Subaru Conversion, CSOB style... Options

[jsteele22]

I've been thinking about what it would take to do a Subaru install
into my 914, and making it as inexpensive (and as home-brew) as
possible. I have a friend who is a machinist with a lot of enthusiasm
for the project, and a nice shop. He's done a couple of adapter plates
before, so I'm confident in that part. What I'm more curious about is
the flywheel. My idea for this is to take the stock Subaru flywheel
and machine it down to a radius of 4-5-ish inches, and then bolt a
stock Porsche (okay, VW) flywheel to it. So the Subaru FW becomes
just an adapter hub. Then, the thickness of the adapter plate is
chosen to get the input shaft to reach the proper position in the
friction plate/pilot bearing.

What do all you hybrid gurus out there think of this ? Am I
overlooking anything glaringly obvious ? (I haven't seen the pieces
in person, just in Haynes & on EBay.) Sure, the assembly will have to
be balanced carefully, but I think we (he) can handle that. The
engine I'm looking at is an EJ25 (165-ish HP) or, more realistically,
an EJ22 (130-ish), so it won't be an axle-snapper like some of you SBC
folks are driving.


Another issue is the engine mount. I've seen pics of Scott's, and
another one (tube steel) that I think Friid had made up, but not the
ultra-secret Renegade design. One idea I had on this is to not use
the stock Suby engine mount points, but instead make the adapter plate
several inches wider than the bell housing. Then each side of the
adapter plate could have an "L" shaped bracket bolted (sideways) onto
it; the bottom of the L would bolt vertically onto the plate at two
points, and the back of the L would point (horizontally) forward to
hang from a cross bar, either in the conventional (lower) position, or
up high across the top of the engine bay. This would take essentially
all of the torque off of the mounting bar bolts, and would leave an
open path for the shift linkage. In practice, I'm sure there would
need to be a little cross-bracing to prevent side-to-side motion, and
also to keep the L from straightening. Again, oh learned ones, what are
your opinions on this setup ? I *think* that suspending an engine
from the adapter plate is essentially what all the Subaru airplane
folks do.


I'm really pretty excited about the idea of putting a Suby in my car.
And it would be even more cool if it turns out to be affordable.

Please let me know what you think....

[lapuwali]

No comments on the flywheel idea. The Kennedy prices for these parts aren't all that bad, and they're known quality parts for bits that are pretty critical for a successful conversion.

The adapter plate mount is an interesting idea, and really it would end up being pretty similar to the U-shaped bar used by Scott and fiid. If you reinforced the crossmember between the rear shock towers and hung some rubber mounts there, then used some tube to connect the rubber mount to ears on the adapter plate, you'd have a very compact and light mounting setup.

[jsteele22]

Interesting... So you're saying that the supports would go from the adapter plate towards the rear of the car, not forwards ?

Also, I'm not real knowledgeable about the 914 chassis, or it's terminology. When you say the "crossmember between the rear shock towers", do you mean the sheet metal panel that forms the rear of the engine bay, or something lower down & farther back underneath the trunk ? I've only got a foggy recollection of what that area looks like. But it sounds like a great idea : put in the reinforcement there, like you suggest, and then basically "hang" the adapter plate from there. IIRC, then the hangers would be basically straight vertical.

[Mueller]

for the flywheel, you could machine out the center section of a stock 914 f/w, and weld in the center section from a suby flywheel....it might be easier to just make a new center section (the bolt circle) and weld that into the 914 flywheel...I believe that is how it was done years back when the conversions started to hit the market

[Brian Mifsud]

Maching the suby plate down to make it an adapter plate isn't an awful idea in my book.

It solves the problem of how to make up the difference between 901 bellhousing and suby bellhousing. Of course the assembly should be carefully balanced after it is bolted together. Note that the bolts used to bring 901 Flywheel and Suby flywheel together are going to have a stronger influence on imbalance since they are going to situated OUTSIDE (radially) of the suby-to-crankshaft bolts. Of course, getting clearance for the friction plate needs to be considered in picking where they end up.

Make sure its very well balanced, and use locktite on the bolts. Make sure they are torqued to spec. Don't want all those parts flying apart. Wouldn't hurt for your machinist friend to put locating pins and holes between the two plates, keyed so you can't assemble them in the wrong orientation (as the clock turns)....

Let us know how it works out.

[TonyAKAVW]

I like the engine mounting idea. The engine mounts on the subaru engine are as I recall, about 2/3 of the way back or more anyway, so its not like you are moving the stress point back a whole lot. However, you now have a big stress at the joint of that L shape. the weight of the whole engine is going to be pushing down right there. Also, at the point where you meet the stock engine bar, you'll have to fabricate something pretty rigid, because there will be a tendency to push that bar out at an angle. Even if all of that is rigid, you may get some wierd oscillations or resonances in the structure. But what you could do is go straight up from the adapter plate and weld in a large heavy plate into the trunk and bolt it to that. You'd have to see what kind of stuff in the vicinity you'd be stressing..

As far as the flywheel goes.. I have both at home and I will take a picture tonight of them and post it here. Its possible this would work, though the tricky part will be cutting new teeth for the starter. As it is normally the subaru flywheel is basically a flat flywheel, versus the 914 design where the pressure plate and so forth sit almost inside the flywheel's perimeter ring. I'm not sure how things would work for the clutch, especially using a porsche design which is made to have that raised outer ring.

Maybe there's some other manufacturer that uses the flat-plate design and you could use their components???

Also I think you'll have to move the flywheel out on a hub which will need to be welded to the flywheel in all likelyhood.

Anyway, that adapter plate/engine mount is a good idea, and if you get it to work you would probably be able to sell them, especially if it was compatible with Kennedy flywheels.

-Tony

[WRX914]

Your ideas sound interesting... I hope it works out well for you. As far as the engine choice, you could not of made a better decision. The WRX engine in the 914 chassis is a real attention grabber. I know you will be happier than heck with the conversioned power plant. The 914 is just plain fun to drive. Couple that with about 275 hp at close to or under the stack weight and you get a lightweight mid engine car that really hauls ass! My 73 teener is currently getting completely rebuilt; Steel gt flares new paint under the hood and exterior. New carpet, seats, stereo, signal lenses, freshly chromed bumpers, custom geared 914 limited transaxle by Brad Meurer, new Kenisis K17 wheels with Falken tires. Simply put, I can not wait until it is done. I will be sure to post pics of my love affair when I am completly done.

[lapuwali]

The mount wouldn't go forward or backward. It would go straight up.

If you had ears on the adapter plate (no L-section, just bits of the plate extending out past the bellhousing), you could hang the whole assembly from those ears. The area immediately above where those ears would be is the raised section of the rear trunk floor between the shock towers. So, reinforce that area some, and just hang everything from there.

[jsteele22]

Okay, so at least it sounds like the ideas aren't totally crazy.

About the mounting, it sounds like a plan : Leave some ears on the
adapter plate, and hang the engine from a reinforcement of the
trunk/engine compartment wall. Will the stock shift linkage now work
as-is, or is the Suby oil pan in the way ?


About the flywheel, I like Mueller's idea about welding in a new
center section to the stock 914 flywheel. I wasn't sure if welding a
flywheel was kosher from the point of view of warpage, but I'll ask
about it. Also, if I go with the bolt-together approach, I like
Brian's idea about the locating pins. Might make for more balancing,
but probably woth it.

Tony, I'm not sure if we're on the same page. The way I'm picturing
it, the 914 flywheel remains basically intact, and it is held in the
exact same position with respect to the 914 transaxle bell housing and
starter, so there are no teeth to cut. The whole challenge is *how*
to hold the flywheel in that position. I haven't done any homework on
this yet, so I'm not sure how much axial distance needs to be made
up. But the differences in Suby vs 914 design and the thickness of the
adapter plate combine to make one critical distance : the distance
from the mounting surface on the end of the Suby crankshaft, and the
plane that the rear (tranny-side) surface of the 914 flywheel needs to
be held in. If the distance is about the same as for a stock 914
flywheel, the "weld-in" approach of Mueller looks more appealing; if
the distance is rather large, then the "bolt-on" approach looks
better. I also don't know quite where the friction plate presses on
the flywheel, but "common" sense would say its mostly out near the
edges. Hopefully there's room closer to the center for the weld-in or
bolt-on solution.


audioculture : that sounds like a cool project. I'm actually planning
to stick to a "mere" 165 HP (or maybe just 130) non-turbo engine. I
just wanna be able to get up to 30 or 65 MPH quickly. There's no way
I could have a 275 HP 914 and not get into trouble......

And a little note : I'm just tossing the ideas around right now
(and hoping my 2.0 L doesn't turn into chunks). This may or may
not turn into an actual project. If it does, you'll definitely
know.

[TonyAKAVW]

okay I think I understand now. I was imagining that you were going to use a subaru flywheel. What you are describing is basically the thng that KEP sells, and what I have for my conversion that I'm working on. the amount of spacing added to the 914 flywheel seems to be about an inch to an inch and a half. Like I said I'll post pictures tonight. That is for a spacer that is pretty thin, maybe 3/8"... I'll measure both of these for you and post it as well. Overall, the flywheel back surface (the surface facing the engine) sits roughly 2 inches from the crankshaft end of the subaru engine. The KEP flywheel is welded together and I _believe_ they use a custom made core section.

-Tony

edit: here's a thread with the progress on my subaru conversion (EJ25)
(also a CSOB conversion, and full 914 restoration as well)

[TonyAKAVW]

Stock flywheel

[TonyAKAVW]

KEP flywheel

[TonyAKAVW]

Looks like the spacing is just under 1.4 inches from the flywheel to the top of the mounting spacer thing.

I forgot to measure the thickness of the adapter plate. Dangit.

Anyway, here's the other side of the flywheel

[Mueller]

for the swap you could do what was mentioned in another thread....sell the 914 transmission, and just use the suby transmission.....cheaper and easier

think of it this way, what happens if the relationship between you and your machinest buddy sours? or he changes professions and now all of sudden you need that custom flywheel again due to some unforseen damage??

it'll be a one-off design and you'll be looking at paying big bucks to have a shop reverse engineer it for you...

[MattR]

Has anyone experienced problems with harmonics by moving the flywheel out that far?

[jsteele22]

> for the swap you could do what was mentioned in another thread....sell the 914
> transmission, and just use the suby transmission.....cheaper and easier

Hmm... Has someone actually done this ? Wouldn't that mean making custom driveshafts ? Also, I don't have a suby transmission, so it may not be cheaper... What about weight ? Is the suby transmission lighter ?

> think of it this way, what happens if the relationship between you and your
> machinest buddy sours? or he changes professions and now all of sudden you need
> that custom flywheel again due to some unforseen damage??

Good point. Maybe we'll make 2. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

> Has anyone experienced problems with harmonics by moving the flywheel out that far?

Yeah, I was kind of wondering about that as well. I'm suprised at how deep-dished the stock 914 flywheel is; adapting it for a suby makes it stick out pretty far. But (physics hat on ...) what contributes to harmonics is the moment of inertia about an axis perpendicular to the crankshaft, and this is still dominated by the flywheel radius (which the suby crankshaft was designed to handle) and only slightly by the protrusion of the flywheel away from the engine (which the crankshaft wasn't designed for). So if the flywheel has a radius of 8.5" and protrudes back about 3", then its the same as a flywheel of radius sqrt(8.5^2 + 3^2) or 9" . It's hard to imagine that that makes a critical difference (physics hat off).

Tony, thanks for the pictures and info. It really helps me to visualize the issues involved. Just for the record, I wanted to say that I DO NOT want to reverse engineer someone else's product, so I think the kind of info that you posted about the KEP flywheel ("just under 1.4"", "maybe 3/8" or so") is about as much as I'd like to know. It gives an idea of what the problem to be solved is, but doesn't speel out someone else's solution. And, like I said before, I don't plan on going into the flywheel business, so this shouldn't (I hope !) raise any problems.



Also, I'm still wondering about the shift linkage. If the engine mount doesn't interfere, will the stock linkage work ? Does the suby oil pan get in the way ? ( I know some folks have shortened theirs, but IIRC, this was partly to allow the engine to ride lower.

[banksyinoz]

QUOTE (jsteele22 @ Oct 5 2005, 07:49 AM)

> for the swap you could do what was mentioned in another thread....sell the 914 > transmission, and just use the suby transmission.....cheaper and easier Hmm... Has someone actually done this ? Wouldn't that mean making custom driveshafts ? Also, I don't have a suby transmission, so it may not be cheaper... What about weight ? Is the suby transmission lighter ?

check out the suby tranny thread
done auto
done most of six speed

[914turboford]

If it were me I would definitely use the Subaru trans. I've done 6 engine/drivetrain conversions and have never used an engine/trans adapter plate. It is way easier to make custom axles than a custom flywheel and adapter plate. And, as mentioned, you don't have custom one off parts (except for the axles). Right now I'm putting 200 hp through my hybrid 911/Ford Escort driveshafts. I made mild steel couplers on my lathe and mig welded the axles into the couplers. I then measured the out of round on v blocks and trued them up in my h press. I've driven the car at about 110 mph and there is no vibration even though I never had them balanced.

You can get a 2wd Subaru trans at the junk yard for less than $100. I think the 2wd's were fairly common in the first gen pre 94? Legacy's.

Also, 914 transaxles were crappy when new and are worse now, IMHO. My 914 shifts way better than a stock 914 did when it was new.

I hate to sound dogmatic but my advice is definitely, absolutely, go with a Subaru trans.
Brian

[lapuwali]

But to get the transverse setup to work, you had to seriously cut up the rear trunk, and no doubt moved the CG back significantly, as the engine is located well aft of the stock location.

I've heard the Soob transaxles are somewhat weak even in the stock application. The 2wd versions aren't all that common these days, considering they've been all 4wd for quite a while now. I suppose you could remove the center diff and block off the tailshaft, but now you're talking trading off the flywheel/adapter plate (which can be bought off the shelf from KEP for most engines you care to name) v. having to engineer your own transaxle mounts, your own shift linkage, fabricating axles, and futzing with convering the 4wd transaxle to 2wd, etc.

I also don't think of the 914 transaxle as "crappy". The tailshift linkage design wasn't the best idea, but with a side-shift linkage, the setup works a lot better than the only two Ford gearboxes I've driven ('90 Exploder and late 80s Sierra, which stands as the WORST gearbox I've ever had to use, by a large margin). The transaxle itself is plenty robust for the application it was intended for: less than 200ft/lbs of torque pushing less than 2500lbs of car.

[jsteele22]

Using the suby trans sounds interesting (I'll search for the thread) but I definitely don't wanna cut into my trunk, and when I replaced my rear wheel bearings, I swore I'd never do it again (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

The 901 transaxle isn't the smoothest thing I've ever shifted, but I don't mind it. As mentioned it's rated at way more HP and Torque than I'll ever throw at it, and I don't have to futz with the shift linkage.

So for now, I think I'll stick w/ the engine adapter approach. But ya never know.