Bore vs. Stroke... "Revisited" - TCCoA Forums
 
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post #1 of 22 (permalink) Old 05-11-2005, 06:53 AM Thread Starter
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Red face Bore vs. Stroke... "Revisited"

Hehehehehehhe

Ok just so we don't start right off the bat with the usual "stroking a 4.6L is useless" argument, lets for the moment forget about the modular engine (with its small bore) and apply this to a large OHV engine (i.e. BBC).

Did anyone see the comparison in the June Hod Rod magazine...

Yes I hate magazines, but at least this time they used the same engine, same cam, same heads, same almost everything except the bore/stroke combination. It was some interesting numbers.

The engine(s):
BB Chevy
Small Bore/Long Stroke: 4.280 x 4.250 = 482 cu in
Big Bore/Short Stroke: 4.560 x 3.766 = 492 cu in
Rod ratio (Long Stroke): 1.54:1
Rod ratio (Short Stroke): 1.63:1
Heads: AFR 335cc CNC ported heads
Cam (Mild Hydraulic Roller): 218/224, 110 LDA, .510/.510
Cam (Large Solid Roller): 253/260, 111 LDA, .734/.732

So anyway, here are some numbers:
Small Cam
Small Bore/Long Stroke:
592 tq @ 3500 rpm
547 hp @ 5300 rpm
Avg: 551 tq/455 hp

Big Bore/Short Stroke:
589 tq @ 3600 rpm
549 hp @ 5400 rpm
Avg: 550 tq/455 hp

Big Cam
Small Bore/Long Stroke:
643 tq @ 4600 rpm
717 hp @ 6600 rpm
Avg: 612 tq/578 hp

Big Bore/Short Stroke:
636 tq @ 5400 rpm
727 hp @ 6400 rpm
Avg: 609 tq/576 hp

So my question is… does it really matter?!?!

And obviously the “correct” solution is the big bore AND the long stoke.

If someone is really bored, they could enter the numbers from the magazine article into a chart and we could do a graphical side-by-side comparison. (I’m not that bored. )

Just thought I would throw this information out since usually magazines tend to do BS comparisons. See… http://forums.tccoa.com/showthread.php?t=64304

p.s. These are the only two magazines I have purchased in something like the last 5 YEARS!!! And now I remember why.

So finally, (sorry this is so long), what is everyone’s opinion on their test? Agree? Is it ? Thoughts/opinions.

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post #2 of 22 (permalink) Old 05-11-2005, 07:33 AM
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post #3 of 22 (permalink) Old 05-11-2005, 07:46 AM
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post #4 of 22 (permalink) Old 05-11-2005, 07:59 AM
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Remember, There is no replacment for displacement, regardless what is done to get the extra displacement, being stroking or increasing the bore.

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post #5 of 22 (permalink) Old 05-11-2005, 08:05 AM
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I would rather opt for a smaller stroke and larger bore, as there is less chance to snap a rod.
But then, too large of a bore can increase the risk for premature cylinder wall failure.

So. Yeah, just get a Big Block Ford :-) Have the Long Stroke, and Big Bore :-)

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post #6 of 22 (permalink) Old 05-11-2005, 08:23 AM Thread Starter
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I have a 472 (.060 over 460) in my truck, a 472 in my boat, and a 472 on an engine stand in my shop.

(The one on the engine stand is getting prepped for a 6-53 blower and will go into my truck. )

Mmmmmmm Cubic inches and Roots blowers....

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post #7 of 22 (permalink) Old 05-11-2005, 08:53 AM
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... back to work everybody, nothing to see here.
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post #8 of 22 (permalink) Old 05-11-2005, 09:52 AM
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Between the two, I'd prefer a big bore engine (my 351C is only .030 over, though. ), but as the saying goes, I'd rather be blown than stroked!

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post #9 of 22 (permalink) Old 05-11-2005, 01:38 PM
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Quote:
Originally Posted by SloMo228
but as the saying goes, I'd rather be blown than stroked!
Keep that to yourself, I prefer being blown AND stroked!










.... So i got a dirty mind..

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post #10 of 22 (permalink) Old 05-11-2005, 02:50 PM Thread Starter
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As does everyone else on this board... you just posted what we were all thinking!!!

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post #11 of 22 (permalink) Old 05-11-2005, 11:19 PM
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I don't think it's a valid comparision to the mod motor. The reason being that the chevy BB's don't have as much valve shrouding as we do.




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post #12 of 22 (permalink) Old 05-12-2005, 02:49 AM
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Quote:
Originally Posted by GreenBird
I don't think it's a valid comparision to the mod motor. The reason being that the chevy BB's don't have as much valve shrouding as we do.
and its a chevy

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post #13 of 22 (permalink) Old 05-12-2005, 06:12 AM Thread Starter
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AND why I said to exclude the mod motor.

I was basically wanting a discussion on the theory of bore vs stroke but the same cu in. This was the first time I've seen someone just change the rotating assembly and do a comparison. I found it intersting that it looks like overall it really didn't matter.

But I guess nobody really wants to discuss it.

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post #14 of 22 (permalink) Old 05-12-2005, 08:50 AM
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I'll discuss it!!!! Saw that but decided not to post to prevent a war. I thought it was much better written than the MM&FF ones. I can't argue the numbers as they are very close. I just wish I could make that NA.

People have been stroking the 5.0 for years for more power. I think as long as the ratio isn't too far off and the intake/heads can feed the displacement, either option is worthy. At least on pushrod motors, swapping out a stroker rotating assembly is cheaper than reworking the block for a larger bore, if possible.


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post #15 of 22 (permalink) Old 05-12-2005, 08:58 AM Thread Starter
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The one thing that REALLY suprised me is that the peak rpm's didn't change as much as I thought they would. It only seemed to be noticible with the big cam. Then it was almost a grand lower rpm with the small bore/long stroke coming in at a lower rpm.

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post #16 of 22 (permalink) Old 05-12-2005, 09:05 AM
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Quote:
Originally Posted by 94 Daily Driven 4.6L
The one thing that REALLY suprised me is that the peak rpm's didn't change as much as I thought they would. It only seemed to be noticible with the big cam. Then it was almost a grand lower rpm with the small bore/long stroke coming in at a lower rpm.
Wouldn't the combustion chamber size make a difference in this particular application?

I think that is ultimately what the mod motor guys are getting at. Since their combustion chambers are a little screwed up they can't benefit as much from the over-stroke as they can from the over-bore. In this case it almost looks like the over-bore isn't taking as much advantage because of the combustion chamber. I would be curious to see how this would all compare if you matched those to each application.
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post #17 of 22 (permalink) Old 05-12-2005, 09:22 AM Thread Starter
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I think the problem with the mod motor is a combination of things. IMHO (and others…) the major issue being the bore spacing (it's tight) and the shrouding of the valves. So you can’t really go too big, and to get cu in, you have to stroke. And that means high piston velocity, and high side loads. But that is why I didn’t want to really go into the mod motor for this specific post. It has limitations that are inherent with the design of the block.
But it is just a matter of time before the right combination shows up (IMHO).
One thing I liked about the test was that they used the same components (and some pretty good components to say the least). BBC Aluminum CnC'd heads probably aren't too cheap.
I may have to enter all that data and make it into a line chart. That would probably help a lot more at looking at the differences. But goodness, that’s a lot of data to enter.

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post #18 of 22 (permalink) Old 05-12-2005, 10:10 AM Thread Starter
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Well that was a waste of time...

Talk about an identical curve!



I still have to do the "big cam"... in which the differences show up a little more, I think.

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post #19 of 22 (permalink) Old 05-12-2005, 10:33 AM Thread Starter
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And now the "Big Cam"...


It looks like up to 5700 rpm, the small bore/long stroke is slightly better than the large bore/short stroke. Then they cross.

So I guess that it depends on the rest of the drivetrain (gear seperation, etc) as to which would be "better" in a drag race. Is it better to have more power for just 1,000 rpm at the top end, or for 2700 worth of rpm in the midrange.

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post #20 of 22 (permalink) Old 05-13-2005, 02:21 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L
Is it better to have more power for just 1,000 rpm at the top end, or for 2700 worth of rpm in the midrange.
I think your sig answers that.


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post #21 of 22 (permalink) Old 05-13-2005, 02:58 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L
Is it better to have more power for just 1,000 rpm at the top end, or for 2700 worth of rpm in the midrange.
With that little difference, I'd go with whichever was cheaper.




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post #22 of 22 (permalink) Old 05-13-2005, 05:20 PM
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While either does have positive sides to it, keep in mind a BBC has much higher flowing heads. The head flow problems on 2V modulars are the main reason the strokers aren't doing as well. Ditto for the 5.4's, where it is compunded by the intake situation.

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