Big bore short stroke vs. small bore long stroke
Moderator: Team
Big bore short stroke vs. small bore long stroke
all things being fairly equall, which makes the most power? has anyone done an actuall back to back optimized test? i am curious as to whether if its the same cubic inches, does it really even matter? lets say you have an 8000-8500 rpm max and 360 ci. which would be the best combo?
-
- Guru
- Posts: 5566
- Joined: Sun Feb 19, 2006 10:19 am
- Location: MA
-
- Guru
- Posts: 1094
- Joined: Thu Sep 13, 2007 1:54 pm
- Location: TX
When everything else in the engine is taken to its logical conclusion, then the bigger bore - short stroke will make more power and spin faster. The most obvious benefit to the big bore is it allows a larger intake valve.
It seems to me that most Pro Stock motors are designed around the largest bore they can fit in the engine and the stroke is what ever it takes to get to 500cid. Others here would know better than I do but I think its something like a 4.7" bore and a 3.6" stroke. If you are talking a low rpm street motor then a longer stroke might be more forgiving of incorrect gearing but in a race motor its been proven over and over to go with the big bore.
It seems to me that most Pro Stock motors are designed around the largest bore they can fit in the engine and the stroke is what ever it takes to get to 500cid. Others here would know better than I do but I think its something like a 4.7" bore and a 3.6" stroke. If you are talking a low rpm street motor then a longer stroke might be more forgiving of incorrect gearing but in a race motor its been proven over and over to go with the big bore.
Unless RPM is restricted, or there are induction restrictions, the big Bore/short Stroke engine wins every time.
Mike Jones
Jones Cam Designs
Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
Jones Cam Designs
Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
-
- New Member
- Posts: 1
- Joined: Wed Nov 07, 2007 4:24 pm
- Location: Kennesaw, Ga
- Stan Weiss
- Vendor
- Posts: 4801
- Joined: Tue Feb 20, 2007 1:31 pm
- Location: Philadelphia, PA
- Contact:
What do you normally use for "C"?
Code: Select all
Bore = 4.165 Stroke = 3.3
Equation (b^2*s^.5*const)*8
Variable Value Evaluated Equation
3.800000000000 957.9890941087856
3.850000000000 970.5942137681117
3.900000000000 983.1993334274378
3.950000000000 995.8044530867638
4.000000000000 1008.40957274609
4.050000000000 1021.014692405416
4.100000000000 1033.619812064742
4.150000000000 1046.224931724068
4.200000000000 1058.830051383394
Bore = 4.7 Stroke = 3.6
Equation (b^2*s^.5*const)*8
Variable Value Evaluated Equation
3.800000000000 1274.1499744793
3.850000000000 1290.915105722448
3.900000000000 1307.680236965597
3.950000000000 1324.445368208746
4.000000000000 1341.210499451894
4.050000000000 1357.975630695043
4.100000000000 1374.740761938192
4.150000000000 1391.50589318134
4.200000000000 1408.271024424489
- John Wallace
- Guru
- Posts: 1511
- Joined: Tue Jan 04, 2005 10:20 am
- Location: was Central Illinois - Now in Sunny Florida!
- Contact:
Big bore short stroke vs. small bore long troke.
This is one of those on going debates. I favor the big bore short stroke, for the obvious reason, big bore allows larger valves, or take advantage of the better cyl. heads. David Reher addresses this question in his articles he writes for National Dragster. He states, torque is being applied by either a large surface area or long stroke, by engines of equivalent displacement. He argues the common belief that the longer stroke creates more torque at a given RPM. In essence the larger bore will create the same torque as a long stroke. Before the question arises, rod length is not an issue, it plays a small part in the equation. You can read it at rehermorrison.com/techTalk. RPM is basically a product of the bore and stroke combination and how much power is made in that range is determined by the induction system(ie. cyl heads, int. manifold, and carburetor) and cam selection. Pro Stock engines run very large bores and very strokes to acheive their cu. in. limit. The cyl. heads are what allows them to make the power and the stroke allows them to RPM to acheive maximum piston speed. Oversimplified RPM is Horsepower, the higher you can twist it the more power you will make. As far as torque the Pro Stocks explode off the line. This opens the other on going debate HP vs. Torque but that is another thread and can be on this sight.
Big bore = more valve curtain area / higher breathing capacity
Small bore = sonic choke occurs at lower rpms than for big bore
If you are going for max effort, choose the bore that will give you the most valve curtain area possible and where that valve curtain area goes into sonic choke just past your max desired RPM.
Small bore = sonic choke occurs at lower rpms than for big bore
If you are going for max effort, choose the bore that will give you the most valve curtain area possible and where that valve curtain area goes into sonic choke just past your max desired RPM.
-
- Member
- Posts: 154
- Joined: Thu Dec 13, 2007 10:22 am
- Location: East Side Detroit
Re:
Question, (I know this is a really old thread) with everything else being fairly equal, which is more desirable in a N/A application:axegrinder wrote:When everything else in the engine is taken to its logical conclusion, then the bigger bore - short stroke will make more power and spin faster. The most obvious benefit to the big bore is it allows a larger intake valve.
It seems to me that most Pro Stock motors are designed around the largest bore they can fit in the engine and the stroke is what ever it takes to get to 500cid. Others here would know better than I do but I think its something like a 4.7" bore and a 3.6" stroke. If you are talking a low rpm street motor then a longer stroke might be more forgiving of incorrect gearing but in a race motor its been proven over and over to go with the big bore.
i.e. max effort big chief headed combinations that limited to a cast single intake. A 550 ci big chief headed combination that peaks ~ 8500rpm or a 650 ci big chief headed entry that peaks ~ 7500rpm?
Both wearing the exact same cylinder heads, bore size, intake and camshaft. Both would be in vehicles of equal weight and transmissions.
Would the smaller 550 ci combination be more desirable with it's lighter weight internals, allowing it to rev quicker to it's powerband?
-Poppy