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130mph floating issue


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When exactly where exactly etc.

 

Are you in MN? Where about if so?

 

I know NOBODY in mn that is into these cars just old muscle. I'm currently in Anoka Mn right now. There is a new nissan that just opened up in coon rapids I'd like to get a group of people meet up as a regular thing, at that location. Are you or do you know people that may be interested in something like that?

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I'm just going by the speedo bub. I've also had the speedo tested- by radar, I'm not 100 percent sure if its 130 that i have not had done by radar. I have at 90 for sure. So I am sure its close. Your not helping so unless you would like to help keep the flaming and the random opinions to yourself or NICO.

 

On a side note: I do enjoy your quote in your sig.

Sorry........I didn't intend to upset you. I was just being a wise acre.

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I will be at Braianrd raceway in the spring/summer. Come on down to Road America :)

 

 

Hey guys. I am about to go racing at Mt Panorama. I expect to be doing about 130MPH or maybe a touch more down the main straight (Conrod straight) I have a slightly deeper than standard front BRE chin spoiler, a short MSA rear spoiler, headlight covers and open bonnet vents.

 

Based on the wind tunnel results (yes I know you can't combine results but I have no other choice) I estimate a reduction of overall lift from the standard 0.422 to 0.111

 

The standard lift of 0.422 requires 287 lb to counter. Do I understand correctly this means at that speed the car is 287lb lighter?

If so that means in theory my car will be 75lb lighter?

 

Is my logic sound?

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I have a picture of the splitter plate. It completely seals the front end so that air cannot get around the radiator or under the car.

Airdam.jpg

 

 

 

Notice that the factory wheelwell ducts are filled with brake duct hose(as well as the airdam ducts). Dual ducts are not necessary but blocking these upturned areas is required. You must also block the sides under the sugar-scoops.

dualbrakeducts.jpg

 

 

I sketched out what happens with and without the upper plate installed on an airdam.

 

Without the plate too much air gets under the car.

240Zsideviewbadairflowweb.jpg

 

 

With the plate installed; less air gets under the car and a stagnation zone expands in front of the car forcing more air to go OVER the car.

240Zsideviewgoodairflowweb.jpg

 

 

 

...

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Okay, I'm confused. What, which "plate' are you talking about? The one on the top of the airdam (bottom of the radiator?) Or a splitter plate (bottom of the airdam)?

 

If the top of the air dam, that's a good start but you would need to install a shroud or tunnel for the air entering past the grill to make all this really work. And you'd want to block off about 80-90% of the front nose as well to make it effective.

Edited by gnosez
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I'm just going by the speedo bub. I've also had the speedo tested- by radar, I'm not 100 percent sure if its 130 that i have not had done by radar. I have at 90 for sure. So I am sure its close.

 

Like I mentioned earlier, the speedo is not accurate at that speed. My indicated 135 was approximately 125; I calculated that from redline in 4th gear using my diff ratio and tire size. The poor little Honda turbo never knew what hit him, but he sure seemed fast on the fly-by I got after I slowed to the 65mph limit.
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Don't worry, I was doing 145mph (RPM/tire/gear ratio figured) once with the MSA Type 3 airdam and it was fine. It feels jittery but I always thought maybe its because you're going to so damn fast which would make steering very responsive. Of course the question then becomes, why are you turning at 145mph. Thats neither here nor there. I know in order to get around club rules that said no louvers we cut louvers on the tire wells from the engine bay to suck the heat out since there is a low pressure area on the wheel side of the well (wasn't on a Z). Maybe the idea of making louvers or something in the firewall so air goes into the valence area and out the slits right before the windshield may yield something neat...

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Keep in mind that the SAME airdam had a NEGATIVE impact when improperly installed. It had a positive impact when sealed to radiator support and sugar-scoop supports, with upper hood seal as well.

Edited by bjhines
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Take it easy chencho! This conversation is way hot. Is 10 miles off at 120 really not that much for the stock speedo, what kind of calibration error do they have? I mean if it's about the tires, then we're talking like 2" smaller than what it's calibrated for. Either way, the exact speed is moot.

Exactly. Plus certain tires my "poof" more than others at higher speeds I would think.

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Man i know i've maxed out my speedometer a few times on the highway in 5th gear at 20 pounds of boost on the Z32 transmission with a few hundred RPM to go before the fuel cut off.. (which means i was prob going 120 mph lol.. damn datsun speedo)

 

I just have a lowered suspension, air dam with a chin, air dam reinforcements and ducting and a BRE spoiler.. felt light but was a hoot =)

 

Sure the speedo is off.. dunno by how much.. but who cares.. scared the hell outta me.

 

I remember going to track days where the speedo was just past 135mph.. with a long sweeping left hander braking down to 110 mph or so. a little under-steer.. but i think with a lower and stiffer suspension and some under body work.. it would be stable

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Exactly. Plus certain tires my "poof" more than others at higher speeds I would think.

 

 

That too I suppose. And simply tire pressure at a given temp. I would actually measure the tire though rather than take the tire "size" into a calculation. Roll the car an measure, the farther you roll the better. I'm sure my autometer speedo is pretty accurate because it has you drive a mile to calibrate, and I think the specs on it are like +-2 at top end.

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If you compare sizes from stock to aftermarket then you will find that many S30 speedos are reading 10% too fast. This is comparing a stock 175/75/14 on a 5.5" rim to a 215/40/15 on a 7" wide rim. The stock wagon wheel had an overall circumference of 76.4" where the common aftermarket tires have a 68.3".

 

http://www.rimsntires.com/specs.jsp?item=Wheel-Tire%20size%20comparer&sw1=175&ar1=75&bd1=14&rw1=5.0&et1=0&sw2=215&ar2=40&bd2=15&rw2=7.0&et2=4&text1=&text2=

Edited by bjhines
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If you compare sizes from stock to aftermarket then you will find that many S30 speedos are reading 10% too fast. This is comparing a stock 175/75/14 on a 5.5" rim to a 215/40/15 on a 7" wide rim. The stock wagon wheel had an overall circumference of 76.4" where the common aftermarket tires have a 68.3".

 

http://www.rimsntires.com/specs.jsp?item=Wheel-Tire%20size%20comparer&sw1=175&ar1=75&bd1=14&rw1=5.0&et1=0&sw2=215&ar2=40&bd2=15&rw2=7.0&et2=4&text1=&text2=

 

Oh did he say he upped the size? That would obviously make the speedo unreliable...

 

That's a nice calculator though. I like the chart at the bottom with compatible tires. I wish it would approximate the tread width, but that's neither here nor there.

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