Flywheel Question
it's a 340 that's externally balanced. It's going into a 73 Dart. I've done a fair amount of research on it, and while I would prefer a T56, a 5 grand trans isn't in my budget. People criticize the drop from 1st to second but I've got a car with almost the exact same drop and it works out just fine. There's a couple guys here with them in their cars and they love them. There are some who are quick to crucify me for it, but oh well.
Well,well
This tranny has ratios of 3.83-2.33-1.44-1.00-.79 and splits;.61-.62-.69-.79
This tranny will work very nice behind small engines with small cams and small,tight powerbands. Like a Jeep 4.0, or pure-stock teener, or a 273.
The 1.2 split is a non-issue, if second is where it should be.
It's the 2-3 split that is killer for a high-winding 340.
To make this work on the street you will want a rear gear of about 2.94. This gives a nice (for a 340) starter gear of 11.26, and a 2.32 od gear,making 65mph around 1875 rpm.Now that big fat truck flywheel will launch pretty hard, for two gears. And then comes third. Where did it go? Outshifting at 6500, the Rs drop to 4030. That makes a powerband requirement in third gear of 2470 rpm, and it will have to pull that from 76mph to redline at 124mph. Can you say Slooow.Your car is now a 3 gear quartermiler, or a 2 gear in the 1/8.
But you say why did I choose a 2.94 rear? Good question. Let's say you don't care about the highway revs. So lets upsize to 3.55s. Right off the bat we are in trouble cuz 3.83 x 3.55 =13.6 starter gear. This gear is frightful to try and drive around town, cuz you barely get the car moving and it's time to shift.Good for racing(maybe),bad for street.
Ok so lets say we start it in 2nd gear. Then 3.55 x 2.33 = 8.27-not so good. This gear will require a lot of slipping with a 340.
But lets continue. Say you are at the top of second again;doing 63mph@6500 and you pull the stick, and the Rs drop to 4030 again. Now third gets to pull this to 102@6500. You are in the wrong gear to trap well. You are gonna have to rev higher or shift. Either will cost you ET.And it's still a 3-gear quartermiler. Echo;slooow.
So what do you do? I know!Lets work the formula backwards. Say you are looking for 110 mph at 6300, cuz that puts your engine just on the downside of the powercurve, and you think it can pull that mph. Heres the math.MPH =( Rpm x TC)/1056 x R1 x R2 Where TC = tire circumference;say with 28s, and R1 = Rear gear, and R2 = tranny gear
So working it out we see that R1 x R2 = 4.77. So what rear will give us 4.77 in overdrive( so we can use 4 gears in the qtr)? Answer is 3.73s Well that seems pretty good.
3.73s will make a second gear street starter of 8.69 which seem ok(barely). And a first gear race starter of 14.28. Which with that truck flywheel is almost guaranteed to be a wheels up launch.(learn to shift before she comes back down, or prepare to get a tow). And the od will be 3.73 which seems ok. With 3.73s, the splits are; .62-.69-.79,
which is excellent.
Now the bad news.
1) In most trannys the O/D gear is pretty weak. So you'll probably blow it up the first time you enter it at 4000rpm.
2) On the street with 3.73s first is useless,(Except for parking on soft ground at the shows) but second is a quite far away. So basically you have a wide ratio 4 speed, behind an engine that wants a very close ratio, and in a car that is easily 10% overweight for a 340.
3) 65 mph = 2380 with 27s
4) That truck flywheel will be very hard for the synchronizers to slow down from 6500 to 4000
5) Opinion coming;I doubt that tranny can handle a 340, so it will likely blow up on the starting line.
6) Have you seen how deep that baby is? Watch out for speed bumps.
Ok enough track bs.
Lets say you care not a bit about how fast your 340 is. That takes us back to the beginning.
Since you already have the 340, put a tiny 2bbl cam in it,a spreadbore/late opening secondary carb on it, call it a big-bore teener, and shift early.This tranny will work pretty good with a high-torque, low rpm engine.And I can tell you from first hand experience,that a 340 with all the teener stuff on it, is prettty torquey
Or get a Mopar tranny; made for Mopars, with tight splits, really tough to blow up. Imagine that you blew all the cash you saved so hard for, on that Aisen and all too soon its coming out in pieces.
Or maybe it will last if you saddle it with real skinny tires. Kinda not what a 340 wants tho, eh?
Now I know you didn't ask for any of this crap, and that you researched the Aisen, but Man, I just hate to see a guy blow his savings and a fairly large chunk of time, on a 5spd dream, just to have it all come undone.
All opinions are those of the poster, and are not to be confused with facts, cuz opinions are, well, just that, and are seldom changed.