Ok so I put most of your comments from page 1 into one place, so I don't get confused by what others have said. And then I will comment in blue.Keep in mind that I'm just a guy with a calculator, that happens to have a GVod. I'm gonna post it out as I go, on account of my computer likes to lock up and loses the draft when it does.
1974 duster
Blueprint 408 stroker (465hp,550ftlb)
Dana 60. will be doing more street driving that track. Tires will be cobra Gt 295’s, but will also have a set of 315 nitto Nt05’s.
Have you given thought on how to fit those 315s into the Duster tubs?
Want it to have great acceleration to keep up with modern sports cars on the street, but not be too geared up that the pedal is so sensitive it becomes not fun to drive
I'm not understanding this comment; so I'll take a stab at it' . Sensitivity at tip-in is always one of:
1) too much low-rpm timing, or
2) primaries that are too big, or
3) too small a rear gear, or
4) a spastic right foot, or
5) some combination of the above.
haha I hope I didn’t make a stupid purchase. Makes sense to me to split 2nd and 3rd gear, have more range in the power band, higher gear for more acceleration and the OD to drop rpm ~600 on the highway.
Oh yeah, yur on the right track. But I see two things in your thinking that I can't agree with; 1) You have a 408, and 2) on street tires, that 3) in a Duster weighs practically nothing to a 408
Ok so with a 408, a 727, a modest stall, on 295 Cobras, in a duster ..... is a recipe for tirespin......... no matter what rear gear you run. And there is NO CHANCE to split second and third. I mean you can but there is NO POINT IN A STREETER Lemme explain Your 727ratios are 2.45-1.45-1.00 adding the .78 GV ratios in Red I get 2.45-1.91-1.45-1.13-1.00-.78od, your splits are .78- .76-.78-.88-.78 So if you are in second-over and shifting to Third your Rs will drop to 88%, which, from 5500 is to 4840, is a drop of 660 rpm, which sounds good but here's the deal; with street 295s and 3.23s, that comes at 85 mph, and in all likelihood your tires will still be spinning. Soooooooooooooo what advantage is there to having the GVod in this instance? Answer; I hope you are somewhere that the coppers ain't. Remember what Rusty said? So that's strike one. Strike two for splitting is;. Between First and Second the splits are very nice and tight, a sucked out 318 would love it, for all the reasons you would think. But will your 408 love it? If your tires are spinning in first on the split, then no. If your 408 spins the tires in second gear then no. I have had those Cobras behind my 367 and she spins them to long past 60 If your 408 cannot roast 295 street Cobras to 60 mph. it is sick. So then, what advantage is the GVod in this instance? For splitting the big 408, IMO, nothing; certainly not anywhere near worth the buy-in.So that's strike Two. Strike three is this; The GVod cannot be backshifted under power. So when going from First-over or Second-over to the next non-over gear the power has to be interrupted while the unit out-shifts. End of the bad stuff. Here comes the good stuff With 3.23s your trip to 65mph cruising speed could end at 3000/zeroslip, maybe 3300 under power in Second over. Dropping into Third-over at 2060@zero slip. Do the math. That is a drop of 38% making the OD EFFECTIVE ratio to be .62. NOT .78 that everybody complains about. So then your shifts would be 2.45-1.45-1.13-.78 That's very nice.
There is no good reason to run 3.23s which do nothing but drop your rpm too low for most street cams, which will want 2400 down to 2200. But it is nearly impossible to give the engine the optimum timing to cruise at those rpms. 2400 is just barely doable with non-computer-assisted timing controls. So, to cruise 2400@ 65mph with 26.7" tires will take, surprise surprise; 3.73s for 65= 2400 in loc-up, up to 240 more at 10% slip. That, you can optimize the cruise timing for. So having settled on 3.73s, you now have a tire-fryer in second gear, to 65=4400@zero-slip, perhaps 5100, at 15% slip, on the tach. No GVod required.
yeah originally I was going to do a 4L80e built trans by Jake’s performance m, but didn’t want to cut up my tunnel that bad and Blueprint Warrenty covered there engine and 727 trans. When I put my nitto 325 tires in I’d like to have a high gear and get those tires to hook for some serious acceleration. so guess I’m stuck with deciding 3:55, 3:73 or 4:10 gears.
[/QUOTE] So now with the math done; lemme show you something; First; you gotta know that the TC has a hydraulic multiplier in it, by the way that it works. This multiplier, at WOT, can vary between 1.8 at zero mph, to perhaps 1.1 at 100 mph. It is like a Torque-Sensitive, CVT, with an overall ratio of 1.1/1.8=.61 or very close to a fourth automatic gear that does the bulk of it's work right on the starting line, but never actually quits. Suppose your engine makes 380 ftlbs at stall. Thru the trans (more math coming), that would math to 380 x1.8 x2.45 x3.23= 5413 ftlbs into the rear axles, at zero-mph. I guaranstinkingtee you the tires will spin. And as the rpm goes up the torque curve, the TC will lose some ratio, while the engine builds torque with rpm, and that will keep the tires spinning, until the power just kills them, all the way thru first gear.
When she hits Second the Rs will drop from say 5800 to 3400, back into the fat part of the torque curve, say 410 ftlbs. And the TC ratio may have dropped to 1.3 or 1.2, so into the rear axles now, you get 410 x1.25 x1.45 x3.23=2400 ftlbs just enough to keep those Cobras boiling. And as the engine climbs up the powercurve, those Cobras will never hook. Not in first, and not in second, unless you pedal it.
So knowing this is possible
IMO Forget the GVod, and leave the 3.23s in there. IMO Give them a chance at least.
My 367 will bust those Cobras loose at 50/55 mph, with just a footstomp. I have no help from a convertor. My second gear ratio is 1.92 x 3.55=6.82. Your second gear ratio, from a footstomp will be close to 1.45 x3.23 x1.25=5.85, or about 14% less than my 6.82. But you have a 408 compared to my 367, so 11% more cubes, and your engine, at 50 mph will be doing 3700, to my 4280. Your's is on the rising side of the torque curve, while mine is on the falling side. I think your 408 will annihilate your tires worse than my 367..................... lol. 3.23s will cruise 65=2640@ zero-slip. This is easy to work out the cruise timing for, which will offer the potential for max fuel-economy. This is also easy to work out the cruise-fueling for again maximizing your potential for fuel economy. And the best news is this; at 32mph on the 2-1 downshift, the Rs will rise to 4140 from 2450 in Second, which means going from sleeper mode, to batchit crazy instant tirespin. And first gear will go to about 50 mph@ 5720@15% slip. Those are nice street numbers.
So, IMO, For your combo; I would leave it the way it is until you get your traction issues worked out. I mean don't get me wrong, I love blowing my tires off every chance I get, but the GVod is pretty much reserved to the final shift on the hiway. My lil 367 has plenty enough power to kill the tires easily to 65 mpg; (295s, Cobras or BFGs). Or even the 325/50-15 BFG Drag-radials I bough for the track. With street suspension, I get 2.2 to 2.4 60fts, and tirespin, they say to over93 mph. And my tach concurs.
I cannot in my wildest imagination think that a 408 wouldn't better that; even with 3.23s. Jus trying to save you a ton of money.
now, if you had a 318, that's a whole nuther story.
