Best handling....lightness vs. distribution vs....?

[AlfonsoR]

Originally Posted by j911brick

Bottom line: There is a reason all the fastest race cars in the world are mid-engine.

My original post suggesting the 914 was because I was thinking that if the OP really wanted to get the balance right he should make his car mid-engine (its been done). Then I thought the 914 is basically just that: a mid engine 911, using many of the same parts and specs as a 911. So why not just start out with a 914?

You just said the word "race car". However, we are not talking about race cars, we are talking about production cars. Except in extreme racing, the advantage of mid engine can be overcome by performing better in the thousands of other variables or keys to winning races. This has been proven by Porsche's 911 winning against the Ferrari F360/430s for several years now.

I like the 914 suggestion, though.

[j911brick]

Originally Posted by winders

Y

Just because the 914 is mid-engined does not mean it will run circles around a 911-based car. Clearly the optimum choice is a mid-engine design. But there is a lot more to handling than engine location.

Scott

Agreed.

[Bullet Bob]

I also agree, BUT the 914 has a lower CG, better weight distribution, and lower polar moment of inertia, so as a platform it has more potential. With the weight in the rear the 911 will out accelerate and out brake a 914 and it has better aero characteristics so it will most likely have a higher top speed. So my guess is the 911 will have more speed on the straights with later braking but the 914 will carry more speed through the corners.

[j911brick]

Originally Posted by AlfonsoR

You just said the word "race car". However, we are not talking about race cars, we are talking about production cars. Except in extreme racing, the advantage of mid engine can be overcome by performing better in the thousands of other variables or keys to winning races. This has been proven by Porsche's 911 winning against the Ferrari F360/430s for several years now.

I like the 914 suggestion, though.

That's because Ferrari's suck! Everybody knows that.

[j911brick]

Originally Posted by Bullet Bob

I also agree, BUT the 914 has a lower CG, better weight distribution, and lower polar moment of inertia, so as a platform it has more potential. With the weight in the rear the 911 will out accelerate and out brake a 914 and it has better aero characteristics so it will most likely have a higher top speed. So my guess is the 911 will have more speed on the straights with later braking but the 914 will carry more speed through the corners.

Actually, I think the 914 has a lower drag than the 911.

[j911brick]

Originally Posted by Bullet Bob

I also agree, BUT the 914 has a lower CG, better weight distribution, and lower polar moment of inertia, so as a platform it has more potential. With the weight in the rear the 911 will out accelerate and out brake a 914 and it has better aero characteristics so it will most likely have a higher top speed. So my guess is the 911 will have more speed on the straights with later braking but the 914 will carry more speed through the corners.

. Better weight distribution and lower CG means it should also stop better.

[Bullet Bob]

Originally Posted by j911brick

. Better weight distribution and lower CG means it should also stop better.

When you slam on the brakes most of the load is transferred to the front tires. In a car with a 50/50 weight distribution you might end up with 70% of the braking done by the front tires and 30% by the rear tires. Since the 911's weight is biased to the rear initially, once the load is transferred you might have 60% braking by the front tires and 40% by the rear tires. With the tires loaded more evenly during braking there will be more stopping power. It all depends on the CG height and it would be interesting to crunch some numbers and see the actual results.

[911st]

It is hard to argue against the advantages of a mid v rear motored car.

However, in the case of Porsche there has been a lot more development done by the factory and privateers on the 911. This gives it a big advantage over anyone wanting to build a race car.

If you are trying to build a class leading 914 you are a bit more on your own and will probably end up adapting a 911 drive train to do it.

Both cars make a great platform.

For a street rod it probably comes down more to personal taste and desire for comfort.

It would probably cost more to build a 3.6 914 with power steering, working AC, and ABS than to just source a good used C2. However, it would be fun.

[j911brick]

Originally Posted by Bullet Bob

When you slam on the brakes most of the load is transferred to the front tires. In a car with a 50/50 weight distribution you might end up with 70% of the braking done by the front tires and 30% by the rear tires. Since the 911's weight is biased to the rear initially, once the load is transferred you might have 60% braking by the front tires and 40% by the rear tires. With the tires loaded more evenly during braking there will be more stopping power. It all depends on the CG height and it would be interesting to crunch some numbers and see the actual results.

Yes it would be interesting and the data is probably already out there. Just compare original road tests from the '69 911 T to the ;69 914/6. Same tires, brakes, motor, so it should be a good test.

[Flieger]

The axis for polar moment of inertia goes through the mass center, so on a 911 the mass center is further back than on a 914. This means that the 911 wants to rotate about the rear wheel more than a 914, which would want to rotate around the middle.

The way I see it, this means that the 911 should go deep into a turn, trail braking, slow down and take a late turn-in, where it can use the quicker angular acceleration of the front wheels about the rear to point the front end towards the apex and then "shoot" towards it, using the rear weight to gain traction, stop the angular acceleration, and get down the track fast in a straight line.

The 914, conversely, should carry speed on a wider arc through the turn, with the wider arc shifting the pivot point out and forward from the rear inside tire.

This seems to be backed up by the driving styles adopted by 911 and 914 drivers.

I would conjecture that weight, power, and tires being equal, a 911 might have an advantage on autocross courses where there are long-ish straights with tight hairpins, and the 914 would be better at Willow Springs, for example.

The big thing is that having weight within the wheelbase means there is no "leverage" of weight off of the front wheels. The weight contributes to traction on both front and rear ends.

[j911brick]

Originally Posted by Flieger

The way I see it, this means that the 911 should go deep into a turn, trail braking, slow down and take a late turn-in, where it can use the quicker angular acceleration of the front wheels about the rear to point the front end towards the apex and then "shoot" towards it, using the rear weight to gain traction, stop the angular acceleration, and get down the track fast in a straight line.

Actually, 911s don't trail brake well. They tend to want to swap ends. The way to do is is set the car up with understeer, turn in early and push the car through the corner. This does not work for auto-x where you need some oversteer so you can rotate the car.

[J P Stein]

Originally Posted by Bullet Bob

Here is a question for JP Stein... How many 911s of any year or model beat you in autocrossing?

Well, we have to go back a few years, but there is this guy named Doug Skinner. Also a few years back, I guy from NoCal. in a GT2.

Here in the last couple years, none. There is a fella named Dave Newman back in PA that has the quickest AX 911 that I know of....it would be a good tussle.

There are a few guys in Miatas that do the deed on us, heavier & less power.
Hopefully that will end with the new powertrain.

[LJ851]

Originally Posted by Bullet Bob

When you slam on the brakes most of the load is transferred to the front tires. In a car with a 50/50 weight distribution you might end up with 70% of the braking done by the front tires and 30% by the rear tires. Since the 911's weight is biased to the rear initially, once the load is transferred you might have 60% braking by the front tires and 40% by the rear tires. With the tires loaded more evenly during braking there will be more stopping power. It all depends on the CG height and it would be interesting to crunch some numbers and see the actual results.

Only when its dry...

[AlfonsoR]

Originally Posted by j911brick

That's because Ferrari's suck! Everybody knows that.

LOL, I'm a Porsche man, but those crappy Ferrari engines make a beautiful siren sound. If anyone decides to junk their POS Ferrari, please let me know. i will take it off your hands for free.

[RSBob]

Interesting thread about weight distribution, and power. Even though my 73 RS spec is well set up for a streeter - oversized T-bars, lowered, bump steer, turbo tie rods, Quaife, etc, I have always been intregued how much better it might be in a 914. As a result, I am building a reasonably priced car, 71 914 with a newly rebuilt massaged 3.0 with Webers and sport exhaust. I find the 911 fairly refined, where as the 914 feels rather crude. The 914 and 911 should be approximately the same weight with almost exactly the same rubber - except the 914 has a complete Elephant Street-Track suspension. The teener also gets the nod with an additional 15 hp - with more low down torque. It will be very interesting to do the compare when it is ready at the end of Jan. From all I have researched for the past year, the 914 should be winner with that sweet flat six song even closer, but we shall see.

[haycait911]

Al, make it as light as possible ( of course ) , get to a comfortable target weight. THEN start messing around with suspension.

ps. you can always adjust suspension for weight distribution so don't be afraid to ditch weight in the front, where it's easy.

pps. just picked up a set of 951 spare-type rims for the '67 - another 20 lbs gone . now I have 1900 lbs in my sights.

[Steve@Rennsport]

Originally Posted by haycait911

you can always adjust suspension for weight distribution so don't be afraid to ditch weight in the front, where it's easy.

For clarity, one cannot actually move weight around with the suspension: all one can do is to ensure equal weights both laterally and diagonally with a proper cornerweighting.

Changing the weight distribution requires moving, relocating, or lightening various components of the car.

Want to make a big difference in a 911? Move the engine & transmission forward by one to two inches. Not a simple job, but it can really help compensate for an overly light front end (which really aggravates understeer as well as cross-wind behavior).

[haycait911]

Originally Posted by Steve@Rennsport

For clarity, one cannot actually move weight around with the suspension: all one can do is to ensure equal weights both laterally and diagonally with a proper cornerweighting.

Changing the weight distribution requires moving, relocating, or lightening various components of the car.

Want to make a big difference in a 911? Move the engine & transmission forward by one to two inches. Not a simple job, but it can really help compensate for an overly light front end (which really aggravates understeer as well as cross-wind behavior).

I probably should have said you can adjust/set-up your supension to compensate as much as is possible for weight distribution.

[winders]

Originally Posted by Steve@Rennsport

Want to make a big difference in a 911? Move the engine & transmission forward by one to two inches. Not a simple job, but it can really help compensate for an overly light front end (which really aggravates understeer as well as cross-wind behavior).

Steve,

This can be hard to do without causing problems with axle life. It's bad enough at typical street ride heights. Lower the car for racing and it gets really bad.

What do you use for axles on your race cars? Stock? Aftermarket?

Scott

[al lkosmal]

Rick,
Good luck with the 914. Post some progress pix.

Don,
My next project will definitely be lighter than the one I just completed (71E), but I still expect that I will make weight compromises to filter out road/tire noise. I'm really not after the lightest street rod, although that is a good thing in many ways........I'm focusing in on power and balance, with overall weight reduction as a side benefit of achieving a great handling, balanced 911. I'm not sure that I expressed that correctly, but the absolutely lightest weight is not my highest priority, but hopefully will be the result of the weight distribution/balance/handling focus. Also, my goal is to improve the power/weight ratio considerably as well.

Steve,
Moving the engine forward sounds like big bang for the buck to me, but may be a bit much for my street rod. However, I will crawl under my 71 today and stare at the mounts for a while. hmmmmm.

PS: Although I am getting sidetracked by absolutely great SC's and 964's....I am primarily focused on a long wheelbase longhood.

Happy New Year,

Al