I don't think this type of mod would have good ROI. Besides many of the better hypermilers shift at 1500 rpms or less. In the end you'd loose low end torque. It might get better mileage on the freeway. But then again it would need some type of tuning.

of course this would in the end be more expensive to do just a single car, but with a tune and a chip made for direct replacement on identical engine set ups, the second and third and so on would be cheaper. There would be no need for more fuel, because the need for fuel would be less, because an increase in power would not be present. basically it would be more expensive than its worth, but would be neat to see the results.

I'm thinking about using a very small turbo (such as a single unit off of a 300zx or similar size) with 8:1 compression and having it completely dyno tuned using Hondata and the stock computer. Hopefully having 75% boost at common driving speeds, while running it as lean as possible. I honestly think better fe numbers would result....

Maybe Ill find a blown up d15z1 and a vx trans and find out....

If you want to see how it can be done check out this recent post in ETList.

Johnathan Goodwin can get 100 mpg out of a Lincoln Continental, cut emissions by 80%, and double the horsepower.

https://tech.groups.yahoo.com/group/ETList/message/7510

Thanks for the compliment

I often go from SD to Fairfield, its a 560 mile trip

I wanted to see if I can make it without stopping for gas. First time I chickened out and filled up at 470 miles because I was un familiar with the area and the gas stops were space 20 miles apart.

On the way back I pulled off 511 miles on 1 tank. I really think I can pull it off with no gas stop. Just gotta stay off that boost. Ill fill a gas log next time I go it should be in the next few weeks.

Im thinking of pulling off the Supercharger belt that way I cant use anyboost at all.

Lets think about this. In order to run any air throttled engine with no (or very little) restriction your going to need to be at or very near full throttle. If you are running boost at highway speeds your intake manifold runners and head ports are going to have to be TINY. So, if you designed an engine like this, it would have about 10-20 horsepower and would be impossible to drive in any form of traffic.

It's been my experience that I can always achieve better FE out of a turbo motor then the same motor NA. The 80s/early 90s saab turbos come to mind, I could get 35-40MPG out of them and they weren't that light and didn't have that small and engine, NA they got less.

The first thing that should be mentioned is obviously you have to stay below 70-80% boost because that point, even well tuned you're going to want to be running rich unless you have water injection and it's just a waste of fuel.

I think the main FE benefits would be using the waste heat at the turbine to help negate the vacuum losses. That is, at 0-30% boost (and obviously as low an RPM as you can) I think you'd see the most improvement.

I think you stated something incorrectly though, you certainly don't want boost and more power for steady state cruising. The point of boosting is that you can have very little power for steady state and downshift and use the boost for accelerating. So you're not using the 'on boost' heavy fuel consumption or extra power all the time, only accelerating.

So running a hybrid setup that would produce about 30% boost at/or around cruising engine speeds would net the highest fe gains correct? Just a thought, I have to find a D15z1 engine to experiment first. Hopefully this winter sometime. It probably won't be in a VX chassis, but if I can see gains in a heavier chassis that is fine with me. I'm considering no intercooler, just heat wrapping ALL piping and the turbo itself to keep heat to minimum..

We'll see, the only downfall is tuning price, I guess using the stock l1h1 o2 with a wide band data logger and a a/f piggy back such as ApexI would be the best, as I could tune it on the road in real conditions.

Sounds like a bunch of fun to me.

For best efficiency start looking at compressor maps and figger out the range of power needed for driving.

At cruise I am at like 15 inches of vacuum, if I was at lower vacuum or in boost if I had a turbo I would be accelerating. Driving steady state at 15" of vacuum means the turbo isn't doing anything helpful. You need an engine with low enough power to need boost while cruising.

Now if you had a 1 cylinder engine that needed boost to maintain 55mph then I think you could pick up some good mileage from that. So how about get a motorcycle engine that is tuned for low speed grunt and turbo it and stick it in a car? That way you don't have pumping losses from engine vacuum while cruising. The engine in my DR650 is a good grunt motor, 37hp and it runs out of steam around 5000rpm. I think it redlines around 5000 as well. Get a motor like that have the cams ground to a lower lift and duration then turbo it and you are set :)

I think it would work but then again I have no real experience with forced induction for anything other than getting lots of power :rolleyes:

That seems more or less accurate imo. The largest range of power w/ the smallest drop in efficiency I've seen is on the smaller TDI engines. Something like 300-200g/kWh from 10-90hp w/ the help of a variable vane turbo. A normal turbo would have a smaller range of power where efficiency was good.