ESE's works engine tuner

[Ocean1]

The only difference the gearing makes to the power curve as seen off an inertia dyno is the run time.
In 1st gear it would spin from 6000 to 14,000 in an instant.
Not long enough to get the correct heat level into the pipe.
I usually run it in 4th gear as this acceleration rate is all but identical to what happens in the data readout on track.
After doing 3 full throttle pulls, the pipe surface is up to temp, I then do 2 recording runs back to back and overlay them.
They are usually then identical within 2/10 of a Hp so I choose one and delete the other.

There have been arguments for years over crank inertia in a racing 2T, with the basic theory being that with more inertia the in cycle speed variation is reduced.
At TDC where alot of work is done compressing the combustion charge, the crank slows down - to where it then accelerates very quickly toward BDC and speeds up as the
piston runs over the transfers.
This theory has been rubbished by some clever minds, BUT, bottom line is that it was discovered instantly when HRC offered total loss setups derived from A kit parts
that simply removing the flywheel lost ALL the overev power.
Ive done it, when I first started using Ignitechs on the old MX based RS125 Honda - ditch the flywheel and it simply WILL NOT rev out.
So the factory and VHM came up with so called " high inertia " cranks to be used with total loss where no flywheel was used.
This also then enabled lighter ones to be used for short tracks, favouring acceleration, or even heavyer ones for big tracks where overev power is king.

Jan has stated that he could find no advantage to so called heavy cranks on the Aprilia, but that I am sure is an artefact of the design being very " heavy " to start with
and making it higher inertia again simply ran into the law of diminishing returns.A very heavy crank is simply too slow to accelerate, and nothing worthwhile is gained in the top end against that loss.
A stock RS125/250 Honda has a VERY light crank compared to the Aprilia that is full of lumps of heavy metal.
I have recently built cranks for a couple of customers with very expensive Rotax derived tandem twins, using full circle wheels with no steps and full of heavy metal balancing like the Aprilia
and all report amazing gains in overev ability,cylinders and pipes etc being identical.

I don't see any contradiction in any of that. I helps me to visualise crank mass, (and every other rotating mass in the system) as a big bungy cord between my throttle and the back wheel, it only costs me overall acceleration potential if I let the bungy cord go before it's recoiled. If the type of racing in question doesn't lend itself to holding on to that bungy cord beyond peak power revs then low mass is the go. Like F1, not only zero flywheel but super light billet HT steel alloy cranks.

[Sketchy_Racer]

Head inserts on an air cooled motor?

How well will these work? I can only assume that the joins are going to make for a less efficient thermal path to dissipate heat from the combustion chamber. But how well will they work?

Has anyone here tried them?

[Frits Overmars]

Why would the power curve be different in every gear? Power at the crank would be the same in each gear, no?

No.

But it is storing energy, all of the energy it absorbed on acceleration. And that energy will be the same over any given pull, no matter what the gear, it's effect is just seen over longer times in higher gears.

True, the energy stored in the engine inertia only depends on the initial and final rpm and on the amount of inertia, irrespective of the rate of acceleration.
But the power generated by the engine is very dependent on the rate of acceleration and the rate of pipe temperature variation. This rate should match the rate of crankshaft rpm rise. As Wob said:

In 1st gear it would spin from 6000 to 14,000 in an instant. Not long enough to get the correct heat level into the pipe.

As the power curve approaches peak the energy stored in the rotating mass begins to shed power back into the dyno load.

You struck me as a bright mind, so you might want to think this over once more
Energy stored in any rotating mass does not become available until the rotation is slowed down. In racer's terms: when we don't want it any more.

[Frits Overmars]

Head inserts on an air cooled motor? How well will these work?

Very well if you're looking for detonation. Not quite so good if you're looking for power.

I can only assume that the joins are going to make for a less efficient thermal path to dissipate heat from the combustion chamber.

Right. And 'less efficient' is putting it mildly. I would describe it as 'catastrophic'.

But how well will they work? Has anyone here tried them?

A mate of mine races a Suzuki T500 with head inserts. It is one of the fastest bikes in its class. But I keep saying it could be a lot faster still .

[TZ350]

Head inserts on an air cooled motor?

How well will these work? I can only assume that the joins are going to make for a less efficient thermal path to dissipate heat from the combustion chamber. But how well will they work?

Has anyone here tried them?

I have not tried a head insert, and I don't think the thermal interruption will be a help but if your determined to go air cooled. A copper head gasket that also forms the squish band and extends out to be a fin or a pair of fins like the one in the picture could help. As it gives the squish a very good cooling path (in air cooled terms) and if you have a flat face across the insert and head the copper will form a thermal path that marries the insert and head fins to a certain extent.



Copper has twice the thermal conductivity of aluminium so will shift heat from the squish to the outer fins faster than it would have traveled through an uninterrupted area of aluminium of the same cross sectional area. The copper will also pick up heat from the insert face and transfer it to the outer head fins.

If I was going the insert way, I would make it as big as possible with large flat faces to maximize the joint area for greater thermal transfer. For head fins I like to use 2mm copper when I can get it and would try 3mm copper if I could find it.

Copper is not that suitable for making a complete head as its too soft and the plug threads pull and the head bolts tend to squish it out of shape over time. I once had 1.5mm of copper metal sprayed over the face of an alloy head so there was a good copper thermal path from the inner face of the combustion chamber shell out to the outer head fins.

The problem was that the polished copper in the combustion chamber oxidizes and goes black. Shiny copper is an excellent radiant heat reflector and black oxidized copper is an excellent heat absorber and is not what we want. But I found a good silicon car wax helped keep the polished copper combustion chamber shiny for a lot longer. The squish area does not seem to suffer from this oxidizing problem.

Because shedding thermal energy through air cooling is more efficient the hotter the radiant surface is, I started looking at copper as a way to shift more heat from the combustion chamber area to the outer fins and therefor run them hotter and get them to do more of their share of the cooling work than they would normally have done. With copper, in theory, if you can normalize the heat gradient more across the head by getting the outer fins to run a little hotter then the inner fins and combustion chamber shell will run a little cooler than they would have before.

[koba]

Lapped taper around the circumference for maximum contact?

[Ocean1]

True, the energy stored in the engine inertia only depends on the initial and final rpm and on the amount of inertia, irrespective of the rate of acceleration. But the power generated by the engine is very dependent on the rate of acceleration and the rate of pipe temperature variation.

Yes I see that, but I was referring to just inertial energy, which as you said is purely a function of mass over acceleration, same on every pull.

You struck me as a bright mind, so you might want to think this over once more
Energy stored in any rotating mass does not become available until the rotation is slowed down. In racer's terms: when we don't want it any more.

Not sure I see that. But I'm not very good at painting these sort of pictures... As revs increase beyond peak and power increase begins to drop is there a point where inertial energy begins to affect revs positively compared to the same engine with less mass?

Nevermind, the picture is clearer.

Edit: which means Wobb's over-rev capacity from heavier cranks can't be sustainable, if you could load the dyno to restrict revs to that over-rev limit you'd see power peak at those revs and then drop as the inertial energy was expended.

[jasonu]

The only difference the gearing makes to the power curve as seen off an inertia dyno is the run time.
In 1st gear it would spin from 6000 to 14,000 in an instant.
Not long enough to get the correct heat level into the pipe.
I usually run it in 4th gear as this acceleration rate is all but identical to what happens in the data readout on track.
After doing 3 full throttle pulls, the pipe surface is up to temp, I then do 2 recording runs back to back and overlay them.
They are usually then identical within 2/10 of a Hp so I choose one and delete the other.

.

This is how Chris and I more or less always did our dyno runs and we got some pretty consistant results. Other 'experts' recommended we do the runs in top gear for some unexplainable reason.

[wobbly]

I have seen inserts done for a aircooled that had something like 6 staircase steps on the mating surfaces.
Each of the steps OD faces were a press fit, and the accuracy was good enough that all the horizontal flat surfaces would also be in contact.
Dont know if this would be better or worse than a conical outer shape to the insert that mated against the same surface on the inside of the
head cover - with the head bolts clamping these surfaces together.
As both ideas support the inner dome over a wide area, maybe the insert could be done in copper to aid thermal transfer to the outer finned cover.

[koba]

Has anyone ever 'solid' mounted a carb before?
I mean running without any rubber Manifold.

I was thinking of recreating the standard MB style with some welding, it would have a plastic section as a thermal barrier but no rubber mounting.

I remember it a mates Rally car we had major issues with the fuel being shaken up in the side-draughts until we got them mounted with enough flex to slow the rattling.
I'm thinking we don't get quite the same shaking...

If it works I should be able to loose about 20mm from the inlet tract.

Anyone have good or bad experience here?

[Sketchy_Racer]

Has anyone ever 'solid' mounted a carb before?
I mean running without any rubber Manifold.

I was thinking of recreating the standard MB style with some welding, it would have a plastic section as a thermal barrier but no rubber mounting.

I remember it a mates Rally car we had major issues with the fuel being shaken up in the side-draughts until we got them mounted with enough flex to slow the rattling.
I'm thinking we don't get quite the same shaking...

If it works I should be able to loose about 20mm from the inlet tract.

Anyone have good or bad experience here?

Yep, I had a solid mount on a old dirtbike. Old XL125s etc all had solid mount carbs. The rubber inlets are usually just for easier manufacture of the reed stuffer on 2Ts I would assume

[koba]

Yep, I had a solid mount on a old dirtbike. Old XL125s etc all had solid mount carbs. The rubber inlets are usually just for easier manufacture of the reed stuffer on 2Ts I would assume

Sweet, I'll give this a go, I was just worried because if it doesn't work I'll have wrecked a carb.

[Drew]

Sweet, I'll give this a go, I was just worried because if it doesn't work I'll have wrecked a carb.

The GL motor didn't like it. But don't piston port bikes usually mount solid? The GT does.

[koba]

The standard MB does too, I think I'm just being a scaredy pants.

[TZ350]

Finally got some time to work on the Beast. Fitted the generator set that Wob sent me, it needed a little modification to fit the GP but it worked out well and everything lined up OK. Changed the flywheel center for a KX80 one, as the KX80 taper fits the GP crank and the rivet holes lined up with the new flywheel. I used high strength epoxy resin to glue the face of the KX center hub to the flywheel and replaced the old rivets with shoulder bolts, hopefully this will work out OK. Will finish the wiring this week, then I will have power to burn for running the EFI fuel pump and the fancy cooling fans.