3.5 N/a vs. 3.6
 

What are the opinions on a h/p, torque, installation cost, required modifications, ect of building a 3.5N/A vs. doing a 3.6 conversion to an early '71T body? Street driven, suspension has been modified heavily, incluing brakes for increased power, larger displacement engine. 915 tranny to be installed as well. Rear tires are 345's on 11.5 inch rims for gripping power. Car has gone on a diet with front end in fiberglass along with rear/lid spoiler combo. I have access to engine builder, machine work and so forth but to me, a guy could build a strong 3.5 for less than the transplant by several thousand dollars. Correct me if I'm wrong. Regards, John.

John,

There is something (in my feeble mind) to be said for an engine built by the gnomes in Stuttgard (or zuffenhausen) that cannot be said for one built anywhere else. If the engine has over a few thousand miles on it we usually assume that its going to stay together and is a good engine.

Finding a good one that has reasonable miles on it is not that difficult and you as well end up with a enhanced fuel injection system on it.

I love to build engines but went the 3.6 route... after selling my 3.2 the cost was not that much.

JoeA

The price of 3.6 motors are coming down they can be done under 10k, if you do it your self and shop, If you dont have either motor I think I would start with a 3.6 that has head gaskets, Just a better motor all around, some guys have done the 3.5 but already had a 3.2, I may be wrong but it looks like 3.5 has about the same hp as a stock 3.6, Im in northen indiana and i have a 3.6 conversion, your welcome to come take a ride, Kevin

With the 3.5, you know exactly what was done, you can do a lot more customization (valve springs, pistons, etc) when it's being built, and you have an effectively new engine when you're done. You can put the money you save into more mods to ultimately make a better set up. In the end, either route will be great.

klaucke what money is saved if he doesnt have either engine, they are starting to be about the same cost, Kevin

At this point I don't have either engine and have tried to watch the threads in regards to these engines. As we all know the motor is pretty much the most expensive part and a good decision is wise (I don't want to make a mistake) and I want to be happy with the end result. The car is only spring thru fall driven and truthfully I haven't put over one thousand miles a year since I've owned it. it is my toy and don't mind putting more in it than I know I can recoup within reason, am I rich no, thus the wise decision process involved. I guess I'm asking those who have either combination as to their opinions. The suspension for a street car has gone over-board, I've got just about everything but a coil-over set-up and have just about all the body pieces except boxed rockers to get. Thus the motor decision begins. Jerry St. germaine and I have discussed various options, and I talked with Bob Farmer as well. I'm checking with the wealth of knowledge on this board as to their opinions and I greatly appreciate all of your inputs. feel free to offer your opinions as I am sure others on this thread are having similar thoughts to mine and want an engine that is powerful, cost effective, and relatively easy to install and maintain. Thanks again. John.

Rationale for my swap was to gain substantial performance and still retain factory reliability. I strongly recommend this swap if your rationale are similar. I like the idea of factory engineering over garage mechanic engineering....essentially turning a 3.2 into a 3.5 probably wouldn't make its way through Porsche's QA regimen for reliability and durability (my opinion only).

I've seen too many "new" homebrew engines fail at the track (3.4's and 3.5's) while my stock 3.6 keeps going without even a hiccup.

Your call ultimately. Don't forget that your engine has some resale value. It made a huge difference in the cost of my project and shouldn't be overlooked.

W/ a 964 or even better a 993 engine you get far more than just displacement, a few examples; twin plug, heads w/ additional cooling fins to compensate for the extra plug, ceramic inserts in the exhaust ports that keep head temps down, knock sensors, adaptive electronics, reliable electronics, factory engineering.

The 993 is even better w/ additional advantages in materials, weight, strength, port and valve size, air metering, maintainance reduction.

3.2, 3.4, 3.5 are highly dependant on the skill and thouroughness of the builder and the deepness of the owners pockets. They can be good, but for the same effort and cost a 3.8liter 993RS engine can be built.

Hi Mike, you want to place a friendly wager that my newly rebuilt 3.2L>3.5L will outlast your used 3.6L???:)

How did 964 3.6L head studs, 964/993 valve guides and rod bolts (among other known problem areas) pass Porsche's QA regimen??? My 3.5L motor has all those issues taken care of. Doesn't sound like garage mechanic engineering to me.

Bill's comments are more on the money, the 3.6L motors are a better engineering platform to start with but is not the best option in every case. I don't know what his or others cost to build but you can build a strong and reliable 3.5L twin-plug street motor with 993 Varioram type power for under 12K if doing it yourself. In my case, the 3.2L wouldn't have been worth much to sell because the valve guides were shot.

Sorry if it sounds harsh, the garage mechanic and q/a regimen nonsense struck a chord with me.:)

Ralph

And don't foreget the improved crank and the valves themselves... my 3.2 actually has some 993 valves in it. Tobias Aichele's engine book discusses some of these changes, as does Frere's 911 book.

The 3.6L motors are a lot more trouble to install in the earlier cars tho. Some of that has been overcome as there is now a body of people out there who have done it.

BTDT

If you don't have a base engine to start with the hands down preference for cost is going to be a 3.6.

If you have a decent Motronic 3.2, as a 3.4 or 3.5 it can easily beat the price of a professional 3.6 install.

Bill,

You have almost a year on your 3.8 engine. What was it in the beginning, a 3.6 that was "massaged" and how do you like it compared to a stock 964 3.6 engine?

Your points about the extra bells and whistles are well taken and in these days where the fuel quality and octane rating are not what they used to be things like a knock sensor and such are very good to have.

Joe

Isn't Bills engine straight out of a 993 RS 3.8?

3.6 has dual plug, knock sensors and 0.1L extra out of factory. No brainer to me.

I bought a perfectly good M64/21 ROW 993vram('97) A whole bunch of 993 RS and RSR parts, a whole bunch of aftermarket parts, had it torn down to bare case and heads, and reassembled by Steve Timmins.

He did a great job, runs very nicely.:)

I don't know how that could be possible. 993 intake valves have 49mm(51.5mm RS)x7.92x110.1 mm stems & tapered 42.5(43.5mmRSx7.95 - 7.94 x109mm exhausts, 964 and 3.2 intakes have 49mmx8.97x110.1 mm & 42.5mmx8.95x109mm exhausts

A buddy of mine just cracked a Cosworth piston in his race 3.4 and rebuild will include some nice big 54mm Ti valves that will be verrry interesting

Ralph,

Please, please...don't take my comments personally. I made that statement based on what I've seen at the track and experienced myself (again...my opinion only).

One can assume that Porsche's QA requirements include a certain consistency in the manufacturing process that would simply be impossible in one-off big bore projects done in completely dis-similar circumstances. I'm sure your 3.5 is superbly built with every nuance looked after with the same dilligence that goes into every engine design at Porsche itself. If everyone could be assured of such quality control by the mechanic that builds their particular engine, I'm sure it would be an excellent choice. If not, a Porsche designed and engineered 3.6 might be a more prudent choice. I am not qualified or experienced enough to build my own engine and as such, wouldn't attempt it (on this scale). Therefore, the 3.6 made more sense. After a year of abuse, I remain quite happy with my decision.

Again, no offense was intended in my commments. Just answering the question based on my own experience and research. Wishing your 3.5 a long and reliable life (until it blows up :eek:....just kidding....really)!

No offense taken Mike, just didn't want to see a blanket statement. I think many of us have seen engine hack jobs, regardless of the displacement. I have also seen a few 3.6L transplants that make me cringe, with basically stuffing it in there and not paying any attention to the details with wiring and hoses.

Who knows, my 3.5L may end up with the same fate as the others you have seen. :) Hopefully the "bet" would take over 200,000 miles to decide and by that time we are both old and gray.

Don't get me wrong, I envy you 3.6L guys to a certain degree. if my 3.2L was perfect I would not have rebuilt it or I would have bought a 3.6L for a transplant and sold the 3.2L with good conscience. I WOULD have torn down the 3.6L though and gone through it before installing just for peace of mind. Can't see the value of buying a used motor of unknown origin, installing it and getting everything dialed in and 5K later it has to come back out because of a broken head stud or worn guides. That is just not a risk I am willing to take. More power to you guys that have and had success (and a little luck!)

If you have a tired or worn out 3.2L that doesn't have much resale value, I still believe the rebuild to 3.4L or 3.5L is the way to go if cost is a primary concern. To build a 3.6L from a 3.2L requires the 76.4mm crank and additional piston machining which then raises the cost to probably not worth doing. A converted 3.6L from 3.2L or a 993 3.6L for the same price? That's a no-brainer!

I think as the months/years pass by and the prices of 3.6L motors steadily fall, this won't even be an argument. I think it will be eventually CHEAPER to transplant a 3.6L then trying to increase the displacement on a 3.2L.

Ralph

There's no reason why a properly rebuilt 3.2L -> 3.5L would be less reliable than a used 3.6L. Especially if the rebuilder has taken the appropriate measures to install stronger components (stronger head studs, rod bolts, valve guides, retainers, springs, twin plugs etc). At least you know the state of your rebuilt engine and what's gone into it ;)

WydRyd, I dont believe he has any engine which is the issue, there is just so many things that are improved over the 3.2, the first is the valve covers, injection etc, im not saying the 3.2 is bad just if i had no engine the 3.6 would be my first choice, Kevin