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Last Post 23 Nov 2012 05:16 PM by  TeamRX8
RX-8 to DSP?
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murph1379
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11 Nov 2008 04:29 PM

RX7 KLR wrote:
No matter what you do to an RX-8 in SP it will always weigh more (up to 200lbs by my calculations) than an S2000, and have less HP/Tq, and the S2K is not nearly a top dog in BSP.

Have you driven an S2000 and an RX-8? The S2000 may have more power above 6,000 rpm, but I'd bet there's more area under the torque (or even HP) curve on an RX-8.

RX7 KLR
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11 Nov 2008 04:48 PM
murph1379 wrote:

Have you driven an S2000 and an RX-8? The S2000 may have more power above 6,000 rpm, but I'd bet there's more area under the torque (or even HP) curve on an RX-8.

Yes, AP1, AP2, CR and Uyeda's BSP S2K. While the RX-8 does have more linear power delivery, it still has to pull the extra weight out of the corners.

Chiketkd
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12 Nov 2008 02:40 PM

I've driven an AP1 S2000 set-up for AS and it was noticeably faster than my RX-8. Even the AP1's have better power-to-weight and torque-to-weight ratios than a RX-8.

While the S2000 has the peaky V-tech system, the Renesis in the RX-8 has a similarly peaky intake system which opens auxillary intake ports as the rpms increase -- the last one opens up @7,250rpms iirc (the dips in the dyno below are when these intake ports open). Torque really doesn't "come on" until 5K rpms and even then, we're talking about 130wtq!!! [:$]

This is a dyno of a stock RX-8 on fresh NGK plugs (with K&N panel filter) -- 180whp and 130wtq is the norm for a BS RX-8:

murph1379
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12 Nov 2008 03:41 PM

And notice that it has 100+ tq pretty much from the get-go? When does the S2000 hit 100ft-lbs, 4,000, 5,000 rpm?

I gues my car hits 100ft-lbs at like 600rpm, but my point is that I think it's got more grunt than the S2000. (not a high bar, but I don't think the RX-8 is as gutless as people want to insist)

jeffh
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12 Nov 2008 05:55 PM
Chiketkd wrote:

I've driven an AP1 S2000 set-up for AS and it was noticeably faster than my RX-8. Even the AP1's have better power-to-weight and torque-to-weight ratios than a RX-8.

While the S2000 has the peaky V-tech system, the Renesis in the RX-8 has a similarly peaky intake system which opens auxillary intake ports as the rpms increase -- the last one opens up @7,250rpms iirc (the dips in the dyno below are when these intake ports open). Torque really doesn't "come on" until 5K rpms and even then, we're talking about 130wtq!!! [:$]

This is a dyno of a stock RX-8 on fresh NGK plugs (with K&N panel filter) -- 180whp and 130wtq is the norm for a BS RX-8:

Nice dyno for a BStock RX-8. For reference on a set of 285's, 5000 RPM would put should put a DSP RX-8 at 35 mph or so. Is there an issue with downshifting into first with the RX-8, or the new MX-5 transmission?

Posted a graph of what a theoretical acceleration curve would look like for an S2000 using a Hondata Dyno and a 2700lb curb weight and used the numbers posted previously for an RX-8 in 2nd gear. You can click here to view it. I'm sure some of you will be surprised. There is of course a certain margin for error with different dynos, etc, but it should give a basic idea. The RX-8 looks pretty torquey to me. [:)]

Chiketkd
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12 Nov 2008 07:40 PM
murph1379 wrote:
And notice that it has 100+ tq pretty much from the get-go? When does the S2000 hit 100ft-lbs, 4,000, 5,000 rpm?

I gues my car hits 100ft-lbs at like 600rpm, but my point is that I think it's got more grunt than the S2000. (not a high bar, but I don't think the RX-8 is as gutless as people want to insist)

Well the dyno started recording at 3,000rpms -- it's hard to say what happened below that. I would say that on the street, the car feels gutless below 3,000rpms.

In the 2nd post of this thread, you'll find the dyno of a bone stock 2002 S2000 with 625miles: [url]http://www.s2ki.com/forums/index.ph...;/url] 

(note it makes 110ft-lbs by 2,500rpms)

jeffh wrote:
Nice dyno for a BStock RX-8. For reference on a set of 285's, 5000 RPM would put should put a DSP RX-8 at 35 mph or so. Is there an issue with downshifting into first with the RX-8, or the new MX-5 transmission?

Correct - my only intent was to illustrate the peaky powerband (with multiple dips). It's definitely possible to downshift an RX-8 to 1st gear.


jeffh
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12 Nov 2008 10:45 PM
Chiketkd wrote:

Well the dyno started recording at 3,000rpms -- it's hard to say what happened below that. I would say that on the street, the car feels gutless below 3,000rpms.

In the 2nd post of this thread, you'll find the dyno of a bone stock 2002 S2000 with 625miles: [url]http://www.s2ki.com/forums/index.ph...;/url]

(note it makes 110ft-lbs by 2,500rpms)

Correct - my only intent was to illustrate the peaky powerband (with multiple dips). It's definitely possible to downshift an RX-8 to 1st gear.

Understood, I'm just trying to keep this on based on autocross speeds, also considering that 1st is an option, but not a great one in an RX-8, the S2000 on the other hand can really take advantage of it. Below 3k is 20mph in 2nd gear with the RX-8. To throw a wrench in the S2000 after looking further into it, to show that it is a faster autocross car, other than the obvious advantage of it's weight/dimensions, an S2000 can utilize 1st gear up to over 50mph (which boosts acceleration considerably, about a 50% increase), 50mph @ 9k in SP trim, compared high 30's for an RX-8. Raise the rev limit for an S2000 and you have a car that should be in BSP.

The RX-8...I'm for it in DSP! [:)]


Chiketkd
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12 Nov 2008 11:03 PM
jeffh wrote:
The RX-8...I'm for it in DSP! [:)]
I just spat my drink up! [8-|]
solo-x
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13 Nov 2008 10:30 AM
The dips in the power band of the 8 are a red herring IMO. You can tune much of that out with ecu tuning and changing the timing of those alternate intake ports/valves. ECU tuning combined with the open intake allowance in SP should net some power gains as well. A lot of the stuff Mazda did with the intake is likely due to emissions requirements more then anything else.
BrianGT
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13 Nov 2008 12:01 PM

Would a non-lsd RX8 be legal for STS? (random question, as I was looking at the Mazda site and saw that the sport model only has the LSD on the MT model)

-Brian

RX7 KLR
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13 Nov 2008 12:23 PM

solo-x wrote:
The dips in the power band of the 8 are a red herring IMO. You can tune much of that out with ecu tuning and changing the timing of those alternate intake ports/valves. ECU tuning combined with the open intake allowance in SP should net some power gains as well. A lot of the stuff Mazda did with the intake is likely due to emissions requirements more then anything else.

That may be true to some extent... I have been looking, with little success, for a Koni Challenge ST RX-8 dyno chart. Most of them use a Motec, so they should be right on what I would expect a fully built SP motor to produce.

Chiketkd
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13 Nov 2008 12:38 PM

solo-x wrote:
The dips in the power band of the 8 are a red herring IMO. You can tune much of that out with ecu tuning and changing the timing of those alternate intake ports/valves. ECU tuning combined with the open intake allowance in SP should net some power gains as well. A lot of the stuff Mazda did with the intake is likely due to emissions requirements more then anything else.

This is Cobb's attempt at tuning out those power dips (note dyno graph shows estimated crank hp):

While the dips were smoothed-out, they still remain. I'll be interested in seeing if there's any improvement with a Motec equipped RX-8.

solo-x
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13 Nov 2008 03:52 PM
Chike, do you know if the Cobb dyno is with a stock intake system? Were all the catalytic converters installed and going through an emissions legal header? With a rotary and today's emissions laws, I can't help but think that the stock intake and header must be a bit on the restrictive side and likely have a bunch of things done in an attempt to get the emissions down. An STU build wouldn't be able to get around things like the stock exhaust header and converters (at least not legally) or stock intake manifold. An SP build can.
RX7 KLR
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13 Nov 2008 04:25 PM

solo-x wrote:
Chike, do you know if the Cobb dyno is with a stock intake system? Were all the catalytic converters installed and going through an emissions legal header? With a rotary and today's emissions laws, I can't help but think that the stock intake and header must be a bit on the restrictive side and likely have a bunch of things done in an attempt to get the emissions down. An STU build wouldn't be able to get around things like the stock exhaust header and converters (at least not legally) or stock intake manifold. An SP build can.

Sipe had a custom intake box, hand built header and high flow cat on his STU RX-8.

solo-x
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13 Nov 2008 05:00 PM
RX7 KLR wrote:

solo-x wrote:
Chike, do you know if the Cobb dyno is with a stock intake system? Were all the catalytic converters installed and going through an emissions legal header? With a rotary and today's emissions laws, I can't help but think that the stock intake and header must be a bit on the restrictive side and likely have a bunch of things done in an attempt to get the emissions down. An STU build wouldn't be able to get around things like the stock exhaust header and converters (at least not legally) or stock intake manifold. An SP build can.

Sipe had a custom intake box, hand built header and high flow cat on his STU RX-8.

That's all well and good, but in SP you can change all the stuff AFTER the throttle body too. Also, Sipe had to make sure the car would pass an emissions test/not throw a CEL without being able to use any o2 fooler or other tom-foolery. A header that isn't built with those concessions would typically make more power. So, combine an alternate intake manifold, different tb (or even ITB's), no cats, no emissions concerns with the header or ECU tuning and I suspect that the torque dips go away and the torque levels increase. Obviously, just a theory, but one proven multiple times by other cars.

ps. You should put some cam gears on those things, move the torque curve down the rpm range. [;)]

RX7 KLR
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13 Nov 2008 05:20 PM
solo-x wrote:

ps. You should put some cam gears on those things, move the torque curve down the rpm range. [;)]

Waste of time... Max legal overbore is where its at. [Y]

whitecivic
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14 Jan 2009 11:17 PM

I'm finding it hard to believe that no one has looked into the results for this years National's and because it was dry both days this is a good gauge. So with Jason's driving his RX-8 in BS with a total time of 82.617 and the winner in DSP getting a 81.772 thats only .845 differents, with that Jason would have finish 6 th in the DSP class in a BS RX-8. So with a super light flywheel, 18x10 wheels (to get all the stick from the tires ) lighten his RX-8 at 350+ and getting 20% more Hp's and Tqr, probably more. That car will dominate the DSP class.

Jason, I get it, if you can get in a class you know you will win in, it's like the holy grail of classing but I'm writing a letter to the SEB with a lot more info, to put the RX-8 in CSP

W.

Chiketkd
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14 Jan 2009 11:43 PM
whitecivic wrote:
I'm finding it hard to believe that no one has looked into the results for this years National's and because it was dry both days this is a good gauge. So with Jason's driving his RX-8 in BS with a total time of 82.617 and the winner in DSP getting a 81.772 thats only .845 differents, with that Jason would have finish 6 th in the DSP class in a BS RX-8. So with a super light flywheel, 18x10 wheels (to get all the stick from the tires ) lighten his RX-8 at 350+ and getting 20% more Hp's and Tqr, probably more. That car will dominate the DSP class.

Jason, I get it, if you can get in a class you know you will win in, it's like the holy grail of classing but I'm writing a letter to the SEB with a lot more info, to put the RX-8 in CSP

W.

Umm...I proposed this, not Jason. Using your same argument, Greg Hahn's A-stock S2000 CR would have been third in BSP this year (0.9 seconds behind Berry's evo). Give him suspension, more power, lightended flywheel, bigger tires, etc and he would dominate the BSP class. Let me write a letter to move the S2000 to ASP! /sarcasm

Seriously, I didn't write a letter to move the RX-8 to DSP, but that doesn't mean I wouldn't be in support of the idea if someone else did. The RX-8 can't keep up with an S2000 in SP trim, and that car is being dominated by the Evos. The RX-8 is too wide and has too many seats to be in CSP. It's a tweener car -- to slow for BSP and too fast for the current DSP.

Btw, don't try to draw too many conclusions from Nats results in '08. One course HEAVILY favored narrow cars, which skews class-to-class comparisons.

murph1379
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15 Jan 2009 05:27 PM
Chiketkd wrote:

Btw, don't try to draw too many conclusions from Nats results in '08. One course HEAVILY favored narrow cars, which skews class-to-class comparisons.

But wouldn't that make his argument stronger, if the RX-8 was that close while being held back by that needle-threading element?

Chiketkd
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15 Jan 2009 07:29 PM
murph1379 wrote:
But wouldn't that make his argument stronger, if the RX-8 was that close while being held back by that needle-threading element?
If anything the winning DSP car (Rowse's E46) was held back more on the East course. Dimensionally the RX-8 is very close to an E36 -- with the E36 actually being slightly narrower.

It has been pretty well established in this thread that in terms of whp, SP weight, dimensions, etc. the RX-8 is a good fit for this class. However, the RX-8 has an advantage as it can run 305 tires like the E46's but makes very little torque like the ITR's. As Whipple summed it up earlier, the real "unknown" is just how much of an advantage having a well-balanced rwd double a-arm car would be in the class. For this reason I'm not writing my letter this year as I mentioned earlier. However, my "suspicion" is that the DSP class will speed up as the more powerful E46 cars are developed further (especially with the move to concrete). If/when the gap between BSP and DSP narrows, then this proposed classing change should have traction with more people.

Just my humble $0.02...
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