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Recently was going through my old DynoTechresearch.com issues from early 90's looking for dyno #'s to send along with an old Phazer Pipe I had just sold and came across this very interesting article that I think explains a lot about recent engine failures, 800 PowerTech in particular.

In Volume6, Number3, Page7, Jim Czekala wrote two pages on "Vaporization and modified carbs" I will quote a few paragraphs and then give my take on it. It has the best and most believable and common sense explanation on what a cold seizure is that I have ever found.

It starts out

"I've come to the conclusion that, while the industry standard Mikuni VM and TM carbs are easy to tune, they do less than a perfect job of vaporizing gasoline, especially at low air velocity and low air and fuel temperatures. Cruising and trail riding , the carbs see high velocity beneath the slides. Engines run safely and powerfully on lean A/F ratios.

When the throttles are whacked open, however, air velocity is temporarily low, and I think that gasoline drizzles into the engine and gets beaten into at least a partial vapor by the hot, spinning crankshaft/rod/piston assembley.

Stale pump or race gasoline delivered by standard Mikuni carbs doesn't have a prayer of being totally vaporized by the time it reaches the combustion chambers. Standard Mikuni carbs are dependent upon the "light ends" of the gasoline to initiate the vaporization process. When light ends are diminished by "staleness", high engine component temperatures are necessary to assure even partial vaporizatiion.

In the old days, we used to mysteriously detonate and seize engines on the dyno when our "light ends" disappeared (with some race gasoline, the light ends were gone within a few days after opening the sealed containers). Safe A/F ratios, BSFC, and EGT's belied the fact that stale fuel was blowing through our engines in unburnable, lava lamp-like globs that only cooled our EGT probes.

HERE IT IS = COLD SEIZURES EXPLANATION

"Cold seizures" are absolutely caused by cold gasoline failing to vaporize. Cold engines being fed nice 12/1 A/F ratios actually see maybe 20/1 A/F ratios if you count only the burnable (vaporized) fuel. Its the lean real A/F ratios that cause the detonation and/or overheated pistons."

This cold seize (poor vaporization lean A/F ratios) is going to present itself with forged pistons (Wiseco's) as what is thought of as a cold seize (four corner seize) but with OEM cast pistons should be a lot less (four corner) as they have a bunch more silicon and expand less with extra heat. But the lean A/F ratios with cold engine with cast pistons which is also seeing heavier dense air because its cold along with poor fuel vaporization will DETONATE much easier. As Kelsey has said detonation will take out those little needle bearings on the rods, probably bad for the crank bearings also and if bad enough will definitely take the pistons out in a hearbeat. My thinking is a little detonation repeatedly may be doing in the 800's. So how easy is it to have this scenario go on. My rev 629 fan big bore takes two miles at 30 to 45mph for the head temps to get up to 200 degrees at which point I will feel OK about using more than 1/2 throttle. This is when its about 20 degrees, takes longer when its colder. Letting it sit an idle won't warm it up, you have to ride with a little load on it. I am very religious about it as it has Wiseco ThunderCat big bore pistons (81 mm) and they are really at risk from this if I ride like some people do.

So a cold sieze (poor vaporiazation) can be the traditional four corner or it could be the edge of the piston detonated off or it may be the detonation over time has taken out the rod bearings or maybe even more. Friend of mine said he just received a bulletin for his 05 800 Renegade to crank up the oil pump. Not enough oil will make the bearing issues worse. My thinking is Doo has the oil pumps set lean for the EPA and treehuggers not for performance or engine longevity or to keep your checkbook fat (broken engine parts). I also agree with Kelsey that more oil makes more HP, the rings seal by hydroplaning on a lip of oil. The bearings need oil. Early on DynoTech disproved some of the miracle HP stuff that was around. They dynoed an engine with Slick 50 and lost HP, only way they got it back was tearing engine down and honing cylinders to get it off. Why did they lose HP, oil wouldn't stick to the cylinder walls. Another process they disproved was called Extrude Hone Porting. Under hydraulic pressure it pumped a slurry of abrasives through the ports, they looked beatiful, the engine flowed more air, made less HP, why, poor fuel vaporization!!

How important is good fuel vaporization? Around 1990 when I started my Lightning R&D business I spent a full month at the U of MN Science and Technology Library reading a few 1000 pages of SAE papers going back over 60 years on two strokes. I came away with two things that I thought would help make better high performance two stroke engines. About a year later a friend of mine called me (Yamaha dealer) and said they had a Yamaha SRV sled that was ported and polished and piped and no matter how rich they jetted it,(fuel was running out of the pipe) it kept sticking pistons. He wanted me to fix it. So I tore it down, analyzed all the porting in the computer and got rid of all the polishing and dialed in the transfers so they were within a few thou in regards to heights and a few other minor port time changes. What I did helped fuel vaporization and when it was put back together they could jet it down and it made decent power and didn't burn down anymore. and they had a happy customer.

To make matters worse, maybe stale fuel where the light ends have gone off some, or not sure about this but our modern fuel may be a little harder to vaporize because of EPA regs and all auto engines are now fuel injected so they can get away with it. I know the EPA has been trying to reduce evaporitive emissions for quite some time.

Good Luck

The above is just a tast of all the priceless info you can find on DynoTechResearch.com for $20 a year , I have been one of their happy
customers from Issue 1 since back in the late 80's.

And it certainly helped me design and build my littl2 629 big bore.

Lightning R&D - 17 Years of Computer Aided Porting - Dealer for SlyDog Skis - Aaen Pipes - Fox floats - FabCraft - etc.
 

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Ok, you are one smart guy!

The rod bearings just went on my '04 MXZ 800 and destroyed pretty much the entire motor. The dealer who tore it down could not find the cause of the problem and even accused me of over revving the motor. If I read your info correctly this could have been caused my detonation? I always warm the sled up. What if this thing is running cold? Would a smart man keep his carb heat on to avoid this issue? Would you put a temp sensor on the sled and watch it religiously? Sorry for all the questions, but my dealer does not have the knowledge to answer these questions, and they probably would look at me funny if I tried to explain this to them.
 

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I am theorizing here or guessing on some of these engines going down in regards to
detonation. But what I am trying to get at is the so called cold seize when you look at the underlying cause (the fuel not vaporizing) could be happening and causing a lot of problems nobody had a clue about. I know I have read that article on Vaporization many times but the short paragragh on cold seize just never clicked until last week.
These stock series lll engines have the goofiest head that has ever been put on an engine. Its called a top hat combustion chamber. When I analyze it with head software it has a squish velocity measured in meters per second of over 40 at peak rpm around 8,000. Over the years I never designed heads with much more than 20 to 25 meters per second max. The books say to high of squish velocity will in and of itself cause detonation. Now when you run that head at about 5,000 RPM it has a more normal squish velocity. Also at that RPM the piston will dwell around TDC much longer and I think what happens is then most of the A/F is trapped in that small combustion bowl and more completely burned, thus giving lower emissions to meet EPA #'s. But at peak RPM's it just isn't an optimum head design. The old 670 heads were a classic hemi head and thats what I reccommend.

As far as carb heat I'm not so sure that will help I think its a matter of the crankcase being up to its stable operating temp. Also giiving these engines enough oil. Kelsey reccommends premix and pretty rich at that. I tell my customers to crank up the oil also, so far they haven't had rod or crank problems. The 800HO just may have to many areas that are at the edge. The powertech by a friend of mines theory may tuned so close that it can go into detonation and then the computer pulls it back. Solution would be to change the tuning a little with a better head with a little lower compression and use that 600HO needle in it to get rid of the scary midrange EGT temps. I would also have a gauge for EGT's and actual water temp. And if it was mine I might have another temp sensor on the crank case to see what the actual running temp of the crank case was and how long it takes to get there with a light load like trail riding at 30 to 45 mph. Haven't done this with mine yet but after writing all this am going to. My stable head temps on my engine are around 225 to 325 degrees but have know idea on the crankcase temp and this is what I think I will influence the vaporization of the fuel the most. On compression #'s the books say high compression pushes heat into the head and piston, and takes it away from the pipe becuase the pipe doesn't pump as well. The result with a 2-stroke is high compression boost the mid range and hurts peak HP. Back in the early 90's there was an italian dirt bike head that had a movable dome on the order of PSI dial a domes except it was under nitrogen pressure so that at low and mid range rpm it was down for high compression and high squish velocity and at peak rpm it raised up for lower compression and low squish velocity. The idea was sound and it worked except not for long as it would bind up up and stick. That would be the perfect scenario to have your cake and eat it to but we can't have both. I kept the compression low on my 629 fan for just that reason as it doesn't have enough cooling so you can't be forcing to much heat intoit with high compression.

So if I had an 800 I'd get Kelsey to make a head for it and go a little conservative on the compression, richen up the oil or maybe even go to premix at 35 to 1 at least. Have a ported 04 800 running with Kelsey's piston's and it worked very well in Cook for a week at 10,000 ft, have to see how it fares in the UP at a few hundred ft, but I think it should be fine. My friend and customer always has had oil cranked up on it and he had the computer reprogrammed which is supposed to help mid range temps and also is adding the 600HO needles and he watches his water temps and warms it up well.

Just thought of one other thing as I blew up one of modded Phazer engines so fast and so bad with to much clutching load and not enough jetting to keep it from detonating by putting in to much helix angle. One of the theories on the goofy moly filled rings which makes sense came from Russ Lemke a good engine builder and racer I believe from WI. He was very happy with the RER sec on the 800's because it really seemed to hold the rpms' consistently. One day one of his buddies comes over with his 800 with the older sec prior to RER and just cleans him. Russ scratches his head and pulls on old sec off the wall and puts it on his 800 and now he's faster than his buddy. His theory is that the RER binds up and doesn't shift when it should, and in so doing under some conditions this is lugging the engine and this can cause detonation big time, thats what I did with that old Phazer. So later one his customers has the dreaded flaking moly filled ring disease and they fix it and they put on an old style non RER sec and no more problems. So that could be another piece of the puzzle.

Good Luck
 

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Who is Kelsey, and how do I get him to make me a head?

I think Mercury used a top hat head on some of the 2.4l. Which I guess would back up what you are saying with the head not working at high RPM's. Those big V6 outboards (except the Bridgeport) weren't design to rev over 6K anyway. Most of them wouldn't rev much over 5K pushing a big heavy boat.

I do know some guys are cutting a squish band in I think the top hat head and possibly reshaping the combustion chamber to make a very good performing head up to about 6800 rpm.

Is this what Kelsey does with these heads, or does he start fresh similar to the RKT head or Cudney head?
 

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qshag said:
Who is Kelsey, and how do I get him to make me a head?

I think Mercury used a top hat head on some of the 2.4l. Which I guess would back up what you are saying with the head not working at high RPM's. Those big V6 outboards (except the Bridgeport) weren't design to rev over 6K anyway. Most of them wouldn't rev much over 5K pushing a big heavy boat.

I do know some guys are cutting a squish band in I think the top hat head and possibly reshaping the combustion chamber to make a very good performing head up to about 6800 rpm.

Is this what Kelsey does with these heads, or does he start fresh similar to the RKT head or Cudney head?
[snapback]718155[/snapback]​
Kelsey is RKT....
 

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Discussion Starter · #7 ·
The series lll combustion chambers have such vertical walls and the spark plug is so far away from the piston dome that its nearly impossible to recut them into a really good hemi head like RKT's or the old 670 heads. The closest ones I come to getting right are with the 700's when I put in the wiseco 670 piston for the original 670's which has a higher dome on it. Was able to recut to a pretty good looking chamber with some decent compression. Doesn't work to well on the 800's though. I did one 600 HO head and it helped it some but I wouldn't reccommend it as the engine is just to close to edge as far as stock porting. Much better with that one to turn it into a 700.

Good Luck

Here is the head for my 629 which is what I would call optimum. Because the bore went from 76 mm to 81 mm had plenty of material to work with and get it right.
 

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Good stuff.................

I also highly recomend either making sure you are burning 40:1 or better with injection.....

also, premixing at 100:1 on TOP of the injection, helps make certain the intake side of the piston is lubed........

Rough intake ports are good in my book too, some go as far as making sure the "tooth" of the aluminum surface points AGAINST the direction of air flow, to cause turbulence and better vaporazation.....(this often requires backwards porting toools, and 99% of port jobs won't include this procedure....

Also remember that gasoline is formulated for CARS, and they have been REDUCING the vapor presure of gas for years, and will likely continue to do so, so it will only get worse........
 

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Great discussion...
Just want to add that the comments relative to port finish really apply to the intake and transfers to aid fuel atomization. Mirror polish is still desred on the exhaust side to help maximize flow..
 

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I have been chasing better fuel atomization since about 1989. Thats how long I have used a sandblasting media that I special order to chew up the intake side of engine. It puts a finish on that's as good or better than sand cast. Have been chasing it because better fuel atomization should increase flame speed in the combustion chamber. Better flame speed should allow more work to be wrung out of combustion pressure before piston moves down the bore too far and rod loses leverage on the crank. I think its also related to an elusive quality I have achieved on some motors called accelerative torque, first learned about it in relation to Nascar engines.

Fuel atomization was one of the things I learned in a month spent in the Science and Tech Library years ago.
Good to know about the reduced vapor pressure of our fuel, that was what I thought also but wasn't 100% sure.

On exhaust port finishes, have an obscure book on porting four strokes from england (Practical Gas Flow by John Dalton) that disagrees about the mirror finish even in the exhaust. Theory being that all ports have a fairly stagnant boundry layer on the port walls. When you use a probe as you move towards the center the flow increases and as you get close to a wall it decreases. The theory is you will always have a boundry layer and better to give it something to attach to than let it attach and then come loose and then reattach. The mirror surface may cause more tumble or swirl rather than an even flow. I don't have a flow bench to prove or disprove it but haven't spent any time since reading that to put on a polished surface, just hit with 120 grit sanding flap wheels for final finish. A heavy mod I did with three 670 cylinders dynoed 245 HP with that finish. The difference between the two is I'm sure very small. One thing I like to do is ceramic coat the exhaust ports to help keep heat out of the exhaust side of the cylinder and hopefully keep it a little rounder.

Good Luck
 

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Maybe a relatively small affect, like you say probably need some flow bench work to verify. My experience is mostly from building KT100 kart motors and some dirt bikes prior to that. Generally I believe that a smoother finish will decrease the thickness of the turbulent boundry layer and thus offer a larger area to unrestricted flow. There may be a point though that the finish is too smooth and allows it to seperate from the wall...Sounds like what you're doing is working well, stick with it
 

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I was all ready to give up on this thing due to the fact that I feel this motor is a ticking time bomb. If I was to port this thing the way you are recommending, put one of Kelsey's heads and his drop in 800 pistons, am I going to have a reliable engine? Well, atleast as reliable as some of the competition? If you think it would be a good engine, who should I have port it for me that is knowledgeable and experienced with increasing atomization?
 

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Discussion Starter · #15 ·
On fuel atomization in the ports. I believe a lot. On that old yamaha SRV the main
thing I did to it was get rid of the polished ports on the intake side and transfers. Before doing that it would stick pistons no matter how rich it was jetted, after wards it was jetted down a few sizes and ran great and didn't stick pistons. Plus that SRV was a fan so it definetly had a crank case that gets warm enough to help vaporize fuel. When you study porting in 4 - stroke intake ports, you'll find you can screw them up so easy just making to tight a curve or just change something a little because the vaporized fuel will fall out of supension and seperate from the air. Just look in a 2-stroke intake passage into the crankcase. Every edge sticking out will turn fuel into a liquid and it will coat that surface. It has to be revaporized in order to be burned.

Good Luck
 
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