Automatic to 4 speed Conversion in '65 Formula S
Besides,
I just plain want a 4 speed with overdrive in the car.
It would be great on the freeway going to shows, and for touring.
I think the 4 speed offers more of the sportiness the Formula S was meant to convey.
Nobody can argue with that!
Here are the A833od ratios
3.09-1.67-1.00-.73od, and here are the road gears with a 3.23 rear
9.98-5.39-3.23-2.36 , and the splits
.54-.60-.73 , meaning that at whatever rpm you chose to shift at, the rpm will fall to those percents.
So let's say your engine sounds good at 2800, like mine ,lol, and so you shift out of first at 2800/22mph. And so in second your rpm will be 2800 x.54=~1500rpm.
I see two problems right away; 1) does your 273 have enough torque at 1500 to to continue accelerating in this 5.39 roadgear?, and 2) will it pull hard enough to satisfy you?
Let's say your 273 makes 140ftlbs at 1500, and so 140 x 5.39 x24/25.5=710ftlbs to the road. This is torque below mediocre. In other words you can cruise at 1500 but don't expect much in terms of acceleration. And that leads to having to hold first gear to a higher rpm.
So where does the hi-compression 273 start to make torque. Lets say it torque-peaks at 3200rpm, and say at 2800 it had 80% of that . This is why she sounds good at 2800, cuz she's loafing at high efficiency. So, for reasonable acceleration she will want to come in at 2800, and that means the 1-2 shift will need to be at 2800/.54=5185rpm/40 mph. You see the problem with that? Me too. Nobody drives like that ALL the time.
And that means at normal throttle openings, on the primaries only, your acceleration will always be mediocre in second gear.
So what is the problem here? Two things; 1) the 5.39 roadgear, and 2) the very wide 1-2 split. How do you overcome that? Well you can re-gear the back and get second gear to work for you at a better rpm, but you cannot do anything about the wide split.
What I like to do is to put the second gear rpm in the fat part of the torque curve at the roadspeed I do most of my driving. So for you that might be 32mph and 2800rpm. This will take 3.91s in the back, for 32mph=~2700 (4.10 would be 2900). So now you have second gear working from say 2500 to say 5000 with a 4bbl cam, which is 28 mph to 56mph.... Do you see the problem with that? Me to; this is a really long pull, in 3.91x1.67=5.39 road gear.
And we're still in second gear. When you hit third at 56mph your Rs will drop to 60% or 3000, and your little 273 is all done; even tho it now has 3.91s. And lastly; 65~ 2400 still with the3.91s.
Ok one more; with 3.91s your starter gear is 3.91x3.09=12.08; kindof a race-track starter. This works great for acceleration when you are in a hurry, but not so much when just cruising.... unless you rev first gear high enough to get into second with enough torque to continue accelerating to what ever speed you had in mind between 28 and 56 mph, at the rate of acceleration that makes you happy.
Ok so what's the conclusion?
The A833od trans will be fine in second gear if geared right, at the back.
With a low-torque engine,read small cubic inch, this compromises all other gears.
I tell you the truth; I had a 367 hi-torque engine putting out over 180psi cylinder pressure; and I had nearly every rear gear in my stable from 2.76 to 4.30, and I could find no love for that transmission, until I installed a GVOD and began splitting those very wide gears. oh and one more thing; That overdrive gear is IMO incredibly weak. I blew up a couple of them just by forgetting that trans was not a 4-speed but rather a 3 plus 1.With my 367,and 4.30s, shifting into that gear took a lotta concentration.
Ok so now, I know you may not want to hear this, but I think I should at least mention it;
The
A999 TF with a hi-stall, operates like a wide-ratio five-speed with a short 5th. And your 3.23s are perfect for it. The ratios are 2.74-1.54-1.00 And the TC might have an internal torque-multiplier ratio of up to 2.0 to 1. Say with your 273 it works out to 1.8, and say it
couples at 1.05 at WOT. And it has a lock-up feature.
When you couple this with a 3.23rear, the road gears might look like
15.93 decaying to 9.29-
5.22-3.39-3.23locked up. 4.5 gears
From 15.93 to 9.29 is about 2 gear ratios, and it's all automatic, operating like a CVT (Constant Velocity Transmission). If you split that space in half you will see that the splits would be .76 or a pretty close ratio. And the in-between gear might be 12.10, so now if you rearrange those ratios and splits it looks like
15.93 decaying to 12.10 decaying to 9.29-5.22-3.39-3.23locked-up, with splits of
.77-.76-.56-.65-.95 Of course the 12.10 is an imaginary gear but kindof shows you what is happening inside the TC. So I call that a 5.5gear trans with a very short final shift.
So what does that mean to your 273?
Well put a 2800TC in there and find out. Going back to the original torque curve, lets say at 3200 she puts out 290 ftlbs, and at 2800 say 260 which is ~140 hp.
So now you nail it and the engine spools up to 2800, and instantly she is putting down
260 x 2.74x3.23x24/25.5=2166 ftlbs to the road, and the result of that is tirespin. So now the TC is ramping down through an infinite amount of graduations to 9.29 ratio as the car is moving and accelerating. So let's say 40 feet out, she hits 9.29 and now the rpm has climbed to (I'm Guessing) 4000, and the torque has fallen to 90% or 260ftlbs, but the hp has climbed to 198hp, on its way to say 235@4800. So I'm guessing the tirespin is coming to an end at about 30 mph, and now you are really accelerating, towards the manual 1-2 shift at say 5200/44mph . So now, still at WOT, the Rs drop to 56% or to 2800...... again, and now the roadgear is only 5.22 so your race is over. You can fix this with more rear gear, but that will subtract from your
65=2700. You could do this with an
A998loc-up (2.45 low) and 3.55s and get about the same first gear, but would tighten up all the splits, with a higher cruise rpm. The roadgears would be
15.66 decaying to 9.13-5.40-3.73-3.55 ,and splits of
.60-.59-.69-.93 This makes second gear 3.4% better.
But 65=2970cruise
So lets stack 'em;... rear gear..........second..... top... cruise.. 1-2 split
First the A833od with 3.23s....... 9.98-
5.39-3.23-2.36; 1975 ..54%
next the A833od with 3.91s;.... 12.08-
6.53-3.91-2.85; 2385 ..54%
next the A999 and 3.23s; 15.93>9.29-
5.22-3.39-3.23; 2700 ..56%
then the
A998 and 3.55s; 15.66>9.13-5.40-3.73-3.55; 2970 ..59%
The T/A box, and with 3.73s; .....
9.21-6.60-5.00-3.73; 3120 ..
72% the ripper
Commando 4spd w/3.23s;...... 9.98-6.20-4.52-3.23; 2700 ..62%
This Commando box shows you why I recommended this box earlier. It gives you tighter splits at every shift (EDIT: except for the T/A box). Check this out;
Commando with 3.55s; ....... 10.96-6.82-4.97-3.55; 2970@65; splits of 62-72-71% This is the best 4-speed for your 273 as regards rapid acceleration; just gear it to put second gear where you want it.
The A998/3.55 will be better off the line with about a 2800TC; 15.66 is a hard act to follow;
15.66x 260ftlbs@2800=4072 ftlbs, decaying automatically to 2374 ... versus
10.96x 290ftlbs@3200 =3178, the best the Commando can do with 3.55s.. if the 273 cannot spin this, or bogs, (shouldn't) then the A998 is the hands down winner.
Traction control and a SureGrip will be mandatory.
So that was at WOT
What about just normal driving? If you like the 4-speed, you gotta have the Commando box. You can run it with the 3.23s and probably will enjoy that combo for a long time. The 6.20 second gear will make 32 mph to be 2555rpm, a bit low to whack it open from, but the downshift gets you 4100, so then yur gone. Also, that 6.20 gear will get you 60= 4800, about right on the power-peak. And 65=5200 about shift-rpm. Then into third at 3750 Badaboom! we are moving right along! And passing from 55 will get you 3200 in third, right on the torquepeak, or 4400 in second at about 90% of peak horsepower if yur in a real hurry.
This is about as Sporty as it gets and still having some cruisability, namely 65=2700 with 3.23s.
I love that Commando box with my 3.55s. Because I have a bigger engine (and a bit more weight;3650), I am sure she would be happy with 3.23s... but I need the 3.55s to hit 93@6150 with, in the Eighth, by gearsplitting; so they are staying.
There are other boxes that can be adapted to the 273, Five-speeds with overdrives , but generally the 1-2 splits are too wide.
