620 Land Speed Record

[Stoffregen Motorsports]

There's a reason racing cars don't use overdrive. Like Jeff said, under 1000hp and it's pointless. Even changing the diff ratio won't solve the matter.

[datzenmike]

The only reason is the 71B fifth isn't made for the constant full throttle strain. The top two gears in a Corvette are both over drives and they are not 1000 hp.

 

Horse power has zero to do with it. It's all about what the engine 'sees' as it's final overall gear ratio. A 12% overdrive 5th with a 4.375 diff is the same as a 4 speed with a 3.90 diff. Both will have the same top speed and RPM. How would it be different?

[Stoffregen Motorsports]

But Mike, the Corvette isn't a race car.

 

You don't want an overdrive in a 200 hp top speed racer.

[datzenmike]

They race Corvettes, so .... race car, stock ones can go 200+ MPH and they have two over drive gears and they are not 1,000 hp..

 

5th 0.81and 6th 0.67 are over drive....

 

 

What does 1,000 hp have to do with having an OD or not? If the engine cannot pull an OD to top speed then the diff can be changed to a higher number.

 

Already said the 71B OD is not a good idea for top speeds. You said the differential wouldn't solve this and I said it does. The engine doesn't care about the OD only the total overall gear multiplication.  A 12% overdrive 5th with a 4.375 diff is the same as a 4 speed with a 3.90 diff. Both will have the same top speed and RPM. How would it be different? Again, not advised but do-able. 

[scooter]

The od ratio is not worth the horsepower loss of driving the counter shaft. You wanna be in 4th.

 

 

Have you considered getting all your gears rem polished and using very thin oils in your trans and your diff? Atf?

[scooter]

Also you may get away running a 63 series dogleg in this application, its not very strong but once you get into 4th it would be okay. Smaller gears and bearings means less parasitic loss.. These things turn way easier if you grab the input shaft than a 71 series.

 

What about using atf instead of grease in the u-joints? It only has to run a few miles at a time.

 

I wanna hear the noise this thing makes, thats one beast of an L series. It doesnt look like a big bore short stroke engine though.

Thought you'd use a z22 block bored to 89 or 90 and de stroke it. Kinda looks like a stock bore l20b to me

[datzenmike]

The od ratio is not worth the horsepower loss of driving the counter shaft. You wanna be in 4th.

  

 

 

The countershaft and every bearing and gear in the transmission is engaged and being turned at all times the input shaft is turning. The countershaft is in a bath of oil and is flinging it around to lube everything. So just being in 4th is not going to save you much power, if any at all.

 

 Fourth 'gear' in a 4 speed isn't a gear at all, just a solid connection from clutch to driveshaft. Thus it is much stronger that any R, 1, 2, 3 or 5th if you have a 5 speed.

[Stoffregen Motorsports]

Already said the 71B OD is not a good idea for top speeds. You said the differential wouldn't solve this and I said it does. The engine doesn't care about the OD only the total overall gear multiplication.  A 12% overdrive 5th with a 4.375 diff is the same as a 4 speed with a 3.90 diff. Both will have the same top speed and RPM. How would it be different? Again, not advised but do-able. 

I'm saying that when you're racing and every ounce of HP counts, the overdrive is a source for power loss.

 

Why would you have the driveshaft spinning faster than it needs to be going and then slow it down with the diff?

 

I think his 1000hp number was an arbitrary attempt at making a point. And I agree.

 

BTW- he's already stated that he found a different trans that will work, and that he's actively pursuing the install, so this is all just a dead horse beating session.

[G-Duax]

The power drain of a set of over drive gears while in 4th gear, is no where as high as when they are being driven through if it's a production trans (helical cut gears), due to the much higher side forces when power is going through them.

 

That is why a helical gear LSD works so well.

When little power is being transmitted through a helical LSD, it acts like an open diff.

But when the power goes up, the diff will transmit huge amounts of power through both wheels.

 

Just saying.....

[datzenmike]

 

 

Why would you have the driveshaft spinning faster than it needs to be going and then slow it down with the diff?

 

 

 

You would match the differential ratio to have the engine operation at the RPM needed for the speed you want to go. 

 

You could run the race in third gear if you wanted, if the differential was too high geared. Many do on a short course and rarely get into 4th. You could also use 4th and 5th gear if the differential was lowered. 

 

 

 

 

 

There's a reason racing cars don't use overdrive...... Even changing the diff ratio won't solve the matter.

 

Yes it can solve the problem. A five speed with a 12% OD with a 4.375 is the same as a 4 speed with a 3.90 differential. So you could run an OD if you wanted and the diff ratio is how it could be done. Lots of cars have over drives, are raced and have huge top end speeds. It gives them good low speed torque through the gears and good top end speeds.

[Stoffregen Motorsports]

Math doesn't solve the problem Mike. I realize what you're saying, and on paper it works out, but in a car on the track, a direct drive is a better way to go.

 

Also, the 620 is a salt racer, which means he'll be going flat out for miles without lifting off the throttle. There are no short bursts on this track. He already isn't going to have enough power and any loss, whether it be friction or whatever, is unacceptable.

[datzenmike]

There is that.

[distributorguy]

In the end, Land Speed Racing is about wind resistance and HP.  The less parasitic loss, the more hp at the wheels, the higher the speed.  Wind has the final say in how much HP it takes to set the record.  This isn't roundy-round junk at 50 -130 mph in a Vette.    

 

I found a solution for the trans - don't run Datsun.  I can REM finish gears in my shop but won't need to with this one.  The tranny I chose runs a special fluid, lighter than a normal ATF. 

 

The engine is only bored 1.5mm over, crank destroked to keep us within the 2L rule.  The 2nd race engine takes it to the limit of the Nismo head gasket.  This one has room for repairs when we damage it.  Not if.  Its only a matter of when.  

[G-Duax]

There are all metal head gaskets in Japan, but they are very expensive.

Over $300 before all the fees to get it to the US.

Talked to Cometic, and they didn't seem at all interested in making an L4, even though they do make an L6 version.

 

Along the lines of parasitic drag, I cut the field coil on my alternator at full throttle using a switch on the throttle, and a relay.

The alternator does it's job at anything besides WOT.

But I seldom hold it wide open for miles at a time. Guess it would be OK if I ran a larger battery though.

 

Also been looking at all the cam needle bearing conversions they make for US pig iron V8s.

 

And, for my Toyota, just running a single, gapless top compression ring, instead of 2.

Ring drag is substantial at higher rpm.

 

Another thing I do to all race engines, is to polish the cylinder bores below where the rings travel.

[distributorguy]

I have a slightly finer crosshatch than most, an extremely fine ring package, and the field coil is dash switched.

[Stoffregen Motorsports]

HKS used to make the composite steel head gaskets. Don't know if they still do. There is another company that makes them, but I can't think of their name right now. The cool thing about them is that they are reusable and rebuildable, and even adjustable by adding or removing shims to raise or lower the compression ratio.

 

If you can't find one, I would just o-ring the block and bring to the track a few OEM Nissan gaskets. Even the GT motors still use OEM gaskets.

 

Hopefully you're not going to use head studs though as they make head R&R a pain in the ass.

[distributorguy]

I am using ARP head studs and a Nismo gasket.  ARP nuts are eaier than stock bolts, and we need more strength.  Over 15:1 compression, naturally aspirated.  Its not likely to see even 50 miles between engine rebuilds.  It'll be ok.  Once the motor is certified (if we back-up a record run), and if we fail the whistle test, then we pull the head.  No big deal.  4 hood pins, so that's not in the way, big pop-up tent to work under on the salt.  

 

Guys, when you offer advice, keep in mind this is Bonneville.  Relaxed pace, almost never full throttle to modulate tire slippage, very high compression, never touch the brakes, light load top speed racing with soft shifts.  Durability is only for RPM, not load until peak speed, then the load is wind not traction.  Its boat racing with wheels and salt and even less traction.  Nothing about it is similar to track racing.  

[Profile]

It's drag racing on a 5 mile dirt/salt track.

[Stoffregen Motorsports]

I guess using studs is the price you pay for such a high CR.

 

I freakin hate em.

[distributorguy]

I've installed SO many sets...  I like 'em.  Once you figure out how to NOT drop and lose washers and nuts it just becomes a way of life.  

 

Drag racing WOULD be like Bonneville if you needed a 3-4 TON car weight to have enough traction to achieve 200 mph.  That weight also has to be perfectly balanced to avoid spinning out.  Grease the track, then compare drag racing to racing on salt.   :thumbup:

[distributorguy]

So I think we have a solid plan for the fuel system.  Carter "black" fuel pump - 90 GPH, 7 psi.  Aeromotive ultra-low pressure fuel regulator with 15 psi gauge, 6AN and 3/8" OD stainless lines throughout.  

100 micron filter before the pump, tank modified with a 3/8" OD outlet for fuel supply.  Both vents tied together and Teed into a roll-over valve so the tank can't leak if we crash.  The pump is wired with a relay, 30A fuse, and impact/rollover switch (From a Ford Taurus).  

 

The carbs will be plumbed later with another 30 micron filter either before the regulator or two filters after the regulator to decrease the chance of debris restricting fuel flow.  Each carb gets its own line from the regulator.   Fuel starvation would become insanely expensive, so we're going to avoid that at all costs!!!

 

I've looked at doing a fuel cell, but most are just tanks anyway, with no real protection from a crash.  The factory tank is legal, and in a very safe place, plus it helps balance the driver's weight.  When I have a spare $1000 and no go-fast goodies to spend it on, I'll buy a Fuel Safe.   I've got $400 into this system, using a LOT of parts I already had around.  It could easily reach $2k if I bought all new goodies.  I still may have to buy a higher pressure pump to get the fuel pressure consistent.  We'll see how this plays out with the SUs for now.  The Webers get installed in about 3 months.  

[Stoffregen Motorsports]

Are the fuel inlet nipples on the SU's removable?  Some of them are not removable, while the threaded fittings vary between applications. Some are BSPT, some are straight threads.

 

Weber DCOE's use a 12mm x 1.5 thread pitch and Mikuni/Solex uses a 12mm x 1.25.

 

It would be nice to plumb -6 all the way to the carbs with fittings instead of hose clamps.

[distributorguy]

My Webers are 10 x 1.5.  Oddly small, but adequate.  I ordered -6 fittings for them, so they'll be well fed! The SUs don't matter.  They're for low rpm use, only to get the truck aligned, balanced, and work out a few bugs.  Plus they are on the spare engine.  The race motor goes in later with the Weber setup.  Their nipples are press-fit.  Only the older ones have banjo fittings.  

[distributorguy]

I stand corrected.  12 x 1.5.  Now I get to reorder.  Not sure where I crossed my numbers.  They mic at 11.88.  ???

 

Last night we got the fuel system basically finished for the test motor.  Need to work out throttle return springs and cable, choke cable, and add tranny fluid.  Then we hook up the battery and see what melts down first.   :thumbup:

[distributorguy]

No melts downs, but the 17 year old jet tubes on my "rebuilt" HS4 SU carbs decided they were never again going to accept fuel pressure.  Who knew fuel lines could fail in only 17 years???  Got the new ones installed this morning.  They hold 3 psi, so the next trick is to crank the motor to get oil pressure, then once the team is around to help and witness the giant blue cloud we fire it up.   :thumbup: