14cc gx160 porting tips/pics

[Gx160Mini]

Old style gx160 head(27mm/24mm)
Going to port it and mill it prob .065 or more depending on clearance
Flat top piston file fit rings
Stock bore
Arc +.020 con rod
NrRacing 307-1006 cam
CM pushrods
1.3 billet rockers
Dual springs
Arc billet aluminum flywheel 6619 (8* advance)
On 110octane
22mikuni
Gov removed

I want some good pics or tips about porting a head to flow great and produce a lot of power. Ex: valve stem(to grind down or not?), how much to go till I break through the oil gallery, and other great tips.
O or D port.

 

[David wulf]

I built a honda 160 with 14 cc head , first is to unshroud the valves . In the chamber the edge is real close to the valves , open it up the about 1/8 to 3/16 ths around the outside .

 

[David wulf]

I also rounded the ports some , the intake more than ex side . don't get the intake too smooth , an 80 grit swirl works good . The EX smooth as possible and the chamber too . If you look at the pic the lump that sticks up around the valve i took down some .

My motor has a black mamba , stock stainless valves and champion rockers . flat top honda piston and head was sanded on a marble tile on 80 grit .

Also ran a buris 9 th thick head gasket and no leaks , don't know comp but she's really loud .

 

[David wulf]

Oh one more thing keep a old valve in the when your cutting in the chamber cause its easy to hit the seats , and when you do have to take it out to cut in the port from the chamber side be careful around the seats .
Don't ask why i know .

 

[vwfan79]

I do mine a lot like David but I will take my intake and exhaust gasket and cut them to match the carb or header then put the gasket against the port and shape my port to match then make a nice smooth transition back to the valve. I take the area around the valve guide down to blend into the guide and get rid of any sharp edges there.

David that head looks nice.

Sent from my Desire HD using Tapatalk 2

 

[Racer67]

Don't want to jack this thread, but have also been wanting to post porting questions so I will just chime in here.

Nice work David.
Could you post a pick looking into the inlet tract?
I am getting ready to start some porting work on a hemi predator and have been trying to get some good info on porting. Just planning on a stock appearing carb and black mamba cam.
My main question is on the intake, people talk about working the SSR (short side radius). On the predator hemi head, the intake floor basically falls off a cliff with a very sharp radius. Some say to widen the floor, but do you also add more radius to the "cliff"?
I was going to draw up some pictures to help explain.
Some good reading on the YZF? forum If I remember right, talk about leaving somewhat of a venturi before the valve bowl area.

Any thoughts appreciated.
I look at these $99 engines as a perfect learning tool for how to make cheap reliable horsepower. I have 3 hemi predators to play with currently.

Thanks again.
Allen

 

[Stangrcr1]

Low floor and radiused to the valve is good for HP. The lower the port floor to the valve, the better it will flow for HP at higher rpm. Low rpm torque will suffer though....


BTW, Illinois sucks. I know. I grew up there. Too many Democrats... :laugh:

 

[David wulf]

Here some of the intake , personally i think i got it a little big . What i did was had the intake manifold bolted to the head and ran the sanding drum in an out till i had them matched . Well got things a little thin and had to epoxy the outside cause it was cutting gaskets . Also my motor screams on the high end but down low 2 to 3 k it lacks a little .
I have a 18 cc head on my air compressor motor and will get it one day and this time just not cut so much and just clean it up .

I have seen inside a NR racings ported head and stock port shape and most the work in floor and bowl area .

 

[Racer67]

I agree 100% on the Illinois comment. I don't live in Shitcago, so not too bad and the company I work for is based here.
Stangr,
I have read about leaving at least 1 cm of straight length in the bowl after the SSR is important. It may benefit lower rpm flow more based on your comments. What I am wanting to do to the hemi head is just improve flow/performance for a fairly mild build with a bored out stock carb and stock flat top piston. My goal is around 20hp and pull start.

David,
Thanks for the pics. Looks good. That is more of a big carb monster than what I am building now. Will probably have to do a big carb big valve engine in the future. Trying to keep pretty basic right now.
Thanks

 

[David wulf]

I agree 100% on the Illinois comment. I don't live in Shitcago, so not too bad and the company I work for is based here.
Stangr,
I have read about leaving at least 1 cm of straight length in the bowl after the SSR is important. It may benefit lower rpm flow more based on your comments. What I am wanting to do to the hemi head is just improve flow/performance for a fairly mild build with a bored out stock carb and stock flat top piston. My goal is around 20hp and pull start.

David,
Thanks for the pics. Looks good. That is more of a big carb monster than what I am building now. Will probably have to do a big carb big valve engine in the future. Trying to keep pretty basic right now.
Thanks

I like the sound of your build but i hear this all the time( mild).
Mild is not 20 HP , 20 hp is a built asss mean motor . The 160 i build is strong but i have no idea the Hp and its not 20 or close maybe 12 - 13 who knows unless you have a dyno sheet .

This is NR racings almost biggest small block . Next is and Open GX200 somewhere in the low 20's . Russell will not even build a predator this big cause it won't hold together .
The 18.6 hp is totally bad ass . Hit the gas on the super powell with 11to 1 gearing and the thing jumps and your doing 45 or so at 9 k really fast . 20 hp would almost be to much .

So what i'am saying build these motors and let see some dyno sheets .

 

[Gx160Mini]

Thanks a lot. The pics are great, so what do you epoxy with, JB Weld? Also would it be bad to grind the valve guides down smooth to the port itself.

 

[Racer67]

David,
I was just basing the 20hp number on the baseline I have with a 200cc BSP AKRA legal clone being somewhere between 12-13 hp (on a given acceleration dyno). I guess 50% increase in power over that may be a little optomistic, but with 6% more displacement, higher CR, open cam, better flowing heads, and bigger carb, I think it might be possible.
I have 3 engines to play with, so I hope to document the change in hp/torque with each change. This can be a real drain on time as it usually takes several runs to optimize jetting for a particular setup.

I will start a new thread to document the hemi head work and other mods.

Thanks

 

[novaracer]

You need some swirl. :wink:

 

[65ShelbyClone]

Old style gx160 head(27mm/24mm)
Going to port it and mill it prob .065 or more depending on clearance
Flat top piston file fit rings
Stock bore
Arc +.020 con rod
NrRacing 307-1006 cam
CM pushrods
1.3 billet rockers
Dual springs
Arc billet aluminum flywheel 6619 (8* advance)
On 110octane
22mikuni
Gov removed

I want some good pics or tips about porting a head to flow great and produce a lot of power. Ex: valve stem(to grind down or not?), how much to go till I break through the oil gallery, and other great tips.
O or D port.

Instead of just planning on 110 leaded gas, figure out what your compression ratio is going to be and then pick the fuel. Too much octane does offer a margin of safety, but it also costs power and money.

As for porting, it is generally advisable to leave the port floor alone, make the short-side radius as broad and sweeping as possible, leave a rough (~80-grit) finish in the intake port, and don't taper the ports any more than 8-10°.

1.) My main question is on the intake, people talk about working the SSR (short side radius). On the predator hemi head, the intake floor basically falls off a cliff with a very sharp radius.

2.) Some say to widen the floor, but do you also add more radius to the "cliff"? I was going to draw up some pictures to help explain.

3.) Some good reading on the YZF? forum If I remember right, talk about leaving somewhat of a venturi before the valve bowl area.

1.) All the OHV utility engines I'm familiar with exhibit this phenomenon. The heads are die-cast instead of using sand cores and that requires that the port shapes allow for removal of the mold dies, so they can't really curve at all. Then the whole valve pocket and bowl is plunged with a mill cutter for speed/ease of manufacturing. It results in the port floor terminating at a sharp edge. In applications where performance is more important, the head can be die-cast with sand cores used to make complex port shapes.

2.) The broader you can make the radius transitioning the SSR to the valve seat, the better.

3.) Tapering the port into the seat is a subject of much debate, but what's more important is that 90% of what you'll read regarding 4v bike heads does not apply to 2v wedge or hemi designs. Furthermore, 5v designs like Yamaha used for a long time have very different porting considerations than even a 4v layout.

Low floor and radiused to the valve is good for HP. The lower the port floor to the valve, the better it will flow for HP at higher rpm. Low rpm torque will suffer though....

Lowering the port floor makes the SSR more critical because the charge has to make a larger change in direction. This also tends to cause flow separation at a lower velocity.

F1 engines, although an extreme example, utilize all the port velocity they can and the ports have such a large SSR that the ports are nearly straight. This is an older Toyota F1 engine cross-section to illustrate:

And this is one of Cosworth's designs:

Also would it be bad to grind the valve guides down smooth to the port itself.

You will get a variety of opinions on that. Shortening the guide protrusion reduces guide-to-valve contact area, valve stem support, and ultimately heat transfer. I prefer to leave the boss and guide in the port and instead streamline them as much as possible.

The loss of valve guide length can be addressed by using a longer guide and longer valves to "rob" length from the port side and put it under the valve spring.Then valvetrain geometry has to be checked and corrected as necessary.

 

[Newoldstock]

All I have to add to this is I blend around the guide rather than cut it.
You want your heads to last and heavy springs are not going to make life easier.

I never tried the push...
But some tell me that a Honda guide can remain stable in the head if you press it back to loose little of that protrution into the port.

Ive used some epoxy in th ebowl of a 14cc head.
I'm not sure its made much difference because the proting itself on that head was not the best.
Only a flow bench could tell me different.
But I used Devcon WR2 and it stayed put.
The head is still in service 4 years on ( on my snow blower these day )

 

[novaracer]

I say remove the guide and make the roof shape match the ssr. Without a bench that is the best rule of thumb and remember the throat diamond should be around 85 to 90 percent of the valve diameter:wink: and the porter trick is emery cloth to get that short side radius shape right. Now the combustion chamber the area around the seats blend the aluminum step around the seats. I polish the chamber and piston crown and exhaust port. Wet sand by hand those areas up to 1000 grit then polish. Leave the intake port at no more than 150 grit I like 80 myself. Now polishing the areas I pointed out might not make power but it will keep carbon from sticking and making the tune consistent. That's the basics from my point of view

 

[novaracer]

Correct me if I am wrong:thumbsup:

 

[Newoldstock]

Your not wrong on what I understand of it and do.

But make a swirl.
That's something I can't comment on.
Enlighten me please.

Some very modest work done on the short side and edge leading the bowl.
A little light relieving around the combustion chamber.
It was a good start I built upon in the following heads.

 

[LSCustoms]

oing 45 or so at 9 k really fast . 20 hp would almost be to much .

So what i'am saying build these motors and let see some dyno sheets .

I will have my motor tuned on the dyno very soon... my gearing is for higher speed too, but the bonanza will be a fun bike to putt around on... the two drag bikes will hopefully be way more aggressive... im curious to see where the bonanza's motor is really at though...

 

[boostdoctor]

Instead of just planning on 110 leaded gas, figure out what your compression ratio is going to be and then pick the fuel. Too much octane does offer a margin of safety, but it also costs power and money.

As for porting, it is generally advisable to leave the port floor alone, make the short-side radius as broad and sweeping as possible, leave a rough (~80-grit) finish in the intake port, and don't taper the ports any more than 8-10°.



1.) All the OHV utility engines I'm familiar with exhibit this phenomenon. The heads are die-cast instead of using sand cores and that requires that the port shapes allow for removal of the mold dies, so they can't really curve at all. Then the whole valve pocket and bowl is plunged with a mill cutter for speed/ease of manufacturing. It results in the port floor terminating at a sharp edge. In applications where performance is more important, the head can be die-cast with sand cores used to make complex port shapes.

2.) The broader you can make the radius transitioning the SSR to the valve seat, the better.

3.) Tapering the port into the seat is a subject of much debate, but what's more important is that 90% of what you'll read regarding 4v bike heads does not apply to 2v wedge or hemi designs. Furthermore, 5v designs like Yamaha used for a long time have very different porting considerations than even a 4v layout.



Lowering the port floor makes the SSR more critical because the charge has to make a larger change in direction. This also tends to cause flow separation at a lower velocity.

F1 engines, although an extreme example, utilize all the port velocity they can and the ports have such a large SSR that the ports are nearly straight. This is an older Toyota F1 engine cross-section to illustrate:

And this is one of Cosworth's designs:

You will get a variety of opinions on that. Shortening the guide protrusion reduces guide-to-valve contact area, valve stem support, and ultimately heat transfer. I prefer to leave the boss and guide in the port and instead streamline them as much as possible.

The loss of valve guide length can be addressed by using a longer guide and longer valves to "rob" length from the port side and put it under the valve spring.Then valvetrain geometry has to be checked and corrected as necessary.

I want to try using a raised intake runner for a straighter shot to the valve. It still will be nothing like these examples, but it just may help a bit. I just hate to put in a lot of effort for minimal gains.