2.7L Twinplug with 901/911 or 915

[stcan]

I am building a 2.7 Twinplug motor for the 71 911

Any recommendation for 901/911 vs 915 transmission.

Pros and Cons of those 2 in the 2.7L?

Can the 901/911 transmission handle the power of the 2.7?

Why did Porsche goes with the 915 starting with 2.4L

[Bill Verburg]

Originally Posted by stcan

I am building a 2.7 Twinplug motor for the 71 911

Any recommendation for 901/911 vs 915 transmission.

Pros and Cons of those 2 in the 2.7L?

Can the 901/911 transmission handle the power of the 2.7?

Why did Porsche goes with the 915 starting with 2.4L

Why did Porsche goes with the 915 starting with 2.4

reliability w/ the bigger torquier engines
I'd go w/ the original 2.7 RS, Mg. case trans, 915/03 or /08, unless the rev range is drastically raised
the /03 no cooler, the /08 a pump & cooler and slightly shorter 5

Alternately 915/44

If using a later Al. case the SC/RS or opt/SC/RS if track only

[Classic 911]

Following


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[stcan]

Thanks Bill,

I already got the 915 915/68?

I also have 911 transmission.

Just deciding on which to use

[stownsen914]

As Bill mentions, the 915 is a stouter trans, hence why Porsche started using it with the 2.4 in '72. A 901/911 will stand up to a 2.7 as long as you don't abuse it. The 915 is probably a better choice, especially if you already have one.

[thetorch]

Your cable driven speedo will not work with that later 915/68.

[MrBonus]

What kind of power are you aiming for? A lot of people are pushing some serious power through 901s with no issue as long as you treat first and second with respect.

[Matt Monson]

If you were considering a 911 mag versus a 915 mag with 7:31, like a 915/02 or 915/06, I would call it a wash. But that /68 is 3.2 Carrera with all the updates, 8:31, etc. and 108mm cv stub axles. You have it,use it.

Personally, like Mr bonus, I like the 911, because of the dogleg, and better shift pattern. The most common 2-3 up and down us in the same axis. You aren’t crossing gates to do it like on a 915. And with an aluminum side cover and bearing plate, it’s pretty solid for an adult driver.

[Bill Verburg]

w/ the same tires and rev limit
here are the speeds in gear
915/08 '73 2.7RS
35 60 87 119 145
915/5/68 '84 US Carrera 3.2
40 71 100 126 159


the /68 is taller in every gear more suited for an engine w/ more torque

SC/RS base
40 63 91 116 142 is closer to what you would want

SC/RS option
40 58 79 100 126 is far sportier but might be unpleasant if a lot of freeway driving is in the cards

[stcan]

I guess on the 915/68 changing out R&P to 7:31 or 8:35 would make it better. And change out 5th to taller gear for highway.

Would that work?

Originally Posted by Bill Verburg

w/ the same tires and rev limit
here are the speeds in gear
915/08 '73 2.7RS
35 60 87 119 145
915/5/68 '84 US Carrera 3.2
40 71 100 126 159


the /68 is taller in every gear more suited for an engine w/ more torque

SC/RS base
40 63 91 116 142 is closer to what you would want

SC/RS option
40 58 79 100 126 is far sportier but might be unpleasant if a lot of freeway driving is in the cards

[Matt Monson]

It would be substantially more expensive to change the final drive than to regear it to suit.

[Bill Verburg]

Originally Posted by stcan

I guess on the 915/68 changing out R&P to 7:31 or 8:35 would make it better. And change out 5th to taller gear for highway.

Would that work?

7/31 cwp moves all the speeds down
35 62 87 110 140

cruise rpm is getting uncomfortable

8/35 is just a tad raised from 7/31
35 63 88 111 141

[Bill Verburg]

Originally Posted by stcan

Thanks Bill,

I already got the 915 915/68?

I also have 911 transmission.

Just deciding on which to use

Just noticed that you have a 911 trans

If it's a 911/01 and using the same rev limit and tires as for the other trans I've posted here
speeds in gears are
36 62 90 119 145

I'd use this trans if it's in decent condition

[stcan]

So 911/01 it is.

Will get it check out to make sure all is good.

Should I go with stock flywheel or Patrick Motor Lightweight flywheel 8.5lbs vs 6.5lbs