Yamaha pipes

[lastminuteracin]

Just an FYI.... Ive used Al's advice for years. I road race so I have lots of time down the straights to look at egt. I also use a trigger so carb adjustments and there immediate results are at the tip of my finger. On good air days I've seen over 1300 many times and never melted a piston. When I started to see those kind of numbers I too had the same questions as many of you do about the melting point of aluminum. It's got to be something with the flame front moving from the combustion chamber to the header and burning there also that makes keeps it alive. I've won lots of road races on the west coast tuning the way Al recommends and have hurt very few motors once I figured it out. I also realize that my experience being able to watch the gauge is entirely different than you guys running 1/8 mile bullrings where you are lucky if you can glance at the gauge a couple times a lap.

 

[arc100]

I had a dyno for quite a while and I tested a lot of different pipes on KT's and I was never able to lower the peak torque RPM by much. Or raise it for that matter, not with the pipe or header length. I could raise the peak torque with different pipes, but always at about the same RPM. You can make modifications to the engine, and change the peak torque RPM, but not much with just the pipe.

I gotta say Al, I found the same thing with my dyno testing. I was very surprised at how little the curves shifted. I did find small gains or small losses by changing header length but it was all in the same rpm regions, the curves were all in the same area. I havent tested a lot of pipes but on the day I tested 4 pipes with various lengths.

 

[arc100]

Just an FYI.... Ive used Al's advice for years. I road race so I have lots of time down the straights to look at egt. I also use a trigger so carb adjustments and there immediate results are at the tip of my finger. On good air days I've seen over 1300 many times and never melted a piston. When I started to see those kind of numbers I too had the same questions as many of you do about the melting point of aluminum. It's got to be something with the flame front moving from the combustion chamber to the header and burning there also that makes keeps it alive. I've won lots of road races on the west coast tuning the way Al recommends and have hurt very few motors once I figured it out. I also realize that my experience being able to watch the gauge is entirely different than you guys running 1/8 mile bullrings where you are lucky if you can glance at the gauge a couple times a lap.

Damn, I must not have hit the "post reply" button.
I was saying that the reason the pistons and surrounding alloy doesnt melt is because of the gas flow inside the engine flowing over the internal surfaces keeping the piston from melting but its a very fine balancing act, as the flow rates change so do the cooling efficiency of the gas flow. Sort of like preventing heat soak to build up because the flow is removing the heat before it stays in contact long enough to soak in to the alloy parts. Like trying to melt the outside of an aeroplane with a blow torch while the plane is in flight. Sure the blow torch can melt the planes skin but the constant supply of cooler air prevents the full heat of the blow torch to get in the alloy skin but when the plane slows down the heat soak becomes more intense.

Also the reason the piston edge burns on the exhaust port is because its like a guillotine for the flame. When you cut or heat a piece of steel to oxy cut you dont start 2 inches in from the edge, its easier to heat the very tip of the edge to start the oxy cut. Same deal with piston. The exhaust side of the piston crown is the most vulnerable area to burning, it never sees any cooling gas.

 

[arc100]

It would depend on where the exhaust reaches that temp. I don't believe your any where near that at the port exit where the aluminum is. I for sure know it's hot enough to anneal the aluminum. I think every body has had a set of cylinders the exhaust side pulled threads out of the head studs. But the tip of the flame is measured well away from the cylinder it's self, and it takes a constant heat to actually melt aluminum. With head temps at 400 degrees and heat rising from below I don't think you can achieve a melting point flame out the exhaust.

I burn a direct torch flame at a crucible for 1 hour to gain enough heat to actually melt aluminum.

More good reading, notice the aluminum head doesn't melt, and these run much hotter and much longer than our pipes and engines.

http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm

Tim, that crucible is like a water bath heater, it spreads the heat softly and over a wide area. Combustion burn is extreme flame heat. Get a piston and heat that sucker with the gas burner you use on the crucible and put the flame directly on the piston, let me know how long it takes for the piston to melt?

Get some chocolate, heat it with a blow torch and see how it melts and BURNS. Then put the chocolate in a water bath and see how gently and consistantly the chocolate heats through without burning the outer parts of the chocolate.

 

[arc100]

there are books out there and they will tell you all about it. (Marks engineering handbook if I remember right) The one I read gave numbers much lower than 900°.
What surprised me was, 7075 did lose half its strength at something like 275°. It's been 20 years since I read that so I could be off, but not by much. (I remember that because I was surprised at how much 7075 lost at such a low temp) In that same book, it said that 2026 retained a lot more strength at a higher temp. The book was in an engineering handbook and had a listing of many aluminum alloys and how much strength was lost at elevated temps.
I was working for Bob Truax, (of snake River Canyon fame) at the time and there was a lot of books like that in everybody's cubicle.
People tried aluminum thrust washers for the Yamaha and used 7075 thinking it was really strong. But they failed a lot, so they stopped using them. I told one engine builder about the 2026 but nothing came of it. I'm pretty sure if they had used 2026 for those same thrust washers, they wouldn't have had the problem they had with 7075.
Comments compliments criticisms and questions always welcome.

FWIW,
http://www.matweb.com/search/DataSheet.aspx?MatGUID=9852e9cdc3d4466ea9f111f3f0025c7d&ckck=1

 

[Mr South 59]

I'm really surprised at that. We have never seized an engine because the EGT was too high. Sounds like detonation to me, and when you get detonation, the EGT always drops. Where on the track did it stick? Coming out of a corner or at the end of the straight? Does your gauge give you a printout or just peaks? I'm really interested.

Al. It a mycron 3plus. It does everthing. And NO. There was no temp drop on the straights. And no, it was not detonation Al. It is very easy to spot detonation on the top of a stuck piston. The sound waves from detonation will pit the piston up everywhere on the dome. This is a 3/4" X 1/8" area melted off of the piston only at the exhause port. 4 laps in a row with the same peak EGT. And yes, it stuck at the end of the longest straightaway.

Oval track guys can not use the EGT gauge to detect detonation. We don't have time to track the EGT temp on these little bullrings. We tune that by the seat of our pants. If you can not feel the performance lose when you go lean or if you can't hear it. You will have a hard time tuning a 2cycle on an oval. That is why I set the warning lights

 

[1fastyammy]

I have a mycron 3plus too and I set my temp lights too. Andrew you are right it is very hard to tune on a small track. It is really just a feel thing. I guess from just running over the years and being around two cycle karts I have got to know them pretty good. You can feel a drop off in power when you go to lean.

I set my first light at 1150 and the second at 1205. I tune to not go over that max number. Engines have run fine and no stuck or melted pistons. I have seen one at Fruitland get up to 1475. The piston was welded to the cylinder. No smoke out the pipe but it sure did have a nice white coating on the pipe outlet.

 

[Mr South 59]

10-4 Frankie. You don't need detonation to stick a motor. Heat will do just fine.

 

[alvin l nunley]

And no, it was not detonation Al. It is very easy to spot detonation on the top of a stuck piston. The sound waves from detonation will pit the piston up everywhere on the dome.
Oval track guys can not use the EGT gauge to detect detonation. We don't have time to track the EGT temp on these little bullrings. We tune that by the seat of our pants. If you can not feel the performance lose when you go lean or if you can't hear it. You will have a hard time tuning a 2cycle on an oval. That is why I set the warning lights

What really surprises me is how much difference there is between yours and my understanding and experience with detonation. I thought I had a pretty good handle on it. Maybe not. lol One thing for sure; nobody can know everything.
One question, are you saying you do have a printout of the EGT at the point where the piston melted?
If that gauge had been available when I was racing, for sure I would of had one on my kart.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.

 

[jack burroughs]

Al, I made my own wrist pin washers out of 7075, 6061 for many yrs, never had a problem with them, but then that time I was racing only with my boys in Rest.Jr. class, and we seemed to never have the same problems that others had.

 

[Taft Racing]

What really surprises me is how much difference there is between yours and my understanding and experience with detonation. I thought I had a pretty good handle on it. Maybe not. lol One thing for sure; nobody can know everything.
One question, are you saying you do have a printout of the EGT at the point where the piston melted?
If that gauge had been available when I was racing, for sure I would of had one on my kart.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.

Yeah I'd agree with you on this Al . Andrews exhaust temp doesnt indicate proper tuning rather the melting of the piston indicates too lean or detonation or both. Its a fact heat melts but would a properly tuned engine actually ever achieve the 1350. I don't think so. Not enough high speed fuel supply. Or too short a flex not allowing the fuel to return in time. That would be my take.

 

[alvin l nunley]

You can feel a drop off in power when you go too lean.

You should replace that first “You” with “I” because my “seat-of-the-pants” feeling was never that sensitive. When I got my 1st Digatron gauge, my first thought was; “my prayers have been answered!”

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.

 

[alvin l nunley]

Al, I made my own wrist pin washers out of 7075, 6061 for many yrs, never had a problem with them, but then that time I was racing only with my boys in Rest.Jr. class, and we seemed to never have the same problems that others had.

Was this with a pipe? In California, several people in the pipe class told me the same thing.

 

[ttownwideglider]

Both 7075 and 6061 are used extensively in our aircraft industry. 7075 is a high nickle alloy thats heat treated one of the hardest alum alloys made, but when its exposed to extreem heat it becomes anneled and softens and looses its strentgh. 6061 however will take much more heat and is not much weaker than the 7075 in their original forms. We use Titanium blades in the turbine section that are exposed to extreem heat and the stage 2 blades have an alumisied coating designed to protect the surface from etching. This coating burns away slowely and is made from a 6061 alloy, we have to inspect this coating at every midlife and overhaul. If enough has burned off we have to send them to RR in Scotland to have them recoated. So my point here is alum alloys will withstand extreem temps without melting quickly. Piston are designed in either a Forged process or a cast ing process . They are alloyed with Silicone and the content of the silicone is what gives them their hardness and heat resistance along with the other metalic alloys used. Thats why so many piston manufactors are so secertative about their blends. The higher the silicone the harder and more heat resistant they are to a point. The hypereutectic blends forged are some of the best pistons made.

 

[jack burroughs]

Yes, pipe and restrictor plates, later without.

 

[pko]

Yeah I'd agree with you on this Al . Andrews exhaust temp doesnt indicate proper tuning rather the melting of the piston indicates too lean or detonation or both. Its a fact heat melts but would a properly tuned engine actually ever achieve the 1350. I don't think so. Not enough high speed fuel supply. Or too short a flex not allowing the fuel to return in time. That would be my take.

Not trying to rock the boat here just trying to learn. But would too short of a flex stuff burnt exhaust gases back making lean or increased temp?

 

[jack burroughs]

Maybe, but as far as I understand it, when the pulse reflects back to the exh. port, it stops the cross flow, object of tuned pipe is to draw A/F mixture out the port, so that there is no spent fuel residue remaining inside the chamber. One thing that showed me just how drastic it is, was at OVRP, 4 karts beginning to run down the long straight and 1 has the pipe fall off, looked to me like the brakes were jammed on.

 

[alvin l nunley]

Not trying to rock the boat here just trying to learn. But would too short of a flex stuff burnt exhaust gases back making lean or increased temp?

I had a problem with my Mac one time where I had accidentally installed the pipe and the header was 1 inch shorter than I normally run it. It would run uncontrollably lean on the top end. Hard to say what was happening or why.
Different pipes run different header lengths. Some run short headers some run long headers. You need to start with the length that the manufacturers suggest.
I used to send a leaflet, with pictures, and people still would not do it right. You would be amazed how many people would call me and tell me the pipe didn't work. "How long is the header" I would ask. "Same length we always run with our Hartman" was the answer, more often than not.

 

[Taft Racing]

Not trying to rock the boat here just trying to learn. But would too short of a flex stuff burnt exhaust gases back making lean or increased temp?

Well the tuned length of a pipe is all about time. The wave has a predetermined time depending on your desired rpm. The sonic wave that emits from the exhaust port when the piston first uncovers the port expands and travels down the pipe untill it reaches the conversion cone. At the half way point of the conversion cone it reflects the wave back to the port. Your flex length or header length is used to fine tune that arrival time. The wave pushes unburnt fresh fuel charge now escaping the portI back into the combustion chamber. Too short a length and it won't have time to complete the task and then you have lost part of your fuel air and the engine runs lean. The other aspect is stinger diameter and length. This also controls back pressure that assist in pushing the charge back by controlling the bleed off rate. Too small or too long a stinger and you'll build too much heat in the piston crown. Again burning a piston. Its allot of fun science and there's no perfect number. You can tune a engine a ton just with pipe design and never touch the porting.

 

[pko]

Maybe, but as far as I understand it, when the pulse reflects back to the exh. port, it stops the cross flow, object of tuned pipe is to draw A/F mixture out the port, so that there is no spent fuel residue remaining inside the chamber. One thing that showed me just how drastic it is, was at OVRP, 4 karts beginning to run down the long straight and 1 has the pipe fall off, looked to me like the brakes were jammed on.

I had to go back and refresh my limited knowledge and looked in jennings book where HE says exhaust pipes draw spent fuels out and also stuff some back in. Timing is key and my thoughts are that flex length is part of timing with design of pipe,etc.