DaveK

iTrader: (21)

I've got a question for all the track guys regarding when to make the decision to add power vs. removing weight on a race car. You answers may help to steer future mods to my PPIHC Evo. If you're unfamiliar with the car, here are links to the 2008 Build-Up and its subsequent 2009 Updates. On race day, the car will run 12.4 miles and gain almost 5,000 feet of elevation, so there's good strain put on all the car's systems.

Here's where I'm at. The car now makes good power, 540 ft/lbs and 460 hp, and weighs 3050 lbs without driver/co-driver. I can run power to weight calculations with all kinds of weight reductions and play with different power levels to see where I'd end up, but I'm wondering which way will yield the best benefit since I can't afford to do everything (unless someone wants to sponsor me some lightweight parts and I'll go buy a turbo ). The class I race in will allow any of the normal weight reductions:

CF hood, save ~8 lbs (Fiber Images or Robispec)
CF trunk, save ~15 lbs (Fiber Images or Robispec)
Fiberglass Rear Doors, save ~90 lbs (Robispec)
Carbon Fiber Front Doors, save ~94 lbs (AMS)
Lexan Window kit, ~20 lbs, would retain glass windshield (AMS)
Lightweight driveshaft, save about 14 lbs (AMS)
Moustache Bar Eliminator, already installed (AMS)
Lightweight Front X-member, already installed (AMS)

I can also swap to a different turbo, as no restrictors are required. Thanks to the AMS V-band kit I'm using, TiAL SS housings will fit, so going with a larger turbo like a 35r is also a possibility. I'm guesstimating that a 35r on my engine setup (2.3 stroker with all the fixins) would probably make about the same torque values I have currently, but probably would be capable of another 150-200 horsepower.

Other thoughts that I've been kicking around:
-current turbo = 6000 rpm shift point, so 5th gear tops out around 120 mph
-bigger turbo = higher rpms = using 1st-4th gear (top speed ~115-120 mph)
-effects of revving the motor higher = more stress & more heat
-lighter weight = less heat on the braking system

Curious to hear your guys thoughts.

Dave

TxEvo8

iTrader: (5)

Losing that 221 lbs does not seem to equate to gaining even 150hp from buying the turbo. Additionally, racing uphill seems as if it would be pretty easy on the brakes, so to me it sounds like the turbo would be your best bet.

Good luck whichever way you go, that sounds like a blast!!

Bueller

iTrader: (1)

I race with NASA in Super Touring. But keep in mind that my experience is very limited with regards to racing because im a rookie racer.

I would say that as you know, this all depends on your application. Racing is different from hill climbs, autox, and so on. Therefore, the same approach will most likely entail different results with regards to what youre actually doing.

For racing, i have realized first hand how important weight reduction is. Running a few fast laps means nothing. Whats important is how fast you can run the entire race. And most importantly, being able to finish the race. People dont realize how much of a big deal it is to finish a race, let alone win. With that regard i would say weight reduction is primary. However, im really not sure how that applies to hill climbs. Are conserving tires and brakes important for you in a hill climb? If they are, i would without a doubt focus on weight reduction.

Btw, your setup is big time baller compared to mine. I need lots of things. Care to sponsor me?

DaveK

iTrader: (21)

Agreed, but that brings up an important question, should I be looking at torque numbers or horsepower numbers when calculating power to weight?

Are there any generalizations when road racing about how much time weight is worth? i.e. for drag stuff, you often see that 100 lbs off the car is worth 0.1 second in the quarter mile. I'm guessing maybe the guys who race in series who get hit with weight penalties might have a good idea of this kind of relationship (though they're probably having to add weight, not remove it).

I'm still not sure what tires we'll be running, as its hard to pick something that'll hook up on both pavement and dirt. On the brakes, we're certainly a bit kinder to them that if it was a hill descent , but on the dirt, there's lots of LFB'ing going on so heat is always a concern. That said, with our ~300whp car last year, I didn't have a hint of trouble from the AMS Rally Brake kit. They're actually smaller than the OEM stuff, b/c last year I ran 15" rally tires. I've got beefier rotors and a ducting kit still to install, so we'll have more heat capacity this year for sure. If I end up running 17" wheels, I can always go back to the OEM brakes if needed.

Thanks for the compliments on the Evo, its been fun trying to get everything setup and finding the $$ to make it happen...makes finding time to strap into the car a bit of a challenge, but well worth it IMO.

Dave

jid2

iTrader: (62)

Loosing weight has no negatives, except cost. I'd pick the biggest contributors - like the doors, and start there.

I would run Pikes Peak this year with the 460 whp you have now, before increasing it even more. It is going to be a whole new animal with 160 more horsepower - trust me. I made a large power increase with my car and it has really changed the comfort level at tracks I already know.

vaughany

Weight would be my choice. It will accelerate, stop and change direction faster. Will be lighter on tyres etc also. However, you will wheelspin more out of slow corners and slide a bit more on higher speed corners so spring rates and tyre pressures etc will become critical. And aero if you are allowed it. In saying that if you find it is worse you can put weight back in the appropriate places. I had a Toyota starlet on gravel. It weighed 620KG (not sure in PD) and I couldn't get it off the line. It just sat and spun. We ended up fitting dive belts to the cage to help at one event.

boomn29

iTrader: (47)

Weight reduction all the way.

Increasing power will also cause extra strain to your trans, brakes, etc. I'm sure you're aware of this just keep it in mind. I'm not sure if getting it too low would cause issues with traction?
fwiw, my car weighed in recently at 3278 with driver, 1/3 tank gas and an autopower 4pt cage. I have a 3263lb minimum to meet for NASA so I was pretty happy with that as I can remove a little more and use more gas for ballast if needed. That'd be about 3110 w/o driver & gear.

What type of power/weight or modification limitations do you have? I know NASA calculates the ratio based on peak whp. They don't care about torque.

Btw, installing that brake ducting kit should do wonders. On the normal track, my pad life has been exponentially increased! Not to mention I don't have to worry about the brakes getting hot or a slushy pedal at all.

And yeah, a little baller bravo from me too. I follow your posts about the car, just something I've never tried and really suck at it on video games (all throttle no brake when I try).

Bueller

iTrader: (1)

I dont know about any generalizations for road racing like the kind of generalizations they use for drag stuff. I can say that we are penalized a certain amount of points if were lighter. The way it works in Super Touring is that we are limited to a specific w/p ratio. There are a few modification factors that we are assessed that changes the equation, one of which is weight. Reason being, it wont be exactly fair to have cars with different weights being calculated by the same ratio. For instance, our limit of w/p is 8.70:1. Lets say you have 1 car weighing 3000lbs, and another car weighing 2000lbs. If both were calculated by that 8.7 ratio to figure out how much power theyre allowed to make, the lighter car will obviously have a major advantage. To help even things out NASA assesses a certain amount of points the lighter you are. The lighter you are the more "mod" points youre assessed. So if your CW is 2000 lbs, youre assessed 1.25 points. So in the end, a car with a CW of 2000 lbs has to have a w/p of no less than 9.95 (8.7 + 1.25). This also applies if you have an extremely heavy car, ie you get points back. This method is supposed to help even things out. So whether your car weighs 2000 lbs, or 4000 lbs, both cars have a w/p ratio that evens them out.

DaveK

iTrader: (21)

None, engine is free and the rules don't have any mention of weight minimums. I think they figure the 9400 foot startline and 10% grades do enough to slow down the cars.

On aero aids we're pretty free to do as we please, but are limited to adding vertical planes (i.e. side plates, or vertical fins on a diffuser). DHP Composites is working on a new wing that should be even better than what we used last year. I'm still unsure of what I'll be doing for a front canard assembly though, as we'll be using some of our alloted inches for sideplates and won't have as much available for the canards.

This makes my head hurt, and I work with numbers! I kind of like the 'anything goes' nature of Pikes Peak, but it means that those with the big budgets can really show up with something wild. There was a 2200lb stroker motor Evo there last year in a different class making ~600whp. I'm not sure if he's coming back, but I'd like to be able to keep up with him if he does.

Marcus Gronholm just announced he'll be out here for the event with an 800whp Fiesta Rally-Cross car, so that got me motivated to bump up the performance of the Evo, even though I'm not competing in the same class.

Dave

nils

iTrader: (56)

yea.. id always prefer to loose weight over gaining power... but it does get pricey...

both will make u go faster.. BUT....

gaining power = more headaches.. stuff breaks, wears quicker

loosing weight = less headaches.. less stuff breaks, wears..

generally speaking.

now go get gronholm... that would be awsome to give him a run for his money

abu

iTrader: (3)

Agree 100%

Balrok

iTrader: (15)

+1, weight. I road race as well so we'll all agree there. However for dirt rally, especially with pikes peak and its "if you f* up, your more dead then the grateful dead" corners, i'd be careful. You'll have to adjust your suspension and tires as already stated to become stable again. If you were to go into a slide for a say 160deg turn, you wouldn't have the muscle memory that knows that this entry is 46.5 mph for a successful drift, instead you'd rocket off the cliff. The whole track will be different, so keep that in mind when making your practice sced. And again with a 35r, you'd have to take the anti-lag (that you know works but don't have yet), heat, shift points, pretty much everything back to the drawing board because it's in a whole different plot.

If I was you, i'd take maybe 100 lbs out, practice, practice, adjust and max it out, then 100 more etc...lots easier on you as the driver/engineer so you know exactly what she's doing and how she's reacting. (The car, not your girl )

meanmud

iTrader: (74)

Marcus Gronholm...............that's worth the price of admission right there

Take weight out

DaveK

iTrader: (21)

Luckily (or unluckily) the dirt we race most of the season is nothing what we find on Pikes Peak. We really only get to make ~4 runs on The Mountain per year. We get three days of practice where they break the mountain into three parts, lower, middle, upper. Each day you get one section, then on race day (July 19th this year) there's one shot. Since time of day and moisture content on the dirt on seems to be different each run, the ability to truely push 100% on every run isn't there like it is when tracking a car...or maybe I just need a few more years under my belt.

FWIW, I'm planning on taking the car out to our one of the new race tracks near Denver to get a feel for some of the adjustable aero stuff we'll have on the car. I figure the fact that I'll be able to turn more consistant lap times should help me find the sweet spot for wing angles and splitter height.

DHP Composites is working to get us a new dual element rear wing, and I'm looking at picking up a set of RobiSpec canards. Depending on time, I may also try to figure out how to flat-bottom the car a bit more...but that's probably last on my list of things to get done.

First change to get done on the car won't be a weight savings mod per-se, but I'll be moving the ACD pump to the floor behind the passenger seat. This will at least take some weight off the nose. Next step will be to figure out what to do with the oil cooler, as IMO it just hangs down too low to be safe in a rally environment. The added bonus of moving these two items is that I'll be able to 'tunnel' up the back edge of the splitter.

Dave

bluestreak

I side with weight, but that is for road racing. More power is only good if you can use it meaning you have more traction than power.

In road racing a good rule of thumb is that an average passenger weight (170 lbs or so) will gain you ~ 1-2 seconds per 2-2.5 miles give or take a few and depending on the course type. This is on a track surface though, never driven on gravel/sand/dirt to say. And there are variations as well. If the weight is closer to the center of gravity it has less affect and if the weight is unsprung it has greater affect.

Lets take your hypothetical weight to power ratio

3050 - 221 = 2829/460 = 6.15 - based on weight loss

or

460 + 200 = 660 3050/660 = 4.62 - based on adding power

By that measure it seems to be sure fire to go with power, and for shorter runs, that will likely be the case. The extra weight only really take a toll over longer races.