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998 valve brand options
https://ausmini.com/forums/viewtopic.php?f=2&t=100270		 Page 1 of 1
Author:  Morbo28 [ Fri Aug 07, 2020 11:00 pm ]
Post subject:  998 valve brand options
Hi everyone,

In my NA 998 I think I'm going to run a 1.156" inlet and 1.062" exhaust. (If it helps, I'm thinking ~10:1 CR with flat tops, about +0.040, I'm running std rockers and a road cam (RE13/266/276 type of range) and std pressure double valve springs. Conservative home throat porting job and valve de-shrouding of head as per GR/Vizard )

Just after advice on good options for valves. I see GR does an exhaust valve of the size I've mentioned. From his website I can't see if he does the inlet size I'm after? I am just trying to decide which I should choose such as:
* standard part number valves of my chosen sizes vs other manufactures eg GR or another manufacturer
* collet types - is it okay to mix ex vs in collet types?
* stem lengths or thicknesses
* (or ideas on whether you think my valve sizes I've chosen are appropriate...)

Cheers
Author:  Morbo28 [ Fri Aug 07, 2020 11:17 pm ]
Post subject:  Re: 998 valve brand options
Eg if looking at std type valves, would i be better with

Image

or

Image

?
Author:  drmini in aust [ Sat Aug 08, 2020 6:35 am ]
Post subject:  Re: 998 valve brand options
I did an 1100 head for a mate's 68mm bore 1108, I used 1.219" 998 Cooper inlets and 27mm exhausts. GR profiled the valve seats and I did a little porting.
You can mix collet types ok but keep valve lengths the same. I used 7000rpm valve springs from Karcraft. Cam is GR's 266SS.

Edit
You could use a 998 head but there's a lot more metal to remove.
Author:  Morbo28 [ Sat Aug 08, 2020 10:11 am ]
Post subject:  Re: 998 valve brand options
drmini in aust wrote:
I did an 1100 head for a mate's 68mm bore 1108, I used 1.219" 998 Cooper inlets and 27mm exhausts. GR profiled the valve seats and I did a little porting.
You can mix collet types ok but keep valve lengths the same. I used 7000rpm valve springs from Karcraft. Cam is GR's 266SS.

Edit
You could use a 998 head but there's a lot more metal to remove.
Thanks Doc. I thought the 1.219" inlet might be too big for my purposes, but do you think that's a good option for me given the specs I'm looking at?


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Author:  drmini in aust [ Sun Aug 09, 2020 5:22 am ]
Post subject:  Re: 998 valve brand options
Definitely.
Author:  kiwiinwgtn [ Fri Sep 18, 2020 7:43 am ]
Post subject:  Re: 998 valve brand options
Morbo28 wrote:
Eg if looking at std type valves, would i be better with

Image

or

Image

?


What springs are you planning on using, I was thinking of turning down some 1300 valves to cooper sizes and using 1300 springs as I have so a good supply of 1300 valves and a lathe.
would this work okay
Author:  drmini in aust [ Fri Sep 18, 2020 7:49 am ]
Post subject:  Re: 998 valve brand options
Hi Bernard,
If using 1300 valves you need 2mm shims under the rockers, and 3mm under the 998 double springs. 12mm flat washers work here.

Because 1275/1300 valves are about 2mm longer.
I have a ported 295 head here with 1300 (Morris 1100S) standard valves.
I will SMS you a pic.

Edit
I would use stock 1300 inlets and turn the exhausts down to 27mm.
Author:  kiwiinwgtn [ Fri Sep 18, 2020 8:24 am ]
Post subject:  Re: 998 valve brand options
drmini in aust wrote:
If using 1300 valves you need 2mm shims under the rockers, and 3mm under the 998 double springs. 12mm flat washers work here.

Because 1275/1300 valves are about 2mm longer.



Hi Kev can I use 1300 valves to match the valves, I always check seat pressures and rocker geometry
Author:  drmini in aust [ Fri Sep 18, 2020 8:26 am ]
Post subject:  Re: 998 valve brand options
You mean springs? Yes if you check pressures and install height.
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