Engine Build Question. (spec)
#1
Engine Build Question. (spec)
Hia, planning my next stage of mods, and a forged build is required.
I've got a 2007 WRX with 58k km on the clock (36k miles), running a mild tune atm.
Induction, STi Topmount, 3' Decat, Remap. 320/360 according to the dyno.
Next I want to go 400+/400+ (i dont much care if its 401 or 420), and for that i need a forged build.
Locally, everyone suggest to go for oversized pistons, but that would mean extra machining costs and this that and the other. Is there any actual "benefit" of doing so? I'd suspect with "only" 36k on the clock, that the cylinders should be pretty neat, and any honing/machining isn't needed, and that I could go with STD size pistons.
Ive also got a question regarding the compression ratio: i can apparently get cosworth pistons with 8.2:1 cr or 9.2:1 cr, but I don't know which to get. Iirc, the stock STi cr is 8.2:1.
I would have though a higher cr is counterproductive to a turbo'd car?
Which brings me onto the next question, head gasket thickness. these seem the be available in .78mm, 1.1mm and 1.6mm. quick calc suggest going for the 1.6mm would allow for cr of 8.2:1, but again, I'm at a loss as to which to actually go for.
Similarly, what else would i definately need to purchase along with this:
Pistons
Conrods
Head Gaskets
Head Studs
Any help would be greatly apprecciated.
I've got a 2007 WRX with 58k km on the clock (36k miles), running a mild tune atm.
Induction, STi Topmount, 3' Decat, Remap. 320/360 according to the dyno.
Next I want to go 400+/400+ (i dont much care if its 401 or 420), and for that i need a forged build.
Locally, everyone suggest to go for oversized pistons, but that would mean extra machining costs and this that and the other. Is there any actual "benefit" of doing so? I'd suspect with "only" 36k on the clock, that the cylinders should be pretty neat, and any honing/machining isn't needed, and that I could go with STD size pistons.
Ive also got a question regarding the compression ratio: i can apparently get cosworth pistons with 8.2:1 cr or 9.2:1 cr, but I don't know which to get. Iirc, the stock STi cr is 8.2:1.
I would have though a higher cr is counterproductive to a turbo'd car?
Which brings me onto the next question, head gasket thickness. these seem the be available in .78mm, 1.1mm and 1.6mm. quick calc suggest going for the 1.6mm would allow for cr of 8.2:1, but again, I'm at a loss as to which to actually go for.
Similarly, what else would i definately need to purchase along with this:
Pistons
Conrods
Head Gaskets
Head Studs
Any help would be greatly apprecciated.
#2
Scooby Regular
iTrader: (52)
Hia, planning my next stage of mods, and a forged build is required.
I've got a 2007 WRX with 58k km on the clock (36k miles), running a mild tune atm.
Induction, STi Topmount, 3' Decat, Remap. 320/360 according to the dyno.
Next I want to go 400+/400+ (i dont much care if its 401 or 420), and for that i need a forged build.
Locally, everyone suggest to go for oversized pistons, but that would mean extra machining costs and this that and the other. Is there any actual "benefit" of doing so? I'd suspect with "only" 36k on the clock, that the cylinders should be pretty neat, and any honing/machining isn't needed, and that I could go with STD size pistons.
Ive also got a question regarding the compression ratio: i can apparently get cosworth pistons with 8.2:1 cr or 9.2:1 cr, but I don't know which to get. Iirc, the stock STi cr is 8.2:1.
I would have though a higher cr is counterproductive to a turbo'd car?
Which brings me onto the next question, head gasket thickness. these seem the be available in .78mm, 1.1mm and 1.6mm. quick calc suggest going for the 1.6mm would allow for cr of 8.2:1, but again, I'm at a loss as to which to actually go for.
Similarly, what else would i definately need to purchase along with this:
Pistons
Conrods
Head Gaskets
Head Studs
Any help would be greatly apprecciated.
I've got a 2007 WRX with 58k km on the clock (36k miles), running a mild tune atm.
Induction, STi Topmount, 3' Decat, Remap. 320/360 according to the dyno.
Next I want to go 400+/400+ (i dont much care if its 401 or 420), and for that i need a forged build.
Locally, everyone suggest to go for oversized pistons, but that would mean extra machining costs and this that and the other. Is there any actual "benefit" of doing so? I'd suspect with "only" 36k on the clock, that the cylinders should be pretty neat, and any honing/machining isn't needed, and that I could go with STD size pistons.
Ive also got a question regarding the compression ratio: i can apparently get cosworth pistons with 8.2:1 cr or 9.2:1 cr, but I don't know which to get. Iirc, the stock STi cr is 8.2:1.
I would have though a higher cr is counterproductive to a turbo'd car?
Which brings me onto the next question, head gasket thickness. these seem the be available in .78mm, 1.1mm and 1.6mm. quick calc suggest going for the 1.6mm would allow for cr of 8.2:1, but again, I'm at a loss as to which to actually go for.
Similarly, what else would i definately need to purchase along with this:
Pistons
Conrods
Head Gaskets
Head Studs
Any help would be greatly apprecciated.
your shopping list will need to include main and big bearings,block seal kit and sealant for block,also inlet/exhaust gaskets and 4 cam seals and 1 front and rear crank seal and possibly rocker cover one's if your in any doubt as theses can leak for fun.
#3
Former Sponsor
iTrader: (3)
The standard cylinders walls are already very thin, machining them further will only weaken a weakpoint even more.
I would go with std piston sizes of 99.5mm
The head gasket needs to be decided once the pistons are in the block. Normally the pistons sit below the top of the block faces (circa 0.3mm below) and use a 0.78 gasket. If the new pistons sit higher than that then use the gasket to space to the same amount. I have just gone through this and my pistons were completely flush with the top of the block so I used 1.1mm gaskets.
As said, a full engine gasket set is needed and LOTS of time to clean everything and prepare prior to reassembly.
I would go with std piston sizes of 99.5mm
The head gasket needs to be decided once the pistons are in the block. Normally the pistons sit below the top of the block faces (circa 0.3mm below) and use a 0.78 gasket. If the new pistons sit higher than that then use the gasket to space to the same amount. I have just gone through this and my pistons were completely flush with the top of the block so I used 1.1mm gaskets.
As said, a full engine gasket set is needed and LOTS of time to clean everything and prepare prior to reassembly.
#8
Scooby Regular
iTrader: (78)
Am i reading this correct ?
70,000.00 FIM = 9,852.38 GBP
40,000.00 FIM = 5,629.43 GBP
20,000.00 FIM = 2,814.71 GBP
sounds bloody cheap to me
or is it
70,000.00 EUR = 58,546.25 GBP
40,000.00 EUR = 33,455.00 GBP
20,000.00 EUR = 16,727.50 GBP
as this sounds stupid prices
Rob
70,000.00 FIM = 9,852.38 GBP
40,000.00 FIM = 5,629.43 GBP
20,000.00 FIM = 2,814.71 GBP
sounds bloody cheap to me
or is it
70,000.00 EUR = 58,546.25 GBP
40,000.00 EUR = 33,455.00 GBP
20,000.00 EUR = 16,727.50 GBP
as this sounds stupid prices
Rob
Last edited by Rob Day; 23 July 2010 at 07:17 PM.
#12
Scooby Senior
iTrader: (3)
Join Date: Jun 2006
Location: Slowly rebuilding the kit of bits into a car...
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The problem is that the engine will destroy your gearbox, clutch and rear diff. giving half a chance.
Sorry ! I know someone running 360/390 on his.
dunx
P.S. An STI transmission transplant may be a better idea !
Sorry ! I know someone running 360/390 on his.
dunx
P.S. An STI transmission transplant may be a better idea !
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