620 Land Speed Record

[Stoffregen Motorsports]

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.

[distributorguy]

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???  

[Stoffregen Motorsports]

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.

[distributorguy]

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.  

[G-Duax]

Still think one of these would be a better choice:

http://www.ebay.com/itm/Halibrand-Quick-Change-rear-end-with-9-extra-gear-sets-/302425598484?hash=item4669f86a14:g:Wa4AAOSwX99ZnfOm&vxp=mtr

[distributorguy]

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.  

[distributorguy]

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?  

[Durty Dave]

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?  

Push truck for the race truck, maybe?

[Crashtd420]

Push truck for the race truck, maybe?

I was gonna say make it the tow rig, but I like that better... I suppose it could do double duty...

[distributorguy]

We barely have enough room in the race trailer to bring a pit bike with, but I'd LOVE to use it as a push truck!!!  It would never, ever be able to haul a 8000+ lb trailer across the Midwest, through all the mountain passes into Wendover.  I'd be afraid its not heavy or strong enough to use as a push truck.  I suspect we'll be close to 4000 lbs for the race truck next year.  On greasy salt.  The push truck is my 1 ton Chevy 4-door long box.  

It would be very cool to watch a 620 push starting a 620 however!

[Stoffregen Motorsports]

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.

[distributorguy]

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... 

[datzenmike]

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?

[distributorguy]

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!!!  

[wayno]

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. 

[datzenmike]

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.

[distributorguy]

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.  

[distributorguy]

In our quest to make more power, I'll be doing some flowbench testing on carbs in the coming days.  We have dual DCOE 50's on it now, which have turned out to be a tuning nightmare with the varying calculated altitude of Bonneville.  I've acquired a set of 2" SUs and if they appear to flow enough for the motor, we can try those on the dyno this Spring after I make a custom manifold to fit them.  They bolt up to a stock Hitachi side draft manifold, but the runners are WAY too small.  By welding portions of 2 different manifolds together, I'm pretty sure I can make them work well.  The true beauty is that a jet change is a simple turn of a 5/8" wrench.  Adjustable jets, not an entire tool box filled with expensive options.  For $14 a pair, I can have 3 sets of needles on hand for less than we spend on Gatorade per day, and that's the extent of tuning we'll face.  

 

I'm still tossing around the idea of no front brakes.  Reduced unsprung weight and they really don't get used anyway.  Its nice to have them, but not essential.  Maybe I'll leave them one more season until we get another driver licensed?  Its more of a comfort thing to have good pedal feel.  

 

Still haven't had time to pull a front hub to see if there's room to drill them with a 5-lug pattern.  Our front wheels are custom, so I'm not sure I want to hunt for another set right away.  Its not beneficial for a higher top speed, so its on the "to do" list, but not at the top.  

 

If I don't hear from Beebani soon, I'll have to order some bottom-taps to make new adjusters for the upper control arms.  The aluminum ones look like the threads are pulling out of them.  Not good.  

[datsunwizard]

If using the SU's, you might want to get a book by David Vizard in which he bench flows SU's and modifies them for higher flow rate. Back in the day, David was considered one of the best on flow theory.

[Stoffregen Motorsports]

I think going to SU's is a step in the wrong direction. No SU equipped L4 has ever made more power than a similar engine equipped with dual PHH or DCOE carbs.

 

For the record, I have always like Mikuni/Solex carbs over Weber carbs. I am not alone in this either. Even Frank Honsowetz likes them better. Most of the top teams use/used them on Datsuns so the knowledge base is much larger than with the DCOE crowd.

 

If you're having problems tuning, why not give Rebello a call and see if you're in the ballpark? For the right price, you could even hire someone to come help you tune at the track. That would probably be cheaper than the investment into the SU's, which you would most likely not be happy with anyway.

[G-Duax]

Do the rules keep you from going EFI ?

[distributorguy]

Actually, that's not entirely correct.  A friend of a friend has spent 2 weeks on the dyno tuning carbs to the end of their lives, and found out that a properly prepared set of SUs beat Webers time and time again for "horsepower under the curve."  Its a matter of sizing correctly, and its a lot easier to profile a needle and chose the correct dashpot oil & spring combo than to tune an idle jet, emulsion tube, main jet, and air corrector x4 a few times a day at Bonny.  In the end, what matters is AFR, and that its consistent.  I'll have hingeless floats so the bouncing won't disrupt float level (and emulsion tube sizing), the throats are actually BIGGER than DCOE 50s, not to mention years of tuning SUs on British cars.  Tuning around a 5000' elevation change throughout the day should be much easier with set of variable venturi carbs!!!  If the flow bench tells another story, I'll ditch the SUs.  

 

I know Vizard's book well on Tuning the A-series and all his flow bench testing.  What I need to know is at which needle station will 1 3/4" and 2" SUs (I have a set of each) flow enough to match out peak head flow - 235+ cfm.  Also, how many modifications might it take to get there, and at that flow, how much of the piston can I cut away to aid in piston lift?  I know how modifying the bridge can result in erratic fuel metering, and splitting the shaft with button head screws on the butterflies can result in a small cfm increase.  Its time to get the flow bench tuned up and ready for some testing!!!  I'll also get a baseline for the Webers.  

 

BTW, as for price, the 2" SUs are a trade for a couple distributor rebuilds, and the 1 3/4" setup is brand new - a trade for an odd-brand distributor test machine that wasn't very precise.  

[distributorguy]

Do the rules keep you from going EFI ?

 

Yes.  Unless the same vehicle/body was available from the factory with EFI in more than 500 units (with documentation).  It would bump us into modified, so the record jumps from 129 to 145.  

[Stoffregen Motorsports]

I guess the next question is how much horsepower you are making now, with the 50's? If you're not making at least 235-240hp with your setup, something's wrong.

 

And your friend did this on an L series 4 cylinder?

[distributorguy]

All the testing was done on MGs.  200+ HP B-series.  Very similar 5-port head setup, although cam in block.  We never got to test the engine on the dyno.  Ran out of time (and money).  We're shooting for 2 dyno sessions minimum this Spring/Summer.  

 

The cool thing about the SUs is that we're not stuck with a set jet size.  Well we are, but the needles can be replaced, and the jet height can be adjusted infinitely.  Want a .001" change?  Easy.    Weber jets are a frickin' mess.  Buy 4 - 180's and you get a 172, a 174, and 2 176s.  They're all over the place.  Junk. I know the guy making the SU needles, and they're spot-on.  So are the jets.  Tunable.  I just hope I can make them work.  Then we can set a record and move on to a crank trigger and EFI.