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620 Land Speed Record


distributorguy

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Back to the professional TIG welder tomorrow.  Made a small change or two.  Now the fresh air gets hammered into the carbs (will have velocity stacks!) and the throttle linkage just got simple.  

 

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I am not sure I understand how this works, what I see is the carbs pointed backwards and when the truck is moving forward it seems to me that the air going by the carbs would try to suck air out of them being the air around them is moving towards the windshield, the faster one goes the more suction that is created, velocity stacks would make it even worse.

This is what I see, now I am no means any kind of expert on this subject.

I always thought that the stock SU carb manifold was good because there was basically only one turn the air mixture had to make before entering the cylinders.

I have a set of 7 inch intake manifold extensions for the L block with fins inside that make the air spin down the extensions after going thru the stock intake/carbs(was on a 510 with a stock single carb manifold, it had a Weber), I have been told the extensions give it more torque, I do not know if that is true, but they were strange extensions so I bought them to keep them from being scrapped, I took them to Canby and they drew a lot of attention, especially being they are so heavy.

I also thought it was better to have all intake tubes the same length, and the exhaust tubes a certain length also to help with exhaust flow(scavenging), I am asking about all this as this is how I learn how things work, getting the info from the folks doing it is the best way.

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He has a cowl induction hood scoop (opening pointing at the windshield).

The windshield creates a high pressure area at speed, thus with the carbs pointing at it, are being fed with higher pressure air, while at the same time the truck is more aerodynamic than if the scoop was pointing forward.

 

It's too early for me to go into intake theory about length, but it has to do with the inertia of the air column moving down the runner, and also sound wave movement in the port, from the point the intake valve opens, out to the mouth of the carb, then back to the valve again.

This wave will make several trips during the induction phase, and getting it just right will give a small boost in power.

Best power will be made on tuning to the first wave, as it's the most intense, but only slightly, and leads to very long intake runner length.

Currant Nascar engines run on 3rd wave tuning, so the intake will fit inside the hood.

 

A person can get lost in figuring this out, as the speed of sound varies with both temp, and atmospheric pressure, and it is only good for a very narrow rpm range.

I have seen many fast engines completely ignore this, and be quite competitive.

You could spend weeks on the dyno, perfecting the intake length, say in Minnesota, and it would be all wrong in a different part of the country.

 

What he is doing here, with 360 degree pairing of intake pulses, is far more beneficial, as it maintains a more steady air flow through the carb.

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Wayno... I saw those extensions at Canby and knew what they were for. But wouldn't it hit the brake master or strut tower? Indeed they were heavy and looked like 5 lb of brazing.

 

I always imagine a long hallway packed with people running towards the exit. When the valve (door) closes they can't all stop, and bunch up under pressure while the people farther back keep moving forward. When the door opens again whey begin moving forward under pressure from the moving column behind.

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To further expand what Duax is describing, the pulses are essentially the measured amount of fuel and air that are packed into each cylinder, on each firing stroke.  As the air pressure changes, so does that volume.  In a place like Bonneville where corrected altitude varies every hour, its a fruitless exercise to try to plan for a specific temperature, barometric pressure, and humidity level unless you are one of the top teams who get to run first every day.  We ran as early as 8am and as late as 6:15pm  last year.  That was equivalent to nearly 3000' elevation change.  Because of that, I tried to keep the runners roughly the same length, and let the chips fall where they may.  I didn't even bother taking a single measurement.  Most folks out there bolt carbs directly to the engine, so this will either cause some laughing or head scratching.  I suspect we'll end up back with Webers eventually.  

 

We used wind tells all over the windshield to verify airflow directions last year - based on turbulence at the base on the windshield.  The cowl scoop works very, very well!  These carbs will be force fed as much as if they faced directly into the oncoming wind, if not more so.  

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I am not sure I understand how this works, what I see is the carbs pointed backwards and when the truck is moving forward it seems to me that the air going by the carbs would try to suck air out of them being the air around them is moving towards the windshield, the faster one goes the more suction that is created, velocity stacks would make it even worse.

This is what I see, now I am no means any kind of expert on this subject.

I always thought that the stock SU carb manifold was good because there was basically only one turn the air mixture had to make before entering the cylinders.

I have a set of 7 inch intake manifold extensions for the L block with fins inside that make the air spin down the extensions after going thru the stock intake/carbs(was on a 510 with a stock single carb manifold, it had a Weber), I have been told the extensions give it more torque, I do not know if that is true, but they were strange extensions so I bought them to keep them from being scrapped, I took them to Canby and they drew a lot of attention, especially being they are so heavy.

I also thought it was better to have all intake tubes the same length, and the exhaust tubes a certain length also to help with exhaust flow(scavenging), I am asking about all this as this is how I learn how things work, getting the info from the folks doing it is the best way.

 

 

And wayno, post pictures of said extensions please, or PM them to me.

I like saving images of weird stuff.....

 

 

Yes Wayne, what Duax said and please post a pic of your manifold here!!!  

 

IMG_6622.JPG

 

IMG_6623.JPG

 

Pretty sure these are them. I wasn't sure what they were until reading Waynos post. He was talking away with someone, as happens at Canby, when I was looking at them. So no good inside pics.  :lol: 

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I don't recall saying they were pretty, unless I said they were pretty ugly, and they are very heavy.

The guy selling them sent a photo of them mounted in a 510 I believe, the stock down draft manifold mounted to these extension runners barely cleared the strut tower, it was very close to hitting the sheet metal in the photo, I cannot find the photo, it may be in the old classifieds somewhere, it is not in my gmail account.

Yes they have coolant holes in them.

They also have angled fins inside the intake tubes at both ends about an inch in, 4 fins in all in each hole, they appear to make the air spin or purposely cause turbulence, the fins are not installed with any kind of uniformity, nor are the fins all the same size or mounted in the same spots, most are mounted around 180 degrees from the other, some touch in the middle, others do not touch, one of the fins is only 90 degrees off set from the other fin, they are obviously home made, the insides of the holes are fairly smooth except for the fins sticking out, way smoother than the outside of the manifolds.

 

I do not have a camera at this time, also if I try messing around with photos on this computer the CPU overheats(over 215 degrees) and Windows eventually gets corrupted, so I basically use this computer to check my emails and lurk on the 2 forums I frequent these days, I rarely log in anymore.

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Well my back room isn't under water, but it is dark and cooler in that room compared to the rest of the house.

They are the way I got them, but they did get wet at Canby, that is the first time they have been wet in my possession, they have a spot on the shelf next to the Weber stuff I have.

Someone spent a lot of time making them, the reason for them being built up like they are is a mystery to me, at Canby it was mentioned that maybe they are so heavy to offset the engine torque created by them, I laughed at that suggestion.

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Well, the interior of the truck is now repainted, and the 2" HS8 SU carbs are rebuilt and set up to run, with the exception of some different float bowl lids on their way to experiment with.  The new intake manifold is mounted.   One carb is installed, the other waiting for time to whip up a throttle lever arm.  Confirmed the correct spark plugs again with NGK and learned a little from them.  Basically they recommend #10 racing plugs if you're over 15:1, 9's if you're 13.5:1 to 15:1, and 8's at 12:1 to 13.5:1 - naturally aspirated.  We're strong in the 9's.  

 

Before the weekend is out, I hope to reinstall all the modified ballast weight, install the 2nd carb, and get ready for the custom throttle cable on its way by figuring out pull angles and building a basic throttle arm and cable mounts.  I also have to take an inventory of fuel line and fittings to see if I have the necessary parts to make gas flow.  That'll one of the worst jobs.  AN fittings are a convoluted disaster.  Difficult to find and order what you need 90% of the time.  Plus I ordered a 5 gallon fuel cell.  We may install it, or we may end up using the stock tank again?  

 

I also have to cut up and modify the hood scoop.  We need to raise it to the maximum height allowed to clear the carbs - 8" above the plane of the hood.  I haven't decided if I want to extend it to within 1" of the windshield as well, as allowed.  

 

We also found out we have at least one more guy joining us on the trip to Bonneville this year!!!  If ANYONE from this forum wants to meet up out there, you are welcome to stop by and say HI either in the pits or in line waiting to run!  

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As of the end of June, the salt at Bonneville is reported to be the best condition in a LONG time!!!  The long-time racers are excited for the first time in a decade+.  They speculate the long course will be 10+ miles long this year by August, far exceeding the 5 mile course last year.  If anyone has Bonneville on their bucket list, this will be the year that the 500 mph barrier is broken for wheel driven cars - likely running an LS based twin turbo setup.  Even the short course is slated to be 4 miles.  4 courses have been groomed so far.  If mother nature plays along, this is going to be an epic year!!!

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Last night the crew gathered and we knocked out a few critical items.  The rear is lowered another 1".  Its as low as we can go without notching the frame, which will come next since I now own a plasma cutter.  We modified the fire suppression system since the carbs have been moved.  The front tow hooks are now bolted in place AND welded, since we shook a bolt loose next year.  The tow bar is rebuilt and reassembled with a fresh coat of paint, and now has a pivot point just forward of the truck to reduce side stresses when turning tight corners.  We've also decided to rethink a bit of the wiring.  Instead of switching the distributor on the dash due to potential voltage loss through the switch, we decided to power the Coolshirt system direct to the battery, around the dash cutoff switch.  

I'll get the fuel system re-plumbed next week, and Monday night we'll scale the truck thanks to Intercomp: a local company who is bringing out scales and their expertise in chassis setup for racing.  They may help us out with the alignment as well?  Until then... a few much needed days off.  

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Yes exactly, plus I have a stock-type Japanese market SU manifold.   We hope to let it run its course here on a chassis dyno first.  Its almost ready to fire up. 

Just need to grab some 110 race fuel from a nearby gas station to get it started and see how far off the carb needle selection is.  I don't suspect it'll idle well - at least not compared to the Weber 50's which would chug along at 500 rpm until the end of time.  

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