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Last Post 23 Nov 2012 05:16 PM by  TeamRX8
RX-8 to DSP?
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RX7 KLR
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06 Nov 2008 02:38 PM
solo-x wrote:

I don't mind having the class improve in speed. The current cars though all have a major handicap. The BMW's have weight, cg height, and suspension design. The ITR has driveline. The e30 has power and suspension design. The 2.5RS has power, suspension design, and weight. Where is the handicap that the 8 is cursed with?

You can't use PAX to say that the 8 won't be competitive in CSP. To say that, you would then have to say the miata would be competitive in BSP. Leave PAX out of it. An 8 is much closer to a CSP type car then a DSP type car. Yeah, the 8 is heavier then a miata, and wider too, but it has a bunch more power. A CSP 8 would look a lot like the new miata in CSP, would it not?

The RX-8 has lack of Tq, the CSP cars make more. [:'(] And our curve is not flat, major dips and peaks as the valves open.

Who said anything about PAX?

solo-x
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06 Nov 2008 03:09 PM
RX7 KLR wrote:

The RX-8 has lack of Tq, the CSP cars make more. [:'(] And our curve is not flat, major dips and peaks as the [b]valves open[/b].

Did I just read that right? Or is there some sort of butterfly in the intake or something?

RX7 KLR wrote:

Who said anything about PAX?

One of the other posts mentioned CSP PAX being close to BSP PAX, therefore the RX8 would get beat in CSP too.

mwood
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06 Nov 2008 03:13 PM
RX7 KLR wrote:

Who said anything about PAX?

Must have been one of those NWR guys...[:P]

solo-x
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06 Nov 2008 03:14 PM

Oh yeah, and the ITR has a major dip in torque right in the middle of the curve.

Remember a post comparing the wheel torque vs. weight of various ESP cars (back when the rally cars when in ESP) in 2nd gear made a while back? What happens when you do that with the ITR, RX8, E30, E36 and E46? I know the gearing of the ITR makes up for that low crank torque number, and I suspect the same is true for the RX8.

RX7 KLR
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06 Nov 2008 03:26 PM
solo-x wrote:
RX7 KLR wrote:

The RX-8 has lack of Tq, the CSP cars make more. [:'(] And our curve is not flat, major dips and peaks as the [b]valves open[/b].

Did I just read that right? Or is there some sort of butterfly in the intake or something?

RX7 KLR wrote:

Who said anything about PAX?

One of the other posts mentioned CSP PAX being close to BSP PAX, therefore the RX8 would get beat in CSP too.

There is a shutter valve and variable intake valves to help give it massive Tq, they open at a preset RPM.

Guess I am blind, the only reference I see about PAX is from you.

RX7 KLR
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06 Nov 2008 03:33 PM
solo-x wrote:

Oh yeah, and the ITR has a major dip in torque right in the middle of the curve.

Remember a post comparing the wheel torque vs. weight of various ESP cars (back when the rally cars when in ESP) in 2nd gear made a while back? What happens when you do that with the ITR, RX8, E30, E36 and E46? I know the gearing of the ITR makes up for that low crank torque number, and I suspect the same is true for the RX8.

Someone smarter than me do the math and figure out if this thing is a class killer.

Car (1st 2nd 3rd 4th 5th 6th FD)
04-'08' RX-8 (3.760 - 2.269 - 1.645 - 1.187 - 1.000 - 0.843 - 4.440)

Dyno (Dynapak 3000) from a T3 RX-8, Green air filter and strait pipe cat-back

solo-x
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06 Nov 2008 04:05 PM
RX7 KLR wrote:

There is a shutter valve and variable intake valves to help give it massive Tq, they open at a preset RPM.

Guess I am blind, the only reference I see about PAX is from you.

Two discussions + same topic = oops! You are correct. Disregard!

Could you not massage the transition points of the shutter valve and variable intake valves to smooth out that torque curve? With a completely open intake system, you could probably do a whole bunch of neat things to improve the shape and height of the torque curve.

solo-x
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06 Nov 2008 04:19 PM

Quick, rough math, assuming 210whp at 58mph and 2800lbs race weight, the 8 accelerates at .466 g's. A BMW at 200whp at 58mph and 2950lbs race weight mathematically accelerates at .426. The R, at 170whp, 58mph 2600lb race weight is accelerating at .411 g's. If you can get me a HP vs. speed csv output in 2nd gear I can plot that more accurately.

The 8 will be a little slower off slow corners that it can't go to first gear on (hrm, sounds familiar) but since it handles so much better, it'll be cornering at a higher speed. It's lighter so it will transition better. It uses the tires better so the fronts or rears won't burn off halfway through a 60 second run. Etc.

Chiketkd
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06 Nov 2008 05:11 PM
solo-x wrote:

Quick, rough math, assuming 210whp at 58mph and 2800lbs race weight, the 8 accelerates at .466 g's. A BMW at 200whp at 58mph and 2950lbs race weight mathematically accelerates at .426. The R, at 170whp, 58mph 2600lb race weight is accelerating at .411 g's. If you can get me a HP vs. speed csv output in 2nd gear I can plot that more accurately.

The 8 will be a little slower off slow corners that it can't go to first gear on (hrm, sounds familiar) but since it handles so much better, it'll be cornering at a higher speed. It's lighter so it will transition better. It uses the tires better so the fronts or rears won't burn off halfway through a 60 second run. Etc.

Nate,

I assume those are race weights with a 150lb driver?

If so, use the same weight for the BMW (E36) as the RX-8. They will both be in the low 2,700lbs range in SP trim w/o driver. If you want to use an E46, then the BMW's weight will be higher (maybe 2,950-3,000), but so will the power as well as they can use the ZHP motor.

DSPBMW
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06 Nov 2008 06:38 PM

If a good BS RX8 is around 2800lbs then a good S/P RX8 should be around 2550lbs.

To many fine details are overlooked when trying to reduce weight.

So we've got about 150lbs lighter, similar power outputs, much better suspension, better weight distribution, a considerably lower CG.......

This just might be a car where there is no good place for it. But it's definately more sports car based (CSP) than sedan based (DSP)

solo-x
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06 Nov 2008 06:55 PM
Chiketkd wrote:
solo-x wrote:

Quick, rough math, assuming 210whp at 58mph and 2800lbs race weight, the 8 accelerates at .466 g's. A BMW at 200whp at 58mph and 2950lbs race weight mathematically accelerates at .426. The R, at 170whp, 58mph 2600lb race weight is accelerating at .411 g's. If you can get me a HP vs. speed csv output in 2nd gear I can plot that more accurately.

The 8 will be a little slower off slow corners that it can't go to first gear on (hrm, sounds familiar) but since it handles so much better, it'll be cornering at a higher speed. It's lighter so it will transition better. It uses the tires better so the fronts or rears won't burn off halfway through a 60 second run. Etc.

Nate,

I assume those are race weights with a 150lb driver?

If so, use the same weight for the BMW (E36) as the RX-8. They will both be in the low 2,700lbs range in SP trim w/o driver. If you want to use an E46, then the BMW's weight will be higher (maybe 2,950-3,000), but so will the power as well as they can use the ZHP motor.

Yes, weights with driver. I was using what I remember of the Mike/Chris e36 weights and the weight of my car this season. The BMW power number is probably on the high side as I think it may fall off quicker then what I guessed at. If someone can get me a dyno plot of a BMW and the 1st and 2nd gear ratios of that car too I could probably throw together something a little more comprehensive.

solo-x
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06 Nov 2008 06:58 PM
DSPBMW wrote:

If a good BS RX8 is around 2800lbs then a good S/P RX8 should be around 2550lbs.

To many fine details are overlooked when trying to reduce weight.

Good point. I've already pulled 60lbs out of my ITR compared to a DS ITR and I've still got the AC in it and stock swaybars. My car could easily loose another 100lbs in the off season, and with the new brake allowance possibly even more. You've got a tough chore ahead of me if you're gonna try to convince me that an RX8 can't loose more weight then a car that didn't come from the factory with sound deadening for the express purpose of saving weight.

gavin
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06 Nov 2008 07:28 PM

Chiketkd wrote:

Gavin,

I'm not sure someone in their right mind would build one. Let's look at a perceived mid-pack BSP car -- the S2000:

  • The 2.2L S2000 motor makes more power and torque in SP trim than an RX-8 (240+whp & 170+wtq iirc)
  • A BSP S2000 should be in the 2,500lbs range (AP1 AS S2000's can touch the upper 2,500's)
  • The S2000 is narrower and has a smaller wheelbase than the RX-8 making it more nimble/tossable

All of these are in the favor of the S2000 and Jason Uyeda previously campaigned his. While he trophied in the car, he was well back from the Berry evo and has since moved onto a different class. Why would an RX-8 fair any better?

Sorry, late to this response, but....huh? Because of of an actual S2000 that was built for BSP, that isnt as fast as an EVO, on national courses that are relatively small and medium grip(that we apparently wont be going to anymore)....a theoretical BSP RX8 (that hasnt been built) is a good match for DSP?? wat?

I thought part of the whole deal for moves was...first you have to build the car for the class and THEN see if its too high or too low for the classification. Am I wrong on this?

PS: No one in their right mind would ever bother to build a FWD car for DSP either, I mean, havent you heard, its impossible to get close to the BMWs.(Hi Nate ;) )

PPS: "Why would an RX-8 fair any better?"..... Got me, but at the last leg of the cali divisionals, Jason dusted off the S2000 and beat the Berry-mobile in a straight fight. What does that mean? I dunno. Course dependent? oh yeah

Gavin
Chiketkd
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06 Nov 2008 09:14 PM
solo-x wrote:
Yes, weights with driver. I was using what I remember of the Mike/Chris e36 weights and the weight of my car this season. The BMW power number is probably on the high side as I think it may fall off quicker then what I guessed at. If someone can get me a dyno plot of a BMW and the 1st and 2nd gear ratios of that car too I could probably throw together something a little more comprehensive.

(Note the dyno plot of a low budget DSP car with a 2.8L M52 and the long post by Terry Fair outlining what #'s a top dollar build can achieve) 

As an FYI, Mark Sipe did a top-dollar build for STU and he got his '05 RX-8 down to the low 2,700lbs range on a very low fuel load (braille battery, race seats, etc). With additional a/c & sound system delete but adding weight back on for heavy 285-305 r-comps (over 265 street tires), I think a realistic SP race weight for an RX-8 would be ~2,650lbs. So I'm in agreement with the 2,800lbs race weight you used (w/ a 150lbs driver). 

Speaking of whp, while dynos can vary from one to another, I'm finding it hard to find many RX-8's with SP legal mods making over 200whp. Most are in the 190whp range which matches the plot that Isley posted.
DSPBMW
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06 Nov 2008 10:17 PM

All the little stuff everyone says/thinks oh it's not a big deal. It's only a couple lbs. And that's right.

But there might be 15 things like that. And 30lbs is definately worthwhile.

Trust me every single allowance in S/P can be a weight reduction oppurtunity.

DSPBMW
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07 Nov 2008 08:15 AM

See my posts below that, by DSP74. Some of the stuff those guys talk about offers ZERO gains......Pistons=NO gains. Coatings are not legal, it isn't legal to be any lighter, stock type and number of valve reliefs. Forged is actually a little bit heavier than cast. Cast offers better thermal stability and therefore better ring sealing.

Rods, crank, etc. Balanced but NO lightening. Very little to be gained if any as far as actuall output is concerned.

Gasket matching the intake=very little gain. If there is a big step then an imeasureable gain will be had. Admittedly a tiny improvement but not measureable. Creating the hourglass port shape at the gasket, that will happen when gasket matching the intake, isn't a good thing. Ideally there would be a smooth taper from plenum to intake valve.

Gasket matching the exhaust will LOSE power.

There very well may be gains in the intake system....The M50 intake and M20 intake flow pretty decent. And while TOP END power will probably be picked up, you will undoubtedly lose low end grunt with a short runner or ITB intake. Maybe a swap to a lower gear and more shifting could take advantage of that. But why. You are giving away the advantage the six has over the ITR-low end grunt.

There are TINY, TINY, TINY gains that may not even be measureable in machining details. But even this depends very heavily on factory allowed specs. For instance crank and rod undersize dimentions (max undersize crank=reduced bearing speed) and head skim etc.

As you can see this magic uber expensive S/P engine just isn't possible. Huge money can be gained with header fabrication I'm sure, but vs a quality currently available part there is only tiny amounts to be gained here.......

Chiketkd
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07 Nov 2008 10:19 AM

gavin wrote:
PPS: "Why would an RX-8 fair any better?"..... Got me, but at the last leg of the cali divisionals, Jason dusted off the S2000 and beat the Berry-mobile in a straight fight. What does that mean? I dunno. Course dependent? oh yeah

Gavin,

You will note that I said "perceived mid-pack cars " when referring to the S2000 in BSP. However, the RX-8 is no S2000 in SP form and never will be -- it will make less hp & torque and be 150-200lbs heavier. The S2000 will always be smaller in size & wheelbase and on the right course these advantages can be used to its favor.

Btw, you don't always need to have someone execute a high-dollar build before a car is considered to be moved. Case in point is a recent Fastrack in which the CSP to DSP move of the RSX (all) was put out for member comment.

At the end of the day, the RX-8 is an inexpensive, fun-to-drive car which doesn't have the power to run in BSP or the light-weight and small size to run in CSP. On paper it looks like a DSP car, but due to the suspension and drivetrain layout it may be too fast for the class as it currently sits. The car sits in a no-mans-land in SP where I guess it will remain for the time being...

P.S. I've personally decided against writing a letter at this time, but may revisit the idea 1-2 years from now...especially if DSP continues to speed up and closes the gap on CSP/BSP. I think the E46's will come to dominance in the class.

skeeter119
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07 Nov 2008 10:58 AM
Chiketkd wrote:

At the end of the day, the RX-8 is an inexpensive, fun-to-drive car which doesn't have the power to run in BSP or the light-weight and small size to run in CSP. On paper it looks like a DSP car, but due to the suspension and drivetrain layout it may be too fast for the class as it currently sits. The car sits in a no-mans-land in SP where I guess it will remain for the time being

I had a similar dilemma when I got the Crossfire classed last year in SP. I wrote a letter requesting it to be classed in CSP since it would have the power of a DSP E46 BMW but weigh about what an E36 weighs and a double wishbone suspension. I basically got a response of it not being in the spirit of the class which was small 2 seat roadsters without much power. I then suggested it be classed in BSP on the same line as the SRT-6 so you could run the supercharged motor with the manual transmission and it got classed there. The problem became it is far more expensive to do a motor and wiring harness swap to get that motor to work in that car than it would be to put together a decent SM2 car with more power. It is had been put in CSP I would have taken the car there but it would have taken so much money to see if the car was even competitive in BSP. Sorry for the thread hijack.

ChrisFranson
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07 Nov 2008 11:22 AM
Chiketkd wrote:

P.S. I've personally decided against writing a letter at this time, but may revisit the idea 1-2 years from now...especially if DSP continues to speed up and closes the gap on CSP/BSP. I think the E46's will come to dominance in the class.

I know we have more development to do in Mike's e36. Not as much in the engine department but we really need to get the car so it's able to use the power it has. There's no reason to think that the lighter weight of the e36 won't offset the power and rear suspension advantages found in the e46.

DSPBMW
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07 Nov 2008 01:49 PM
ChrisFranson wrote:
Chiketkd wrote:

P.S. I've personally decided against writing a letter at this time, but may revisit the idea 1-2 years from now...especially if DSP continues to speed up and closes the gap on CSP/BSP. I think the E46's will come to dominance in the class.

I know we have more development to do in Mike's e36. Not as much in the engine department but we really need to get the car so it's able to use the power it has. There's no reason to think that the lighter weight of the e36 won't offset the power and rear suspension advantages found in the e46.

Yeah all the cars are pretty close. The E30 has a subpar rear suspension and less power, but is smaller and lighter. E36 more power better suspension but bigger/heavier, and E46 more of the same on all acounts.

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