The V8 Owners Forum -

As I'm working on a blown lump and the main issue seems to be getting the exhaust gasses out as quick as poss would it be feasible to have the exhaust valves replaced with std size inlet valves and seats? (the older slightly smaller ones maybe)- as this must be cheaper than using after market types and there isnt as much requirement for bigger inlets!

Also is it a major job to push out the guides and replace them with bulleted ones?

TC

TC

No you can't use inlet valves in the exhaust they would burn up in no time, but you do not need to replace the seats to fit 1.4" exhaust valves, just have them recut for the bigger valves.

It is also more important to have both the inlet & exhaust valve inserts cut back to valve seat size and the throats opened up to match which is good for approx 35BHP on an otherwise standard engine.

As for the guides, are the existing ones worn, if not just have them bulleted/ ground down in the ports and if required for the cam lift reduce the height of the tops of the guides as per cam manufacturers spec otherwise the collets will hit the valve guides on full lift. Most people grind the guide in the port so approx .25" is left protruding from the roof of the port.

Kevin.

So basically just cut down the protuding stem in the ports and not bullet them? Could do that in the mill I rekon!
Sorry but not quite sure what you mean about cutting back the valve seats

If you look at the valve seats and where the valve makes contact with the seat you will see that there is an excessive amount of seat which can be removed and then you need to blend in the bowl area in the port to match

The standard inlet and exhaust seats can be re-cut to take 1.63" inlet and 1.4" exhaust valves if required, but what ever the valve size it is important for flow to have the excess material removed. You will need to have the seats done at a machine shop wth proper equipment bur you may be able to do the port blending yourself.

Kevin.

Can you remind me what std (later) valve sizes are?
And is this kinda what you mean? Crude drawing sorry but have put the "remove to" bits in red... make sense?!

TC

Thats it, once the seats are recut it will become obvious where metal needs to be removed from.

The seats themselves are pretty hard so best to get them relieved when being cut for the new valves. and then you can clean up the bowl areas with rotary tools in a drill.

Best ask a question as to what is best for this job as I don't know.


Personally I think the metal that surrounds the guide should be left as is although you could clean off any rough spots, its the shape it is to promote swirl which I consider important except in full race engines running between 3.500-7500RPM.

From your own sketch it gives a indication of how much this simple mod improves flow and why it is so effective.

Later post P6 valve sizes I think are, In. 1.575" Ex. 1.375"

I could mail you a couple of pics if you like just PM me you e-mail address

Kevin.

I'm looking at buying a set of valve seat cutting tools, and I have a snap on die grinder and carbide burrs which are good, not sure if taking as much as you are saying out of the seats should be left to a pro though!!!

What do you mean by relieving them whilst being cut?

p.s. I now have an email button!

TC

What I meant was if you were having the seats recut for larger valves at a machine shop, then you could have them cut the inserts to actual valve seat size and then you could just blend in the area below the seats behind the valve heads.

With the mail button you cant attach docs or pics and have to put them through a hosting site as when attaching pics to a post on the forum. It's much quicker to use standard e-mail format and attach pics.

Kevin.

Sorry didnt realise that! Any ideas how much getting bigger valves/seats put in would cost? You can use tom@topcatproduction.co.uk

Also interested in this. I was planning on fitting 1.5" exhaust valves to my stage 3 heads which currently have the larger wasted stem valves in. I was going to get this done by V8D, who quoted me £30 per seat (inc. seat), plus the valves which are about £120. Stuff in yank land is better and cheaper though, just stuggling to find a supplier of suitable valve sizes!! Spoke to Ferrea and they put me on to a local dealer, who hasn't got back to me yet! Isky valve seats aren't that expensive either. Will be getting my quote for just the machine work later this week hopefully so will let ya know.

blown is the way forward

Maybe they would knock the price down a little more if they had 2 pairs to do...! Same with the parts! Take it you are still going TT?