Lightweight flywheel options and selection criteria.
I acquired it with the thought that it would be a cheap alternative to a Gear Vendor or TKX to get an OD for longer road trips and around town driving.
For a 450hp 340, bad idea man . The gears are too far apart and your 340 will fall off the cam every stinking time. I had the same idea, and it took a GVod, run as a splitter, to keep the engine in it's operation range.
That worked really well but HAVING to split every gear all the time, on the street, got old.
If you do this with the GV, I highly recommend to take the factory od gear out, and ship it to me before you blow it up. ..... cuz I got two od boxes here in the which that gear is mysteriously missing lol. (I blew them up) With the GVod you wont be needing it anyway, and if you do blow it up, I found out, that it can take the rest of the trans out with it.
but I gotta tell ya, that box, by itself, was horrible with my 367 cubes and a 230* cam, never mind what it might be with 25 less cubes and a cam 3 sizes bigger. Sell it, friend, just sell it.
For your application, I think I would like a Commando. The 3.09 is not as far away as it is in the od box, and the rest of the gears are just like the 2.66 box. So if you gear right for your track, that 3.09 might be just the thing to get you launched. I run it on the Street with 3.55s and about 430 hp now, and I really like it. But, to be accurate, I'm running OOTB alloy heads, and cylinder pressures over 185psi. and I'm running those KB107 pistons that IIRC are 502 grams? So, I'm real happy with the factory flywheel. For me, First gear is now a dump-it and go deal, and I can get her down to 3.5mph, which she will idle along at, all by herself, for as long as needs be.
but forget that od box; she's just for a lo-perf engine with a super-broad flat torque curve, like say one running a 114 Lsa, lol.
Oh BTW,
You cannot backshift the GVod under power. Well you can but, you run the risk of busting it. When you downshift, the unit should already be in direct-drive mode, and your engine to road-speed should be more or less matched. I have tried back-shifting with the unit fully in overdrive, and have gotten away with it. But if you engage your engine clutch with the GVod unit not fully engaged, and the unit is caught mid-shift, you run the tisk of braking it. Which will cost you 50% of retail plus shipping to rectify. For that reason, I highly recommend to not try to use it as a splitter for auto-cross. It only takes a split second even at idle to break it. Yes I did bust mine by accidentally leaving it engaged in reverse.
So if you can't use it for autocross, then you might as well not lug the extra 23 pounds around right? at least that's what Ima thinking.
This Commando/GVod works very well for me, but to be honest, knowing what I now know, if I was to do it over, I'd just get a 5 or a 6-speed, depending on how bad I wanted to parade. Or, I'd just get a Second HotRod, and NOT try to run a dual-purpose machine.
BTW
I use the term parade loosely. I can't begin to tell you how much I hated it when I was running the F-body od box, and having to buzz the engine up to more than 3000/3500 rpm, to catch Second gear at 54%, just to have some torque at the new rpm. I hated my car sounding like a Mustang.
The Commando is 62%, and so, I buzz her up to 2800, which drops in at 1740, and my small-cammed 367, easily pulls that up. Whereas
with the od-box, the split is 54% which from from 1740, is 3220. I know it's barely 420 rpm, but think about it; the split in your 2.66 box is .72, so from 1740, if yur 340 can even pull that, Second is only 2410. that is a long way from 3220.
Some guys have a hard time understanding math, so here are the various gear ratios and their associated splits;
2.66-1.92-1.40-1.00, splits of .72-.73-.71
3.09-1.92-1.40-1.00, splits of .62-.73-.71
3.09-1.67-1.00-.73, splits of .54-.60-.73
Whatever rpm you up-shift at, the next gear will come in at the split,
IE, in the od box if you out-shift First at 6000, then Second will come in at 6000x.54=3240, so that's a powerband requirement of
6000 less 3240=2760. therefore did I say no 450hp 340 can touch that. at best, your powerband will be 1500rpm..... with maybe 200 more at the bottom if you know how to build.
Second is better, again shifting at 6000, third will drop in at
6000x.60=3600, for a powerband requirement of 2400, but still beyond your combo. Whereas
both of the other two have a 2-3 rpm drop of
6000x .73= 4380, which is then, a powerband requirement of 1620, which fits your 340 fairly well.
There is one other trans, the 1970 T/A with ratios of
2.47-1.77-1.34.100, and splits of .72-.76-.75
In this box you get the same tight 1-2 split, but the next two , are even better; 6000x .76 is 4560, for a powerband requirement of 1440, an excellent match to your 340. With this box you might be able to lower your shift-rpm say 200rpm which would then shrink your powerband requirement to 1390. Compare this to the OD-box at 2400; which is a completely different animal.
I once had one of these. I loved it. But First gear with 3.55s was just not making me happy. 2.47 x3.55=8.77; can you say sloooow off the line?
Sell that od-box. All it is to you is spare parts, and only if they fit, which is iffy. NONE of the gears nor shafts swap into the 2.66 box.
Happy HotRodding, again, lol.