TheSamba.com :: View topic - 388 ring and pinion vs 412 ring and pinion

Tue Jan 11, 2011 10:55 pm

Just built a 1915 motor for my bug that I will be using for weekend cruising on the streets and highway. Should I go 388 or 412 r&p? What are the advantages of either one?

Tue Jan 11, 2011 11:37 pm

388 is stronger than a 412, except the brazilian 388 that is.

Tue Jan 11, 2011 11:44 pm

What's the rest of the motor?

Wed Jan 12, 2011 12:12 am

4.12 is the best R&P for a street car. Much better grunt in the lower gears.

Wed Jan 12, 2011 12:29 am

Depends on tire size too. If you are close to stock height on the tire, like Bruce said 4.12 would be better.

Wed Jan 12, 2011 1:10 am

I like the 4.12. Depends on the 4th you plan on running though.

I had a 4.12 and .82 4th in a bus with a 1915 and 195/60s out back and it was a little rough uphill. Third gear downshifts etc.

The same tranny with 205/65s and a 2276 runs up Baker and Cajon grades at 75+ and never comes out of 4th. :wink:

Wed Jan 12, 2011 6:04 am

Didn't see that this was a double post........ :?

Go here and plug in the numbers for your particular transaxle and tires to see what speeds with what rpms your car is running.

Just remember that even with different rear ends, there are different 4th gear ratios. 0.89 or 0.82

The standard VW trans for a 1972 Karmann Ghia has these ratios:

1st 3.80

2nd 2.06

3rd 1.26

4th 0.89

ring gear 4.13

http://www.kabamus.com/garage/gears.html

Great website for this.

Kelly

Wed Jan 12, 2011 7:46 am

Cohibra45 wrote: Didn't see that this was a double post........ :?

Go here and plug in the numbers for your particular transaxle and tires to see what speeds with what rpms your car is running.

Just remember that even with different rear ends, there are different 4th gear ratios. 0.89 or 0.82

The standard VW trans for a 1972 Karmann Ghia has these ratios:

1st 3.80

2nd 2.06

3rd 1.26

4th 0.89

ring gear 4.13

http://www.kabamus.com/garage/gears.html

Great website for this.

Kelly
Thanks for the link, what i'm looking at appears to be very comparable. I'm running 195x60's on the rear and looking at a 4.12 r&p with .82 4th gear. Is this a good application in your opinion?

Wed Jan 12, 2011 7:50 am

gerg wrote: I like the 4.12. Depends on the 4th you plan on running though.

I had a 4.12 and .82 4th in a bus with a 1915 and 195/60s out back and it was a little rough uphill. Third gear downshifts etc.

The same tranny with 205/65s and a 2276 runs up Baker and Cajon grades at 75+ and never comes out of 4th. :wink:

My tire set up is identical to your 195/60s with the same size motor. The only difference is i'm in a bug. Have you ever ran a 3.88 r&p with a .89 4th? When you refer to uphill being rough are you saying that it loss power?

Wed Jan 12, 2011 8:06 am

Yes. Heavy bus loaded with parts or for camping. Wasn't terrible, but I wanted to climb the grades without losing too much RPM and wanted to maintain speed.

I have a friend with a 3.88 and .82 4th in a double cab. It's a bear up the hills but flys on flat ground.

Wed Jan 12, 2011 8:10 am

Depends on if you want to Rocket down the Highway, and how many miles it will be used on the Highway...

I run a 3.88 R&P in a Street Rail, its all over the highway speeds and being a Light Rail the pick-up and go is not bad either, this is with a mild manner 2110, Single Carbed w/14" Wheels w/.82 4th....... RB

Wed Jan 12, 2011 9:57 am

Bruce wrote: 4.12 is the best R&P for a street car. Much better grunt in the lower gears. that depends on the motor.

Thu Jan 13, 2011 1:13 am

mark tucker wrote: Bruce wrote: 4.12 is the best R&P for a street car. Much better grunt in the lower gears. that depends on the motor. A 4.12 instead of a 3.88 will make any motor feel like it has more grunt.

Thu Jan 13, 2011 1:41 am

You need a dyno graph of YOUR engine to know where it makes torque at, THEN you can pick the gears that keep you in that sweet spot that
YOUR engine makes for the speeds that you normally drive.

Don

Thu Jan 13, 2011 2:28 am

That's what I did in a round about way. My torque peaked about 3400 at 160 ft/lbs and that RPM is perfect for my bus on the freeway.

Thu Jan 13, 2011 8:53 am

You must know your engine size, rear tire size, wt of car with estimated wieght in it, and most important of all what your intention of driving or environment is.

Bugs and light cars i like the 3.88 with either the .089/.082 4th or 4.12 .089 for a heavier bus. With a smaller than 2000 cc engine Id likely pick the 4.12 .089 combo. 2000cc and up the 3.88 in other cases.

Thu Jan 13, 2011 9:02 am

my 2028 has a 4.12, my 2332 had a 388. the 2332 would blow away the 2028 badly.so size does matter !! and the 2332 had 31"x16 wide tires.and the 2028 has 28" kinda skiny 8" wide tires.witch gives it more gear.

Thu Jan 13, 2011 9:15 am

My bus has a 1776 3.88 on 16" Fuchs. I don't know what the 4th gear is but it came out of a late Super Beetle vert so I think it's a .93.

It's flat on it's face up hills and only wants to cruise at 60mph on the highway. If you put your foot into it it will do 70mph.

Thu Jan 13, 2011 9:26 am

mark tucker wrote: my 2028 has a 4.12, my 2332 had a 388. the 2332 would blow away the 2028 badly.so size does matter !! and the 2332 had 31"x16 wide tires.and the 2028 has 28" kinda skiny 8" wide tires.witch gives it more gear.

You get more gear because it is skinny?

I always found that effect by height.

Thu Jan 13, 2011 11:50 am

no gerg because it is only 28"tall and skiny , vs the 31"tall and fat. the fat and skiny have very little to do with it other than looks. it might be I get more skiney with my gear :shock: