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Race Prep Miata race-only chat. 949 Racing - Rim & tires

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Old 07-31-2015, 08:52 PM   #461
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Jason says that heavier dyno reclass cars are equally as fast as lighter dyno reclass cars. I disagree vehemently.

BTW, I've seen dyno reclasses for very light cars (~2100lbs) in the 17.4:1 range. Greg nerfs light cars, which is completely illogical.
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Old 07-31-2015, 09:04 PM   #462
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Take two PTE* dyno class cars. One is classed 139whp and 2390lbs. The other is classed 151whp and 2610lbs.

Aero drag is equal between the two cars. With big tires, my best guesstimate at the power it takes to maintain ~100mph is about 60whp. The 139whp car now has 79whp to accelerate its 2390lbs weight (p/w ~30.2). The 151whp car gets 91whp (~28.7).

Which car accelerates faster? Which car can make up the tiny deficit of the extra weight out of every corner? Which car can better utilize corner exit speed and get alongside a competitor? Which car is going to be harder to get a run on?

Competitive PT cars are heavy. Dyno vs. points doesn't play into it.
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Old 07-31-2015, 11:36 PM   #463
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EC nationals is at VIR, on a given 2:20 lap around full course (ok I'm slow) I'm doing over 80mph for 1:30 of that lap. Almost all of it full throttle and extremely little of it at my lateral traction limit.
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Old 07-31-2015, 11:37 PM   #464
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Meanwhile at Laguna Seca..

2015 NASA Western states championships
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Old 07-31-2015, 11:58 PM   #465
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Sooo has anyone seen the Ecotec swaps? I have no clue how the engines actually hold up while racing, but they're easily obtainable for ~$300. The sway doesn't affect the front sub-frame or the steering rack. How feasible would it be to do the swap and have say.... 145rwhp, with quite a bit of torque?

Maybe it'd be better suited for a TTD/PTD setup since they can make 200rwhp N/A fairly easily.
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Old 08-01-2015, 01:48 AM   #466
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<p>
Quote:
Originally Posted by Codersozer View Post
I think the rx7 was points built. Thus proving Jason's theory right.
</p><p>&nbsp;</p><p>Pretty sure this is called non-sequitur logic (and really doesn't make sense). &nbsp;Its cool, I get that Jason makes a nice jargony argument, but&nbsp;it still doesn't change that higher weight/higher hp cars at the same p:w ratio will be faster than a lighter one.&nbsp;</p>
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Old 08-01-2015, 04:59 AM   #467
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Quote:
Originally Posted by Seefo View Post
... Its cool, I get that Jason makes a nice jargony argument, but&nbsp;it still doesn't change that higher weight/higher hp cars at the same p:w ratio will be faster than a lighter one.
Tighter tracks with top speed just above 100mph will flip that order.
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Old 08-01-2015, 12:50 PM   #468
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<p>
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Originally Posted by NiklasFalk View Post
Tighter tracks with top speed just above 100mph will flip that order.
</p><p>&nbsp;</p><p>Autocross would disagree with you. I guess I can see a particular configuration that might be so, but for PTE/w2w racing you are going to have a tougher time passing with the lighter car anyway, so unless you qualify better, it would still be advantageous to have the heavier car.</p><p>I drive CMP regularly, which is about ~105mph top speed at the fastest section. &nbsp;I am still not faster than the SC PTE/D&nbsp;miata. &nbsp;Driver difference I am sure is a factor, but they certainly put enough space between the two of us out of the carousel, T8, and T12 that its a no brainer. That said, a track with no significant straights and high speed corners might favor the lighter car, but probably only in a longer race.</p>
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Old 08-01-2015, 02:20 PM   #469
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Make the weight difference extreme and the Sevens vs Corvettes (2.5 times the weight but the same W/P) we have here tells a different story.

Making tires work with the weight is key.

But we have not used our longest track in a couple of years. 0.7 mi straight with high entry speed makes it a power/drag thing. No way to defend a position if you are down 5hp against similar drag.

Two drivers with identical qualifying times, the higher power car will always (have a much better chance to) win.
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Old 08-01-2015, 02:29 PM   #470
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Quote:
Originally Posted by NiklasFalk View Post
No way to defend a position if you are down 5hp against similar drag.
Quoted for truth
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Old 08-01-2015, 07:38 PM   #471
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<p>
Quote:
Originally Posted by NiklasFalk View Post
Make the weight difference extreme and the Sevens vs Corvettes (2.5 times the weight but the same W/P) we have here tells a different story. Making tires work with the weight is key. But we have not used our longest track in a couple of years. 0.7 mi straight with high entry speed makes it a power/drag thing. No way to defend a position if you are down 5hp against similar drag. Two drivers with identical qualifying times, the higher power car will always (have a much better chance to) win.
</p><p>I can't really comment on the Sevens/Vettes, but we are both in agreement otherwise!</p>
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Old 08-01-2015, 10:21 PM   #472
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Not arguing that acceleration wont be better for the heavier reclass car. (hp - drag power) to weight ratio is important. But the acceleration difference is more subtle than you'd think. Plus there is more to a fast lap than just straight speed. This isn't drag racing...we have corners n stuff. Certainly the answer is at least a bit track dependant. Certainly the answer varies for TT vs PT as well.

But hey, everyone is free to drink the kookaid of their choosing.
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Old 08-02-2015, 02:08 PM   #473
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HP comes into play huge when you're in traffic as well. Being able to compromise your line and exit speed and still be able to drag race is huge. Anyone who has watched multi-class racing knows this.

TT is a different story. In a flying lap like TT with controlled traffic you don't have to deal with these compromises.

TLDR: light cars need everything to go fast... high hp cars can pick and chose where to go fast.
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Old 08-04-2015, 08:36 AM   #474
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So what's up with the 2100lb miata winning TTE WC?
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Old 08-04-2015, 10:09 AM   #475
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Local guy, "home track"?
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Old 08-04-2015, 11:00 AM   #476
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Could be. I'm interested to hear everyone's opinion.
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Old 08-04-2015, 11:03 AM   #477
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What was the TTE lap? Record is a mid 1:43 held by an 2400# NB2 points car driven by some California wannabe.
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Old 08-04-2015, 12:08 PM   #478
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Looks like a couple seconds off that wannabe's record...

Justin Ross 1:45.449
Car: 1990 miata points car
Engine: stock
Intake: custom
Header: stock
Downpipe: custom
Mid-pipe: racing beat
Ecu: stock
Power: 119hp, 113ft/lbs
Shocks: koni 30 series
Springs: 700lbs and 375lbs
Swaybars: 27mm eibach and msm
Wheels: 15x9 +35 indotech
Tires: 205 RR
Weight: 2163
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Old 08-04-2015, 12:11 PM   #479
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Lap times look weak behind him. Doesnt look like any of the PT guys double dipped. I did a 1:52 in street car that we drove there from Ohio at MRLS last fall. Would hotter weather account for some of that?
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Old 08-04-2015, 12:17 PM   #480
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The loose nut behind the wheel is _never_ a factor in bench racing.
:-)
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