Biggest Valves with Standard Seats

cammmy · Post by **cammmy** » Mon Feb 25, 2013 1:30 pm

Hi Everyone. I did a search but could not narrow it far enough to find a result.

As I'm rebuilding a 3.9 with forced induction and will be having the seats 3 angle cut to the same hight. Is it worth going one further and having them machined to accept larger valves?

DW500(2) 1.630" 4.595" £5.83 x8 = £46.44
DW501(2) 1.400" 4.595" £6.44 x8 = £51.52

(2) - Stainless steel [21-4N]/tuftrided with a wafer tip

Des Hamimill says 1.625" and 1.4" are the largest that will fit on the standard seat but Real Steel seem to sized these to fit?

Will this have good results with mild port blending and the inlet matched to the head, or is more extensive work required?

stevieturbo · Post by **stevieturbo** » Mon Feb 25, 2013 2:18 pm

You'd be better spending the money on a light port job, than larger valves.

cammmy · Post by **cammmy** » Mon Feb 25, 2013 3:43 pm

I was planning on doing the port work outlined in Des Hammill's book i.e. tidying and improving the throat areas and blending into the seats but without going overboard or enlarging the ports.

Will that not be enough to make use of larger valves when supercharged?

sidecar · Post by **sidecar** » Mon Feb 25, 2013 4:09 pm

cammmy wrote:Hi Everyone. I did a search but could not narrow it far enough to find a result.

As I'm rebuilding a 3.9 with forced induction and will be having the seats 3 angle cut to the same hight. Is it worth going one further and having them machined to accept larger valves?

DW500(2) 1.630" 4.595" £5.83 x8 = £46.44
DW501(2) 1.400" 4.595" £6.44 x8 = £51.52

(2) - Stainless steel [21-4N]/tuftrided with a wafer tip

Des Hamimill says 1.625" and 1.4" are the largest that will fit on the standard seat but Real Steel seem to sized these to fit?

Will this have good results with mild port blending and the inlet matched to the head, or is more extensive work required?

The DW valves do fit, V8 Developments fit them to their stage III heads.

stevieturbo · Post by **stevieturbo** » Mon Feb 25, 2013 4:13 pm

If you're doing that anyway, then larger valves will be fine. Was just talking more from a cost point of view. Port shape, especially the throat area is where most gains will be. Not so much valve size. Even better shape standard size valves would be good. Don't go so big the valves end up shrouded, or there is little valve seat left

cammmy · Post by **cammmy** » Mon Feb 25, 2013 4:52 pm

Cool. Yeah I'm planning to improve the ports anyway. Not going to go overboard with the valves but figure it may be a worthwile thing to do. Less than £100 for the valves and I'm having new guides fitted and the seats cut anyway, figure it would be worthwhile to add these at the same time.

Flying Phil · Post by **Flying Phil** » Sat Mar 16, 2013 8:39 pm

Years ago I fitted larger valves and had the valve seats and throats bored larger to suit. However I was also using a solid lifter cam and stronger valve springs - when I was racing the seat inserts started to pound into the head casting and soon the valves would not seat and leaked.......

cammmy · Post by **cammmy** » Mon Mar 18, 2013 12:38 pm

I won't be seeing above 6k rpm. I do have aftermarket springs but they are the real steel ones for their blower cam (hydraulic) and I don't think the spring rate is that high.

Do you think this would still be an issue when not racing?

Flying Phil · Post by **Flying Phil** » Sat Mar 30, 2013 6:59 am

sorry for delayed reply - but if you are using a hydraulic cam it should be "kinder" to the valve seats and so should be ok.

cammmy · Post by **cammmy** » Tue Apr 02, 2013 9:49 am

Cool, thanks

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