Twin cam head design

[BobbyBreeze]

'The total intake port length of a ProStock engine at 10,000 rpm has only slightly less energy than the muzzle energy of 0.177 caliber pellet from a reasonable high powered air rifle. So air is heavy – if we add to this the fact that the energy is equal to half M(mass) times V(velocity) squared (1/2MV^2) we can see that when port velocity goes up the port energy goes up far faster and when port velocity drops the port energy drops far faster. Putting that into prospective if a port is made 20% too big the port energy drops by 44%. In basic terms that equates to a 44% drop in the ports ability to ram a cylinder by means of it’s velocity derived momentum. When it comes to combating reversion, especially at low speed port velocity is very effective. Kill the velocity below a certain level and you effectively kill torque at the lower rpm levels while not necessarily garnering any power advantages at the top end.'

Found a good series of articles by David Vizard. They are sort of based on chevy/ford v8's etc but still an interesting read and covers a lot.

Starts off with some flow bench stuff

http://www.gofastnews.com/board/technical-articles/980-porting-school-2-super-cheap-flow-bench.html

EDIT/ This is what he says about Jap 4valvers

'In spite of the forgoing we find that most production 4 valve heads have intake ports too big for the job. Why is this – certainly if strong torque curves and absolute output is the criteria then I have to say I think a lot of designers have walked down the wrong path. Maybe it’s emissions and that is something I am far from being an expert at. But as far as making power I do have experience on Cosworth DFV F1 engines and all the four cylinder derivatives of such plus the Cosworth YB (four valve Pinto). In the class I raced the latter in my engines were, in their final form, untouchable! Outside of that it’s Mitsubishi, plus a little Honda and Subaru. Although not so much with the Cosworth heads it seems, in the main, that the heads for Japanese manufactures typically have ports ranging from a little to be the way to big. The heads I did for Ryan Garcia’s Mitsubishi were a prime example here. The race ported head he was using was based on a casting that had ports way oversize straight from the factory and why the manufacture would do this remains, to me, something of a mystery. '\

So it looks like putting the biggest valves in there possible would be the first thing to do.

[forced]

So it looks like putting the biggest valves in there possible would be the first thing to do.

Why though?

Increasing the valve diameter by 1mm will increase the circumference of the seat by Pi ......3.142 mm.

At the same time the seat is wider in diameter so the minimal extra flow that the longer seat gives is offset by the seat being closer to the wall of the combustion chamber.

It's certainly nothing I'd look at when there's cheaper ways to make power, unless you're made of money.

More lift makes more sense to me.

Steve

[kpr]

fill those big stupid ports. just got the "tinyport 4age" going. first impressions untuned, goes damn well.

[Spencer]

So it looks like putting the biggest valves in there possible would be the first thing to do.

Why though?

Increasing the valve diameter by 1mm will increase the circumference of the seat by Pi ......3.142 mm.

At the same time the seat is wider in diameter so the minimal extra flow that the longer seat gives is offset by the seat being closer to the wall of the combustion chamber.

It's certainly nothing I'd look at when there's cheaper ways to make power, unless you're made of money.

More lift makes more sense to me.

Steve

Beacuse on some engines it can be done cheaply and if you already have big lift cams why not? if your going all out it will only be a fraction of your build cost. You kind of took his remark out of context it wasnt a blanket statement, it was refering to bigport japanese engines of the 80's. Which on some you can got a couple of mills over I know on early 3gse's you can add 2mm which is 11%+ in surface area increase which is alot

[Truenotch]

fill those big stupid ports. just got the "tinyport 4age" going. first impressions untuned, goes damn well.

Awesome! Was looking forward to seeing how that turned out.

[Mick Doohan]

So it looks like putting the biggest valves in there possible would be the first thing to do.

Why though?

Increasing the valve diameter by 1mm will increase the circumference of the seat by Pi ......3.142 mm.

At the same time the seat is wider in diameter so the minimal extra flow that the longer seat gives is offset by the seat being closer to the wall of the combustion chamber.

It's certainly nothing I'd look at when there's cheaper ways to make power, unless you're made of money.

More lift makes more sense to me.

Steve

Beacuse on some engines it can be done cheaply and if you already have big lift cams why not? if your going all out it will only be a fraction of your build cost. You kind of took his remark out of context it wasnt a blanket statement, it was refering to bigport japanese engines of the 80's. Which on some you can got a couple of mills over I know on early 3gse's you can add 2mm which is 11%+ in surface area increase which is alot

your quite right .. and that is also why you deshroud valves you also get nicer valve top angles as well as a few other bonus's

fact is most jap motors performance orientated have 9-12mm of lift stock ... so bigger valves makes proportionally gives far better gains

[Truenotch]

BMW Valvetronic setup is really interesting. The shape of the intake port in this vid is interesting as well.

[lowlancer]

fill those big stupid ports. just got the "tinyport 4age" going. first impressions untuned, goes damn well.

Awesome! Was looking forward to seeing how that turned out.

also really keen to see

[BobbyBreeze]

Yeah keen to see this tinyport 4age! Keen to fill up some ports on a Datsun A series head i have here so results etc would be awesome.

Regarding the larger valves - was a statement regarding Japanese 4valve heads with their tendency to have far too much port volume. The ports have far too much area for the valves, so one can fill in the ports, or go with larger valves to increase port velocity (as the valve and seat is the major restriction to flow). Seeming larger valves are best for power and torque that should be the first mod. Cram in the biggest ones you can then grind the ports measuring the flow and port volume regularly. When the flow starts dropping of with respect to volume you stop.

Also really interesting his idea of running different sized valves in a 4valve head to create swirl. 2 valve heads make a lot more torque up to 4000rpm than 4valve heads because of the inherent swirl that is created by the valve layout. His idea is to run different sized valves to create swirl, and also to stop cross-flowing between the inlet and exhaust. Makes sense.

[bubblegoose]

@kpr

what were you using to open the valves on you flow bench. cam and degree wheel?

[lowlancer]

I'm curious as to whether port shape makes a huge difference. Ie: Round vs oval, and why?

[BobbyBreeze]

I'm curious as to whether port shape makes a huge difference. Ie: Round vs oval, and why?

Doubt the shape at the manifold face makes much difference really. Its more of a space issue than anything else i think. I.e. get the required area in without hitting water jackets/pushrod holes etc.

I'd say its just port area/volume that makes the difference. There are a lot of high performance heads that have all the different shapes - round, oval, rectangular etc.

The shape of the port throat does make a difference however - like biasing the port to create more swirl, raising the floor to straighten the shot onto the back of the valve etc. All ports have to slowly merge into the round shape of the valve so its only the outer section near the face that has the different shape. And this outer section has the least restriction to flow.

[Testament]

a circle is best, but it depends on the rest to the head architecture, coolant and oil galleries, valvetrain etc. they might put in a different shaped port to get more area/volume in the available space. that and transitioning from a single port to two valves also.

[Truenotch]

I saw an amazing thing today...

A NISMO head from an LZ series nissan engine. Basically an L16 but with an alloy DOHC head designed for competition only. The intake ports are beautiful, they head down on a steep angle and barely curve before the valve face. The valve angle in these is really steep and the exhaust ports are fairly small. It pretty much looks like an alloy bathtub that holds cams!

Found some pics of them:

http://www.datrats.com.au/lz-T.JPG

http://www.datrats.com.au/lz_twin_cams.htm

Used in Formula Pacific/atlantic, Group 4,5 and C.

They are in the Group C skyline silhouette in LZ20R form:

http://www.banpei.net/category/tags/nissan-silvia-turbo

I thought the steep port angle was pretty cool, and was a sweet thing to have a look over.

[Truenotch]

Found some more interesting info and think this is a fitting place to put it:

Honda guys talking about soundwaves etc:

http://www.team-integra.net/sections/ar ... icleID=466

Some guy with a computer program:

http://www.gt40s.com/forum/gt40-tech-en ... study.html

And how NOT to do a set of trumpets!!!

[macabre]

rat rod honda?

[Black Francis]

F20C into FWD would be interesting, wonder if it's been done before.

Pretty sure the Ant Te Rito that has the CRX delsol in SS2000 runs an F20c, and I think the car was built by Mr Strong originally - provided I remembered the conversation right.

strong ran a car with the same specs in nz kiwi2 rally champs a couple years back

[mikuni]

Found some more interesting info and think this is a fitting place to put it:

Honda guys talking about soundwaves etc:

http://www.team-integra.net/sections/ar ... icleID=466

I haven't looked at it in depth yet but the first bit that I read (bottom of the first page) is bullshit

Notice that with invididual throttle bodies (ITB's) you lose this resonance effect because the reflected wave escapes out into the engine bay (or the atmosphere) and is not stored and returned by a plenum/acoustic chamber. ITB's do NOT use ram theory to get that extra kick at peak torque because they usually in race form do not have a plenum. In some street ITB's, a plenum is attached for practical reasons (sound deadening and filtering). They rely on very very large amounts of passive cylinder filling based on the piston's effects and use tuned air horn height and tapered diameter (with an S-shaped velocity stack opening) to get the N/A pressure boost effect

The pulse doesn't 'bounce' off the plenum it does so off the general mass of dense air at the opening to the trumpet.

[FuzzayD]

Found some more interesting info and think this is a fitting place to put it:

Honda guys talking about soundwaves etc:

http://www.team-integra.net/sections/ar ... icleID=466

I haven't looked at it in depth yet but the first bit that I read (bottom of the first page) is bullshit

Notice that with invididual throttle bodies (ITB's) you lose this resonance effect because the reflected wave escapes out into the engine bay (or the atmosphere) and is not stored and returned by a plenum/acoustic chamber. ITB's do NOT use ram theory to get that extra kick at peak torque because they usually in race form do not have a plenum. In some street ITB's, a plenum is attached for practical reasons (sound deadening and filtering). They rely on very very large amounts of passive cylinder filling based on the piston's effects and use tuned air horn height and tapered diameter (with an S-shaped velocity stack opening) to get the N/A pressure boost effect

The pulse doesn't 'bounce' off the plenum it does so off the general mass of dense air at the opening to the trumpet.

Is the pulse negated or resonated by the throttle butterfly before it reaches opening of the trumpet?

[mikuni]

I haven't looked at it in depth yet but the first bit that I read (bottom of the first page) is bullshit

Notice that with invididual throttle bodies (ITB's) you lose this resonance effect because the reflected wave escapes out into the engine bay (or the atmosphere) and is not stored and returned by a plenum/acoustic chamber. ITB's do NOT use ram theory to get that extra kick at peak torque because they usually in race form do not have a plenum. In some street ITB's, a plenum is attached for practical reasons (sound deadening and filtering). They rely on very very large amounts of passive cylinder filling based on the piston's effects and use tuned air horn height and tapered diameter (with an S-shaped velocity stack opening) to get the N/A pressure boost effect

The pulse doesn't 'bounce' off the plenum it does so off the general mass of dense air at the opening to the trumpet.

Is the pulse negated or resonated by the throttle butterfly before it reaches opening of the trumpet?

No. Although opinion varies on how much restriction butterfly type throttles introduce. A lot of testing and tuning has been done over the years with slide (and other types of) throttles and although these can offer a slightly higher peak power output because of having no restriction, the way in which they open give detrimental characteristics during throttle actuation. Some people also say turbulence induced by a wide open throttle butterfly isn't a bad thing. Either way, with what we are playing with its probably best to just stick with butterflies etc