How to soup up a Briggs flathead cheaply??

I was wondering if anyone out there knows anyways to get a little more power out of your stock flathead engine cheaply? Any ideas?

Bandit1 wrote:

I was wondering if anyone out there knows anyways to get a little more power out of your stock flathead engine cheaply? Any ideas?

Ive seen a few videos, FearlessFront said he shaved the brows, and turned down the head something of an inch for compression, and i think changing to a better than stock spark plug coundlnt hurt..

There might be some other things..but I typically dont mess with the internals that much..

Check out this link and look at the Double Sparkplug head for a flat head..

About mid page! click here

I always wanted to try a motorcycle or atv carb on one other than that you could do an intake exhaust and i like to run e3 sparkplugs.

your best bet would be to search out what they did back in the 50's on the original flathead fords and adapt it to a single cyclinder design., also there are other flathead style engines that have been modified over the years. Look at wisconsin v-4s etc.

A mild port and polish job is free if you do it yourself. all you need is a cheap HF electric die grinder (dremel) and a few fine stones and polishing wheels. The idea is to carefully and gently smooth the airflow through the port. Intake ports should be slightly rough, exhaust ports should be as smooth as possible.
go lightly, its very easy to cut through the casting and screw it up
practise ona scrap head

ANY engine can benifit from an increase in airflow. However the carb will need to be adjusted to compensate.

A free flowing airfliter and exhaust, mild polish on the intake and exhaust ports, and a thinner head gasket can all add up to few more ponies.

Some guys have been known to make their own headgaskets fron sheet copper. Opening up the carb downstream from the butterfly can pick up a bit, as can opening up the throat upstream of the butterfly. BE VERY CAREFUL DOING CARB MODS OF THIS TYPE. ANY CHANGE IN THE AIRFLOW OF A CARB WILL CHANGE ITS JETTING DRASTICALLY. THIS IS ONLY FOR THE ADVANCED.

Has anyone here ever tried to modify there cam to hold the valves open longer and faster?

Bandit1 wrote:

Has anyone here ever tried to modify there cam to hold the valves open longer and faster?

I have seen some videos on people doing something like that. I dont have one to use at the moment, but I honestly think it was beacuse they were hooking up a "turbo" to the engine..not recommended for off road use..haha!

I do and have heard of different valve spring set ups..but im to novice to give advice on that stuff..

I personally asked FearlessFront if shaving the brows had made any significant difference, and he said not really. He said, the big difference at all was that he switched factory connecting rods with forged and that has made his murray what it is today...

I have a lot of scap engines that I can use so I think I'm going to do some experimenting on them.. I have shaved the head on one engine but now it is preignighting causing a loss of power did I shave it to much??

Chopperhed, what do you mean opening up the carb.. Drilling holes in it?

Bandit1 wrote:

I have a lot of scap engines that I can use so

Share the wealth..I have three engines that need connecting rods..got any?

A lot of the engines are damaged from lack of oil or the rod went through the side of the motor. So not many are good but what size of engine you need one for?

Bandit1 wrote:

A lot of the engines are damaged from lack of oil or the rod went through the side of the motor. So not many are good but what size of engine you need one for?

I have two Kholer 16ish horse and the 20hp opposed briggs..I havent pulled them apart because I have alot of projects going, but I do need a running engine soon..

I posted the Kohler's model numbers on here, let me see if I can find the link..

here is the link

The oppoesed twin I have a video of it

20h sound right?

Sorry man, I don't have anything that'll work for you. What happens to the connecting rods that were in them?

No one has suggested the smog pump supercharger?
http://www.turborick.com/dirt.html
https://www.youtube.com/watch?v=rS8LgJQME0Q&feature=share&list=ULrS8LgJQME0Q

Never thought of trying a smog pump as a supercharger otherwise i would have done it by now

Bandit1 wrote:

I have a lot of scap engines that I can use so I think I'm going to do some experimenting on them.. I truer shaving the head on one engine but now it is preignighting causing a loss of power did I shave it to much??

Chopperhed, what do you mean opening up the carb.. Drilling holes in it?

I just meant enlarging the carb throat before and after the butterfly, This would increase flow and intake velocity at the same time

Ive tried a E3 plug in a mower - i didnt see any significant increases in power ( back when i was trying to super tune my '82 dynamark mower for better 'fuel economy and power' .

Best mod would be the carb change , foot throttle ( crisper response) - maybe try different plug heat ranges, try running a synthetic oil and or high test gasoline.

I dont suggest bypassing the governer , unless the motor has been properly prepped for higher RPM's.

As i found out - best way to get more power - a bigger motor. Unless a vtwin has been modifed to make more power - id suggest a big old twin flathead briggs motor .

Well Im using a 11 hp and I have 12.5 and 14.5 carbs. Do you think it would make much difference to switch to one of those carbs or would it just flood it out?

theoretticly it shouldgive more power, but it might flood it out because the engine's not tuned for a bigger carb

I had an 11 horse flat head with a 18.5 horse carb on it i did git a power increase but reliabillity was terrible it flooded alot.

The 11hp and the 12.5 should be about the same carb. I have seen the large one piece and the smaller walbro's on both. Can't speak for the 14.5 but it may work. Another trick some people do is to modify the intake valve to accept the exhaust valve retainer, and install an exhaust valve spring in it's place. It's a bit stronger then the intake spring. Without decking the head, you could use the 11hp head (25 Cu) on the 12hp (28 Cu) block. It will raise compression, but you loose flow. For unmodified motors this may be an option, but once opened up for more flow, the 12hp head on the 12hp motor will produce more power. (Dynamic Vs. static compression)

I put an 11 hp head on my 12.5 hp engine in my yardmachine. I noticed a slight difference in power but it is hardly noticeable.

i used a spring compressor and i diagrinder with a multi carb bit. Sandpaper too. Took the valves out grinded the intake and exhaust port out. Sanded them down smooth. Put it back together. Now i have lots of power in my opposed. plus i run racing fuel mixed with alcohol.

On my flatty, all I really did to it was mill the head down .010 of an inch, shaved the eyebrow on the block casting, ported the intake and exhaust ports. The valves got lapped and installed, then I put in a piston and connecting rod for a 28cu.in. ohv briggs for a little more strength (everything got a dab of red loctite for assembly). After that, I ported the intake manifold and installed a carb from a 14hp. Once that was done, I installed the head ( more loctite) and put it all back together. Bad part was, I now had so much compression, my weak 10 year old stater couldn't turn over the motor fast enough to start it up. So I bought a new one that worked much better.
I do run a slightly colder spark plug grade 93 fuel to prevent pre-ignition.
It didn't make a huge difference, but as u can probably tell from my vids, it has a lot of torque. That helps in the deep stuff, it keeps the motor from bogging out.

One more thing... Use shell rotella or rotella t 10w-30 engine oil. It has a high amount of zinc which is good for motors with flat-tappet style valves. And it used in diesels, so it is a really tough oil. I use it in my jeep.