Stroke to bore to rpm redline

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MX Quad Dad · #11 Post by **MX Quad Dad** » Mon Feb 13, 2006 5:20 am

I find this real interesting, but can't help thinking something isn't right. I am in no way qualifyed to make statements on this topic but would like to say what dosen't make sence to me, so these are questions and my thoughts that may need some input.

I have a hard time believeing one rule fits all.
Differant piston size or weight dosen't make a differance?
Differant piston type (cast or forged) dosen't make a differance?
Differant metal or alloy dosen't make a differance?

Is the 5000 number an instant destruction point or is there already a safty margin in there?

I would think the number would verry by how long you would hold it at or near the critical point.

Don't the cup cars rev over 9G (bigger bore and stroke)?
How high do the F1 engines rev?

I don't mean this to be a smart a$$. It just don't make sence to me (I may just be dence(sp?)). Besides I calculated it by Sandstorms formula and came out way over, so I must have done something wrong.

Sandstorm · #12 Post by **Sandstorm** » Mon Feb 13, 2006 5:43 am

Indy cars rev to 17,000 rpms. The bore and stroke is very small so the formula works.. A piston can only be allowed to travel so far so fast before it will simply start to fall apart.. Call DAB Racing he'll explain it to you.. www.wasatchquad.com ask for Dave or ask any competent builder..

wanablaze · #13 Post by **wanablaze** » Mon Feb 13, 2006 5:53 am

This doesn't make sense to me because the larger the engine, the more likely it is to blow (at the same rpm.) Somthing is missing, a ratio or percentage of some sort.

claas900 · #14 Post by **claas900** » Mon Feb 13, 2006 6:02 am

..heres some F1 info F1 engines here idle at 7 to 8 grand,rev to around 18k..but there a 3.0 liter v10...very small motor for a v10..A 450cc motor 94mm piston with 63mm crank is about 33.96 cu.in. ,or about .55 liter..I think my #'s are right??

Sandstorm · #15 Post by **Sandstorm** » Mon Feb 13, 2006 6:02 am

Larger engines have lower redlines. Again you guys are asking the wrong guy. I don't build motors DAB does. He know his shiat and thats why I went to him.. I have seen his stuff run and I own his stuff.. Beddy time for me... l8tr

MX Quad Dad · #16 Post by **MX Quad Dad** » Tue Feb 14, 2006 3:09 am

I know I am thick headed and it is sometime hard for me to understand, but I still say there is to many veriables for one formula.

Now if I read your formula correct its stroke x bore x redline. just useing a ruler to convert to inches. I get stroke=under 2.5", bore=almost 3.75" and a factory redline of 11,600 so 2.5x3.75x11600=108750. Unless I am doing something wrong (which is entirerly possible) the piston would decentgrate before 5500 RPM. so either I'm doing something wrong or part of the formula is missing. I even converted the bore and stroke to feet then came up with a low number @755

Sandstorm · #17 Post by **Sandstorm** » Tue Feb 14, 2006 3:34 am

There are some very smart people on planetsand. Ask this question over there.. Somebody will chime in as that is the site of 100hp Banshees and all go fast machines.. I don't know what formula DAB punched in.

J. Delaney · #18 Post by **J. Delaney** » Tue Feb 14, 2006 5:11 am

You have to divide by 12 after the multiplication is done to change the answer from inches to feet. Then you still have squared feet so if you divide by 2 you will get an answer that lines up with what everyone else says should be a safe operating speed.

3.82"X2.5"x11600rpm=110780

110780/12"=9231.6 sqft

9231.6sqft/2=4615.8ft

I think that's how your supposed to do it, but I never made it past pre algebra in high school so don't blame me if it's wrong!

wistech · #19 Post by **wistech** » Mon Feb 19, 2007 8:20 pm

Id say let the rpm's be dammed . It helps with he vibration.