How about a 180 (30cc) glow motor?

[Ian Inverarity]

Craig,

Valid point, spark ignition petrol engines are a different kettle of fish. I agree there are a lot of different affects that come from methanol and nitro, but I still think we should be paying attention to the top level road racing stuff!

I alluded to this earlier, to put it in perspective the A100 (actually 17.2cc) is about 16% larger than the A-90HP (actually 14.8cc), but in capacity only. It is being fed by the same carb and disc sizes, same case port sizes, same header sizes and pipe. So maybe it is just inefficient because it is effectively being starved? A lot of work to build a completely larger engine, but maybe that is the key. I suppose the rest of the engine is being made to flow 16% more than it was designed for, thus it isn't really happy to rev where high flow rates are needed.

I dont think I can fix that problem on my engine, if it is the problem.

I am pretty sure the liner OD's are the same with the A100 liner just 0.5mm thinner wall.

 

[EatMyShortsRacing]

Ian,

All those flow areas are addressable.. and I will do that to my engine (I have a plan, me and Mr Dremel).. I also have some larger pipes (Steve Muck 90 and bigger) to play with. I think though only a little dremel work will be needed to make that engine breathe a lot better. I will be interested to see if that really is the case. The carb is 1mm larger than the 90 carb and I would say the disc wont be restricting the flow that much. I believe it is inside the engine and maybe the exhaust that are the issue. Both these areas are addressable

EMS Racing

 

[Mark]

EMS,

I may have not have explained myself correctly, I was talking about the relation between the bore width and the port width and height and the amount of time they are open for which is called port/time area, not the bore/stroke ratio. I'll speak to you more on this later but have to go, see-ya.

 

[Allen Waddle]

I think something you all may be missingin the a90 and a100 debate may have something to do with maxuim rod angle. do to the bigger bore and same stroke and i am assuming same rod it may change the rod angle from optimum.

I do have a couple of questions about the a 180's. Do they have alternate fring pistions(is one at top dead center while the other is at bottom dead center? I dont see how thay can be and be ballanced with the v configuration. Are the two crankcases sealed from each other? I know that one of you have said that you have one of these engines. Please try to answere these questions and i ams ure your answere will bring new questions to mind.

Thanks,

Allen

 

[EatMyShortsRacing]

Mark,

There is a sneaky lil comma in my message which does refer you to the port/time area...

Allen,

The stroke of the 100 is also increased, but the bore stroke ratio has changed so yes the rod angle will have changed.

The A180 has 2 sealed crankcases and fires alternately (180 deg.)

 

[Mark]

Oops,

EMS I read to fast, my last post was for Nitrocrazed.

From what he has said about the port sizes being the same as the 90 that is your problem 100%, not just the exhaust either, the whole lot. I read the Graham Bell book many years ago but found it not as good as the one I have, trouble is I don't know what it is called because it was given to me from a friend and it has all been photo copied except the front pages. I only have from the contents page to the last page. I don't know if the G. Bell book discusses port/time area which is most important for what you will have to do on the 100.

Nitro, I think the main reason for not putting the disc valve setup on gp bikes is it makes the engine very wide and this is a main design factor the bikes are always trying to reduce, also what you said about bore size with 4-strokes and valve sizes in relation to rpm was spot-on but don't forget that if a 2-stroke breathes from the walls then there would be more surface area the wider the bore was which means you could have a wider port window without having to raise the port height which would not steal as much torque as what raising the window does, my guess is it must not be as pronounced as the 4-strokes or there may be other issues that I know nothing about like really short strokes may reduce torque so much that it won't pull itself into it's power band I don't know I'm just guessing.

Nitro I didn't realise the V180 had a single carb, do you think it is possible to mount a second carb, one carb for 2 cylinders is a disgrace for a 2-stroke because the wave pulses are so important from intake to exhaust and if you put 2 together it destroys the effect the pulses make. To tune it I was going to hook up an exhaust header temp gauge to each pipe and just turn the needles until they run at the same temp.

 

[Mark]

Ian,

I almost forgot about 2-stroke bike cranks.

You'll love this, they actually press the cranks together on the big end rod pin and then bash them until they are balanced and running true and yes if your thinking wow how can they stay balanced after the abuse they get when racing well they can slip and do but not often.

 

[Ian Inverarity]

Craig,

I already maximise the port areas in the inlet and exhaust of both my 90's and A100. I do not touch the transfers in the case tho. Thus I cannot increase the flow areas any more (except the case transfers, which is hard to do). Both engines have 12mm ID carbs and 20mm ID exhaust headers.

Allen,

The rod length of the A100 and A-90 is the same, thus, yes there is more angularity in the A100. What effect does this have? I would guess it would create more friction losses.

As Craig says the A180 fires 180 degrees apart, but is effectively 2 engines as the cases are idepedant withe the cranks featuring their own counterweights. The angle of the vee is less than 90 degrees. Actually I have had little testing with the A180V, but so far my problems with it are mechanical not performance related.

Mark,

Yes a bigger bore gives wider ports but also less tall ports. I have never analysed this in terms of time area, but presumably they achieve some sort of maximum around square.

It is a shame you cant name that other book, I would be very interested to read it.

You may be right about disc's being too large for the bikes, that is one of their disadvantages.

Changing the A180V to duel carb would not be easy, infact proably the only way I can think of would be to mount case reads on it. No small task either. I have zero experience of reeds.

If you mentioned the bike cranks in reference to the earlier discussion of multi cylinder engines, I am aware of this method of crank construction. I myself have trued up single cylinder zenoah cranks that get out of alignment. But the problem with this sort of construction on a multi cylinder engine is the time and expertise required to assemble it, which puts them beyond the capabilities of the average modeller. Besides at the end of an 8 cylinder crank you are relying on the last crank pin to take the 20 HP when it is the size of a 3.5 crank pin! Possible tho.

This discussion is getting very interesting! ;D

Ian.

 

[Propjockey]

I hate beating a dead horse......but what the heck!

What about the Conley? Nitro powered V-8. True it's a four stroker--true it's expensive as @#$%^.........but it's a nitro powered V-8!

 

[EatMyShortsRacing]

Ian,

I am considering piston porting for one thing on the 100. That will let it breathe more.

Craig

 

[TimD]

Ian,

I almost forgot about 2-stroke bike cranks.

You'll love this, they actually press the cranks together on the big end rod pin and then bash them until they are balanced and running true and yes if your thinking wow how can they stay balanced after the abuse they get when racing well they can slip and do but not often.

Just like a CMB crankshaft? Run- out galore if revved very hard! 1 piece crank and a drum rotor would be my choice.

The time area argument rears it's head at last. Brian Callahan is a big advocate for this, and he seems biased towards long strokes. Seeing he and Prof. Blair are collegues I guess he would have a better understanding of it's relevance than most people.

Something to keep in mind when discussing the benefits of port width is reliability and the piston's tendency to want to jump out the port if it is too wide. If you need to put windows or bridges in ports (YUK) to prevent this happening then to me that appears that it isn't the right way to go.

 

[Ian Inverarity]

Tim,

The zenoah cranks get out of alignment from hydraulicing, they can easily get 1mm runout! Imagine truing up a 4 or 8 cylinder engine after a hydraulic!!! :

The time-area makes good sense to me. Simply comparing crank angle measurements does not tell the whole story, rod length and bore/stroke also affect the actual port duration. The problem with time area is it is not a simple thing to measure, but I am sure it is a valid concept.

No one has specifically discussed making ports wider, but the reliability thing is based upon the width of the port versus the bore. On a stock Picco 67 EXR the exhaust port is 0.9 of the bore diameter. Most othere engines I have measured are around 0.85. I have made a few 0.9 without any trouble whatsoever. On ringed engines it is a different story....

Craig,

I once asked Dave Marles on his forum about piston porting. Dave has done a LOT of engines over the years and has seen lots of this stuff. He said the performance benefits were minimal to non-existant. I have added piston porting to engines, but I never really knew if it was a benfit. Yes it allows more into the port, and short-cuts the flow for the charge under the piston, but it would also interupt the normal flow of charge up the transfer port, and the port is not enlarged in that area to take additional charge. Besides the area of most transfer port entries and sections (in good modern engines anyway) easily exceed the area of the window port in the sleeve. So I have not added piston ports for years. Of course the K-90 has piston ports.

I think the engine needs to be fundamentally larger to perform properly.

Ian.

 

[TimD]

I think the engine needs to be fundamentally larger to perform properly.

Ian.

Ian,

Can you be more specific? Are we still talking the A100 here and if so are you talking about the case being larger to accomodate larger passages, and possibly the rod length and port height to maintain the correct timings?

Is the exhaust stub area larger or smaller than the exhaust port area at BDC?

Tim.

 

[Ian Inverarity]

Tim,

Sorry, I do mean the A100 here. I am talking about larger case, carb, disk, exhaust header, pipe etc, possibly rod length, but remember the K-90 has the same stroke and rod length as the A100, so that geometry cant be too bad!!! 8)

For a 30cc motor, you just size everything appropriately.

Yes the exhaust stub area of the A100 is larger than the window port area, by about 20%. This is after I enlarged it to match the header.

Ian.

 

[TimD]

O.K then,

We need someone to do the time / area calculations for the A100 and the K90 and compare them. The stroke / rod length thing can't be the cause if it is the same as the K90 as those things pull some big RPM's. We seem to be getting closer to an answer through process of elimination!

 

[Ian Inverarity]

Tim,

I guess that someone would have to be me! 8) Since the motors have the same rod length and stroke I think that would effectively just compare the timings of the engines? Not sure. I printed out Brian Callahan's method of working out time area, but never tried it. I have all the info measured to do it tho, but it didn't look like much fun. My software cannot tell me this info, and I was waiting for Marty to integrate it into their EAS software because I am lazy......

Unfortunately (for the continuity of this thread) I am going to Mildura this weekend to play boats with Mike Gilman (Gene's friend, the other Gillman!) so it may be a while before I do such calculations...

I'm taking a radar and GPS too.... ;D

Hey Gene! I will see if I can turn him from the Dark Side (Gas boats! )

Ian.

 

[EatMyShortsRacing]

Ian,

Piston porting works if your passages in the case are inadequate. How you do the porting is another issue as I have only seen a couple of engines with factory piston ports that I believe are right. The concept that the ports should narrow towards the liner is another thing to keep in mind... accellerating the gasses into the engine..

Now take those 2 pieces of information and put them together you will get an idea how the piston ports should work...

EMS Racing here comes another SC engine!!!

 

[Ian Inverarity]

Craig,

The old Rossi 90 that I once owned had psiton porting as the only method of feeding the secondary transfer ports. I doubt this would have worked very well as the piston ports were not fully open during the while transfer period. Later Rossi's abandoned the idea and still kept the piston port, but had a port linked to the case as well. The K-90, which has sleeve porting almost identcal, has a common large single transfer port in the case to feed both ports in the sleeve.

I think I know what you are describing about accelerating the gasses. I am not adding piston ports to my engine tho, cutting those liners is no fun. They change shape..... :

Ian.

 

[Mark]

Ian,

Get this for crude engineering.

I use to race a Z1000 engine in a sidecar some years ago and that is a 4 cylinder and it has a crank that is pressed together so that it can have roller bearings in the big end and you think this slips, bloddy-oth when you dump the clutch off the start the force is huge so they weld the pins so they don't slip but what happens when you need to change a rod or big end bearing, out comes the grinder, very messy, expensive but very true.

I have the formula for the time/area calc if anyone is interested.

One other thing Ian, is the intake on the V180 only controlled by one disc valve at the carb? I'm beginning to think I will have to build my own twin cylinder if I want one that performs correctly.

TimD,

There is a maximum width you can make a port which is worked out by a percentage of the bore width, bridges are terrible things to put in ports because they create hot spots in the bore and can expand out into the path of the piston and rub against it, plus you also get a flow restriction but it can be compensated from the wider port but then again you can't go to close to the other ports or you get short circuiting of the charge this again I think is worked out from the bore width not 100% sure though.

 

[Mark]

Ian,

I can do the calc for you but I have to know the RPM it runs at, what RPM you want it to run at, the duration of all ports in degrees, the capacity in cc and the hard one is the area of the ports measured across it's chord not around the cylinder and the angle of entry on the ports if there is any must be included. If a port enters the cylinder on an angle it will appear to be bigger than what it actually is, otherwise I can tell you what size they should be going by the formulae that I have.