Hey guys, i thought that would be very usefull for me and for many many people here.

The problem is that when a man going to buy an engine, he is looking at specs, right? BUT WHERE exactly is he looking? I'll tell you. Torque and top rpm. Well, the guys who don't know what the other things in specs are (like me), that's we are going to find out.

Well, we need an example and to make that thread twice usefull for me, i'll put the specs of an OS SPEED .21 VZB-R Vspec:

SPECIFICATIONS
Stock Number: OSMG2081 X
Displacement: 0.211 cu in (3.46 cc)
Bore: 0.653 in (16.6 mm)
Stroke: 0.630 in (16.0 mm)
Practical rpm: 3,000-40,000
Output: 2.5 hp @ 34,000 rpm
Weight: 11.3 oz (320.5 g)


The specs are from www.osengines.com

The specs with the X ignore them.

Well. From that chart i post, the only things that i kinda know are:

Practical rpm: That engine can run between 3,000 - 40,000 (the 40,000 is the top)

Output: Now that's what i want to know. When it says "34,000 rpm @ 2.5 hp", it means that untill that rpms it have that torque?

Weight: i think thatis cleared. It says the weight of the engine meausured in ounces and grams

NOW WHAT ABOUT THE OTHERS. Please, if you are not sure on what you are writing, at least write the words "I THINK" [)]

displacement is basically the volume of space a piston travels.
stroke is how far the piston travels from the bottom if its stroke to the top.
bore is the diameter of the piston.
2.5hp @ 34,000 rpm means that the engine has 2.5 horsepower at 34,000 rpm. thats probably that engines peak horsepower. less or more than 34,000 rpm and that motor wont have as much horsepower

What do you mean by "displacement is basically the volume of space a piston travels"

here is a picture(hahah i know its horrible but its the best i could do)

the yellow part is the displacement

You mean like that one: I made it as soon as possible

yea you got it but its the area inside the sleeve that the piston travels. what did you use to draw that?

the red in my pic

Go START/PROGRAMS/ACCESORIES/PAINT. That simple I don't have photoshop or something like that If i had photoshop, i would paint the crankcase too

i did mine in paint too lol but yours looks 100 times better

what youwish said is correct, but the 2.5HP is wrong. Its probably only putting out about 1.5HP a highly modded 21 (like the Picco/jammin and v-spec) puts out 1.75HP on the dyno. There's a few post in the engine forum of dyno runs (stock and modded) posted by Colt4g63 (or Adam at ABmods)

yea the engine manufactures tend to overstate the horsepower ratings of their engines. i'll believe what they say when i see results of a dyno

Yeah i see, but where i can find results of a Dyno?

You can PM Adam for ask if he has a dyno for a engine. I f he does then he'll either show you or tell you the specs. (HP, TQ, RPM etc...)

It's a theoretical value based on simulations. I entered all data for the OS RG in a simulation program and got a number very close to the rated one.

can you do that for any motor?

If I have time and feel like it. Also need to have the engine in hand to take all the measurements. It takes a while to measure.

yea that does kinda sound like a hassle

The bore and stroke specs will make a factor in the engines characteristics. The OS uses an over square engine design. Thats an engine that has a larger bore than stroke. This favors a fast revving engine with higher RPM capability. The italian mills use under square design, the bore is smaller than the stroke. This favors higher torque, but will rev a bit slower and not have as much high RPM. With this said, one factor you don't see is the rod length. This will also change the engines characteristics. If two engines have the same bore and stroke with everything being identical except for differnent rod lengths, they will differ in the power band area. Both might produce the same power, but the longer rod engine will have a torque at a higher RPM, while the shorter rod engine will have a fatter torgue band and it will be lower value. If you lengthen the rod on a long stroke, you will move the power band up. This has been done before. If you install a longer rod and shim the bottom of the sleeve the same to compensate, you will make the engine have power in the higher RPM range. Also, take into account, that the big bore short stroke design works with a hot plug (advanced spark timng) while a longe stroke uses a medium plug ( less advanced timing). This is due to piston dwell timing. The long stroke engine has the piston hanging at TDC and BDC for more crank degrees than a short stroke engine. If I've lost you guys by now, go over this engine article so it explains this a bit more, at least the rod ratio part.

http://www.e30m3performance.com/tech...atio/index.htm