Engine/Transmission (1998.5 - 2002) Which Turbo would be Best Value for me?

[NoSeeUm]

How did things change for you after you hung the S400 off the bottom? (I'm assuming the new rpm cutoff is less than 2000, but how much?)

I just got back from a trip. This trip was taken using SW4 and TST0 the entire time.



I was off a bit on my rpm's. Traveling 60 mph I am @ 1670 rpm in 5th and I am @ 2250 rpm in 4th. Snoking's chart seems pretty much spot onfor 3. 55 gears. I would guess my weight was around 14-15K GVW. Typically on a flat my boost was 3-4 psi and my EGT's ran about 800F.



I can spool up to around 25 psi boost in 5th on a steeper grade. That also put my EGT's up to 1200F or a bit over, where I typically down shifted if it went on for very long. Many grades the EGT did hang out at 1150F and 23 psi boost. That seemed to be a real sweet spot for boost.



I am pretty happy with the way the s400 is working at such low rpm considering the fueling potential of the M4's. I found I could pull much better at 65 mph @ 1800 rpm when I was on the freeway a short bit. On steeper grades the EGT hung out at around 1100F at around 20 psi of boost on the steeper longer grades. Its just a bit fast for me for anything other than a freeway. 60 mph is my normal for a two lane highway.



Running in 4th gear was absolutely worry free, exactly what I wanted, with the rpm's @ 2250. My engine runs really smooth and relatively quiet there. I can press the diesel peddle and pass with little EGT concerns. I made 38 psi boost on one pass up a grade accellerating back up to 60 mph to pass another guy towing a horse trailer. EGT never broke 1200F.



The M4's and the Smarty tuning will smoke a good deal if I am not careful between shifts, especially the dreaded 3rd to 4th (yeehaw, with my brother driving ), otherwise the truck is just a towing monster with no smoke at any other time.



My fuel economy was 15 mpg.



Jim

 

[jkidd]

I recently went from 4. 10 with 285/75/16 to 3. 55 gears. My average EGT went up. It is great for driving unloaded at 75mph, but towing in California is 55mph (+ no more than 5mph so you don't get a ticket)



with 285/75/16 and 3. 55 at

60mph I am now at 1600RPM (too low)

65 1720RPM (Acceptable, but might get a citation)



In 5th 60 at 2200rpm nice for going up hills, not so great for cruising

65 at 2380rpm



My next set of tires will be 245 or 265 thought about going bigger, but then 6th would be too tall.



Try a chip and boost elbow, it will help.



You don't have to go Smarty, Edge EZ, comp, I really liked my Van AAken (get it on Ebay for $200)

 

[dpuckett]

I just can not understand why someone would buy a truck with 3. 55 gears when they know they will be towing with it?? It just makes no sense..... QUOTE]



I havent done a lot of towing with a 24v engine, so I may be comparing apples to oranges here, but the 93 I had a few years ago consistently towed a GCVW of 23-24K hauling hay from central KS to ColoSpgs in 5th gear at 65-58mph. Peak boost was 28ish. Had a H1C with a 12cm housing; rarely got over 900deg (post turbo), and that was on the 2 steep-ish hills along the way. Normally ran 6-700 on the flats. It had 3. 54 gears and got in the low teens for MPG. I got 14 on one trip.



I'd say you need more air. The only way I know of to lower boost pressure and increase air mass is head porting or a cam. Neither of which is bad, but may not be cost effective. Sounds like a boost fooler is in order, along with a box of some sort. Or do a p7100 conversion :-laf



Daniel