stat housing mod

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

Right im talking about swirl as the charge enters the cylinder...not necessarily in the port, but as it leaves it. hence why the ports are offset.....
are you saying that you dont want swirl in the cylinder of a 16v??

The shrouding of the inlet valves by the edge of the chamber would cause quite a bit of tumble.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

no you want tumble not swirl. Look at swirl as a vertical rotation and tumble as a horizontal rotation.

If you have swirl in a 2/3 inlet valve per cyl arrangment then the valves all flow differing amounts.

The renault heads are pretty much the only 16V heads that have badly offset ports like these. Look at any 'decent' head and its bang on square, the VX XE head is a good head as far as port design goes.

Swirl is bad basically.

The megane head is how it should have been. The benefit of the megane head is clear to see, also due to the poor machining on it a good clean up will yield quite impressive gains. Also due to the small ports the power band is wide and you don't have the delay for air speed to pick up as you do with larger ports.

The ports are pretty much bang on in the middle of the 2 valves so theres no swirl to worry about and the tumble does its job, kind of.

The megane head as crappily cast and machined as it is equals the williams in power but has a wider and higher torque spread due to the head only. The inlet manifold and injection and TB are nothing to write home about and 99% of meganes have crap like EGR and so on messing things up.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

yeah i understand what swirl/tumble are!

So what your saying is, having more tumble will give you better net gains than more swirl?

I can see what your saying, but any ammount of swirl in the cylinder is going to be a good thing...

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

matey, ignore books, your tutors or any other crap in your head. Why didn't you give her your number? Muppet...

straight ports means the mixture will flow equally through each valve and the mixture can then tumble.

If the ports offset then 1 valve will flow more than the other, the mixture will do what it wants, you cannot say go down there, at the corner start rotating about then make sure equal amounts go through the valves then once in the cylinder keep swirling but don't impede any more mixture coming in.

1 port will flow more the other will not flow as much due to the mixture carrying on stright to the easiest port, it then swirling causing dead areas around the other valve and the swirl in the cylinder further blocking flow into the 'dead' valve.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

LOL....!!

yeah i can see what your saying....

But its all about NET GAINS. More torque will be got from good swirl. fact. more torque will be got, as you say, from equal flow into the head i.e straight.
with an offset port you get the swirl but unequal valve flow, and conversly with central ports you get equal valve flow but less swirl. so its circles and round-abouts because its the overall gain that counts.

Look at the williams F7R...2.0 16v 150BHP
VX20XE...2.0 16v 150BHP

Two different approaches, but the same power....get what im saying?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

also, like i said, the fact the inlet valves are masked will provide tumble.

but once again its all a comprimise.....volumetric efficiency will no doubt be reduced

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

williams is 150 but using a superior engine management setup and speed density.

20XE is the poorer GM head with MAF SFI management. C20XE is the coscast head which is superior but again with SFI MAF management. Also very basic SFI. C20XE was 156bhp.

If the VX lump was speed density based it would be better. If the head was the right way round it would be better still.

VX also has milder cams.

You can through in the 1.9 alloy MI16, it has mild cams and big valves with good ports and chamber design, great exhaust design 160bhp.

A 16V head with good tumble will out power and swirl based 16V head.

Tumble is basically swirl but turned through 90 degrees.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

Oh well, good job im using the Megane head!!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

send it to me, send it to me, send it to me, send it to me, send it to me...

You got an idea on the headwork mate? JB has been asking me lots via pms etc. if you send me pics of your work etc I can offer my opinion if you want.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

yeah will do...
Â£200 for the 34.6mm valves to be fitted + a skim...not too bad. Then i'll fettle up the ports, havnt really put much thought to actual re-shaping, or indeed if its necessary.
what u reckon??

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

a clean up is better than hacking away at the ports making them bigger mate.

Who is doing the machining?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

A local firm. its a one-man company, but he's got one hell of a set-up!

do you reckon it'll need any re-shaping? its been ages since ive looked at the bloody thing properly, and its round in my garage so im not gan round now!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yeah I think JB mentioned him to me, said you knew him or summat.

The bowl area and short turn radius as always need the most work.

When you go round and look take some pics and I'll highlight the bits, easier that way matey.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

yeah well the inner radius was gonna have a bit of work anyway, but i'll get pics....i'll tell you what i think first!! cheers mate

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

is that 200 including the price of the valves? i assume not...i look fwd to seeing how close them valves are....i reckon they will be nigh on touching.

well just to go against the grain i will try raising the floor of the port Very Happy

along with some work (somewhere somehow) in the bowl area like u say.

i was thinking of making a proper job of this head...ie, new guides, new seats (recut) new everything....but then i think i am wasting my money a bit, as if it feels any better (ie not like i just put a std head back on my car returning to std trim) then i would rather put the money into the willy head...

was this head off that fucked one u picked up stan? looks well worn in places, ie the camshaft journals on the carriers or quite scored, the valve stems look more worn than others ive seen...shall measure but sure theyre ok...

im learning, not afraid to admit. im just gunna get stuck in and have a go....and see what happens...if it doesnt work then so what...i wont do it that way next time...

im rambling now, lol.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

"im rambling on now" LOL!!

no i bought it off ebay with the intention of using it!!

valves cost Â£60

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

will this local engineer put the new seat in as wel? can he do the lot? have u seen any of his work to be confident?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

thats what he's doing....fitting larger seats, then cutting them, then a skim. havnt seen any of his work, but his reputation is excellent. his workshop is tip-top.

your getting me worried now....what if he uses angle grinder to cut the seats?!!!

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

lol....

can he grind valves?

sounds good....ill get his details off u shortly.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

i'd say so

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

when u gettin ur work done...ill wait and see how urs faired Very Happy

also when u tried to grind 33 into std seats it didnt work did it...std seat is only 32.5 so even for 33s ud need new seats right?