Y27JLC

Can someone put into normal terms what is involved in forging an engine, what it does and rough costs. And the same for closed deck and semi closed etc. And would this be better done using an sti block or wrx?

bigsigh

iTrader: (4)

replacing component parts of the engine with items that have been created by forging , rather than casting, as this produces a stronger unit. ie. forged piston is stronger than cast piston.

its common to use uprated bearings when you have the case split.

so new bearings, forged rods, forged pistons, its good practise to replace seals and gaskets , then sometime uprated headstuds, and good quality headgaskets.

It replaces the weaker items within the engine with parts that can take the stresses involved when increasing the amount of air and fuel you are forcing into the engine to make more power.
as for cost it will vary greatly, but is extremely unlike to cost less than £1k if you are doing it all yourself and £1.5k upwards depending on the spec you decide is necessary for your goal.

Closed deck blocks have a lot of material supporting the cylinder wall between it and the casing, a semi closed less so and open deck has the least. Closed deck giving the most support is renowned as the strongest for higer power builds, (ie 500+) there are plenty of forged open deck blocks making great power.

you also have the option of pinning a block or a closed deck conversion. which will add the support to the open / semi closed blocks.

bigsigh

iTrader: (4)

a stroker increases the volume of air in each cylinder by increasing the length of each 'stroke' of the piston.

Using the 2.0 engine casing with the crankshaft from the 2.5 engine and some custom pistons is generally the way to go , and makes your 2000cc engine into a 2100cc give or take , no experience here as i have never built a stroker myself (yet)

Y27JLC

Thanks for the rapid replies! My car apparently runs 340. Althought i only have a printout for 300 from the p/o, im hoping to get it rolling roaded locally to see exactly what it is. Im not looking to get massive hp just want to make sure its not going to blow up. Poor prevention and all that jazz.

FMJ

iTrader: (2)

Basically if you just want to forge the weak link (the pistons) then they can be got for about £450 (for Mahle or similar). To fit them its obviously a complete engine split which will require new head studs, head gaskets, new engine seal and gasket kit, new bearings cambelt kit (£150+ depending what parts you use). All of those bits including pistons is going to set you back way over £1000 just in parts. Plus the heads will need to be skimmed and block face resurfaced ideally (several hundred more)

Now the variables come based on other parts you use and how well you want the work done.

For example if like many you are forging a block that has spun a bearing things like the oil pump and modine may be junk. You would also probably want the block acid dipped to clean it all. So modine about £180, Oil pump £150-£300 Acid dip maybe £120.

Things like oil pumps and water pumps also have life expectancies so if you are rebuilding a block even it it didn't have any issues do you want to risk using a part that is worn and may ruin your new build?

If the crank is worn or damaged then it is general frowned upon to grind an Impreza crank so most people go for an STI nitrided one for about £500. Rods start at about £400 if you want stronger then stock.

You can see how it's all adding up.

Then while it's all apart if you are doing track days you may want a baffle plate for the sump (£150ish) or a baffled sump which will cost more.

The oil pick up is a weak point so a killer B one can be bought instead.

Do the heads need any work? There are valves springs and cams to think about.

Then there is the work involved in fitting it all correctly.

So yeah you can forge the pistons for about £1000-£1500 and replace most of the essential parts. Plus the labour.

But if you want to go with rods and crank and also get rid of the old oil pump and modine etc then you are getting on for maybe £2500-£3000 in parts plus labour.

Then it depends what parts you want? I went for Omega Pistons which instead of £400-450 which Mahle cost are about £840. The sky is the limit.

The costs of doing this to closed, semi or open are the same really. At your power open or semi deck is fine.