Transmission gearing

[DannyPip]

Hello all,

I currently have a longbox in my car. Unknown what 3rd is honestly, but it's an LRE from 2009 or so(and I think it's a "short/long" with 1.26 3rd and 4.12 ring).

I am building a shortbox as that seems to be the consensus. I have built a bunch of swing trannies before, so don't worry, I've got this.

Anyway, I have a couple of early 60s boxes with 4.37 ring gears. They both have stock ratios of 3.80/2.06/1.26/0.89.

I will have a 1.22 bus 3rd shortly to use, and have deduced that this is a) desirable and b) "long-short".

The question is, how much of an actual difference will the 1.22 3rd make in the Northeast tour: LRP, Thompson. Palmer, and NHMS? It's 125 rpm difference when shifting up there around 6-7k.

Here's a comparison screenshot of the two short gearboxes: long third on left with short third on right.

Disregard P-metric tire size, diameter of the tire is all that matters, and is correct at 22.5".

[problemchild]

Many different theories so you won't get a consensus. Third gear choice is very track dependent, mostly effected by the speed of 3rd gear corners. So much is situational, depending on the transmissions in the cars you are racing with at any given time. If you have the short 3rd and are racing with 3 cars running 1.22s, then you may have an advantage, or vise-versa. Or your advantage may be negated because they slow you up when you are supposed to be faster.

Conditions, including wind, can also be a factor. In the days when long box or short box were common at the Glen, the LB would win when there was a tailwind on the back straight, and the SB would win with a head wind.

[DannyPip]

Thanks, Greg. The plan is to keep the longbox with 1.26 3rd as a spare. It seems everyone runs shortboxes everywhere now. No longer switching to the longbox for LRP or the Glen(they don't run there lately at all).

I could build both short boxes I have with different 3rds, 1.26 and 1.22. The question I'm asking is do I build the 1.22 3rd shortbox and just call it a day? Maybe build the other shortbox and keep that as a spare?

Spares are great to have, and currently I have the storage room.

[nrider42]

Thanks for posting the ratios and that chart. I have been pondering this issue as well. I am new to vee racing and I am finding that attempting a pass is easy...completing a pass is another matter. Draft passes are usually done in 4th gear but making a move under braking in the twisty bits is done in 3rd. Having a little more grunt out of the turn seems desirable. I have never seen a torque curve for a decent vee motor (surprising eh) but I wonder how flat it is up there? Maybe it wouldn't make much difference?

I know I tried several passes in the hairpin at the end of the big straight at Pitt and each time I lost places instead of gaining because I was pulled up the hill. I also was lagging coming out of the back section of Summit Point compared to others.

Most of that is likely driver error and rolling more speed through apex would create a better exit. I do like to collect excuses for my inadequacies and this gear is on the list. I have no idea what gear is in my transmission yet. At this point I am assuming it is the wrong one. I guess I will just drive faster.

Cheers,

Nate

[Hardingfv32]

Everything Rice said applies ... IF ... you are in a very competitive race with another competitor. How often have you found yourself in a situation where you were equally match with someone during the whole race?

Basically, you will almost never have the need for a particular third gear. The 1:26 is fine compromise.

Unless you have a top on the line National engine and are a very good driver, there is no track in North America that requires a long box for a SCCA FV.

Brian

[FVRacer21]

Danny,

If you have a longbox with a 1:26 3rd, that is a good overall box.

Lime Rock - perfect -
Thompson - you will feel pain coming out of the hairpin, but since it is hard to pass going into the bridge turn, not a big issue.
New Hampshire - The pain is in the uphill after the hairpin (3) beyond that - no problem
Palmer - I cannot think of any turn that is that slow that the 1:26 will not work

Now, are most people running a short box with a 1:22 3rd. - yes. Is it slightly faster - I would say yes - but only if you are ready for it,

My current car has a short with a 1:26 3rd (short/short), because it was what I had laying around at the time, and it is usable.
But my feeling is if you are looking to preserve the engine, it is not what you rev it to, but how long you stay at high revs.
At New Hampshire I had to shift twice outside the oval, once over the front hill and once over the back hill; as I did not like stretching the lower gear just to save a shift if over 6500.

The other question is how does your engine perform - is it a high horsepower engine or is the power lower down?
If you engine runs out of power over 6400, then the long box is better. (Update - See Brian’s comments below, this also goes back to Greg’s comments about it depends on the track. )

The Long/Sort and the Short/Long will be very close. The shift points are similar and where you run the gears is identical.

The last advantage of the Short/Long is since more people are running it, you can compare revs at points on the track better - that is if they are telling the truth...

ChrisZ

[Hardingfv32]

I have built a bunch of swing trannies before, so don't worry, I've got this.

So a FV tranny is just like any other swing axle?

What preload are you using on the pinion and diff side gears? How are you configuring the syncros?

Brian

[veeten]

Long Box at Daytona and optional at Road America and lots of Florida drivers use Long Box at Robbling Road.
This assumes running spec slicks

[Hardingfv32]

The other question is how does your engine perform - is it a high horsepower engine or is the power lower down?
If you engine runs out of power over 6400, then the long box is better.

I am not sure this is correct. Assuming the engines have equal power but peak at different points, then you want the SB for the 6400 engine. You want to make the best use of the power at the low end of the curve.

Setting up a FV is really about forming the largest area under the power curve. You will fined that being at peak power rpm at the end of the straight is not always the answer for best lap times. That is not to say there are times while racing when it could be benifitial.

Brian

[DannyPip]

Everything Rice said applies ... IF ... you are in a very competitive race with another competitor. How often have you found yourself in a situation where you were equally match with someone during the whole race?

Basically, you will almost never have the need for a particular third gear. The 1:26 is fine compromise.

Unless you have a top on the line National engine and are a very good driver, there is no track in North America that requires a long box for a SCCA FV.

Brian

I have a long box now. All I know is everyone says to run a short box.

I'm building a short box. Just trying to decide between 1.26 or 1.22 3rd, for the tracks I run, which are listed in my first post. I've never raced anyone, yet. Driver school in spring and then into the fray next season. I could be slow, I could be fast. I guess the answer is we'll see?

And honestly I have no idea if my motor is torquey or more of a revver. Next year.

[DannyPip]

Chris, I thank you for your most helpful reply. I really appreciate you sharing your northeast knowledge.

[pacratt]

...it's an LRE from 2009...

DannyPip,
A Lybarger box will be stamped "LRE <build/rebuild dates>" above the ring gear side plate on the diff AND stamped "SHORT" or "LONG" with the 3rd gear ratio above the starter mount.
Glenn

[Stumpthumper]

Danny, it might also be helpful to know that John Piscatelli (spelling?) ran a long box with us in the northeast and was the guy to beat. I think anything you you use to connect the engine to the wheels will serve you well until you decide if it's holding you back.

[DannyPip]

DannyPip,
A Lybarger box will be stamped "LRE <build/rebuild dates>" above the ring gear side plate on the diff AND stamped "SHORT" or "LONG" with the 3rd gear ratio above the starter mount.
Glenn

Yes, I said it was an LRE longbox. It definitely has a 1.22 3rd. This explains to me how the guy I was following both up the hill after turn 3 and out of the bowl at New Hampshire pulled away.

[pacratt]

Yes, I said it was an LRE longbox. It definitely has a 1.22 3rd. This explains to me how the guy I was following both up the hill after turn 3 and out of the bowl at New Hampshire pulled away.

DannyPip,
LOL...sorry...I mentally lost those facts as I went deep into all the other posts.
Glenn