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I finally got back out to the workshop tonight and got to spend some time on the intake ports. Given the limited time spent I think they came out very well. There was a lot of work blending the seats into the bowls. There were very big steps from the seat machining that took a while to sand out.
This is a different head (my current race head) which runs RB26 intake valves and +1mm oversized custom exhaust valves. It's been decked around 2.5mm (100 thou) and has the ports more open than the head I did above. I floated the valves in this head @ 8500rpm due to old valve springs and the valves got hammered up into the head distorting the valve. I am installing Supertech RB26 intake valves as replacement to the OEM RB26 valves, and the standard Mazda Supertech +1 inconnel Exhaust valves. I'm also upgrading the valve springs to the Supertech heavy duals.
I purchased 2 Neway cutters and have just done all the valve seats with a 4-angle valve job. I also replaced all the valve guides with bronze ones and reamed them out with a 6mm carbide tool.
The cutters I purchased are a 45 / 30 degree cutter and a 70 / 15 degree cutter. They can just do the exhaust valves, but can expand out to do up to 34mm valves too. I also picked up an expanding 6mm pilot guide and an easy turn handle. They are fairly easy to use with the entire head taking around 2 hours to manually do the seats.
All up they come up pretty nice. Intake seats are a bit over 1mm, with the exhaust seats between 1.5 and 1.8mm. It's a fairly easy job for anyone interested in doing this yourself, it just takes a bit of patience. These Neway cutters cost me around the same as taking it to a machine shop and so far I've done 2 heads with them with a third coming up.
Also, the RB26 intake valves fit straight into the Mazda valve guides and if you use the Nissan valve cotters, lock in nicely to the titanium retainers. They are pretty much a direct replacement to the Mazda valves.
Here is a good pic that shows how far the head has been decked. You know it's serious when there are flats on the exhaust and intake stud mounts. I was going to CNC the chamber on this head too but ran out of time... it's got to be all back together by Friday night!
Lucky I have a wife that lets me work on the dining table!
Wow, that's a ton of decking. Did you cc the combustion chambers?
--Ian
No, this head has been run before so I'm just fixing and updating the valves / valve springs. The block runs Wiseco 10.5:1 pistons so I'm pegging this around 13.5:1 compression ratio. I actually thought about decking it a bit further to lift it to 14:1 but I'm a bit worried about valve clearance with the high duration / high lift cams I run. It's already extremely tight in there with only a few degrees each way from valve on valve and valve to piston interference so I don't really want to muck with it.
The Supertech RB26 intake valves are nice... the have very slender stems on the valves. I think they will flow a bit better than the OEM RB26 valves. I almost bought the +1 sizing which would have put them +2.5mm oversized but decided against it as it would bring the valve to valve clearance tighter.
08-27-2016, 10:44 AM
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