318 overbore question

[Kreutzer]

Hey everybody!
I got my hands on an lonely 318 and it turns out it has been bored .040 over and the crank mains and rods have been cut .010. I'm wondering what kind of displacement a 318 has with a .040 over bore?

 

[RustyRatRod]

Bout 324.

 

[Kreutzer]

Cool thanks.

 

[rumblefish360]

Wallaceracing.com is a Pontiac guy with a lot of calculators and of course, CID is one of them.
RRR was correct. It works out to 324.49
Cubic inches. If you build it well, it can do some damage.

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[yellow rose]

Bore x Bore x Stroke x .7854 = x number of cylinders

3.950*3.950*3.313*.7854=40.598175*8=324.7854

And that means it is actually 325 CID because once you go over by any amount (324.001) you must round it up.
If your bores are more than .040 over nominal you can do the math. If it's over enough you may get to 326!

 

[AJ/FormS]

324.49

(Bore/2squared)(pi)(stroke) x 8

 

[yellow rose]

324.49

(Bore/2squared)(pi)(stroke) x 8

That's still 325 what all is said and done.

I don't think NHRA uses the bore squared method. That's why I don't use it. The one I posted is what they use. At least they did back in the day. Id have to find my new rule book and see if it's still in there. NHRA is THE word on displacement if you class race. The two formula are only .3 off but that may get you slapped by Glendora if you ain't careful.

 

[AJ/FormS]

I don't care about class and rounding, and I bet neither does Kreutzer. I care about accuracy.
I also don't care if I'm right or wrong.
That's the formula we were taught in gradeschool, so if it's wrong, then I'm wrong, and so is every trig. book ever written. So tell them about the class rules and wrong-way rounding.

I'm going with

Bout 324

 

[yellow rose]

Well then do your math because there are no 340's, or 454's. They have all been rounded up.

I stand by my math.

 

[AJ/FormS]

Here's rounding; it's a 5.3 liter. heehee

 

[rumblefish360]

Oh good GOD!

REALLY!?!?!?!?!

 

[yellow rose]

I love splitting hairs with AJ. I wait to see how long a post I can get him to write. So far, in this thread, I ain't doing so good.

I'll try and do better next time.

 

[rumblefish360]

Baha ha ha ha ha

 

[Kreutzer]

324.49? Im gonna call it a 325!

Thanks for the answers!

 

[AJ/FormS]

If you go 60-over and round down she'll be a 327.........................
If you do that and swap a 3.58 crank into her she'll be a 355, if you round up.
If you................

 

[rumblefish360]

If you put your left out and your right foot in, put your hands on your hips... And pull your knees in tight......
And the pelvic thrust drives you insane

3.58 X 4.07 = 372.58 (I say 373)

 

[RustyRatRod]

Why not call it a 325? Ford calls the 302 a 302 and it doesn't even round to 302. It also doesn't even round to 5.0. The Ford 400 is actually a 402. The Chevy 396 from 1970 on was actually a 402, but marketed in cars as a 396 and trucks as a 400. It's all about marketing.

 

[yellow rose]

Why not call it a 325? Ford calls the 302 a 302 and it doesn't even round to 302. It also doesn't even round to 5.0. The Ford 400 is actually a 402. The Chevy 396 from 1970 on was actually a 402, but marketed in cars as a 396 and trucks as a 400. It's all about marketing.

I just did the math on a 302. It comes up 301.5936.

Can't remember the 400 dorf numbers but IIRC it was a 4 inch bore.

Chevy was as cheap as they come and when they redid the 396 they didn't want to reprint all the media crap and all the badging. At least that is what I read years ago.

But the 302 comes out to just over 301 and a half and is rounded up. AJ's math may differ from mine.

 

[RustyRatRod]

I just did the math on a 302. It comes up 301.5936.

Can't remember the 400 dorf numbers but IIRC it was a 4 inch bore.

Chevy was as cheap as they come and when they redid the 396 they didn't want to reprint all the media crap and all the badging. At least that is what I read years ago.

But the 302 comes out to just over 301 and a half and is rounded up. AJ's math may differ from mine.

I am sure you are doing it right, because you put the 4th digit in the ".785" and I don't. You also used "3.313" for stroke, which is correct, instead of "3.31" which I used........but for my little piddlin around, it gets me close enough. Besides, I've always thought it was stupid to say "I have a 306" when I still have just a 302 but it's only .030 over. Everybody knows what a 302 is. What the hell is a 306?

 

[yellow rose]

I have seen guys get burned by not doing all the math, but you are correct. Dirt bikes are notorious for advertised displacement and actual displacement not matching. A 380 KTM is 360 or something close.