Spark Plug ?

C

circletech

New member
I turned my flathead into a stroker this winter 4.75 rod Alum flywheel Been running a Autolite 4093 plug I think there could be a better choice We run different tracks from short to long on the dirt with open rules in Northern Indiana I keep eng temp around 400 to 425 just think im missing something?
 
I'm guessing you have a non-stroker with a 4.475 rod & .590 compression height piston....Even so, the spark plug's main function remains the same. Spark when it's told to do so by the coil. If it's doing that properly (not mis-firing or fouling) and building adequate temperature (as you stated it is,) then there's really not much gain to be found in spark plugs. Even in the stock class stuff, we've tried them all and found that the one that works best is the one that is the correct heat range and simply works.
Now, put a better breathing carb, or bigger cam, etc on it, and you'll see some real power increase. Easy to make power with fuel as well- Hot fuel will wake up just about any engine - just be ready to replace parts more often. ;)

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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com
Celebrating 25 years of service to the karting industry
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circletech said:
I turned my flathead , into a stroker this winter 4.75 rod Alum flywheel Been running a Autolite 4093 plug I think there could be a better choice
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maybe you’re not aware of what the term, “stroker” means, but putting a longer Rod in an engine does not increase the stroke, or make the engine a “Stroker”. Not that it’s not a good idea mind you. Increasing the Rod length to stroke ratio can be a help. The ideal ratio is thought to be about 2 – 1. The clone is far from the ideal ratio. Anything you can do to get it closer is generally thought to help.

I’m not familiar with that Autolight plug, but I’m wondering why you think there could be a better choice? I’m a big fan of searching for the right plug, so I’m interested in your view on how you could improve your performance with a “better” plug. Not really “better”, that’s not the right word, maybe “better suited” for your application.

At one time I had a book from Autolight listing all their plug numbers and heat ranges with corresponding numbers from other manufacturers. That book got a lot use.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
Your the first one to tell me what I have always been taught and believe To stroke and eng one must change the lenght of the throw of the crank yet many of the people I have talked to in the karting world say change the rod and piston ???? no one can tell me how this make a stroker - just saying- didnt make sence but just going with the flow lol The only reason I have stuck with the autolite is because that is what came with the eng. when bought last year used just wondering what others are running and if there might be a better choice of brand if so for what ever any reason
 
A longer rod just moves the piston up in the hole unless the hole in the piston is moved up also!! It still moves the piston up and down the same distance.. A 406 c.i. Motor is still a 406 with 5.7 rods or 6" rods
 
The reason to go with a longer rod is to change the rod angle, the longer the rod the less rod angle you have, this creates less stress on the bore at high rpm , especially on the thrust side of the bore.
 
Jon Brogden said:
The reason to go with a longer rod is to change the rod angle, the longer the rod the less rod angle you have, this creates less stress on the bore high rpm , especially on the thrust side of the bore.
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a very good explanation. The thing is, the clone, the Briggs and the Predator have rod length to stroke ratios so far from ideal, the small increases you can get from available rods is almost insignificant. Just my theory mind you. I suppose any increase would give you some benefit.

There was a time that 1.8 was thought to be a good ratio, but in today's European two strokes, I see many with a ratio of 2.0, Rod length to stroke.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Something about plug heat ranges; as a general rule, the higher the compression the colder the plug. Take for instance, (where I have my experience), the KT 100 can use an extended tip plug with a stock 11 cc combustion chamber, but a stock komet, with a 9 cc combustion chamber, needs a retracted gap plug.

A stock four cycle would most definitely want a hotter plug than a modified.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Alvin, The thing is, This topic is about an American Briggs flathead that all ready has a 2 to 1 rod ratio that was made that way from the large availability of longer rod lengths and shorter compression height pistons.
Circletech, I also prefer using the NGK B8HS surface gap plug in my mod flatheads, mainly because of the ease of not having to index the plugs grounding electrode out of the way from the valve.
You could say it's "better suited" for a mod flathead.
 
Freezeman said:
Alvin, The thing is, This topic is about an American Briggs flathead that all ready has a 2 to 1 rod ratio that was made that way from the large availability of longer rod lengths and shorter compression height pistons.
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apparently I don't have the Flathead information. Sorry about that. I have the clone information, which is not 2 to 1, but I don't have the Flathead information. Can you post it, the Rod length and the stroke for a Briggs Flathead? Of course I'm speaking of the stock Briggs.

Your explanation is a little unclear. To me anyway. And what do you mean by shorter compression height pistons?

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Alvin, A stock 5 horse Briggs Flathead has a 2.438 stroke and uses a 3.875 length rod. This Flathead that Circletech has posted about is using a 4.75" rod.
When a longer rod is used on a stock stroke crank a piston that has a shorter compression height is normally used in order to not have the piston extend too far out of the top of the stock cylinder. Here is a link to a ARC's web page that list pistons bore sizes along with the compression height that it has. http://www.arcracing.com/servlet/the-Pistons-and-Rings/Categories
Here is a nother link that defines and shows what compression height is. https://www.google.com/search?q=pis...FEKnE8AGJ4IHwAQ&ved=0CDcQsAQ&biw=1280&bih=705
 
Freezeman said:
Alvin, A stock 5 horse Briggs Flathead has a 2.438 stroke and uses a 3.875 length rod. This Flathead that Circletech has posted about is using a 4.75" rod.
When a longer rod is used on a stock stroke crank a piston that has a shorter compression height is normally used in order to not have the piston extend too far out of the top of the stock cylinder. Here is a link to a ARC's web page that list pistons bore sizes along with the compression height that it has. http://www.arcracing.com/servlet/the-Pistons-and-Rings/Categories
Here is a nother link that defines and shows what compression height is. https://www.google.com/search?q=pis...FEKnE8AGJ4IHwAQ&ved=0CDcQsAQ&biw=1280&bih=705
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and so the information I was given that the Flathead has a 2 to 1 Rod length to stroke ratio is wrong, even with the long rod. And instead of, "shorter compression height" would it be better to say; higher pin bore location?

I wonder what problem is created, if any, by moving the pin bore up that much?

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
NGK BU8H best plug for a flathead in my opinion. Put it in and be done with it! No need to worry about a gap or the piston hitting it etc...
 
NGK plug. Great plug. Got a outlaw flathead and a regular plug gets destroyed by the valve cause of the massive cam
 
curtracer said:
How often do I need to replace the NGK plug. Running wka stock . JIMMIES rule still apply ?
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I think that depends a lot on your budget. With a real tight budget you could run them until they foul. They usually foul after you shut off the engine, and you find out they're fouled the next time you try to start it.

Spark plugs were very high on my budget priority list. The engine got a new spark plug at every outing. That's extreme, but it's the way I did it. A new spark plug and a plug wrench always accompanied me to the grid. It's somewhat different with a two cycle, but I think the reasoning is sound.

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