Valve sizing

[Dell'Orto]

Im currently in the middle of building a angry little 4K, and am at the stage where I need to do something to the head to make it better.
I've done some research and found A15 exhaust valves are pretty near a straight replacement, but are only 1mm larger in diameter.
Is it worth the effort of machining it out to only gain 1mm in head size?
At the other side of the equation, there are some Mitsi intake valves which are 6mm larger in diameter So is it also important to keep the sizes equal? ie stock intake is 36mm, stock exhaust is 29mm - so if I were to go with the Mitsi intake valves, would I then also have to get 35mm exhaust ones?

Help would be appreciated, spam will be deleted


Thanks


Brad

[RedMist]

Personally I think you are going about this the wrong way. What are you attempting to achieve with this engine? IE How mucho HPo? Then build your engine to suit your goals.

The 1mm oversize is 5.8 % bigger in valve area with at least that in flow (around the valve) Is that big enough for you?

Mitzi valves are a 23% increase in valve area.... silly.

And yes, you will need to increase the size of your exhaust valves if you end up going down the mitzi route. Remember your engine is nothing but a simple pump... put more air in... more exhaust needs to come out.... unless that is if you want to leave it in the cylinder?

Still wether or not you need to change valves could depend totally on how good a flow work you complete on your head.. or flow to whatever standard that is.... once you complete the first question.

[Dell'Orto]

Well ideally, I'd like to manage 100hp at the fly, but its probably not possible without spending huge $$...and a 4K isnt what I'd consider a good investment definately after
From what research I've done, there isnt really alot of point doing alot of port work on the 4K head without going to larger valves, though thats going by other peoples experiences.
Yeah I wasnt meaning just increasing intake valve size, more keeping the increases equal...ie is it critical to increase both by the same amount, or is it ok to go say 6mm bigger on the in. and only 5mm on the exh.?

[Virtual Genocide]

Glenn aka Dunny on club-k has his race starlet running 100hp at the fly. http://www.club-k.co.nz/Full024.htm

It is std bore, altho he runs a pretty agressive cam profle and the engine has been built by a top notch engine builder.

I woun't say 100hp is unacheiveable. But you'd have to seriously think if its worth all the money.

[RedMist]

Well ideally, I'd like to manage 100hp at the fly, but its probably not possible without spending huge $$...and a 4K isnt what I'd consider a good investment

I know you'll find this blasphamy, but have you thought about G13 twin cam? I've seen 140 at the wheels out of one of those. And if you can find one.. it should cost you about the same as a rebuild.

[RedMist]

Standard Bore 4k (1290cc) uprighted, ported head, larger valves, single valve springs, decked block, ACL flat top pistons with valve pocket cut outs, 5k rods, std crank. Modified, winged and baffled sump, modified oil pick up, custom uprighted engine mounts, with engine set back and left, modified cross member, custom inlet/exhaust adapter plate, custom 4-2-1 extractors heat wrapped, TRD inlet manifolds match ported to head, twin 45mm side draught Weber carburettors, 10mm fuel line, custom recored KE70 radiator boxed in. Gearbox K50 5 speed, modified shifter, double diaphragm pressure plate, standard clutch plate or K40 4 speed with modified shifter and short shift kit

Thats a shit of an investment for only 100 flywheel hp.

[Virtual Genocide]

Yeah thats right come to think of it.... my engine is 88hp atw so thats about 100flywheel hp.

His must have been more

[Dunny]

It's 100hp atw not fly, engine is still in development which = more hp to come, remember it's only a 1290cc push rod engine.

I think you would be surprised how little it cost to build, as you'd know things are much cheaper when you know or have some who knows what works and what doesn't. ie not spending money on stuff which is a waste of time.

Hp is not the be all and end all of quick laps times, I'm sure a few people on here who are at sprint and or race days will know how the car goes.

[Dell'Orto]

I know you'll find this blasphamy, but have you thought about G13 twin cam? I've seen 140 at the wheels out of one of those. And if you can find one.. it should cost you about the same as a rebuild.

Mmm, but a G13 wont bolt right into a KE70 I'm being lazy, hence why staying K series. Plus a rebuild is costing me 3/8ths of $&#$% all...parts are $200, the only real cost is machine work.

Its annoying how people who say they're using larger valves in K engines dont say what size they are

[Dunny]

Its annoying how people who say they're using larger valves in K engines dont say what size they are

When it comes to race cars & engines if all secrets were given away it can somewhat disadvantage you

[Dell'Orto]

Yeah this is a good point. Doesnt help me alot though
So I guess oversizing them too much would be pretty well detrimental too?

[RedMist]

This looks interesting... its a google cache... as the original site looks down.

http://72.14.203.104/search?q=cache:EuX ... =clnk&cd=1

[Dell'Orto]

That is rather interesting, good find! So maybe I should go with the Mitsi intake valve and leave stock exhaust!!

[RedMist]

another page from the same site... you might want to do a google search and try to find all the cached pages... its very interesting read.

http://72.14.203.104/search?q=cache:Y1L ... =clnk&cd=2