Best gearing for turbo street use

[Martin S.]

My 68 with stock trans 4.125 RP and 195/65R15 rears buzzes along at around 4,000 rpm when I need to keep up with traffic. Problem is the oil starts heating caused by the under-decklid turbo when it revs that high and with 240 lb-ft for torque at 5500 rpm the engine doesn't need to rev to make power. The heads always run cool. It would be happy at 3300 rpm or so. I'm looking for advice to re gear the trans. The choice would be to swap the RP for 3.88 or Weddle 3.44 and the other option is a bus .82 fourth gear. I imagine there would be a big gap beween 3rd and 4th that way. Anybody have any experience re-gearing for a big turbo on the street?

[Fiatdude]

Put the 3.44's in there and it will be perfect for making the turbo grunt around on the street --

[Martin S.]

Great, that's what I thought too, thanks!

[richie]

All that will do is slow the fan down too much and over heat the heads which are probably already suffering with the extra under decklid heat your turbo kit adds

I think a stock 68 4.12 trans will probably have a .82 4th in it already so the 3.88 would seem your best option, but if its just a street car then look at pulley speed as well, if you gear it taller then maybe speed the fan back up with the Porsche top pulley swap[ I have never done this pulley swap but have heard good things from some who have]


cheers Richie

[Zach Gomulka]

68 trans will have a 4.12 x .89.

Porsche pulley works great to speed up the fan

[richie]

68 trans will have a 4.12 x .89.

Porsche pulley works great to speed up the fan

Thanks Zach, real feedback is so much better than hearsay     did every market place around the world get the same ratios?

cheers Richie

[Zach Gomulka]

68 trans will have a 4.12 x .89.

Porsche pulley works great to speed up the fan

Thanks Zach, real feedback is so much better than hearsay     did every market place around the world get the same ratios?

cheers Richie

I would assume the 1200/1300 powered Beetles we didn't get here still used the 4.37 x .82?

[nicolas]

 the transmissions i had for my type3's (4 swing axle gearboxes) came with 4.12 RP but also had the 0.82 gear. but it does lower the rpms quite a bit compared to a 4.37.

[Martin S.]

the transmissions i had for my type3's (4 swing axle gearboxes) came with 4.12 RP but also had the 0.82 gear. but it does lower the rpms quite a bit compared to a 4.37.

So your type 3 swing axles had a bus 4th gear? Normally the gearing was the same between type 1 and 3. The only vehicle that got the .82 4th gear was the bus.

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