3.6 vs 3.2 transplant, which one would you choose

[HK911]

What is the difference in effort (hours required) in upgrading my 1977 911 2.7 sporto to a

(a) 3.2 with 915
(b) 3.6 with 915
(c) 3.6 (964) with g50?

I dont have the mechanical knoweldge to try this so i will be getting someone else to do it but i need to budget for the labour.

Thanks

[dickster]

in answering your thread title i would go for the 3.6/915.

the other i dont know.

[IROC]

Well, a big part of the hours on yours right off the bat is the sporto to "something with a clutch". For better or for worse, that will be about the same regardless of engine (except for the added effort on the G50), so that shouldn't affect the engine choice.

As for the engines, I just swapped a 3.2 into my '76 and it is really a very straightforward swap. A 3.6 is quite a bit more involved.

I'm not going to attempt a quote of hours other than to say that you have them in the right order. :>) Any one of these projects (a., b. or c.) will cost you more than the car is worth right now, most likely. Unless you're really in the mood to spend alot of money, I'd go the 3.2 with a 915 route.

Mike

[gerry100]

Not an expert, but one reason Porsche went to the G50 was that the 3.2 motor was pushing the design limits of the 915 tranny.

Therfore it would seem that a 3.6/915 combo would be ill advised.

3.6 / G50 would be my choice. Only a mechanic who has done it before can ber accurate on labor hours.

[Joe Bob]

Originally posted by gerry100
Not an expert, but one reason Porsche went to the G50 was that the 3.2 motor was pushing the design limits of the 915 tranny.

Therfore it would seem that a 3.6/915 combo would be ill advised.

3.6 / G50 would be my choice. Only a mechanic who has done it before can ber accurate on labor hours.

Personally the 915 can handle the extra hp...they went to the G50 for smoother shifting and hydraulic clutch......but it's only an opinion.

[Dantilla]

I have a 3.2 in a '73. Relatively easy swap, and I can autocross in SCCA's ASP class. A 3.6 would push me into a higher, more expensive class.

With a 915 with a 7/31 r&p, the car can accelerate faster than my brain.

[Rick Lee]

I'm surprised Marcesq hasn't chimed in here yet. We did this in his car last summer. It was pretty straightforward. Probably a two-weekend job. Check it out: http://www.pelicanparts.com/MotorCity/marcesq1/

[HK911]

Thanks all for your input.

Richard: Yes i saw the link to Marcesq site before already, and had a look through it. As i am not that game to do it myself i'd like to get a feel of how long it takes someone (who knows what they're doing) to do the transplant.

Currently i am leaning towards a 3.2 with 915 as it seems like an easier fit.

[widebody911]

A 3.6L with a 915 is fine for the street, but pushing it on the track. The 7:31 will give you NASA-esque accelleration, but the experience seems to be the 7:31 won't last.

On the track, the 915 - even with the 8:31, is marginal. A cooler helps, but you have to treat it carefully.

I forgot to turn my cooler on for the first session on Friday, and had the thermostat on the cooler set too high. When I came off the track after a 25-minute session, I was getting a lot of R&P slop, which went away in subsequent sessions when I ran the cooler the entire time. I figure I'll have to rebuild the trans again some time next year.

[Kevin Stewart]

I dont believe the 3.6 is that much more involved, you pretty much have to do the same things to install either one, the 3.6 will require some additional parts and you can add a bunch of money, i did a 3.6 this year and its awesome, the only reason i would lean toward a 3.2 if i were you is if i could get the 3.2 with the tranny and parts to install with the motor, then the 3.2 may be a better value, but if you had to source both , then i would go with the extra cash out lay and get a 3.6, smoother more up to date eqiupment, Kevin

[Carrera Sled]

Originally posted by HK911


(a) 3.2 with 915
(b) 3.6 with 915
(c) 3.6 (964) with g50?

How about a 3.2 w/G50?

[Rick Lee]

Putting a G50 in your '77 is gonna be time consuming and costly - even if you buy one that's been modified already. You have a pedal cluster and hydraulic system to deal with - lots of fun and $$$.

[masraum]

a 915 is much more straight forward than going to G50. Going the G50 route will be more involved.

Yes, the move to G50 was that the 915 wasn't rated to comfortably handle the torque of the 3.2 in stock street form. The 915 can be made to handle more, but remember, that one of the things Porsche was worried about was longevity and reliability. In Paul Frere's, Porsche 911 Story, he says, I believe, the primary reason for the G50 was to better handle the increased power of the larger engines.

[Jack Olsen]

The G50 is a better transaxle, but there are some significant trade-offs. The biggest is cost, since you need to either go to coil-overs or make some serious mods to the torsion tube setup in order to git a G50 into an earlier tub. The hydraulic clutch also means changing to a later pedal cluster. The second biggest sacrifice is that (as I understand it) you have to push the engine further back in order to fit the G50, which hurts your weight distribution and degrades the car's handling. When you're adding a bigger engine, there's a weight penalty right off the bat. Pushing the engine further back only makes it worse. With the 915, you can actually cheat the engine placement in the other direction, improving the car's weight balance. (And what's more, the G50 weighs more than the 915 no matter where you put it.)

You can't consider all models of 915 to be the same box. The 74-and-earlier 915 have the shorter (7:31) ring and pinion, which uses a smaller input shaft, and are less robust than the later 915 transaxles. Up until 1977, the 915 case was made of magnesium, which is great for weight, but kind of soft for holding bearings in place. (There's a billet retaining plate made that addresses this problem.) Aluminum-case 8:31 915's are plenty strong enough for a 3.6 used on the streets. A cooler is a smart idea for any track use.

With track use, a transmission gets significantly more heat-related stress than in street use. One persistent misconception is that guys who have not done a motor swap don't need to worry about their 915's on the track. If they had a temperature gauge on their trannies, they'd be a lot more concerned. With just about any size motor, a transaxle is going to get way above its optimal operating temperature. Gear oil starts to break down at about 200 degrees, a much lower threshold than engine oil. With or without an engine swap, a tracked 911 is going to get much hotter than this. I've seen 260-degree tranny temps when my motor was running at 235. With a cooler, this drops right down.

[Bill Verburg]

I would recommend a 3.6 w/ late 915 & cooler. In general each generation of a particular unit is better/improved than the previous iteration.

A 993 w/ 915/67,69 or 72 is an awesome combo.

as discussed above the G50 is lots of fuss for very little benefit.

The biggest additional item needed for any 3.6 over a 3.2 is the sheetmetal/rear engine mount mods needed on the 3.6 otherwise the swaps are very similar.

[dean]

I did install a G50 in my SC. I did have to move the motor back 3/4". I don't notice a change in the handling. Maybe if I tracked the car I would but I don't. The G50 weighs 20 lbs more than the 915 I removed. If you go to coilovers you wouldn't have to move the motor back. The install is a fair amount of work. I heard Patrick gets $7k for the conversion. And I think personally, it is worth the fuss. But I always say that.

[dean]

Oh yea, If I was paying someone to do the G50 conversion I don't think I would do it.