Jump to content


Photo

620 Land Speed Record


  • Please log in to reply
566 replies to this topic

#561 Stoffregen Motorsports

Stoffregen Motorsports

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 3,901 posts
  • Location:Cool, CA
  • Cars:http://www.4wdandsportutility.com/features/rover/0611_4wd_1957_range_rover/viewall.html

Posted 10 November 2017 - 09:26 AM

Work has proceeded, slowly.  Last month I managed to assemble an S10 rear axle - 2WD with a 2.72 gear set and a mini-spool.  This will help us overcome our loss of traction, and get our wheels spinning a little faster so we can possibly get our top speed where we need it.  We lost 40 mph due to wheel spin.  Very disappointing. 

 

The axle is larger and beefier than the stock rear axle, same width.  Its modified with C-clip eliminators.   I just need to get it installed and build up rear disc brakes.  Then the old axle goes into the 620 at the other end of the shop - the parts truck is getting built back up into a driver.  I have to decide if its getting painted or not before I go too nuts assembling it.  Its actually amazing how many leftovers we have from building the race truck.  Do we build a clone of it in street trim?  

The S10 axle was a score then. 2.72 is pretty damn low, but then I have zero experience on the salt.

 

I built a race car out of spare 510 parts, mostly leftovers from my dad's and my brother's cars. Set the pole at SPIR in its first race. Then DNF'd because of a dirty fuel tank...

 

Paint or no paint depends on the look. How does it look now? Rusty is cool, as long as it's not swiss cheese.



#562 distributorguy

distributorguy

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,135 posts
  • Location:Metropolis, MN
  • Cars:77 Datsun 620, 73 Datsun 620

Posted 10 November 2017 - 11:27 AM

2.72 has a theoretical top speed of 202 with our setup.  40% wheel spin allows us to barely set a record.  Hell, we capped out on speed for 3/4 of a mile.  We have time to get up to speed.  Get traction, add power, and voila!  

I was told to go with the highest gear ratio we could get.  I should have listened... 



#563 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,302 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 10 November 2017 - 12:32 PM

Like racing on ice. Isn't there a way to increase traction???? 

 

Narrower rear tires? Same weight on less footprint.

 

Can solid tires be used?


Posted Image

#564 distributorguy

distributorguy

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,135 posts
  • Location:Metropolis, MN
  • Cars:77 Datsun 620, 73 Datsun 620

Posted 10 November 2017 - 12:58 PM

If you ever drove down a washboard gravel road filled with potholes, would you want solid tires?  

 

Our current tires are Goodyear Frontrunners - 24" tall, 5.5" wide at the sidewall.  If we go up to a 25" tire like the fronts, they are significantly narrower, as are the 26"ers.  We run 55-70 psi air pressure.  We were faster with lower pressure (like having additional shocks).  

 

Increasing traction is the name of the game.  We can't use any electronic traction control, or at least I don't think we can.  I think that falls into the "no aftermarket electronics" group of rules under Production class.  We've added several hundred pounds of sheet steel in the bed to add weight, although we may take a different course of action and shift the weight rearward, while of course adding more.  One of the key features I added was a set of custom leaf springs, more like you'd find in a 3/4 ton modern truck - thicker, wider leafs, and more of them to handle all the weight we stacked in place.  Essentially we went from 3 1/8" thick leaves to 4 1/4" thick leaves, and we've pushed them almost flat with ballast.  I may add a "factory" overload leaf in place as well?  Because of all that, I don't see the need to add traction bars, but maybe it would help?  Basically make the front of the leaves a 4-link.  Then we need an additional safety loop under that link in case we break it.  Another 1/2 day project and $300 that may pay off?  

 

Due to how rough the course is (like a rutted frozen/snow covered lake) , we have to find a "nimble" suspension setting that allows the tires to follow the rough course, while keeping contact with the salt at all times and not bouncing.  I'll work with Viking shocks locally to try to develop something that'll help.  I'm afraid to go away from the torsion bars since they work so well.  Coil-over shocks are far more restrictive, although we could add more front weight bias and lower the front end more if the springs were stiffer.  

 

Keep throwing ideas at me guys!  We need all the help we can get!!!  



#565 wayno

wayno

    Datsunahaulic

  • Senior Member
  • PipPipPipPipPipPipPipPipPipPip
  • 12,986 posts

Posted 10 November 2017 - 01:33 PM

No matter how fast or slow you go on a washboard surface your still on a washboard surface, the faster you go the smoother it gets the less a shock and leaf will effect anything as your riding on the very tops of the washboard by then, it's like skipping a rock on water, your in the air more than you are on the ground.

I suspect you cannot add a wing to force it onto the ground, so your left with rake and weight to play with, if you could play with sheet metal on the bottom it would make a very big difference, but that is not stock and likely not allowed in your class, your back to rake and weight again.

Did you see any difference when you added weight, it would seem to me that the lower the rear the harder it would be to control the front as it will even make less contact on the surface, to me it seems like you need to get the best angle/rake, and then when you add weight it has to be even distribution between front and back to keep it at the best angle. 


 

 


#566 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,302 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 10 November 2017 - 02:11 PM

What about narrower front tires, like pizza cutters. Less effort to push them through the salt.

 

Or narrower ones on the back so more pounds per square inch coverage.


Posted Image

#567 distributorguy

distributorguy

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,135 posts
  • Location:Metropolis, MN
  • Cars:77 Datsun 620, 73 Datsun 620

Posted 12 November 2017 - 12:13 PM

We are running the narrowest tires made on front, and we'll add them in the back.  

 

As of our last few runs, we were at roughly 48/52 F/R weight bias.  We can go up to 55/56 rear bias and it shouldn't be trying to spin out.  Front caster angle is corrected to 8+ degrees, and will be more once I modify the upper control arms to allow more.  This stabilizes high speed steering, and the thing drives straight as an arrow at 110 mph - one hand on the wheel type driving even on the rough surface.  Watch the Youtube videos I posted to see.  

 

I'd love to lower it more, add a "drip tray" belly pan) under the engine bay, etc... but it would risk us losing a record if we achieved it to a protest.  I can alter the hood scoop to push more air around the windshield, and that's the only legal aero called out in the rule book.  At this point, our best money will be spent on tuning and hp.  I'm sure we fell short of our goal by a mile - too many thing didn't happen that we needed to happen with the camshaft and AFR tuning, fuel, spark plug choices, etc...  We can and will make a lot more power next year.  Beginner's growing pains.  Its not going to come easy.