SStrokerAce

http://hotrod.com/toc/thismonth/

Bore vs. Stroke

For years magazines have told you that a longer stroke makes more torque and big bores are good for horsepower. We built two Chevy engines identical except for bore and stroke to find out. Turns out it doesn't make a bit of difference, at least in this case. Have car mags been lying all these years?

Go Buy it..... good story and some good comments by Darrin Morgan of Reher Morrison.

I'd type more but a kitchen knife put my right hand outta commission.... hopefully the medical super glue will prevent stiches tomorrow!

Bret

Bersaglieri

OMG, thats not your cam makin' hand is it?!

-Dustin-

Damon

Ouch, sorry to hear about the finger. I once chopped the entire tip of one of my pinky fingers off with hedge trimmers. Don't ask- long, stupid story. Docs did a nice job re-attaching it (amazing the things they can do) but I still don't feel anything right out on the tip of that finger.

The engine test resuts make sense to me. Bigger bore is more surface area for the expanding combustion gasses to push against, but a shorter lever arm to work against. Longer stroke is a bigger lever arm to push against, but less piston surface area for the gasses to push against. 6 of one, half dozen of the other.

I suspect that valve shrouding in the smaller bore motor would eventually put a limit on how much flow you could get from the heads (valve diameter limits and such) and therefore how much HP, but in a street motor that isn't having every last fraction of power squeezed out of every nook and cranny it doesn't surprise me that the results would be the same.

Now all you have to do is throw in some discussion about rod length and you've got the makings of a thread that is sure to have 200 replies arguing back and forth about what different people have tried or seen or heard about. "My engine has a 7" stroke and 4" rods and revs to 8000 without any problem..." etc, etc etc.

Racer1283

A better story might have been done building two identical 383's, except one having 6 inch rods, and the other having 5.7 inch rods. I think the diffence between the two would be so small, it would show it's not worth the bother, at least on a street machine.

SStrokerAce

They changed the rod lengths in the motors in the story which was dub to me... brings that variable in. Screw rod ratio....

Seriously it's a good story, worth the read.

The BBC has more problems in terms of breathing on different bores.... so it was a better choice than a SBC IMHO

Thanks for the words guys, sleeping with this feels sooo goood. j/k

UB told me that I should eat Mickey D's so I would stay out of the kitchen!

Bret

OldSStroker

FWIW, Bret is a fine cook and a great cookie baker. His omelets are to die for, especially the hotdog, mustard and meat sauce ones. It runs in the family; his Mom and Sister are also great cooks.

He still runs with scissors though. Some things never change.

Freiberger's test in Hot Rod was actually fairly well contolled. I especially liked that he discussed the bore/stroke topic with high end builders like Reher and a Cup engine builder. The Cup guy said something about "significant" gains with a rod length change (I believe) but tempered it with the statement that finding 3 hp in a Cup engine is a HUGE accomplishment.

The best conclusion was something like "use the largest bore and the longest stroke you can...there's no replacement for displacement!"

Denny McLain

Very good and very informative. The best I've seen out of mag in some time. Think I've only read it about four times as there is so much information.

kmook

Nice.

Single?

OldSStroker

Yeah, Bret is, Ken.










His sister and her fiance' own a liquor store. How nice is that?

unstable bob

That's the main reason Bret is choppin' off fingers. He is runnin' with booze bottles, along with those scissors!

And Pops, I heard some stories about you, booze, and riding mowers...

Mindgame

I have a feeling that Bret would make somone a great wife!

I can see it now...... Bret on one of these matchmaker shows......

"Yep, I make a mean omelet and I can tune a small block chevy at the same time!"



-Mindgame

SStrokerAce

Oh jesus...

And Ken your not my type.... and my brother in law is a Ford guy... AT LEAST he's a car guy, you think he could stand OldSStroker and I at dinner otherwise?

Baking cookies is thinkin time for me... Like when I had court for 6 traffic tickets. It's better to think over makin cookies than it is setting bearing clearances ya know. A little extra or too little salt, sugar whatever is not going to hurt, a little too much or too little bearing clearance... well you get the idea.

Hey MG if you know any wealthy women who have a big garage and aren't too bad on the eyes I'll be a house husband any day of the week then.

Bret

unstable bob

Ken never told me he was gay. In fact, he once told me he was going to be coming to my area to visit a woman!


LIAR! LIAR! Pants on fire!!!!

PS: PC after note: I have no problems with anyone's sexual preferences. I only have problems with people who don't drink beer!

SStrokerAce

I second that!

number77

Question, was the original rule of thumb "more stoke makes more tq and more bore makes more hp" based on being able to rev the big bored-short stroke engine high and thus *hp comes more naturally higher RPMs*

or was it based on non equal terms, as making heads flow for high rpms engines, and big intakes for long stroke engines?