porting 8hp briggs

[briggs33]

ok what i want to port is a 8hp briggs and stratton engine no points 1996 model . OK i want to make the engine breath better so i started shaving the eye brow. should i shave the parts between the cylinder and the exhaust and intake plus between the exhaust and intake or just intake and cylinder and exhaust and cylinder. Also what about what the carb meats up to the block is there a way to port that?
What im really trying to do is make more top end speed what should i do? ohh and if i were to make up and exhaust how long should it be because i know there is an amount of back pressure that and engine should have.

Sorry about the questions im just interested lol

 

[minidragbike]

The best thing would be to deck the block enough so there doesn't need to do any eyebrow blending. Yes from valves to bore, and from valve to valve.

Port match carb to block. Port the short side, under the valve seats.

The exhaust will need to just be a long pipe. Then run your motor and see were the heat stops. Then cut it off a inch after that.

 

[65ShelbyClone]

I have an 8hp Briggs block sitting down stairs that I started porting a long time ago......I'll have to go look at it to see what I did.

 

[GTO]

I have an 8hp Briggs block sitting down stairs that I started porting a long time ago......I'll have to go look at it to see what I did.

How about pics?

 

[stubbysteve]

again try g-team.com they have a video that shows how to modify the engine and everything you need to know. $35 includes shipping and handleing. It is about 3 hour long. And worth every penny. But remember it is for the bottom shaft engine but the same thing can be done for the side shaft engine. everything is the same except the mounting area and the oil pan.

 

[65ShelbyClone]

How about pics?

That's what I had in mind. :wink: I'm going to wait until it's daylight, though.

There is a limited amount that can be done to a Briggs flathead without using epoxy or welding. The ports have square corners without much room to smooth them out.

 

[briggs33]

cool cant wait to see the pics shelby!

 

[65ShelbyClone]

This is the 8hp Coolbore block I practiced on. I forgot that I had already epoxied it, but these will give you an idea:

http://img.photobucket.com/albums/v521/65ShelbyClone/Public/8hpport1.jpg
http://img.photobucket.com/albums/v521/65ShelbyClone/Public/8hpport2.jpg
http://img.photobucket.com/albums/v521/65ShelbyClone/Public/8hpport3.jpg
http://img.photobucket.com/albums/v521/65ShelbyClone/Public/8hpport4.jpg

Also notice that the deck has been milled all the way down to the valve seats. :biggrin:

This is the exhaust port, obviously with no epoxy. This is mostly what the intake port looked like before porting and filling. That's what I meant by "square corners" and why it's IMO a pain to do good porting on production flathead blocks.
http://img.photobucket.com/albums/v521/65ShelbyClone/Public/8hpport5.jpg

Just for kicks, here is an old, OLD '50s vintage Model 14 that I started hot rodding. Notice the tiny flywheel. Ignition timing is factory adjustable, has 1.00" valves, titanium retainers, and I milled the head quite a bit. It's hard as heck to rope start with high compression and almost no flywheel.

http://img.photobucket.com/albums/v521/65ShelbyClone/Public/ironBriggs.jpg

The intake port was actually a very good shape to begin with and easy to make bigger and better. It's long and sloping with no sharp turns like the aluminum blocks. The valve guide was huge, though. As you can see I addressed that too.

http://img.photobucket.com/albums/v521/65ShelbyClone/Public/model14valveguide-after2.jpg

Here is the deck porting I did on the 24ci/10hp flathead that was(keyword here) the victim of my turbo/EFI effort. Some people recommend doing this, some recommend not. You choose.

http://img.photobucket.com/albums/v521/65ShelbyClone/Public/ironBriggs.jpg
http://img.photobucket.com/albums/v521/65ShelbyClone/deckported2.jpg

This is the intake port from that 10hp. Notice those oh-so-familar square corners...

http://img.photobucket.com/albums/v521/65ShelbyClone/port1.jpg

EDIT: Generally you want to make the short side radius of the port(in the case of a flathead, the top of the port) as smooth and sweeping as possible. Don't focus on making the port bigger, instead try to make it smoother and more efficient.

 

[briggs33]

great pictures and that old motor was really neat but i will go ahead and try the porting. thanks alot!

 

[GTO]

Hey thanks for the pic's. :thumbsup:

 

[65ShelbyClone]

You're all very welcome. :smile:

I also have a 2hp flathead and a Honda GX140 that I did the same kind of stuff to except the Honda got a big titanium intake valve. I was thinking about attacking my Kohler K301 with a die grinder too, but I think I'll just try to get a bigger twin cylinder engine instead(preferably OHV).

 

[Taylor]

Hello,
Couple questions for you guys. Here is some porting I did to a 8hp Briggs and wanted some pointes and tips for what I did wrong and right and what to do next time....

Exhaust

Intake

Later,
Taylor

 

[65ShelbyClone]

I think you did alright for a first try. You didn't hit the valve seats, so that's good.

One thing about the exhaust ports is that they are often too big to begin with. They look terrible for flow, but it's not generally necessary to remove the pipe threads from the intake port.

 

[Taylor]

I think you did alright for a first try. You didn't hit the valve seats, so that's good.

One thing about the exhaust ports is that they are often too big to begin with. They look terrible for flow, but it's not generally necessary to remove the pipe threads from the intake port.

Thanks for the word of advise! I have a 5hp vertical block thats no good I am going to practice on next....

 

[65ShelbyClone]

Good, get all the practice you can. I had probably ported at least ten blocks and heads before I played on the 8hp I posted pictures of. I have two 4hp Tecumseh lawnmower blocks I will probably use for practice as well. If I can make the ports in those look good, I can port anything. :wink:

I also recommend reading whatever you can about head porting. Standard Abrasives has a basic guide on their site, but there are other more comprehensive articles floating around the 'net.

 

[smallbikes88]

how does it run? thats the real test!

 

[65ShelbyClone]

I thought since the engines were trash already, I might as well get some clear pictures to illustrate what I meant about the short side radius. The 8hp is on the left and the old turbo 10hp on the right.

 

[Taylor]

65shelby,
I did find the standard abrasives article read it and printed it out for further refrence. Tomorrow I am going to start poting that 5hp block. I'll get pictures of an before and after.

Taylor

 

[Taylor]

65Shelby,
I got to thinking about some ports and such and kinda came up with this-

I got to thinking about how the port works. It swirls the fuel around until it gets to the valve and dumps out. Kinda like a toilet right? It swirls the water until it drains out the bottom.... Now if you think about that it takes a certain amount of time to get the water down..... SO it takes a certain amount of time fopr the fuel to get there, Correct? Following me here?
Now what if you instead of cutting the port round and waiting on the fuel to get there cant you try to cut in a shape of a "D" so that the fuel has to go right to the valve? It would not swirl and you wouldnt have to wait on the fuel to get there....And it would create some more power.....

--------------------------------------------------------------------------

This is a old Briggs 6.5 HP vertical shaft OHV. A guy down the street brought it to me because they carb is gummed up and when I pulled the carb this is what found.... Is this what you are sorta talking about for a "D" shaped port? Should I make it similar? Or not quite that way?

This is a little something that I thought of when just kinda thinking about how much I can grind that cam for a 3hp with out starving it for fuel.....

Taylor

 

[Motra]

Just to add my two cents worth, which probably isn't even worth two cents. Briggs33 says he's after more top speed. Seems like regearing would be a lot easier and cheaper and way more effective. Porting, if done correctly, can improve power but if the engine is governed there won't be an increase in top speed. Porting can increase the RPM range on an ungoverned engine which would give some added top speed but an 8HP engine in a minibike has plenty of power to pull higher gearing without mods and would be more reliable.