Gearsets/final drives/ecu programming for liquid cooled engine transplants

[ydeardorff]

I have been talking with a tech rep in regard to transplanting my WRX turbo into my sterling. The list keep growing of what to know.
One of things I'm looking into now is this:
The stock gear-set, and final drive along with the ECU programming were designed for the original car that had a aerodynamic value of X, and a weight value of Y.
Well in the new application for the sterling X, and Y have changed dramatically. So the given values set by the factory are no longer applicable, they are in fact wasteful.
So I am working with this tech rep to find out if there is a way to change the gear sets, and the ECU values in a way that will reflect the new application for the sterling. It could render much higher MPG's as well as better HP/torque curves due to better fuel/RPM/gear ratio application.

I do not know the Aerodynamic rating for the sterling so the X is missing to the equation. Does anyone know of any information on this? Having the aerodynamic value of the Sterling's body would help immensely to figuring this all out.

Any takers?

Yaughn

 

[letterman7]

How do you determine aerodynamic ratings, Yaughn? I didn't even know there was such a thing, other than the term "brick" and "slippery"... not usually used in the same sentence. You might want to talk to the guy in Oz who is working on several Suby items for sale for dune buggies. He made his own gearset (I think, at least he made the pinion) and he might be the one to talk to for practical info on the gearing. But then, he's using the Suby gearbox as well, not a VW. I forget - are you transplanting the Suby gearbox as well?

 

[ydeardorff]

Yes, its subarugears.com
Very nice guy! I think hes a member here as well

What I'm working out is a more in depth engineering perspective regarding the drag co-efficient of the sterling itself. But as far as I know, no one has ever wind tunnel tested a sterling before to find its drag co-efficient.

By readjusting the values of the ECU and adjusting the gearing to reflect the new values of the X and Y mentioned before a huge savings just in gasoline alone could be had, despite running a much more powerful engine.

 

[letterman7]

But as far as I know, no one has ever wind tunnel tested a sterling before to find its drag co-efficient.

That's because it's horridly expensive. I did have the opportunity to do that, though, years ago at the Boeing plant near Philadelphia. A relative of my family works there and asked about the tunnel rentals - NASCAR teams use it, so it is available for "normal" people to use. The cost? $2000 per hour, not including any data streams from Boeing, tuft or wand tests or anything else. All that was extra, of course....

If anyone wants to bite, I still might be able to put it together, though that particular family unit divorced last year...

 

[ydeardorff]

Where Im going to school next year has one as well, and in the dept that Ill be studying. However, it is designed for scale models, not full size cars.
If I was able to swing it as an assignment that would be great, but scale models of a sterling are not available to test.

And Yes Rick,
Im mating the WRX engine to a 99 legacy 5 speed. Its not the perfect option, but it is the best option for the price in this case.
However if I was to speak in terms of the most desired option, it would be the dual clutch paddle shift conversion for the Subaru trans-axle. But that's another 3K on top of the flipped diff setup.*whaah*

I have heard of people claiming up to 50 mpg with a bug motor installed. This is due to the fact the engine doesn't have to work as hard to move the lighter, and more "slippery" body through the air.
So it stands to reason if there is a way to adjust the gearing and ECU for a liquid cooled engine setup, a similar reaction can be had. Having a car that not only looks great, but gets even 35mpg or more while pushing 150 or more hp would be an outstanding benefit in all regards.

 

[Tullio]

I have a feeling you are doing something that I also tend to do.

Make things way more complicated then they need to be.

All you need to do is make sure your engine is spinning at the optimal RPM to push the car down the road using the minimum amount of gas.

You will not have to re-tune the ECU. The ECU is already tuned to have the best compromise of HP, fuel economy and reliability. If you were taking a truck engine (tuned for a lot of low end torque and not a lot of high end HP) then that's a different story. But a Subaru engine is already tuned to have more HP than torque and is already a (relatively) light weight car. You just need to get the gearing right.

If you are going 65MPH at 7000RPM, you will waste gas. If you are going 65MPH at 1200RPM you will have no power.

I have actually done all the gear ratio, final drive ratio, engine power and tire size calculation for my Sterling already.

So, pick an optimal engine speed (lets just call it 2000RPM). Now look at the gear ratios for the trans you are using and the final drive ratio and figure out how fast the wheels will be turning in 5th gear at 2000RPM.

Now, you have to know what tire size you are going to run. Calculate the speed of the car with whatever tire size turning at whatever RPM you figured out in your first calculation.

Now you know how fast you will be going at 2000RPM in first gear.

If your just a little bit off from where you want to be, you can adjust the tire size to compensate and that will change the whole calculation.

If you are a lot off, you will have to change the gears. There are plenty of manuf's who make aftermarket gear seats. Pick out a new set of gears and run through the calculations again.

Again, unless you are going to be tuning the engine to make more power, it will be a waste of money to try and screw with it.

FYI - I plan on running a 500HP modified STi engine (mid engine) hooked to a 6 speed manual trans with a PPG close ratio gearset, a stock final drive ratio with a 19" rear wheel, a 28" diameter tire which will net me 200.1 MPH in 6th gear at 5000RPM

And yes, I fully intend on topping it out (legally) when it's all said and done.

 

[letterman7]

I have heard of people claiming up to 50 mpg with a bug motor installed.

*laugh* I have yet to see solid proof of that from anyone. At best I've gotten 32 on the highway with my current stock setup. My old car with a smaller engine (but dual carbs) got at best 23 on the highway, but I tend to run my engines rich.

Gearing is where it's at. Those that claim the fabled 50mpg may have a "freeway flier" transaxle or something similar.

 

[ydeardorff]

I have run the numbers thus far based upon 18" wheels, a 3.9 final drive with the stock 99 legacy gear set. With all this put into place, and guessing at the Drag co-efficient I came out to a 189 possible top end speed at red line.
Now of course I am not going to do that, I would never take my car that fast due to it's rarity, and how much work I have already put into it let alone when its finally done. Nothing against your desire to do so Tullio, But I am not skilled enough to drive any car that fast, and even if I was, too much can go wrong even if I was in the middle of the Bonneville salt flats to risk me screwing up my purdy car.

Now, a Dyno run up to full speed/power, sure!*rock on* Then its on paper, and the car is chained to the floor, where much less can go wrong.

The current idea is to increase the stock power from 240 to 350 CHP (this will put the car at 1:5.1 hp to weight ratio which is exactly where I want it to be). In this car with this engine setup, the HP to weight will be on the bleeding edge of still street-able. Anything more is a track only car, and would be very difficult to control on the road in everyday driving.

However, Being able to maximize the cruising rpm at high way speeds would be great for when Im not inclined to be an idiot tearing through the gears. Especially if I were to drive the car any long distance,(say to Carlisle) would be a nice added feature. And if a little research would help that, then Ill poke around till I find out what my options are.
Subarugears doesn't offer any lower final drive than a 3.9 (last time I looked). I'm not sure of the options on gear sets for the legacy transmission, its not the most popular model for aftermarket stuff.

But if a new gear set is transplant-able into the legacy transmission to offer the proper gearing then great. The sterling weighs about half of a WRX, so it doesn't need to drive as high in the RPM range to keep the car going along even on hills.
The stock WRX gets about low to mid 20's on the highway according to the window sticker. So If that could be tweaked to say 35 then excellent!

I hear ya Rick, Lots of claims, but little proof. Perhaps like that old Isuzu ad [ame]http://www.youtube.com/watch?v=vRn3s3b3sH4[/ame] (not the right one but close) , where the Isuzu Joe says "It goes 200 MPH!" then the quote reads below him (Downhill in a hurricane)*proud*

Under the right conditions, say a 10 mile downhill slope with a tail wind, a sterling could probably achieve 100 mpg average over that stretch by idling down the hill. LOL

 

[thestevie]

If I was able to swing it as an assignment that would be great, but scale models of a sterling are not available to test.

Didn't someone in England make scale models? Maybe you could get in touch of one of the owners and rent one? I'm sure they would be quit happy to get their hands on the wind tunnel info...

 

[ydeardorff]

If thats the case, when I transfer next year, it may be a possibility I will have to ask.

 

[Tullio]

I just may have 2 of those aforementioned models at my house.....

*nothing to see*

 

[ydeardorff]

Very nice!

I wonder if it could be replicated?

I might be interested on one. Although the proportions look a little off, it might still be usable.

 

[letterman7]

I do have one of those scale models from Alex, about 4" long. I don't know how accurate the readings would be, though, since it won't have the real car's open nooks and undercarriage. But.. I guess you never know until you try!

 

[ydeardorff]

Many of the initial wind tunnel tests deal with just a clay model to start anyway. So drivetrain and other components are removed from the equation.

If the model is close enough in it shape it should work. But again I dont have access to the wind tunnel (yet). But if the opportunity was to present itself. I would jump on it.