit of Piston Slap when cold

[dav 0]

Thanks chaps

 

The bores still has all the honing marks and is in good condition, so do you think it will still need re-honing when fitting the forged pistons?

[Kevin Bacon 5]

VR's slap with cast pistons anyway!

 

If the thrust side of the bore is smooth, rehone it (if still round!), otherwise should be OK but as Gaz said, make sure the bore is big enough to take the forged piston you want to use first.

 

Don't expect much more than 80K from the bottom end with forged pistons though!

[PhillT 0]

80k... would a rebuild be needed at this point then KevHaywire?

 

I'm fitting some forged pistons to my G60 lump I'm building

[dav 0]

The thrust side is still showing all the original honing marks.

The engine was form and S2 and it bent a conrod after fitting a larger turbo, thus the move to forged internals.

Thanks for the info.

[Kevin Bacon 5]

Oh right, so they're not for the VR then?

 

PhillT, that's the average life expectency of the pistons in aftermarket conversions, they migh give load more miles, or sometimes less. They don't last as long as cast pistons. OE made forged piston engines are better, such as the Skyline, STI impreza etc but they still don't match cast for longevity.

[GazzaG60 0]

most impreza are cast, just high elasticity cast kev but i agree with what you are saying. usually a factory forged is a half way house. the cossie is the classic forged piston engine that lasts about 50-80k without a build.

 

for new rings id always rehone. its the making of good combustion and compression.

[dav 0]

Nope not for a VR,

 

J.E direct replacement forged pistons for a BAM (s2) engine, Pauter Rods and Race Ware fasteners.

 

Best get the block checked by a machine shop to make sure, even though the honing looks like new…

[Kevin Bacon 5]

Yeah, it kind of puts me off forged pistons tbh. I'd like the engine to last longer than 50-80K given the expense!

 

Are there not any strong cast pistons out there that can take turbo punishment?

 

Dav, I've heard some bad things about Raceware, which is why I went with ARP rod and head bolts.

[PhillT 0]

ah I see.. well if I make it past 5k miles I'll be happy :lol:

 

always read that ARP bolts are the ones to go for

[dav 0]

May have to rethink the raceware,

the s3 internals were supposed to be strong enough, but one banana rod later...

[GazzaG60 0]

its all about the depth of the ringland kev as to weather a cast piston is any good. many in the US use stock 9a pistons in turbo motors with compression lowered another way. they hold 300hp no worries 1bar plus boost. not sure on vr ones but IIRC the word was good. i only paid £260 for the wiseco's so it wasn't too bad. worth looking at different forged pistons though as some require more clearence than others. some even have a clearence against boost level type plan.

 

ive gone arp rod and head bolts. i put arp ford 289/302 in the 9a rods and the scats have arp 2000 anyway.

[Kevin Bacon 5]

Yeah I've also gone for ARPs top and bottom too. The VR is good for 450 crank power on standard internals I'm told. I'll rebuild it in the future with Crower rods and forged pistons, but for now, a good old spacer will suffice as I'm initially only going for a bar to 17psi. One bar with a GT30R is good for about 350 whp.....which will probably be more than enough for me, but the potential for 550-600hp is there if required.

[GazzaG60 0]

wont a 30r be on the small side. isn't a 35r more usable. suppose its whether you want a mid-range torque curve or not. either way the GT is the way t go. i only went sc61 cos i couldn't afford/justify the extra and the advantages on 2wd are less as a slower spool can help keep traction.

 

thinking of the gearbox.

 

subarus suffer where they get boosted and the smaller turbo ones create a torque spike bout 3500. this rips out 3rd and 4th gear (all one unit) changing to a bigger turbine smooths this out somewhat and the spike is less destructive. trade off: lag

[dav 0]

Engine is being put togeather,

thanks for your help.

Dav.

[Kevin Bacon 5]

wont a 30r be on the small side. isn't a 35r more usable. suppose its whether you want a mid-range torque curve or not. either way the GT is the way t go. i only went sc61 cos i couldn't afford/justify the extra and the advantages on 2wd are less as a slower spool can help keep traction.

 

thinking of the gearbox.

 

Should be OK as it's an ATP modified 30R (GT30 exhaust turbine, GT37 compressor) with 0.86 A/R. Very similar to the popular T3/T4E hybrid used on VRs for years, but obviously less the normal journal bearing downsides, not that it's a problem on the VR anyway due to the exhaust gas pressure..... it'll have enough top end flow for me. It'll hang onto 25psi past 6K easily, whereas a T3/T4E will drop to 20.

 

Know what you mean about the box. If I could afford it I'd be going quaife gearset and cromo driveshaft sets......although the former is not known for it's long life!