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Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 517948 times)
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wobblywalrus
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« Reply #2805 on: June 04, 2017, 12:56:54 AM »

Pete, there is a Consumer Product Safety Commission here.  They will be the first contact.

Woody, I think I am the only nut racing one of these bikes on Landracing.com.  There might be limited interest.  This will be the first of a few posts.

The engine had been raced for ten years and had over 200 dyno pulls while parts and settings were being developed.  I could not get the power to set records and a fellow who gave me a lot of advice retired.  The other specialists on these engines were not saying anything about what they did or they were full of carp.  It was time for a new approach.  Virtual modeling was used and the Dynomation method was selected.  There are three methods in the program.  One is a simulation model with minimal use of wave action.  Another model predominately uses wave action.  The third model combines the two to have a hybrid model.  The third model is what I used.  The answers made the most sense and the wave action piece of the tool was very valuable.

Measured data was entered into the program such as burette based compression ratio and head flow data at 28 inches.  The cam profiles were approximated using cam card data until Kibblewhite gave me digital cam files.  They measured the cams to make them.  This is very important to get good results from the program.

There is a relationship between cam duration and performance according to Vizard.  Shorter durations work better at higher altitudes.  This will be a Bonneville engine so typical salt flats climatic data was entered. 

The stock tappet buckets are 28mm diameter.  They will handle cams up to 0.380 lift.  This includes the WebCam #813 grind cams and there are good all-purpose knockers.  The tappet buckets on this head were bored out to 30mm. This is as big as they can go without overly weakening the cam support bearings and brackets.  This allows net lifts up to 0.400 inches.  A WebCam #208 grind has 0.400 net lift.  That is what will be in the new engine.  This are is the biggest cams I can reliably use.

The next post will be about peak RPM.
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wobblywalrus
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« Reply #2806 on: June 05, 2017, 01:04:20 AM »

My last post is incorrect.  Vizard talks about compression ratio vs duration.  It is on page 70 thru 72 of "How to Build Horsepower."  The engine's compression ratio is the same irrespective of altitude.  The pre-combustion cylinder pressure does change with altitude. The virtual modeling showed me that a medium to high compression ratio engine at  Bonneville is like a low compression engine 'cause of the thinner air.

It is important to minimize duration for higher altitudes so as to keep the compression pressure pushing down on the piston rather than escaping out of the exhaust valve.  Also, it is important to not close the intake valve too late so as to start building compression.  This is what I think I see from looking at all of the graffs and tables.

This engine flows very well at low to medium valves lifts as is typical of a Cosworth design.  This makes limiting duration especially important.  The engine is very effective at dumping cylinder pressure when the exhaust valves open and and it is also very good at not building up cylinder pressure until the intake valves are shut.

The maximum lift is 0.400 due to structural concerns.  There are a couple of cams to choose from with lifts similar to this and different durations.  The cams with the shortest durations were chosen for the reasons above.   
     
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revolutionary
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« Reply #2807 on: June 05, 2017, 09:41:18 AM »

Wobbly, in my previous career life, we used to bump up the compression on comp engines running at Denver to 17+:1 in order to make any power up there. If there is no air to begin with, you better compress it all you can. 

The tough spot is that it is extremely hard to do with a small bore engine like you have. The best option is to start where you are, dyno the thing and move the cams where you want, then get a new piston blank with a blob dome and clearance it to barely fit and clear the valves now that they are in the right spots and make a new set of pistons off that. It is a major pain but that will do the trick.
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wobblywalrus
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« Reply #2808 on: June 05, 2017, 11:42:06 PM »

The flow in these Cosworth motors tumbles across the piston crown to get mixed up before ignition.  A high crown can mess this up and this is especially true in a engine like this with a big bore and short stroke.  This is a 13:1 crown based on the volume of the standard combustion chamber.  The 14:1 crown was really tall and pointy.  This crown height seemed like the best compromise.  It gives 11.9 to 1 compression on my head which has bigger intake valves and the metal removal needed to put them in and unshroud them.

A long term goal is to run in the UK again at the Yorkshire Mile, the promenade in Brighton, Santa Pod, and maybe Pendine.  This lower comp ratio might be the best.  It can be hard to get race gas over there and everything is close to sea level.


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RansomT
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« Reply #2809 on: June 06, 2017, 08:26:16 AM »

Yes!  While you do consider static compression, dynamic compression is more important.  grin Those cams should work really well.
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wobblywalrus
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« Reply #2810 on: June 07, 2017, 09:19:02 AM »

The cams give the best dynamic compression of any available.

The model was made using 10-point approximations of the cam profiles.  This is durations at .006 lift, durations at .050 lift, and total lifts for intake and exhaust lobes.  I had to buy the cams based on 10-point analysis and have them digitally profiled by Kibblewhite.  The profiles arrived with the cams last week.  The engine model is invalid.  The profiles give much different virtual performance than the 10-point approximation.  Use actual cam profiles from the beginning with virtual modeling is my advice to all of you.

The intake mach number is 0.48 at peak power rpm.  It should be 0.5 to 0.6.  The intake valves are 2mm larger than standard.  A 1mm increase would have been OK.  Modeling shows the mach number would be just about perfect.  The stock seats could have been reworked and there would be no compression loss from the metal removal to install the bigger seats for the 2mm larger valves.  The 13:1 static compression would be retained.  It was a mistake on my part to use those 2mm bigger intake valves.
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wobblywalrus
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« Reply #2811 on: June 09, 2017, 08:36:07 AM »

Another three feet of floor was poured in the shop, a dedicated outlet installed, a new cord and plug of adequate and proper design was put on the chop saw, and a blade stop was made from a stainless steel bolt.  Now the saw is up and running.  It was suggested the outlets be installed high on the walls in this forum.  This was done.  Theses outdoor use covers keep chips and swarf off of them. 


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Peter Jack
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« Reply #2812 on: June 09, 2017, 11:09:24 AM »

That's a good looking installation Bo. I'm surprised those guys were so Mickey Mouse in their performance. The saw looks like a really good piece overall.

Pete
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wobblywalrus
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« Reply #2813 on: June 14, 2017, 12:51:22 AM »

The saw works well.  This is the first of many lobsterback sections that will be made from 304 stainless.  These are time consuming to make with a Sawzall.


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Peter Jack
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« Reply #2814 on: June 14, 2017, 06:53:38 AM »

Would you not be better off buying bends from an outfit like Burns Stainless and cutting the required segments with the saw. The inside of the pipe, which is the part that counts will be much smoother and you won't go through nearly as much in the way of welding supplies. Often it's easier to remove the supplied clamps and devise other methods of holding tubing down to cut it. Very often I don't use a clamp at all. U-bends stay put when just hand held in place against the back rest. Just keep your hands clear of the blade.

This is the way I normally cut tubing when I'm building custom headers.

Pete
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wobblywalrus
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« Reply #2815 on: June 15, 2017, 12:44:48 AM »

This is a Burns stainless 45 degree bend I tried to splice by cutting it through the mid point in the bend, removing a pie slice, and welding it back together as a 64 degree bend.  The metal on the inside of the bend is thick from compression and it is thin on the outside from being pulled when being bent.  Getting good penetration on the thicker metal was hard.  I blew lots of holes through the thin sections and fixed them by welding up the edges of the holes.  It sorta worked.  The insides are rough and look like bowel cancer.

The voltage and wire speed had to be changed as I worked around the pipe from thick to thin metal and back again.  I got minimal penetration or blow through unless the settings were just right.  There is a talent deficit here.  Awfully wrong settings happened more often than just right.

The lobster back rings are a lot more work to make.  The metal is of uniform thickness all of the way around and it is a lot more predictable to weld.  Some trial and error is used to get just the right amount of penetration.  Then I leave the settings alone and weld the entire circumference using them.  The inside of the weld is much smoother.

The variable thickness would have been no big deal when gas welding.  A fellow automatically compensates for it when welding.  The wire feed does not do that.  The wire comes out at the same speed and voltage regardless of the thickness of the metal.  Maybe when my skills get better I will try cutting and splicing bends again. 


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Peter Jack
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« Reply #2816 on: June 15, 2017, 10:19:03 AM »

You should never have to splice a bend. Cut the bend at the desired angle and then just weld on a straight piece or a bend that goes off in a different direction.

You're quickly learning why anyone who's serious about building racing exhaust systems uses tig to fabricate them. The result is a much better product using a much simpler procedure.

Keep working at it Bo. Hand skills will continue to improve. Most of us have been at it more than a few hours.  grin grin grin

Pete
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wobblywalrus
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« Reply #2817 on: June 16, 2017, 07:48:54 PM »

The local steel supplier gives me a good deal on metal.  It is the fab shop price.  So, I ordered a 20 foot length of 304 stainless with 16 gage wall thickness and 1-7/8 inch OD.  The OD is 1.9 inches.  Odd.  The gage is not quite 16.  There are no ASTM stamps on the outside of the tube.  It cuts a lot easier with the chop saw than the tube I have with ASTM specs stamped on it.  What the heck?  Further investigation and measuring shows me this is 48mm tube made in Taiwan.

The carp is some inferior alloy and it does not slip fit into the ASTM size collector made by Burns.  A lesson is learned.  I need to find a local supplier for American or Canadian steel made to ASTM specs.  Burns Stainless is good steel made here to ASTM specs.  It is sort of expensive in long lengths with that UPS or Fed X shipping.   
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Peter Jack
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« Reply #2818 on: June 16, 2017, 09:24:36 PM »

Bo, go read all the technical information on stainless on the Burns website. The material from your supplier may not be inferior material, just a different material intended for a different purpose. There are a lot of different stainless alloys. The first thing to do would be to find out what your supplier sold you.

You do have to stick with either imperial or metric units for the tubing you're using. Just make the decision and stick with it.

Pete
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wobblywalrus
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« Reply #2819 on: June 17, 2017, 09:49:49 AM »

It was sold to the supplier as being 304.  It is weaker and easier to cut than Burn's 304.  At my job this is something I deal with.  We have "spec steel" that has the spec number painted or printed on it with the heat number.  There are matching mill certs for the heat saying it is OK.  There is nothing stamped on this pipe and no mill certs are available.  We call this "commercial grade" pipe to be polite and politically correct.  We have other names for it, too.  It is OK for this exhaust system.  Spec steel will be used for critical parts.   
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