Cylender head guros
Turbo Mini Forums

Right not to far off doing a head for my turbo build and was looking at valves and im not sure on how big i can go or should go for that matter...

now am i right to think if you measure the guide to guide center line distance in my case 34mm and then take half to size on each valve looking at 27ex and 37in so that would be 13.5 ex and 18.5in leaving 2mm between valves but is that to thin?

i think ill have hardened seats installed in the head as well

first am i right to think the listed valve size is the outer most measurement?

second should i be trying to jam the biggest valves i can get in there to get more volumetric efficiency?

third what distance should be between valves to prevent it cracking?

forth am i a fool and just get a benross head done and shipped all the way to aus?

lol thoughts?

I would have thought on a small bore that such a big inlet valve would not work.

If something is worth doing, it's worth doing half of.

How many times have we been down this road?
In a small bore head there's no point in fitting larger than 32/28 valves. If you are not satisfied with this, go large bore.

I'm using 33/29 on a 12G295.

Computer simulation confirmed that bigger inlets and it started to lose power.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

i take it the bigger valves being closer to the chamber wall is worse than a smaller valve with loads of space to breath?

No, small bore valves at 1275 sizes in 214N.

EDIT: Errr... might be large bore... can't remember.

Edited by Paul S on 3rd Jul, 2014.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

is 34in 27ex a better combo then?

I will test a 32 (ground down 33mm) 1275 valve shortly on a 202 head on the flowbench . it comes down to smaller valves having a higher Cd . so generally they are more efficient ( given an optimised seat of course) but have less curtain area . So there is a sweet-spot where the gains from the extra area are offset by the lower Cd. That in turn is dictated by the variable aperture created by the valve seat and the areas directly before and after (chamber & cylinder wall) . Hence the huge gains from a tiny back cut on a valve and near to no effect of enthusiastic grinding near the manifold end .

in aus why not contact graham russell ?

Edited by Sir Yun on 3rd Jul, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

You can improve the Cd with a bit of fettling particularly at low lift, but the lower flow velocity and momentum of the larger valves also have a negative impact.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

looking at the following seat design

chamber into
20tho wide 15 degree
30tho wide 30 degree
30the wide 45 degree
15tho wide 60 degree
40tho wide 75 degree
into bowl/port

not sure if its possible it cut such a complex seat tho those angles and scaled with are taken from vizards book

if anyone has flowbench numbers i'm interested.

Vegard : The csa of the port itself is quite substantial . why would the port not support a bigger valve ? i know the throat is tricky and probably needs filling to get the ssr to work.

Paul S : what simulation do you use ?


As far as the seat goes : sure you can cut that seat but even a really fat straight 45 with a valve with a 30 degree back-cut is pretty decent.

Edited by Sir Yun on 3rd Jul, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I run 33 27 in my 295...it gives good figures IMO

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

i fail to see why a 202 casting with the correct work done cant flow as well or better as any other 5 port mini head

im sure ive read in several mini tuning book and articals the 202 is the best head to start with given it is much more work to shape it but you can get results

my 1152cc engine is not going over 6k rpm due to its kent 274 cam and long stroke so massive port are not what i want im looking for strong air speed its bad enough to have not enough valve for the engine cc but i do think now looking at it more that 37 27 is to much for the head only because the valve gets to close to the chamber wall and begins to shroud it just like the std valve and chamber shape in the 202

but a big valve will flow more at lower lift to a point roughfly the same amount as the distance to the chamber wall as lift after that it gets shrouded and loses flow so i guess the thing to do is keep the valve allmost the distance of your valve lift to get the best match?

also remembering its worst where the gasket line is before and after this you can pull it back ill have a better look afta work as to how close the 37 will be lol

I could run some calcs to see what kind of csa you need for the piston demand you get.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

anyone know or care to measure up the big/small bore std casting intake ports?

I have casts of a 202 head and a modded 940. they are at my other house (sounds grander than reality ) so you would have to be patient

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

.

Edited by Sir Yun on 4th Jul, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

triple post

Edited by Sir Yun on 4th Jul, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I ran some numbers and even for a stroked 1098 with 68 mm pistons (+135) you only need about 1 inch diameter hole worth of CSA when you rev to 6800.

Ergo don't enlarge the port at all. it is too large as it is ( CSA wise).

look carefully at the sectioned small bore casting on Russell's site. There is more usefull info for small bores in that than half of what is in Vizards yellow book.

http://russellengineering.com.au/performance-cylinder-heads/

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/