attention engine tuners

[KnifeEdge_2K1]

please read this article before posting any replies

http://www.sportcompactcarweb.com/te...c_engine_work/

i fail to see how you can have a stroke to rod ratio greater then 1:1

you can increase the length of the con rod infinetly, but there is a limit to how short the rod can be, the shortest the rod can be without the piston ramming the counter weights is the 2x the radius of the crank, if you can some how fit the piston into the middle of the crank assembly still the rod length is limited to the radius of the crank. in these two situations the stroke to rod lenth ratio is still 1:1 and 2:1 respectively

further more, in the article it states that people are increasing the rod length to raise this ratio, but increasing the rod length has no effect on the stroke of the pistons and thus would decrease the ratio, counter productive if a high ratio is what's desired

[h00t_h00t]

I don't think there are that many engine tuners here, most of the people on this forum aren't out of school yet.

[digitalcraft]

I'm out of school. Out of college too.




(I'm not an engine tuner though >.> Although I have friends that are. Two are VW nuts, two are Subaru nuts.)

[h00t_h00t]

On the subject, changing the ratio isn't a great idea on all but the most highly tuned racing engines, for street and occasional track-day use its a waste of money.

[KnifeEdge_2K1]

true, but so is every other modification other then tires and brakes

I just like to know this stuff, whether im going to use it now or in the future is unknown, but if i were to attempt a project on my car, id like to have every bit of knowledge i can get my hands on

i just realized i can use related rates to figure out whether a high or low stroke/rod ratio is desirable, but seeing as how i've been out of practice in this topic for quite some time id rather not attempt it, as it can be a long and painful process

[hightower99]

Knife edge you siad you could not think of how to get lower than a 1:1 rod to stroke ratio?

but you then wrote one that is 1:2 as far as I can see. If the rod is exactly the radius of the crankshaft throw and the piston can come down inbetween the counter weights (they just need to be spaced out) then the rod length is half of the total stroke length.

Anyways if you want better power try to get the highest rod:stroke ratio you can (i.e. you want 2:1 not 1:2) this leads to better combustion control as the piston accelerates more slowly away from TDC and puts more of it's force into the crankshaft and causes less friction between the piston and cylinder walls. of course the offset is that with longer rods you have more weight in the engine so don't try to get any more than 3:1 the golden ratio is between 2:1 and 3:1 where the advantage in friction and increased power transfer is highest without being overly heavy.

Oh and hoot-hoot you should only talk for yourself I consider myself to be a engine builder/designer by hobby. However I like to find my own designs and ways of making engines better (cause I don't really like the fundamental flaws of current reciprocating piston engine design)

[johnnynumfiv]

^I don't believe anything you say hightower, show us some dyno graphs or pictures or something of engines that you've made.

[hightower99]

^I don't believe anything you say hightower, show us some dyno graphs or pictures or something of engines that you've made.

In due time I will be posting a thread about one of my projects.

I haven't made any full size engines yet but I did do some work on a '93 ford taurus (I don't have any pictures of the work done)

Most of the stuff I do are designs and ideas that take me a long time to translate into real working pieces, I have a few small engines (between 5 and 23cc single cylinder) that I have made to test some of my designs but I don't have a digital camera to show you any pictures.

[KnifeEdge_2K1]

Knife edge you siad you could not think of how to get lower than a 1:1 rod to stroke ratio?

but you then wrote one that is 1:2 as far as I can see. If the rod is exactly the radius of the crankshaft throw and the piston can come down inbetween the counter weights (they just need to be spaced out) then the rod length is half of the total stroke length.

Anyways if you want better power try to get the highest rod:stroke ratio you can (i.e. you want 2:1 not 1:2) this leads to better combustion control as the piston accelerates more slowly away from TDC and puts more of it's force into the crankshaft and causes less friction between the piston and cylinder walls. of course the offset is that with longer rods you have more weight in the engine so don't try to get any more than 3:1 the golden ratio is between 2:1 and 3:1 where the advantage in friction and increased power transfer is highest without being overly heavy.

Oh and hoot-hoot you should only talk for yourself I consider myself to be a engine builder/designer by hobby. However I like to find my own designs and ways of making engines better (cause I don't really like the fundamental flaws of current reciprocating piston engine design)

that's why im confused, the article refers to it as stroke/rod ratio, not rod to stroke ratio

[h00t_h00t]

Knife edge you siad you could not think of how to get lower than a 1:1 rod to stroke ratio?

but you then wrote one that is 1:2 as far as I can see. If the rod is exactly the radius of the crankshaft throw and the piston can come down inbetween the counter weights (they just need to be spaced out)

The piston can't come down any further than the cylinder, the piston rings would come out and smash against the cylinder on re-entry. You can't space out the weights either because then they would get in the way of the other cylinders. So you would need inadequatly thin counter weights or need to build an completly customised block and crackshaft and if you are going to do that its not modifying.

I find it hard to believe anyone that has access to expensive engineering equipment but no digital camera. Infact anyone that can afford a computer to come and argue this with me should also be able to afford a camera. They are around £50 now for one good enough to take "proof of existance" pictures.

[hightower99]

The piston can't come down any further than the cylinder, the piston rings would come out and smash against the cylinder on re-entry. You can't space out the weights either because then they would get in the way of the other cylinders. So you would need inadequatly thin counter weights or need to build an completly customised block and crackshaft and if you are going to do that its not modifying.

I find it hard to believe anyone that has access to expensive engineering equipment but no digital camera. Infact anyone that can afford a computer to come and argue this with me should also be able to afford a camera. They are around £50 now for one good enough to take "proof of existance" pictures.

You could in theory extend the cylinder and piston down in between the counter balance weights if they where spaced out enough. Of course you would end up with a very long engine (because between each cylinder there would be room for a counter balance weight) My point was that it is not a mathmatical impossibilty, highly unlikely and not a very smart option but not impossible. I also stated that you should not be trying to get the lowest rod:stroke ratio so I wonder why you brought that up?

Next all the things I own are things that I have saved up for and bought because I need them (I have 2 computers and several metal working tools) Most of the heavy equipment and other expensive things that I sometimes use are owned by friends or family and are open to my use. I have never liked digital cameras and I am happy with my old olympus when it comes to taking pictures.

[BjD]

please read this article before posting any replies

http://www.sportcompactcarweb.com/te...c_engine_work/

i fail to see how you can have a stroke to rod ratio greater then 1:1

you can increase the length of the con rod infinetly, but there is a limit to how short the rod can be, the shortest the rod can be without the piston ramming the counter weights is the 2x the radius of the crank, if you can some how fit the piston into the middle of the crank assembly still the rod length is limited to the radius of the crank. in these two situations the stroke to rod lenth ratio is still 1:1 and 2:1 respectively

further more, in the article it states that people are increasing the rod length to raise this ratio, but increasing the rod length has no effect on the stroke of the pistons and thus would decrease the ratio, counter productive if a high ratio is what's desired

Hightower's right, you've got the ratio back-to-front Not your fault though as the article contradicts itself too...

An area of tuning just now being exploited by import engine builders is altering of the rod length to stroke ratio. The bigger the stroke-to-rod-length ratio (commonly referred to as the "rod ratio") ... etc

"Rod length to stroke ratio" is the proper way around, yet they then go on to refer to it as the stroke-to-rod ratio.

Counterweights are often at a reduced radius from the crank centreline, so you could in theory approach having a shorter rod than the stroke, but the ratios of 2:1 and above they discuss in there would mean the little end of the rod would descend past the crank centreline, which is, well, silly

In short, they've got it back-to-front.

[Rockefella]

Next all the things I own are things that I have saved up for and bought because I need them (I have 2 computers and several metal working tools) Most of the heavy equipment and other expensive things that I sometimes use are owned by friends or family and are open to my use. I have never liked digital cameras and I am happy with my old olympus when it comes to taking pictures.

Good, because many of us want to see your prior works, which you've talked about repeatedly.

[hightower99]

Good, because many of us want to see your prior works, which you've talked about repeatedly.

I have no idea how to get a real photograph into the computer and onto the internet without a scanner (don't have one)

It didn't work when I shoved them into the DVD tray???

[h00t_h00t]

You also have no idea how dubious it sounds when you can afford to build custom engines but not a digital camera or even a mobile phone with a camera.