AnthonyJ

All this talk of BMWs and Cossies has got me thinking about how much power you can actually get out of an Impreza. This is particularly applicable to me now that there is a very saucy 911 turbo floating around near where I live. That car is the only thing that I have ever seen eclipse every aspect of the Impreza in the pouring rain - it is quicker off the line, it is faster on the straights, and I think it is probably faster round the twisty bits as well (he had disppeared by that point!). This got me doing some sums:

Porsche 911 Turbo: 420bhp / 400lbft 1600kg
Porsche 911 Turbo eater: 380bhp / 380lbft 1300kg!!!!

Which means, assuming my car is about 1300kg, I need an Impreza that can produce at least 380bhp and similar torque. Hell, while I'm there, let's aim for 400 of each! So you guys out there who know your stuff: What could you do to get that kind of power out of an Impreza while still keeping it driveable?

"Why don't you just buy a Porsche 911?" I hear you cry. "'Cos I'd rather pay off my mortgage!" I say back! The Subaru delivers such an enourmous amount of grunt for the price that, now I'm addicted to the power and need more, the cost of upgrading my Scooby to any car that is noticeably quicker as standard would be a very expensive exercise. So I thought I'd pick some of your brains and ask if there is a cheaper way. How could you build a fire breathing 400bhp+ Impreza? Has anyone else already done this - if so, how has it gone?! Does the car still handle OK? How much power will the gearbox / diff / clutch take?!

Can you do it with clever use of hybrid turbos, water injection, extra boost, forged pistons etc, or is it easier to tear the whole engine out and start with something bigger?!?!

Fosters

regardless of the engine, wouldn't the drive train require replacement? what happens to the wrc cars - theirs can't be standard, surely?

TFyus

full wrc engine n transmission minus restrictor is bound to make 400 bhp

rw

Mad Max

Guys, nothing in an Impreza is engeneered to stand 400bhp and 400lbft. Gearbox, differentials, clutch, etc, etc, etc...

Really, it would be a miracle if the car held in one peace for more than a couple of miles.

But, to answer your dementia, you can always put a porche engine in the scooby... i'm sure it would fit (a good shoe horn would help) .

[This message has been edited by Mad Max (edited 06 June 2001).]

AnthonyJ

I've heard various people talking about this subject who expressed surprise at how much of a hammering the drivetrain can take. Apparently, they were saying that the key to it is the clutch - if your current clutch can take the abuse then the drivetrain will too. I have no idea if that is true or not, but it wouldn't surprise me if the clutch was (I'm trying desperately not to use the phrase "weakest link" at this point) the first bit to go!

Presumably, it also depends on how you drive the thing. Revving to 6k and dropping the clutch in a standard car has got to cause more damage than putting your foot down in 3rd or 4th on a car running 40% more torque hasn't it?

cryptwalk

Hi, my pal has a 93 wrx that is supposed to be running 350-380 bhp, but is unproved at the moment as it's not yet been on the rolling road due to someone crashing into the front of it.
Here is the list of engine modifications:

Blitz hybred roller bearing turbo
Hks front mounted intercooler
Uprated head bolt's and metal head gaskets
Full decat down pipe through to hks hyper muffler
Blitz induction kit
apexi avcr boost controller
Apexi afc fuel controller

What bhp this car is running is unknown at the moment due to it being in the body shop.
Wheather this sort of power is relyable without changing pistons is unknown at this time.

However the guy's at rc developments said to expect 350-380 bhp.
I have been in it and have to say it is extreamly quick, but when it gets rolling roaded the truth will be known.
I'll keep everyone posted with the progreson report as soon as it's back on the road.

AnthonyJ

I like your style Mad Max (now why hadn't I thought of that?!). But hang on a minute... won't I need a Porsche drivetrain and transmission as well?!

WREXY

Have a look at this for big big power, those Aussies don't muck around.

Adam M

Anthonyj,

what you are suggesting is more than possible.

I am aiming for 450bhp and 450 lbft, but I am not discussing how, until it is up and running.

Firefox (J) is in the throws of constructing a car that will break 600bhp, and is hoping on the right fuel to be looking at more like 700bhp.

The transmission is a big concern.

i have no idea whether or not the diffs and prop shaft will take it, but upgrading to high power handling quaifes shouldnt be too expensive.

gearbox and clutch are the main concern.

Mine has an uprated twin plate AP clutch, but this is not rated for much more than 350lbft if that. Straight cut gears are a probability for this kind of thing, with less losses involved but noise will be awesome.

the ways you have suggested will certainly help, any breathing mods and charge cooling mods will be essential.

Principally upping boost will deliver the power you want, the problem is longevity. you would need to run some serious boost to get to that power, and even if mapped to avoid det, the pressures will be too great for standard internals to last long. This means uprated rods, and pistons etc.

Basically if going internal you might as well strengthen everything. Crank may not be necessary!

Larger injectors will be required as 380s that are standard on earlier cars and british pre my99 were 380s, which will not flow enough fuel for more than 300bhp.

Upping boost cannot be achieved with increasing charge temp, unless you have a turbo that is more efficient at that boost.

increasing boost meas you have to have means of modifying ecu. At this kind of level, you dont want less than a motec.

And then there is mapping, once the engine has been professionally assembled.

All in all, for between 5 and 10k on the engine alone, depeding on who does the work, and what you decide to build will get you the numbers you are talking safely!

then add about 2k for ecu and mapping, and an infinite supply of clutches, gearboxes, driveshafts etc.

Once built though, you will eat most things for breakfast!

PS. most of this came from my own accumulated knowledge (stef and other critics), yes this may well be info regurgitated from other people, but so is everything else I have ever learned, since I am not a pioneer.

AnthonyJ

Thanks for all the great info AdamM - I understood pretty much all of it!!

My main concern is the starting point - my car is a 98 WRX, not an STi. I've already got an HKS system and air filter mapped through a Possum. From the sounds of it, the breathing mods will be find but I'd have to bin the Possum.

The question is: Would I be better off selling the WRX and buying an STi as the basis for starting on this journey of discovery and (hopefully) mad fun! Presumably if everything is being strengthened and rebuilt then it doesn't matter too much what the starting point is (although my engine is an open block which I am informed does cause problems). What do you reckon?

Excuse my naivity, but as you say, I am trying to accumulate the knowledge by talking to other people. There doesn't seems to be anywhere where all of this is written down!

Sam Elassar

anthony

first
it won't make a difference what you start with. it is all very clinical as every thing will have to go at some point or another. so it will be a ******* car if you know what i mean.

second
it is very difficult ( impossible ) to extract that much power of the subaru engine. i think you start to reach the limit of the engine design. torque maybe but not BHP.
falkland perfromance tried that with mountune racing and the engine almost blew up 3 times on the engine dyno until they had to modify the big end bearings to stop them from melting. cossie pistons, arrow rods, closed deck. the max powermountune racing was able to get was 350-360lb/ft and 330-340bhp at 1.5 bar through to 5700rpm tailing off to 1 bar after 5700rpm after max power was produced.

for your type of power you would need to either start with the legacy 2.2l block or get a 2.2 or 2.5l stroker kit. greer motor sport tried that but i am not sure if they managed to succeed or not. i am not sure though if there is a stroker kit for the legacy i am sure there will be in Aussie land.

scoobies are not really made for straight line speed. the 911s you are talking about have got 3.3l and 3.6l so there is a lot more displacement that you can't really beat.

have you ever thought of a cossie engine with subaru handling ? obviously you well need to use the cossie gearbox and diffs. now that is an idea

firefox, will probably know a lot more about tuning subaru engines than anyone on here but i would doubt that he will say anything probably throw in a one liner as usual just confirming his presence

Sam Elassar

ANTHONY
the cossie engine has a stronger block and also tuners are more familiar with it than the subaru block. i did not mean to say it is not possible very thing is possible. but i would like to find a tuner who has done it before before a give that much money away. there is a lot of 400+bhp cossies around but there is not that many subruas ?

adam
rogolies car does not apply as it is running a huge turbo and i don't think you will be able to drive it to wrok every morning

how often does nicky grist use his car ? i am talking about something you would use every day.

firefox
i can't beleave i got you talking . so what is your new project then what engine are you going for ?

i was just highlighting that it is not that easy and even some established tuners had difficulty with the subaru engine

Scooby

Going back to the original story, tis a shame you didn't see his progress round the twisty bits as I suspect that is one area where the Scooby is superior in the wet.

911's suffer from a fundamental design flaw, with the engine sitting over the rear axle...

I've seen plenty of tail happy 911s in my time including 4wd versions.

Funniest sight has to be a 4WD Rally Cross 911 Turbo with 900 BHP at Brands....Schanche's Zakspeed escort made it look ridiculous the way it aways lost the back end on the tarmac just after the knife-edge!

firefox

I would love to tell you all about my new project..


But I have used up my posting quota on this BBS for this year.. sorry

J.

Adam M

Sam, rigolis car is an extreme example, and no I wouldnt drive it to work, but it also has much more horsepower than is being saught here. I am sure a detuned version will be perfectly possible.

on another note, it is the people who own the cars who prevent the power being attained.

Tuners can do anything with enough money. But most scoobs are/were worth too much to play around with too much.

There is no reason why the scoob cant do what the cossie can. The cossie engine is simply naturally much stronger as it is steel and comes with cosworth internals anturally. this makes it a better starting point.

The subaru simply needs its weaknesses addressed. once this is done, why cant theer be mor power available.

Bob Rawles car runs 350 bhp day in day out, with no internal mods. You don't think spendinga shed load of money will release another 50? I do.

Putting the cossie engine in the scoob although an interesting suggestion is negating the whole scoob advantage of low weight engine, with a centre of mass which is practically on the floor. The cosworth engine is talling than I am and made of steel, I would dread to think what would happen to the handling.

By the way, the rigolis is the first I thought of, there are many more in japan running 400 to 700 bhp, it is just s question of what you want to spend, as ever.

MorayMackenzie

Adam,

Would you know where I could get hold of a 2.2litre legacy block?

Moray
( )

firefox

I'll post... not only to disagree with you Sam... and do the one liner

If they suffered from melted bearings, then that points to an issue with oil flow/cooling.

I have run my car at 1.5 (approx) bar to REDLINE for a while... and suffered no problems... I had done several tracks days too.

As long as you maintain oil pressure and temp to the bearings (and assuming the engines are built right) 400'ish BHP should be feasible (in theory)


In theory a stroked engine is worse than a larger bore engine (upto a point) due to the rod ratio (stroke against length). stroking an engine increases the angle the rod/crank force is at, and that puts a larger strain on the main bearings/block

Anyway... I cant say too much

J.

AnthonyJ

Sam,

Why is a cossie engine any better then? If it has the same displacement, is it just a stronger block, better design, or are there stronger parts for it?

The Legacy engine option is interesting! Can you actually fit a 2.5l engine into the Impreza bay?

Has anyone had much luck with water injection? SteveL suggested that it might be the next logical (and reasonably cheap) way to get a bit more grunt out of the engine. Presumably that allows you to run more mid-range torque but doesn't give you much more power at the high-end though? What kind of power could you get running that with a hybrid turbo? Has anyone got a similar setup?!?

Firefox - are you going to give us your one line of advice??

Adam M

sam is almost right.

but not quite.

The rigolis car sin australia get well over 300bhp with a 2 litre (more like 600).

WRC cars without restrictors will be well over 350 with torque well over 400. I know they are a lot more money, but they have to use a standard block.

I dont see why just because 1 Tuner has failed at this, sam seems to think it is impossible!

Sam is right that 2.2 minimum is am easier way to go, but sourcing the parts is that much more difficult. I have a 2.2 closed deck block already so there is no problem starting where I am starting from, although I dont want to risk a bloody rare block for the sake of an engine project. It is easier to stroke a 2.0 to make it 2.2 such as on Nikki Grists 22b which was in banzai.
Kits exist for this from BPM or Jun. Stroked engines inherently produce more torque but apparently are less willing to rev? havent heard this reported on though.


If you are doing this much work, then starting anywhere is pretty irrelevant. You may want to start with an older car as its value afterwards may be affected.

STIs over normal cars have things like alloy suspension bits, and useless front anti roll bars. These arent really important, so a wrx will be fine.

J is unlikely to post on this topic, true, but his knowledge is far to specific anyway, when we are talking this generically, it doesnt take a genius here by any means.

Anthony, if you want to start down this path, and are serious about it, be prepared for major expense. I know a source of closed deck 2.0 blocks, and also some other fun parts.

Link is fine, but once you start going into realms of 1.5 bar you need to run on a three bar map sensor. I dont know much about this but from what I gather it is very difficult to map.

There is a lot to think about here, and I wouldnt attempt it without some serious trusted help in the engine build department. You could try the likes of autosportif but again they are expensive. Dont rush in on one persons recommendations. Good engine builders for subarus are extremely rare, and you will here a lot of bragging stories from people with no firm evidence.

Adam M

do you want closed or open deck?

cos I have a closed one somewhere

rjh

No idea if it'll fit but how about the 3.0l flat 6 engine out of the new Legacy?? This is 200bhp (ish) in standard form - it can't be beyond someone to bolt a turbo on the side + get some really big power!!

Richard

ScoobySnack

Just a thought...............

You said "Porsche 911 Turbo eater: 380bhp / 380lbft 1300kg"

Why not bring the weight radically down. I thought 1300Kg was for a standard car.

What about the type RA, or go for some serious removal of the interiors

J

Adam M

It is a compromise. At 1300 kg, you still get air con, sound deadening and electric windows. You can shed more, ras are about 100kgs lighter, but is the weight reduction worth the comfort loss, when it can be made up for by increasing power?
albeit with more difficulty.

RJH has the right idea.

I believe the 3.0 flat six fit, apparanetly it is only a little bit longer?????
but there are easier, more tried and tested options inbetween.

farbeit for me to spil the beans, but look around over the next three months or so, and 400bhp monsters will be appearing, some with more (J wheer are you - not saying a word I promise)

MorayMackenzie

that's it adam, keep the beans close to your chest.

wall

350+ hp/lbft is definitely attainable reliably. When living in Australia I attended a WRX Club meet where I got to drive a modified MY98. Now, the guy was cagey about what mods he had, and had not dynoed the car (didn't care about numbers), but I promise the thing made my Sti5 feel positively s-l-o-w. At low speeds it was very drivable and tractable, albeit a little lumpy, but as the revs rose it just flied. The difference in speed from a standard WRX (220hp) to my Sti(280hp) was far less than the seats of the pants difference from my Sti to this car. So, ...340-350hp? I'd say it was making that, and the same if not more torque. The guy had been driving post mods for about 5000+miles (it was the first thing I asked) and had had no problems, except substituting the standard clutch pretty early on. Oh, and a set of tyres

wall

[This message has been edited by wall (edited 07 June 2001).]

[This message has been edited by wall (edited 07 June 2001).]

BugEyed

Well, I don't know about 400 bhp, but we all believe that the STi "only" produces 280 BHP, don't we? They wouldn't lie to the little old public about the power to avoid breaking the "Gentleman's agreement" of only 280 BHP along with Mitsubishi, Nissan etc., would they?

As for Cossies, 400 BHP can be got reliably only from an engine that is close to race spec. The touring cars in the late 80's were only producing 450 BHP reliably, and that was with a non-standard block, the Cossie (not Ford) crank, rods and pistons, oil cooled pistons, a very BIG turbo, and some wild cams. Not exaclty suitable for driving to Tescos.

In conclusion, a reliable 350 - 400 is possible only if you build it from all the right parts, and if you are willing to put up with an engine that suffers from an aggressive cam and some turbo lag. Otherwise, it will not last.

Perhaps it is not a coincidence that the Porsche is a 3.6 litre engine producing only 400 BHP and not 750 BHP for the road?

ChristianR

iTrader: (1)

I am surprised no-one has just said a one liner like, buy a cossie.

AnthonyJ

A change to six cylinders would, presumably, be a hell of a lot more complicated than sticking to four bigger ones?!

In terms of a shopping list then, it sounds like a small increase in capacity would be a good starting point. With regard to stroke kits, I must admit that I had always heard that the shorter the stroke the better the engine revved (the so-called "over-square" engines). On the other hand, I derive most of my pleasure from that big fat wodge of torque rather than high-end screaming revs (providing the stroke kits don't reduce the rev limit!). In which case, perhaps changing the stroke might suit me! Having said that, my current block is open deck, so would I have to change that first anyway?

From what you guys have been saying (and thanks for all the info & advice), the 2.2 or 2.5 block might be a better approach. Although you say block, presumably in both cases it is basically a replacement engine with all the gubbins isn't it (i.e. every component of the engine is replaced)? Are all the "interfaces" to the rest of the car the same in those cases? In which case, could I keep the same transmission, turbo, ECU, echaust, breathing mods etc.? I realise that the transmission may need some work at some point, but I would feel happier if the whole thing bolted together in more or less the same way!

So what are the advantages / disadvantages of the two approaches? Does one offer a bigger range of power? Is one more reliable? Does one method cost a lot more than the other?!

MarkCSC

Being a thicky but..

What is the difference between an open and closed deck block?

Mark

matt d

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Mad Max:
<B>Guys, nothing in an Impreza is engeneered to stand 400bhp and 400lbft. Gearbox, differentials, clutch, etc, etc, etc...
[/quote]

This may have just been spiel, but I heard from someone at Subaru that the P1 chassis and components are rated up to 400bhp. I never asked about power upgrades, it was just volunteered, so I suspect they were not just fibbing and that you could do up to about 370-380 without knackering it. A standard scoob would probably need a new clutch, and any other bits which are different to the P1 (or STi, WRX type RA etc before we start another argument!)