Here's something that you can't calculate.
Firstly; consider
But I think I get what yur saying.
When you whack it open from Zero mph, it spins and goes.
But when yur tooling around and already moving, it seems sluggish; is that it?
If yes, then you have GOT to figure out your flash-stall. Here's why;
consider this graph;notice it is for a 5.2Magnum
View attachment 1715781293
Of course your 5.9 will be different but you get the idea.
So with this 5.2;
Suppose you have 3.55s and
the 46RH has ratios of 2.45-1.45-1.00-.69od. and
27" tires have a roll-out of 84.8".
So whatever is coming out of the flywheel, by the time it gets to the road, it is being multiplied by 2.45 x 3.55=8.70.
Now, study the torque line on this graph.
Say you had this engine with a 1600 stall. The torque at 1600 is say 264, so 264 x 8.70=2300ftlbs to the rear axles(ignoring losses.)
Now go look at the torque at 2800. I see about 292, so 292 x8.70=2540 an improvement of 10.56%.
But this does not tell the whole story; go look at the power difference; 80@1600 versus 155@2800, which is nearly double! You cannot touch this with gears.
Now lets see how this plays out on the road. Lets say you are cruising around at 32mph, in second gear. With 3.55s your tach will be reading around 2140@4% slip. You get the urge to speed up. With a 2000 stall, the TC will spool up to say 10% slip, so 2200rpm. At 2200 on the graph, it looks like about 107hp. But if you had a 2800, the power there is
155ish, an increase of ~45%. And we haven't even downshifted yet.
Now remember this number, plus 45%
Ok now, lets dump those 3.55s and install 3.91s. I like 3.91s because 4600 in Second is about 60mph (@10% slip) .So second gear is almost all used up power-wise.
At 32mph now your rpm in second will be 2350@4% slip. When you step on it, the rpm might spool up to 2600@10%slip.. On the graph this is
~140 hp. But your cruise rpm has jumped from 65=1980 (by the math) in loc-up, to 65=2180, so
As to hiway fuel economy; the general opinion is that any change in rpm, when expressed as a percentage will be double the loss in mileage. So from 1980 to 2180 is a increase of 10.4%, so you can expect a decrease in fuel economy of 5.2%.. If yur getting 18 now, then you can expect a loss of .94 mpg on the hiway, now down to 17.1
Which way you do it is up to you; but I would go stall..... because
1) you have a loc-up, and
2)
because of what happens on the gear change at light throttle. Suppose you had 2000TC. Suppose you are just driving around, and stop at a stoplight. When you take off easy, you might be looking at a 3000 rpm shift.. On the 1-2 shift at 3000, mathematically the Rs would fall to 1800.
But with the 2000TC slipping your tach could be reading, well, 2000/ and up to 100hp is available.
But with a 2800, then, up to 155hp is available ................. Oh yeah!
Now, to be fair, I don't think you can give your engine the timing it wants with that small cam, at 65= 1900.. But by 2200 yur getting close, and I do think that by 2400, you can. I cruse at 2240 and my engine likes 60*; however, I can only give her 57, and it hardly makes a difference. So Ima thinking 65=2200 is about the lowest rpm I would cruise that engine. And that would be 3.91s again
Now; if you were to combine those 3.91s with a 2800, that would be a heckuva thing.
Again cruising at 32 mph, the rpm will be close to 2350 in second gear,at 4% slip. Dialing in throttle, the Rs will rise to 2800, with up to 155 hp available (to the 5.2Magnum), per the graph. If you need more, the KD would provide 32 mph @4200@10% slip and looks like 225hp....... but don't get too excited; 4200 is close to redline with this 5.2, so altho it downshifts and blasts off, this is shortlived .
But your 5.9, with the 214* cam will power peak near 4600, so you might outshift first gear at 5000, and with 3.91s that would be 38mph. So then you would only be in first for maybe a second. On the 1-2 shift at 5000, the Rs would fall to 2950 mathematically, but with the 2800 and slipping 10% your tach might be saying 3250 in second. Second gear is good to 5000=65mph at 10% slip; the third reason to use 3.91s.
If you can only afford one of these, I highly recommend a minimum 2800TC. It will put a super big smile on your face every time you take off, and at every low-rpm shift, that would normally fall to say 2200 or less.
After the 2800 is in, the 3.55s should be fine for a very long time.
That's my opinion and I'm sticking to it,lol.
BTW
I have run the 2800 with every rear gear from 2.76 to 3.55, plus some others, behind a Smoggerteen that was stock except for a 4bbl and headers. I liked every one of those; but believe it or not, I liked the 2.76s best. Not for acceleration obviously, but for the fact that;
when I nailed it, the Rs spooled to 2800, then sorta hung there all the way to 65mph, with the Thermoquad moaning the whole way,lol. With this combo, 65 was about 2400, no loc-up.
Oh yeah one more thing; the starter gear with 3.91s is; 3.91 x 2.45=9.58..
At 2800, this is putting down about 292 (on the 5.2 graph), so
292 x9.58=2798 ftlbs into the rear axles. For an automatic trans, that is a very big number, and guarantees a lotta lotta tirespin.
Compare that to the current say at 2200 stall
3.55 x 2.45 x say 280 ftlbs (still on the graph) =2435. That is an increase of 14.9% in max torque available.
But again, look at the horsepower difference; say 120 to 155 equals 29.2%.
Now I'm just guessing at your stall being around 2200.
If you have a higher stall, then the gains will be smaller.
And I sure wouldn't pull a 2600 out for a 2800, no way.
But with a lock-up, there is no reason to just go 2800,lol.
