Food for thought.

FlatheadsForever87

FlatheadsForever87

Member
I have a question for the gurus, veterans, thinkers, engine builders, and any other flatheaders out here that has had me thinking since the very first time I went to the track. Here it goes, what all can be done if there was no rules other than it has to be or appear to be stock parts on it. Anything else goes, such as flattop1s genius idea to plug up air horn and breat through the back side where the Welch plug goes. Tips, tricks, and mods like these that have been thought of through the flathead prime time. Also a question for the savvy tech men and women. What are the most clever things you have seen folks try to pass through the tech barn or what sneaky stuff happened to pass by you once or twice through the years. Apologies for the long winded blog. I'm honestly excited and can't wait to see the things you all know of. The more detailed the better.
 
usetabe A Stock Appearing Flat head class,

Looked just like a boxstock
Do anything you want but all outside parts have to look exactly as stock.
Dave Turner made some real good thumpers

.
 
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Making a bigger bang is more about more airflow, compression and type of fuel, then it is about putting enough fuel to it.

Stock looking briggs boxstock carb can be altered/adjusted so you have both low and high speed fuel setting.

Your pickup tube limits the potential for maximum fuel flow.

The amount of fuel it lets thru it becomes your high speed top end fuel flow adjustment.

The key to understanding it IMHO is top end has the highest piston speed.
To adjust for the faster piston speed, you either have to ignite the fuel sooner or burn less fuel.
Since there isn't any advance on it your only option is to burn less fuel per burn at high speed.
Yes you burn less fuel per burn but because your burn the lesser amount more often at high rpm, you still consume more fuel.

Slower piston speed gives you more time to burn fuel.
It allows you to use more fuel per burn.
But because rpm's are down, even though you use more fuel per burn over all fuel flow is less.
 
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paulkish said:
Making a bigger bang is more about more airflow, compression and type of fuel, then it is about putting enough fuel to it.

Stock looking briggs boxstock carb can be altered/adjusted so you have both low and high speed fuel setting.

Your pickup tube limits the potential for maximum fuel flow.

The amount of fuel it lets thru it becomes your high speed top end fuel flow adjustment.

The key to understanding it IMHO is top end has the highest piston speed.
To adjust for the faster piston speed, you either have to ignite the fuel sooner or burn less fuel.
Since there isn't any advance on it your only option is to burn less fuel per burn at high speed.
Yes you burn less fuel per burn but because your burn the lesser amount more often at high rpm, you still consume more fuel.

Slower piston speed gives you more time to burn fuel.
It allows you to use more fuel per burn.
But because rpm's are down, even though you use more fuel per burn over all fuel flow is less.
Click to expand...
Anyway you could explain how one would alter or adjust the Carb outside of the norm?
 
FlatheadsForever87 said:
Anyway you could explain how one would alter or adjust the Carb outside of the norm?
Click to expand...
Simple mods would be to use a carb gasket to trace marks on both the carb and block. Use a Dremel tool to blend a port match between the two. This will wake it up substantially.

Remove the butterfly and throttle shaft, reassemble them outside of the carb, and use a Dremel, files, and/or sandpaper to make the shaft and plate as thin as possible to free up air flow, it's advisable to keep the diameter of the throttle plate as original as possible.
Using a stock throttle plate, you can use a .700 or .710 straight flute reamer to bore the carb without running into idle problems that are too bad. Much larger and you will need to make your own throttle plate out of a penny or something.
Don't worry about trying to plug up the air horn and bring the air through the back of the carb, there's not much to be gained there. Just smooth the edge where the air horn meets the carb bore.

I used to use a 94-SS cam, but that looks to be discontinued now. An 03-SS has .290 lift, so it should work well.
Is that the kind of stuff you're looking for?
There is much more that can be done depending on the thickness of your wallet.
 
FlatheadsForever87 said:
What does it take to convert it? I have been thinking about the little slot on top of the pick up bowl. If that was sealed wouldn't that make for a completely different animal?
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FlatheadsForever87 said:
What does it take to convert it? I have been thinking about the little slot on top of the pick up bowl. If that was sealed wouldn't that make for a completely different animal?
Click to expand...
Knock out the Welch plug and remove the swirl and throttle shaft. Bore the carb, ( I think we used to bore them 3/4”). Mill the throttle shaft for a larger butterfly and that part is done. Now flip it over and remove the short pickup tube. Mill a slot from the fuel outlet from the pump to the hole where the short tube was. Install a gasket, then a plate, then another gasket and then the tank. The plate only has a hole for the long tube and bolt holes. Bore the jet on a taper and use a high speed adjustment needle from an old 8HP horizontal engine. This is for methanol. Don’t know how well this would work with gas. The fuel pump will now force fuel directly into the jet. You’ll need to enlarge the two metering hole behind the jet also but I can’t remember how much. Seems like .060 and .030, not sure.
 
Bob Evans said:
Simple mods would be to use a carb gasket to trace marks on both the carb and block. Use a Dremel tool to blend a port match between the two. This will wake it up substantially.

Remove the butterfly and throttle shaft, reassemble them outside of the carb, and use a Dremel, files, and/or sandpaper to make the shaft and plate as thin as possible to free up air flow, it's advisable to keep the diameter of the throttle plate as original as possible.
Using a stock throttle plate, you can use a .700 or .710 straight flute reamer to bore the carb without running into idle problems that are too bad. Much larger and you will need to make your own throttle plate out of a penny or something.
Don't worry about trying to plug up the air horn and bring the air through the back of the carb, there's not much to be gained there. Just smooth the edge where the air horn meets the carb bore.

I used to use a 94-SS cam, but that looks to be discontinued now. An 03-SS has .290 lift, so it should work well.
Is that the kind of stuff you're looking for?
There is much more that can be done depending on the thickness of your wallet.
Click to expand...
Yessir! Good stuff. As far as cost goes let's pretend for a while that money is not a problem. Thanks for chiming in. I'm sure Mr. Carlson, Flattop 1, Jody, Mr.Dover and Mr. Glenn has a few mind blowing tricks up their sleeve. Let's hear em fellas.
 
In 2007 there was a guy building a scratch built .850 stock appearing carb called the Cyclone SA. I don't think he was in business very long, but it was a really good carb.
He was an advertiser here, and he sent me one of them. It worked VERY well. Maybe someone else remembers these carbs.
But good luck finding one.

Stock appearing was never a really popular class, it was pretty much cheaper to build a Limited Modified.
Internally they were pretty much a Modified, with the added expense of machining the eyebrows, adding big valves, ultralight 3hp billet flywheel, stroker kit, etc.
It was a fun and creative class though.
 
I was wondering, has anyone ever built a simple slider mechanism for the coil so you could advance the timing while running? Small outboards have had these for years. It seems this would improve performance tremendously.
 
leoofc said:
I was wondering, has anyone ever built a simple slider mechanism for the coil so you could advance the timing while running? Small outboards have had these for years. It seems this would improve performance tremendously.
Click to expand...
Look around on the Jr drag sites. Pretty sure it's a legal mod for those fellas. Sure would make things a lot more simple tho
 
I used 66% RC mix (I think Torco still ships it) and mixed it with methanol. It's about $70 a gallon though. That's enough for over 6 gallons of a 10% mix, or over 12 gallons of a 5% mix.
The Klotz stuff is nitropropane.

Real nitro will build heat in significant amounts with total mixes as low as 5 to 10%. You also need to jet larger with real nitro, and there ain't no way it'll pass a water test. :)
 
Bob Evans said:
In 2007 there was a guy building a scratch built .850 stock appearing carb called the Cyclone SA. I don't think he was in business very long, but it was a really good carb.
He was an advertiser here, and he sent me one of them. It worked VERY well. Maybe someone else remembers these carbs.
But good luck finding one.

Stock appearing was never a really popular class, it was pretty much cheaper to build a Limited Modified.
Internally they were pretty much a Modified, with the added expense of machining the eyebrows, adding big valves, ultralight 3hp billet flywheel, stroker kit, etc.
Click to expand...
Wasn't it Mike Clements that built the Cyclone carb? -- Chuck
 
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