What are the merits of a short ratio box on a track?, Will it make significant reductions in lap times? Options

[nine14cats]

I've got a stock ratio G50 box in my track car. Currently I'm using 2nd through 4th at Infineon, Buttonwillow, Laguna Seca and Thunderhill. I haven't been to Reno-Fernley yet but will be there later this year.

Would it make a significant improvement in lap times to shorten the gearing between the 2nd through 5th gearsets and take advantage of the 5th I'm not using? I wouldn't do it during the season, as I'm still getting used to the car and my RPM' (and speeds) entering turns should go up as I gain more experience in the car. But I just don't see getting into 5th pretty much at all on any of the tracks....

Thanks,

Bill P.

[flesburg]

I honestly do not know, but I think:

that if you have an engine with not a lot of torque, and you are loosing so much power on an upshift that you "lug down", and if you are a really great driver and are currently getting 100% out of the car, then shorter gears may help.

However, if you have a lot of torque, and are pulling hard at each upshift, then I doubt that you will cut off much lap time. A race engine with a very narrow torque range, that makes most of its torque at high rpm, say from 6500 to 8000, and it is a dog under 6500, and you are dropping off to say 5000 after each upshift, then a set of shorter gears might help.

In our DE car we are using a basically stock 3.2 L engine and a stock geared 915 trans, and at HP I use only 3rd and 4th gears, and I really only want to go to 2nd after turn 6, and am well into the torque range of the engine on every upshift from 3rd to 4th. I do not think I could gain much from gear changes. I can gain a whole lot more by growing bigger ****s and turning in at higher speeds, IE the car has more potential than the driver currently has. And gears will not help with that..

[turboman808]

He just said the same thing. If you got a narrow power band then it is very benificial. With a wide power band it won't do anything and could even slow you down.

I purposly set up my civic to top off in 2nd gear at around 78mph. I was aiming for 75 but seems to hit 78. Great for autox.

I say the less shifting you have to do the better.

[lapuwali]

The current fetish for more gears in street cars is, IMHO, purely marketing. A 6-speed in a 9000-rpm car like an S2000, ok. A 6-speed in a Corvette, however...

Remember that shifting more means you're going slower, since each shift is going to take some time (0.1 sec to 0.5 sec, depending on how fast you can shift). That's time when you're not accelerating. So, shifting less is always a good thing. On an engine with not only a lot of torque, but a nice flat torque curve, you shouldn't have to worry so much about what gear you're in, so you should be able to reduce the number of shifts you make to a minimum.

That said, besides helping to keep you in a narrow powerband if you have such an engine, a close-ratio box may be useful if you visit a lot of tracks with wildly varying layouts, because you won't have to regear from track to track. You can simply use the gears in the 'box as you need to: 2nd, 3rd, 5th on Track A; 2nd, 4th, 5th on Track B. A close-ratio 'box may also be useful in situations where you're regularly fighting traffic and having to adapt to another driver's speed for a few corners, and you may find yourself between gears in your usual pattern from time to time.

Back when I raced bikes, though, I leaned towards bikes with broader powerbands, and there were a few I had that required fairly little shifting. One only required two gears at Sears Point, which has a pretty wide variety of corners. I'd only have to downshift once for the hairpins at each end, and could remain in top everywhere else.

[nine14cats]

Hi James,

That was my thought, that by regearing I could take advantage of the box at the main 4 tracks I run. The 2nd to 3rd RPM drop is a tad too much in my opionon, the 3rd to 4th feels right, and the 4th to 5th is non-existent due to the OD gearing.

My thought was to shorten up 3rd, 4th, 5th with some more even spacing. Hayden at WEVO gave me a nice little gearshift spreadsheet and he gave me gear ratios for my 914-6 WEVO box that took advantage of the 3.6L's torque but kept the shifts in the meat of the power band. 5th became usable at the longer tracks and the cars top speed gearing was set ~146MPH. My current gearing is much higher than that in 5th right now. I was pulling 131MPH in 4th gear last weekend.

Just doing research.....keep the comments coming....! (IMG:style_emoticons/default/clap56.gif)

Bill P.

[DanT]

Bill, I agree with most of what has been said so far. Your car has so much torque I am not sure you are going to gain anything except shifting more.

Have you checked the prices on G50 gears and what not? Can you say Big $$$$?

My advice and I am sure Rich Walton would agree....learn to drive what you currently have to its fullest and then when you get there, it will be time to make modifications.

You have at least 8-9 seconds at TH CCW before you have gotten to the full potential of you car as it currently sits.

I should have taken the time to ride with you last weekend, but got busy with my mosquito abatement issues (IMG:style_emoticons/default/biggrin.gif)

i am sure I could have gotten you down to a 2:04 or :05 (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/poke.gif)

[Brando]

As the above mentioned... It is power-band reliant.

But also the type of track you are on may be the determining factor. If you're on an auto-cross course where you won't ever see 4th or 5th, then you might want a much shorter gearbox. but for large tracks where you will frequently see triple digits... You get the idea. Maybe you might want two different gear-stacks on hand to swap in and out. Or another trans altogether for tall gears (where you have lots of speed) and one for short gears (where you have lots of low-speed cornering).

[nine14cats]

Hi Dan,

2:05's should be attainable pretty easily as I left so much time at 1, 3 and 9. Makes me want to (IMG:style_emoticons/default/barf.gif) !

I talked to Rich at JWE about some of the handling traits I was experiencing and we discussed how some subtle adjustments to the car will calm it down in the exit of the high speed stuff. Rich advised no radical tweaks...just minor ones as the car is plenty fast. He said he has no doubts he can stick the car in there at 1:58's!

Yep, I know seat time is the answer...but I still want to understand the gearing effect.

Bill P.

[nine14cats]

The end goal for me is to be a competent driver in a car that is GT class prepped and competive on the track or at an AX, although much like our previous car, tie goes to the track setup. My competitive AX days for TTOD are gone. I used to get within thousandths of our quick AX guys, but my car now is just not setup for an AX contender. And that's okay. I'll adjust a swaybar and swap on stickier tires, but I'm not going to change the car for AX anymore.

Multiple gearboxes is a nice idea, but I'd prefer to have a geared box that gets me around the tracks and AX course all in one. So flexibility in gearing is what I'm after.

All I can say is that it sure is alot of fun!

Now I just wish I knew the next time I'll be out on the track....

Bill P.

[brant]

seems like an important piece of information is being left out of this discussion.......

lower gearing promotes faster acceleration.
ask some guy in a camaro at the drag strip, which rear end he would rather have

shifting can take time, but a car with quicker acceleration can also be 10 or 20mph faster at the end of the straight due to its gearing. agreed this is much more beneficial on a race engine with a smaller powerband. But the truth is, that you can not get your car geared best without putting it onto a dyno and defining your power band.

one last thing... at high speed (tripple digits) gearing comes much more into play due to aero resistance. Wouldn't happen on many autox courses, but makes a big difference at the end of the 1/2 mile front straight when your hitting 120 or 130

brant

[John]

In my opinion, several of you are right.

A Dyno needs to be utilized to determine your torque band.

Gearsets need to be selected so that on shifts, you never drop off your torque curve.

A top speed needs to be determined and the tallest gear needs to match this top speed (top gear in stock transmissions tends to be overkill for track work and some cars will pull harder/go faster in 4th than in 5th).

A gearset that is not used is useless in a racecar. It just adds weight (something that many of you have worked really hard to reduce).

I'm sure that I read in another thread on this website that proper gearing can make the car FEEL like it has much more power (and I believe that). Stock gear ratios were a compromise to get better fuel economy not maximum performance.

Better acceleration out of a corner allows one to carry more speed for longer duration than slower acceleration (especially when maximum velocity is about the same).

My whole dilema in the swap the gearset deal is how do you know what will be a worthwhile change since gearsets are not inexpensive. I've been too chicken to experiment.

just my $0.02 (If I just had $0.02 for each of my opinions.........)

[racerx7]

i am sure I could have gotten you down to a 2:04 or :05 (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/poke.gif)

(IMG:style_emoticons/default/smiley_notworthy.gif) (IMG:style_emoticons/default/smiley_notworthy.gif)

Too me that is very fast, if you did it in a daily driver.

How many times have you been to thunderhill? What kind of car/tires/ power to
weight ratio, etc...

[Trekkor]

Bill, where does your engine redline?

When does the power start?

Example: my power is on at 5000 rpms and pulls all the way to 7300.
My MSX 901 box is perfect for that powerband. Every upshift puts my engine in the powerband if I take the motor to 7000+ rpms on track.

Thats what you need.


KT

[nine14cats]

My current track car is a 1980 911SC with a 1995 993 pre-vario 3.6 liter hydraulic lifter motor. The motor is dead stock except for 1 5/8" headers mandated by the Porsche Racing Club GTL classification and Phase 9 mufflers. The car has been lightend and has a full cage with bracing to all of the suspension points. The car has RSR coilovers all around and 27mm Smart Racing AR bars front and rear. Adjustable plates, fuel cell, and Getty 993 body kit. Runs 11 inch slicks up front and 13 inch slicks out back.

The motor was dyno'd at Jerry Woods Enterprises on their engine dyno last year. Here are the numbers:

RPM HP TQ
----- ------ - ---------
2500 87.1 182.9
3000 112.4 196.7
3500 137.7 206.6
4000 172.2 226.0
4500 208.6 243.4
5000 246.1 258.4
5500 264.3 252.3
6000 287.6 251.7
6500 282.6 228.2

Essentially flat torque curve from 5000 RPM through 6000 RPM. Actually pulls well from 4000 RPM on up. Redline is 6800 RPM. This last weekend I was bouncing off the rev limiter in 4th gear approaching turn 1 at Thunderhill. 25 inch diameter in back makes this ~131MPH. This was the first time for me at THill in the car and 7th time driving it.

I can tell you that the hit at 5000 RPM is huge. The car just takes off like a rocket. But at Buttonwillow or Infineon, for the speed I'm carrying into some of the turns, 2nd is too short and 3rd is too long, placing me in the 4000 RPM area which is not in the optimal torque band. So even though car is still a rocket ship and I can still out accelerate many cars, there is acceleration left on the table.

After the engine was dyno'd I had Hayden Burvill at WEVO suggest some gearing for my tranny to keep the shift points in the meat of the power band.

The stock gearing looks like this at 6800RPM shift points:

1st Gear = 0 RPM rev drop =max speed 42.0
2nd Gear = 2800 RPM rev drop = max speed 71.3
3rd Gear = 2146 RPM rev drop = max speed 104.2
4th Gear = 1371 RPM rev drop = max speed 130.5
5th Gear = 1409 RPM rev drop = max speed of 164.6

Graphically it looks like this (RPM on left axis, speed at top)....

[nine14cats]

Continued.....

The stock gearing looks like this at 6800RPM shift points:

1st Gear = 0 RPM rev drop =max speed 42.0
2nd Gear = 2800 RPM rev drop = max speed 71.3
3rd Gear = 2146 RPM rev drop = max speed 104.2
4th Gear = 1371 RPM rev drop = max speed 130.5
5th Gear = 1409 RPM rev drop = max speed of 164.6

Altenative gearing (shorten up 3rd, 4th, 5th)

1st Gear = 0 RPM rev drop =max speed 42.0
2nd Gear = 2800 RPM rev drop = max speed 71.3
3rd Gear = 1681 RPM rev drop = max speed 94.7
4th Gear = 1459 RPM rev drop = max speed 120.6
5th Gear = 1409 RPM rev drop = max speed of 146.8

As you can see, the rev drops land squarely in the meat of the powerband.

Fun stuff to analyze! (IMG:style_emoticons/default/clap56.gif)

Graphically it looks like this (RPM on left axis, speed at top)....

[nine14cats]

I keep a log book of my car settings and other stuff. I try to learn from it and be consistent in what I do. And I'm getting smoother in the car. My in car videos show me this. (IMG:style_emoticons/default/clap56.gif)

But at some point my trans will need "freshening" (IMG:style_emoticons/default/happy11.gif)

When it does, maybe short ratios will drop me another second or two on the track?


Bill P.

[Sideways]

I keep a log book of my car settings and other stuff. I try to learn from it and be consistent in what I do. And I'm getting smoother in the car. My in car videos show me this. (IMG:style_emoticons/default/clap56.gif)

But at some point my trans will need "freshening" (IMG:style_emoticons/default/happy11.gif)

When it does, maybe short ratios will drop me another second or two on the track?


Bill P.

The analysis you have done is exactly what you need to look at. Unfortunatly you should analyse every corner of every track. Work out the segment times (times between sections of the track) and work out where the gains are going to be the greatest. THis will give you a good starting point, then finding the correct combination of gears is the next (G50 are expensive). You will have to make some sort of compromise but the analysis you are soing is great, this is exactly what I did when i was building my 914 with a G50.

Of course you make up more time between the exit of a corner and the entrance of the next corner so being able to acclerate at a higher rate will allow you to do this.

[Brad Roberts]

Bill,

lets chat.

We just tested our Rothsport built G50 in essentially the same car at Willow Springs.

Our 3.6 car with stock G50 at THill was running 1.54's at the 25hr. on Slicks

The "slow" driver was turning 56's (with the crows nest)

We geared it for Fontana and Willow Springs maxing out at 165mph.


B

[Brad Roberts]

FYI: Randy Pobst was driving our car stuck in 5th gear running 2:05's..LOL at THILL.

You will inch up on it. It doesnt happen overnight.

B

[Brad Roberts]

Kevin Roush tested for us and ran 1:26's on his second lap in our stock 3.6 powered 993 with the short ratio box. He was right against redline in 6th (perfect) as he started into turn one.


B