The Baja Bug - First Timer's Thread

[EnjoyNukaCola]

She nears 4000 by the time I'm going about 60 mph. .82 to .77 isn't huge but I'm thinking it'll drop me about 1000 rpm by that time. There's plenty of torque in the 2000+ rpm range so lugging it hasn't been an issue. I just wanted to know if anyone ever does this, all I see are people using close ratio gears.
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Brian]

what are the specs on your transmission now?
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Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[EnjoyNukaCola]

5.38 R&P, stock gears. I could also go to a 4.86 but I like the short 1st gear WAY too much.

https://weddleindustries.com/products/new-products/new-sportsman-gear-ratios
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Brian]

Is that with your 31's?

http://johnmaherracing.com/calculators/gear-ratio-calculator/
_________________
Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[EnjoyNukaCola]

Yes. I need to do more driving with different GPS apps before I can say exactly where I'm at, at what RPM.

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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Brian]

With 31's at 4k in 4th with the same gearing I'm at 80. Which is the same that you have below, but put the r&p at 5.375 which is what I assume you have. 5.38 is just rounded up.

http://www.ratwell.com/mirror/sandlizrd.baja.com/gears.htm

So if that chart below is your actually setup, I would say don't change it or plan on a 5 speed
_________________
Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[Dark Earth]

A pretty cool formula is ...

RPM= (MPH x 336 x Ring and Pinion x gear ratio) / Tire Diameter

80mph x 336 x 5.38r&p x .82gr = 118,583.808 / 31 = 3825 rpm

It's best to actually measure your tire diameter because sometimes it's less than advertised which would yield a higher rpm.
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My Build: '69 Baja - Dark Earth Version

~I'm almost done. I just lack finishing up.~

[dustymojave]

Tire diameter or even rolling radius are often used. But for a number of reasons, I disagree with using either.

The REAL story in calculating how far the car rolls in one revolution is far more accurate using tire circumference. The tire will change diameter some as it spins, centrifugal force being what it is. And tire resistance to that varies. Air pressure in the tire also influences the diameter and rolling radius of a tire. Regardless of those issues... The whole circumference has to get around to accomplish a revolution of the wheel.With radial tires, that varies quite little regardless of air pressure, tire temperature, load, or other factors. This fact caused a lt of trouble for NASCAR and other circle track racers when race tires became radial construction. The old bias ply tires were quire predictable in expansion with temperature and air pressure. Racers had long since learned to adjust handling in circle track racing by adjusting the relative tire pressures from side to side. In the 80s, I fabricated and pit crewed on a Super Modified circle track race car racing at places like Saugus Speedway, over the hill from NC's home. I remember checking tire temps across the tread with a contact pyrometer each time the car came in off the track. Then adjusting air pressure while using a tape measure around the tread to attain the relative tire diameters we wanted to get the desired handling characteristics. We were VERY fast!

That's me driving the car off the track after winning a Trophy Dash at Saugus.

I used a 1/4" wide x 10' measuring tape to wrap around the tread. It's difficult to get consistent measurements with a wide curved blade tape.

So, of course...the calculation formula for deriving the speed and RPM has to change to deal with using circumference instead of diameter or rolling radius or radius. Note that measuring tire diameter with a tape or believing the numbers on the sidewall to calculate the tire circumference may not get the same results as using a tape. What change is required in the formula depends on what formula is used. NC being an engineering student, he should have no trouble calculating the change needed.

VW Bug and Busses are notorious for having wide ratio gearboxes from the factory. Going for wider ratios would tend to increase the likelihood of the car bogging when shifting from 3rd to 4th and would require winding the engine to a higher RPM before up-shifting. May not be a problem in practice.
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Richard
Offroading VW based cars since 1965
Tech Inspection 1963 - 2012 SCCA/SCORE/HDRA/MORE/MDR +
Retired from building Bajas, Fiberglass Buggies and Rails in the Mojave Desert. Also Sprints & Midgets, Dry Lakes, Road Race cars. All types New and Vintage
SoCalBajas Member
Kicked Cancer's A$$...1st and 2nd round...Fight ain't over yet.

[EnjoyNukaCola]

That's cool Richard, thanks! My top speed is 68mph at 4200rpm according to GPS app. It likes to cruise at 55-60.
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[dustymojave]

So a taller 4th gear would probably NOT increase your top speed and might make it difficult to achieve 68mph. That top speed is typical of 5-1600 race Bajas with high compression engines and 002 or 091 gearboxes.
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Richard
Offroading VW based cars since 1965
Tech Inspection 1963 - 2012 SCCA/SCORE/HDRA/MORE/MDR +
Retired from building Bajas, Fiberglass Buggies and Rails in the Mojave Desert. Also Sprints & Midgets, Dry Lakes, Road Race cars. All types New and Vintage
SoCalBajas Member
Kicked Cancer's A$$...1st and 2nd round...Fight ain't over yet.

[BmxBug]

Hi there experienced people. I just picked up a rebuilt 002 3 rib for my Baja. Can someone link me to the best possible thread for installation

[EnjoyNukaCola]

It gets pretty loud at that RPM and the handling gets kind of sketchy at that point, especially if its windy out so its probably best NOT to go faster than that. The Bug weighs much less with this trans than the Bus it belongs in, so at high rpm its not under as much load. I'm surprised its so far off mathematically, Rick Wright said I'd get 65mph at 3200rpm. I'm going to buy a Berg temp dipstick and see how it does after some highway trips.
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Dark Earth]

Here's an online RPM/MPH calculator ...

http://www.race-cars.net/calculators/rpm_calculator.html

It seems like the rpm the gps app calculated is high. Maybe it didn't account for fourth gear (.82) ?
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My Build: '69 Baja - Dark Earth Version

~I'm almost done. I just lack finishing up.~

[Dark Earth]

Also ...

If you're getting your RPM reading from a tachometer wired to the distributor, and your MPH from a gps app, you might have your tach set to 6 cylinder instead of 4 cylinder. Sometimes the setting in under the rear cover of the tach.

I hate to beat a dead horse here, but something just doesn't add up with the figures you have.
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My Build: '69 Baja - Dark Earth Version

~I'm almost done. I just lack finishing up.~

[EnjoyNukaCola]

I have an Autometer Sport Comp 5" tach with shift light set to 4200, and not the cheaper Autogage line either. It's over 250 new and I did buy it on Ebay used for a fraction but I believe it to be a well made tach. Idles at 900 give or take.
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[EnjoyNukaCola]

There's 4 wires out the back. Power, ground, coil and night light. Model 3904 is what I have and it doesn't calibrate electronically so maybe PO cut the wires and stuffed them back inside the shell?
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Dark Earth]

I'd try borrowing another tach from someone and drive at 50 mph. You should be at 2400 rpm like your chart above says. That's the same RPM using the formula and the online calculator too. I'd start there to eliminate the tach as the culprit.
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My Build: '69 Baja - Dark Earth Version

~I'm almost done. I just lack finishing up.~

[EnjoyNukaCola]

Richard explained tire characteristics very well. Then there's aerodynamics - standard Bugs are not too bad but Baja Bugs are wind sails. I also have a Solex 30 on my 1600 dual port which requires more pedal effort versus a dual carb setup.
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"when i go to drive it i get to like 5-10 mph it is at high rpms and gets higher the faster i go when i shift up to second the rpms drop is this normal or what and this is my first vw please help"

[Dark Earth]

Also, here's a link ...

http://www.autometer.com/media/manual/2650-1244.pdf
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My Build: '69 Baja - Dark Earth Version

~I'm almost done. I just lack finishing up.~

[Dark Earth]