Displacement

[Kooldino]

So I got into an argument with some Greek on the phone tonight that calls himself "perv works" or something.

We were talking about displacement.

He said that changing the length of your rods will change your displacement.

I disagreed, and told him that changing rod length would only change compression, and that if you want to change displacement, you'd have to change the BORE or the STROKE of the engine, since Displacement = bore x stroke.

If you think about it, if you make a rod longer, you're not changing the difference between the max and min height of the piston, you're just SHIFTING where it sits.

When you go with a longer stroke, for example, you're changing the difference between the max and min height of the piston...the max height will be HIGHER, and the min height will be LOWER.

Nick and I always get into these arguments, because he is a big jerk.

I couldn't find data to back me up, but I'm pretty sure I'm right. Can anyone find anything credible to prove either one of us wrong?

 

[Captain KRM P5]

changing it WILL change your displacement - point one for Perf. called "stroking your motor"

ewwwwwwwwww.....

 

[Kooldino]

Found this crap so far...
http://www.holley.com/HiOctn/TechServ/TechInfo/IECPTech5.html

 

[Kooldino]

changing it WILL change your displacement - point one for Perf. called "stroking your motor"

ewwwwwwwwww.....

I thought "stroking your motor" was when you change the STROKE, via the crank? Can you back up your statement?

 

[Captain KRM P5]

when you stroke, you need both a different crank AND longer rods - so says the mechanic standing behind me

 

[Kooldino]

when you stroke, you need both a different crank AND longer rods - so says the mechanic standing behind me

Perhaps, But if you chage ONLY the length of the rod, you're NOT changing displacement. Only compression.

 

[Kooldino]

This looks promising...
http://www.rbracing-rsr.com/compstaticcalc.html

Don't forget...displacement = stroke x bore x number of cylinders

the above site defines stroke...

Stroke-- The distance the piston travels in the cylinder

SO, REGARDLESS of how long or short the rod is, it's STILL going to travel the same distance.

HOWEVER, if you change the stroke, it is now travelling more or less, depending on whether you went with a taller or shorter crank.

 

[Kooldino]

AHA! I found what i was looking for. Buried in an old thread...

posted by Keith@FP...

Whoa whoa whoa!

Big_ben, you're wrong. Totally, utterly wrong.

The only way to increase the stroke is with the crank. The rods will NOT affect the stroke.

Look at it this way. The stroke is the difference between the upper limit of the piston's motion and the lower limit. What determines this? The crank - specifically, the offset of the rod bearing journals.

Shortening the rod will move the upper and lower limits down the same amount. This will lower the compression ratio, but the stroke is unchanged.

To lengthen (or shorten) the stroke, you need to change the crank. It can be done with an offset grind on a stock crank or with a totally new crank. Ideally, you should also change the pistons and rods to move the wrist pin up higher and maintain a decent rod ratio. But the crucial element is the crank.

Sory, Ben, but TK is right here. Whether the specs are appropriate is another matter and cannot be determined without some study. We actually cut a block in half to work out our Miata stroker setup.

Keith

http://www.mazdamp3.com/vbb225/show...erpage=15&highlight=displacement&pagenumber=9

 

[Captain KRM P5]

i may admit defeat on this one (bows)

 

[Kooldino]

i may admit defeat on this one (bows)

Now let's see if perfworks does.

I'll always argue w/ him about stuff that I'm 99% sure I'm right about, but he never listens.

I'm just gonna start posting all of our arguments here. hahaha.

 

[perfworks]

Now let's see if perfworks does.

I'll always argue w/ him about stuff that I'm 99% sure I'm right about, but he never listens.

I'm just gonna start posting all of our arguments here. hahaha.

Well well, you again dana amaze me how you NEED to have the pissing match with everyone. You have to prove your dick is just that small heh!
Well continue arguing by yourself . It really sounds pretty good. Lets see what else you can come up with.

 

[twilightprotege]

Kooldino is right. 100%

 

[igdrasil]

Then, to add some pepper to this discussion:

How changing rods will affect displacement on turbo application?

 

[Pro Fiz]

Yeah, Kooldino is right.

 

[Kooldino]

Well well, you again dana amaze me how you NEED to have the pissing match with everyone. You have to prove your dick is just that small heh!
Well continue arguing by yourself . It really sounds pretty good. Lets see what else you can come up with.

:wtf: :bs:

I need to have a pissing match w/ everyone? Dude, when you say things that I think are wrong, I don't have a right to disagree? You amaze ME at the fact that you won't even concede that you were wrong.

So next time you argue w/ someone over something, it will be a pissing match. Right. God forbid people argue.

As for my "dick being that small", that's another argument you'll lose. Just ask your girl.

 

[Kooldino]

Then, to add some pepper to this discussion:

How changing rods will affect displacement on turbo application?

 

[twilightprotege]

changing rods will not effect the displacement of the engine. period.

the only way to change the displacement of an engine is to change the bore size or the stroke size. there are no two ways about it.

 

[LinuxRacr]

Kooldino, all you did was proove that no one is perfect! Relax brotha!! If you find yourself in that situation again, the best thing to do is not argue, but to take a break, go find the facts, and let them do the talking. And when the facts speak, don't be an ass about it! I just learned something new anyhow...good facts.

 

[Kooldino]

Kooldino, all you did was proove that no one is perfect!

??? Who said anyone was perfect??

Relax brotha!!

Uh...if you read the posts, you'll see that I am relaxed...if anyone wasn't being relaxed, it was Perf.

If you find yourself in that situation again, the best thing to do is not argue, but to take a break, go find the facts, and let them do the talking.

How did i NOT do exactly what you just said? Nick and I argued on the phone. He wouldn't listen to me. So I told him that I'll post about it, and see what people come up with. Then I went and found the facts...and posted about it. Then I let them do the talking.

And when the facts speak, don't be an ass about it!

??? Ok, I know Nick and you are boys and all, but come on man..."don't be an ass about it"??? What's that??? I'd LOVE to see how I was an ass when I proved myself right. If ANYTHING, Perf was the ass on the phone...

Nick: Chaning rod length will change displacement

me: Nah, that will only change compression. To change displacement, you either have to bore the block or change the crank.

Nick: Oh, so now YOU'RE gonna teach ME about engine theory? Yeah, right.

I just learned something new anyhow...good facts.

That's what the forum is all about. But please, don't exaggerate what happened in this thread and insinuate that I'm being an irate ass, and go on to tell me how i should handle arguments, when I've cleary done what you reccomended anyway.

Why do people come down on me when I prove people wrong???

 

[perfworks]

First off.
Back off dana. Linux was expressing a thought he had on the situation.
Second. My wording on the phone was WRONG. YOU HAPPY? I know the difference between increasing and decreasing compression, or calculating adjusted displacement.
As you know i have been working about 18 hours a day. Im sorry if i didnt make clear to you about my argument on bore and stroke theory. You had asked me a question at 200AM and i didnt respond to it correctly. I am human and do make mistakes like everyone else on this planet. I was also not arguing on the phone with you. If it came down to calculating the added or subtracted displacement of an engine thru internal design characteristics i can assure you that i would have come to the same conclusion as yourself. As far as our conversation i had a slip in thought. Take it as you may but i had alot of things on my mind and didnt think that because i was quoted wrong that it would become this entire show on a public forum.
When i mentioned to you in an earlier post about being in a pissing match , you do it all the time with me and others. BUT, its cool . I do it too. It wasnt meant to be aggresive towards you. You like myself have that tendency to argue till we get our points across. I just differ from you in that i dont come on to this forum and make someone look like they are ignorant because i want to be right. If we had a conversation about something which i might have been right about and you didnt agree, i DONT come onto the mazda forum to post and say I JUST ARGUED WITh SO AND SO ABOUT SOMTHING TELL ME THAT HES WRONG

but anyway, **** it who cares. Your still my friend. Were cool.
We will always argue like family.
Your a b**** with a big mouth.