75 replies to this topic

[McGuire]

How about a folded manifold with trap door bypass valve(s) as in current production car practice...but instead of the ugly-ass black recycled pop-bottle plastic, the manifold is fabricated in metal tubing and then plated, to suggest some hypothetical musical instrument?

[edit] then the carb is plated or polished a contrasting color, with an bell-type intake trumpet the same finish as the manifold...]

[McGuire]

styling ideas...I am thinking a french horn-type arrangment with the carb right in the center of it in more or less the original position and the tubing concentric around it, but there are a million ways you could go with it...

[McGuire]

Originally posted by Canuck
I understand wave timing just fine - messed with the Buell's ugly breadbox for days trying to make something just as functional but a little more pleasing to look at.

The guy who has the local H-D store tells a story of a guy who bought a Buell Cyclone...when he took delivery, he removed the airbox housing, threw it on the ground in the parking lot and rode away. Guess he couldn't stand to been seen that way even on the ride home.

[Greg Locock]

I like the idea of an annular slide, that would give you a nice robust compact linkage.
The UWA FSAE car had straight slides last year, so that approach is do-able.

Now, would you map them against engine speed AND throttle position?

[desmo]

One of Boretti and Martinelli's SAE papers from a few years back seemed to imply that it was simply mapped against rpm on the Ferrari. Could the benefit be significant for incuding TP?

[Canuck]

I was thinking something along the lines of a nut and bolt arrangement, but I haven't figured out how to spin the slide back and forth without making it ugly.

[Canuck]

About coatings and treatments...

I was talking to a gentleman the other day regarding valve springs in this engine series. He commented that he's developed a single beehive spring (rather than the standard triple-spring setup) that he uses, but first he bakes them at 400'F for 35-45 minutes.

My first thought is that if such a thing were beneficial, the manufacturer would do it, but then I recall that like the S&S engine example above, spring manufacturers must be cost-competitive so perhaps there's merit here.

Can one of you shed some light on this?

[Greg Locock]

Hmm. Process cost for baking spring in oven 2c per spring?

Cost of 2 extra springs? 2 dollars (WAG)

Cost of winding beehive instead of normal spring? don't know.

It sounds like his solution is cheaper, lighter

By the way 400F is not hot enough to do anything much to steel I'd a thunk, since the phase diagram looks very dull up until 1333 F, apart from the magnetic change, which he doesn't quite meet.

[McGuire]

Quality valve springs are chrome-silicon Kobe steel, oil-tempered. All other materials are way less better and I wouldn't use anything else in a critical application. I can't imagine any benefit from a short baking at 450F, other than a tiny bit of normalization. Probably won't hurt though... this is another of those desperate measures everyone took with the old vanadium springs (like tumbling and various microfinishes) before decent spring alloys arrived.

I am not a big fan of single beehive springs unless the specific application is fully investigated and validated. The theory is that with every coil a different diameter, every coil has a different natural frequency so they are "self-damping"...which I suppose they are, But. With no dampers they are still noisy as hell...when you listen in on them they will scare you to death. I see a few suppliers now offer beehive springs with damper and that pleases me.

A 2" intake valve at 6000 rpm is not a terribly critical application anyway. Any decent spring package should do fine.

[Greg Locock]

Any shape of spring will still have a surge frequency along its free length, it's just much more difficult to work out accurately for a non linear spring. You might see some interesting effects as the spring lengthens and shortens as the valve moves, but there is a tradeoff in fatigue damage, as the coil bound coils come into play the stress field in them builds in an unhappy way (at a guess). When they are coil bound they are operating in radial compression, when they are free they are in torsion, somehow the forces have to move around very fast in the transition. If they are moving fast that implies big stress gradients, lots of localised energy to move dislocations and grow cracks.

Valve springs are one of the most gob smacking pieces of 'simple' technology around, when you compare their fatigue properties with any other mass produced item.

[Canuck]

I thought the part of the idea of the single beehive spring was to eliminate other springs/dampers to reduce friction and heat. Doesn't running a damper kind of defeat that idea?

I never really put a lot of thought into the life a valve spring leads - pretty amazing piece all things considered.

I see PSI is making Ti-based valve springs now.

Edit to add - what constitutes a quality spring? Every manufacturer has a handful of specs they list their springs with, at the end of the day how do you know spring A is better than spring B? As an example a triple-spring set with 195lb springs and Ti collars from V-Thunder (Comp Cams motorcycle line) retails for $149.95, a Canadian line AV&V with 175lb/Ti collars retails for $169.95, Crane 175lb springs/Ti collars for $134.95...On high end of the scale, the big lift spring sets can run to $300 (for 4 stinkin' valves!).

Now - considering both Comp Cams and Crane offer automotive valve spring sets for big-lift/big pressures and Ti caps for $450 for 16 valves, I think the bike guys are gettin' reamed. (so says the guy selling $100,000 bikes ) Even the cheapest motorcycle spring set is still $5/valve more expensive.

[McGuire]

Originally posted by Greg Locock
Any shape of spring will still have a surge frequency along its free length

exactly, a valve spring is just a spring, like any other. Interesting cyclic rates tho.

[McGuire]

Originally posted by Canuck
I thought the part of the idea of the single beehive spring was to eliminate other springs/dampers to reduce friction and heat. Doesn't running a damper kind of defeat that idea?

welll, the beehive spring is to some extent self-damping, which I suppose it is... to some extent.

[McGuire]

Originally posted by Canuck


Edit to add - what constitutes a quality spring? Every manufacturer has a handful of specs they list their springs with, at the end of the day how do you know spring A is better than spring B?

quality materials as described, and the ability to utilize these materials and execute. For that, knowledge and experience.

[Canuck]

Going back to the original question and the rather stunning revelation that stroke plays little in the production of torque...

I was on Gale Banks site reading a couple of articles. Now, Mr. Banks doesn't strike me as your average dummy, but when answering the question "Why do diesels make so much more torque than gas engines", stroke is one of the answers Why do Diesels make so much torque?

Torque - a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the centerline of action of the force to the axis of rotation

This was my understanding of the relationship between torque and stroke - at least until the other day. Now ignoring the trade-off in valve size, why doesn't the stroke act as a lever?

Don't get me wrong - I'm not disagreeing with what I've been presented here, I'm just trying to get my head around it.

[McGuire]

I am familiar with that piece of technical/PR writing and it is wrong.

Note the common formula describing the relationship between mean effective cylinder pressure and torque...

MEP in PSI = torque in lb ft x 48pi / CID

...does not distinguish bore from stroke; it speaks only to displacement without regard to bore or stroke specifically. And from your engine sim experiments you have seen it is true.

In order for a simple machine (a lever for example) to produce a mechanical advantage, it must muliply either distance or force. For example: a lever of 2:1 proportions will multiply distance 2x (and divide force by 2) if the action is applied on the short end of the fulcrum, or it will multiply force 2x (and divide distance by 2) if the action is applied at the long end of the fulcrum. But if the lever's ratio is 1:1, it cannot multiply force or distance. Both will be equal on each side of the fulcrum. You can see what is happening here: a simple machine can manipulate the force or distance of an action but it cannot change the total amount of energy available in a mechanical system.

So the crankshaft is a lever, but what is its motion ratio? In an IC engine, one cycle of the piston & connecting rod assembly will always produce one rotation of the crankshaft, whether the stroke is six inches or six feet. It's a classic crank-arm linkage: it simply translates the linear motion of the piston into rotary motion at the crankshaft, and at a straight rate as demonstrated in the formula for MEP and torque shown above. In the standard English conception of torque, the foot in the lb ft of which we speak is the arbitrary one foot from the center of the shaft where we measure it.

[Canuck]

Ah I get it now.

Besides the foot-in-mouth smilie, I need a lightbulb one for times like this.

Thanks McGuire - I like learning new stuff.

Are you familiar with the Vern Ott designed plain-shell v-twin developed for Mid-USA?
Very Nice.

[McGuire]

Originally posted by Canuck
Are you familiar with the Vern Ott designed plain-shell v-twin developed for Mid-USA?
Very Nice.

No, sorry. I have heard of it but really don't know anything about it.

[McGuire]

I would sorta like to give hypereutectic cast pistons a try in a mildly-tuned, air-cooled V-twin sometime.

[Canuck]

KB/United Engine supplied the stock PP100 hyper pistons. They've proven incredibly tough considering the poor state of the engine in general. Even with significantly out-of-round bores, they're still quiet (or maybe it's just the rocker noise drowning them out).

I had a client bring in a bike with one hell of knock, but still running. Once we pulled the front head and cylinder the source of noise became evident - a crack in the skirt running from the front of the right pin boss almost all the way around to the left. He'd put over 100 miles on it trying to get back into civilization with it knocking away like that. That the skirt didn't break off entirely is amazing.

I've read what KB has to say about their hyper pistons - what do you see as their advantage over a good forged piston?

The Mid-USA engine is a very nice piece. One-piece Falicon 4" stroke crank, 4.25" bore, KB pistons with "3 points of contact" setup to run in-line with each other despite side-by-side Carillo insert-bearing rods (my only concern is the piston setup). About the only thing they didn't do that I'd like to see is a 3 or 4 valve head. It still makes over 100lb-ft from 2000-6000rpm with 135 peak hp. It's capable of turning 7300rpm in street setup, though it stops making power before that. 7300rpm is unheard of in street American v-twin world.

[McGuire]

Originally posted by Canuck


I've read what KB has to say about their hyper pistons - what do you see as their advantage over a good forged piston?

Dimensional control for nice tight skirt-to-wall clearances, high thermal efficiency... interesting proposition in an air-cooled engine.

[Canuck]

Can you elaborate? Those are nice features, but what are their benefits?

[Lembit]

Originally posted by Engineguy
For a four valve head:
Intake dia. / Exhaust dia.
.38 x Bore / .33 x Bore
("practical" maximum)
to
.40 x Bore / .32 x Bore
(requires perfection in spacing & machining)

Is it possible, that you have an error here?
Ford Zetec 1.8 l engine from the beginning of the nineties has a bore of 80.6 mm. and intake valve of 32 mm and exhaust 28mm. These numbers work out as .40 x Bore for Intake valve dia. and .35 x Bore for Exhaust. As this is a production four valve head from an 130 hp engine, this is far from all out racing head.

So , where is the catch?

[McGuire]

Originally posted by Canuck
Can you elaborate? Those are nice features, but what are their benefits?

A tighter piston fit will get you decreased leakdown and blowby, superior squish (reduced piston rock) and improved piston ring, piston, and cylinder wall life. With a cast HE piston in an air-cooled engine I would even hope to see a measurable improvement in BSFC.

With their crazy heat expansion characteristics, some forged pistons require as much as .0075" skirt-to-wall clearance, which is pretty appalling when you think about it. In water-cooled V8s I have run .001" with HE pistons with no problems. I have a SBC out there in a pickup truck tuned to 460 hp running the small water pump and block cement up to the core plugs. The guy who owns it beats it like a rented mule and it has clocked 140K miles, still runs great.

A formative part of my thinking on this subject is no doubt all the time spent in the dyno cell. Standing right next to a running engine with the exhaust piped out of the room, you hear stuff. An engine with forged racing pistons will produce unbelievable piston slap until its temps come up to normal, and it is not a pretty sound. And that's standing next to it. You don't even want to know what it sounds like inside it's so scary. Sets you to thinking...can't we do better than this?

[McGuire]

Originally posted by Lembit
Is it possible, that you have an error here?
Ford Zetec 1.8 l engine from the beginning of the nineties has a bore of 80.6 mm. and intake valve of 32 mm and exhaust 28mm. These numbers work out as .40 x Bore for Intake valve dia. and .35 x Bore for Exhaust. As this is a production four valve head from an 130 hp engine, this is far from all out racing head.

So , where is the catch?

Well, that was another of those rule of thumb deals. Actually, the maximum valve size that will fit in a given cylinder is a function not only of the bore diameter but also the valve included angle. The greater the VIA, the bigger the valves you can stick in there. For instance, if you set the valve faces parallel to the bore (180 degree VIA) there is no limit.

[Canuck]

Superior squish was not something that occured to me.

Most v-twin forged pistons run .002" clearance (though of course that is double the HE specs). I have noticed they are quieter than forged versions when cold. I'd wanted to use HE pistons on this build but KB doesn't do custom piston runs under 100 units. That's a lot of engines for a small guy like me.