11 replies to this topic

[luismx123]

hey all.
so I got my hands on an old 998 head which I thought id give porting a go. I'm fairly good with tools and sculpting so why not...
Tried my luck this evening on the outer exhaust ports with a double cut carbide Burr - ball shape) and it was all going well until the Burr started catching and wobble the machine in my hands. The Burr started to bounce around in the throats and it got me really worried so I stopped for now...

is there a way to stop this from happening? is it speed dependant? I tried various speeds but not sure what the best was anymore :/
I'm thinking of getting some grinding stones instead as they seem to be a bit safer and take a bit longer - which would be a good idea to get a good understanding of what I'm doing ;)

some tips would be cool!

[DeadSquare]

" some tips would be cool! "

 

 

                                                              

Ahhhh.   I remember

 

ABDULLA   COOLTIPT

 

 

Lovely cigarettes !     I used to smoke them at school.

They came in an aluminium tin, which didn't crush in your pocket.

 

[DeadSquare]

Right !   Where was I ?

 

The best thing that you can do, is just to polish the ports to a shine, to minimise any turbulence.

[Turbo Phil]

What kind of speed are you running the burrs at ? To slow and they’ll chatter and dull up rapidly. You’re usually looking at 15,000+rpm and up to 25,000. It’s certainly critical to use the stones at a high speed to otherwise they clog up and material removal is slow.
Polish the exhaust ports if you must, but do not polish the inlets. A 60grit finish will get the job done and create a small amount of turbulence on the boundary layer which helps to reintroduce any fuel which may be stuck to the port walls.

Phil.

Edited by Turbo Phil, 09 December 2019 - 09:10 PM.

[luismx123]

Right !   Where was I ?

 

The best thing that you can do, is just to polish the ports to a shine, to minimise any turbulence.

 

yea i thought as its a no gooder anyways Id go for the full on 12g295 replica shape of ports and chamber. I have a 295 lying around so Ill use it as a template and see how far I can get ;)

 

 

What kind of speed are you running the burrs at ? To slow and they’ll chatter and dull up rapidly. You’re usually looking at 15,000+rpm and up to 25,000. It’s certainly critical to use the stones at a high speed to otherwise they clog up and material removal is slow.
Polish the exhaust ports if you must, but do not polish the inlets. A 60grit finish will get the job done and create a small amount of turbulence on the boundary layer which helps to reintroduce any fuel which may be stuck to the port walls.

Phil.

ah ok then Ill try faster tonight! I definitely wasnt near 25000 as that would be the max speed on my cutter and i was at stage 3 of 6. I started really slow first, like number 1-2 and that went well and then not sure if i bumped the speed up and then the chattering/jumping occurred. In a video from vmaxscart he goes over porting basics and says the burrs are for slower speeds? Maybe thats where I got my idea from to keep the speed down :/
I got my hands on some stones this morning so Ill try refining the current bowls with them, then once Im more confident Ill try the carbide cutters again. 

How do you get deep into the port/bowl? I found that once I got in as deep as possible - removing the valve guide hump - I got the burr trapped on the ground with the tip and the shaft on the short side radius of the seat which caused the machine to bind and fling itself around... 

[Turbo Phil]

The small bore heads are a pain in the guide boss area as you’ve discovered. I use a very small ball shaped carbide to remove most of the material. Once you’ve created some room you can go in with a larger one.
Don’t run the carbides to slow, you need to run them at a decent speed and keep some pressure on them (don’t polish) or they’ll soon dull up and become almost useless.

Phil.

Edited by Turbo Phil, 10 December 2019 - 09:03 AM.

[DeadSquare]

Bill Blydenstien was a great believer in exhaust scavenging, and his exhaust ports looked as though they were chrome plated.

[mini13]

Ah! diy head porting,

The best bit if advise I can give is don't bother, send it out to someone to get it done! ?

By all means have a crack as it's great to get an understanding, but be aware that most of the gains happen at the valve/seat and in the lead up to it. And soon as you disturb the guides your into cutting seats.

[luismx123]

The small bore heads are a pain in the guide boss area as you’ve discovered. I use a very small ball shaped carbide to remove most of the material. Once you’ve created some room you can go in with a larger one.
Don’t run the carbides to slow, you need to run them at a decent speed and keep some pressure on them (don’t polish) or they’ll soon dull up and become almost useless.

Phil.

cheers will give that a crack. Im also having difficulty getting in from the manifold face, but i guess a longer burr would be needed...cant be asked to spend 30ish euro on one just for the fun of, so ill try to do what i can with the bits i have now. Would make things really easy though getting in from the manifold face to clean up the top of the SSR which i cant get to from the chamber and the last bit of the valve seat bump that blends into the port as my burr is just that half centimeter too short -.-

 

Ah! diy head porting,

The best bit if advise I can give is don't bother, send it out to someone to get it done!

By all means have a crack as it's great to get an understanding, but be aware that most of the gains happen at the valve/seat and in the lead up to it. And soon as you disturb the guides your into cutting seats.

i know i know Its just good for me to see what really goes into doing a head. I like learning and if i manage to get one done without breaking it, Ill invest more and do a head for my mini, then possibly more. Its all a hobby I guess ;) My 12g295 head will be handed over in bubble wrap to a professional as Im never going to do that one myself... not until ive done 10 standard heads though....
Also doing the work myself shows why it costs so much from the pros. More appreciation for the craft ;)
I also managed to knick the seat a bit with the bouncing burr, so Ill get them recut if the head is of any worth once its done -.- got a friend with the tools so a beer or two will have to do ;)

On a side note... something that amazed me was the difference the 12g295 head has from the standard one AND a 12g202 head I have lying around. When I got the 295 head and stuck ma finger in there, my initial reaction was like "jesus thats rough, oh god theres an edge there that needs to be sanded...pfeeewwwww". Now after doing some work on the standard one and sticking my finger in the 202, the difference is staggering and I realise why the 295 head works so much better. The intake feels as if it were already ported. The exhaust however is fairly similar... but what ever. Just really interesting for me as a nooby

[DomCr250]

With time and patience you can improve the flow by a decent level. 

 

It's a bit scary the 1st time you see the bit running at those speeds, but by the time you are covered in a fine layer of metallic dust you will be OK with it.

 

Yes, you will never get to a professional standard, but you can still make a difference and learn a lot about port flow at the same time.

 

Remember, even the best cylinder head guys started at the beginning by trying stuff out and learning along the way.

 

I was lucky enough to go to Cosworths F1 engine design facility once - one of the managers told me that the 'old man' - AKA Keith Duckworth reckoned he could tell how well an engine would 'flow' just by running a finger around its ports.  The engineers would get upset because he would run his finger across all the latest head casting designs, just as they came out of the casting process and still cooling down.  He'd then pronounce a single port shape as being the best - they'd flow bench all the heads to prove him wrong, but Keith was always right.  Nothing like learning on the job and having experience.

[Turbo Phil]

As already mentioned the biggest gains in flow are from improving the valve seat and the area directly above and below it. The chambers in particular shroud the valves massively on the small bore (295 excluded) heads. Even on stock valve sizes cutting the chamber walls back shows huge improvement.
Beware in removing to much of the exhaust guide boss on the small bore heads or you’ll quickly find fresh air. Multi angle the seats and if using the stock type valves apply a 30degree back cut to narrow the seat, this modification alone shows excellent gains.
The 1275 castings are far easier to work on and thankfully 99% of my work involves these.

Phil.

[luismx123]

With time and patience you can improve the flow by a decent level. 

 

It's a bit scary the 1st time you see the bit running at those speeds, but by the time you are covered in a fine layer of metallic dust you will be OK with it.

 

Yes, you will never get to a professional standard, but you can still make a difference and learn a lot about port flow at the same time.

 

Remember, even the best cylinder head guys started at the beginning by trying stuff out and learning along the way.

 

I was lucky enough to go to Cosworths F1 engine design facility once - one of the managers told me that the 'old man' - AKA Keith Duckworth reckoned he could tell how well an engine would 'flow' just by running a finger around its ports.  The engineers would get upset because he would run his finger across all the latest head casting designs, just as they came out of the casting process and still cooling down.  He'd then pronounce a single port shape as being the best - they'd flow bench all the heads to prove him wrong, but Keith was always right.  Nothing like learning on the job and having experience.

yea you are right when it comes to the speed. Had a good 2 hrs tonight on the head and got more comfortable with that whine the motor makes! bone chilling but you get used to it - thank god.

Its stories like these that are really interesting and always great to hear - however, might just be me, but many of these types of "specialists" keep everything to themselves. In no way do i want to offend anyone with this statement but here in my area, the older mini generation that are basically the "experts" complain about the youth not knowing anything and not trying their own stuff but when you ask them to teach you, they say "no, I learnt by doing, you all should do the same"....HA, jokes on us! I cant just walk to my neighbour anymore and pick up an old 1275 for a beer or two and duck around and see what goes. One guy I know ported/built 20+engines for himself until he started doing it for money. He said he paid nothing for any of those engines back in the 80s....

 

I understand you cant explain everything and lots needs to be learnt by yourself, but....yea.

As already mentioned the biggest gains in flow are from improving the valve seat and the area directly above and below it. The chambers in particular shroud the valves massively on the small bore (295 excluded) heads. Even on stock valve sizes cutting the chamber walls back shows huge improvement.
Beware in removing to much of the exhaust guide boss on the small bore heads or you’ll quickly find fresh air. Multi angle the seats and if using the stock type valves apply a 30degree back cut to narrow the seat, this modification alone shows excellent gains.
The 1275 castings are far easier to work on and thankfully 99% of my work involves these.

Phil.

Im planning on copying the 295 chamber shape once im done with the ports/bowl. 
A cool thing I did - not sure if this is standard porting technique, but I shaved down a sanding ball (the pink ones) to fit into the exhaust and shaped one to fit into the inlet. All i did then was stick the ball in vertically and shave away. Ports looking really good up until the manifold side of the valve guide boss as the ball doesnt go down that deep. Going to get some more bits tomorrow and shape them to fit in there. 

Photos will come soon, once im happy with the looks!