As you can see, I have a 4.7 Extended cab. I think I've done all of the "affordable" tuning options, up to and including 212x cams and a high-stall converter. Short of fitting a blower, I think I'm done under the hood!

Now I'm thinking of altering the gearing. Mine has the 3.55 axles (yes, its 4x4) so I know it ain't going to be cheap. When I was buying my truck, I test drove another 4.7 that was definitely a bit quicker off the line than my (standard) truck that I eventually bought. At the time I didn't know about the two axle ratios (but as there aren't many Dakotas over here, it wouldn't have made any difference as the rest of the truck was much better).

My question is what ratio to go for. I've felt the difference between the 3.55 and the 3.90 and like it but was wondering if 4.10 is too low for the road, as that's where it spends 90% of the time.

By my calculations the difference between the 3.55 and the 3.90 is aprox 10%, whilst the difference between the 3.55 and the 4.10 is 15%. I really want the kick off the line but highway cruising is still quite important to me. I think that at 70mph the revs would be around 2400rpm on the the 4.10, as oposed to the 2100rpm it does now. Sounds ok to me but has anyone here done it?

Thanks for any info.

 

I personally have never had 4.10 gearing in a stock dakota, so I am not able to answer that question, but, is your dakota still stock height? Have you changed tire sizes to a larger size? A 3.92 gear would be fine for a stock truck but I feel that a 4.10 might be a little deep for running down the highway.

 

lots and lots of vehicles have come out of the factory with 4.10, 4.30, 4.56 or even deeper gears. they don't seem to blow up. don't fear the 4.10s. everything will be fine.

 

The 3.92s will turn about 2,400 rpms at 70

 

u have 212 and and a stall? i wanna see videos? what kinda power are u pushing?

 

I have no idea what power its got! Its got AWD so need a 4 wheel dyno AND I'm running M/T tyres which I don't think would appreciate the experience! The last time I put it on the strip was with the cams but before the High-stall was fitted. It did 16.04 @ 84mph.

Although they said the 212x cams were fine for the road, with my current gearing (3.55) I found they actually made it bit slower off the line but better once she got going. The high-stall isn't that high, probably about 3-400rpm over stock but makes all the difference. If I were doing it again I'd actually get it made just a little bit higher. Hence the enquiry about the gears.

The sad thing is, its probably only marginally quicker than a standard 4.7 with the 3.91 gears. This is of course only my opinion, based on a test drive over 5 years ago!

 

I have made the change from 3.55 to 3.92 gears. Although mine is '98, 5.2, auto, 2WD the change was fine for all driving. It was about 200 RPM higher at 70 MPH. some improvement in 1/4 but can't give you hard numbers. Lost about 2 MPG. By the way, when I was looking I couldn't find a 3.92 in a V-8 the guy at the salvage yard told me the ones from the 4 cyl. were the same. I got one out of a 4 cyl. put it behind my 5.2 and have never had a problem. hard driving and a lot of trailer pulling.

 

Thanks DodgeLive. Its good to hear from someone who's done the swap. It also confirms my gearing calculations are ok. 3.55 to 3.92 adds 200rpm@70mph and 4.10's would add about 300.

I think that whilst going to all the expense of a gear change, I might as well go for the one that gives most difference (within reason, NOT 4.56's!), as it looks like its only 100rpm difference @ 70mph, whilst giving an extra 5% torque over the 3.92's.

Thanks for all your info. Will let you know how it goes. Won't be for a while though!