Tom 400 CFI

THEORY>

If you add cylinders to an engine, does the power increase DIRECTLY with the added cylinders?

Eamples: A 25 hp single 500cc engine. If you literally bolted eight of these together, would you then have a 200 hp 4.0 liter? if you bolted two of these together, would you have a 50 hp 1 liter?

A 350hp, 346CID Corvette engine. If you bolted two of these together, would you have 700 hp?

Or would the power be greater than that? Or less? Does the power increase DIRECTLY? Or are there other losses/gains that I'm not taking into account? I believe that the changes are DIRECT. It seems to me that if you double the cylinders (All Else Being Equal -AEBE) the torque will double at a given RPM, and therefore so should the power.

The reason why I'm asking this is that a friend and I were discussing two different engines: A 2 stroke Honda, V-4, 500 race bike engine. This engine makes 200+ hp at 12,000 RPM. The motor to which we were comparing is the most recent Honda CR 125, which makes about 30 hp at 12,000 RPM -if I'm correct. If the power changes DIRECTLY with cylinders (AEBE) then a four 125 cylinders bolted together would make "only" 120hp out of 500cc's compared to the above mentioned V-4 that make over 200.

Our descussiong revolved around what the deal is with the discrepancy. I believe that bolting cylinders together should icrease power directly, adn that teh 125 just isn't tuned the same as the V-4, 500. He feels that there is some inherent gain realized by mulitple cylinders. -ie, 2+2=5

Please comment.

Tom 400 CFI

One other thought; I KNOW that there are some advantages the Honda V-4 has over 4 CR 125's bolted together;

two crank seals instead of 8,
one water pump and pump drive instead of 8
less rotating mass from a shorter crank
one oil injection pump and drive instead of 8
better inherent balance

But I don't think that this would account for the 80 hp difference between the V-4 500, and four CR 125's theoretically bolted together.

Don't read into the example too much. I'm just telling you what spurred this thought. Please just discuss the theory. Thanks!

Fast3rdGen

hmmmmm very interesting......kinda like havin 4 blown alky hemi motors on a tractor pull. wish i had more insight...but i'll keep my eye on this post.

RB83L69

No, you are right, it should be direct. But that is of course assuming that everything else about the 2 engines is the same.

What actually doubles is torque. Torque is the amount of energy removed from the fuel and converted to mechanical work. Double the number of gasoline molecules, with all else being the same, and you will double the torque. HP = torque * RPM * a constant; double the torque at a given RPM, you also double the HP.

Different engines can have vastly different abilities to ingest gasoline molecules at a given RPM; so it's not at all correct to try to compare 2 different designs that way.

Tom 400 CFI

RB, thanks for reading and the comment. I agree that comparing the two engines is apples to orange's: the CR125 is NOT the NSR 500 motor, with 3 cylinders and three crank pins chopped off. It is an entirely different motor, with different breathing characteristics.

With regard to my friend and my discussion, I'm vindicated! Hey Chris, you reading this...ya FACK!

ede

i'm too confused to post anything right now.
no more than i know i'd have to agree if they were equall then the hp or torque would double. i believe i heard on tv once that the mulit engine pulling tractors put a stronger engine in front of a weaker one when they share a common output shaft, but i forget why.

jcb999

it was used in tanks..

It did have double the torque. But hp was less than 1.5 times the V6. Friction will prevent the rpm needed to double hp.

ede

i don't understand why the friction would be differant from 2 seperate engines of equal size than 2 engines of the same size joined together.

Apeiron

I'd have to imagine there'd be some kind of increased rotating mass from whatever means was used to couple the two engines together.

TransAm12sec

Trying to explain your thoery, think of it as a regular V-8. Lets say a TPI. If half of the spark plug wires are off, you would not have half the power of the motor. Too many factors come in. Half of the engine would be taking away power because it is resisting the movement of the engine. And not all cylinders produce the same amount of power in an engine. Like if a V-8 made 800 hp, not all cylinders are producing 100 hp. Fuel/air ratio and many more that I cannot think of.

Power does not go directly through. Again, think of how you loose horsepower on a chassis dyno, compared to power at the flywheel.

Its hard to explain this in words, but I'll keep trying.

So yes, if you add cylinders, you will have more power(think of it with spark plug wires) But when you have two engines as you say bolted togeater, the power is not going directly through.

1MEAN92RS

Yeah, it would be best to consult a team that competes in tractor pulls. This one is way out of my league, but I do not believe the hp increment would be proportional to the cylinders.

JERRYWHO

How about a V-12 sbc

http://www.falconerengines.com/prod04.htm



Jerry

redbird_400

.

Gta-Paladin

Apeiron what are you doing in BC Follow me out here?

Apeiron

I was born here.

Tom 400 CFI

No ****. That's because you have FOUR CYLINDERS DRAGGING down the other 4 that are still running! This is not an indentical, 1/2 displacement, 4 cylinder engine. Invalad example. Grrr. If you're going to answer, please use scientific, PROVEN information. Not wild anecdotal theory.

RB's answer was the only scientific, calcualted one in this thread so far. After reading his answer and thinking about it more, I agree with him, and I fell solid about it. If you want to shoot "bench racing" examples around, how about this one:

Take two IDENTICAL engines (say 250 hp 350 TPI) and throw them on two crankshaft dyno's, side by side. Each TPI engine is throttled up and produces 250 hp. You have two identical engines, side by side, producing 250 hp, on two seperate dyon's. Got that part so far? at this point, we have a TOTAL of 500 hp being produced, combining the rating from the two dyno's.

Now what would happen if the output shaft's on each of these engines had a gear machined into it. Now you place an IDLER gear in between, and connecting these two motors. What would be the output from that idler gear??

MORE than 500 hp from some mysterious benefit of having 16 cylinders??

LESS than 500 hp because of some mysterious additional friction that suddenly rears it's ugly head when the two engines are connected??

NO!! You'd still have 500 hp folks! Is an idler gear beween two cranks any different than two cranks connected together end to end? NO!!

Those of you thinking about inertia, RWHP vs FWHP, etc, etc, KISS! Keep It SIMPLE! What does RWHP vs FWHP have anything to do with adding identical cylinders to an engine??

And yes, in an 800 hp V-8 each cylinder IS producing 100 hp. It is producing 1/8 of all the torque being produced, and it is doing so at an RPM that mathematically equates to 100 hp.

RB, again, thanks for the mental "adjustment". I'm where I should be again, Thanks.

Apeiron

Actually, it is.

laiky

The discrepancy is simple, an NSR500 can only be leased from honda for 1 million dollars apiece per year!!!! it is honda's premiere motorcycle engine for the motorcycle equivalent of formula 1.

In other words if you compare a gasoline burning prostock engine (500 cid, 1800hp) to a 502 crate motor!!!

Tom 400 CFI

Holy cow dude(laiky). If you READ my second post, you will see quite clearly that I said NOT TO PAY TOO MUCH ATTENTION TO THE EXAMPLE, but instead focus on the CONCEPT! I know the CR 125 engine is not the NSR 500 motor, which I stated quite clearly in my third post!! Jeesus Krist!

No, it's not. Why don't you entertain us by attempting to explain how it is different (aside for the MINOR friction imparted by the gear) which doesn't matter here, because it is a theoretical example! Are you actually going to try to explain that connecting two motors via a gear vs a coupler inline, is going to yield different results?! This should be good...

Apeiron

Settle down already. If you want to discount friction and rotating mass and treat this like an "ideal" engine (and apparently you do) then you're right. Two identical engines coupled losslessly (is that a word?) will have twice the output of a single one. If that's what you wanted to hear, you should have just said from the beginning you wanted to ignore parasitic losses. Saying you just want to discuss the "theory" doesn't get anyone anywhere if my theoretical model includes friction and yours doesn't.

Tom 400 CFI

10-4 on the "settle down". I was trying to keep this thread somewhat focused. The disconecting four spark plug wires post kind of threw me for a loop, because it SO doesn't apply to what we're talking about here.

Ed Maher

Tom, you're right. Besides whatever loss is introduced via the coupling mechanism, you would have twice the torque @ RPM and thus twice the power. Apeiron is right, an idler gear would introduce more loss than a direct inline connection. In fact, unless my head isn't on straight this morning i'd swear that a direct inline hard connection would be lossless and hus, yes you'd HAVE to get twice the power. Unless someone can tell me where you get extra friction from welding the 2 cranks together

Marin

if you have 2 4-bangers with cranks that are welded together, you get an approximate of 1 4-banger with twice the displacement and a twin-spark system.

Why?

Considering everything else is the same, two pistons would press down on a "common" crank at the same time, thus the total surface area would be twice as large, twice as much air/fuel would go in, thus twice as much 'boom'.

Ideally, since

HP@ Z RPM ~= (Torque@ Z RPM)*Z

you'd get twice as much HP.

Now, not everything is that simple.

You don't necessarily get the same effect as having a chamber of double the size. A single flame front would propagate differently in one hemispherical chamber, than two simultaneous flame fronts in two smaller hemispherical chambers.

It would be a little hard to synchronize the two engines. Small differences in A/F mixtures during fire and small differences in timing could produce interesting effects.

Also, the friction loss of having twice as many bearings, etc. needs to be taken into account (this was mentioned before).

Also, I am anxious to know how the Inertial Loading Forces would propagate on respective rods, especially because there would always be a small difference in timing, unless you use super-extra-modern electronics. How would the common crank handle twice the torque? It seems it would be more fragile, being twice the length and having the same diameter.

But in theory, both the torque and HP would be twice as big. HP is an estimate of efficiency of a highly-optimized-high-performance air pump, which is what automotive engines are. You'd put twice as much air out (in theory) at any given RPM, thus twice the HP (not only peak HP, but HP across the RPM band).

Now, I like KISS (Keep It Simple, Sally ), but I can't help but think of crank load. There is always a reciprocating force and it's hard for me to think of how to construct the two engines so that the force one exerts doesn't affect the other. Some crazy torque converting setup?

BTW, here's a good coverage of basic engine theory:

http://www.tqhq.ee/tech/index_e.htm (no, I am not Estonian)

BTW, I haven't heard you guys mentioning a W12 engine .. that's not a typo.. The cylinder banks are arranged in a W.

nagga

i think in a superchevy mag a lil while back this guy bolted two 90* V6s together and threw them in a nova, was a bad look motor, ill try and find the mag somewhere to give u more information

Bird_of_Prey

Chevy Rumble
may 2002

a 64 Chevy Nova out of Lake Havasu, Arizona.
it's got two 4.3L chevy V6 engines.
"..the vibration damper of the rear engine was removed from the font of the crankshaft and replaced with an aluminum flexplate on a special mount. That flexplate was then joined with a matching flexplate on the black of the front engine, synchronizing the two engines in the proper firing order. Aiding this cylindrical blend is Jaguar's XJ12 distributor, fitted in the back of the front engine, providing spark for a dozen plugs, if not the specifis internals suited to this application. Then again, this was just another peice of the puzzle, and soon Brownsberger had devised a corrct ignition system utilizing an MSD 6AL electronic module, and the results provided perfect timing."

and so forth.. he had to make a custom manifold so he could equilly feed both engines with a good mixture. the cooling system used a covette radiator, 180* thermo. and ducting the two blocks together via freeze plugs. the firewall was backed up 18 inches to allow room for both motors in front of it. a 700r4 was used with a 9" ford rearend. some frame/suspension mods to handle the extra load of the weight of the two engines.


thing looks sweet in the pictures of the mag but i don't know if i'd ever go to that much trouble to have an oddity..


on a side note, arn't supra engines, the 3.0L inline six, like two three cyl. engines put together? i can't remember the fireing order but making the front most cyl. as the no. one, 1&6-2&5-4&3?
supra's are monstrocities of car-kind.. in my view.. but they get the job done good.