"square" motors? good idea? 88X88 90X90.5? advantages?

[69bajakid]

Hey ppl

looking into building a new type 1 motor some day soon..want to use a 3 peice case..some type of aftermarket case will do.

i started thinking it would be neat to build a square motor with equal bore and stroke..
the motor would prob be run with a turbo..but can you guys see any advantage to running a square motor? 88X88 would be fun..and easy.. 90X90 would be even better other then the thinner cylinders..

altho they are thick compared to anything but machine in 88mms..

let me know what you think

thanx
Cale

------------------
"Its not how big you build it, Its how you build it big"

[GL181]

Usually stroker motors, or motors with extremely long strokes make lots of torque but cannot rev as easily as large bore/small stroke engines. It makes sense if you think about it. If you have a 2140cc engine (88x88) it will probably make a lot of torque, but will be short on revs compared to a 2110cc (90.5x82) engine. Think about it for a moment, when a big bore turns the same rpm as a stroker, the average piston speed of the big-bore is about 7% less. This means less wear on the big bore's bottom end because there's less load. Now before I encite a riot, please note that a stroker is clearly not at a disadvantage to a big-bore. The reality of it is that strokers usually make more torque than a big bore because the longer stroke allows a larger volume of gasses to be compressed and exhausted in the engine's cycles. This is why you frequently see strokers in street machines, while high-rpm cars use a large bore/small stroke combo. My reccomendation for a street driven car would be to select a fairly large bore with a medium stroke. Keep in mind that any change to the engine's stroke can have a huge effect on the engine's performance throughout the rpm range, much like the rod ratio. Stay conservative, and focus your money on things that make power like good heads, induction, and cams. Select each peice as part of a "package" and you'll be more than happy with your little engine's performance!

Best of luck and happy motoring!
gary

[69bajakid]

Actually my car is more of a class 5 unlimited/non race baja bug
so i need torque..

Cale

------------------
"Its not how big you build it, Its how you build it big"

[ray greenwood]

Not sure how it relates to air-cooled...but Audi swears by "over square" motors in all of their cars. They claim...and it seems to hold true...that the use of long stroke smaller piston diameter is what makes their five valve technology work. It keeps port velocities very high and allows 3-smaller intakes that all require less time for fuel air mix to "skirt around" the valve head. By that logic...longer strokes with conservative valves would be the requirement...conversely shorter strokes...or possibly strokes equal to piston diameter (square) would need or could use larger valves and or less of them to create the same effect. Velocity at the port being the sought after key here...bearing in mind that they are all injected. there was an article about this in february 2001 euroipean car magazine. Ray

[JohnConnolly]

I know one thing; large bores increase emmisions.

And (correct me if I'm wrong), I believe that a 2.2L engine sweeps the same displacement regardless of bore/stroke, in every degree of rotation, ASSUMING the rod ratio is the same.

I also feel the "square engine" concept is one merely idealized by guys that want a "perfect" shape (circle, square, etc), and it bears no real relationship to the engine in OUR application. new cars have displacement limits to deal with, we do not.

That being said, you are crazy if you don't build as much displacement into the engine as possible! If you are in a limited displacement racing class, THEN you have to deal with bore/stroke issues, but if not, don't bother, build it as big as you can. Chevy guys have argued the small bore/long stroke vs. large bore/small stroke thing forever, and it's never going to be settled.

[Steve Arndt]

Chicken and egg syndrome. 5 valve because it is better? Or 5 valve because they need to fit all the flow they can in a small bore oversquare package? You tell me
http://www.cyclenews.com/features/rc45.asp

Steve


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ray greenwood:
Not sure how it relates to air-cooled...but Audi swears by "over square" motors in all of their cars. They claim...and it seems to hold true...that the use of long stroke smaller piston diameter is what makes their five valve technology work. It keeps port velocities very high and allows 3-smaller intakes that all require less time for fuel air mix to "skirt around" the valve head. By that logic...longer strokes with conservative valves would be the requirement...conversely shorter strokes...or possibly strokes equal to piston diameter (square) would need or could use larger valves and or less of them to create the same effect. Velocity at the port being the sought after key here...bearing in mind that they are all injected. there was an article about this in february 2001 euroipean car magazine. Ray<HR></BLOCKQUOTE>

[ray greenwood]

Steve..it sounds almost like you read that exact article...I would swear that was the header on the add. Audi/VW water cooled equipment has almost always been long stroke small bore. They were doing research over the last decade to see if they wanted to move away from that configuration...as they were designing so many new blocks anyway...now would be the time. The gist of the article wasn't wether square or non-square was better....the gist was that the five valves were not necessary on their engines if they had been more square in displacement configuration. i.e...their testing on the same engines...2.0's, 1.8's and Vr6's...showed much better flow and horsepower on the long stroke motor with five valves compared to two three or four valves. Same volume, same exhaust port total area...less time to actually fill and exhaust the cylinders through five smaller valves than two large valves. John...you are correct that a 2.2 is a 2.2 and has the same volume wither the cylinder is wide or long. But...if the pistons in the two engines are moving the same speed....remember that the exit is at the end of the cylinder...there is going to be more time involved to empty the long cylinder than the short. Since the piston doesn't slow down for anything...there will be more presuraisation of the exhaust charge in the long stroke at the same piston speed. In most cases that would be a good thing. If it happens to be one large exhaust valve...the exhaust has to skirt that valve to exit. They flow research that VW audi was doing seemed to suggest that smaller valves offered lower resistance in both direction in filling an overly long stroke. God knows its hard to argue with the figures they get out of the dinky little stock motors they are using...itseems to work. What they also alluded to was that the magic itself was not done really by that valve function itself, but in the more elaborate tuning it offered them in their valve timing and exhaust manifolding. The lessons of too large of a valve in short stroke motors was learned long ago as well in v-8's. Mostly before head porting became a flow bench art on an everyday basis. Ray

[danimal]

>>>one is a 90.5 X 84 (2160) and the other is 94 X 78 (2165).<<<

even with a 2165.22cc vs. a 2165.21cc, there is apparently a small difference in h.p... i'm not sure exactly why.

one thing we do know is that the pra motors favor bore over stroke, but that may be a function of head flow capabilities.

this motor is based on the don jiskra dyno file, it runs pt level 6 heads(40x35.5), webcam 121125(?), and 8.3:1 c.r.

for those of you that question the accuracy of the dyno2000 program, i've included a quote from autospeed.com:

"...In all cases, the power and torque curves that were drawn by the program were within 10 per cent of the factory figures at all rpm. This is a very good result." http://www.autospeed.com/A_0270/P_2/article.html

dan
oceanstreetvideo.com

[This message has been edited by danimal (edited 09-08-2001).]

[JohnConnolly]

Dan,

for kicks could you up the compression on DJs engine to 9.25:1? TIA

John

[JohnConnolly]

Ray,

I think my point is being overlooked.

If you have an engine, let's make it something I'm familiar with, Aircooled.

one is a 90.5 X 84 (2160) and the other is 94 X 78 (2165).

If the engine rotates 15 crank degrees, the amount of "air" that passes thru the port is the same in either engine. The longer stroke engine has the piston move further, but it's a smaller bore so the air is the SAME as the shorter stroke/larger bore.

Since this is the case, velocity thru the port is the SAME, right? The only change woudl be the smaller bore engine would likely use smaller valves and velocity thru the valve opening would be higher (but not the port).

So, I fail to see any advantage with a small bore engine other than emissions, since large bore engines can fit larger, or more, valves in it.

Perhaps I'm missing something.

[69bajakid]

SO if i was to build a type 4 motor with a counterweighted 71mm crank and 103mm bore
2366 ccs... or i could make a 2332 type 1..would they make close to equal power ?

an John C!! your from salt lake city UTAH?
i JUST came back from MOAB utah.,..and drove right though salt lake..ohh i could have gotten all those parts i have been wanting!
its ok though..im going back in a few months.

later
Cale

------------------
"Its not how big you build it, Its how you build it big"

[danimal]

>>>for kicks could you up the compression on DJs engine to 9.25:1? TIA<<<

hi john,

142hp@6k, vs. 149hp@6k
torque is 137@5k, vs. 143@5k
bmep is 162.8, vs. 169

>>>if i was to build a type 4 motor with a counterweighted 71mm crank and 103mm bore
2366 ccs... or i could make a 2332 type 1..would they make close to equal power?<<<

2366.37(71x103) vs. 2366.19(94x85.24):
148hp@6k vs. 144@6k
torque [email protected] vs. [email protected]
bmep 158.8 vs. 157.1(!)

lets increase head flow(aircooled.net stage7, 44x37), c.r.(9.25), and cam profile(fk87), 48ida's:
182@6k vs. 179@6k
torque 180 vs. 178
bmep 190.6 vs. 189

i'd be glad to send these dyno files to anyone who has the dyno2000 software, so you can check the results for yourself... maybe i made a mistake

like i posted before, there are no mathematical h.p. advantages to rod length; but longer rods do provide less side loading of the piston, and they have been proven on numerous dyno tests to give more power.

remember that the holy grail of head porting is to always achieve the magic % ratio of input vs. output cfm... nothing else matters... in the case of the stock type 4 head, bigger valves will only help up to the point where you cannot compensate for the limited flow design of the exhaust port, and it alters the i/o ratio.

by compensation, i mean using the iterative testing feature of the engine math program to design a type 4 exhaust lobe profile in the cam that will increase the exhaust flow... but when does increased duration turn into flow reversion of the combustion chamber?

torque is not a factor when overall displacement is the same, because with the better flow %'s of the type 1 head, i can use the engine math program to design a cam that produces torque wherever i want it... i could even tell the head porter to make the flow ratio whatever i wanted it to be, i.e., match the i/o cfm of a type 4 head.


dan
oceanstreetvideo.com

[James2]

Dan, run me a combo, will you?

Try a 1915, with the stage 7 heads, and a 110 engle cam, 1.25 rockers. 1-3/4 headers, dual 45 DRLA with 38mm vents.

Do this, and I will take my type 4 engine and put in the farm tractor.

[Spyke]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ray greenwood:
SNIP...John...you are correct that a 2.2 is a 2.2 and has the same volume wither the cylinder is wide or long. But...if the pistons in the two engines are moving the same speed....remember that the exit is at the end of the cylinder...there is going to be more time involved to empty the long cylinder than the short. Ray<HR></BLOCKQUOTE>

But if the PISTONS in the two engines are moving at the same speed, the engines aren't at the same rpm, so they aren't flowing the same amount of air, so what's the point?

The long stroke engine will have a higher piston speed at a given rpm. At a given rpm, both engines will have the same amount of time to empty the cylinder. It's simple math, they HAVE to.

Take a 500cc cylinder spinning at 6000rpm. That translates to 100 revs/sec, so each rev takes .01 seconds. 1/4 of that time is spent on the exhaust stroke, so any 500cc cylinder at 6000rpm is on it's exhaust stroke for .0025 seconds. The bore never figures into the math. (And hopefully I did it right, it's early and I'm not a morning guy...)

Obviously the cam timing will figure in to the amount of time a cylinder has to actually empty, but the point is, the piston itself has .0025 seconds to go from bottom to top on each exhaust stroke, regardless of bore.

I'm with John on this one, the "more time to empty the cylinder" explanation doesn't make sense.

Regarding the whole bore vs stroke issue for 5 valve engines, look at the engine in the Yamaha R1. 20 valve, 1000cc inline four cylinder, 74 x 58 bore/stroke. I can't remember the hp rating off the top of my head, something around 140? In any case it's pretty healthy, and nowhere near "square". Granted, the engine spins tons faster than an Audi ever will (well, at least a stock Audi that's covered under warranty)but if it's power you want...

-Craig
www.teamyikes.com

[ray greenwood]

The time point was mis-explained on my part. There is more than one thing at a time going on here. In a taller column...longer stroke...there is a longer distance to be covered. At the same rpm...the piston on the long stroke will be moving faster in the same time interval,(covering more distance)...which is one revolution at a rate of 4000 per min. If the valve were too small...and the available exit volume of the valve were too low...you have a restriction...and you achieve resistance against the piston coming up on the exhaust stroke...same problem in reverse on the intake stroke. The good thing is, that this "compression" keeps port velocities high. The exhaust is pressurised out of the exhaust port. Keep in mind that the valve is not just sitting still. It is moving, and will soon be reducing its open area. This is if the valve is too small. Most people opt for larger valves. To a point, this works.When the valve becomes too large...the exhaust charge has to skirt around the diameter of the head...before entering open space....but still, this has at least aleviated resistance to the upward movement of the piston, which is not going to slow down. It will compress what is in front of it. Now with port velocities reduced,because of an oversized valve, they are further reduced by the fact that exhaust or intake charge has to skirt too large a diameter head. Ford discovered this phenomena in the early 70's in their boss 289 and boss 302 racing engine programs. Audi, and Mitsubishi among others found that they could get better flow characteristics by achieving the same valve areas with more smaller valves...therby limiting the amount of travel distance around the valve head and subsequent frictional velocity loss incurred. How does this relate to the short stroke? Same volume...wider piston shorter amount of distance...and lower piston speed at the same rpm...remember for example: if you have 4000 rpm and a 66mm stroke versus say an 80mm stroke...thats 1320 meters per min one way versus 1600 meters per min one way...but the same gas volume on each stroke...no matter what the length. The short stroke is going to require a larger valve because it has less stroke to get rid of that half liter plus of exhaust gas in...through one hole..which is moving...and decreasing at some point. It will also have the same reduction in port velocity problem, trying to skirt an exhaust or intake valve that is too large. Time was a poor choice of words on my part. It is actually distance versus volume through an exit at a constant speed. But remembering that velocity equals distance times speed (in an unpressurised world) this has the added factor of a fast moving piston behind it. Some of the published results among the VW audi testing, where exhaust and intake area at max lift were the same...but only #'s of valves and valve diameter varied show impressive changes I.E. same engine different heads. Of course they were looking for their own results (european car and I think ABT tuning and a few other people). The particular test that sticks in my mind was all on the same engine, a Vr6. Probably not much better of an explaination...but I try.Ray Ray