tglandon

i have a LQ4 that has a Magnuson MP122HH supercharger on it. it tows good if i hit it at the bottom in 3rd gear 3k rpm. my problem is that is almost 70 mph. i cant go over the bigger mountain passes that fast when the speed limit is usually 55 mph. that puts the rpms closer to 2k. I tow a pretty heavy with the truck loaded and a 9k lb trailer.

What will help in the 1.5k to 3k rpm range? Choices are:

1. Change pulley to get more boost. i want to stay within the chargers reliability/efficiency range. I think i wouldn't go above 8 lbs of boost..
2. Tow Cam. looking at Vinci "HD tow stick", or "Towing and Performance". But i am not sure what makes a good supercharger and tow cam..
3. Exhaust Headers. Shorty or long with 1 3/4 or 1 5/8 primaries into 2.5 collector.
4. Gears. i have 4.10's and p265 size tires. maybe 4.56 or 4.88's but not looking to change tires size back to stock or go bigger.

I am not looking to start a diesel/gas fight.. I am not going diesel. My first house didn't cost as much as a new diesel these days. just looking for comments about the options above. I am not wanting/needing to get more max Torque/HP. if i spin it up above 3k rpms i get enough already. just looking for improvement from 1.5k to 3k range.

3wide

" i cant go over the bigger mountain passes that fast when the speed limit is usually 55 mph. that puts the rpms closer to 2k. I tow a pretty heavy with the truck loaded and a 9k lb trailer.

What will help in the 1.5k to 3k rpm range? Choices are:

4.56 gears would get you around 2750 rpms at 55mph and 4.88 gears would put you at 3000 rpms at 55mph of course that is 3rd gear.

If you are loading the truck up and hauling that heavy trailer and just spit-balling here of course and you are doing this at least 50% of the time, I would go with the 4.88 gears IMO. That would keep in you in your torque peak of that motor even if you slowed down to 45-50 mph while slowing down for a grade and or a slower vehicle in front of you.

DEWFPO

I would agree with 3wide's coments above.

If you don't want to make more HP or TQ don't mess with the pulley.

Even tow cams have a hard time in the 1,500 rpm range on a gasser.

The headers won't buy you much either if your already making enough power and they typically don't shine until you get way up in the power band. Unless your current exhaust system is a big restriction, which it might be since you have a huffer.

The key thing you said was that if you could keep it 3K rpm going up hills you'd be happy. And, you don't want to go to a smaller tire so gearing is your logical answer.

DEWFPO

tglandon

One more thing, I had been running the factory chip from Magnusson and just sent it to Westers Garage so they could update it, knowing what my towing concerns are. i installed it this last weekend and this will help. it seems to have a different personality. I need to let things settle out, but it is evident that the G80 Eaton differential is not working properly. One tire wheel spin in the wet.

TXsilverado

iTrader: (19)

Drop your transmission to a lower gear on steep climbs. TADAAAAA!

smokinlmm

^^^ This, gas motors hate to be lugged down in the lower rpms. If you want to pull grades at low rpm get a diesel...

tglandon

thanks for you input, but i dont want to run in second at 4k for a few miles at a time up the cascades. The supercharger has me close, the Westers chip update has me closer. I know diesel has advantages, but it is not for me.

The best input so far is 4.56's especially if i have to go in and fix the G80 Eaton Diff anyways.

3wide

Not really, I will explain why since gearing is my day job. Engine torque output and gear ratio make a multiplier which gives you effective torque at the rear wheels.

Current set up with 4.11 and I used 425 foot lbs just as a metric for this.

425 x 1.0 x 4.11= 1,746.75 torque at wheels

Set up I recommend with 4.88 gears.

425 x 1.0 x 4.88= 2,074 torque at wheels.

As you can see gearing is giving you torque to pull your load not an RPM which every is quoting. Analogy is how Tractor Trailers can pull 80k plus pounds they use gearing to give the more torque to pull the load.

A lot of people are afraid of gearing on forums mainly because they don't understand it. I have a relatively stock 07 Chevy crew cab with a 4.8 and 4.10 gears because I know the motor and I know it needs gearing to be work properly for me. I still get 18mpg and it is tuned properly by a local tuner.

Pick gearing for the torque not some RPM that people think the government says will give you MPG. Trucks are not made to loft along at 1600 rpm at 70 mph with a full load.

smokeshow

iTrader: (16)

Work on improving your intercooler system efficiency. Pretty simple and non-invasive but can net you some substantial gains for long durations at steady state. Maybe start with a better heat exchanger.

tglandon

thank you for all the ideas..

i know that a gas engine will never pull as good as a diesel. I just want to make it pull better and i am taking small steps that way.. i cant afford to do this all at once.