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SteveA · Feb 1, 2021

Fast Eddie said:
No then!

At 325g they’re not as heavy as they look, not much heavier than stock 850 pistons.

Steve, I don’t think I suggested they didn‘t work! Just seems to me that removing all that metal, only to basically add some of it back onto the piston, seems like unnecessary work when you can get just as good squish, that’s a lot easier to set up (flat squish band + flat piston = very easy to fine tune) without all the work, and have a slightly lighter piston as a bonus!

Design a piston and have it manufactured, one piece of work, but serves as many engines as you have batches made.

The heads were taken as blanks, valve angle set from first principles not re-angled. Second piece of work but needed for every new head. Unless you only build race heads!

If you are a factory team that can get part worked items it isn't really any more work to do it.

I think what Jim Schmitt is asking for is the chance to start from the same baseline the factory team did and have the widest range of options open.

I think what I hear is sound; that the first issue will be to manufacture a fairly standard item that could be used by anyone. Evaluate product and market and go from there.

The baseline Fullauto is already a good race head, even with standard valves, for a 750.

Today, I doubt I will personally buy another new head. I tend to think volume market is replacing worn out heads with a handful of people doing what we have done and build new engines from scratch each year!

Unless the race classes are changed and the use of the Commando twin based racer becomes a really good racing option again!

Madnorton · Feb 1, 2021

Fast Eddie, do you have the calculations from the forged AN Omega pistons, from what I remember the CR was good.

Fast Eddie · Feb 1, 2021

SteveA said:
Design a piston and have it manufactured, one piece of work, but serves as many engines as you have batches made.

The heads were taken as blanks, valve angle set from first principles not re-angled. Second piece of work but needed for every new head. Unless you only build race heads!

If you are a factory team that can get part worked items it isn't really any more work to do it.

I think what Jim Schmitt is asking for is the chance to start from the same baseline the factory team did and have the widest range of options open.

I think what I hear is sound; that the first issue will be to manufacture a fairly standard item that could be used by anyone. Evaluate product and market and go from there.

The baseline Fullauto is already a good race head, even with standard valves, for a 750.

Today, I doubt I will personally buy another new head. I tend to think volume market is replacing worn out heads with a handful of people doing what we have done and build new engines from scratch each year!

Unless the race classes are changed and the use of the Commando twin based racer becomes a really good racing option again!

Absolutely agree with the big valve idea in new FA heads Steve.

But I would definitely urge John NOT to spend (ie waste) any development time and money on full hemispheres.

Fast Eddie · Feb 1, 2021

Madnorton said:
Fast Eddie, do you have the calculations from the forged AN Omega pistons, from what I remember the CR was good.

Yes, but remember the forged Omegas I had were NOS 1970s flat topped jobs, and not as per the ones currently on offer at AN.

A flat, raised top piston (raised around .110” IIRC) can easily be set to give a nice .030 - .040” squish and, depending how much the combustion chamber has been hacked out, will give 10.25-10.5:1 compression ratio.

Hence our conversation from a while ago, I don’t understand why AN ones are domed? The only effect of this is to have no squish, or a tight squish with diesel levels of compression ratio!

But, despite playing with the NOS Omegas I never ran them, I went with JS pistons which gave me 10.5:1 and were a third lighter than the Omegas.

The reason I get a bit on my soap box about the squish is I’m convinced it works, especially for road use. In a race engine running proper race fuel, I suspect the benefits are much reduced, but in a road bike using modern fuel I believe it helps immensely. How else can anyone explain being able to run a 920cc street Norton with 11:1 compresssion ratio on today’s pump fuel with no issues ?!

Madnorton · Feb 2, 2021

These new Omega's are forged, all that went before were cast according to Omega, (they still have some blanks from the 70's) The standard size 850 AN Omega forged piston with pin, rings and circlips is lighter than the GPM cast piston of the same size. The domes were were added at the request of Joe, but it only reflects the WISECO AMA pistons, yes, we still have odd ones which is not much use other than historic value, and they are very heavy.

There is a motorcycle engine builder in our neck of the woods that builds modern MX two stroke engines that use a forecourt pump mix 16:1 at 16,000rpm. These bikes are used worldwide. I'd say the fuel these days is pretty good.

Hudriwudri · Feb 2, 2021

Fast Eddie said:
Opening the combustion chamber out to a full hemisphere just seems like such a backward step to me.

Tuners of other makes are busy welding combustion chambers up to get a squish band !

I will look if I find pictures of the weld up squish head I did for a dominator a couple years ago.

Kind regards

Christian
@Madnorton
16:1 seems imho quite high, cuz that's about what the speedway guys use on methanol with pretty late intake closure timing.

jaydee75 · Feb 2, 2021

Hudriwudri said:
Christian
@Madnorton
16:1 seems imho quite high, cuz that's about what the speedway guys use on methanol with pretty late intake closure timing.

I think he was talking about 16:1 fuel/0il ratio in a 2 stroke.
Jaydee

Madnorton · Feb 3, 2021

No that is CR, and each bike is dyno'd on their onsite dyno before being shipped out.

B+Bogus · Feb 3, 2021

I've heard from the motorsport crowd that modern fuel has much better anti-det properties than old 4 & 5 star pump fuel, but I guess the motors we're discussing are unlikely to be running regular unleaded...

Steves · Feb 3, 2021

B+Bogus said:
I've heard from the motorsport crowd that modern fuel has much better anti-det properties than old 4 & 5 star pump fuel, but I guess the motors we're discussing are unlikely to be running regular unleaded...

I believe way back when at the start of the internal combustion engine, the options were lead or alcohol as additives. Alcohol was (is) better for pre-detonation, lead was good for wear. They went with lead. That is maybe over simplified or just plain wrong, but I think it's something I read a long time ago on the back of my wheaties brekky box.

cjandme · Feb 3, 2021

Sounds about right to me.

Bernhard · Feb 3, 2021

Steves said:
I believe way back when at the start of the internal combustion engine, the options were lead or alcohol as additives. Alcohol was (is) better for pre-detonation, lead was good for wear. They went with lead. That is maybe over simplified or just plain wrong, but I think it's something I read a long time ago on the back of my wheaties brekky box.

There was a lot of intresting snippets on a packet of breakfast cereal. . . . . . . some even had a plastic toy.

SteveA · Feb 5, 2021

Madnorton said:
No that is CR, and each bike is dyno'd on their onsite dyno before being shipped out.

If that is a 2 stroke, is the 16:1 compression a calculated total compression?, adding primary compression to secondary compression?

Or just secondary compression?

SteveA · Feb 5, 2021

Steves said:
I believe way back when at the start of the internal combustion engine, the options were lead or alcohol as additives. Alcohol was (is) better for pre-detonation, lead was good for wear. They went with lead. That is maybe over simplified or just plain wrong, but I think it's something I read a long time ago on the back of my wheaties brekky box.

Simplified, but near enough.

One of the reasons Vintage racers rely on alcohol fuels is that their engines have shallower fins than later designs, so the cooler running of alcohol remains critical!

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