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#541 distributorguy

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Posted 28 August 2017 - 04:11 AM

Parachutes are required over 175 mph.  

If the course wash slushy, they'd either move it or stop racing.  Its hard to describe the conditions without being there to experience it.  Its like hard packed snow over wet snow.  In the afternoon, the water comes up to the surface so its more slippery hard packed snow.  In the cool and breezy evening, the water evaporates and/or recedes and the surface dries out.  

 

Yes, I need enough braking to stop a 4K lb. truck - but not lock up on a slippery surface.  If (when) we get to breaking 150, we add a chute.  One of the things I learned at Bonneville this year was how to pack a chute.  Cool stuff.  



#542 datzenmike

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Posted 28 August 2017 - 05:33 AM

Drove my old VW on a frozen lake. Doors and fenders cut off. Top speed? 45. Any faster the engine (32hp?) was able to over power the rear wheels and no amount of steering would keep it going straight and around and around it went. Sounds similar. Can you increase traction with more aggressive tread tires? Maybe narrower ones in front? Like pizza cutters?


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#543 distributorguy

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Posted 28 August 2017 - 05:50 AM

We have pizza cutters on all 4 corners.  Basically motorcycle tires - Goodyear Front Runners.  Tread won't help.  Weight helps.  If you keep your center of gravity forward of your center of pressure (using ballast) you can gain weight and never spin out (like Burt Munro's explanation of throwing a rear-weighted dart).  For those who don't know, that's a "World's Fastest Indian" reference.  

Frontal air pressure versus traction is quite a thing.  Mad science.  Many equations I don't understand, but I'm decent at interpreting principles and experimenting.  The key is to go as light as possible without losing an unacceptable amount of traction.  And keep down-force on the drive wheels.  



#544 datzenmike

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Posted 28 August 2017 - 06:42 AM

I like Hopkins.

 

Can you deflect more wind up and over the cab by lowering the front? and back?


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#545 Stoffregen Motorsports

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Posted 28 August 2017 - 08:21 AM

If you keep your center of gravity forward of your center of pressure (using ballast) you can gain weight and never spin out (like Burt Munro's explanation of throwing a rear-weighted dart).  For those who don't know, that's a "World's Fastest Indian" reference.  

 

I can picture the cigar and toothpick now.



#546 datzenmike

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Posted 28 August 2017 - 10:54 AM

Sometimes a cigar .... is just a cigar.


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#547 G-Duax

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Posted 28 August 2017 - 11:07 AM

How did this go from the salt, to Monica Lewinsky ?



#548 distributorguy

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Posted 28 August 2017 - 11:49 AM

LOL!!!!

 

The truck is as slammed as far as I can take it without removing the inner fenders (they're already heavily modified - so much that I had to modify the clutch pedal), and the back needs a little rake for down force on the bed cover - maybe more than we have?   At this point, we can't go lower without removing the crossmember under the front of the oil pan, which I'd be afraid would open the oil pan to hitting the course more than it already can.  

 

I can deflect more air over the cab by stretching the hood scoop to the absolute legal height limit of 8", and extend it closer to the windshield.  That's the only allowable aero advantage we can take in production class.  I was able to mount wind tells on the hood scoop opening to see that air is in fact entering the scoop at the windshield.  Probably too much.  I will restrict the hood opening at the air cleaner to prevent more air from entering the engine bay.  I cannot push air from the radiator out the hole in the hood, as that's considered "venting" - illegal in production class for aero reasons.    Picture a late model Lotus to see how beneficial it could be.  

 

We have tight steering at 110, so I think front downforce is ample.  We are VERY close to 50/50 weight distribution.  Maybe even a little rear biased at this point.  That's the next step before disassembly - back on the corner scales.  



#549 distributorguy

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Posted 30 August 2017 - 07:37 AM

Maybe a dumb question, but given that traction doesn't exist on salt, is there ANY benefit to upgrading from 26 spline axles to 30's?  I can't fathom it would matter.  Either way, I have a GM 10-bolt diff and a 7.5" ring gear.  Weak, but it only sees 200-ish hp and very limited traction.  



#550 Ooph!

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Posted 30 August 2017 - 09:21 AM

Just thinking about your lack of traction at speed. If you have downforce on the front you should need less weight percentage statically on the front. My logic being as you move along the air pressure is forcing the front of the truck downward giving the steering wheels traction.

But in the rear it's a truck and probably have very little downforce if any.

 My experience is Dirt track racing, and generally use a larger rear weight percentage, mostly for traction on exit (on the throttle)

 54% rear is a very common number, if you watch these cars ( dirt modified and Late models ) depending on adjustments and track conditions the left front wheel can sometimes come off the ground, although not desired it does indicate how much force and weight is being transferred to the rear and yet there is still wheel spin.



#551 Stoffregen Motorsports

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Posted 30 August 2017 - 09:25 AM

Maybe a dumb question, but given that traction doesn't exist on salt, is there ANY benefit to upgrading from 26 spline axles to 30's?  I can't fathom it would matter.  Either way, I have a GM 10-bolt diff and a 7.5" ring gear.  Weak, but it only sees 200-ish hp and very limited traction.  

That's a good question. I think you're on the right track and that spline count doesn't matter. The only difference that may matter is the axle shaft diameter. At speed, there has to be a ton of loading on the axle, and maybe a larger shaft will be more durable. It is, after, a semi floating axle and I wouldn't want a wheel coming off at high speed due to a broken axle.

 

Are the 30 spline axles larger than the 26 spline shafts?

 

Just thinking out loud.



#552 distributorguy

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Posted 30 August 2017 - 06:33 PM

Ooph,54% rear weight at 130 mph is going to make the truck spin out unless we double the weight in the rear or more, and also add weight in the front.  Throw a rear-weight biased dart as hard as you can and hit the board.  I dare you.   B)  I think we're already 49/51 F/R at this point which is sketchy.  A little front aero lift an we're screwed.

 

Even 32 spline axles still take 1.400" ID bearings.  My guess is that it'll break the ring gear before we come close to breaking an axle.  I built an '87 S10 back in 1991, with an '86 IROC 5 liter tuned port motor, put 33" mudders on it, and beat the hell out of it off road for a few years.  Eventually I broke the ring gear driving to work one morning on a mild incline, under light throttle.  Besides, if we break an axle it'll have C-clip eliminators on it so the axles will be retained and a wheel can't go flying off.  Unless the outer bearing also comes apart simultaneously???  



#553 Stoffregen Motorsports

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Posted 31 August 2017 - 07:56 AM

I don't know anything about the S10 diff or axles, so you are ahead of me on that one.

 

Even with c-clip eliminators, the wheel can fall off if you break a shaft. The bearing can only take so much before it lets loose.



#554 distributorguy

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Posted 31 August 2017 - 01:09 PM

Its a sealed bearing, pressed onto the axle, then bolted to the housing.  If the axle breaks, it'll more than likely be inboard so you have time to come to a stop before it exits the vehicle.  You're right - not always does it "work as planned,"  but the likelyhood of losing an axle is much lower than c-clips which worked great off-road.  Its still a much larger gearset than the 620 axle uses.   Maybe not stronger, but larger.  



#555 G-Duax

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Posted 31 August 2017 - 01:35 PM

Still think one of these would be a better choice:

http://www.ebay.com/...99ZnfOm&vxp=mtr



#556 distributorguy

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Posted 31 August 2017 - 02:34 PM

I don't because its not allowed in Production class, and it takes more hp to operate.  It'll come later, with a V8.  Maybe a Cummins twin turbo V8.