Question on adding lightness.

I'm working on the diet part.

Just need to bring the plasma cutter home from work one evening.

I'd lke some lighter seats, lower too. My helmet hits the roof at the moment.

Shawn

Lightness overall is a very good thing to be sure. As noted, where the lightness comes from is as important as how much is removed. Like everything, it's a compromise.

TIGMOTORSPORTS mentioned removal of the inner bumpers, a good thing. Other stuff: inner fender liners, A/C and heater parts, sound deadener, hood and trunk inner bracing (but this makes the panels very floppy!), swap cast iron manifolds for tubing headers, aluminum radiator, aluminum intake manifold, light flywheel, all kinds of stuff. I don't know what race class you run but if they allow it scoot the engine back as far as possible. I did that with the Abomination so now it's a 'front mid engine' car and handles worlds better than a stock Spitfire. (Having owned at least a dozen Spits, I know first hand.) The Jensenator is getting the same treatment for the same reason.

MrJoshua wrote: Porsche bragged about having lumps of weight on each axle in the 928... Who knows if it is just marketing hype...

While they may have added the weight for stability, I wouldn't be surprised if they did it more for NVH concerns. If you're getting a vibration at certain speeds and can't or don't want to redesign the part to get rid of the vibration, adding a weight to it is a very easy way of shifting the natural frequency of part outside of the frequency of the operating conditions so the vibration disappears.

Bob

Porsche was actually bragging about how having the engine on top of the front axle and the transmission on top of the back improved the handling beyond just evening out the weight distribution. I didn't mean to imply they said they intentionally added weight.

Mr. Joshua is right, they did not just add weight, or the aluminum body & engine would be a waste. It balanced the car and for a GT it made sense. The classic analogy was befween a 50 lb. barbell, a 50 lb. dumbbell, and a 50lb. cannonball. A car with a very low polar moment of inertia might make a great autocrosser, a higher PMI would give the GT car better high speed stability.

Is the T/A going to be mainly an autocross car or a road race car?

I have always been under the impression that the more powerful car (power:weight) will be faster because on just about every track, there is more time/distance spent accelerating in a straight line than there is cornering.

I'm not sure that holds true on your typical autocross course, though...

This is mainly for autocross. It's going to stay street driveable as well so I can't go too crazy with it.

I have a 1969 MG Midget that is an ex road-race car, the previous owner and I are in the process of going through the car and correcting the problems its aquired from sitting for the last 30 years.

The rebuild is taking longer than I expected and the racing bug is biting me something fierce.

I decided to build up my fun car to do some autocrossing in the meantime so I'm trying to stay pretty low-budget if I can.

Thanks for all the input guys.

Shawn

problemaddict wrote: I have always been under the impression that the more powerful car (power:weight) will be faster because on just about every track, there is more time/distance spent accelerating in a straight line than there is cornering.

Not in my experience. Ask Lotus and classic Mini drivers about that :)

Trans_Maro wrote: This is mainly for autocross. It's going to stay street driveable as well so I can't go too crazy with it. I have a 1969 MG Midget that is an ex road-race car, the previous owner and I are in the process of going through the car and correcting the problems its aquired from sitting for the last 30 years. The rebuild is taking longer than I expected and the racing bug is biting me something fierce. I decided to build up my fun car to do some autocrossing in the meantime so I'm trying to stay pretty low-budget if I can. Thanks for all the input guys. Shawn

Fellow second-genner here... While those bumpers are heavy, if you are streeting the car, I wouldn't remove them (or the door bars) without some sort of cage structure. You don't want to end up with a motor in your lap.

That being said, things like a glass hood and decklid, along with removing sound-deadener, lighter seats, etc will go a long way to make that sucker fun (and keep it safe).

Don't move that engine unless you want to end up in a crazy class - as it is you are probably on your way to a C-Prepared build, which can get deep fast (are there, doing that).

Step 1: lighten as much as physically possible w/o regard for balance

Step 2: corner weigh the car and then start altering suspension bits to help rebias weight

Step 3: if corner weighing and rebias doesn't get you there, add some balast and repeat step 2

This way you've reduced all possible weight and only added back what's 'absolutely necessary'

Wasn't there a really good article recently on corner weighing and how to rebias weight with silly little (no-cost) tricks like removing/shaving down spring rubber isolators, adjusting ride height on some corners (via adjustable shocks), moving battery location?

You can only shift weight diagonally by monkeying with spring perch adjustments, not front/back or side/side.

Gimp:

I'm planning on staying in ESP so there's only so much I can do without building a cheater car.

The turbo would bake the paint off the factory hood if you ran without the heat shield so a 'glass hood is right out.

Door bars are staying, I have to drive this thing on the street too. Bumpers might not leave completely, just get a whole lot lighter.

Corner weight adjustment isn't a real problem on this chassis, thanks to the oval-track boys.

I've ended up in a goofy class before by changing too much. I've got to sit down and go over the rules again before I start really changing things.

Shawn

Keith wrote: Not in my experience. Ask Lotus and classic Mini drivers about that :)

I thought Minis and Lotus were pretty good in the power/weight ratio.

Shawn

Trans_Maro wrote: Gimp: I'm planning on staying in ESP so there's only so much I can do without building a cheater car. Bumpers might not leave completely, just get a whole lot lighter.

I'll have to double check, but to stay ESP legal I think the bumpers have to stay unharmed.

Circle track supply is the best thing that happened to my car, or at least what's left of it. LOL

Lefthander and Howe set me up with a very nice, very light, and pretty cheap upper and lower control arm package. That might be worth looking in to.

Trans_Maro wrote:

Keith wrote: Not in my experience. Ask Lotus and classic Mini drivers about that :)

I thought Minis and Lotus were pretty good in the power/weight ratio. Shawn

We had been comparing heavy powerful cars with light not-powerful cars, keeping the power/weight ratio constant. If that changed without me noticing, I apologize for the confusion.

My classic Mini isn't that good in the power/weight ratio, actually. 80-ish hp, 1450 lbs. That's only 110 hp/ton.

LocostSmitty wrote: Mr. Joshua is right, they did not just add weight, or the aluminum body & engine would be a waste. It balanced the car and for a GT it made sense. The classic analogy was befween a 50 lb. barbell, a 50 lb. dumbbell, and a 50lb. cannonball. A car with a very low polar moment of inertia might make a great autocrosser, a higher PMI would give the GT car better high speed stability.

Sorry guys, I completely misread Joshua's post. When he wrote "having lumps of weight on each axle" I thought he meant they added lumps of mass to the axles to improve the handling, not that they spaced the engine above one axle and the trans over the other to improve the handling.

Bob

Keith wrote: We had been comparing heavy powerful cars with light not-powerful cars, keeping the power/weight ratio constant. If that changed without me noticing, I apologize for the confusion.

Wow, sorry you took that the wrong way Keith.

Gimp:

I've got Speedways control arm setup sitting in the shop for the car.

Shawn

weight > balance.

high weight > low weight

rotational weight > static weight

My car is a Yugo, so this stuff matters A LOT. If you're going to race with less then 80 hp, better make the weight count. So, my BIGGEST weight priority is rotational weight- I've got a lightened flywheel, lightweight wheels, lightweight tires, lightweight clutch, lightweight brakes, and pulled 5th gear out of the tranny, since I'd never need it.

Of course, I got rid of all the obvious unneeded stuff- interior, spare, jack, etc. But I'm spending a lot of extra time getting rid of high ounces- headliner, glass, unneeded bracketing, rear view mirror, I'm even swiss cheesing the pillars and roof structure. If I had a sunroof, that would certainly go.

Why high? Imagine lifting a 8" crescent wrench. Not too bad. Now tape it to the end of a 10' stick and lean from right to left with it up in the air. Feel the difference?

Why rotational? Tie the same wrench to an 8' rope and swing it around your head. Now it's tough to hold on to.

The hood and the rear deck are on my radar.

My car currently weighs 1250 lbs. wet. I'll get it down to about 1050 when I am through, which will probably make me too light. Then I'll add weight where I want it for perfect balancing. When I do add weight, it will be at the outside corners (dumbell effect, per Mr. Joshua)

On general weight reduction:

Heater was mentioned. Nice thing about this one is it also reduces fluid (at 8 lbs. per gallon).

Fuel tank is often overlooked. A small fuel cell is a lighter tank, with less fluid weight, and can be located where desired for distribution.

Gimp:

Are you running a manual steering box or are they awful in a car this heavy.

I like the quick ratio in my power steering box and I'm not sure if a manual swap (that isn't too heavy to drive) would have a ratio that is too slow to be responsive.

Shawn

SVreX wrote: On general weight reduction: Heater was mentioned. Nice thing about this one is it also reduces fluid (at 8 lbs. per gallon). Fuel tank is often overlooked. A small fuel cell is a lighter tank, with less fluid weight, and can be located where desired for distribution.

I dont think I would pull the heater out of a street car. Even if you only drive it when it is warm, it will still be usefull for defoggin the windows and to bleed off extra heat if the engine starts running hot. but thats just my $.02 and does not reflect the veiws and opinions of the parent company and it's affiliates

I missed the street car part.

I was discussing more general weight reduction concepts.

There's a LOT of things I wouldn't remove on a street car (like the aforementioned bumper cores)

He DID mention a plasma cutter!

Trans_Maro wrote: Gimp: Are you running a manual steering box or are they awful in a car this heavy. I like the quick ratio in my power steering box and I'm not sure if a manual swap (that isn't too heavy to drive) would have a ratio that is too slow to be responsive. Shawn

No sir. Front tires are 16x12, so I need power steering. I think everyone running a second gen in CP is running power steering.

Power boxes have better ratios, and on a car that size it's like an extra deck chair on the titanic.

Yes, I found the ratios for the stock manual box tonight.

4 turns lock-to-lock.

No thanks.

Shawn