UberTeg

http://www.airflowresearch.com/artic...le03/A3-P1.htm

Cliff notes: They changed a stock chevy 350's 1.64 r/s ratio (similar to b18c's) to 1.91:1 and ran 11:1 compression on 87 octane gas! The theory is, larger r/s ratio causes the piston to dwell at TDC longer, which gives the cylinder more time to fill with air, and more time for the combustion to complettge resulting in a more efficient combustion process (better gas milage). And because it dwells so much, you can retard timing to make the same amount of power! I did a few quick calculations, ,and a b16 crank in a b18 block will give you a 1.85 r/s ratio. Imagine how much power you can make with 11:1 compression with 93 octane with boost!

p.s. Does JE make those shorter pistons for our motors? if so, we could increase the r/s ratio furthur!

Joseph Davis

You may be able to make more power... more power pushing down on the top of the piston that is... but you lose power to the wheels due to less advantageous leverage. A "shitty" RS ratio helps the rod turn the crank, and results in more effective torque. It's application of mechanical force. You end up with pretty narrow power bands in engines with high RS ratios.

I have some charts I drew up somewhere for rod angle and piston speed of our LS engines at a certain rpm and crank angle, sort of a nismo chart on crack. I never got all the information I needed in re speed of combustion processes to apply it the way I wanted to... or try to apply it... reality has an interesting way of warping theoretical or homebrew physics theories, and all the tuners with equipment to monitor cylinder pressures are pretty hush hush about any real details. I gave up. *shrug*


[Modified by J. Davis, 12:43 AM 4/9/2003]

UberTeg

The amount of leverage the piston has on the crank depends on the stroke, not very much so with the r/s ratio A lower r/s ratio puts LESS torque on the crank.


And who cares if you lsoe a little bit of torque thru less leverage when you can make that torque up thru 12:1 + compression rations on 93 octane


[Modified by UberTeg, 8:50 AM 4/9/2003]

UberTeg

will u at least agree that a longer rod will put more torque on the crank than a shorter rod with the same crank!?

BTW I ownz jo0

Joseph Davis

Refresh your innumerate *** on some trignometry, bucko.

The stroke will change torque, yes, but so does rod angle. Examine how RS ratio changes for a given stroke alter the rod angles seen during the power stroke - the only one that matters for this purpose. The rod is a lever, and the angle determines leverage.

Leverage... levers... simple machines used for torque multiplication... ever take a simple engineering physics class?

Arturbo

In most cases, yes.

Mase

I'm going to have to agree w/ j.davis on this one.

Joseph Davis

Sure... if you want to retard the ignition all to hell to start the combustion process early to bandaid your use of crappy detonation prone 87 octane, you can bring a hell of a lot more force to bear on the crank when it's at or near TDC. Examine the crank angle at or near TDC... you aren't encouraging it to spin so much as loading up your crank journals and compression loading your rods. Real efficient tuning theory there!

Examine the crank angles at which it is the easiest to spin it, and you can bring the most power to bear the easiest. At those crank angles, the long-rod-high-RS setup is already stopped dwelling at the top of the bore. With the rate of flame front propigation being more or less fixed, you lose power at low rpms and you only gain extreme efficiency at a certain narrow rpm band. That's some great dynamics for a steady state diesel generator, or for cars once they make a CVT that can handle over 135 hp for over 50K miles at less cost than the national debt.

None of this goes into the bad aspects of low RS, or the shades of grey inbetween.

And j00 0wn nothing here

UberTeg

Anyways... the shorter stroke may apply less torque to the crank, but the piston speed is decreased, so you can rev it higher with less wear and tear on the piston rings. The B18B's piston speed at 7000rpm is close to that of F1 cars at 15000+ rpm. Not to mention the longer rod can rev higher because the piston dwell at TDC is longer, giving the cylidner mroe time to fill with air. Eventually, every pisotn engine reaches a speed at which it just cant make anymore power because it cant fill the cylidners with air quick enuf. Longer strokes raise this limit. SO umm, higher r/s ratio's own jo0 joseph (and mase).


[Modified by UberTeg, 9:09 AM 4/9/2003]

Full-Race Geoff

if either of you care to get some real scientific data, i can get it for you.

UberTeg

Its ok to retard cuz u have 11:1!

Dur, thats why you dont retard timing that much. Its all about tuning! Dont bring peak cylinder pressures at TDC! Tuning tuning tuning! And if you are worried about low-end power loss from peak pressures at or around TDC, take a look at your ecu's timing maps! Theres a reason timing is advanced in vacuum, because the flame travels quicker! This just proves its all about tuning!

Again, this is why we have ignition maps, tune tune tune! You can advance the timing. To compensate for the fixed flame speed! And spell propagation correctly plz

Audi makes a CVT transmission that can handle a significant amoutn of torque alreadt tard

UberTeg

Yes plz, unless it proves me wrong, then keep it to yourself


[Modified by UberTeg, 9:25 AM 4/9/2003]

Joseph Davis

Whoa the f*** up there, nelly! How did we go from RS ratio to stroke? We can debate that, but you aren't thinking of the matter at hand... or the big picture anyway. You're envisioning the combustion reaction and the force exerted on the piston in a steady state combustion reaction just fine. Now, graph the dynamic changing nature of the combustion force on the piston across the entire rpm band... I'll even grant you the ability to have a perfect fuel/air tune which isn't likely to happen IRL in a streetcar.

Feeling vindicated?

Notice the parts of your long RS combustion event, while the piston is dwelling at TDC so conveniently, don't match up very well with the angles that the crankshaft turns easiest at. You have to play the two off against each other, and the long 1.9+ RS ratio makes for a nice peaky power band due to the overlapping "windows of opportunity" of 1) ideal combustion event for max piston force and 2) ideal crank angles for transmitting kinetic enrgy efficiently and 3) the more or less fixed time rate of the combustion event. Not only is your peak TDC tuning thrown all to hell, it's pretty hard to apply the long RS ratio setup IRL to get a driveable car.


Are you stalking me? Someone give you a pass to TOO's underground board so you could read my post circa, what, 98? 99? Your rpms are too low, at 7K the LS engine's piston speed is still pretty mundane, but 8500-9000 it gets interesting - exceeds the piston speed of the last F1 cars that Senna was running by a ms or two.

[/quote]Not to mention the longer rod can rev higher because the piston dwell at TDC is longer, giving the cylidner mroe time to fill with air. Eventually, every pisotn engine reaches a speed at which it just cant make anymore power because it cant fill the cylidners with air quick enuf. Longer strokes raise this limit. SO umm, higher r/s ratio's own jo0 joseph (and mase).[/quote]

Cool, you bring a million dollars and build the ideal engine. I'll continue to do what I've been doing for years... picking a stout OEM engine, not worrying about the things it costs a lot of money to change, and being wildly successful modifying the things that I can change affordably.

I'll argue theory with you all night, though. My wheels have been spinning about cars far longer than your have.



[Modified by J. Davis, 1:44 AM 4/9/2003]

Joseph Davis

Your statement

... and....

kinda sorta disagree with each other. Applying the largest average of piston force on the crankshaft when it's at it's optimum angles is much more difficult with a high RS engine.

At lower rpms, you have lost a LOT of dynamic compression at the point you have to fire your mixture and so you lose a LOT of torque.

At middle rpms things are OK, but not great.

At high rpms the dynamic compression, duration of the combustion event, and crank angle all line up pretty well and the power climbs sharply. Then it starts falling off just as suddenly.

Graph the average power out over the rpm band, and despite the impressive peak you're still under the average dyno curve for a more moderate RS. Like the B16's 1.74 RS you were bashing It would work, maybe, with S2000 gearing and shifting reactions I'm not going to credit most people with possessing. For the average Honda? No. I'm not even going to comment on the average Honda owner....

UberTeg

I never said you wouldnt lose low-end power, just saying theres ways to sort of make up for it. And i'm sorry for changign tracks to stroke, i was trying to indirectly comparing the b16 to the b18 a higher r/s ratio has the possibility to make more power cuz it allows a higher compression and/or more boost

UberTeg

Ur righ they do disagree, it depends what ur looking for.. less trian on the motor, or more power at the expensive of more load on an already high revving motor on the crank/rod journals.

boosted hybrid

Essentially stroke and rod length boil down to Torque=Forcexradius. Radius is the name for the point of where the rod meets the crank, and crank meets what is called the "ground". If you applied the force through the radius directly you'll have the most torque onto the crankshaft, since its your output. The shorter the rod, the less radius you'll put onto the crank on the combustion stroke (your transfering the force into the crank at an angle, which lowers the overall torque on the crankshaft). The longer rod will have less of an angle, and will transmit more force through the crank, therefore more torque will get placed onto the crankshaft. Its just the basic torque equation.

Its 8:00am, my brain is dead. Its nice to see that h-t.com is actually having a semi engineering/physics approach to something for once!

Arturbo

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">. Its nice to see that h-t.com is actually having a semi engineering/physics approach to something for once!</TD></TR></TABLE>
You were not here all night like I was. Alot of delete work went into this topic.

Full-Race Geoff

jeff, your edefinatley right, but it is true you are not considering dwell times and side loading. The shorter the rod length, the more extreme the cylinder side walls are loaded as the pistons is dragged across them.

remember basic physics/kinematics/statics classes wher eyou determine the force components in the X and Y directions, using sin and cos? (i know you do, just spelling things out for others) but you are only considering forces in the Y direction (the forces that turn the crankshaft) not forces in the X (forces that are wasted due to friction) from the shorter rod being at more extreme angles.

i have some SAE papers at school that break this down. i wont be able to get them until thursday but if either of you guys actually care, i can dig them up thurs afternoon.

internet BS and conjecture really irritates me, thats why i dont really post anymore. One particular person on h-t just posted soo much garbage that made absolutely zero sense and didnt have a clue what he was talking about, yet was sooo convinced he had half a brain, that i dont think i made a constructive post in 3 or 4 weeks. oh well, rants over, ill get you real info if u want.

boosted hybrid

I spoke with my dynamics of machines professor this morning after class. He pointed out alot of interesting things that I havent thought about before with the basic slider-crank/combustion engine combination. I am going to do a tech article for my website that incorporates his ideas, and mine into a very informative article on 4 cylinder engines. I will post all the info on here, but I am going to make some programs that illustrate what I am talking about in excel, and make a user friendly interface so you can just fill in numbers and it spits out the answers.

Honestly, honda-tech is a great board. I consider it the best above the other honda boards, but lately there has been soooo much junk posted its unbelievable. I am going to be doing alot of tech articles over the summer with numerical calculations to prove/unproven alot of the theories that people still hold on too.

Full-Race Geoff

whoa thats cool as hell jeff, i started a papaer two summers ago left it dormant then started it again on rod/stroke ratios (slider crank mechanisms) and their effect on cylinder strenghts.

i am getting surgery this summer which will leave me indoors for a large part of it so i will be working on these topics alot. also the effect of a pulse converter (true merge collector) and a host of other topics.

it would be cool to work with you jeff. as for the junk, it really bothers me becuase about 8 months ago, before a particular few joined h-t it used to be a much much better place.

boosted hybrid

That would be great to work on this stuff together. Keep in touch, I am sure there is ALOT of interesting data out there to find.

Joseph Davis

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Its 8:00am, my brain is dead. Its nice to see that h-t.com is actually having a semi engineering/physics approach to something for once!</TD></TR></TABLE>

Well, like Arturbo said a lot of revision/delete went into it. I was simulateously talking to Uberteg on AIM, and it was supposed to be a spank-war or something, but I didn't know how well that would go over. If you note the very neutral tone of Uberteg, famous for calling everyone tard, in his last two posts you'll see he probably felt the same. I dunno though, the kid's not quite human.

He (Uberteg) is onto something, and gave up due to lack of sleep (like I did) but I think he's a little extreme in re the street applicable RS ratio... he was using the B16A model to bash. I also doubt the effort required to reengineer the rod length, RS ratio, and combustion dynamics to what you want is worth it for anyone other than an obsessed engineer with a huge budget trying to delve into advanced combustion process... good theory to know, but I'll boost what I've got and not worry about it.

boosted hybrid

After all the ugly math models, I can simplfy everything down to cylinder wall stress, piston velocity, r/s to powerband comparision, etc. Although the models will only be for the engineers to understand, the simplified version will describe the physical truths of the different honda engines. Let it be noted that I am only going to consider 4 cylinder engines in my analysis, so 3, 5, 6, 8, 10, 12 cylinder engines are on there own although with some modification the models will work with their engine configurations.

SiRkid

good stuff.
I hope geoff gets some of that info!