Previous engine tunning experiences have almost always been accompanied by mods to engine internals to cope with increased stresses/loads....at what point to people consider changes to cranks/rods/pistons etc,and is there any merit in changing cams for ones with a different profile,or does this engine not need/respond well to this sort of approach?
What about cylinder head mods for better breathing,or again are the standard ones pretty good or the effects too small in this engine?

No one any comments then?

The Impreza heads are considered quite good by some. For moderate power increases on modern engines often the internals are up to the job already. The UK/Euro spec cams limit the power over 6000 RPM compared to the STi items. But then the STi with a bigger turbo, forged pistons and shorter ratio gears is ideal for revving a bit higher.

A factory turbocharged car with a low compression ratio is relatively easy to get power out of with "bolt ons" but the more committed like to go internal to run silly power :D I am not yet one of those.

Weak points vary between models in terms of what bolt ons they arrive with - so there are some cars with good injector/intercooler capacity that then spoil the show with a crap turbo (MY99/00 Euro/UK), and 92-96 models have a nice big turbo, but a tiny intercooler and inadequate injectors. The new STi looks promising with variable valve timing and a good turbo and intercooler, along with what may promise to be a very strong gearbox (?), but then you might need 50 BHP more to give the same acceleration so do you really gain anything in terms of reliable Subaru power to weight ratio with standard internals?

The Impreza alloy block is not fabled for being strong it seems. Sometimes wish I had a Datsun, Ford or Mitsu ;)

I hate to say it, but I would still start with an Evo next time. It seems if you attend to the clutch and the warpy brake discs and get the conrod bolts uprated there is very little in you way from making exciting power with the chassis to manage it.

On my MY00 I would think about going internal if I went beyond about 330 BHP. I really would think about an Evo then...

[Edited by john banks - 6/27/2002 8:42:47 PM]

Almost all Subarus have weak conrod bolts, a cheap upgrade, cheaper than destroying the engine.

john,

dont you believe for a second about the strenth of the evo internals.

Mark Sheed of MA developments has a completely stripped engine in preparation for a rebuild with uprated internals and he is looking for 400bhp.

He claims that a lot of the evos power figures like in all tuning circles are not "real". Just like with subarus you get a lot of bullsh1t claims.

Agree with submannz about the con rod bolts, but you need to take the engine out to change them so you might aswell uprate all the internals.

Evo does have a steel block, but once you close deck the block on the subaru, I cant see why it should be the weak point.

I would start considering internal mods on any subaru engine at about 330bhp too. Especially on the sti, where the con rods and bolts are the same but the rpm are significantly higher.

Oh no Adam, slippery slope has me well and truly sliding... I think I will be speaking to you and Mark sooner than I had thought :D :rolleyes: :)

I had thought from previous posts that the rods were the weakness, and not the rod bolts, as they apparently break on the main beam of the rod?? Also, while the impreza block is not fabled for being strong...Does it break??? Does it effect horsepower??? What problems does it create?? Surely WRC cars etc have no problems? A std stiff block, does look to be pretty good, as is the simple design of the short ( steel ) crank, and using the block as main bearing carriers, I would have thought better than simple main caps as used in most straight 4's
True I have only heard of a few evos' blowing up, but i suspect that is more due to engine management than anything else, apart from them being less common, due to their strangely high prices, especially sec. hand, which do keep them away from most. I would also hat to be buying parts for an evo. Most suabaru parts can be bought for semi-reasonable money, and they are definately a lot easir to work on the any evo. As for the impreza brakes..How many evo drivers have warped discs on their cars.. I dont think that despite their big brembos, that their brakes are perfect. Nearly all evo drivers I have come across have been thru discs at an alarming rate...pad deposit build up, or warping...lol

Guys,

IMHO we are looking beyond the obvious here.
The weakest link in the Scoob is the drive train.
Gearboxes are made of chocolate and break just as easily :(
I`ve yet 2 c an impreza over 300bhp which hasn`t eaten at least 1
gearbox :( So the first thing I`d recommend to any1 thinking about serious power is "make sure your drivetrain is up2 the job".
The std internals are capable of 300bhp plus if you have a decent
one, by only upgrading the breathing system ;) Alan G`s, Andy F`s and mine all being fair examples ;) Figure out what u want then work from the road back ;) Once u know the drivetrain will take it then look at internals.

L8r
Pete

Trouble is Pete how can I sort my drivetrain out if I am not up for a dog box? Some have a theory that the STi boxes will hold up better, but others who have the STi boxes seem to find this is not the case....

John,

U know the score m8, I didn`t have the £ for a dog but in the
long run it would`ve worked out less expensive bud :rolleyes:
It`s either that or restrict tuning to say no more that 300BHP :(
Or alternatively, don`t drive them like u stole it :D

Pete

Thanks guys for this response...I too am worried about the gearbox issue having had to attend to this in the past on other cars ...as the torque being put through increases...the gearboxes die!...it's interesting to hear that 300 bhp is a ceiling before considering internal mods...can you easily get steel rods/bolts for the Scooby...also,with mention of the crap turbo on the MY 99(my car)..which is the best(not TOO BIG) replacement for a car used mainly on the road...