I am planning on machining a new Cylinder Head for my son's Pulling Garden Tractor over the winter. It is a single cylinder Kohler Flathead engine. Any thoughts on what is the best location for the Spark Plug? I know some people say it needs to be directly over the Exhaust Valve, some say centered on the piston, any thoughts?
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Spark Plug location on Flathead 1
- Thread starter CSLufkin
- Start date
BrianPetersen
Mechanical
Nevertheless, I agree that if you are going to be making a custom cylinder head, you might as well twin-plug it. I'd put one over each valve, offset towards the cylinder.
The advantage of the second plug is reducing the timing advance by 10* which means the piston is closer to TDC and therefore less energy to overcome as it travels up to rock-over. Also with a little research on the second plugs location will give you a nice even burn pattern on your piston
Cheers
I don't know anything but the people that do.
Cheers
I don't know anything but the people that do.
In general detonation starts far away from the plug and in hot areas, so putting the plug near the hot exhaust valve, but in a location with a good combustible mix seems like a good spot.
Dual plugs should be widely disbursed to make all parts of the chamber close to a plug. Mechanically difficult.
The Harley K model was a pretty highly (factory and aftermarket) developed air cooled flat head engine. Supposed during displacement tech inspection or protest tear downs the factory mechanics or riders would take the cylinder heads, wrap them in shop rags and sit on them to keep them from prying eyes.
Here is a modern (dual plug) version.
headNote the block is also "relieved" to take part in mixture flow or whatever.
Are you allowed to modify ("relieve") the block too?
The Beach Boys were singing about it in 1963.
"She's ported and relieved and she's stroked and bored.
She'll do a hundred and forty on the top end floored
She's my little deuce coupe
You don't know what I got"
In one of Andy Granettelli's books he claimed he more-or-less invented "relieving" flat head Ford blocks for high performance, and that the factory started including that feature. Of course he also "designed the Chrysler 300 engine."
With the mile-long combustion chamber it seems physically tough getting a high compression ratio. And the long chamber brings along a related propensity to detonation even when inoculated with multiple spark plugs.
These guys, (and air cooled BMW specialists) advocate dual plugs for engines with far more more compact combustion chambers than yours.
Dual plugs should be widely disbursed to make all parts of the chamber close to a plug. Mechanically difficult.
The Harley K model was a pretty highly (factory and aftermarket) developed air cooled flat head engine. Supposed during displacement tech inspection or protest tear downs the factory mechanics or riders would take the cylinder heads, wrap them in shop rags and sit on them to keep them from prying eyes.
Here is a modern (dual plug) version.
headNote the block is also "relieved" to take part in mixture flow or whatever.
Are you allowed to modify ("relieve") the block too?
The Beach Boys were singing about it in 1963.
"She's ported and relieved and she's stroked and bored.
She'll do a hundred and forty on the top end floored
She's my little deuce coupe
You don't know what I got"
In one of Andy Granettelli's books he claimed he more-or-less invented "relieving" flat head Ford blocks for high performance, and that the factory started including that feature. Of course he also "designed the Chrysler 300 engine."
With the mile-long combustion chamber it seems physically tough getting a high compression ratio. And the long chamber brings along a related propensity to detonation even when inoculated with multiple spark plugs.
These guys, (and air cooled BMW specialists) advocate dual plugs for engines with far more more compact combustion chambers than yours.
>"The advantage of the second plug is reducing the timing advance by 10* which means the piston is closer to TDC and therefore less energy to overcome as it travels up to rock-over."<
Don't think so. As the piston & rod approach TDC (rockover?), they are slowed primarily by the crank, not PSI--likely even at low flathead RPM. Also, the crank has lots of leverage when the piston is near TDC and BDC (rockunder?).
"When the eagles are silent, the parrots begin to jabber."
Winston Churchill
Don't think so. As the piston & rod approach TDC (rockover?), they are slowed primarily by the crank, not PSI--likely even at low flathead RPM. Also, the crank has lots of leverage when the piston is near TDC and BDC (rockunder?).
"When the eagles are silent, the parrots begin to jabber."
Winston Churchill
BrianPetersen
Mechanical
That's not the issue. The issue is that if you have "slow" combustion, you need more ignition advance. This leads to combustion occurring longer before TDC and longer after TDC. Whatever combustion is occurring further from TDC, is happening at a lower effective compression ratio, and is not as fully utilized. A fast-burn chamber with less ignition advance, and as much combustion happening close to TDC as possible, will make more power (by making the engine more efficient).
Ford flatheads overheat if advanced more than 4 degrees static + 10 degrees vacuum advance; lots of advance is not needed. I believe other flatheads are similar. I think you are drawing inferences about the need for advance based on the shape of the combustion chamber that may appear to be rational but in practice are not.
There is really only one way to get high compression in a flathead (in an existing engine); larger bore or longer stroke or both -- increase cylinder volume. To get flows in and out of the cylinder requires a certain amount of area above the deck (distance between the deck and cylinder head), but increasing the flow area lowers compression.
As far as Andy Granatelli; there were many true innovators in the flathead world "back in the day", I don't think I'd call him one of them. Barney Navarro just died this week, check out his work.
Relieving is of questionable benefit on all but the full-on race engines. Similar results can be achieved thru shaping of the head surface, which is one of Navarro's tricks. Relieving necessarily stops short of the cylinder walls, the head surface doesn't. And relieving decreases the compression ratio... Wonder why you don't see any modern flatheads?!
There is really only one way to get high compression in a flathead (in an existing engine); larger bore or longer stroke or both -- increase cylinder volume. To get flows in and out of the cylinder requires a certain amount of area above the deck (distance between the deck and cylinder head), but increasing the flow area lowers compression.
As far as Andy Granatelli; there were many true innovators in the flathead world "back in the day", I don't think I'd call him one of them. Barney Navarro just died this week, check out his work.
Relieving is of questionable benefit on all but the full-on race engines. Similar results can be achieved thru shaping of the head surface, which is one of Navarro's tricks. Relieving necessarily stops short of the cylinder walls, the head surface doesn't. And relieving decreases the compression ratio... Wonder why you don't see any modern flatheads?!
automotivebreath
Automotive
Here's a link to some testing done for Briggs & Stratton on
a flat head modification. The results show substantial
reductions in BSFC.
a flat head modification. The results show substantial
reductions in BSFC.
As stated earlier relieving the block is "old school tech" on flatheads for pulling tractors. Spend some time on a flowbench and dyno and you will soon find that out, yea it looks cool and sounds neat to tell people about doing it.
The flatheads they build for pullers are nothing like the old Fords in technology. These flatheads are spinning upwards of 9000rpms on alky in some classes.
Look around the pits at the pulls, see many dual plug heads? Ever wonder why? Think nobody thought of it before and tried it? Might give you a clue to it's value in a pulling engine. Look around in the pits at where others have their plug located it will give you some ideas on location. One thing to remember the combustion chamber design will play alot in your location.
Yes, I actually do work on flathead pulling tractors . . .
The flatheads they build for pullers are nothing like the old Fords in technology. These flatheads are spinning upwards of 9000rpms on alky in some classes.
Look around the pits at the pulls, see many dual plug heads? Ever wonder why? Think nobody thought of it before and tried it? Might give you a clue to it's value in a pulling engine. Look around in the pits at where others have their plug located it will give you some ideas on location. One thing to remember the combustion chamber design will play alot in your location.
Yes, I actually do work on flathead pulling tractors . . .
- Thread starter
- #13
Thanks for all the responses guys. I knew I was asking the right bunch of experts.
This engine will not run on alcohol. My son pulls in the stock class now and is preparing to make the jump next year to Altered. This is all new to me and we are trying to build a tractor on a shoestring. I have full acess to a CNC Machine shop and Weld/Fab. shop so I thought we would make as many parts ourselves.
I had not looked at the Dual Plug concept, very interesting. In a stock Kohler Points Ignition you set the timing around 20 deg. BTDC. That seems like a lot, but it is what they need. Could this be reduced if the plug were moved over the Exhaust Valve or a second plug added? Is there any advantage to reducing it?
Brucepts: Are you saying that centered over the Exhaust Valve is the best setup? That seems to be the norm. I am just looking for as much opinion/data as I can get ahold of before I finalize a design.
Thanks to you all.
This engine will not run on alcohol. My son pulls in the stock class now and is preparing to make the jump next year to Altered. This is all new to me and we are trying to build a tractor on a shoestring. I have full acess to a CNC Machine shop and Weld/Fab. shop so I thought we would make as many parts ourselves.
I had not looked at the Dual Plug concept, very interesting. In a stock Kohler Points Ignition you set the timing around 20 deg. BTDC. That seems like a lot, but it is what they need. Could this be reduced if the plug were moved over the Exhaust Valve or a second plug added? Is there any advantage to reducing it?
Brucepts: Are you saying that centered over the Exhaust Valve is the best setup? That seems to be the norm. I am just looking for as much opinion/data as I can get ahold of before I finalize a design.
Thanks to you all.
"Conventional" thinking says put it over the exhaust valve but think about the space you need to have over that valve in the combustion chamber? Really wanna lose all that compression? Your head design will have alot more to do with location. You will not see a big reduction in timing in any location on a stock class engine assuming 4000rpm's?
As for machining the head, I do mine on a manual mill and handwork it to final design. I have a head blank I use for flowbench R&D and then copy that design over to my alum blank.
I'm in the same boat as you . . . building on a shoestring. I designed and built my own flowbench (now help others do the same thing on my website) fabricated my dyno. Purchased a mill, lathe and various other shop toys for less than the cost of a good NQS Pro Stock engine. Nice thing about doing it yourself, nobody knows what you have in your engine. If you buy an engine everybody knows what the other engine builders build.
Do I win? I enjoy pulling and do it at a very reduced cost in the class I run in. So in a way I win everytime I go out I spend alot less money to not win maybe $100.00? So in a way I am "winning" and having fun running what I build and not what someone else built for me! Right now I'm more focused now on flowbenching and building flowbench parts than building engines/parts for others so the tractor sits.
Anyone can buy power . . . but not anyone can make power.
As for machining the head, I do mine on a manual mill and handwork it to final design. I have a head blank I use for flowbench R&D and then copy that design over to my alum blank.
I'm in the same boat as you . . . building on a shoestring. I designed and built my own flowbench (now help others do the same thing on my website) fabricated my dyno. Purchased a mill, lathe and various other shop toys for less than the cost of a good NQS Pro Stock engine. Nice thing about doing it yourself, nobody knows what you have in your engine. If you buy an engine everybody knows what the other engine builders build.
Do I win? I enjoy pulling and do it at a very reduced cost in the class I run in. So in a way I win everytime I go out I spend alot less money to not win maybe $100.00? So in a way I am "winning" and having fun running what I build and not what someone else built for me! Right now I'm more focused now on flowbenching and building flowbench parts than building engines/parts for others so the tractor sits.
Anyone can buy power . . . but not anyone can make power.
- Thread starter
- #15
Very nice brucepts. You and I are on the same page. Except that my kid gets to do the driving, but I really enjoy building/tuning and always have. I used to be into Hot Rods and such.
What is your website address? I have always thought a small Flowbench and Dyno would be great fun to play with.
What is your website address? I have always thought a small Flowbench and Dyno would be great fun to play with.
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1
- #16
New guy here.
Several years ago my partner and I were designing an intake and exhaust port for an overhead valve engine and couldn't decide where to put the spark plug. In an effort to determine the effects of plug location (and play a little) we built a new head for a friends alcohol fueled go cart Briggs & Stratton. We rented a portable dyno from one of the local cart shops and actually dynoed the engine with 6 different plug locations and with the stock magneto system and with a MSD-6AL ignition.
Bottom line on this engine; except for having to change the amount of advance the power stayed the same regardless of the plug location and ignition type being used.
Ron
Several years ago my partner and I were designing an intake and exhaust port for an overhead valve engine and couldn't decide where to put the spark plug. In an effort to determine the effects of plug location (and play a little) we built a new head for a friends alcohol fueled go cart Briggs & Stratton. We rented a portable dyno from one of the local cart shops and actually dynoed the engine with 6 different plug locations and with the stock magneto system and with a MSD-6AL ignition.
Bottom line on this engine; except for having to change the amount of advance the power stayed the same regardless of the plug location and ignition type being used.
Ron
- Thread starter
- #17
- Thread starter
- #19
Actually there are a lot of dual outlet coils around
any will work. I just mentioned the Harley coil because I use them on my Norton race bike..It works well and fires both plugs at the same time...
I didn't mean to sound so cranky I appreciate all who post here...
The real danger is doing things without being challanged... and that is why I post my comments expecting just that....
Cheers
I don't know anything but the people that do.
any will work. I just mentioned the Harley coil because I use them on my Norton race bike..It works well and fires both plugs at the same time...
I didn't mean to sound so cranky I appreciate all who post here...
The real danger is doing things without being challanged... and that is why I post my comments expecting just that....
Cheers
I don't know anything but the people that do.
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