No problem on the 5" spacer, lack of weight change idea. Move into a topic and not understand exactly what is being said makes it easy to imagine something that isn't there. Since I am building this as a street car I have looked at the idea of gas mileage! HA!HA! Some HotRods get fairly good mileage and looking at old Olds Toros and Caddys I saw highway mpg numbers of over 20mpg. Not bad for a "******" toy. Everyone has always told me two first statements (if you can have two of them!) You won't be able to keep the front wheels on the ground! And with all of that weight in the back you won't have any decent handling and will spin the rear end out when trying to corner! I countered with the same answer, Tires! You need enough to conteract the rear weight bias in order to handle and you need enough to spin rather than "flip the front end"! I guess it is a real balance and of course having good suspension to work with it helps.
I never did say what the car was but it is an Opel GT. I always wanted a mid-engined sports car and years ago figured that it would be neat to build a "Sports-Street Rod".. As you said, no real big product lines to find a nice aluminum housing bolt on differential so I am left to figure out how to make my own. Same with cylinder heads, Olds engines don't come cheap like building small block Chevy or Ford stuff. If I can take off around 100lbs with a set of heads and the differential swap that will help the *** heavy situation.
I appreciate the performance numbers. I have seen lots of Street Rods built with the Olds THM-425 but never any kind of performance numbers on them. You can join the THM-425 mid-engine group on Yahoo and check out some of the photos and info. I used to have a stack of articles pulled from various magazines through the years and back in '95 I went on vacation to Florida/Disney World and lost it somewhere along the trip. It was my boredom fighter that I could open up and re-read the articles. I am sure that I had your car articles in them, it seems very familiar.
THM-425 : TurboHydramatic 425 Conversions
I stuck a link to your photos on the Group Link listings.
One of the Fiero guys built a gear driven replacement for his chain drive case that allowed him to reverse the input to the transmission and reverse the trans/turn the engine around. Others have flipped the stock Toro differential. I just figured it made sense to try something lighter and modify that to work.
Interesting on the weight change and the front/rear bias. Turning the engine/trans around will shift the couple of hundred lbs. of the transmission maybe 18" or more from the rear of the rear axle centerline to the front of it. Compared to that a manifold change from cast iron Toronado to Aluminum Edelbrock won't be a big change since the location won't shift, just a weight loss.
1.25g steady state is pretty damned good for a street toy! I will probably run non-performance 2.70-1 type ratio. Still with an ultra-light overall weight it should run fairly well.