Disadvantages of a 71-73 chassis

[zcp m3]

Hey every1,
I'm new to this forum and trying to research different chassis and engine options for a possible project in the future. I really like the looks and minimalist nature of the early 911's, specifically 71-73. My goal for horsepower is in the 450rwhp range. Obviously modifications to the suspension, brakes, and drivetrain are in order.

In this thread I'd like to hear opinions on how well a 71-73 will hold up under that kind of power, as well as the downfalls and negative qualities of those years.

Thanks,
-Zach

[Elombard]

Might consider backdating a 90-94 car. They already have the bigger brakes and Coil over suspension.

The main things that come to mind are:
72- later have a 915 which can ultimately be stronger than a 901
The Swing arms on the pre 73 cars are steel instead of Aluminum, easy enough to change for the kind of mods you are talking about.

There really is not a huge amount of diffence structure wise. The main difference people always talk about is the pre 77 cars are not galvanized and the rust issues that this brings.

The 934s started with one of these chassis and they had HP in that range in quali if I remember correctly.

As long as you do a "tube frame" in the back and all of the well documented reinforcements you should be able to make it work. I think there is several of them on the tracks.

you might look at a thread by 911 teo - do a search. he is building a ~400hp early car (NA) and he is throwing the book at it to make the structure up to the task.

If you decide you want one I will trade you my 73 RS look for your ZCP M3 :-)

[89911]

I don't there any disadvantage to these years compared to older models other then galvanization. As long as its rust free, go for it.

[randywebb]

the later cars have some stiffening pieces added - you can do that tho

by chassis do you mean the unit body? if so then the above is about it.

search up the thread titled structural reinforcement for more info

[zcp m3]

Originally posted by Elombard Might consider backdating a 90-94 car. They already have the bigger brakes and Coil over suspension.

The main things that come to mind are:
72- later have a 915 which can ultimately be stronger than a 901
The Swing arms on the pre 73 cars are steel instead of Aluminum, easy enough to change for the kind of mods you are talking about.

There really is not a huge amount of diffence structure wise. The main difference people always talk about is the pre 77 cars are not galvanized and the rust issues that this brings.

The 934s started with one of these chassis and they had HP in that range in quali if I remember correctly.

As long as you do a "tube frame" in the back and all of the well documented reinforcements you should be able to make it work. I think there is several of them on the tracks.

you might look at a thread by 911 teo - do a search. he is building a ~400hp early car (NA) and he is throwing the book at it to make the structure up to the task.

If you decide you want one I will trade you my 73 RS look for your ZCP M3 :-)

Thanks for the info. I actually came across your car in the for sale section! Mighty fine example and honestly one I'd consider as a platform for my project. Too bad im at least two years away financially.

[911pcars]

The early 911 tub is not strong enough for that much power, but it grew progressively stronger (more rigid) over the years due to thicker sheet metal and other design changes. In any case, a 911 with 450HP needs serious assistance, probably a roll cage along with other bracing at strategic locations.

Look at this thread I started on the topic:

Structural Reinforcement

The objective is to pick a MY chassis that requires a minimum amount of chassis reinforcement to make up for any deficiencies in the basic structure along with the least amount of extra weight. It goes without saying that rust is not a structural element, and you'll have better luck finding a later chassis w/o corrosion issues to deal with. When done properly, a good roll cage makes up for a lack of thick-enough sheet metal. And for those for whom a slippery slope is all to familiar, inheriting someone elses race car project is a good start w/o as heavy an investment. Except for the very latest versions, most 911s of any era can be backdated to the early, long-hood look, although w/450 HP, you'll probably not venture too far back due to tire width requirements.

In addition, unless you're racing for the gold, 450 Hp pushing a few extra pounds isn't going to make much of a difference.

Sherwood

[GrantG]

Originally posted by Elombard
The main things that come to mind are:
72- later have a 915 which can ultimately be stronger than a 901

Well, 450whp is about 530hp at the flywheel - I think this is well past 915 capacity (not to mention 901). I think you'd need a beefy 930 or G50 box for that...

[Jack Olsen]

There's a car in northern California a lot like what you're describing. It's Henry Watts' car (he of 'Secrets of Solo Racing' fame). He put a built 993TT motor and its G50 in a 1972 chassis with a 993 rear end a full cage and a lot of other mods. He races it pretty regularly and needless to say, he's very fast.



I don't think you could build it for less than six figures.

[pwd72s]

Jack, how difficult was it to put the G-50 into a '72 Chassis? Pretty extensive mods? I agree...450 horses is a LOT for a 915 to handle...

[Jack Olsen]

A few people have done the G50 swap on this board. It's expensive and involved -- not really a great bang for the buck mod.

But if you want a no-excuses car with that kind of power, then it's probably cost-effective in the long run. Replacing blown-out 915's is going to get old after a while.

[DW SD]

You can get a shortened G-50 bellhousing transmission for $4k - $5k on top of purchase price ( I think) through Patrick Motorsports. That eliminates the need for torsion tube modifications. It is significantly heavier, though.

The rear shock mounts (at least 1971) are smaller than later, so if you mount coil overs, they must be mounted upside down (springs down).


I think the beauty of these cars is low weight. Mine is at 2200lbs w/ a few gallons of fuel in the tank. Maybe 450rwhp isn't necessary? My car dyno'd at 275 rwhp and it goes very well. That w/ a '95 3.6.

Power to weight at 8 to 1 (lbs per wheel HP).

For reference, the new Z06 Vette = (3200 lbs / 505 (crank HP, though) multiply by .8 for drivetrain and you are right @ 8 to 1.

Just my $0.02.

Whatever you do should be fun!

Doug

[Green 912]

If you like the look of the early longhoods but want a street or streatable car the thing to do is perhaps rethink the HP number. There is much fun to be had in a lower HP but well set up 911. 911s are not all about the HP. What do you plan to do with the car? Cool street ride, race, DE some of each? (The later is not a good combo overall imo)

[ficke]

I would think the biggest disadvantage of using a 71-73 chassis as opposed to a newer one of equal shape would be cost, I would use a cheaper newer car. You are going to buy all new finders, hood, etc. any way so the look could be any thing you want , I would get a newer tub and save some $$.

[tfiv]

What are you putting in the back that's going to make 450?

[Jays72T]

+1

[QUOTE]Originally posted by Elombard
[B]Might consider backdating a 90-94 car. They already have the bigger brakes and Coil over suspension.

Backdating is the way to go in this case. Try to find a cosmetically challenged car for low $$ and go from there.

[jeff1hughes]

Here's another vote for backdating. Early chasis are getting top dollar right now (damn, I wish I still had my 'S'), and you never really know what rust issues you'll uncover once you start working on it. If you are in a smog test area, look for a '76. They were galvanized and had no factory stock air pump, reactors, or EGR system.

[zcp m3]

Interesting. I've always heard of 993 bodies on 964s, etc but never backdating. Sounds like a good way to go structurally and the fact a G50 would fit in there.

[ERH]

Looks like someone had the same idea

zuffenhaus C2 to '72 RSR project...

Ed

[DW SD]

Only negatives about backdating are 1. the offsets on the wheels are wrong and to get the right look, you'd have to have custom fuchs or centerlocks made. 2. In CA, you have to smog later chassis >75.

The 964 / 993 are killer chassis from which to start, though. I have to admit, I'd have a hard time backdating a 993, though, since I think they are gorgeous. 964s are very nice, but I prefer the early longhood widebodies.

Doug

[zcp m3]

Yeah i definitely couldn't backdate a 993, way too pretty. A 964 sounds like a pretty viable option though. Nice strong chassis with a solid motor/trans to build off of. Big brakes and nice suspension as well. I wouldn't worry about the offsets cuz i planned on custom Fuchs from the beginning.

Thanks for the ideas guys!