SCCAForums.com

ChrisSwearingen:

 

So on a car with my setup 750# front 400# rears, natural frequency somewhere around 2.6 hz front and 2.25 rear (thats from memory so you might want to calculate your own frequency) what should the shock dyno plot look like?

http://www.optimumg.com/techtips_techtips.htm

 

ChrisSwearingen:

*Note: it goes to the dyno on Saturday, I will post that info as well.   

 

Did you make it to the dyno and if so, how did it go?

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Andy Hohl

Thanks Kyle for the drive in the Shelby GT this year

96SM2:

ChrisSwearingen:

*Note: it goes to the dyno on Saturday, I will post that info as well.   

 

Did you make it to the dyno and if so, how did it go?

Oh you guys remembered I said that...

It went pretty well. It's a dyno dynamics dyno so the numbers are a little lower.  Last years motor made 119 on that dyno.  On a superflow at sea level, last years motor made 149.  SO..

Drum roll please.....  This years number is 170.  If you apply the same % increase that should be around 220 at sea level.  To me, the number is less important than the comparison between the two motors.  I have 42% more power this year.  

Chart is last years motor versus this years.

 

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Chris
51 SM2

ChrisSwearingen:

96SM2:

ChrisSwearingen:

*Note: it goes to the dyno on Saturday, I will post that info as well.   

 

Did you make it to the dyno and if so, how did it go?

Oh you guys remembered I said that...

It went pretty well. It's a dyno dynamics dyno so the numbers are a little lower.  Last years motor made 119 on that dyno.  On a superflow at sea level, last years motor made 149.  SO..

Drum roll please.....  This years number is 170.  If you apply the same % increase that should be around 220 at sea level.  To me, the number is less important than the comparison between the two motors.  I have 42% more power this year.  

Chart is last years motor versus this years.

 

 

Ok, now add another 40% and we're talking. :)

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Jesse
-2002-2006 E-stock 93 MR2 (sold)
-2007-2008 XP Spyder

129STS:

Ok, now add another 40% and we're talking. :)

But then what would I do next winter?  The limiting factor right now is the bottom end.  I have the appropriate external parts to add another 14- 25% right now.  I just don't have time before San Diego to rebuild the bottom end, nor do I want to do it mid season, so I guess I am stuck with this for this year.

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Chris
51 SM2

129STS:

Ok, now add another 40% and we're talking. :)

Something about a pot and a kettle comes to mind here. Which stock Camry motor do you drive again? ;)

Chris, that actually looks like a nice healthy curve to have while you continue to shake out the suspension. It can be hard to tune springs and shocks when you're doing nothing but holding on between corners. One of the things I'm looking forward to in my car is being able to turn the boost down to focus on chassis tuning.

My mind always goes back to the "underpowered" CSP and DSP cars that are often faster than the majority of the SM/SM2 classes.

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Randy Noll

rnoll98:

Snip 

One of the things I'm looking forward to in my car is being able to turn the boost down to focus on chassis tuning.

Snip

I see you and a co-driver signed up for the San Diego Tour is that your car?  If so might I suggest 2 or 3 psi as optimal boost for chassis tuning? 

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Chris
51 SM2

If it's Randy's car, he's going to have to rename the thread to "SM2 MR2 Build"...

What type of spring rates are you guys running on the NA/NB, with the 275's and FI?

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In slow, out fast.
In fast, out backwards.

rnoll98:

129STS:

Ok, now add another 40% and we're talking. :)

Something about a pot and a kettle comes to mind here. Which stock Camry motor do you drive again? ;)

For last year, we had plenty of power.  We got the chassis working pretty well, and now we want more power.  Plus, it gave me a year of figuring out that you can't exactly drive an XP car like an ES car.

 
And our stock Camry engine is still making 250+ at the wheels, and we're only 2035 lbs.

 

 

PS: For a SM2 Miata, I think my goal would be 300-350 at the wheels with typical gearing.  Just a 25-75 hp more than the car Ian took 2nd in a few years ago.  I'd be doing everything in my power to get the thing as narrow as possible too, and be using that as an advantage against the larger Vettes, RX7s, etc.  The MR2 is nice since it's kinda narrow, yet puts down the power.  It's just a lot heavier than a Miata....  at least a 2nd gen is.

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Jesse
-2002-2006 E-stock 93 MR2 (sold)
-2007-2008 XP Spyder

rnoll98:

Chris, What's YOUR ideal shock setup. Give the wolves something to chew on and they'll go nuts :)

Let's fire this back up.

Koni 2812s  750# front springs/ 400# rear

Front valving 233

Rear valving 150

 

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Chris
51 SM2

129STS:

Ok, now add another 40% and we're talking. :)

 

Same dyno, same motor, smaller pulley and bigger injectors 

 

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Chris
51 SM2

Now make the rest of the car as good as a top notch CSP car and you're there, Chris!

 -Andy M.
 

Are you sure you have that chart right? Any shock dyno chart I have ever seen shows rebound as a negative number.

boxboy:

Now make the rest of the car as good as a top notch CSP car and you're there, Chris!

 -Andy M.
 

And how much does a top notch CSP car weigh?   Just kidding Andy, thanks for the encouragement.  Based on this thread and what you know, other than a top notch CSP driver, what am I missing?  Still working on the spring rates a bit.  I "think" the CSP guys are a bit heavier on each end than I am and have a slightly larger front bar.

 

CHRISFP78:

Are you sure you have that chart right? Any shock dyno chart I have ever seen shows rebound as a negative number.

 I pulled the shock dynos directly from the info on the Koni site.
 

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Chris
51 SM2

Could be a type. Those charts look like classic roadrace valving. Typically you need the knee to move back about an inch per second on an autox car because of the slower wheel speeds. If you run on a bumpy lot, the bump would be correct but the rebound would need to move back the 1" per second or so IMO. If you are running high spring rates, like say over 500in lb than the rebound is to soft on the upper end of the scale (over 4" per second).

Thanks to all of you who questioned the shock dyno I posted from the Koni literature.  Because of you I learned two things today.

1) Guy Ankeny has to be one of the most patient and helpful people on the planet.  I called him twice today and got smarter each time.  He sent me the chart I asked for the first time, then when I called him back, he sent me the chart I really wanted and explained both of them to me.  Guy and Pro Parts, can't go wrong with them.

2) My dyno doesn't look like the sales brochure.  (Even if you flip it over)

 

 Let's talk about this one for the front of a Miata with 750# springs

 

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Chris
51 SM2

Much, much better. The knee is in the right place for  an autocross car. Now It's just a matter of getting the forces correct for your driving style. Is your car around 2000 lbs. If so I think that set up will

work well for you.  Might be a little soft on the rebound side if you run on a smooth surface.

 

Chris 

My car is 2247.8 lbs give or take, based on how much fuel is in the tank.  Add 210 for the driver and we are at 2460.

We are about half and half on smooth versus bumpy lots, but for this year I want to err on the smooth/Heartland Park side.

Thanks for the feedback. 

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Chris
51 SM2

Okay, having been called out for making Andy H's ears bleed in Ft Worth, and also battling sound at a local event even with the muffler on ( more power = more sound, go figure) I am doing something about the exhaust.

From the header back, it currently has a high flow 2.25" cat about 18" of 2.25 stainless to a 12" resonator, more 2.25" stainless to a Racing Beat muffler to a resonated tip.  And thats still too loud, but just barely.  The whole sound discussion thread aside, I have no problem being quiet where we need to, its just one more of the challenges we have to face, on the other hand, if I can pick up some gains at non sound controlled sites I will.

The current "plan" subject to your feedback and what the exhaust shop tells me is 3" resonator 18" long to 3" stainless to a shortie dual chamber muffler of some sort, more 3" back over the axle to a flange.  From there it's either a turndown and ear plugs for Andy, or a BIG muffler of some kind to a turndown that is still under the rear of the car.

Any suggestions as to brands and or configuration?  Will it a) be quiet and b) make power?

Any suggestions will be greatly appreciated.
 

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Chris
51 SM2

Chris,

 What's with all the exhaust pieces?  With what you described, I bet your exhaust is AT LEAST 15-20 lbs heavier than mine - which consists of a header & pipe to the diff, with an 18" resonator welded in the middle of the pipe.  I have a turn-down at the end.  That's it.  I do have a flowmaster I can hange across the back under the trunk, for a site with tight noise restrictions - but I've never had to use it for an event.  Guess I'm lucky we don't have sound-restricted sites. 

 -Steve

 p.s.  Your car seems a bit porky for an NA Miata.  My '99 was right at 2,200 the last year I ran SM2, and that was with A/C, an A/W intercooler, and the larger 1.8L brakes.  An NA should be lighter.  

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Steve Garnjobst
#75 XP
'99 Mazda Mutant