Need some help?

[brooklynporsche]

I just found out that the transmission in my 1981 Porsche is from a 1974 Porsche part# 915 301 101 0R. I need a 915 transmission that will work with a 3.0 Engine.
What are my options? I was thinking to sell it or trade for another working transmission. How much does a 1974 transmission go for?

Thanks in advance

[SC-targa]

The 74 will work fine, but does not support the electric speedo in your car. It has a lighter mag case and a shorter final drive ration that many like, but goth are less robust than the later aluminum case unit.

[brooklynporsche]

Thanks SC-targa
Are you saying that I should go ahead and keep the tranny. Also is this 5 spd or 4 spd

[Kemo]

I was under the impression that the 74' 915 transmissions had the 7.31 ratio which I have read "feels like adding 50hp". With that in mind, it might be beneficial to find a gear driven tach and enjoy the short gear ratio

If not, you could probably work out a trade with someone wanting to upgrade...

Personally, I would keep it.

[brooklynporsche]

I was expecting the worst. Original someone sold me the car with a 2.4 CIS engine. Once I found out I was extremely disappointed but everything worked out I was able to sell the engine and get me a 3.0 engine. Now you guys are telling me that the tranny will work and in addition will add more HP. WOW that sounds good. Thanks Kemo

Thanks

[Kemo]

well, technically, the 7.31 doesnt add any horsepower, it just makes good use of the gears. I think you might lose a little bit on top end. Bruce Anderson has written a really good book on getting horsepower out of 911s. So if you get a chance, pick up a copy of his Performance Handbook. Its a great read...

Long story short, if you want good performance from a stock 3.0, get the SSI heat exchangers with a cool muffler. Combine that with the 74 transmission and you will have a fun, reliable car.

post some pics as you go along if you get chance

[brooklynporsche]

I will thanks Kemo. The project is still a long way from being finished.

[RWebb]

keep it and maybe modify it if in good shape

search up the Best Year for a 915 thread for ideas on strengthening it & think about changing the gears a tad for best performance.

The earlier (Mg cased) 915s are lighter, which is what you want in a sports car -- as long as nothing breaks.

You need to think about your goals for the car...

I have a 3.2L hotrodded motor with a '75 trans. When I get a lot of $$ I don't need I may change the gearing a bit, but it is not too far off right now.

[tcar]

Originally Posted by brooklynporsche

Now you guys are telling me that the tranny will work and in addition will add more HP. WOW that sounds good. Thanks Kemo

No, that's not what they're saying. The transmission cannot ADD horsepower.

The car will feel more responsive on acceleration due to the lower gearing. This will be fun. (Like adding HP out of the chute.)

The top end (top speed) will suffer a bit as a result. At top gear redline the car may be 5 or 10 mph slower with the early transmission.

Also, cruising on the highway, the engine will be revving higher and noisier if that bothers you (wouldn't me).

I would keep it.

Hmmm, the 2.4 CIS motor is a '73.5 on a '74 tranny. Interesting. Wonder if it's from a late '73.5 with the '74 tranny.

Keep it.

[brooklynporsche]

thanks guys. I'm also in the process of rebuilding my 3.0 to a 3.2 short stoke twin plug and adding SSI heat exchangers. Will this work?

[RWebb]

yes, but depending on your revs & usage, the SSIs may be a bit confining

they should be fine for a street motor

[brooklynporsche]

Yes definately a street motor. RWebb I'm curious what would you recommend instead of the SSI? Headers
Thanks again