Drag racing gear ratio.

[vwracerdave]

I play around with my street legal 1350 Lb. Dunebuggy at the drag strip and race it in street class. It has 120 HP 2007cc and can be driven anywhere. I run the 235/60-15 Mickey Thompson ET drag radials. I use to have a stock geared 4.12 R&P and would run the 1/4 mile in 3 gears shifting at 6400 RPM and crossing the finish line around 6500 RPM in 3rd gear. Buggy would run 14.0's. I switched to 1.48/1.04 3 & 4 gears. It now runs 14.10's in the 1/4 using all 4 gears and crossing the line around 6000 RPM's. You'd think the close ratio gearbox would run faster in the 1/4 then the stock gear ratios. Anybody have any theories why?
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[66brm]

Wasting time changing gears? Perhaps a taller diff ratio instead of lower gear ratios.
By that I mean you're driving a light car so the engine should be capable of pushing it faster, staying in a gear and under power rather than shifting gears, on ,off,on ,off, on off.
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Do you have any torque figures from the engine? The Super I ran a lot had a 3.88 with a 1.41 3rd for 1/8 mile, and a .93 forth for cruising. I felt like the rpms would be too high for the engine to try and run a full 1/4 in 3rd, so I would just shift into 4th at the end. It didn’t matter too much for me e.t. wise for bracket racing. The combination of the higher 3rd, and stock 4th brought the rpms back down around the peak of the torque curve, and really made the engine work to pull the 4th back up to speed, while 1-3 were very equally spaced and kept the engine wound up. The simple time factor of adding another shift is adding time, but maybe the jump from the 1.48 to the 1.04 is loading the engine more.

[Dougy Dee]

Your clutch might be slipping..

Your 3 gear run (stock 1.26 3rd) should see 97mph top end.
Close ratio 4 gear should see 108mph.
What MPH are you seeing?

[Ohio Tom]

Theory:

1. I don't know you at all, but how fast are you shifting?
if you are slow, then it's costing you ET.

2. Your current ratio box should be just about right for your application.
Changing.

3. Agreed with Geoff, we need more info about the powerband of your motor.
How does it handle the 1-2 shift? Does it fall on it's face for a second? or does it pull right thru?
What rpm are you shifting at?

Personally, I really think the 1.48/1.0 combo is great. I have built several boxes with those ratios and worked out great.

[rayjay]

Plot your power curves and your gear ratios to see what the motor is doing after each gear change. This is sop for road racing. Nowadays there are G meter performance computers that can tell you a lot about what is happening. They are used a lot for road race driver coaching [ mostly for well heeled 'gentlemen' 'racers' who are slower than poop ].

[vwracerdave]

[jpaull]

Dave,

Have you had enough runs to see if 14.1 is the best with the new setup?

Sometimes the track and other circumstances are greater differences then the change itself. If you only had 3-4 passes, you still might find a quicker pass is yet to come.

[Stripped66]

[Alstrup]

Yeah, well, I am by no means a drag racing expert. But 14,0´s, in a buggy, with 120ish hp, is good. My guess is that you have hit the sweet spot with the tree gear shift. From the sound of it the engine does not have the upper rpm torque to pull the lower gearings faster.
Let me guess, - W120 cam?
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[vwracerdave]

60' & 330' are the same and they should be. Both trans have 4.12 R&P and stock 1-2 gears. With the 1.48 3rd I'm .10-.15 faster in the 1/8 because 3rd gear are different. It realize it takes time to shift into 4th and I feel the gap between 1.48 and 1.04 is too much for the power band. I'm not expecting much but I felt I should be 2/10 ths quicker with the close gearbox.

Yes I'm running a W-120 w 1.25 rockers. It is a great drivable street engine in my lightweight Dunebuggy.

Maybe 40 passes with the close 3/4 gearbox. With 100's of passes on the stock transaxle shifting at 6400 always ran the fastest.

If I lost 40 Lbs, it run 13.90's but that's another fairy tail story for another day.

It sure was fun beating the Corvette.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[Dale M.]

Have always though a 1/4 mile was to long for VW engines, they seem to top out really well in 1/8th mile and seem to be overcome by bigger engines (more cu in - torque) in 1/4 mile...

And on a dyno what rpm range does torque curve start to flatten.... That is where its all at, shift or die....

Dale
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“Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.

"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[Stripped66]

[gears]

We were running a VERY fast car in the '80s. Our next step toward quicker 1/4 mile times was going to be to utilize a slipper clutch & tall 1st gear, with the intention of using only 3 gears. But we sold the car and went surfing instead ..
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[Alstrup]

[jpaull]

x2 on the 125 with 1.25s, I have ran13.4 on street tires and full weight bug with 2180/w125/1.25s

[vwracerdave]

I originally built the 2007cc for my Ghia and chose the W-120 for lower RPM street driving with the heavier car. With the engine now in the much lighter Dunebuggy I have always believed the W-125 and bumping the CR would work well and still be very street drivable.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[spencerfvee]

[wardvwracer]

I'm surprised that you didn't retain that .2 gain with the gearbox change, honestly. "Back in the day" that was what my brother and I gained with our gearbox changes with our street cars. Would be curious about how quickly you're shifting into 4th. .2+ is a long time IMO for a 3/4 shift.

I doubt you're looking to tear into your engine because your gearbox swap didn't turn out like you expected. However sometimes its important to look at both as a package. I would echo the recommendation above about the W125 cam. Its under-rated and can wake up an engine. I built an 78x90.5 for a gentlemen who had a buggy and swapped a W120 for the 125, bumped the compression to 9.25 to 1, and re-used his 44 IDF's and 40x35 MOFOCO cast-in larger ports, and added a 1 5/8" merged exhaust. It was a very different engine, and ripped! He was thrilled at the power increase without any decrease in overall drivability.

One more comment on the gearbox. Again, "back in the day" my experience using a 3.80/2.06/1.48/1.04 gear stack, with a 4.125 R&P, made a big difference in the overall performance of the car. Much more enjoyable on the street, and when we needed to freeway the car, the 1.04 would do 65 mph fine.

I bet the buggy is more fun to drive on the street with the new gear stack. The drop between 2.06 2nd and the 1.26 3rd sucks. In all my "stock" ratio gearbox builds that I've done recently I've used an early 1.32 3rd. Much better transition and can be used with high horsepower set ups at the track as well.
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David Ward
ACME Berrien Buggy Street/Strip racer build
1963 Single Cab
1969 Beetle Convertible
63 11-Window Kombi Bus
Cornpanzers

[74 Thing]

Dave, I wish I had a 125 cam sitting around I would send it your way.