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]

QUOTE (TonyAKAVW @ Oct 7 2005, 04:52 PM)

I like the idea Mike, but I see two flaws with it and one spot where it could be improved. First flaw I see is that all of the rotational torque of the engine and transmission are now going to be placed on the transmission mounting ears. The distance between those is substantially less than the distance between the original engine mounting points on the car. Maybe the rotational torque isn't too significant, but it seems like suspending the whole mass from three points might be scary. Even the 911 engine mounts have _some_ spacing... The second flaw was pointed out already, but could be improved by using both the stock engine mounts (repalced with solid blocks of metal) and the adapter plate as well. That would provide two points of attachment along the axis of the support bar which would stiffen up the structure a lot. You could then fix the first problem by coming out into a Y shape and maybe even use the stock mounting locations?????? Oh, another thing... All of this would have to sit pretty low, because of the oil pan on the subaru engine... This would bring the center of mass of the engine up higher which kinda sucks. -Tony

I agree Mike's drawing won't work, but only because of the oil pan issues. Again, like Mike said the ORIGINAL 914/6 mounting system used ONE BOLT at the bulkhead to hang the engine, so 100% of the torque loads were fed through the transmission ears.

The KEP adapter plate is approx. 1/2" thick, and it's Al. They don't seem to have any problems with adding that additional spacing between the transaxle and the engine.

You are not going to bend 1/2" of Al without applying VERY serious loads to it. Just as magnesium is 1/3 the strength of Al, so Al is 1/3 the strength of steel. A 1/2" plate of Al is just as stiff and strong as a 1/8" plate steel, and weighs about the same.

There's no reason the "ears" on the adapter plate couldn't use smooth, wide-radius bends. Indeed, it would be a very good idea to do so. The only stress riser there would be the hole you'd need for the bolt to mate it do the tube you'd hang the whole thing from, and you could radius/chamfer the hole.

If the ears had 1/2" of material to either side of the hole, that would give you one full sq. in of material in each ear. Al has a tensile strength of 20,000psi, so both ears together would be able to hold 40,000lbs, or roughly 150 Type IV engines. I'd say that's a pretty good safety factor, considering the worst loads it would see short of a major crash would be about 2000lbs (engine flopping around from several G of flopping around over bad bumps).