Gearing for SoCal Tracks

1colbrz · 12-09-2012, 11:27 AM

I'm building up a car to run some POC and maybe NASA races in SoCal. The car will race in the V3 class. Does anyone have information on what gearing cars are running at Willow Springs, California Speedway, and Button Willow?

Thanks,
Gerry

PatrickB · PatrickB's Garage

The latest trick in V3, is a really tall 1st gear (70 mph) then close ratio after that.... I don't know what the exact ratio's are... I'm still in JP/R6.

winders · 12-09-2012, 09:22 PM

Quote:

Originally Posted by PatrickB

The latest trick in V3, is a really tall 1st gear (70 mph) then close ratio after that.... I don't know what the exact ratio's are...

Sounds like my tranny....

Be prepared to spend big dollars on a new mains shaft (best bet is GT Gears) that has a changeable first gear.

Scott

Cory M · 09:58 AM

Tall 1st, ~150mph top speed, and aim for ~1000-1500 rpm drops between gears. For budget reasons some people only do 3,4,5 - new gears and a new mainshaft aren't cheap. Jeff at AASE, Kevin at GAS, and Matt at Guard are all good resources to get this done and can recommend gear ratios.

Matt Monson · 12-10-2012, 08:51 AM

Only our 915 main shaft has slip fit gears and it is a unique gear. ie you cannot put a stock 2nd on it.

All of our g50 and g96 based main shafts have 1st cut right on the shaft. But 2nd is always changeable, which is not usually true on factory 6 spds.

Regards,

Matt Monson
Guard Transmission llc

1colbrz · 12-10-2012, 10:53 AM

Hey guys, thanks. Sounds like they are setting the boxes to operate as a true 5 speed. Gear 1st for the slowest corner and 5th for the highest speed straight and fit the other three in with decreasing rpm drops as you move up the gears. That is how we geared our formula cars. It makes diving in the pits a problem (hard on the clutch), but we towed the cars around most of the time.

With 7500 rpm, 25.6" rear tires, and an 8:31 RP that would give about:
14:31 for a 1st gear (66 mph)
25:26 for a 5th gear (153mph)

Sound about right?

Thanks,
Gerry

John Rogers · 12-10-2012, 06:26 PM

Several years ago (many now it seems) HSR West did a CA Speedway event and invited some of the PRG cars from northern CA to come down. I remember getting passed by a couple of ex-factory cars from Europe at turn one going flat out. So was I and they were hitting about 168 MPH or so through turn 1 while I was buzzing along with my 914-6 2L car at 135 or so. The owner of a white one said it was geared so his foot was flat on the floor and on the speed limiter in turn 1 and was the same gearing they used at Willow Springs! He did mention that on tracks that were shorter such as PIR in AZ that their mechanic geared them so top speed was "only" 150 MPH or so and he a closer set of gears.

I think my GEARS program is still on here somewhere and that can tell you what different ratios will do and is extremely accurate.

ted · ted's Garage

Top speeds vary at the different So Cal tracks.
So you might have to compromise and gear the top mph for Cal Speedway.
The top speed at Big Willow and Cal Speedway could be 10 to 20 mph faster than Chuckwalla and Buttonwillow.

If you are going to buy new I'd try Patrick's 70mph 1st gear for those slower starts when you might drop it into first to keep it in the power band.
Then just space the gear stack from 70 to 145?

My non porsche V8 race car has a quick change (weismann 5spd).
We gear for 145mph top speed at Coronado, Monterey, Sonoma, Buttonwillow and Chuckwalla.
165mph for Big Willow and even a little higher mph for Cal Speedway.

1colbrz · 12-11-2012, 09:33 AM

John and Ted,
That is pretty quick up on the big end but seams reasonable. Sounds like 5th gear would range from 1:1 to a 2 over depending on the track.

Gerry,

Matt Monson · 12-11-2012, 09:54 AM

Quote:

Originally Posted by 1colbrz

With 7500 rpm, 25.6" rear tires, and an 8:31 RP that would give about:
14:31 for a 1st gear (66 mph)
25:26 for a 5th gear (153mph)

Sound about right?

Thanks,
Gerry

How powerful is your engine? That 5th might be a tick short depending on your powerplant.

What we will often do for the California tracks is use a 4th gear that is good for nearly 140 mph with an active 1st that tops out around 70mph. Then at most tracks you are driving it as a 4spd, and only really use 5th at Cal Speedway or for very short sections on a couple of the other tracks.

With your specs:

1st 2.125 70mph
2nd1.550 95mph
3rd1.260 117mph
4th1.080 137mph
5th0.941 157mph

Talk to Kevin Roush at GAS. He's a bit of a 915 guru and has a lot of experience building narrow body air cooled cars that can run with the water pumpers...

1colbrz · 12-11-2012, 10:06 AM

Matt,
I don't have the numbers off of the engine yet. It is in process of build up. I can tell you that it is a 2.7L, high compression, with mod "S" cam cams, and mechanical fuel injection. I should be able to weigh in somewhere under 2400 lbs with driver. It seems that +/- 250hp is the number I keep hearing for cars in the V3 class.

Gerry

Matt Monson · 12-11-2012, 10:17 AM

Sounds similar to what Kevin was running a couple months ago when I was out there. Here's a video:

I think the car is usually V3 but he ran it as a GT3 that particular day. Was quite the battle between him and Eric's swapped Boxster

ted · ted's Garage

Quote:

Originally Posted by 1colbrz

John and Ted,
That is pretty quick up on the big end but seams reasonable. Sounds like 5th gear would range from 1:1 to a 2 over depending on the track.

Gerry,

I agree.
2400lb 911 300hp or less do you need to gear it over 135mph for the roval?
make it a 70 to 135 box?

winston cup V8 #s were 800hp 2400lb.
whacky 28x14,25x13 tires.

John Rogers · 12-11-2012, 10:29 AM

Something no one has mentioned yet is what is your experience level? Are you used to driving all these tracks and going those speeds? It took me a while in the 914-6 that weighed 1800# with a 220HP engine to be able to go flat out around turn 1 at the CA Speedway as my "brain" was saying lift - lift - lift and the same thing at Willow Springs turn 8! I would suggest gearing for the lower end of the possible speed spectrum and work up until you are in a comfort zone. If you have splitters, air dams and rear wings then you have help, we never did and the smoooching of the tires when getting close to traction limits takes a bunch of getting used to.

1colbrz · 12-11-2012, 10:43 AM

Matt,
Thanks for the video. If that doesn't bring a smile to your face not much will.

John makes a good point. It's been a while for me but in another life I did hold an SCCA National Lic and a USAC F2000 lic. I've circulated at "Big" Willow in the 1:25's in formula cars and 1:28's in full body GT cars. Whether I can do that anymore, who knows, I'm older now. But, I do have twin sons that are 20 yrs old and they might be able to keep up that pace. We'll see!

Gerry

Cory M · 12-11-2012, 12:47 PM

who is building your car?

1colbrz · 12-11-2012, 01:02 PM

Cory,
I'm doing the build myself with help from various sub-contractors.

Gerry

ted · ted's Garage

Quote:

Originally Posted by Matt Monson

Here's a video:

an active rear wing too.

KTL · 12-12-2012, 09:46 AM

Quote:

Originally Posted by ted

an active rear wing too.

Yah need to thicken those wing uprights or put some cable stays/guy wires on there!

eric523 · 12-12-2012, 09:53 AM

Quote:

Originally Posted by ted

an active rear wing too.

yeah...first time doing 160 mph+ in that car and some changes were necessary after seeing the video.

I thought that white car had a 3.4L in it? Would have been pretty darn quick for a 2.7L.

I would expect those V3 cars to see about 150mph there. I know they are doing at least 140.