It looked so simple at first!

[scarsofcarma]

Nice progress, keep it going I want to see what this can do when its done.

[GySgtFrank]

Originally Posted by scarsofcarma

Nice progress, keep it going I want to see what this can do when its done.

Thank you for the encouraging words. I'm hoping to be pushing into the one G plus skidpad range for grip (on a reasonable street tire) without it being glaringly obvious what I've done. The RX-7 was pretty good at close to .8 G when they came out. I'm hoping to equal or exceed most of the new high end cars for handling. That and the ability to haul it down from speed quickly.

I have never seen anyone else doing anything quite like this to a first gen. So I'm in uncharted territory as far as I know. My experience with other cars is that the unequal length A arm suspension is markedly superior to the MacPherson Strut suspension in most respects. It also allows me to tuck a really wide tire under there, and contact patch is King (for the most part) when talking handling.

I have read up on what a lot of the folks running first gens in racing have done and what they have found effective. The good part is that they have been used in racing, and winning more often than not, for so long that there is quite a bit of experience out there. Unfortunately, while their insights have been valuable, they are limited by class rules which would preclude anything remotely like what I am doing up front. The rear suspension is a blatant copy of what others have found to work on their track cars. I have merely tried to make it more livable on a street driven car.

I'm kind of itching at the bit myself to find out whether I have been inspired or that I'm a flippin' idiot. Bets could go either way at this point.

[scarsofcarma]

Originally Posted by GySgtFrank

Thank you for the encouraging words. I'm hoping to be pushing into the one G plus skidpad range for grip (on a reasonable street tire) without it being glaringly obvious what I've done. The RX-7 was pretty good at close to .8 G when they came out. I'm hoping to equal or exceed most of the new high end cars for handling. That and the ability to haul it down from speed quickly.

Yeah 1+ G is a benchmark I'm aiming for as well. I know I've experienced that before on Laguna Seca riding in a Porsche 911 on slicks. Just amazing how well that car gripped... especially while braking. It was like throwing an anchor out the back.

Racetrack tarmac is very smooth and sticky though. Not at all like the crappy street surfaces we usually drive on. 1+ G on street tires is possible sure, but it largely depends on where you're driving.

Originally Posted by GySgtFrank

I have never seen anyone else doing anything quite like this to a first gen. So I'm in uncharted territory as far as I know.

For now yes, but I will be modifying my FB to this extreme as well just wait and see lol

Originally Posted by GySgtFrank

My experience with other cars is that the unequal length A arm suspension is markedly superior to the MacPherson Strut suspension in most respects. It also allows me to tuck a really wide tire under there, and contact patch is King (for the most part) when talking handling.

Yes there is no doubt the double-wishbones provide a better contact patch for the tire... I had a few MKIII Supra's and I drove an FD a few times which also have that setup.

However imo there is sometimes more to be said for the MacPherson in terms of feedback. It's like a tuning fork for the tire it really picks up all the minute sensations from the road. I found the driving experience of the FD RX7 and the MKIII Supra a bit more numb in that regard.

Don't get me wrong, I'm not saying the cars were any slower in my hands because they weren't MacPherson. It's just that I was slightly less confident about what the limit of the tire was, and were not even talking about a big difference. Maybe 10-20% less feedback felt like to me.

On a track that difference wouldn't seem so big, but on a mountain road with a generally lousy road surface, with no runoff areas, feedback from your tires is everything.

Originally Posted by GySgtFrank

I have read up on what a lot of the folks running first gens in racing have done and what they have found effective. The good part is that they have been used in racing, and winning more often than not, for so long that there is quite a bit of experience out there. Unfortunately, while their insights have been valuable, they are limited by class rules which would preclude anything remotely like what I am doing up front. The rear suspension is a blatant copy of what others have found to work on their track cars. I have merely tried to make it more livable on a street driven car.

I'm kind of itching at the bit myself to find out whether I have been inspired or that I'm a flippin' idiot. Bets could go either way at this point.

Yeah I am also very interested to learn about what has been tried and done on high performance racing FB's that were not so limited by class rules. Millen's RX7's, and those group B FB rally cars for instance were pretty extreme.

[GySgtFrank]

Originally Posted by scarsofcarma

Yeah 1+ G is a benchmark I'm aiming for as well.

It's what I'm shooting for, doesn't mean I'll get it. I'll give it my best shot anyway. I don't know about the feedback issue, you may be right on that. I wonder how much of that is due to the weight of the car though, the FD and especially the Supra aren't exactly lightweights. That's the biggest reason I chose the 1st gen over the FC and FD chassis. (I don't actually hate the other generations, just returning the harassment others have dished out ) The first generation RX-7 was ridiculously light for a street car. I thought about going with a swapped Miata for this reason, but the RX-7 chassis should be stiffer than the convertible chassis and there is very little difference in their weights.

I know the SLA suspension will keep the tire in better contact with the road, providing more ultimate grip. So between the grip factor, and the need for tucking in large rubber, I decided to go this direction. A widebody with an increase in track width would have been more effective, but I want to keep it approximately stock in appearance. I would imagine that a widebody would get a lot of scrutiny from any law enforcement in the area. Between the large rubber and my upgraded brakes I should get pretty decent braking performance as well.

As you said there is a big difference in quality of the road surface between a racetrack and normal street driving though. Race cars can get away with a lot of things that won't work on the street. I'm trying to come as close as I can to that level of performance without losing the ability to drive it regularly.

[scarsofcarma]

Originally Posted by GySgtFrank

It's what I'm shooting for, doesn't mean I'll get it. I'll give it my best shot anyway. I don't know about the feedback issue, you may be right on that. I wonder how much of that is due to the weight of the car though, the FD and especially the Supra aren't exactly lightweights.

Yeah a Supra is a heavy beast but weight is not always bad. A Supra is not a flickable or tossable car but it turns better than you might expect. There are lots of heavy cars that can manage 1+ G. More weight on a tire (to a point) creates a greater coefficient of friction and helps grip. More weight allows for more static grip in the tire, as well as more weight available for weight-transfer in grip driving. But of course, more weight works the tire harder so it wears and possibly overheats faster.

There are many great cars in the world that are heavy but through clever engineering actually make that extra overall curb weight an asset like the GTR.

In the general sense of performance, the ratio of power to weight is more important than the actual power or weight numbers themselves. In the truest sense of performance though, power is king as long as you can find a way to put all that power to the ground. That's what makes cars like the GTR and 911 so impressive.

Originally Posted by GySgtFrank

That's the biggest reason I chose the 1st gen over the FC and FD chassis. (I don't actually hate the other generations, just returning the harassment others have dished out ) The first generation RX-7 was ridiculously light for a street car. I thought about going with a swapped Miata for this reason, but the RX-7 chassis should be stiffer than the convertible chassis and there is very little difference in their weights.

My bridgeported RX3-SP, fully caged with a Ford 8.8" rear end in it was in the 2300 lb range when I corner weighed it. But so what? That car had no traction. When I swapped its engine in my FB (just a street car with a full interior) I was actually able to put the bridgeport power to use. The FB was way faster, but on paper it should have been slower.

Originally Posted by GySgtFrank

As you said there is a big difference in quality of the road surface between a racetrack and normal street driving though. Race cars can get away with a lot of things that won't work on the street. I'm trying to come as close as I can to that level of performance without losing the ability to drive it regularly.

That's exactly my goal as well. I drive sports cars not just for fun, but because I know they can out handle and out brake those other cars with incompetent drivers that cause accidents all the time in urban areas. Or help me dodge the grossly overpopulated deer population in rural mountain areas.

[Anoesis]

[chrisflaco_fc]

Great thread, I'd love to see what exactly you have in store for the motor later.

[GySgtFrank]

Originally Posted by chrisflaco_fc

Great thread, I'd love to see what exactly you have in store for the motor later.

Thanks. I'm not quite sure which way I want to go on that myself yet. I'm trying to get all of the supporting hardware in place first. I will be shooting for the 350 HP level and staying rotary, so it will probably be a single turbo 13B REW based engine, we'll have to see when I get to that point.

While I was off playing farmer, I'm temporarily home as you can't cut corn in a snow storm, I ordered the upper A arms and hardware from pitstopusa.com. The parts are already here and exactly what I ordered. Which for those of you that know of my supplier travails, came as a pleasant surprise.


new upper A arms by GySgtFrank, on Flickr

They are Joe's Racing upper arms made for racing, but should work for what I want. They provide for adjusting camber and caster with minimal fuss using spacers (the blue things in the back) and slugs to adjust side to side and up and down for roll center adjustments. The arms are replaceable in different lengths if I need to change the camber gain as the tire moves through it's arc. They use a standard screw in ball joint, which I will pick up locally.

The only concern that I have is that the arms are suspended with non compliant bearings instead of rubber or poly bushings. Which is great for free movement, but they may be a bit harsh on the street. They are not the load bearing arms, so it shouldn't be too bad. The only way to find out is to try it I guess. Appropriate since this whole thing is one big bloody experiment anyway.

[RXtacy]

Looking really good Kevin. Keep up the good work. I look forward to seeing it at DGRR!

[GySgtFrank]

Originally Posted by RXtacy

Looking really good Kevin. Keep up the good work. I look forward to seeing it at DGRR!

Thanks Mike. I finished up the other wheel arch and was trying to figure out how I was going to mount the arms this weekend, while I had a little time off. I came to the conclusion that I need to get some ball joints before I can finalize how I'm going to do it though. I need a week day off so I can do some shopping at the local race chassis shop.

[RXtacy]

Originally Posted by GySgtFrank

Thanks Mike. I finished up the other wheel arch and was trying to figure out how I was going to mount the arms this weekend, while I had a little time off. I came to the conclusion that I need to get some ball joints before I can finalize how I'm going to do it though. I need a week day off so I can do some shopping at the local race chassis shop.

Sounds overpriced already

[GySgtFrank]

Originally Posted by RXtacy

Sounds overpriced already

This is Kansas. Local redneck circle track shop. Prices don't look too bad. Not O'Reilly's level of pricing though.

Need a couple of threaded upper ball joints, so normal auto parts stores aren't an option. Could order on line, but I want to make sure they're going to actually fit before I plunk down the dollars.

[GySgtFrank]

If anyone needs more proof that I'm an idjit.


upper arm by GySgtFrank, on Flickr

When I put the upper mounts in they needed to sit where my new frame rails were at in order to get my Instant Center/Roll Center correct. Sooo. More cutting and fitting will be called for. Waiting on a digital caster/camber gauge so I can do final positioning on the A arms. (This is where I think it has to be, we'll see)

Setting my roll center to 1/2" above the ground and centered on the chassis. Initial setting for caster will be 5 to 7 degrees positive. Camber will be at zero with my adjustment all the way down. I'll use spacers to set that where I need it later.

[GySgtFrank]

Done with farming, back to work on the car and the never ending build thread.

Trying something different can be ... trying. I think I finally have the right side upper arm in position. 1.5 degrees camber, 6 degrees caster, 10 degree down angle on upper arm, 0 degree angle on lower arm. With full adjustability to make changes (which was what I was really after). Time to weld it in again. I've had to cut out so many previous ga-genius ideas that my engine bay looks like something from the Texas Chainsaw Massacre movies. Lots of grinding ahead.

[GySgtFrank]

Doesn't look like much, but a lot of work to get this far.


Front frame arch 2 by GySgtFrank, on Flickr