Bore stroke combination ?

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Bore stroke combination ?

Post  powerstrokeace on November 28th 2013, 5:37 pm

Guy's I have 2 motors that are of different bore and stroke but within 2 cubic inches. So this is the bottom ends
4.250 stroke and 4.562 bore which is 555 ci.
the other is
4.50 stroke and a 4.440 bore which is 557 ci
so the heads are the same (A460) intake (old A460) carbs 1050 (8896) and the cams are the same as well. are these going to perform the same given the same converter and cars weight. or will one perform differently because of its different bore stroke combination?

Ace

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Re: Bore stroke combination ?

Post  kim on November 28th 2013, 6:03 pm

big bore short stroke is going to hit the heads harder.

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Re: Bore stroke combination ?

Post  Lem Evans on November 28th 2013, 6:41 pm

The intake valve will like the bigger bore.

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Re: Bore stroke combination ?

Post  supervel45 on December 4th 2013, 4:53 am

No, not sure how much. I would Think the torque curve would come in more, toward the top end on the short stroke, and would rev. a little quicker, and higher. I allways liked a 427 Ford over the 428, for the shorter stroke, bigger bore, and it was the Race engine, and the 428 was the heavy car street crusier when it came out. I bet someone has some Dyno Sheets on file to compare, that are close to these. Ironic 377 and 383 are 6 cubes apart, and have the same deal. Like Lem said the Intake valve will be unshourded more, and slower piston speed, and TDC dwell time will be longer, are benifits. In a light car I would pick the short stroke, big bore anytime. Bottom end may have less stress,and a stonger crank, because of the pshysic's in play, and don't forget rod angle ratio, and cyl. distorition, ring seal ect. ect. ect.


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Re: Bore stroke combination ?

Post  kim on December 4th 2013, 5:21 am

Cam should not be the same. The valve timing is going to be faster and shorter ATDC for intake events on the short stroke big bore. The long stroke small bore would benefit from a slower opening ramp rate and an extended opening time, that BIG swing, is going to put a long draw on the intake and would benefit from a later closing and slower closing ramp.

Big bore can work more like a poppet valve, and thus also works well for broader torque curve, higher cylinder pressure average at lower RPM, as well as facilitate higher RPM...

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Re: Bore stroke combination ?

Post  supervel45 on December 4th 2013, 8:09 am

Kim, So would the long stoke, small bore, need the less agressive ramp profile, make it have the advantage over the short stroke big bore, as far as valve train durability? If I comprehending your statement correctly? I agree with what you are saying, on cam choices, but never thought about it in this aspect.    If the same cam where used in both I would think, the short stroke would breath a little better, with like cams, due to the slower down piston speed, and the unshourded intake valve,  is why I mentioned the slightly higher RPM? Also, the original question, did not pose that as a variable, in the comparison.

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Over Square Bore and stoke

Post  supervel45 on December 4th 2013, 9:42 am

The 557 has a over square bore and stroke, ie, longer stroke than bore diameter. The 455 Pontiac is the same in this regard. I think some Vodoo, I do not understand, may come into play here too. I hope someone  will chime in,  who builds and dyno's both them, to expain it, if their is any merit to the statement?The 455's seemed week off the line, and came on like scaled apes on the big end, in the heavy TransAms. Could have alot to do with rear gearing also? Seems the 557 would be a grunt motor for truck pulling,(long arm crank, more leverage, due to lenght of throw, heavier arm, is slower to set in motion, but once moving gains momentium increasing torque, by extra weight, towards rod jurnal) and the 555 the screamer for light dragsters (short arm crank, more speed, and lighter arm, easier to set in motion) , to me, anyway. Traction in a light car on the launch may favor the short stroke also, as it may not shock the tire's on the hit, from a dead stop, as hard? Both good combinations in the right appliciations.

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Re: Bore stroke combination ?

Post  kim on December 4th 2013, 12:22 pm

supervel45 wrote:Kim, So would the long stoke, small bore, need the less agressive ramp profile, make it have the advantage over the short stroke big bore, as far as valve train durability? If I comprehending your statement correctly? I agree with what you are saying, on cam choices, but never thought about it in this aspect.    If the same cam where used in both I would think, the short stroke would breath a little better, with like cams, due to the slower down piston speed, and the unshourded intake valve,  is why I mentioned the slightly higher RPM? Also, the original question, did not pose that as a variable, in the comparison.
But that is why you wouldn't build the two combinations the same, and should never see an apples to apples comparison. Magazine rags do this all the time, put together a mismatch dyno mule to show part x or y's greatness over similar yet different products.

As for more durable valve train, Opening rates can be extremely dramatic, and have little affect on overall stress, its the closing rates and the ability to control valve bounce that tends to beat the sheet out of things. Either is going to do OK, the longer stroke combination needs a much longer/later valve event, and then to build cylinder pressure has to get the valve closed as abruptly as it can... where the short stroke big bore, will have lots of "lag" time for lack of a better word where the intake closing can take affect and not really hurt performance, yet allow lots of cylinder pressure to build.

Oversquare undersquare, it doesn't make a real big difference its simply a comparison of numbers. The 454 Chevy is oversquare, and does fine.... the 289 ford is undsquare and did fine.. As many on this and other forums have repeatedly pointed out, the engine is an air pump, maximizing its pumping capability by a well selected group of parts will ensure it does its best. Its always the combination of parts that make one better than the other.

The long stroke combination would work better if someone were already working with a smaller head, smaller valves and less runner capability.

The short stroke big bore would work better with a larger bore head, bigger valves, larger runner cross section.

The cam should look significantly different for both combinations irreguardless of head.

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Re: Bore stroke combination ?

Post  supervel45 on December 5th 2013, 4:18 am

Alot of good info. I agree about the magazines and how the question is laid out. 454 Chevy is 4" stroke to 4.25" bore, so it is not over square, like the 455 Pontiac. No big deal, I get your point. I guess the poster could run both shortblocks, with like components, and compare timeslips. These topic's are good as alot of information, gets laid out, and they are not boring, it seems. I will say I learned a few things, that I never even considered, from this thread. Thanks for the information and your post Kim, very well written.

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Re: Bore stroke combination ?

Post  IDT-572 on December 5th 2013, 4:35 pm

Most of my life I have heard the Chevy guys say a 460 ford would never make a good race engine. Their reasoning was it was a truck and big car engine with a real long stroke to make tons of torque and not hp.

It would burst their bubble if they knew it had a .150 shorter stroke than their wonder full 454 and a .470 longer rod, plus a .110 bigger bore.Twisted Evil 

And that's just a couple of many reasons the 460 makes good power.
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Re: Bore stroke combination ?

Post  kim on December 5th 2013, 5:55 pm

IDT-572 wrote:Most of my life I have heard the Chevy guys say a 460 ford would never make a good race engine. Their reasoning was it was a truck and big car engine with a real long stroke to make tons of torque and not hp.

It would burst their bubble if they knew it had a .150 shorter stroke than their wonder full 454 and a .470 longer rod, plus a .110 bigger bore.Twisted Evil 

And that's just a couple of many reasons the 460 makes good power.
Its a truck motor when you pinch it down with teeny tiny heads and 2bbl carbs.....

Problems always been getting aftermarket vendors to offer quality components to let it do what it can. Had it not been for the 5.0 mustang, I think "ford" enthusiasts would still be digging junk yards for 351C castings, as well as the few remaining 429 CJ castings.

Thank the powers that be, that the 5.0 mustang stomped Camaro and Corvette alike through the 80's to make FORD a power name.

Lord knows NASCAR had done everything in its power to prevent the people that could rub magic on them ole stock ford parts from succeeding.

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Re: Bore stroke combination ?

Post  69bluehotrod on December 5th 2013, 8:03 pm

powerstrokeace wrote:Guy's I have 2 motors that are of different bore and stroke but within 2 cubic inches. So this is the bottom ends
4.250 stroke and 4.562 bore which is 555 ci.
the other is
4.50 stroke and a 4.440 bore which is 557 ci
so the heads are the same (A460) intake (old A460) carbs 1050 (8896) and the cams are the same as well. are these going to perform the same given the same converter and cars weight. or will one perform differently because of its different bore stroke combination?

Ace

Ace in that well stocked shop you are bound to have a set of rods & pistons to make a 588!!!!
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Re: Bore stroke combination ?

Post  powerstrokeace on December 6th 2013, 12:13 am

69bluehotrod wrote:
powerstrokeace wrote:Guy's I have 2 motors that are of different bore and stroke but within 2 cubic inches. So this is the bottom ends
4.250 stroke and 4.562 bore which is 555 ci.
the other is
4.50 stroke and a 4.440 bore which is 557 ci
so the heads are the same (A460) intake (old A460) carbs 1050 (8896) and the cams are the same as well. are these going to perform the same given the same converter and cars weight. or will one perform differently because of its different bore stroke combination?

Ace

Ace in that well stocked shop you are bound to have a set of rods & pistons to make a 588!!!!


Well not yet. Depending I. The next rebuild on the 555 motor it could become a 598 if I replace the billet scat crank in it. Maybe it's not billet. But I really like all the comments and I ended up with 2 cams built for the 555 deal and I'm currently doing a 557 to replace the 514 I broke. So the heads are in Oakley hand getti g fixed up real nice ( they were a mess from some one else). And got a set of Diamond pistons from him today that are at the machine shop as we speak. I still have a roller cam that is smaller but I could not say what the opening rates are. But it was spec out for one of my 514's

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Re: Bore stroke combination ?

Post  supervel45 on December 6th 2013, 9:39 am

IDT-572 wrote:Most of my life I have heard the Chevy guys say a 460 ford would never make a good race engine. Their reasoning was it was a truck and big car engine with a real long stroke to make tons of torque and not hp.

It would burst their bubble if they knew it had a .150 shorter stroke than their wonder full 454 and a .470 longer rod, plus a .110 bigger bore.Twisted Evil 

And that's just a couple of many reasons the 460 makes good power.
I was always told that the 351M/400 had the wrong geometery, and could not work by the Chevy guys. When their 350's got beat, they accused me of haveing a 460, LOL.

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