GRM Exclusive Reveal: Exocet Spec-A

you could always separate it from the engine harness, and run an EZwiring/painless/whatever chassis harness.

basically what i did. except my carbed engine made life super simple

It's not a fully standalone harness on the NB. It's still tied into the car a fair bit from what I recall. Definitely not GM levels of standalone harness.

Stay away from 2001-05 stock computers, the immobilizer is VERY effective and a PITA. You can do it if you keep the stock key, ignition switch, column, immobilizer and ECU.

tuna55 wrote: I want an Exocet, and I don't think the weight distribution is a big deal, but... he's right, sort of: Pagani Zonda: 44% front 56% rear Ferrari 458: 42%/58% Lamborghini Aventador: 43 % - 57 % Audi R8: f/r (%), 39/61 But those were all mid engined cars Viper (old one): 48/52 Viper (new one): F/R, 49.6/50.4 Corvette ZR1: 51 / 49 Ferrari California: 47:53 Ferrari FF: 47/53 Ferrari 599: 47%-53% Aston martin DB9: 50/50 So it's not totally cut and dry, and I believe there is a lot that can be done via suspension tuning to make up for those differences.

Most of those cars are either very unforgiving (Viper, Zonda) or have AWD or traction control or both.

In reply to dculberson: Excellent point, Sir

Vertical load increases possible traction,I believe that to be a fact that can't be overlooked.Of course there are tons of other factors affecting the handling balance but regardless of weight balance every car can be balanced.Of course you'll be essentially reducing the grip of the "good" end to work with the other,if I'm building something light,powerfull and short I'm going to aim closer to 60 percent rear weight.

All this talk about v8 expects. Have you guys considered producing a chassis to use a c5 Corvette frame / drivetrain.

Like this:

http://item.mobileweb.ebay.com/viewitem;PdsSession=bbc20ef013b0a47a19c3e513fffabe3b?itemId=140815538181&index=1&nav=SEARCH&nid=31226562451

cost factors

Apexcarver wrote: Are there (preexisting) provisions/designs for a windscreen and wipers? I know that many states require one for road cars.

Is there going to be anyway to add this?

Very cool concept - I'm impressed by the price point!

davidjs wrote:

Apexcarver wrote: Are there (preexisting) provisions/designs for a windscreen and wipers? I know that many states require one for road cars.

Is there going to be anyway to add this? Very cool concept - I'm impressed by the price point!

I plan on using one of these: http://m.westmarine.com/webapp/wcs/stores/servlet/Product_11151_10001_13860_-1?cid=chanintel_google&ci_src=14110944&ci_sku=13860 on a future build. My local inspection shop says that a wiper is a wiper...

That would satisfy in Colorado, the law says something about needing a way to clear the windshield. The mechanism is not specified.

Although only a boating store would call a wiper arm on a bolt "inexpensive" at $78.

mistanfo wrote:

davidjs wrote:

Apexcarver wrote: Are there (preexisting) provisions/designs for a windscreen and wipers? I know that many states require one for road cars.

Is there going to be anyway to add this? Very cool concept - I'm impressed by the price point!

I plan on using one of these: http://m.westmarine.com/webapp/wcs/stores/servlet/Product_11151_10001_13860_-1?cid=chanintel_google&ci_src=14110944&ci_sku=13860 on a future build. My local inspection shop says that a wiper is a wiper...

You can get an electric one cheaper:

http://www.speedwaymotors.com/Stainless-Deluxe-12-Volt-Electric-Wiper,38962.html

In reply to dculberson:

Or manual from the same company for less than $20.00:

http://www.speedwaymotors.com/Hand-Crank-Manual-Windshield-Wiper,2301.html

tuna55 wrote:

kevlarcorolla wrote: All the talk of the perfect weight balance being 50/50,so why are damn near all the highpowered/lightweight race only/super cars in the 60+ percent rear heavy territory?.

I want an Exocet, and I don't think the weight distribution is a big deal, but... he's right, sort of: Pagani Zonda: 44% front 56% rear Ferrari 458: 42%/58% Lamborghini Aventador: 43 % - 57 % Audi R8: f/r (%), 39/61 But those were all mid engined cars Viper (old one): 48/52 Viper (new one): F/R, 49.6/50.4 Corvette ZR1: 51 / 49 Ferrari California: 47:53 Ferrari FF: 47/53 Ferrari 599: 47%-53% Aston martin DB9: 50/50 So it's not totally cut and dry, and I believe there is a lot that can be done via suspension tuning to make up for those differences.

kevlarcorolla wrote: Vertical load increases possible traction,I believe that to be a fact that can't be overlooked.Of course there are tons of other factors affecting the handling balance but regardless of weight balance every car can be balanced.Of course you'll be essentially reducing the grip of the "good" end to work with the other,if I'm building something light,powerfull and short I'm going to aim closer to 60 percent rear weight.

Warning: Educational Content

It's so, so much more complicated than "hey, a Ferrari is 40/60, so that's the best".

Here's a condensed reading list if you want to really know why:

Race Car Vehicle Dynamics (Milliken) Especially chapters 4, 5, 6, 7, 10, 12, 16, 17

Tune to Win (Carrol Smith)

Engineer to Win (Carrol Smith)

Here's a quick summary:

If your only goal is lap times, you would be better off with a 60/40 weight distribution with all the car's masses tucked in next to each other. You would also be better off with inboard suspension, no room for a passenger, and full aero. The ideal suspension tune would be nearly undrivable on the street, and you would die backwards every time you hit a bump in a corner. There is not a linear sliding scale of "Camry to FXX" and there are no magic numbers when it comes to the "best" anything when talking about specific characteristics of a car's kinematics. All the marketing material and magazines that you've read talk about reducing the polar moment and front weight as a universally good thing. I think these things are what makes the Miata so much fun, and I don't think changing it in the Exocet will make it better.

Here's a less quick summary:

Weight distribution is dictated by packaging, and many, many characteristics of the car are tuned appropriately for that mass distribution. There are a lot of complicated things going on like instant centers, roll couples, anti-geometry, camber curve profiles, ride frequency analysis, etc. There is no "right" weight distribution, and there is no "making up for those differences". 50/50 is only an "ideal" if you have a relatively low-powered RWD car with identical tires. If you don't have the restriction of identical tires F&R, you can put weight distribution wherever you want and still tune the kinematics to make the car handle. The Delta Wing and FWD BTCC cars are extremes on the distribution scale, and they both are incredibly balanced and quick around a corner. The engineers aren't "making up" for the weight distribution "deficiencies", they simply designed the kinematics for the mass distribution. At that level of design, you aren't "taking away grip" to balance the car. The distribution of masses (how you get that overall weight balance) affects things a lot, too.

In a street car with a relatively low CG (Miata), you can fudge the weight distribution a bit, but if you take Miata kinematics out of their comfort zone, things will get ugly in a hurry. The Miata has all of those things tuned for 54%F to 50%F. Reducing the car's weight makes these changes less important, as you'll have less overall weight transfer. On that note, the grip of a tire is not linear with normal force, your traction ratio goes down with force (2x the force might equal 1.9x the grip).

For transient reasons, the "perfect" full-bodied race car would have around a 40/60 weight distribution with most of the roll stiffness in the rear. Moving the masses inwards decreases the polar moment of inertia, which makes the car more responsive but less predictable and forgiving. This mass distribution is good for transient reasons (balanced braking, good turn in, allows for earlier power in a corner, etc), but it requires a lot of skill to make it perform. For these reasons, those cars are very twitchy and will snap on you if you aren't careful. As an analogy, a modern fighter jet is incredibly maneuverable because they are incredibly unstable. You can only fly them because the active controls constantly keep it from going ass-first. The Miata/Exocet is not a fine-tuned unforgiving racing car, it's meant to be easy to drive and fun.

You can get an Exocet on the road for well under $10k, and that is only possible due to the extensive use of the Miata's mechanicals, including suspension points. Have you ever driven a Miata with a ton of weight in the trunk? It's scary, as the rear's roll stiffness (not just ARBs, this includes roll couple analysis to determine) can't cope with it. When you drive an Exocet, it feels exactly like a Miata, except simply more fun in every way. The predictable handling, transient response, etc only works if the weight distribution is in that sweet spot of approximately 55-48% front weight.

The Point: When we took our street-tuned 1.6 Exocet to Atlanta Motorsports Park last weekend, we had the track's owner flog it around. He had just done 20 or so laps in his 999 Supersport, a mid-engined single seater tube-frame race car with a tiny polar moment and a healthy rear bias. The kinematics were very well designed for the car. The owner couldn't stop talking about how much more fun and forgiving the Exocet was to drive compared to the 999. The 999 was undeniably faster (especially with 300bhp), but he pointed to the weight distribution and increased polar moment of the Exocet as making the car easier to drive and toss into a corner.

You're not going to be able to build the ultimate road-course car for $10k. The Sonic 7 with updated kinematics is close for around a $25-30k build cost. Something with a full body and aero would be even better. The Exocet is a car with fun as it's main goal. Its weight makes an easy to drive car (Miata) much, much faster without being expensive or ruining the friendliness.

Please send me one, I'll give an independent eval

In reply to Keith Tanner:

You know, I bet the owner would be willing to trade a Sport kit for an FMII and a few other goodies (exhaust, clutch, bushings). PM me if you're interested.

In reply to Warren v:

Keith! DO ETT!

The FMII would be put into our planned showcar build instead of the T25/MegaSquirt we were planning. We'll also make brackets and spec silicone hoses to give our customers a bolt-in option for the FM goodies.

That would be cool to see happen

Damn, I'd really like to drive one of these. Especially since my local track is a tight, technical course with a relatively low top speed......

Warren as I said earlier I like the project,I also stated being aware that far more than just weight distribution contributed to how a car drives.Thanks for the lesson btw but my well worn copies of your proposed reading suggest it wasn't needed. My last two builds for very very different sports focused on weight distrubution and the centralization of mass,those 2 cars have won every event entered over 3 seasons of racing and by far the best things on 4 wheels I've ever driven(not saying that much as I usually drive E36 M3 boxes). I understand exactly the intent and price point this project is intended for,only reason I posted was the impression being put out that weight distribution isn't a big deal when it clearly is especially when you do keep all the pickup points etc of a donor car that drives fantastic with closer to ideal'ish 50/50 AND 140hp but add weight to the nose,probably lose a little to the rear and then add 2 or 3 times the power.You give an example of how scary a miata gets with weight in the trunk,why wouldn't adding weight up front effect in the same but different manner?. Again,keep up the good work and I look forward to following along.

kevlarcorolla wrote: Warren as I said earlier I like the project,I also stated being aware that far more than just weight distribution contributed to how a car drives.Thanks for the lesson btw but my well worn copies of your proposed reading suggest it wasn't needed. My last two builds for very very different sports focused on weight distrubution and the centralization of mass,those 2 cars have won every event entered over 3 seasons of racing and by far the best things on 4 wheels I've ever driven(not saying that much as I usually drive E36 M3 boxes). I understand exactly the intent and price point this project is intended for,only reason I posted was the impression being put out that weight distribution isn't a big deal when it clearly is especially when you do keep all the pickup points etc of a donor car that drives fantastic with closer to ideal'ish 50/50 AND 140hp but add weight to the nose,probably lose a little to the rear and then add 2 or 3 times the power.You give an example of how scary a miata gets with weight in the trunk,why wouldn't adding weight up front effect in the same but different manner?. Again,keep up the good work and I look forward to following along.

Hah, right you are. I should have done my research. I will be the first to admit that the Miata (and therefore Exocet) is not an ideal platform from which to build an higher-class road course car. You've moved well past your training wheels and can handle something much more responsive.

The main thing I want to disagree with you about is that the Miata-powered Exocet is not front-heavy. From lifting and moving around a stripped Miata unibody (with top left back), it's apparent that the balance point is about one inch behind the shifter. That's about 44.5 inches from the front contact patches, and therefore within rounding error of 50/50. That's without the fuel tank. The CoM of the Exocet Sport is 43%F before adding the fuel tank. The fuel tank is about 13" further back in the Exocet than the Miata. The A/C compressor, P/S system, blower, heater core, and a ton of dash electrics are removed from the front of the car, and those accessories are way up there (those belt-driven accessories are included in my numbers about the 1.8 Miata's backbone). The Miata's unibody was not the thing offsetting the front weight of the powertrain, it's the seats, fuel tank, and rear subframe assembly. No part of the conversion makes the front weight increase relative to the rear. Removing the unibody is a neutral change, and the only thing moved forward is the ECU. I really need to find a friend in Atlanta with corner weights so I can point at some non-UK-derived numbers for you.

As far as the scaryness of driving a front-heavy Miata, you and I both know that the Miata resolves almost all of its rolling moment through the front wheels and won't be affected until things get worse than 55/45. Very different than extending the roll couple over a soft rear end. I'll take a little bit of predictable push over snap oversteer any day.

i actually prefer the way my v8 exocet handles with no front sway vs my turbo miata.

its just more predictable and planted to me

No worries,I can see the miata powered version working REALLY well but thought the weight distrib discussion was related to the v8 version.It would be nice if heavy/sloshing items like fuel could be kept well inside the wheelbase,pkg'ing is just about the toughest thing in building projects like these.Moving fuel or other things rearward is a double edged sword,makes the weight look better but makes it tougher to catch the rear.It'll still drive just fine but my mind is always trying to make stuff better-can't help it. I agree regarding sway bays,if you can get low,wide and light enough to do the roll control without them the car just gets better.I went barless about 6 yrs ago with no regrets.

im on NOW 14k/8k after the last event. went up another bit in the front due to some dipping and other goofyness in the front end

with that, 15x8-32 with 225/50/15 hoosier R6s i love it

In reply to v8exocet:

Is that kg/mm?