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Old 31-10-2006, 11:26 AM
Big Pete Big Pete is offline
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I thought a few folk might be interested in some pics of the head I've been working on for a chop I'm finishing off. I had to pull the head to sort the valves out, so while I had the top off anyway I thought I might as well improve the gas flow situation a bit. I have'nt gone to town on it, as I don't have the time or the inclination, so I just removed the worst offenders.

The inlet ports have almost no swirl affect, and without major welding and rework it isnt something that can be fixed, so the ports are pretty much untouched apart from cleaning out the casting flash and blending in the valve seat inserts, which had a bloody great lip on.

The biggest problem was the combustion chamber wall shrouding the inlet valves, especially at low valve openings, so I cut the walls back to allow more room for the mixture to get into combustion chamber without slamming into the walls. I lost a bit of compression and some squish by doing this, but the improved gas flow should more than make up for it.

The picture quality isnt brillinat as my camera struggles abit on close up stuff.


before any mods, see how close the walls are to the inlet ports.


closeup of the inlet port


die grinder ready go


completed head with nice large easy flowing radii around the inlet port.
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Old 31-10-2006, 09:25 PM
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Taff Taff is offline
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Wish i knew about stuff like that, just been bitten by the get more from yer motor bug, unfortunately, the old how fast do you wanna go, depends how much you wanna spend rings true...
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Old 01-11-2006, 09:56 AM
Big Pete Big Pete is offline
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Its not that hard to do most of the basics TBH Taff, if you're interested I can recommend some fairly real world type tuning books, mostly aimed at cars, but the principles are the same. However, there are almost certainly lots of
"Make your Harley do 200mph!!! Top tuner sells his secrets in this book for only $29.95" type HD specific books available on the net.

I reckon it worth reading up on it even if you're paying someone else to do all the work and just buying bits, because it helps you decide if your tuner knows his stuff, or if the new Wondergadget (TM) that claims to make your engine give 40% more power and make you more attractive to women is actually worth using as anything more than a doorstop.
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Old 01-11-2006, 10:28 AM
kiffer38 kiffer38 is offline
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nearly all cylinder heads come out of the factory as straight castings, with only the mating surfaces machined, the inlet and exhaust ports are always an odd shape with bits o flash, and bumps in that shouldnt be there, a lot of improvement can be made by just cleaning of the flash and smoothing out the air passages but its not realy worth taking a risk with trying to increase the size of the ports unless ya know what ya doing, because if ya make a mistake and take to much metal out, it can make things a lot worse, because the air coming into the engine might get slowed down by creating a bounce effect, where the incoming air coming in, cant get in quick enough, and it creates positive preasure, slowing down the air flow( i hate trying explain things) always seems sound wrong, but i think i know what i mean
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Old 01-11-2006, 11:17 AM
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Quote:
Originally Posted by kiffer38
nearly all cylinder heads come out of the factory as straight castings, with only the mating surfaces machined, the inlet and exhaust ports are always an odd shape with bits o flash, and bumps in that shouldnt be there, a lot of improvement can be made by just cleaning of the flash and smoothing out the air passages but its not realy worth taking a risk with trying to increase the size of the ports unless ya know what ya doing, because if ya make a mistake and take to much metal out, it can make things a lot worse, because the air coming into the engine might get slowed down by creating a bounce effect, where the incoming air coming in, cant get in quick enough, and it creates positive preasure, slowing down the air flow( i hate trying explain things) always seems sound wrong, but i think i know what i mean
Tis true, you have to get the shape right, its often worth raising the port roof to increase the bend radius down to the valve, but you need to be carefull not to eat into the bottom of the valve spring seats. Sometimes the bottom of the port needs to be built up using plastic metal to increase the radius where the port turn towards the lower edge of the valve. Increasing the swirl helps too, but the design of the head in the pics just didnt have the meat to do it, and it would have been a major rework job to to.

The problem with making the ports to big is that there is then a larger mass of air to accellerate , and your volumetric efficiency suffers at high revs. The pressure variations you're on about are more to do with the port length, which governs the reversion pulse frequency, its one of the factors that generate power bands on engines. It can be harnessed to act as a form of boost, F3 cars had variable geometry inlets for a while to get a better spread of power and the reason that lots of modern cars have a "snail" inlet manifold.
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Old 01-11-2006, 11:40 PM
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I thought suzukie already sort those probs out with thier TSCC effort
and as a note, never ever let me near a engine with a die grinder
as the said engine would be rendered useless in 10 seconds, not that i`m heavyhanded by anymeans
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Old 02-11-2006, 02:02 AM
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What's the word on the swirl effect in the inlet port then?
I see contradicting reports about having the ports polished and ported, to zoom the mixture in ASAP, then i'll see one about it being better with rough arsed walls to agitate the mixture and get it rollin about.
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Old 02-11-2006, 11:57 AM
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I would never polish them, seen reports and although on same type engines, but different engines, on the same dyno, so figures are fairly indicative, but not gospel, I have seen better reults with tidied but rough, as opposed to all poilshed up

was explained to me many years ago, but forgotten a lot of it through the mists of time, but somehting to do with it affecting the atomisation of the fuel, strangely I beleive that the polished sides lead to the fuel gathering and actually staying opn the walls, whereas the rougher surface with the air going past prevent this, sort of throwing it back into the air???

was explined to me by an old boy that really new his stuff, maybe I got it a bit confused but it made sense and still does to me!! LOL
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Old 02-11-2006, 12:11 PM
rob rob is offline
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thats what i thought too, D-T, get the inlets the right shape, (no lumps, bumps or casting flash), then sand blast 'em, (or similar), but polish the exhaust ports to a mirror, get them gasses OUT!!
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Old 02-11-2006, 12:12 PM
pyro pyro is offline
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It all depends on so many factors, at low revs a rough surface seems to work better, but at higher revs a smooth polished surface appears to work more efficently. This is to do with (IMHO) the fluid dynamics of the air flow,at lower speeds the rough surface causes eddies that help keep the mixture even, at higher flow speed the important thing is scavenging the cylinders to get the mixture though quicker and expunge the exhaust gases.
I used to drag Z9's and tried a variety of heads, rough, smooth and fully polished.

For me, best results came with a completely polished head and ports, cos the engine was revving its nuts off most of time. for road use I would smooth out the ports but not polish them.
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Old 02-11-2006, 12:39 PM
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Quote:
Originally Posted by pyro
It all depends on so many factors, at low revs a rough surface seems to work better, but at higher revs a smooth polished surface appears to work more efficently. This is to do with (IMHO) the fluid dynamics of the air flow,at lower speeds the rough surface causes eddies that help keep the mixture even, at higher flow speed the important thing is scavenging the cylinders to get the mixture though quicker and expunge the exhaust gases.
I used to drag Z9's and tried a variety of heads, rough, smooth and fully polished.

For me, best results came with a completely polished head and ports, cos the engine was revving its nuts off most of time. for road use I would smooth out the ports but not polish them.
Scavenging.........not heard that word used in engine speak in years takes me back to my yoof and 2 stroke diesels,and stoichiometric ratios...........but to me the man is right, you cant burn the new fuel and xs air mix if the cylinder is still half full of exhaust gases. Get the wate out as quickly as possible. Some of the two stroke folk use swirl to scavenge the cyclinder more efficinetly than a linear type flow. I tried it on an 85 hp yamaha outboard, with reasonable results.....not sure on true performace increase but it burnt a lot more fuel and the plugs were good, and with the addition of a lightened flywheel it reved like fook...........but it was a dammed expensive bang, more than once!
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Old 02-11-2006, 03:34 PM
Big Pete Big Pete is offline
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Quote:
Originally Posted by Taff
What's the word on the swirl effect in the inlet port then?
I see contradicting reports about having the ports polished and ported, to zoom the mixture in ASAP, then i'll see one about it being better with rough arsed walls to agitate the mixture and get it rollin about.
a mirror polish on the port walls can lead to fuel separating out, depends on a lot of factors, like temperature and gas speed. Don't think I'd do it on a HD with their normal single carb induction system.

Swirl is a whole different thing, its about getting the mixture rotating in the cylinder and generating turbulent flow. The turbulence gets more of the mixture past the spark (and keeps the fuel well distributed through the air)and hence better ignition, it also means that the flame front spreads more uniformly across the combustion chamber. That in turn gets better combustion and reduces the risk of detonation.

The best designs have the port offset from the centreline of the combustion chamber, so as the air comes in it swirls around the cylinder like water around a plug hole.

There have also been experiments where the air is additionally swirled around the centreline of the port, so theory is that you get better usage of the valve opening and hence more gas flow, and more flow=more power.
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Old 03-11-2006, 12:29 PM
Blackjack Blackjack is offline
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Years ago I had a pre unit Triumph.

It was apparently the factory development engine for an order from the Swedish army for 12 Gyrocopter engines. It had 32mm carbs, 11:1 compression ratio, and E4220 cams which are the balls out factory race cams.

The engine had been in a few Tritons, but was pretty much unridable. It was supposed to make something like 70 hp on the factory dyno at 6500 rpm, but I'd say that at 6,000 it was probably making 50, and at 5,000 next to bugger all. Which meant you needed a close ratio box and pretty low overall gearing to get it up to the rev's where it made some power.

With a rebuild using 9.5:1 pistons, 30mm carbs and setting the valve timing for maximum duration instead of maximum overlap, it probably lost 10 hp or more off the top. But what it did have was a much broader spread of power.

That meant stock gear ratios, and 20 and a gnat's cock mph per 1000 rpm gearing in top. Which in turn meant it was faster, both in terms of top end and getting there.

My point being that more isn't always better as far as HP is concerned.

Good indicator of how usable a street bike is going to be is the area under the dyno curve rather than the peak HP figure.

It's cheaper too.
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Old 03-11-2006, 12:45 PM
Big Pete Big Pete is offline
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Definetly, theres no point putting a drag motor in a road bike, it would be a nightmare to ride. Those gas turbine powered bikes are a joke for the same reason, Aero turbines have nowhere near the throttle response required for a usable road vehicle.
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Old 03-11-2006, 05:44 PM
martindodger martindodger is offline
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Blue print your motor is the way i go for reliable power
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