[xxxxxxxxxspshultz]

A couple of weekends ago I towed our ATV's (about 2500 lbs total) up to a friends land that just happened to be above 10,000 feet. There were quite a few 7%+ grades and the Barney mobile was working overtime to get up them. I was in 3rd gear and doing almost 45 while others were passing me like I was sitting still. At these altitudes the truck has lost a lot of power.

I have Edelbrock headers and y-pipe, a full 3" exhaust system including cat, open element air filter and a 52mm TB. The tune up has about 8,000 miles on it. The tires are the stock size of 235x70x15. At the normal 5000 where I live and with no load it does just fine.

Right now I have the 3.55's and so was thinking of maybe swapping in some 3.92's. But what I'm afraid of is destroying my highway mileage. At the posted 75mph speed limit I'm at about 2400+ RPM's.

Has anyone ran 3.92's and the NV3500 trans with 27" tires especially at speeds of 75 - 80 mph? I really don't want to be driving at 2800 RPM every where I go. Or would 3.92's make any difference at all?

Edit: Ah crap, didn't realize I was in General Parts. Can a mod move this to the right section?

 

[jpayne80]

Gears are going to be your best option. I would personally opt for the 4.10, but check local salvage yards or craigslist for a rear axle with the 3.92 gears. Installed, new gears will run you around $600 and the used axle will be nowhere that high.

 

[JimLusk]

I going to go negative on the gears for this reason. All you will accomplish is to move your problem to another gear in the transmission and kill your mileage for normal driving. It will be easier to get moving on a hill, but the hill climb will not change. You need more power and that will come with cubic inches or, at the least, a performance upgrade to the PCM.

If it were me I'd be looking at how to get a 5.9 in there the easiest/cheapest way possible.

 

[Hahns5.2]

Yeah, you don't want those gears with those tires with that tranny if you like to drive fast, I'm coming up with 2650RPM at 75. IMO a 5.9 swap will kill his mileage just as much as a gear swap.

For altitude you need boost :stirthepo

 

[hskrRT]

Gears aren't going to kill your mileage that much. Especially when towing, it may actually make it better. Make sure you aren't running in OD towing.

 

[xxxxxxxxxspshultz]

Actually I don't have OD, well, kind of not. I have the NV3500 and 5th gear is .73. I can't even touch 5th going up some of those hills. Heck, even on a very slight incline above 10,500 feet, accelerating in 5th just doesn't happen. I was actually shocked with how much power I lost at those altitudes.

I think no matter how I cut it, I'm gonna have to take a hit in highway MPG's to be able to tow like I want to tow. The truck isn't quite a daily driver so I guess in the long run a few less MPG's isn't that big of a deal.

I'm wondering how much HP I lose at 10,000 feet to 11,000 feet and how much more HP I'd have to make to be able to keep it at 65 mph up those steep grades (the speed limit on those grades is actually 65). The truck now is probably making 230hp - 235hp realistically (at sea level of course).

The next items on my upgrade list are a Hughes or M1 intake, 1.7 RR's and an SCT tune but I just don't know if that will be enough.

 

[xxxxxxxxxspshultz]

Double post. Grrr.

 

[xxxxxxxxxspshultz]

Hmmm.....is a turbo affected at high altitude like an NA engine is?

 

[hskrRT]

An M1 is actually going to amke it worse as it makes less torque. If you want pulling power try to find a Kenne Bell SC set up for sale. I've seen a couple recently being sold. But with any forced induction set up have to worry about intake temps. Especially when pulling uphill under a load.

 

[xxxxxxxxxspshultz]

Can a SuperCharger or turbo actually compensate for changes in altitude? I think if they can then it's probably the best way to go.

 

[hskrRT]

They will help, but they will be effected by altitude changes like a n/a motor will, but they will still provide the "boost" for more power over n/a. About the only thing that creates it's own atmosphere and isn't affected by altitude as much is nitrous.

 

[JimLusk]

A turbo would be the best bet for power when you need it and not when you don't. Unless there is one that is California Air Resources Board compliant I couldn't run one. That's why I got a Durango with the 5.9. A turbo will help compensate for higher altitude, too.

 

[Hahns5.2]

A turbo will make the same boost at all altitudes because the wastegate controls boost.The pressure differential between the atmosphere and manifold does change with elevation and also varies with boost level (the higher the boost the less % change) but not as dramatically as an NA engine.

With my old turbo setup (truck is currently torn down for a rebuild) I was making 320 ft/lbs at the wheels at only 1800RPM, and over 350ft/lbs from 2750 to 4100RPM, that'll tow some shit.

 

[viking]

A turbo or blower will for sure help your situation, id go for turbo first choice.
Hahns is correct about the altitude variations will not affect the turbo charged engine as much.

 

[xxxxxxxxxspshultz]

Sweet! Thanks everyone. I really appreciate the time.

Turbo it is! I have very little time working on a turbo vehicle (1990 Eclipse GSX) so this will be a big learning experience doing a system from scratch. I probably won't go for max HP but just to get back what I'm losing at high altitudes and then maybe a little more. I'm thinking it would need to be intercooled (air-to-air just for installation convenience and to keep intake temps down). I'm thinking the turbo should be sized to keep me in the sweet spot when towing (1500 - 3500 RPM's). I really hate lag. Hate it hate it, hate it.

Also, I'm not sure if I want to do front mount or mid mount only because of my Edelbrock headers I have on it now. I'm not sure how the larger primaries on those headers will affect the turbo. I do still have my stock exhaust manifolds sitting in the garage.

Oh, and then I want to keep the electronics simple. I really don't want to do a standalone system. Just seems like a lot of work for a simple tow application.

Then there's the exhaust. I think my current single 3" exhaust should be able to handle what I want out of it. It's 3" from the headers all the way back. And I definitely want to dump the blow off back into the exhaust system to keep the "Pssh!" sound to a minimum. For me that sound was cool at first on my Eclipse but after a while it just got kinda annoying. I suppose I would want to dump it after the last o2 in the exhaust. Truth be told it would be nice to make it as quiet as possible to keep it on the sneaky side.

Question is; Will I really do this? Probably a 50% chance of happening but, I should be able to do this for under $5k which is far less than a buying another truck which my wife will love. And that makes spending the money easier.

 

[Hahns5.2]

You're confusing the BOV and WG. The BOV vents boost from the cold side when you let off the throttle, the WG vents exhaust around the turbine to limit boost. You do not want to run your BOV into the exhaust :jester:

 

[xxxxxxxxxspshultz]

Ah damnit! Haha! Like I said, a lot of learning.
But yeah, quiet is goood on both sides. The guys in Japan had some mighty damn loud ones when I was stationed there.

 

[emjohn4]

About nothing, really. Forced induction was mentioned, and that will work - but consider how cost effective it is vs. just going 45mph for those long hills the few times you tow that load.

If my 3.9/5-spd can two three quads...from 1000' to 7700' in 120 miles...your 318 should be able to do the same. I've got the 3.55 rear.

A set of 3.92's would be my route, if I was really concerned with the towing.

 

[xxxxxxxxxspshultz]

No matter what I really want more power out of this truck and I do want to mod it.

I found an RPM calculator and plugged in .73 final gear, 3.55 rear gears, 27" tires (they actually measure about 27.3") and 75 mph. It gives me 2419 RPM which is what my Torque app shows (approximately). I then added in the 3.92 gears and I get 2671 RPM @ 75mph. I'm not sure if that's good, bad or even accurate.

Something else that I thought of today was what about building up a poor mans 408? It would make gobs of torque, would cost as much as adding in a turbo but be a bit less complicated and could still be fun when I'm not towing. But I really haven't done a lot of research on what a low cost 408 would put out for HP/TQ nor do I know if the NV3500 could handle the extra torque during towing. And I don't know exactly how reliable it would be as a tow engine.

 

[Hahns5.2]

408 is gonna eat a lot more gas than a turbo 5.2, just something to think about. I get the same mileage as stock and have way more power/torque.