STi pistons in a UK Spec MY98
11 July 2001, 10:14 AM
#1
Scooby Regular
Thread Starter
Join Date: Apr 1999
Posts: 1,035
Likes: 0
Received 0 Likes
on
0 Posts
Mark,
I assume that you're talking about the forged STI pistons..
The bores should be ok, but this should definately be checked carefully when you have the work done. Damage to the bores is quite unlikely unless the slap has been allowed to get very bad for a long, long time. Subaru recon that there is no reduction in engine life as a result of slap, but I'm not quite so sure
If you just want to cure the slap, a very slightly overbored (but otherwise standard) no. 4 piston should take care of it. This would be the cheapest fix as you're only changing one piston and you don't have to split the block to do it - the piston can be taken out through the top of the block. This fix worked fine on my car (also a MY98), and it's been fine ever since.
If you want to tune your car, it may be worth taking the opportunity to fit better internals (forged pistons, rods and rod bolts, Sti exhaust valves) but this is likely to be pretty expensive). If you do go this route, you can get better aftermarket forged pistons for less than the STI items (BPM / JE / Cosworth etc). Definately have the rod bolts upgraded even if you decide to retain the standard rods. You could have the rods prepared to make them a bit better (crack tested and bead blasted), but they are still a bit weak for very high power applications).
Cheers,
Alex
[Edited by AlexM - 11/7/2001 10:19:28 AM]
I assume that you're talking about the forged STI pistons..
The bores should be ok, but this should definately be checked carefully when you have the work done. Damage to the bores is quite unlikely unless the slap has been allowed to get very bad for a long, long time. Subaru recon that there is no reduction in engine life as a result of slap, but I'm not quite so sure
If you just want to cure the slap, a very slightly overbored (but otherwise standard) no. 4 piston should take care of it. This would be the cheapest fix as you're only changing one piston and you don't have to split the block to do it - the piston can be taken out through the top of the block. This fix worked fine on my car (also a MY98), and it's been fine ever since.
If you want to tune your car, it may be worth taking the opportunity to fit better internals (forged pistons, rods and rod bolts, Sti exhaust valves) but this is likely to be pretty expensive). If you do go this route, you can get better aftermarket forged pistons for less than the STI items (BPM / JE / Cosworth etc). Definately have the rod bolts upgraded even if you decide to retain the standard rods. You could have the rods prepared to make them a bit better (crack tested and bead blasted), but they are still a bit weak for very high power applications).
Cheers,
Alex
[Edited by AlexM - 11/7/2001 10:19:28 AM]
07 November 2001, 05:30 AM
#2
Scooby Newbie
Join Date: Nov 2001
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
I have a MY 98 out of warranty and the old Knock problem is rearing its head.
Has anyone any experience or advice on the fitting of STi spec pistons in a bid to cure the problem? Does it bring any great advantages or is it a complete non starter?
Thanks for any help.
Mark
Has anyone any experience or advice on the fitting of STi spec pistons in a bid to cure the problem? Does it bring any great advantages or is it a complete non starter?
Thanks for any help.
Mark
07 November 2001, 09:01 AM
#3
Scooby Newbie
Join Date: Nov 2001
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
If you mean the #4 cylinder knock problem, try installing a decent fuel rail (meaning, not stock). Upgraded pistons will withstand more detonation, but that isn't really fixing the problem.
Ben
Ben
07 November 2001, 09:55 AM
#5
Scooby Newbie
Join Date: Nov 2001
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Sorry Andy, Incorrect terminology on my part. It's slapping from cold - goes when it warms up. Car's done 22000 miles (in the year i've had it)
Does the slap wear the bores out?
Mark
Does the slap wear the bores out?
Mark
07 November 2001, 12:16 PM
#6
Scooby Regular
Join Date: Aug 1999
Posts: 7,957
Likes: 0
Received 0 Likes
on
0 Posts
sorry, have to congratulate alex on an excellent response, very imformative.
Alex since you hasd your number 4 piston replcaed without splitting the block, is this because it is number four or can they all be done without splitting the block? I was under the impression that there were other factors meaning the others arent so easy to remove.
Alex since you hasd your number 4 piston replcaed without splitting the block, is this because it is number four or can they all be done without splitting the block? I was under the impression that there were other factors meaning the others arent so easy to remove.
07 November 2001, 01:27 PM
#7
Scooby Regular
Thread Starter
Join Date: Apr 1999
Posts: 1,035
Likes: 0
Received 0 Likes
on
0 Posts
Adam,
Operating on the basis of received wisdom as usual, but I believe that all cylinders have a window to allow you to remove the gudgeon pin and withdraw the piston through the top of the block.
I don't know why it might be more difficult for other cylinders though I'm afraid.
Cheers,
Alex
Operating on the basis of received wisdom as usual, but I believe that all cylinders have a window to allow you to remove the gudgeon pin and withdraw the piston through the top of the block.
I don't know why it might be more difficult for other cylinders though I'm afraid.
Cheers,
Alex
Trending Topics
07 November 2001, 01:51 PM
#8
Scooby Regular
Join Date: Nov 2001
Location: Leeds - It was 562.4bhp@28psi on Optimax, How much closer to 600 with race fuel and a bigger turbo?
Posts: 15,239
Likes: 0
Received 1 Like
on
1 Post
Just out of interest what other parts could be replaced.. as I have a strange feeling that I will have me engine in bits soon...
Is it worth sourcing things like sti crank, cams, flywheel??, and then getting forged pistons, sti head gasket.., is there any difference to the inlet valves? I presume the exhaust valves are sodium filled or whatever... Does the sti still have **** fuel lines? Is there a list anywhere of what is uprated on the sti, so that If I was rebuilding I would know exactly what to uprate?
and obviously a link ecu!
David
Is it worth sourcing things like sti crank, cams, flywheel??, and then getting forged pistons, sti head gasket.., is there any difference to the inlet valves? I presume the exhaust valves are sodium filled or whatever... Does the sti still have **** fuel lines? Is there a list anywhere of what is uprated on the sti, so that If I was rebuilding I would know exactly what to uprate?
and obviously a link ecu!
David
07 November 2001, 04:10 PM
#9
Scooby Newbie
Join Date: Nov 2001
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Cheers for the info!
I'll start saving for the upgrade. The slap isn't bad at all yet, although I do worry that the Autobahns out here and my constant need to cane it where I can will wear it out quicker.
Do you have any suggestions on where I should get it done? i.e. professional job, reasonably priced etc....
Cheers
Mark
I'll start saving for the upgrade. The slap isn't bad at all yet, although I do worry that the Autobahns out here and my constant need to cane it where I can will wear it out quicker.
Do you have any suggestions on where I should get it done? i.e. professional job, reasonably priced etc....
Cheers
Mark
08 November 2001, 11:08 AM
#10
Scooby Newbie
Join Date: Nov 2001
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
The STI cranks are, as far as I recall, the same forged units used in all the other 75mm stroke EJ engines. You could swap in a 79mm stroke crank from an EJ25 and get about 135cc more displacement, if that interests you. All sorts of things become possible if you are willing to tear the engine apart.
Ben
Ben
Thread
Thread Starter
Forum
Replies
Last Post
Mattybr5@MB Developments
Car Parts For Sale
1
18 November 2015 07:49 AM