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620 Land Speed Record


distributorguy

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Iiternet and cell reception out here is awful!!  Just grabbed onto the hotel wifi, took 4 minutes to load this page.  

 

According to everyone who has been here for years, this is the worst salt they have ever seen.  Most of the big teams left Sunday or Monday.  

 

Here are the runs we've made so far:

99

102

105.9

107.8

 

Seems slow, right?  

Jump on an online wheel speed calculator and plug in our data:

3.89 diff

1;1 gearing in 4th

24.5" tall tire

8100 rpm

The salt is BRUTAL!!!

 

Potential speed is 151.8   Wheel slippage and traction loss here is amazing bad.  We're trying for 110 today, but first we have a big problem to fix:  One of the 5/8" upper control arms bolts from Beebani vibrated loose on our last run, and bent.  We'll have breakfast and be at the hardware store when the door opens at 9 am.   We also need to change jetting again - carb jetting is roughly 25% off from where we started.  I've been soldering and drilling all our jets until the AFRs look good and we get as close as we can.  Right now I just need to go WAY smaller on air correctors and see how it plays out.  

 

Error on my part:  the distributor needs to be on a separate switch from the main power, as the driver uses the Cool Shirt for quite a while, feeding power to the ignition for a along time with the truck not running.  

 

So far we have only been running the 2 mile rookie course, trying to work out all the bugs.  Hopefully we get a chance to hit the 3 mile short course to see what the extra mile will deliver.  It should get us up in speed significantly.  I'd be thrilled to break 110, given the conditions.  For now we're still faster than the 240Z team here from Japan.  

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According to everyone who has been here for years, this is the worst salt they have ever seen.  Most of the big teams left Sunday or Monday. 

 

Error on my part:  the distributor needs to be on a separate switch from the main power, as the driver uses the Cool Shirt for quite a while, feeding power to the ignition for a along time with the truck not running. 

Bummer. I'm sure it is still a valuable experience. A bad day racing is still better than a good day at work.

 

I've run into that problem with electric fans. Now any motor gets put on a relay.

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I hate those 5/8ths upper control arm bolts, they were always working loose in my work truck and then breaking, it sucked when they broke as the front of the truck dropped into the pavement.

In the end the threads got stripped out in them holes(driver side), and I had to buy longer bolts that threaded all the way thru the back and stuck out by the shock, I then put big washers on the bolts and then threaded a lock nut on them and tightened them up till I could not tighten them anymore, it collapses that piece of metal on the shock side of the shock tower, never had them break or work loose since, I also used a much harder rated bolt.

I had them 5/8ths bolts break several times(5-6 times?), sometimes only one of them, sometimes both of them, they always broke when I touched the brakes.

I always tell everyone that is switching over to disc brakes on the early trucks to drill them holes out and tap them for the bolts used in the disc brake 620/720 trucks.

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I could hardly wait to log on and see some results for today.  Hope it went well!

http://www.scta-bni.org/sw-race-results.html

Is the website with results, but the short course for th 15 & 16 is not up.  To find his truck in the 14th results, look at short course on the 14th and car # 1724.  I feel part of this as I've been watching the progress like everyone else for a couple years.

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Well we started out yesterday morning with a DNF.  Disappointing, but not surprising.  I tried a pretty drastic jetting change to learn something.  I learned not to do that.  

 

Then we got another member of our crew behind the wheel to get his rookie license, at 107 mph.  Our main driver pulled a 105 after that.  He lost some speed trying to use 5th gear - because at this point we're throwing in the kitchen sink to see what works and what doesn't.  We are currently sitting on the short course grid ready for the track to open for the day.  

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Losing speed in 5th means you are power limited. From 4th to 5th may be a 12% change and it's too much RPM drop. Changing the diff to 4.11 is a 5.6% increase in RPM. If your 5th is say a 12% OD change, this will result in an overall 6% change. The engine may tolerate this amount.

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I hate those 5/8ths upper control arm bolts, they were always working loose in my work truck and then breaking, it sucked when they broke as the front of the truck dropped into the pavement.

In the end the threads got stripped out in them holes(driver side), and I had to buy longer bolts that threaded all the way thru the back and stuck out by the shock, I then put big washers on the bolts and then threaded a lock nut on them and tightened them up till I could not tighten them anymore, it collapses that piece of metal on the shock side of the shock tower, never had them break or work loose since, I also used a much harder rated bolt.

I had them 5/8ths bolts break several times(5-6 times?), sometimes only one of them, sometimes both of them, they always broke when I touched the brakes.

I always tell everyone that is switching over to disc brakes on the early trucks to drill them holes out and tap them for the bolts used in the disc brake 620/720 trucks.

Are they 5/8" thread or 5/8" hex?

 

A Gr 8 5/8 fine thread bolt can take about 180# of torque, while the 7/16 fine thread bolt can take only about 60#.

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Just remembered something...

Really rough track surfaces can cause enough vibration to keep the floats/inlet needles from working properly.

Had that happen on a super kart (back then called FKE-3) with the stock float style carb that I built for a buddy.

Went to a large Tillotson HR carb, and the problem went away, plus had adjustable jets :)

He ended up winning the 93-ish SWRA champion ship with that set-up.

 

Was looking at using 4 of their big HD (44mm) carbs on mine, but was taking forever to find 4 matched carbs unless I was willing to pay through the nose for NOS ones.

 

You being from the land of 10,000 mosquitos, there has got to be some vintage snowmobile shops around (for next year). 

Walbro also made a carb in that size called the WD.

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Are they 5/8" thread or 5/8" hex?

 

A Gr 8 5/8 fine thread bolt can take about 180# of torque, while the 7/16 fine thread bolt can take only about 60#.

You need a 5/8ths socket to tighten them bolts, the threaded part really isn't that big, when Nissan went to disc brakes they went to a 3/4 inch head/socket, the threaded part is a lot larger.

I believe he has aftermarket BEEBANI upper control arms, I don't know what size holes the upper control arm mount bolt shaft has, but they likely are small to keep the upper control arms from moving around a lot.

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Just remembered something...

Really rough track surfaces can cause enough vibration to keep the floats/inlet needles from working properly.

Had that happen on a super kart (back then called FKE-3) with the stock float style carb that I built for a buddy.

Went to a large Tillotson HR carb, and the problem went away, plus had adjustable jets :)

He ended up winning the 93-ish SWRA champion ship with that set-up.

 

Was looking at using 4 of their big HD (44mm) carbs on mine, but was taking forever to find 4 matched carbs unless I was willing to pay through the nose for NOS ones.

 

You being from the land of 10,000 mosquitos, there has got to be some vintage snowmobile shops around (for next year). 

Walbro also made a carb in that size called the WD.

Side drafts have been used for years in offroad racing. I wonder how they handle it? They probably run the float levels a bit higher and maybe even have extended float vents.

 

Softer carb mounts (isolators) would definitely help.

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5/8 bolts. 3/4 wrench. The rotation of the heims may have grabbed the lock washer and loosened the bolt. I'll reconfigure the assembly maybe with a thrust bearing?

 

I'm now on a search for a close ratio gearbox and a low3s gear set. I still need to do some calcs after reviewing all the GoPro videos to document gauge readings.

 

The carbs were working great - we simply ran out of gears and rpms. We weren't lacking power. The truck pulled hard to 110 where we were going 8100 rpm. Across the 3 mile mark. We were able to pull 9k easily in 3rd. It's a matter of traction loss and not enough gear to get where we wanted to be. We will make appropriate changes and revisit the salt next year.

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If you use a 3/4 inch wrench to tighten the bolts holding the upper control arms on then you do not have the weenie bolts holding the upper control arms on I have been talking about, the ones I have been talking about use the 5/8ths  inch wrench/socket to tighten them.

I guess I don't know a lot about the 620, I thought when they changed over to ball joints they also used a collapsible column, but DMike says they used a solid column thru 1979, it appears the 620 had a lot of changes made to it over the 7 years it was made, but the column was not one of them.

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Yes Beebani!    I'm required to make a larger flange to mount outside the heim, so if they come apart, the flange will hold the heim in place.  That flange later bound up when the alignment was done (unknown problem to me) and that allowed the heim movement to loosen the bolt.  I'll make new spacers to allow full heim movement without making contact and red loctite at that time. Problem solved - and thanks for your offer to repair the issues I had, but they were my fault and I have them mostly corrected already.  

 

I think the biggest thing we learned from this trip to the salt is just how much wheel slip we can expect, so that we can set the truck up properly for next year to reach the speeds to set a record.  If we were really turning 8100 rpm in 4th, on pavement that's 152 mph.  152/110 = 1.38 = 38% wheel slippage.  We need roughly a 40% taller rear gear ratio, and more hp!  Anyone have a good idea there???   What options do we have around a 2.50 ratio with a 6-lug pattern without building custom?  

 

We also learned that:

ERC fuel sucks.  Their 100 octane unleaded may be required to burn at the rpm we run (break 9000 in 1, 2, 3.)

We shouldn't have any front brakes mounted.

We should use rear disc brakes.

We can run a little hotter spark plug.

We can probably advance the timing a bit - to make up for crap fuel.  

A close ratio trans with a push start is the only way to go!!!  

The ignition needs its own dash switch.

We need more suspension travel, AND more rear ballast.   

Probably 20 more items on the checklist for next year, but those are the big ones.  

 

I'm not so sure the carbs were having an issue with the track - its greasier than it is rough.  Jetting was the largest carb issue - caused by the fuel and radically changing air density.  The 5 mile tow to/from the paddock was brutal, and caused most of the other problems we experienced.  Once we started leaving our truck by the start line overnight, less things rattled loose.  I'll need to recheck the float heights, as I suspect they changed from the beating they took, but no spacer or isolator will eliminate the 9" deep holes in the road we have to drive.  Imagine orange traffic cones sticking only half way out of several holes along that road!

 

Time to start doing more homework and clean up the mess in the shop fro Monday...

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Wasn't the salt surface wetter this year than most? Isn't this a contributing factor to wheel spin? Next year may be drier.

 

A 720 2wd mid ratio transmission with the zx input gear set gives...

 

1st... 2.972..... needs a big push off.

2nd.. 1.702.. 43%.... 4,560 RPM drop to 2nd from 8,000

3rd... 1.171.. 31%.... 5,520 " to 3rd from 8,000

4th... 1.000.. 15%.... 6,800 " to 4th from 8,000

5th.... off the charts OD forget it.

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Mike, I think I have both of those transmissions - if the 1980 is a wide ratio?  COOL!!!   I have a new Chevy 3500, so we can push until the truck is ready to take over!  

 

If you watch this video, the AFR was in a good range the evening before, when it was 88 degrees and 14% humidity.  The morning this was filmed it was 72 degrees and 35% humidity and the top-end mixture went crazy rich, yet it was still our best time because the salt is drier in the morning, and traction  is better.  Yet we were still clocking 151 mph by the tach, 110.7 by the GPS.  

 

https://www.youtube.com/edit?video_id=pFAYzhYWV0Y&feature=em-upload_owner

 

Yes, this year was WET.  A lot of the old timers who have been racing for decades walked away on Monday, yet plenty of folks still set records throughout the week.  It just shows that if you plan for the worst, you can still succeed.  

 

That Wagoneer diff may work great, or it may leave us sorely disappointed at 127-8 mph?  I'm willing to do some research and figure out if it will pan out.  I'll also go measure the Cutlass 12 bolt diff I have with a 2.55 ratio and see if I can get shorter axles for a reasonable price.  

 

I can't wait to do some serious dyno tuning to figure out what we were missing.  

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