Geared For Success. AIR-TECH

    Here is something I’ve seen time and time again; People build a really nice engine set up but don’t spend any time or money on to build a complementary transmission. In order for your engine to perform at it’s best,  wouldn’t it make sense to have the right gearing in the transmission? Before you think you have the right gearing, consider what the car is going to be used as. Is it a daily driver? Or Friday/Saturday night car? Some other things you might consider would be where you live, and whether you will be mostly driving around town or through steep mountain passes.

    For a daily driver, I’ve found that engines like to be between 3200 and 3800 RPMs for extended periods of time. That doesn’t mean you can’t rev higher than that for short distances. It means if you’re on the freeway for any length of time, your motor will be at its best in the 3200-3800 RPM range. Meaning your oil temp should be in a safe operating range. Your oil pressure should be good and you should be turning the fan fast enough to get enough air to your heads and cylinders. Keep in mind here that an air cooled VW engine never came with a harmonic damper. You can extend the life of your motor if you keep your RPMs in that range for extended periods of time. I have found that going over RPM and due to the engine harmonics has harmonics, you will have premature wear on your internal parts.

    What about a Friday, Saturday night car? A Friday/Saturday night car is made for short bursts and this doesn’t apply. Also, a Friday/Saturday engine does not have near the life span of a good daily driver. There is no such thing as a 9 sec daily driver that will go 100K miles with out a frequent tear downs.

    Now that we have decided on the kind of motor we have, we have to figure out the gearing part. You will need to know what size tires you have or how tall they are. You should also know what ring and pinion and gears you have. Most of you will have stock gearing. The big question is: how fast do you want to go down the freeway? I would suggest that you don’t get too carried away when deciding this. I always shoot for 80 to 85mph in fourth at 3800 RPMs. For a Friday/Saturday night car we might want 80mph in fourth to be at 5500RPMs. This will get us the acceleration from stop light to stop light.

    A lot of companies have calculators to figure out where you are now and what it will take to get you where you want to be. Here are some examples that we’ve come up with: A 65 bug with a stock trans (4.37 R&P) with a SR165 tire will be at 73mph at 3800rpms. A 69 bug with a stock trans (4.12 R&P) with the same tire will be at 80mph at 3800rpms. A 62 bus with a stock trans (4.37 R&P + 1.39 reduction boxes) with a 195/65/15 tire will be at 55mph at 3800rpm. A 67 bus (4.12 R&P + 1.26 reduction boxes) with a 195/65/14 tire will be at 64mph at 3800rpms. A 69 bus with a stock trans (5.37 R&P) with a 195/65/14 tire will be at 62mph at 3800rpms. A 73 bus with stock trans (5.43 R&P) with a 195/65/14 tire will be at 60mph at 3800rpms. A 76 bus with stock trans (4.86 R&P) with a 195/65/14 tire will be at 69mph at 3800rpms.

    With that information,  I either just made your day or really scared you. Here is what you can do: A taller tire ups the MPH and lowers the RPMs. A smaller tire will lower the MPH and raise the RPMs. Most of us prefer a certain tire size, so the next step for us would be to choose the right gears. If this is a daily driver, I would choose a ring and pinion that best suits my needs and leave 1st through 4th stock. If this is a Friday/Saturday night car, I would change 3rd and 4th gears. If you have an early bus (Pre 1967) then you have a few choices. You can put in a high R&P and keep your reduction boxes or get rid of the reduction boxes. On a bay window bus, I would just change the R&P.

    I see people changing just 4th gear on all types of cars and I can’t lie, I’ve tried that too. The fact of the matter is, the split between 3rd and 4th is usually to great. In other words, you will be pulling a hill and in 4th you’ll find that the engine is lugging, but in 3rd you’re winding in out too much. Been there done that, it’s not a good thing to do.
    Here are some common reasons people choose to re-gear: If you’ve got a Baja bug or manx, you will probably put a big tire on the back because that’s what it needs to get the hight or look you want.. But now, 4th gear is very rarely ever used. If you have a street bug and add low profile tires, you’ll need another gear. Any early bus that wants to keep up with traffic on the freeway will need taller gears. A bay window bus with a bigger motor that can pull the weight will also need taller gears. A Friday/Saturday night car that needs to pull harder stop light to stop light will likely want lower gears.

    Keep in mind, that the right gearing has as much to do with your engine lasting as does building a good engine.

If you have questions on what you should do or not do then you should call a transmission shop that deals with VW transaxles or some of your VW venders that are knowledgable in gearing.