Oversized valves - SR20 intakes / exhaust

smy0003 · Postby **smy0003** » Tue Aug 09, 2016 10:35 am

This escalated quickly. I'm looking forward to the results.

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Magpie · Postby **Magpie** » Tue Aug 09, 2016 10:44 am

There are already 2 BP motors running the SR20 valves and springs (that I know of) however these were commercially done. Hence is commercial in confidence as is the CNC data on the head porting.

What Madjak is doing by in his home shed is impressive, not to mention showing his progress, methods and logic!

madjak · Postby **madjak** » Tue Aug 09, 2016 3:41 pm

Well I did a first pass on the CNC machine last night and the model lined up very well. There are a couple of tweaks to the 3D model that I need to make to make it machine the entire combustion chamber. I need to widen the cut by around 0.1 - 0.2mm on all four sides and also tweak the curvature slighty at the base of the bowl. Other than that it works well.

First Pass: with a 0.1mm margin on the final cutting surface. These cut areas are basically the unshrouding parts of the cut.

Second Pass: roughing again but with no margin. you can see where my model wasn't quite accurate. We are only talking tenths of a mm though so I need to tweak the model in these areas. This shot was taken part way through a pass.

All up I should be able to complete a combustion chamber in around 1.5 of machining... so thats less than a day to do a whole head.

As for the valves, I'm picking up a SR20DE head on the weekend, so I'll mount the valves up and make sure the springs, retainers etc all work

noobee · Postby **noobee** » Tue Aug 09, 2016 7:07 pm

would be nice to have such a thing in the shed!
what sort of cutter is that,what rpm etc? looks like you are plunging straight down the sides or is that just a little chatter.
Mick

madjak · Postby **madjak** » Tue Aug 09, 2016 8:16 pm

It's a fairly old 6mm ball nose cutter. I'm running it at 12000 rpm and moving it around 20mm/sec with a cut depth of 0.2mm. I should probably be moving it a bit slower and running a new tool but I'll leave that for the finishing passes. The finish looks rougher in the photos than it does in real life and will be sanded and polished once I'm finished all the chambers. I might try running a 6mm end mill instead as it will get into the corners around the valves a bit more which will remove that small ridge from the factory seat tooling.

The bit isn't really liking hitting the valve seats and that's inducing a bit of chatter as it moves on and off the seat. Some of the seats are proud, some sit under the camber surface so machining the tops makes them all equal and blends the surface into the chamber. It would be better to not touch the seats as it would make the cutter last longer but that would be tricky.

Magpie · Postby **Magpie** » Tue Aug 09, 2016 8:23 pm

Be interesting to see if it changes the torque curve.

Postby **Okibi** » Wed Aug 10, 2016 12:22 am

So cool

noobee · Postby **noobee** » Wed Aug 10, 2016 6:28 pm

so,tool speed around 225 meters/min? 6mm dia cutter @ 12000
Mick(the ex machinist.lol)

madjak · Postby **madjak** » Wed Aug 10, 2016 7:13 pm

noobee wrote:so,tool speed around 225 meters/min? 6mm dia cutter @ 12000
Mick(the ex machinist.lol)

I get 1.2m/min! 6mm dia cutter @ 12000 is correct.

I can't crank the speed much higher as the bed has to move the head and since the machine isn't that powerful I have to be careful how fast I'm moving it.

madjak · Postby **madjak** » Wed Aug 10, 2016 7:24 pm

Here is a close up of the finish. The little lines are from the ball nose cutter running at 0.2mm apart. I probably should run them closer but I don't have the patience, plus I think they will rub out with some 400 grit sandpaper easy enough. I'll be polishing the chambers so there will still be a bit of hand work to finish from here.

You can see my DIY porting on the chamber next to this one. I'm not planning on running the cut any further. I'll polish the head by hand from this point so I'll run this cut now on the 3 other chambers.

Next experiment is to try back cutting the SR20 intake valves on my hobby lathe. I figure I'll mount the valves in a 6mm collet that I'm using on the CNC mill into the lathe and then slice the back of the valve off at 25degrees. Can't be that hard right? A nice new carbide bit should make a nice clean finish and I can always sand it a bit to get it smooth. I'll just take it nice and slow so as to not deflect the valve.

manga_blue · Postby **manga_blue** » Wed Aug 10, 2016 7:43 pm

I'm envious, but also curious. Do you have an estimate of the volume of metal removed in the combustion chamber and the impact it may have on compression?

madjak · Postby **madjak** » Wed Aug 10, 2016 7:57 pm

manga_blue wrote:I'm envious, but also curious. Do you have an estimate of the volume of metal removed in the combustion chamber and the impact it may have on compression?

I could figure it out in 3D... but most likely I'll do the standard CC test once the valves are installed. Then when I know the combustion chamber volume I'll deck the head to suit my target compression. At this stage I'm just removing as little metal as possible to get closer to what I'd consider would be a more ideal flow from the valves. If the seats weren't installed it would be much easier to machine out but with them there I'm being careful to not touch them too much. The CNC process will make each chamber much closer in volume and flow more consistently than any DIY porting could achieve.

For a crazy supercharger build I'm aiming for 11.5 to 12:1 compression but I'll talk to Dann first and see what we recons.

madjak · Postby **madjak** » Fri Aug 12, 2016 1:06 am

Here is a quick mobile video showing the roughing pass.

datfreak · Postby **datfreak** » Fri Aug 12, 2016 7:01 pm

You have the best toys

madjak · Postby **madjak** » Sun Aug 28, 2016 2:45 am

The combustion chamber a finished a while back. Here is a video showing the polished chambers.

I also machined up a tool to knock out the valve guides. They are in pretty tight so they need lot of persuasion.

Tonight I spent some time on the intake ports. The stock head casting is fairly rough and there are big steps from the seat to the bowl which can be easily blended out. There are also some big ridges on the short radius that can be smoothed out. All up im pretty happy with my first attempt at porting. I think I've managed to get them all fairly close.