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Croatan_Kid

Croatan_Kid

How's your hammer hangin'?
Joined
Nov 4, 2007
Location
New Bern
Sorry in advance for such a long, drawn out post. I like to be detailed and complete to avoid confusion.

1999 Silverado, reg cab, long bed.
4.8/5 speed
Just wrapped up an SAS, kinda fine tuning a few things and getting it how I like
I used a 79 Dana 60 up front, the rear is an AAM 11.5 courtesy of an 8.1L powered 2500HD

It's just a little guy, only on 35s and probably going to stay that way. Decent sized tire, plentiful, affordable, etc. Since the 2500HD was a gas truck, it had 4.10s and I figured with 35s that would be fine and normally it would be, however it seems that it doesn't really like the 4.10s. On the highway at 65mph, I'm below 2000 rpm..again sounds great, but I feel like I'm lugging it in 5th gear if I'm below 50-55. It's certainly lacking what little bit of low end it had in stock form.

I've got a fairly aggressive tune, dual e-fans, very free flowing pipes, intake, etc. Next plans are some stainless shorties (because longtubes won't fit anymore) and a nice Comp cam...and more tuning.


So, the question is: Do I continue to rock it as is and see how it feels after the cam? Sure it would have more power, but my RPMs wouldn't change and I'd just be forcing more power through the same setup. I'd like to make the NV3500 lead a long and happy life under my truck. Plus, there's a good chance I might be out of the proper operating range of the cam and it might fall flat on it's face.

OR, do I snag some 4.56s or 4.88s, bite the bullet and swap some gears? I just put the matching 4.10s in the front a few weekends ago with a Lock Right. I've still got dig into the rear axle, throw in a Detroit and throw away the G80. Money nor setting up gears are my deciding factors, I just want to get it right.


Here's some RPM/MPH figures, all are using a 35" tire and in 5th gear:

4.10s, 65mph = 1920 rpm
4.10s, 75mph = 2215 rpm

4.56s, 65mph = 2140 rpm
4.56s, 75mph = 2470 rpm

4.88s, 65mph = 2285 rpm
4.88s, 75mph = 2650 rpm



With that said, I'm only second guessing myself so much because it's only one step lower in gears. It proves itself on paper, but I figured I would get some second opinions. 4.56 seems the be the best choice with a 35" tire. When I go on a road trip it'll be in this truck, so a hair less than 2500 RPM at 75 sounds better than just over 2600. I'm pulling off 16mpg as is and it wouldn't hurt my feelings at all to keep it that way. The only reason I considered a 4.88 is because they're quite a bit cheaper than a 4.56.


Thanks for reading, I'd like to hear some words of wisdom from other people!
 
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Why not put it in 4th gear if you feel you're lugging it at 65mph? Yeah you'd have to wind it out, but otherwise you'd have to listen to that thing turn 2500rpm all of the time on the interstate...
 
4:88 seem to be just about right. I think its your motor more than anything. My 97 2500HD LOVES 3000 rpms!
 
Feels like I'm lugging in 5th gear under 55. I leave it in 4th until then. I have to wind it up between gears as is, but you can't really hear this truck much anyway, it's my quiet ride. The old K30 I have has 5" stacks and if I had to listen to that at 2500 rpm, I'd be concerned.


Once you wind this thing up above 3000, it'll leave town, even with the 4.10s. I can only imagine how it'd feel with 4.56s. The short stroke of the 4.8 is what's killing it with the extra weight from the SAS and 35s. The torque starts to roll in about 2500-3000 rpm. I'd run 4.88s, but it would be killer on the highway unless I stepped up to a 37. I'd run a 4.63 in a heartbeat, but they don't make that ratio for an HP60 that I've seen. They're available for the AAM 11.5 though.
 
you could run a 4.63 in the rear and 4.56 in the front. Those are pretty close, and in the dirt it wouldnt matter much. If you felt thats the best of both worlds on the road, its what id do...
 
5th gear/OD isn't for "low-end" pulling... it's for moving your rig down the interstate at the least RPM/most efficient means. Do you *really* need to stomp down on it in OD and get mad acceleration? IOW, drop a gear and wind it out to get 80/90/100mph if that's your need, but leave the final gearing. FWIW, my '91 Mustang GT runs 2000-2100rpms in OD doing 65-75mph. If I want to scoot, dropped to 4th and matted always does just fine. :D

You mentioned the tune... does that also account for the change in final gearing/tire size? While not as crucial with your rower as it would be with a 4L/6L tranny, incorrect VSS signal might play a part?
 
Oh, I agree about the 5th gear deal....and certainly dropping down a gear helps, it's just lacking a little help. It almost doesn't want to accelerate any rolling down the highway. Know what I mean?

The tune is set up for the 4.10s and 35s. VSS signal is dead on according to the speedo vs. a GPS.

I've considered a 6.0 swap...the NV3500 would live behind it just fine probably. I've seen guys do it.
 
I agree. I like the 4.8 for what it is. I've whooped plenty of 5.3s and 6.0 trucks, but I think the 5 speed is what helps with that :D The cam I'm looking at should yeild some nice torque gains.

Specs:

Comp Cams PN - 54-455-11
265LR HR12
265/273
@ .050 - 215/223 and .604/.610
LSA or 112 with a +5 grind

I filled out a Comp Cams suggestion sheet and that's what the rep sent me. I looked it over and it seems to be a nice little cam. If nothing else, I think a regearing would help the motor relax a little and it wouldn't feel like I'm dragging a parachute all the time. Hell, mileage might go up a hair.
 
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