Gearing at various racetracks

John Rogers · 07-24-2003, 09:22 PM

As was noted in Milt's post about going to Willow Springs, the gearing selection for a track can be a real expensive proposition! I have two trannys, one stock geared and one with a close ratio, lower 5th gear that I though was good for most tracks except Willows. I finally got so I could drive pretty much full bore though 8 and 9 if I wanted to and found that it worked really well. I tried the stock geared tranny and while it lets the engine run at lower RPMs, it is hard to make any power. With the large amount of torque (205 ftlbs) from a low reving big 4 it was easy to drive. Now I will have to live with a very high reving six and the gearing might be too high. The stock tranny might be good for Bonneville or some place? I was curios what others run for top end gears figuring a top speed of about 125 or so?? Oh yea, I disconnected my speedo for the same reason Chris said!!!

red-beard · red-beard's Garage

John - The smaller 6's only make power at the high rpms. The larger displacement 3.0's and 3.2 with the longer stroke have a much larger power band.

Mark (Confused) was the owner of the Black slant nose 6 on last weekend's run. You might talk to him about the larger Plants. He has 3.0 in his 6.

campbellcj · 10:43 PM

LOL, I actually just reconnected my speedo so I could try to check some entry & exit speeds. But everywhere except the 7-8 area and the front straight, I was too busy staying on the track to look down!

So John, have you decided on a -6 engine (size/config) yet, or still planning?

My -4 was not nearly as seriously built or powerful as yours, but I definitely know what you're saying about the torque curve differences. I have been driving small sixes for 13 years now and every time I hop into even a 2.0 914-4, the difference in powerband is immediately noticable and really affects the way you drive. My old 2.4-four would pull pretty well from maybe 2000 to 6000, while the 2.2-six practically wants to stall at anything under 4000...but from 5000-7000 it screams.

bumble · bumble's Garage

John,

I built a transmission (correction - I HAD the transmission built for me! When WAYNE PRODUCES HIS TRANNY BOOK - hint - hint - hint this will no longer be necessary).

Tranny is side-shift 901 coupled to a 2.7L engine on carbys giving 180HP at the wheels. Engine is set to max out at 7000rpm. The car is really a dedicated tarmac rally car but the tranny seems well suited to track work as well.

CWP is 7:31 on a Quaife. Tire diameter is 25" (205/16 55)

Ratios are:

1st: 15:36 (C) 2.4:1 - new
2nd: 18:34 (F) 1.889:1 (standard 2nd gear)
3rd: 20:31 (I) 1.550:1 - new
4th: 23:28 (O) 1.217:1 - new
5th: 27:25 (V) 0.926:1 (originally 4th gear)

Top speed is about 200kph (125mph) at 7000rpm with really great ratio spacing and a usable 1st gear - especially if you're into AX. The only downside is it runs 4000rpm at the speed limit (about 70mph). But it's never really used as transport anyway :-).

To do this I had to find 3 new ratios made of unobtanium - BUT an effective solution (assuming std ratios) might be to flip some of the existing ratios thus minimizing what you need to acquire:

e.g.:

1st: Remain as is if you can live with the super low 1st

2nd: Remain as is (you can't change this without a lot of $$$) and it's quite a good ratio anyway.

3rd: Take existing 5th 31:22 (ZD) 0.710:1 and flip to make 22:31 (?) 1.409:1 (funny, I don't see this combination on the ratio chart so there may be a problem I'm not familiar with - someone may want to clarify this?).

4th: to remain as is - 27:25 (V) 0.926:1

5th: Use the existing 3rd 23:29 (N) 1.261:1 and flip to make 29:23 (Z) 0.793:1

The effect of this will be to:

1. Give you a lower top gear (originallly 166mph - yeah right!) now 148mph @ 7000rpm

2. Give you a shorter jump from 2nd to 3rd - at the expense of -

3. A longer jump from 3rd to 4th

4. At no cost other than time and a few gaskets.

One step up from this would be to make 4th (27:25 (V)) into 5th and get a new 4th (24:27 (Q)) so you have a really tight set for the purchase of only one ratio.

Cheers,

Mark

John Rogers · 07-25-2003, 06:46 AM

Thanks Mark, that is probably something like we'll do after I do the next race at Willow Springs to see how it works out. The six is a motor built last year at Donnie Kavig's shop for another vintage race car and they went up to a full on RSR motor later??!! It has about 200 HP according to the dyno sheets and should produce similar speeds to the four I had, but be MUCH more reliable.

07-25-2003, 03:33 PM

John; I have a 2.7 twin plug that just dyno'd out at 196.5 h.p. We rebuilt the gearbox using A F Ka Q V and has ZF limited slip. I've gotten limited track time since the rebuild but I like it so far. On the short track at Willow I can get good power in 3rd through the skid pad turn and two other spots that I used to lose power if I shifted to 3rd.

John Rogers · 07-25-2003, 06:01 PM

Thanks for the input. I think my high gear is an "X" but we aren't sure? I guess the best setup is like the yellow 356 that was at Willow last year and was geared so that top speed was right at the speed limiter chip setting as you could hear it in 8 and 9 cutting in and out?

SteveStromberg · 07-25-2003, 07:20 PM

Take a look here: http://forums.pelicanparts.com/showthread.php?threadid=53880

Zeke · 07-26-2003, 01:47 PM

I have T and Y for 4th and 5th. Chart shows something like 115mph @ 6000 with 23.5" tires. You might need the Z with the six. Don't know what Chris C. has for 5th, one of the Z's, probably the taller one. He was complaining about it being too tall.

campbellcj · 07:40 PM

I currently have stock 914-4 gears...WAY too tall for a small six in track use, like 1200-1500rpm's below where I would want to be. Will probably do either a U or V for 5th and a Q for 4th; I'm gonna play with the spreadsheets some more this week. My tires are 23".

PCA7GGR · 07-27-2003, 07:37 PM

Ibelieve that a "flipped" ZD 5th becomes a M 3rd. It is a very common conversion. I ran A-F-M-S-X and a Quaiffe LSD with a stock 3.2 - worked well for Butonwillow, Leguna, Sears and Thunderhill.

07-27-2003, 07:59 PM

I have a second box which has stock 6 gears. I'm planning on it becoming an MSX box also, so it will be A,Ga,M,S,X. I plan to switch boxes when running Buttonwillow, Thunderhill, WillowSprings big track.