So I have been playing with the idea of adding a couple more tubes to the back of the Anklebiter. If you were to replace the back half of a 914 with tubes where would you put them? Here is a rendering of the original cage (red), drivetrain (Grey), and points that need to be tied in (green).
What would you do?

Here is my first draft, any thoughts?

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Dam. Just cut the body off the pan and build a whole tube frame

I would like to keep the passenger compartment intact, I know it seems like a contradiction but I would like a nice stockish interior with a pretty stock passenger tub.

Overkill?

This is the feedback I am looking for, I want it to be able to handle at least 500hp but I don't want to add unnecessary weight by going over board.

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Ury, that stock starter looks heavy ...


Aha, i see you replaced it in the second pic ...

I was thinking of yours when I was working on this Ury, it is amazing how much more complicated things get when you cut off the rear frame rails.

For example, i think in the rear going from the top of the shock towers to the transmission mounts, just the X brace should be plenty as long as you still have the stock cross member where the transmission hangs off of.

Andy

The plan would be to eliminate all sheet metal behind the firewall but I would replace the stock cross member with a tube between the mounts.

More examples, some better, some not so much (IMHO), just food for thought ...

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I like the design you posted. You really do need many of the bars because of the load paths, but IMHO it isn't overkill as long as you use correctly sized bars. With sparing use of .035 and .049 wall tubing you can keep the structure light in incredibly rigid.

The tube from the long too the motor mount wont be doing much the way it is, and would be better served meeting the cage w/ the other tube.

Likewise, the inner vertical from the motor mount up to the hoops will not be as strong as if they go to the "shoulder"

Last (and probably way overkill, but i've been doing Baja Trucks) would be a support from the upper shock mount down to the motor mount.

Could probably lose the bar between the trans mounts, there wont be any stress in that direction back there.

Tube wall thickness is another factor, I like the concept of using more light tubing versus less heavy tubing. No need to worry about racing rule books so any size that is appropriate is fair game. I like Jim's ideas, I was thinking 1.5 dia. what wall thickness would you guys use and where?

Cost no object I would go the route Hari Matsuda went. Not to shabby for a 72 year old. Actually these pics are a few years old.

Hari ran a few different cars but he did things with a 2.0 186 HP four / 1730 lb car that others running six's COULDNT do. The four cylinder was 100lb lighter than his later 3.4 car. The light weight car just by weight alone was 1-2 seconds per lap faster than the heavier cars. I am a believer in light weight versus BIG Horse Poo. Quicker and faster to a stop.

The orange car in the pics is the 3.4 that weighed in at 2080 lbs. Evil on the track.
When Hari was 69 years old he considered converting this car to street legal.

Hari's latest configuration was this.

... complicated??? that photo should simplify things for you based on your drawings... he doesn't have half ( if any) of the triangle bracing you've implemented in your cad drawing. however those sharidon bodied 914 photos Andy put up are when you have a 3.6 track monster and probably need the extra bracing... you don't need to re-engineer the wheel, these cars have been around for some time now. take a tip from the track guys. if you can find some photos of that otto's venice guys' car, he knows his stuff too. did you know he has the fastest time at the streets? last time i stuck my head underneath the rear fender there were a bunch of Ace Hardware washers off-setting he rear 930 calipers to the rotor. its not rocket science mate, lots of these guys are running with early 1900's lotus logic.

500hp puts you in a different crowd than my car. Here are I few that I've found over the years.....

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I have more pictures but I'd have to spend the next day scanning them. As you can see, everyone has thier own ideas on how to do it. There is no right way or wrong way just different ways.

A Celette would be slick for a tube chassis. You'd have all the suspension pickup points, enigne and transaxle mount locations and if you ever wrecked her you could replicate the chassis. Some cool photos in this thread! I totally agree with sir Andy though. Stiffening is a good idea but the 914 chassis is pretty good. 500 hp good though?

The 914 chassis is far from good. I think the factory chassis stiffness is on the order of 2500lbs/deg. That is really weak. The factory chassis is a noodle.

As for the tube chassis. I would use 1.5x.045 and 1.5x.065 tubing. No need to get really big. Sheridan's car is probably the best engineered solution. It was done by a professional race car engineer. If you are going to do it I would toss the factory rear suspension and come up with something different. Mount the engine, tranny and suspension to an independent cradle. Then you could fix the 914 problems. The problem isn't flex in the rear of the chassis though. It flexes in the middle. So you will not gain much buy changing the rear. Plus the rear is pretty light because it is all sheetmetal.

Thanks for the input guys, lots of great pics. I am going to try to remember my statics and mechanics of materials classes from when I was in engineering so I can calculate some loads. I figure if I use predominantly .065 wall tubing the entire rear structure should weigh around 50 pounds.

I agree the center of the chassis is where the 914 is lacking. I don't agree the entire chassis is bad. The rear and front sections are very nicely built for a street car. Stiffening where the shock towers crack in the engine bay side and a support for the inside suspension ear are always a good idea. There is alot of overkill being built into 914's. I think it's just because guys like to build stuff.

BTW: I have zero chassis stiffening in my car. Yep. Zero. The rear of the chassis is just fine. Infact I removed the internal brace (boxed structure) just above the rear engine tin that crosses from tower to tower. I have in excess of 350 hp now with a very heavy engine. About equal to the weight of a big block chevy.

If I Ax'ed on a regular basis or raced, I would rethink this. But for a occasional thrashing like Monument National Park or a trip to and from Mount Wilson these cars rock!

It would be interesting to gauge what is happening to the chassis ahead of the rear firewall though...

Dana, Build it like you want it. We love your work.

Top of shock tower (bridging the hidden gap between frame rail and tower) and suspension ear are the two most important points. Much more is overkill and excess weight. IMO.

Just build more stuff and take more pictures!

You build it and some will like it, some won't. Some will say it's too heavy, some say it's too light. Some will say it should be painted black, some say paint it white. You get the picture......

some one needs to design a full tube frame car...the buggy guys can build these things cheap.. Throw on a fiber glass body and youd have one hell of a DE car!!

Well as long as it weighs less than 75 pounds, doesn't bend, and looks sexy, I will be happy!

There are plenty full tube cars with 914 bodies on them.

Were I going to the trouble of building a tube frame, the first thing to go would be the Mac strut suspension & swing arms. Double A's all the way....just like a real racecar.

Color me crazy, but i think the Anklebiter deserves a fully functional trunk.

The car is going to be too nice to have a crappy "race car" subframe ...
Andy

I am willing to make a nice interior but I think an actual trunk that can hold things is entirely too practical for this project. I want this thing to be as close to a street legal race car as is possible. And never fear, I assure you it will be done right and not look crappy.

Are you still in school? If you are you should grab a copy of SolidWorks and model what you are building. Then you can use the integrated FEA software to mess with tube sizes. Its quite easy to use (and there are some great tutorials about building tube frames in it on Youtube), and would really help you out with choosing tube size.

That is actually a really good idea, the formula sae teams use solidworks to analyze their frames so I should be able to find a computer in the engineering building that has it on it. Solidworks also offers a student edition for $100 ($2900 less than retail).

Ohhh to have the time to entertain these things!!!

Dana,

How's my old rommie doin? How is Becky? How is Laurie? Hope all is well.

Yep, I've used it on a few frames. The beam analysis feature works really well.

Plugging away at my architecture degree and looking at grad school, Beckie and my mom are doing well. We have a little house and a couple dogs, Life is good!

I'm not too good with this kind of stuff, but as far as solid works goes they have a nice set of tutorials on youtube http://www.youtube.com/user/solidworks... I believe they explicitly cover frame design in the tutorials. The FSAE team I'm on uses NX for frame design, I'm not sure what is used to analyze it though....

As I said I'm not very good at this, but squares are bad, triangles are good. These two seem to jump out at me.

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Sorry, but I can't give you much better advice. I haven't really been involved in that aspect of our car's design...

My Qs are in blue. You already have the crosses to the tranny points done so those are redundant for this conversation.

Inside the blue circle... Why would you go up there? To me, the strong point to tie into is the tip of the blue arrow as that's what ties forward. I would ignore anything above it.

So top of shock tower forward to that point (my blue bar) is the strongest and most important piece in my mind.

Outer suspension point is strong by default. Inner ear needs some bracing. Doesn't make a huge difference where you go with it, I just put a blue bar to the strongest point in my thinking. Your green bar that goes lower is fine. Or just use Chris's kit (Tangerine).

Given that weight is important in your build, I just want to see you only add bracing where it's most effective, and not where it's really superfluous.

IIRC, the "Birdcage" Maser was a very early tube-frame design, and not necessarily all that successful I think. You'd probably do much better to check a modern racer, or maybe one of the Sports Racer (e.g., DSR) cars for ideas rather than the Maser.

--DD

200 tubes

Eh, those are easy joints. They are almost all nice and square. Try this one, its 8 bars into one in the front and 6 into one in the back with about a 1/16" gap for welding.

Sorry for the hyjack Dana. I'll use it as an excuse to say that triangles are good, though this frame is overbuilt. Most of the tubes should be .035" wall. For reference, with all 1x.065" tubes this frame weighed 65lbs.

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