620 Land Speed Record

[distributorguy]

We get to run a hood scoop, so I took a Camaro scoop (late model) with a rear vent and stretched it to 8" high.  That should get air through the engine bay for cooling, to some extent, and allow fresh air into the cowl for the air cleaner since its a low pressure area.  I know air wont flow both ways, but its the best chance I have to get direct outside air into the air box.  I can't vent it forward by the rules, unless I build a different hood scoop to do so.   Since aerodynamics will play a larger role at 130 mph, I chose to use the scoop primarily for aero and whatever happens with venting is hopefully also beneficial.    

 

I've never needed water wetter.  In this case, I suspect its necessary.  We did use distilled water.  I always have some around the shop for topping off batteries.

[Duke]

On the topic of float bowl vents, from my understanding they should be vented into the air box, especially if it will be seeing any kind of pressure higher than atmospheric.  If the float bowls are not vented into the box, the pressure differential between the intake air and the float bowl can cause a lean condition.

 

In other news, 1 month until Bonneville!  We are hopefully going to be firing our car this weekend, can't wait to actually hear it run!

[distributorguy]

Thanks Duke - it makes perfect sense when you spell it out for me like a newb!   

T-28 and counting.  

[distributorguy]

I'm so glad that we're running out of things to work on before August 12th!  

Last night I finished the install of the fire suppression system, and finalized the install of an additional firewall brace on the driver's side.  The new air box is 100% installed, and we have 5 throttle return springs, as 2 are required per carb, plus there's one on the pedal to help with all the solid linkage, should binding occur under load?  The air filter is now held in with bail clips for ease of inspection.  

 

We're building a scatter shield for the transmission bellhousing - 1/4" plate construction in 2 pieces so it can be unbolted and removed while the transmission is in place.  I had a ballistic blanket custom made, but by using different motor mounts when installing the race engine, we now have significantly more room around the transmission, so we'll run both.  The tech inspectors should be ok with that.   

 

Tomorrow the team will gather to start the race engine for the first time.  This will make or break the trip.  Finger crossed.  If the starter can handle the compression with our current battery, we'll build a stout battery hold-down.  Something that'll survive a few rolls, should that occur.  

 

Today I hope to receive the SFI rated flat roll cage padding for the helmet support structure I still need to build.  My goals are to have that done before the weekend is out, wife allowing.  

 

Then its off to the chassis dyno next week, once the carbs are dialed in a bit closer.    

[distributorguy]

Last night we fired up the motor and broke in the cam - all went PERFECTLY!  I'll try to get a YouTube video posted and linked.  Its one of the loudest naturally aspirated gas engines I've ever heard.  If you were on the exhaust side of the truck you had to yell at the top of your lungs to have a discussion, and even then it was difficult to hear.  It doesn't sound much like a Datsun anymore.  Time to grab the Bose headphones off the lawnmower to get some tuning done - although 1/3 turn in on each idle mixture screw and it runs right at about 12.2:1!  Easy to get it at 13:1 with another smaller adjustment - no load at 2000 rpm cam break-in speed.  No idea what the rest of the fuel curve is doing, yet.  

 

Our driver also built a tow bar that we can quick-connect to the push truck to tow to/from the pits.  

[Crashtd420]

Congratulations... can wait to hear it...

I laughed when I first fired my motor, I planned for every possible failure and nothing happened.... damn thing just ran and sounded good....

Glad nothing happened to hold up Bonneville..... can't wait for the results and videos to come....

[distributorguy]

 

It started hard - just getting fuel into the huge carbs, no choke, on a very cool night.  Likely 120+dB in person!  Sorry for the low-res video.  

[Crashtd420]

Sound was all I cared about in that video... it sounded wicked.....

I love the sound of an l series motor...

[wayno]

It's alive!!! :)

[datzenmike]

I don't think the cam needs any 'break in'. That's for push rod V8 chevys that rely on splash oiling from the crank. They need revving enough to throw oil around. The L series cams are filled with oil under pressure and drilled to lube the rockers. If you painted the lobes with a lubricant you're good. The two different metal surfaces will wear in by themselves with more than enough oil even at idle.

[distributorguy]

Mike, this cam is beyond your wildest dreams, as far as lift, duration, and centerline go.  Let's just say I lost well over .100" on the factory base circle diameter when the new blank was ground.  Its not everything I asked for, but close.   I'd throw specs at you, but its a bit of a secret until we get out to Bonny.  

 

The surfaces needs to be broken in. The cam is rubbing on a rocker arm the same way it would rub on a lifter. Hopefully the hardness and the coating on it hold up for a while.  Seat pressure is 125lbs -  higher than stock to make sure valves don't bounce "over the nose".  

 

And today I'll finish welding up the helmet cage with a swinging arm to help exit the cockpit, now that its been approved by the council!!!  Yay!!!! (doing my happy dance)

[datzenmike]

The surfaces needs to be broken in. The cam is rubbing on a rocker arm the same way it would rub on a lifter. Hopefully the hardness and the coating on it hold up for a while.  Seat pressure is 125lbs -  higher than stock to make sure valves don't bounce "over the nose".

It sure is. Racing oil or ZDDP additive?

[Charlie69]

If it is a new cam with black on it it needs brok in.  Hihg in zinc motor oil or zinc additive for first 500 miles or the lobes will flatten and the metal will be all over in the engine.

[distributorguy]

Amsoil break-in oil with zinc, another bottle of zinc additive, and of course a good cam lube were all implemented.  Yes, the cam was heat treated and had a black coating, secret stuff I'm not privy to.  Whatever Schneider uses, which they claim is a process that can only be done "properly" in 1 or 2 places in the US.  

 

It looks like I need to go MUCH smaller on air correctors, as fuel mixture is good through 4k.  Stays at about 12.25:1.  Then it goes leaner as rpms go above that.  Only takes about 2 seconds to get from idle of 1200 up to 7500 rpm, with no load.  It wants to rev far past that, but that's the point where it passes stoichiometric, so I ran it up there once.  Today I go on the hunt for Weber air correctors.  I think we have one local shop with a good selection.  Worst case scenario, I solder mine shut and drill them to size for the dyno Thursday.  

 

Yesterday I got the helmet cage finished, with approval from the tech committee.  The 5th point for the seatbelt was welded in place.  The interior got a fresh coat of paint.  The grille badge was installed along with taping the headlights so if they break we don't leave glass on the salt.  A lot of the finishing touches are being completed.  It feels good to know we're almost ready to pack up and haul West.  

[Stoffregen Motorsports]

Doesn't Pegasus stock Weber jets? They're in Wisconsin. A day away by UPS.

[distributorguy]

Their selection is ok.  I thought they were a couple states over - MI or OH.  ???  Pierce has all sizes and they give me good prices as a sponsorship kind of deal, but not really.  

 

I found 4 spare air correctors and soldered them up.  Tonight I'll drill, fit, and test to see what happens.  

[G-Duax]

Question,

If jetting at say 1000' altitude, how much will it change at 3000' at the salt?

[distributorguy]

Rumor has it, only a air corrector change or two will be needed at altitude.  First time out there with a truck, so I guess we'll see how that plays out.  I'll have a leaner main jet and lots of air correctors to play with.  I just made my spare set into 130's and I know the 160's are really lean here, so I'm saving those for the salt.  Its amazing what you can do with a small torch, a little solder, and a set of jet drills.  It was much easier to polish them up in the lathe as well.  I think just the flux alone added enough solder to change a jet size!

[G-Duax]

Soldered/re-drilled a lot of jets over the years, but mostly single cylinder bike engines.

I've been warned about differences in depth of filler solder, small differences in bore finish, etc., from one jet to another on multi-carb set-ups.

But I'm sure you are aware of that........

[distributorguy]

Yep.  The most critical seems to be the length of the "choked" hole.  They need to be similar or flow is restricted radically different.  I haven't noticed much of a difference with the larger bore step in side the jets being different however, as long as the transition is smoothly tapered.  Its nice having a mini-lathe to polish these up and smooth things out.  Even the factory jets in these carbs were all over the place.  Its going to be a PITA at the salt.  

 

I need to see what changes take place with these new jets and order up the real thing tomorrow to have in a kit for the salt.  Then I can keep messing with the oddball spares and use those for soldering.  FOr now its back to gluing down rollcage padding.  Sniffing glue and drinking beer.  Tomorrow morning I'll tune when its not 95 with 90% humidity.  

[Stoffregen Motorsports]

That's funny. I have a story...

 

Building my second 510 race car back in 1994, passed out in the back seat area while using some kind of solvent to remove the glue leftover from the removal of the headliner. Woke up drooling on myself.

[G-Duax]

Are you sure it was the glue ?

 

[distributorguy]

My guess is that on the dyno I'll need to take the mains jets richer by a step and drill out the air correctors a bit.  Mixture is close, but relatively unstable at high rpm.  This morning's test was better than before, but mixture at high rpm was scattered, like you normally see at idle.  Hopefully I'm not losing a cylinder already.  The Australian dude who built a motor similar to this lifted his head tuning on the dyno, and I don't think we're far from doing the same.  Its a really abusive way to tune.  The good news is that we (I) still have 3 weeks to correct anything that happens.  

 

I think that cat has the right idea...

[G-Duax]

Not sure I would be that brave (trying to tune a 15:1 cr engine on a dyno).

 

Think you could simulate salt flats altitude using a thicker head gasket at twin cities altitude?

[distributorguy]

The altitude change is more about air density than compression ratio.  Going to 14:1 with a thicker head gasket will leave me with the same dynamics, likely requiring the same fuel mixture.  

 

The dyno session isn't going to be looking for peak power.  It'll be some (relatively) easy pulls to 4, 5, 6k as fuel mixture gets closer and closer to ideal.  I'll likely shoot for 13:1 so that we're closer to correct on the salt.  We'll reserve pulling to 8k+ for the salt.   If I can see peak torque numbers, I'll have a good idea of where we'll land for hp.   Tomorrow.   :sick:

 

 

By the way, built a severe-duty battery hold down cage last night.  Ran out of metal so its 1 strap away from being finished and installed.