why the 1.8 16V heads are cack

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

Another thing for me to moan about.

The renault 16V heads are pretty poor, sure they deliver the goods and I suppose 140bhp for a road going 1.8 of 80's design is ok. Its very far from perfect though.

So why is it cack? Well theres a few reasons.

1st we shall assume the casting is perfect, identical to the shape on the drawing board.

We shall also assume the standard valve seat machining is perfect and there is no crappy short turn radius thats been cut the seat grinder.

In effect the heads pretty kuch where a reasonably ported head should be.

Also all chambers are identical in size and each cyl has an identical compression ratio.

So assuming its 140bhp net we shall bump it up to 150bhp just to be nice with a reasonable torque spread.

All very good you say, nay I say.

Fundamental flaws.

Combustion chamber, the chamber is quite large and the included angle is around 40 degrees, not to far off but could be narrower.

If the angle was narrower then the head would be narrower as the cams wouldn't have to be so far apart, narrower also means lighter into the bargain!

The CR around 10 is nothing amazing, it can go higher. The dimple left from casting on the chamber roof shouldn't be there. If the roof was flat then you would have a tiny bit more compresion and also no pocket for carbon to build up in and glow.

The chamber has a nice bit of squish, a wee bit more isn't practical to get fromt he head.

Its a relatively clean burning chamber but if the CR was higher and the squish better then it woudl burn cleaner.

This alone would net not only power gains, but improve response, accel, emmisions and economy.

Exhaust port. The exhaust port, the bosses around the valve guides are a bit excessive and can 'catch' the flow. It seems to affect some head more than others though, some have carbon built up around the step between the guide and the boss, but its partner less than an inch away can be clean. All things are not equal...

The port itselfs a bit big, if the floor was higher and flatter then scavenging would be improved, this would mean less need for overlap so a milder cam could be used and an increase in low rpm tractability would result.

If the floor was raised then the short turn radius wouldn't be so steep, again aiding flow, although not much exhaust gas passes over the short turn radius making it shallower removes the 'dead' space.

The port is thankfully central to the 2 valves, which is always nice.

Inlet port. This is pretty crap. On the older pre megane heads the port is offset and way to large. The megane port is about 2/3's the size and central to the valves. On the 1.8 head the flow is biased to 1 of the valves, in theory some would argue it induces swirl in through 1 of the valves, but swirl through and into 1 valve and the other valve is doing not much flowing means either the valves wasting energy or as I see it swirl is preventing that valve flowing anything in.

The port angle is such that the port runs parallel to the head face. Not very clever at all, taking into account a rough idea of a 40 degree combustion chamber angle the mixture still has to turn through 50 degrees to get into the chamber. Its done over a relatively short distance. But if the port was inclined even 10 degrees improvements of flow into the chamber would be impressive. Gains at all rpm points would be noted, a more homegenous mixture would be in the chamber and it would burn better. Again this would mean some cam timing could be removed to retain the same characertistics.

Cooling. This is rather poor. The cylinder head should be an even temp front to back and side to side as shoudl the cylinders in the block.

Why? Well even temp means even needs, 1 chamber will run the same way as another chamber. If 1 chamber runs hotter than another then to prevent 'issues' the hot chamber needs the timing pulled back or more fuel dumped into it. Neither is a good option for power production, emmisions or economy!

The thermostat and top rad hose should exit at the belt end of the engine, the BULK of coolant flow shoudl pass through the block cooling the bores, up into the head at the box end then back along the head and out to the radiator. This will ensure a nice even temp distribution. As it is the BULK of flow goes out the pump round number 1 cyl, up into the head again at number one then along to the box end. Result the cylinders get hotter towards the gearbox.

This means that either the timing or fueling has to be altered to try and amend this problem. The car runs batch fire and a single knock sensor, so 1 thing affects ALL cylinders!

Anyway as always this was a product of development over design. Development is only required due to the ignorance of designers!

The engine could have been a real stormer with more power and torque, a far wider power band but its not.

I never even went into crapness of the manifolds or the block either.

Site Subscriber Joined: 11 Feb 2005 Posts: 2929

So how much of this is fixable? Or is it not Pheesable?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

without a new head casting not much.

It is of course to make worthwhile gains on it.

Gains are easy due to the crap casting mainly!

Site Subscriber Joined: 10 Jun 2004 Posts: 2317

Crazy idea , but have you ever thought of designing a head? Sounds like you'd be pretty good at it!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

I have lots of head drawings, engine drawings etc etc but I am in no way qualified to do anything remember and I don;t happen to have a foundry in my garden, thats next years project.

But yes I would be good at it.

Site Subscriber Joined: 13 Oct 2004 Posts: 4722

u shuold take more time off from the fourm chris

goes away for 2-3 days

then comes back and writes massive intresting posts!

Level 10 User Joined: 18 Jun 2004 Posts: 614

Your above post. Sound's like your back on full form to me.

Site Subscriber Joined: 15 Oct 2004 Posts: 1139

u fancy beefing up my 1.8 8valve?????

just a suggestion Wink

Site Subscriber Joined: 28 Jan 2005 Posts: 3547

Chris H wrote:

I have lots of head drawings, engine drawings etc etc but I am in no way qualified to do anything remember and I don;t happen to have a foundry in my garden, thats next years project.

But yes I would be good at it.

Im doing mechanical design and manufactor, i could submit the drwings to a contact and have it built!

Site Subscriber Joined: 05 Jan 2005 Posts: 569

Very interesting read.

Are these faults the kind of thing Renault have worked on over the years to produce the 182Bhp engines used in the Clio 182?.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

i was having similar thoughts about the 2.0 BE yesterday...if there was just a little more cylinder spacing, u could have massive bores, and drop the stroke to have a screamer of an engine.....

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

Not really finch, they have brought down the port size etc which has made a world of difference but theres not really been a drastic re-design of the head. It IS an improvement though.

The megane head makes 150bhp, its rated the same as the williams, the megane has rougher valve throat machining lines and uses milder cams, but the powers the same as the williams but has more torque, the megane lump also has egr etc etc all chucked in. the simple port re-design is what brought about the extra power.

aye Stan.

Cooling would also be less of an issue as well. I have often thought about a nice de-stroked 1.4/1.6 16V lump, just to see how high it would go, but it'll never happen.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

the meg cams are milder than the 1.8...shows the benefits fo the re-designed ports ur talking about!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yes thats why i said it! Laughing

hows the job mofo?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

could ta! planning own business tho.....

hows things north of the border?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

shite mate, same as always

Level 1 User Joined: 20 Jun 2005 Posts: 34

Well my english isn`t so good so if I understand right,

Megane head is basicly ported 1.8 head?

So if I want to do some engine tuning it doesn`t metter if I take 1.8 or 2.0?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

no.

If you want to look at it that way then the 1.8 is a very badly ported megane head whioch was ported by an idiot.

The megane head is the better head.