Optimizing the 818R for power/weight classes

[Wayne Presley]

I'd like to have a discussion of how to optimize the 818R in NASA or any other P/W type of class. Here's what I'd do on my own ca.
1:trim the door skins down the tape line and put the front edge of the door in closer to the body instead of the FFR vents. May have to trim the back edge of door to allow angle mounting.


2: drivers only windscreen
3: hard cover on passenger side.
4:full ducting from nose to radiators
5: no front cut outs other than center radiator inlet.
6: full bottom on the car, wider in front and rear to the limits of the tires
7: take off passenger side engine cover hump
8: make custom multi element diffuser
9: Multi element wing
10 build the motor with cams, big valve ported heads on a 2.5 shortblock with 9.5 CR forged pistons. Have it make spec hp/wt from 3000- 7500rpm


Anyone else have any ideas?

[Bill Waters]

A few:

1. DS rear vent used for cold air intake - boxed-in so as not to create high-pressure area in rear compartment (this was a Wayne Presley idea you shared with me in past I am reminding you of). Same deal for PS, where oil cooler is placed
2. twin-scroll turbo and headers
3. l like #5 above except - what about brake ducting?
4. improve front splitter - FFR one may not be optimal


I am sure I'll think of others - glad you started this thread.

Where would you put fuel cell - behind driver in stock location or in PS location (or other)?

[Wayne Presley]

I'd put the cell behind the driver, that's the safest place in the chassis.
"3. l like #5 above except - what about brake ducting?" I'd pull the air for the front brakes from the radiator openings IF needed.

[Bill Waters]

yep - IF is right -and it may not be needed, especially since I have the excessively big brake option.

[FFRSpec72]

I'm shooting for 8:1 so I'm going to have to add balanced weight that I can remove. So I figure that my car will be about 2200lbs with me (165lbs), I have scales so will be weighing as I progress.

[Wayne Presley]

the Elises we race have 11.5 " brakes and don't have brake fade problems at Road Atlanta or Sebring so I don't believe that the 818 with the 4 piston Wilwoods will have any issue.

[Sgt.Gator]

Replacing fiberglass body panels with carbon fiber is probably not enough of a weight savings to be worth the cost. However I have wondered if it could be built without most of the body panels as an exoskeleton type car......that would drop the weight a lot. But if you wanted that it would be better to buy an Exoskeleton kit car in the first place.

We will need front brake ducts. If not I will be amazed. Every fast car I race against has front brake ducts, or the owner is in process of installing them!
Possibly rear brake ducts, but maybe not.

Added weight:
I will be installing a trans cooler with pump. Most people won't bother with this but I'l be doing it. I have a trans temp data logger on my Legacy 5 speed and it gets hot after after 20 minutes of racing.
I think an oil cooler will be mandatory for racing.
Can the passenger side engine cover hump be put to use as a cold air scoop? Otherwise, yes, cut it off and put a flat piece on there. Either as a TMIC, AWIC, Oil Cooler or Trans cooler scoop?
A place for a Cool Shirt system and electric hookup.

I'm not sure yet where the safest place for a fuel cell will be. If we had a strong rear crash bar to keep the engine from being shoved into the mid mounted fuel cell I would agree with you, behind the driver is best. But I can see an argument for having it in the passenger area, walled off with firewall on all sides too. Has anyone corner balanced the car with both options yet, and both empty and full of fuel? That would probably be the determining factor.

As far as your engine choice, that's entirely depending on which class you want to race in and what trans/ratios you have in mind. They need to compliment each other.

[Santiago]

I'll second Gator's remark that a class needs to be settled upon and then go from there. In NASA two factors loom large for the ST options, tire size/type and weight. There's a fairly large swing in legal power once you start playing with selecting the tires you want to run. Like Tony, I don't think I'll have to worry much about losing weight; it'll be more about zeroing in on the lowest legal weight (which is almost certainly going to be heavier than what I could readily take out). I'm also looking at ST2 putting us in that 8:1 vicinity, so it isn't going to take an all-out engine by any means.

For that matter, the type of track use you intend also influences what coolers/ducts one needs as well. If you're thinking Time Trials, brake ducts may not be any sort of concern at all depending on how you like to run that format. Our sprint races are 35-40 min, and most of these guys are using brake ducts. And enduro can be anywhere from 3hrs to 25hrs, and I'd be surprised if there's any good team that doesn't have a full compliment of ducts and coolers there.

So to me, that means the Q is "What do you do to maximize your performance in the given class restraints?" The obvious answers:
1. Zero in on weight.
2. Maximize mechanical grip.
3. Address aero for fast tracks.

So the last one sort of suggests that your frequented tracks also factors into what gear you run. We're mostly medium speed tracks here in the Midwest, save Road America. You can build aero to RA, but the returns on the investment will only be seen once a year (on a NASA schedule). Better to build aero for the medium speed tracks, which means less concern for drag penalties (not that you ignore it, just that it doesn't bite you in rear as badly as it does elsewhere).

I like the aero plans Wayne suggested, though for my own needs retaining 2 seats is important (I instruct and love to have friends along for rides, so passenger capacity is a must). I would add that something could be done with the rears of the wheel wells. I'm HUGELY in favor of angled doors over legacy solutions, but more can be done front and rear (think DTM without all the harsh angles).

So back up to #2: Mechanical Grip. Why this isn't on the table is a mystery. Tires and weight are governed by class restrictions. But from there (in the ST classes) you're free. Widen the track, damn the stock fenders (flare them). Lower the center of gravity as much as inhumanely possible. We're not off-road racing, so if it can be put on the floor, that's where it goes. A full under-tray is planned anyway, so make it tough - here is a good place to consider the more exotic composites along with good old fashioned rub strips. I love thinking about aero, but the reality is that you get serious dividends on it only at higher speeds. Mechanical grip pays dividends all the time, and in some classes there are no rules for how you go about achieving this. So back to basics: track and c.g.

Last, folks are still debating safe fuel cell areas; to each his own. But honestly, if all that troubles you is the lack of rear crash structure, we're not helpless here. Build it. Put the cell where you think best. Mine will be behind the driver, and I'll have additional bumper bars that extend past the plane of the supplied bumper cover. So bye-bye bumper. Bye-bye fenders and bye-bye anything else that gets in the way of the build the way you want it.

Best,
-j

p.s. -In our region (Midwest) ST2 is dominated by a stupidly fast Lotus Exige Cup who runs neck-and-neck with our AIX champion (for those out of the loop, that's ST2 power levels up against a 1,000+hp beast). So that's my bogey. I may not be the driver to take it to him, but I know his car is a good foil against which to consider what I'm building.

[Rasmus]

I'd like to have a discussion of how to optimize the 818R in NASA or any other P/W type of class. Here's what I'd do on my own ca.
1:trim the door skins down the tape line and put the front edge of the door in closer to the body instead of the FFR vents. May have to trim the back edge of door to allow angle mounting.

That is brilliant. I'm stealing the idea and passing it off as my own!

8: make custom multi element diffuser

What's that? I know what a rear diffuser is but what's a "multi element diffuser"?


Is that a Double-decker diffuser like the F1 rule benders had?


Or a multiple expansion chamber rear diffuser?

[Wayne Presley]

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