What's you're opinion... stroke vs. bore
 

Let's say, for comparison sake, that we were comparing 2 engines, both were measured at approximately 502 cid. One motor is a 4.25 stroke and 4.34 bore, the other is a 4.00 stroke 4.47 bore. All other components are the same.

What's your opinion on these motors?
One better for lighter boats?
Or they both the same... a cube is a cube no mater how you measure it?
Are they going to have different aspiration needs?

I'm curious if the runner velocities do anything weird on the large bore/short stroke combos, and how bad piston speed gets on the opposite.

Wow , long time since I've seen your name.

This subject has been rehashed many times. Some people believe more stroke is better, some more bore, and others say cid is cid.

None of the less, will be a good subject for winter time.

How does the 8.1 run compared to the 8.2, guessing the larger bore would breath better and make more power across the board depending on cam, intake, heads and exhaust.

I would say Bore for unshrouding reasons, but I also would say if you are building engine and machining parts why not spend a few bucks more and do both? to me I would rather have the gen^ block with bigger bore for future builds worse case...

Stroke give you mechanical leverage. (rod center is farther from the crank center) but also increases rotational load. If I had to do just one for the most improved performance, I would do stroke for a heavier boat.
I would go the shorter stroke and bigger bore in lighter boat to possibly increase rpm response (reduced rotational load).

OR, a couple of beers later, the first crank might be in the second motor, rod length and wristpin height allowing! :cool-smiley-011:

:ernaehrung004::popcorn:

Kinda like puttin money on a drunken bar brawl with two guys who have the same strength however are a foot difference in height. Lol.

All bs aside first thing that comes to mind is the longer the stroke would have a broader power band with more torque at lower rpm while the shorter stroke making its peak hp and torque at a higher rpm. Not sure if one vs the other would ultimately have skirt wear prior to the other giving same hours of use. Another thought is the longer stroke would also increase swept volume in the cylinder but personally only see advantages if was to be turbocharged etc. long jevity one vs the other???

Good question. While you are at it hopefully someone explains why Mercury always uses the 557 cu in platform.

what about aspiration? Does anyone think there could be a difference in need for aspiration? Would the shorter stroke benefit more from a larger volume runner, and the longer stroke benefit more with a slightly smaller runner volume? I'm thinking it would benefit more from the velocity, but the difference is prolly more theoretical than physically realistic.

tim, agreed but you're venturing outside the bouns of the scenerio... bor or stroke, not bore and stroke. i think we all agree that both is better. :cool-smiley-011:

Take a look at this graph.
Combustion pressure greatly falls off (pressure decay) right after TDC and is near nill by the time you get to the area the longer crank arm would give you ' much more leverage.'

On the bigger bore side of this subject, don't forget, the larger piston has more surface area than a smaller one. Same psi against a larger surface area = more force.

Just throwing in info without really getting into a possible debate on this subject.

http://performancetrends.com/Definit...essure-Lrg.gif

that depends now on what the fuel delivery is,carb or port injection.

I rather be stroked,than bored.:Dwe are talking about our girlfriends,right.

I guess I just get the most for my money if it's apart just do both.... be done with it...

Largest bore shortest stroke with the shortest Rod shortest deck height is how you make power. The longer stroke will have more frictional losses due to the longer stroke. also with the shorter stroke/ piston travel you can spin the motor 10,000 rpm and not have to worry about piston speed. Just a little more food for thought in a big block the larger the piston you can stuff in the bore the stronger the piston. :-)

The 4" stroke 4.47 bore is a better motor. But both will be very similar.

Tim, technically speaking, a 502 stroker motor is doing both. Keep in mind, you cant bore a Gen IV 454 to 4.500 bore. Besides, I'm also looking at engines available to purchase. So doind both isnt an option. Plus im looking at a higher cost for the shorter stroke.

New or used engines, I guess the other issue for me is used engines, I will NEVER buy used engines again, I wanna know exactly what I got going on...

I would go with bigger piston..thats not a 454 block and gives you more options later....

My pick would be large bore short stroke. Id simply prefer a 502 block setup, over a stroked 454.

i have seen some 489s and 496s make good power but imo the best bang for the buck is bigger bore vs bigger stroke.it unshrouds the valves and helps airflow.

OP regardless of price I would steer clear of a 454 with a 4.340 bore. Sounds like a very worn out motor to me.

I just noticed that as well. Yea I would stay away from that setup. If it's a chevy block it's dunzo..

I noticed this at first but thought it may have been a typo and I would let someone else comment about it. Since it went 3 pages and not a mention of it thought it better to. With that said. There are some old 427 tall deck blocks that will go 4.600 it's only certain block numbers that will do it. But that's old school stuff and not really worth the effort in my opinion.

Hmm... you guys are throwing in a lot of assumptions. lol Nobody ever said anything about a used engine... or a 454 bored to it's limits.

Let's not let or imaginations get carried away, try to stick to the scenerio in question... This is a STROKE vs. BORE thread, not "Factory 502" vs. "Worn out 454 stroker" comparison. Strictly speaking... I was looking for opinions on how to make power... stroke or bore. I guess I could've used different measurements to make it more realistic to what i'm looking at, but the 502 cid seems to be the most common stroke vs. bore comparison i could come up with for this thread.

Thanks everyone for your input. I still enjoy all the other considerations.:popcorn:

Mike Tkach happens to have one of those sitting around he going to build something out of. Old 427 tall deck 4 ring truck block .

there are many variables that need to be addressed such as compression ratio, cylinder head flow, cam profile... etc.. intended usage.. but IMO bore size influences HP while stroke influences torsional twist (torque).. again this is a general vague statement... many factors unanswered

You said availible for purchase, that sounds used to me... If not then post more detailed info and it does seem the bigger bore is a better choice over stroke, you left many variables on the table for us to assume or guess at.

Bore stroke
 

BIB,

We performed simulations to gather data addressing your questions. Both are based on a BBC.
The example engines were;

Big bore / short stroke;

Bore __4.500”

Stroke_4.000”

Rod length_6.385

Rod Ratio__1.596

Displacement__508.939 CID


Small Bore / Long Stroke;

Bore__4.365”

Stroke__4.250”

Rod Length__6.784”

Rod Ratio__1.596

Displacement_508.789 CID

Rod lengths adjusted to equalize the rod ratio variable.

When comparing the peak piston velocity data stream from both engines the long stroke is

6998.3 FPM
Vs
6586.6 FPM_____ for the short stroke.

While the piston speed is 6.25% higher (+411.7 FPM) in the long stroke engine, all other parameters, including CFM demand at the intake and cfm demand at the piston crown are identical in both engines. Airflow requirements are the same.
This would dispel the myth that long stroke engines and higher piston speeds “eat up head flow and camshaft” at a greater rate than short stroke engines. Airflow demand is based upon swept volume and RPM

It would appear the tradeoffs of bore unshrouding vs. frictional loss etc. would result in a zero sum game however the answer wasn’t that straightforward.

Bob

Swept volume is swept volume... no ifs and or buts about it... the bore size vs stroke question I understood to be 4.470/4.00 vs smaller bore vs longer stroke... the 4.470 would allow for better flow and with that being said!! WTF put a 4.250 crank in it too... these's no replacement for displacement!!! says the oldest guy in med school

the real question one should ask is where is the point of diminished return??? :wizard:

adk,

It gets more interesting when you run the full simulation on these two engines. The results are not exactly what you would expect. I'll post the sim asap

Bob

Bigger bore shorter stroke add more rpm and CRUSH the stroker motor!!! says the oldest student in med school!!! lmfao!

swept volume is swept volume... as I said earlier... the needs are both the same... however.. the big bore/shorter stroke has the potential to dominate over the counterpart... that being said a cylinder head with a bit better flow characteristics would be of an advantage to the BB/SS engine... now put on your thinking cap and see where I'm going with this...

It's been tested and with everything else the same there is no significant difference in power or torque

you would RPM the shorter stroke engine thus making a notable difference in HP just sayin

i remember reading an article steve schmit wrote a long time ago,it addressed a class that was limited to 400 cu in.he said he went with a larger bore and smaller stroke because it had less shrouding around the valves,he was winning so maybe he was right.that was a long time ago.

I see alot of big power forced induction engines today running smaller stroke and big bores. Maybe it's a combination of the fact the larger bores help unshroud the valves , along with modern valvetrain technology to allow them to spin the small stroke setup to a higher rpm and more reliably , than possible years ago. Idk.

Guess we should've addressed the race vs. pleasure variable.

RPM is limited in most pleasure cases. In most engines, you're not going to just keep raising the rpm. Typically speaking your going to run around 5200 - 5800 peak. Over that RPM i could understand how that would be an advantage with a 12,000 RPM funny car.
Plus just because your pulling more HP doesn't mean you've got the torque to keep a boat going. Which brings us to size of boat/application questions. And I think most people running large cid engines don't run flat bottom 18 foot race boats. Plus.... look to my left... if I'm the one looking for opinions about bore vs. stroke, i'm talking about a very heavy twin engine baja. :cool-smiley-011:
I like the stats above about flow. Originally i was thinking a larger bore would require the same volume in a shorter stroke would require more volume, but if RPM is static, the flow would be the same.. still need 502 cubic inches of air for each rotation.

Biggest cubes you can afford and right cam for TQ....