In reply to Keith Tanner :
Didn't see where you said same power/weight. My mind is in rallycross mindset where the weight spread difference between cars is low, but the power difference is 100-250 or so for 2wd and 150-400 or so for AWD, so "power" can roughly equate to "power/weight".
I specified power/weight as a constraint in every post 
Keith Tanner said:irish44j said:Keith Tanner said:Given a certain power/weight, the light car will have better transition and braking behavior. The more powerful car will have an advantage once aero drag starts to come in to play.
or, at venues with big hills. Panthera, where we run, has a pair of ~1000ft uphills, where power cars make up a ton of time. One of the main reasons I just engine-swapped my e30 lol....I could beat everyone on flat courses, but would lose by 10+ seconds in these hilly courses.
Obviously, boosted Miata is the answer ;)
Hills shouldn't affect cars with the same power/weight any differently. It's engine power vs mass, and going uphill doesn't change the mass. Aero drag increases exponentially with speed and (in our over-simplified thought experiment) will affect all cars the same so power/drag overwelms power/weight.
If you're assuming a set weight, then you're talking about cars with a higher power/weight ratio. I can't think of a situation where more power (at the same weight) will make you slower unless the driver is a meathead or the car has some sort of uncontrollable powerband.
The original question was specifically comparing light, low-power cars with heavier, higher-power cars.
In reply to Keith Tanner :
I should probably pay more attention then 
It would be kind of odd to see what comes up that is equal in power to weight. Like a 2000lb 100hp CRX vs... what? A 150hp 3000lb car? Most rallycrossable things with 150hp weigh a lot less than 3000lb and most 3000lb front drivers have much more than 150hp. And the CRX will eat their lunch on a tight course because it is narrower. On a rough course a heavier car may stay controlled better, since unsprung weight goes down as a percentage of weight as vehicle weight goes up (or rather, there is an asmptote for unsprung weight that medium-weight cars like Neons have already hit)
I expect that 914-6 to be bad fast as long as the course is smooth.
I expect a 914-6 would be pretty close to an ideal RWD rallyx car. Light, powerful, low polar moment, lots of weight on the driving wheels.
It's definitely difficult to come up with good examples of various cars with the same power/weight without going extreme. I was generalizing in my posts, not trying to come up with specific examples. But I've owned a 1200 lb 175 hp car, and putting that up against a 500 hp 3200 lb car (like that fourth-gen Camaro could be) would be a legit comparison. Heck, a baja bug or dune buggy would probably serve as a rallycrossable lightweight example if it were allowed to run.
Disclaimer - I've only rallycrossed once, and it was in a rental Hyundai on stock tires on a course that was heavily watered for dust abatement so it was basically a mud bog. I couldn't get enough speed to do anything so it was mostly a useless exercise in throwing mud. But I view it as autox with a need for suspension travel.
In reply to dps214 :
Yes I was thinking of even starting with a 924S if I eventually get to that point. Pretty light compared to late model 944's
I'm looking at rallycrossing something that is 250hp/300ftlb but weighs 4000lbs but 53/47 weight distribution. So I just hope not to be the slowest. Since full weight reduction might get you to 3600 lbs.
MrChaos said:I'm looking at rallycrossing something that is 250hp/300ftlb but weighs 4000lbs but 53/47 weight distribution. So I just hope not to be the slowest. Since full weight reduction might get you to 3600 lbs.
That doesn't sound all that far off my Jeep other than being a bit down on power. The Jeep is about 4300 lbs, close to 350hp (at the crank), somewhere around 55/45 weight distribution. Between the size, weight and locked center diff it pushes pretty badly in tight sections (kicking it into 2wd helps, but then putting down power is a challenge). In more open areas of the course, however, it's downright quick. Power-wise you should be fine, as I've never had a point where I could put my foot down without wheelspin, even with limited slips in both diffs.
I'm not all that competitive overall (and it varies a good bit depending on the course), but people have commented that on courses where we've had faster slaloms I'm getting through the slalom as fast or faster than the fastest overall cars (and in some cases I'm seeing noticeably higher top speeds than they are, partly because a lot of our really fast drivers are in power-limited cars).
In reply to rslifkin :
Crown Vic P71
MrChaos said:In reply to rslifkin :
Crown Vic P71
That should avoid the understeer problem being RWD. Your biggest issue will likely be fitting through tight areas without whacking cones just due to how big those are (mostly in terms of length).
MrChaos said:In reply to irish44j :
this is apparently going to start showing up this year and will likely give MR and the z28 a run for its money. its apparently a 914-6 with a 3.3 in it.
Yeah, it was at sandblast a couple years ago. I think they made it about 1/4 mile into the first stage before it broke, or something like that. It's really a pretty car with NO expense spared in its build (all kinds of custom/one-off stuff on it). Will be interested to see how it does, and will leave my commentary at that. There are "opinions" about it in the stage rally community for sure.
Keith Tanner said:irish44j said:Keith Tanner said:Given a certain power/weight, the light car will have better transition and braking behavior. The more powerful car will have an advantage once aero drag starts to come in to play.
or, at venues with big hills. Panthera, where we run, has a pair of ~1000ft uphills, where power cars make up a ton of time. One of the main reasons I just engine-swapped my e30 lol....I could beat everyone on flat courses, but would lose by 10+ seconds in these hilly courses.
Obviously, boosted Miata is the answer ;)
Hills shouldn't affect cars with the same power/weight any differently. It's engine power vs mass, and going uphill doesn't change the mass. Aero drag increases exponentially with speed and (in our over-simplified thought experiment) will affect all cars the same so power/drag overwelms power/weight.
Just to clarify: Since I assume you mean "compared to a long flat straight" in your argument, that's true. But because SCCA rallycross rules would never allow a flat straight of that size (since the fast cars would be doing like 100 on one), it's not a direct comparison, as the "flat" courses have more turns to keep speeds within regs. The long straight uphills naturally keep the speeds more in check and so are longer.
Like any racing, have to take the rules into consideration when making decisions as well of course. And we all know how SCCA likes to be rules sticklers...
Again, power/weight. If you have the same power/weight, then the fact that you're climbing a low speed hill versus running along a low speed straight makes no difference. Gravity acts the same way on an incline or on the flat. Your example of M50 vs M42 is not assuming the same power/weight, I'm guessing you're assuming the same chassis so you're really comparing low power/weight to higher power/weight.
Long ass straights bring aero drag into the equation, and this affects both the light/low power and heavy/high power cars equally so the high power cars have an advantage.
Keith Tanner said:Again, power/weight. If you have the same power/weight, then the fact that you're climbing a low speed hill versus running along a low speed straight makes no difference. Gravity acts the same way on an incline or on the flat. Your example of M50 vs M42 is not assuming the same power/weight, I'm guessing you're assuming the same chassis so you're really comparing low power/weight to higher power/weight.
Long ass straights bring aero drag into the equation, and this affects both the light/low power and heavy/high power cars equally so the high power cars have an advantage.
Yes, Keith, I understand that. But if you read the rest of my post, it's not 1) 1000-ft flat straight vs 2) 1000-ft uphill straight. The long flat areas in SCCA rallycross have technical elements (slaloms, offsets, etc) to keep speeds down below a certain speed - where lower-weight cars (which are usually lower power and more nimble) are typically faster, even with less p/w. An open uphill straight with no technical elements is a straight-up power-to-weight race. And an M3 has better power to weight than a NA Miata. It will beat the Miata up a straight hillclimb every time, stock for stock. While that would also be the case in a flat straight, that's a moot point, because no flat straight would be allowed within SCCA rules, It absolutely isn't the case in a flat slalom - especially on gravel and dirt where you can't overcome or mitigate the turning traction vs. heavier weight by slapping on more tire.
Again, we're not talking about flat straight vs. uphill straight here, when it comes to SCCA rallycross. Our course layouts would not be allowable if they were on a flat field rather than on the sides of a mountain. This is where "building to the course" comes into play. Theoretical only comes into play when there are no outside factors involved (like rules, and surfaces, and traction).
In rallycross, aero is of minimal concern to anyonw. The speeds aren't significant enough.
cliff notes: a flat course layout isn't designed the same as a hilly course layout in rallycross (due to speed limitations, rollover risk, etc) - therefore they cannot be directly compared as a straight graph of power-to-weight efficiency.
I was simplifying. All else being equal, similar power/weight, etc. The fact that you're climbing something means nothing if you're talking the same power/weight. That's all. I wasn't commenting on the complexities of real-world course design or SCCA rules or slaloms. Just the fact that an incline doesn't change the way that cars with the same power/weight will behave. It's high school physics.
Keith Tanner said:I was simplifying. All else being equal, similar power/weight, etc. The fact that you're climbing something means nothing if you're talking the same power/weight. That's all. I wasn't commenting on the complexities of real-world course design or SCCA rules or slaloms. Just the fact that an incline doesn't change the way that cars with the same power/weight will behave. It's high school physics.
A point which absolutely nobody was contesting; rather everyone else in here is commenting on real world Rallycross applications.
rslifkin said:MrChaos said:In reply to rslifkin :
Crown Vic P71
That should avoid the understeer problem being RWD. Your biggest issue will likely be fitting through tight areas without whacking cones just due to how big those are (mostly in terms of length).
Huh? RWD understeers badly.
If you wait until corner exit to rotate, you done effed up. That is the bane of RWD: You have to do all your turning before the corner, in a sense. Front drive you just mush around pointing the steering where you want to go and the front wheels paddle you around.
irish44j said:MrChaos said:In reply to irish44j :
this is apparently going to start showing up this year and will likely give MR and the z28 a run for its money. its apparently a 914-6 with a 3.3 in it.
Yeah, it was at sandblast a couple years ago. I think they made it about 1/4 mile into the first stage before it broke, or something like that. It's really a pretty car with NO expense spared in its build (all kinds of custom/one-off stuff on it). Will be interested to see how it does, and will leave my commentary at that. There are "opinions" about it in the stage rally community for sure.
Having seen similar weight/suspensions design ACVWs run, I bet it would not be fun unless the course was super smooth. Just too much unsprung weight. You can't control the car when it is boinging everywhere and you can't keep it from boinging when the suspension weighs almost as much as the rest of the car...
There is only so light you can make a suspension and have it live, which is why I think of 2200ish pounds as the effective lower weight limit.
In reply to Knurled. :
RWD can still understeer, but it doesn't have the AWD with too-tight center diff issue of just plowing the front wheels in tight turns unless you get it sideways. It's easier to avoid overloading the front tires once you get the car set up well and get used to driving it when you're not driving the front wheels (unless you can just throw it stupidly sideways and catch it later).
Huh? RWD understeers badly.
i think that's just your 300lb skidplate talking :)
MrChaos said:In reply to rslifkin :
Crown Vic P71
Been there, done that, highly recommend. Take a grand to your local police auction and bring one home to run with.
Everybody will think it's awesome, it handles spectacularly for my noviceness, is heavy sure, but if you're not running a stock class you can shed lots of weight.
RevRico said:MrChaos said:In reply to rslifkin :
Crown Vic P71
Been there, done that, highly recommend. Take a grand to your local police auction and bring one home to run with.
Everybody will think it's awesome, it handles spectacularly for my noviceness, is heavy sure, but if you're not running a stock class you can shed lots of weight.
I drove one years ago at an out-of-region event and it was a blast (plus it can carry like 8 wheels in the trunk). That said, it depends on what the goal is. If it's just to have an awesome time (and yes, everyone else WILL think it's awesome as well, for sure), P71 is an inexpensive and awesome choice (or better yet, a Crown Vic wagon with P71 underpinnings!). If the goal is to "win," it's probably not very high on the list of competitive RWD rallycross cars. Yeah, I'm sure there is someone someplace who does well in one - but if it was really a competitive car in rallycross, everyone would have them since they're so cheap and available compared to most of the cars running in RWD classes
As a starter car for rallycross though, it's tough to beat for cheap, ease of driving and having fun. I'll be honest, I've considered getting one myself (the wagon, of course) just for E36 M3s and giggles.
Knurled. said:irish44j said:MrChaos said:In reply to irish44j :
this is apparently going to start showing up this year and will likely give MR and the z28 a run for its money. its apparently a 914-6 with a 3.3 in it.
Yeah, it was at sandblast a couple years ago. I think they made it about 1/4 mile into the first stage before it broke, or something like that. It's really a pretty car with NO expense spared in its build (all kinds of custom/one-off stuff on it). Will be interested to see how it does, and will leave my commentary at that. There are "opinions" about it in the stage rally community for sure.
Having seen similar weight/suspensions design ACVWs run, I bet it would not be fun unless the course was super smooth. Just too much unsprung weight. You can't control the car when it is boinging everywhere and you can't keep it from boinging when the suspension weighs almost as much as the rest of the car...
There is only so light you can make a suspension and have it live, which is why I think of 2200ish pounds as the effective lower weight limit.
Yeah, not sure what the specs are on that car. I know it has Fox Racing suspension with external reservoirs (an unusual choice for a rally car, frankly) and appears to have a lot of travel based on pics I've seen of the suspension. Looks like they just did Sandblast 2018 and haven't rallied it since. I saw it on its shakedown runs and it looked pretty composed on a really choppy surface, but we know rallycross isn't rally and has different requirements...
irish44j said:Huh? RWD understeers badly.
i think that's just your 300lb skidplate talking :)
Nah, it's the 200+ft-lb breakaway diffs I'd run.
Seriously, though, RWD sucks for turning in because the front wheels lock SO easily when it is slippery and there is not enough weight transfer to justify any kind of brake bias at all, even before you figure that the front wheels have no drivetrain inertia (natural ABS) attached to them.
And turn in improves dramatically with an open diff, or maybe a clutch diff that has been neutered to have no preload like only 50-60lb or so ( smirk ) but putting power down then becomes a bit difficult. I'd been hoping that the Locker would be the best of both worlds, giving good turn-in and great exit traction, but between rain and other mechanical failures, I don't have much to go by. Well except this, anyway.
irish44j said:I drove one years ago at an out-of-region event and it was a blast (plus it can carry like 8 wheels in the trunk). That said, it depends on what the goal is. If it's just to have an awesome time (and yes, everyone else WILL think it's awesome as well, for sure), P71 is an inexpensive and awesome choice (or better yet, a Crown Vic wagon with P71 underpinnings!). If the goal is to "win," it's probably not very high on the list of competitive RWD rallycross cars. Yeah, I'm sure there is someone someplace who does well in one - but if it was really a competitive car in rallycross, everyone would have them since they're so cheap and available compared to most of the cars running in RWD classes
As a starter car for rallycross though, it's tough to beat for cheap, ease of driving and having fun. I'll be honest, I've considered getting one myself (the wagon, of course) just for E36 M3s and giggles.
Main reason is there are no other RWD cars locally that are suitable and budget friendly. S197 GT's are still 8k+, anything LS is 8k+, I dont want a miata(currently own 2 and am selling 1 of them) plus a hardtop puts them in the same price range as the mustangs/ls cars, 350z/G35 are out because of plastic core supports, E30's dont exist, E36/46 non basket case cars dont exist, RWD Volvos dont exist, AWD is boring, etc
Also note i will be driving the car 110 miles one way to rallycross.
Currently for sub $7k rwd cars on my local CL that would be rallycrossable I have like 8 c4 vettes, 6 VW beetles, 3 El Caminos, 12 panther platform cars, a fiero, a 01 tundra 2wd with a supercharged LS2, 4 regular cab short bed manual tacoma's,and a smattering of reg cab v8 domestic 1/2 tons. Though usually there are about 5 944/924's on there but not right now.
You'll need to log in to post.
