620 Land Speed Record

[distributorguy]

I wish longevity was part of my design, but the truth is that I'm happy if the engine holds together for 50 miles.  I'd of course appreciate more.  I was stuck with some pistons that weren't exactly ideal for my build in the past, and now those are destroyed, so I get to take it to the next level now.  

[datzenmike]

Longevity is relative. In this case long enough to get the job done. For a regular Datsun years and hundreds of K.

[Stoffregen Motorsports]

The $2000 price on a custom crank was about what we used to pay for Scat cranks back when I worked for Rebello. That was almost 20 years ago.

[G-Duax]

Not to be too negative here, but maybe just getting some successful runs on it before reinventing the wheel would be a better approach ?

 

Stock L-series rod bearing diameter has been working just fine for many people, running 10K+ rpm in Japan for decades,

But big bores have been a weak point, some blocks breaking through on the boring machine, as Stoffregen mentioned, and I have seen before.

Edited August 19, 2019 by G-Duax
spelling

[distributorguy]

I have 3 blocks that each need to be sonic tested.  We'll go as far as we're allowed with the best block.  The one we're using now is about 2/3 filled with block filler, and it appears we can go further as we have zero cooling issues.  We need to make the crank shims first, then finish the crank as we determine bore size, then order pistons, deck the block dead last.  There is a plan in place to make sure this isn't an unnecessarily weak time bomb.  Now that the EFI is well tuned, we should have better durability than in the past - tuning DCOEs at different altitudes.  I don't care if we end up at 87.5, 88, 88.5, wherever.  If we know this number before the crank is ground, we can pick whatever offset we chose and correct displacement.   

 

The reason to make the rod size smaller isn't a choice I'd recommend unless there's a reason for it.  Chevy rod bearings however are available in tri-metal with coatings for cheaper than a set of OEM quality Datsun aluminum bearings.  Plus it allows you to stroke the crank without welding.  

[G-Duax]

See a lot of Nascar engines going smaller still, like Honda journal size.

Might just be for qualifying engines, don't know.

Hell, they even run titanium valves with 6mm stems on those large intake valves, again, may have been for qualifying.

Bought a bunch of them for my Toyota, and a few sets of 5/16 stem valves for the Datsun, but need some undersize guides to run them.

 

Did you consider building an extra engine to haul with you next year ?

[Stoffregen Motorsports]

I worry that grinding the rod journals too small would cause the crank to break at a rod journal.

 

Main bearing shims are a great idea. What would you make them out of?

[distributorguy]

The cool thing about making the rod journals smaller is that they can go narrower as well, and grind a huge radius to prevent cracks.  Then guide the rods with the pistons for lower friction.  

 

Nascar is probably going to Honda sizes to make the rods significantly lighter, plus there are great bearings available for high rpm use.  

 

We've always considered building a spare engine.  My engine builder friend never got around to assembling it.  Been in the works for 4 years.  Now that he's invested in going out there with us, hopefully his motivation will increase?

At this point I think we have all the bugs worked out, just fine tuning the design.  These are all things I wanted originally, but couldn't afford or ran out of time.  Knowing what we need to accomplish, we'll still likely run into next summer to get the truck running on the new motor.  Once I figure out which block to use, I may send it out to someone with a 5 axis CNC to make sure the bores don't drift.  

 

I need to figure out how to make the bearing shims.  They'll either be tool steel, or install a set of bearings and bore them to size.  I haven't taken any measurements yet to know if that's feasible.  

[Valvebounce]

I just read this whole thread beginning to end yesterday. (sick day off work)  
 

Quite a hefty read.
Be interesting to know how fast your truck could go on a sealed road. I've had datsuns with less power, no safety gear, and lots of second had/original parts up to speeds above the record you're trying to break. (but with plenty of mods that would NOT be legal for your class) It's very flat where I live, so lots of roads where you can wind her right out. (just don't get caught!)
But that's the challenge isn't it?   

I'll be following this thread now for sure. 

[distributorguy]

I just had a long talk with our tuner last night.  We agreed that if we can do a standing mile run at 125 mph, we can break the record.  We just need to make enough power to do so.  

[Stoffregen Motorsports]

I remember the GT4 510s had a top speed of about 130. Some of that was likely the road course gearing, but a huge limiting factor was the box for a body. Luckily, the 620 has a slightly more aerodynamic front. And your motor should make more than the 230hp we were getting out of the L16s at the time.

 

125 mph seems doable to me.

[distributorguy]

We're likely not running the same tire diameter and rear gear ratios.  Frontal area is still huge.  For some reason we're still struggling to get over 200 hp however.  Still in negotiations about the FIA head, but I don't have enough info about it to make a legitimate offer.  I'm pretty sure this next engine build, done on a legitimate schedule, will result in better power numbers.  This time I get to design the pistons, which should be a small improvement over the old design we used in the past.  I think I'll try to get a different cam ground as well.  I'm bleeding off way too much cylinder pressure with the one form Schneider, despite the fact that the wear pattern is beautiful and the numbers it provides are theoretically ok despite that they are radically different from what I asked for.  

[Stoffregen Motorsports]

A full race L20B should be in the 250 hp range. A street driven 2300 makes 240, with 10:1.

 

You've got some work to do!

[distributorguy]

I should mention that's 200 RWHP, not at the flywheel...

Honestly the highest dyno number I've ever seen from an L20b is about 232 at the crank.  250?  Maybe with a SSS or FIA head?  I can't take mine any further.  No turbulence at .700 lift, its got to be the cam... its always been suspect.  

[Stoffregen Motorsports]

Yes, 250 at the crank. I built a few L20Bs for guys running vintage classes that made that amount of power.

 

200 at the wheels is good.

[distributorguy]

Well, I have an L18 crank with stock size journals prepped and ready to send off for offset grinding and indexing.  Sonic tested my block and its got plenty of room to bore to 88+.  While I'm getting the bottom end sorted its time to work on building a different head.  A quick chat with Dave Rebello and I'm second guessing my previous strategy.  I may be building custom intake manifolds soon as well...???

[datzenmike]

L heads are that good. When I lift the slides I can see all the way to the intake valve through my home made intake.  Shortest path between two points is...

[distributorguy]

My 1" thick throttle bodies have shortened my intake significantly.  Its time for longer, straighter intakes or a revision of velocity stacks.  The ultra-long intake I made for SUs made gobs of torque.  I may make an intake for the ITBs that gets them up into the hood scoop?  

[Valvebounce]

Only if you can do it without any sharp corners. The longer your runners, the lower number harmonic wave you can get. (At the specific rpm for that length) I once read that in R&D Jaguar achieved volumetric effeciecy over 100% (that's like forced induction!) At that one rpm with very long runners.

you know your gearing and tyre size. So you could build your manifold for a second or third harmonic at the rpm where you'll set your record. Also tunemployment the length of your headers to that engine speed, and spec your cam into that power range too.  To overcome that wind resistance you'll want to be right in tje sweet spot

[distributorguy]

Actually, our engine already reaches 115% VE - easy to trace in the Megasquirt software.  The numbers would be higher if our head ports were smaller?  Its time to take some volume measurements.  I'm pretty sure our SU manifold was long enough to hold a couple Liters.  Pics are on Insta at @jschlemmer

[G-Duax]

The higher the sonic wave number is, the less efficient it is.

Most nazkar engine intakes are tuned for the 3rd wave, just due to their relatively low rpm (for a race engine), and cramped engine bays.

Best efficiency is achieved with first wave length manifolds, but they are very long unless you are dealing with a 15-22 thousand rpm engine.

Second wave is shorter, but you start to loose large percentages of efficiency.

Third wave is less, and 4th isn't really worth messing with.

This is just manifold length, volume isn't really a consideration, just so it's not so small that air flow speed (from memory) exceeds around 300 ft/sec at max rpm.

The speed of sound at the temp you are seeing inside the manifold, and the barometric pressure determines runner length.

The air gets hotter the closer it gets to the head, unless you really isolate head temp from the manifold, so trying to get to the true speed of sound is difficult at best.

So calculations on paper can only get you close, lots of dyno time is needed to dial it in, and if you are not doing that at the altitude you plan on running at, you are just maybe getting in the ball park.

 

Some manifold runner length formulas say to use the peak torque RPM, which on a lot of race engines is 80-85% of the max HP RPM.

A second wave pulse is around 10%, a 3rd wave is 7%, and the 4th is around 4%.

 

And sorry, but I wouldn't trust VE numbers derived from a mega squirt at all....

 

[datzenmike]

Works best with individual runners and carbs or a large plenum. While the peak is real it isn't that narrow and ramps up and down over hundreds of RPM on either side. Chrysler did a lot of research and experimenting with this. It's power that's not 'free' but there for the taking.

 

 

Technically the slant six also had this incorporated into it's intake...

 Single stock bbl B&B carburetor.

 

When I was 19  I made an adapter plate and added a 318 2 bbl carburetor to my '64 slant six somewhat like below. From 45 to 90 it would stay with a friend's 283 Chevelle. The exhaust manifold was split front 3 from back 3 and it had dual exhaust with straight through Walker continentals. Christ it was loud.

 

 

Lord, this was 50 years ago!!!

[distributorguy]

I have a slant 6 A100 in the shop right now, with that same manifold...

 

As for intake design, a lot can be learned from seeing what other people are doing at Bonneville.  Basically they test air horn length and use those to tune the intake with as short a system as can be installed.  

 

Duax, VE is how all the tuning is done in MS.  If you can't trust the numbers, you can't tune it.  Everything basically remains fixed, and VE is altered to tune.  You can't change displacement, the injectors are a fixed orifice, and fuel pressure remains constant.  The amount of fuel you use is based on VE.  

[G-Duax]

Funny, when I tune an EFI system, I look at the A/F readings through the rpm band , and adjust pulse width to get to where I want it.

I also use my adjustable fuel pressure regulator to adjust the fuel flow through any set injector size.

[distributorguy]

I run the fuel pressure at the ideal setting for the injectors,  AFR is only a percentage of the adjustment, VE table is what is variable to get the pulse width into the correct range.  If you can get to the point where this works properly, the auto-tune works beautifully on MS.  Whose systems are you tuning?   I've also played with FAST, not AEM yet.