94 Caprice Wagon 5.7L project--46 MPG so far

[elhigh]

I'm dying to know what kind of fuel economy this battlewagon gets with a towing ratio in the rear. If it cracks into the 30s, that would set everyone's idea of what a thrifty car has to look like on its ear.

[ThatDudeOrion]

Originally Posted by elhigh

I'm dying to know what kind of fuel economy this battlewagon gets with a towing ratio in the rear. If it cracks into the 30s, that would set everyone's idea of what a thrifty car has to look like on its ear.

In my car with the same powerplant, I swapped the auto trans for a manual, which as we all know is more efficient and happens to have a much higher overdrive in my case 0.70 vs. 0.50. It wound up reducing RPM at a given speed by ~500. Which resulted in about a 10+% improvement in my MPG.

I would expect his mileage penalty to be about the same to maybe somewhat higher going from 2.14 to 3.73 rear ratio, as it will raise RPM's by ~750, but I don't think the efficiency losses are quite as high going from lighter duty axle to heavier duty axle as they are when comparing manual transmissions to automatic transmissions.

My manual trans swap also came at a weight penalty as I think the transmissions weighed about the same, but I also chose to upgrade to some heavier duty chassis/suspension components at the same time. So I would say the weight difference between his axle setups would be accounted for in my guesstimate.

[ThatDudeOrion]

Also, I've deleted all the stuff from the accessory drive except the alternator, and instead of a mile of serpentine belts and idler pullies, I cobbled together an inexpensive alternator only low position mount that I'd be happy to share with you if interested, overall cost was less than half what the pre-fab alternator relocation kits go for.

And can I ask you for more specific's on how you wired in the kill switch? I don't EOC much, but when I do, I just put it in neutral and turn the key off. Is this bad? In what way is the kill switch better?

[elhigh]

The kill switch eliminates the possibility that you'll accidentally lock your steering column. That Would Be Bad.

Having the kill switch ready to hand makes it easier to use, so you'll spend more time in EOC. More is gooder. And restarting is as simple as either letting the switch go and the clutch out.

On some cars, like my HCH, keying off loses you some distance while the computer briefly goes to sleep and doesn't catch the odometer signals. It's small but it's not nothing. I guess a grand total of about a mile or more is missed by the computer per tank, about 150 feet at a time.

[pete c]

Awesome job getting that boat to close to Prius highway mileage.

The only thing I think you could have done better would have been leaving the rear alone and finding a trans with a wider range of ratios. The vette/camaro 6 speeds likely don't have high enough gears. GM does have a truck 6 speed. I would think this has a stump puller first and a really high OD. I have a friend who has one behind a lightly modded duramax. Holy crap is that thing quick. I suspect that it would bolt up. Of course, you'll have to pay more to find one, but, it would have saved you the rear end work.

[ennored]

It IS a wide ratio trans:

"Manual transmission swap--NV3500 transmission from 1996 Chevy 1/2 ton truck"

Wide Ratio Gearing Option in Dodge 1500 & GM Full-size Light Trucks:

1 2 3 4 5 R
4.02 2.32 1.40 1.00 0.73 3.55

[mwilliamshs]

Originally Posted by pete c

...The only thing I think you could have done better would have been ...finding a trans with a wider range of ratios...GM does have a truck 6 speed. I would think this has a stump puller first and a really high OD. I have a friend who has one behind a lightly modded duramax...

Behind a Duramax you'll find the Allison auto or the NV5600 six speed manual. The NV5600 weighs over 350 lbs and has a top gear ratio of 0.73:1. It's a good unit but a poor fit for this application IMO.

[funkhoss]

Originally Posted by ThatDudeOrion

One of my biggest wins has been running a laptop with the tuning software $EEHack, I can make fueling changes in real time and approximate a lean cruise which the stock LT1 pcm can't do. You may want to look into this if you haven't already.

That seems like a neat program--I'll have to tinker with it when I have some more time. Thanks for the tip. The best part is that it's free!

Originally Posted by ThatDudeOrion

Also, I've deleted all the stuff from the accessory drive except the alternator, and instead of a mile of serpentine belts and idler pullies, I cobbled together an inexpensive alternator only low position mount that I'd be happy to share with you if interested, overall cost was less than half what the pre-fab alternator relocation kits go for.

I would be very interested to know more about your low mount alternator setup.

Originally Posted by ThatDudeOrion

And can I ask you for more specific's on how you wired in the kill switch? I don't EOC much, but when I do, I just put it in neutral and turn the key off. Is this bad? In what way is the kill switch better?

Basically, my kill switch interrupts the power supply to the sensors in the distributor. When you interrupt the power, the sensors stop sending information to the ECU, so the ECU thinks the engine is turning 0 RPM and immediately cuts both spark and fuel.

I wired up a normally closed relay in line with that power supply. The wire you want to interrupt is the one going to pin B14 in the ECU--it's a red wire. I then ran a switch into the cabin (and mounted it on the shifter) that when depressed grounds the relay and opens the circuit.

If you have more questions about how I wired it, just let me know.

The kill switch lets you turn off the car without having to take your hand off the shifter. It also gives you better data, since the MPG gauge (and other electronics) stay on the whole time. A quick bump on the clutch (if you're moving) gets everything going again.

I've driven several people in my cars who had no idea that I was EOC-ing until I told them.

[funkhoss]

Originally Posted by pete c

The only thing I think you could have done better would have been leaving the rear alone and finding a trans with a wider range of ratios. The vette/camaro 6 speeds likely don't have high enough gears. GM does have a truck 6 speed. I would think this has a stump puller first and a really high OD. I have a friend who has one behind a lightly modded duramax. Holy crap is that thing quick. I suspect that it would bolt up. Of course, you'll have to pay more to find one, but, it would have saved you the rear end work.

I did consider what you are suggesting--not the transmission in the Duramax trucks, though, but rather the five speed transmission that came in 3/4 and 1 ton pickups in the 1990's (the NV4500). With an NV4500, I could theoretically have enough ratio spread for towing and economy, and leave the same rear end in the car all the time.

However, there are a few reasons that I ultimately didn't go that route:

-The NV4500 is a fairly expensive transmission, even used, and pretty much never shows up in U-Pull yards around here. It would have cost at least 10 times what I paid for the NV3500. It also weighs twice as much as the NV3500 and would have required more extensive floorboard and crossmember modifications to fit.
-The NV 4500, besides being heavier, also has more parasitic losses and much wider "gaps" between the gears than the NV3500--all of which would make it less efficient.
-And if I went with the NV4500, I'd be running a "light duty," high-geared rear end while towing--and as I discussed earlier, there are many reasons that isn't a good idea.

-Funkhoss

[spdfrk]

You could do a bit better by putting a 1oz of NMF per quart in the transmission and diff. Also try 1 tsp of tungsten disulfide per quart too. Really worked well in my Suzuki Swift GT electric...