Head Inlet Port Shape

[Batfink 201]

Dr Sarty and Kyepan came over last night for a little comparison of throttlebodies and we noticed so interesting things to do with the port shapes.

 

Justin (Kyepan) brought over some nissan sunny gti-r throttlebodies and these direct to head units have a slightly oval shape

In comparison the standard mi16 longmans inlet is circular to match the mi16 head shape.

Now the mi16 touring car throttlebodies have a similar oval shape which seems incompatable with the standard port shape. It seems to be wider and narrower than the head.

Now this gave us lots of questions before we gave up for the night

 

1.Whats the optimum port shape?

2.Would the touring car design help feed air to each valve better (on the 16v head)

3.Would this be a similar way of thinking to the nissan ones as again the sunny engine is a 16v

4.Why does the mi16 head have that little notch at the top?

 

We were all loving the build quality of the sunny throttlebodies, expecially as it was a mass produced car. sadely the port spacing is a significant amount wider than the mi16 head but theres a possibility that these will be superior to bike body conversions in our view, but manifold design would be critical.

 

I really should have snapped a few pictures but I was holding a pint of guiness so i've drawn a diagram

 

 

[Sandy 189]

The notch at the top is for the injector nozzle. Round ports are generally considered to flow best for a given area, flattening out the port shape might improve flow and wave action at the edges, but without being able to properly test back to back, you're probably wasting your time. Given that some people have achieved around 95lbft/litre with round ports on the 16v XU, you can't hope for much better than that.

[Tom Fenton 1,524]

Surely the notch in the standard Mi16 head is for the injector spray pattern?

 

With my mate who co owns my 205 Mi track car we have looked at the Pulsar bodies a couple of years ago, we came to the conclusion that without remaking the standard Mi16 alloy engine mount bracket they were not going to fit in a way that would flow nicely, so at the moment we are going down the bike bodies route.

[Batfink 201]

i forgot about the injectors having always run throttlebodies on my mi16 It was late and I was tired in my defence

 

Certainly to get the mi16 head to match my throttlebodies would require more work than was necessarily worth doing. We wondered if the mi16 touring cars used different heads or welded the ports to get a completely different shape. Sandy - I was going to speak to Mark and see if he could shed light on the design and why it may have been done

If the nissan tb's were to be used there was plenty of metal to open up the manifold into a more circular shape.

 

it made good discussion anyway!

Edited January 7, 2008 by Batfink

[James_R 3]

Just for comparision the Redtop head Vauxhall designed has a wide flat port shape, and it's much smaller than the Mi port, and that produces 75lbs/Litre std, and with the simple addition of bodies usually jumps to 85lbs/Litre something the Mi/s16 never seem to attain in standard to bodies form.

 

Also the Clio 1.8 16v and williams heads have even flatter wider ports,

 

I'll get some pics up of a redtop head back to back with an 6 head when I dig them out the shed this week

[Batfink 201]

interesting - does this mean that peugeot went against the norm with its head design in going oval on its 16v engines?

[DrSarty 90 1 Cars]

interesting - does this mean that peugeot went against the norm with its head design in going oval on its 16v engines?

 

I mentioned last night, that my memory told me the head ports were round. Here's my (Mi) head:

 

Of course this matches up with Kev's (beautiful) diagram. So why does the TOCA manifold, for Kev's throttle bodies have oval ports just like the Nissan set-up, UNLESS the head was different, OR there was a linking manifold of some description which mated oval to round? If so, why?

 

Edited January 7, 2008 by DrSarty

[Doof 11]

For reference heres a link to some pics of the vauxhall XE engine

 

http://images.google.co.uk/imgres?imgurl=h...l%3Den%26sa%3DG

[James_R 3]

Good find, but it's next to eachother you realise how tiny the XE ports are

[Miles 331 1 Cars]

If my memory is right the Later EW and ES engine have the port's like the Vauxhalls and most other's now

[Mandic 0]

I once read a flow report about inlet trumpets and how their bellmouth shape influences on inlet flow, which indicated that best was round/circular shaped trumpet with oval shaped bellmouth (looking from aside), and far worst was oval shaped trumpet.

 

On the other hand "D" shaped exhaust port give best flow for given area.

 

Cheers

 

Ziga

[Batfink 201]

 

heres my inlet manifold shape.

 

I noticed the longman one effectively blanks off the injector dimple in the head port which might have an effect on the flow

[oli-pug 6 2 Cars]

Am i right in thinking flattening of the inlet ports will improve flow at low valve lift, and may improve swirl?

[Doof 11]

Probably way off the mark here, but injectors pretty much blast straight at the opposite wall right? I remember being surprised that the pattern of a correctly set up injector is quite narrow. (see here http://www.injectorcleaning.co.uk/spray.htm)

 

Would it perhaps be so that the fuel splats against the other side and follows a pattern something like this:

 

 

Would maybe mix the fuel really well? Or maybe im talking complete cobblers and the fuel never makes it to the other wall?

[B1ack_Mi16 67]

I noticed the longman one effectively blanks off the injector dimple in the head port which might have an effect on the flow

 

The dimple could just be welded shut in the head anyway, like I did on the head on the 2.3 16v.

 

[DrSarty 90 1 Cars]

The dimple could just be welded shut in the head anyway, like I did on the head on the 2.3 16v.

 

**IF** I ever decide to put ITBs on my 2.2Mi (Lotus ones I think) in the future, I may well do this too: a neat trick.

 

However: Batfink's original question still stands. Why has the TOCA ITB setup he wants to use got oval ports, when the standard Mi head has round ones? And so:

 

1) Did the TOCA 16v head have matching oval ports? Was this standard OR via machining?

 

2) Was it just used 'as is', with the Longman's oval ports mating straight up to round ports on the head? Or was a manifold of some description used to convert between oval to round? The black plastic spacer in itself is actually acting as a very thin manifold. It was only about 10-12mm thick if I remember.

 

Kev: I dunno if I've missed something here. But judging by your photo, the Longman's TB/manifold (metal) ports seem round and only the plastic spacer is oval (at least on the head face anyway)? Is this plastic spacer thingy round on the TB face and oval only on the head face? If so, is this some form of deliberate 'flow convertor' piece? Because it is not just blanking off the injector notch, it is a flat bottomed oval.

 

My mind is just ticking as to whether there are any advantages in copying this plastic spacer (at least its port shape changing characteristics) when fitting throttle bodies?

Edited January 8, 2008 by DrSarty

[Sandy 189]

The BTCC bodies I had on my Accord engine had the port "raised" from the standard position, presumably by fill welding the bottom of the port and opening up the top to make it a bit more downdraught. If you were to try and acheive the same thing with an XU head, you would probably end up with an oval port. My advice to you though Kev, would be find the right person to do the head and accept their advice;)

[Batfink 201]

Rich - The plastic spacer matches the shape of the inlet manifold

 

Sandy - I certainly know of someone your way

[jas-E 1]

Theres alot of factors involved with port design, and the fact that you are comparing a race spec engine to a road going mi16 is probably why theres so many differences.

 

Id say that the race engine has oval ports as you can get a much smoother shape transition going to the two valve openings on the other end of the port which reduces air friction at high revs ensuring more air going into the engine. The round ports are better for air at one end, but the change of shape of the port to the two valve openings would be more drastic, which would have loads more friction at higher revs.

 

The mi16 engines probably have round ports to get more air in at the bottom end of the rev range to ensure driveability and response for town driving for example. Race engines however are designed to be at max revs most of the time, so a smoother change in shape would defo be an advantage.

 

The race engine injectors are much further away from the head to provide better charge motion going into the engine, but this increases emissions, which is why the mi16 engines has injectors right next to the head.

 

Another reason for the oval ports could be cooling flows. The race engine will be giving out more heat so will require a higher coolant flow rate. An oval port could provide an advantage over a round one. That might not be an issue when designing the engine though.

[Batfink 201]

if they taught this sort of thing at school i'd have been a grade A student Facinating stuff!

[M_R_205 5 1 Cars]

im not an expert but would the flatter oval shape not be best, as when flowing air has to fill a space (for instance when the mi16 port opens up inside) it creates terbulance and slows the air flow, on the oval ports there would be lessless terbulance as the port does not get much wider inside,

 

Im not sure if that makes much sene so heres a s*it diagram, on the left is the mi16 port shape and the right the red top port shape, not perfect diagrams but you get the pic, the blue lines on the mi16 diagram shows where the terbulance would ocur

 

 

 

Just a thought...

[DrSarty 90 1 Cars]

Kev: ref the plastic bit.

 

Does that mate with the head?

 

I'm sure it does. The other side, in fact as pictured, mates to the manifold & TB set-up.

 

What I'M asking - and a picture would paint a 1,000,006 words - is whether the TOCA race engine had round OR oval inlet ports x 4? That is my key question.

 

Secondly: when you offer your TB set-up (including the plastic 'jobby') to your typical Mi head (i.e. which has round inlet ports as pictured several times), how do they match up? Is the oval diameter the same as the round port diameter or larger?

 

Stop working and get measuring!

Edited January 8, 2008 by DrSarty

[Batfink 201]

lol I'll pick up my spanners tonight and start taking them apart.

I'll also ask if I can get a picture of a touringcar head

[jas-E 1]

im not an expert but would the flatter oval shape not be best, as when flowing air has to fill a space (for instance when the mi16 port opens up inside) it creates terbulance and slows the air flow

 

An oval port would be better for power than a round one, thats why it was used in the mi16 touring car engine.

Edited January 8, 2008 by jas-E

[Batfink 201]

i've emailed someone in europe I know who can get his hands on old WTCC stuff so will see what he can find out