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Author Subject: forged pistons needed?
gti-dan

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Location: Yorkshire

Registered: 03 Jan 2010

Posts: 461

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Post #1
Right im considering my options on tuning - i had planned to build a bored and stroked 2.2 engine which i really still want to do - but would effectively mean i couldnt compete in the sprints and hillclimbs that i want to. To do that i need to remain under 2000cc.

So if i went for some cams which required pokets cutting in the pistons - would i have to buy proper forged pistons or could i just have the OE pistons machined - i presume with ITB's, cams, raised compression - i'd still only be looking at maybe 210 bhp tops? So could i just use the standard pistons?

(presume i could offset the lowered CR from the pockets by skimming the head??)
Posted 2nd Apr 2010 at 14:16
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chris with a pug

Seasoned Pro

Location: Southampton

Registered: 16 Feb 2003

Posts: 5,366

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Post #2
it all depends on your budget really, personally if you are going to do all that work, I would get some hi-comp pistons and get the most out of the other mods
Posted 2nd Apr 2010 at 14:53
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #3
deeper pockets wont alter the compression ratio massively, nor will skimming the head as you can't take that much off them safely (0.25mm)

the wilder you go with the cams the more valve clearance you'll need as well as the more you will need more compression, get some specced up pistons then you can get whichever cam will run to the limits of the rest of the bottom end and valve train.

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Posted 2nd Apr 2010 at 15:24
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gti-dan

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Location: Yorkshire

Registered: 03 Jan 2010

Posts: 461

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Post #4
welshpug! that makes sense - can get thye pistons custom made to optimise the CR and pockets and get all that right - is there cheaper way of doing this rather than getting wossner forged pistons? i.e. yes i need custom pistons made but do they need to be expensive forged ones? - its fine if they do but not sure if its an unnecessary expense if only going to maybe 210 bhp.

If you do need forged pistons for that power do ou reckon id need forged rods?

What do you reckon to reground, lightnened, polished cranks?

Cheers.
Posted 2nd Apr 2010 at 15:30
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

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Post #5
I don't know the limits of stock rods and bottom end, also there's no need to get a crank re-ground if its still within tolerance, but getting the whole rotating mass balanced can only make good sense in reducing vibrations and imbalances, the cost isn't great in the grand scheme of things either.

there may be something out there cheaper with regards to pistons, but it wont be a lot I doubt.

I'd speak to Sandy Brown now as he has built up a few contacts and I believe may have a chosen design or spec for this engine.

I have seen in the GM world that there are cast aftermarket pistons available at about half the cost of forged, but there seems to be nothing out there for the XU engine, that's the benefit of being such a widely used engine I guess.

(they do happen to be the same bore afaik, but how suitable they'd be for use in an XU engine I can't say)

________________________________________

need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Posted 2nd Apr 2010 at 15:50
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

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Post #6
Im faced with the same problem, I wouldnt mind entering the car in a few rounds of a tin top or DMN championship next year, but my 86.5mm pistons take me out of the 2000cc category and lump me in at the smaller end of the bigger engine capacity cars. Stupid rules reall as 25cc will make f*ck all difference, and it means if you want to run forged pistons you have to put them in an unbored engine and hope they seal ok and dont slap about too much, madness.Crazy

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
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Posted 2nd Apr 2010 at 15:55
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

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Post #7
gti-dan wrote:
Right im considering my options on tuning - i had planned to build a bored and stroked 2.2 engine which i really still want to do - but would effectively mean i couldnt compete in the sprints and hillclimbs that i want to. To do that i need to remain under 2000cc.

So if i went for some cams which required pokets cutting in the pistons - would i have to buy proper forged pistons or could i just have the OE pistons machined - i presume with ITB's, cams, raised compression - i'd still only be looking at maybe 210 bhp tops? So could i just use the standard pistons?

(presume i could offset the lowered CR from the pockets by skimming the head??)


Sounds like I'm doing exactly what you want to do later on, keep your eyes on my build and see if it turns out any good LOL

________________________________________

R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 2nd Apr 2010 at 15:58
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welshpug!

Capt Pedantic

Location: Bigend, Wales.

Registered: 27 Mar 2007

Posts: 25,817

Status: Offline
Post #8
Just have to find a decent block in that case, it seems to vary a hell of a lot how much they wear.

________________________________________

need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Posted 2nd Apr 2010 at 15:58
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

Status: Offline
Post #9
welshpug! wrote:
Just have to find a decent block in that case, it seems to vary a hell of a lot how much they wear.


I'm going to declare the overbore and run in the next class up now, sod starting again after all the money etc. has gone into my existing block. The laptimes between winning cars in class D (up to 2L) and class C (2L and above) were'nt a million miles apart, if I cant be competetive I'll ditch my current cams and slot in some 320 race cams and go for broke Crazy

________________________________________

R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 2nd Apr 2010 at 16:03
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gti-dan

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Location: Yorkshire

Registered: 03 Jan 2010

Posts: 461

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Post #10
How does boring the engine help with the seal and prevent slapping?

You might want to check aswell - you might not even be able to enter the class with the larger engines even if you wanted to.

In hillclimbs and sprints - you can not run a larger capacity engine if that would put you into a larger capacity class. So e.g if classes are "1600 - 2000" and then "2000 +", a 1.8 could go to 1999 but a 306 gti can not go to 2000 etc.
Posted 2nd Apr 2010 at 16:04
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

Status: Offline
Post #11
gti-dan wrote:
How does boring the engine help with the seal and prevent slapping?

You might want to check aswell - you might not even be able to enter the class with the larger engines even if you wanted to.

In hillclimbs and sprints - you can not run a larger capacity engine if that would put you into a larger capacity class. So e.g if classes are "1600 - 2000" and then "2000 +", a 1.8 could go to 1999 but a 306 gti can not go to 2000 etc.


You want a perfectly round and onsize bore prefeably, not a oval one that has had a 120 thousand miles of wear. Seems a crying shame to put a

________________________________________

R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 2nd Apr 2010 at 16:07
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petert

Newbie

Location: Sydney

Registered: 18 Mar 2007

Posts: 38

Status: Offline
Post #12
It's really not all that bad. Firstly, some classes allow first overbore to cater for engine reconditioning. Secondly, your standard cast pistons will probably have a bore clearance of approx. 0.001". Forged pistons can run from 0.003" to 0.005" without any problems. Depending on the block, you may only need a cleanup to get the bore clearance right.

In regards to pocketing however, you could easily drop from 10.8:1 to 10.4:1 by machining the standard pistons. I'd deck the block at the same time to recover the lost CR and improve squish distance. Far cheaper than new pistons.
Posted 3rd Apr 2010 at 10:15
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daveyboy

aka Jim Davey

Location: Southampton

Registered: 01 Oct 2007

Posts: 8,648

Status: Offline
Post #13
petert wrote:
It's really not all that bad. Firstly, some classes allow first overbore to cater for engine reconditioning. Secondly, your standard cast pistons will probably have a bore clearance of approx. 0.001". Forged pistons can run from 0.003" to 0.005" without any problems. Depending on the block, you may only need a cleanup to get the bore clearance right.

In regards to pocketing however, you could easily drop from 10.8:1 to 10.4:1 by machining the standard pistons. I'd deck the block at the same time to recover the lost CR and improve squish distance. Far cheaper than new pistons.


Thats a little late for me now Smile but the next class up should still be reasonable, plus I'll be running as a novice for 12 races so circulating at the back of the grid in an underpowered car may help to keep me out of trouble Dry

________________________________________

R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars
Posted 3rd Apr 2010 at 14:48
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