Hi all,

I'm considering using a Subaru engine & gearbox in a mid-engined project I'm designing at the moment. I've been digging around and found some handy tips already (such as contacting Saker for a 2WD conversion for a box!) but I have some further questions...

I'm looking for around 400bhp to start with, but don't want to stretch the engine too far, so was thinking that it might be better to start with the flat 6 rather than the flat 4 - has anyone turbo / supercharged the flat 6 successfully, and are there any "known" problems? Are there any reasons that the 6 is weaker than the 4 in the first place?!

Also searching for general info on the flat 6's and the boxes they come with at the moment (which cars used them, if any are better than others etc) so ANY info you have to offer would be gratefully received

 

A nice 2.5 with the right bits will deliver 400 bhp/400 lbft reliably.
A 6 speed box will cope with that and more reliably.

Flat 6's are only found in Legacy cars in turbo form sometimes, but i think are rare.
I feel you will have more heartache with the flat 6 than the 4 pot .

A good guy to discuss this with would be David at Welcome to the API website who has a Japanese supply source for his large company.

 

Graham, the flat 6 in EZ or EG format was never Turbocharged from the factory

If you want to turbo one you either run it with a very low boost set up, which seems pointless as it will still not be up there with a mildly fettled 4 pot turbo, or you go the whole hog and strip the engine, building it properly as a Turbo engine with the correct pistons and compression ratio for it to work.

There are several versions of the Subaru 6 pot, the EG33 which is a 3.3 litre lump from the SVX, or the EZ30, which is from the Outback/Legacy. Early EZ30's have Siamesed exhaust ports which is no ideal for Turbocharging, later ones run individual ports.

I'd stick with a 4 pot myself

 

Tim:
What about the twin turbo Legacy in Japan? iirc called 'B something' and some of the Prodrive guys drove them in the 90's? (as company cars, not competition)
Just curious.

 

Many thanks for the thoughts so far. Your comments on rebuilding the flat 6 were the primary reason for asking - I wondered if the parts are readily available to do this, interchangeability of internal components between the 4 and 6 if they aren't available etc. Obviously lowering the compression would be essential to the plan - wouldn't be the first turbo conversion I've done, just first subaru flat!

The main reasons for wanting the 6 pot were 2 fold - the 400bhp was intended to be a starting point, and it is also (so I've been told) similar in dimensions to the other engine option (Porsche) but if 400/400 can be reliably had from the 4 maybe I should rethink - be lighter too which fits with the whole project!

 

Graham, the Legacy GTB was/is a twin turbo 4 pot

You can certainly get the rods and pistons for a 6 pot turbo build, as it has been done, but everything will be custom, unless you find a supplier who can provide you with the full kit (inc exhaust manifolds), it's a relatively popular mod in the USA.

Getting 450 of each is affordable on a 4 pot, going beyond that, reliably, costs, costs a lot, suddenly a Porsche Turbo engine looks cost effective

 

Thanks again Tim W - if it can, and has, been done before I may still consider it then - after all if I can fit a 6 pot and later find it a rubbish plan the 4 pot should drop in with space to spare

The other reason for going 6 is that the car is a GT style and will likely do some (very) long trips. Past experience tells me that the larger the engine (in both capacity and no. of cylinders) the more comfortable it tends to be!

From your comment on the EZ30 Siamese ports - Did the EG33 come in siamese / individual options as well, or was it always individual?

 

The EG33 SVX lump has always been individual port. The EG33 is a big engine, it's effectively a 4 pot EJ22 with an extra pair of cylinders.

The EZ series were a completely new design, the bores are much closer together and as a result the engine is much more compact, IIRC only 20mm longer than a 4 pot!

 

Some reading: Subaru Engines

Pat's experiments

 

Excellent stuff Tim, really helpful!

I think I'll keep my eye open for a complete car to strip as it would be helpful if I could use the hubs etc, plus take a shed load of dimensions without having to worry about trips back to the scrappy when I realise I've forgotten one.

I'd also like to see just how much of an angle Subaru run on their driveshafts, I've heard it's quite aggressive before and that reading confirms it. One of my key problems with the change from a Porsche set up to Subaru was the length of the Scooby gearbox (would stick out the back of the car), and the relatively short distance between the outputs and the back of the engine - I'd need at least 3deg angle on the driveshafts to move the rear cylinders clear of the proposed wishbones!

 

You could always mate a Subaru engine to a Porsche gearbox...

 

Yes that was a consideration as originally I planned to use Porsche hubs to get easy access for wheels large enough and stonking brakes, unfortunately had a bit of a budget crisis which means to avoid a Q plate I need to go age related, i.e. use enough bits from a donor car. Originally it was going to be all new parts so that wouldn't have been an issue!

 

Have a read of Renton's thread on his mid engined Escort (!) project, there's been a fair old discussion about gearboxes in there.