Originally Posted by sb427f-car

Absolutely great points, but I still think you are missing THE point of the test.

More BORE or more STROKE ONLY

The article didn't disagree with the ability of the heads given larger valves for more bore. Mater of fact they even stated this with examples from Pro Stock motors and NASCAR Cup motors. What they did point out was production engines go the reverse because of less emmissions and butter cylinder filling characteristics, FOR THE APPLICATION that is.

You guys keep changing the test as there is only one variable they were trying to test, the length of the stroke.

Also mentioned was the small block theory where changes in bore and stroke are more pronounced. Will we see a comparision of this? Be interesting.

Yet another side bar...Reher-Morrison did a simlar test with two monster sized 610+ (I forget the exact cubes) but results were very similar. Total difference in HP, 20.

Again, I am not advocating that your sponsors and builders are wrong, I'm just pionting out the fact that you keep changing the test. With both mills optimized for the application, I too agree that the Bore motor will probably win out, but after reading the article, it makes more sense as to why you should start @ the top side of the motor and work back, as you have implied.

Accept nothing, challeng everything!!!

Originally Posted by sb427f-car

The following has EXCERPTS (paraphrasing) from HotRod Mag's June 2005 issue. A premedia publication. Article by David Freiburger and photography (which I don't have sorry fells) by author.


First of all...we've all heard for years the above mentioned "theories" but where have we all seen them? Various magazines and or discussing with various gear heads, ect. Stop and think for a second, have you ever challenged the idea that Bore > Stroke or vise versa? I know that I had even bought into most of these ideas, until last evening so...without further adue.

First, the motors:

Two, for all intensive purposes, equal cubic inches, big block chevy's. The big bore motor measures up @ 4.560x3.766, displacing 492. The big stroke motor measures up @ 4.280x4.250 for 489 cubes. The variance is .60%, or really negligable. Strokes for the math challenged are different by nearly half an inch (.484) and the bore is over a quater inch (@ .280). The other decently significant difference between the motors was the rod ratio. This was to keep the engines as "close to practical" for the experiment in the rod ratio. The short stroke used a rod shoter than typical that measured 6.135". The long-stroke was 6.535". This put the rod ratios at 1.63:1 and 1.54:1. Finishing out the short block were identical fasteners, head studs, Scat cranks and rods, a custom set of J&E pistons made specifically for the test. Both motors were topped off with AFR's 335 CNC-ported heads and the bottom end was buttoned up with a Milodon pan for Gen V BBC filled with Royal Purple 5w30.

When the motors were tested two different cams were used. One cam was a tame hydro roller, the other a more perf. oriented solid roller. Hydro roller was speced @ 218/224 @ .050 on 110 LDA with .510/.510 lift, which is pretty mild for a BB. The solid roller speced out at a more normal hi po cam for a big block (though still decently mild) @ 253/260 @ .050 ground on a 111 LDA with .734/.732 lift. Both the cams were run on a 1.7 rocker. The only difference was the lash seetings were moved around to alter the duration to effectively find the best AVGERAGE power in both motors. (I'm not going to get into this...read the article ).

Inconjunction with the cams...Cometic custom-mad MLS head gaskets were used to alter the comp. ratio. For the small cam, a monster thick .125" gasket was used on the big bore, to yield a 9.076:1 comp. ratio and on the big stroke a 9.039:1 comp ratio. For the big cam, a .040" gasket was used yielding 10.87/10.83:1 respecitively.

Induction was through a 975-cfm race demond carb atop an Edelbrock Performer RPM for the small cam. Same carb but a Weiand Team G single-plane was swapped in for the big cam. The set up exhaled through Hooker headers with 2" primaries and 18" extentions with Flowmasters (small cam only).


The test results

As most stated...we'd think that the big bore motor will make more HP with more RPM and the long stroke motor will make more TQ, especially down low.

Out of the box NO difference was really noticed. After some tuning, only minimal "wiggle was seen in the curves that supported the traditional theories: The long stroke made more low end and the short stroke made more top end, but not nearly the margin you've been lead to believe all these years. We're talking about differences of 7lb-ft and 12hp @ most." The author points out that even this much difference could be attributed to the very negligible difference of 4ci.

Upon further examintation of the short blocks...

The common theory is that a longer stroke acts as a longer lever arm on the crank and therefore offers better torque than a short block. Though this is not what the test discovered. What factors into this purhaps? A little thing called piston speed. Piston speed = (STROKE x RPM) / 6. So...@ 7000 RPM, the 4.250" stroke has a mean piston speed of 4,958 feet per min. The short stroke has a mean piston speed of 4,393 fpm. "That's a 11.4% reduction. Long-storkes with increased mean piston speed diossipates combustion press. more quickly than the slower piston speed of the shorter stroke, and is there fore less effective @ power production, but the concerpt of Brake Mean Effective Pressure (BMEP) conflicts with that argument. BMEP is the theoretical average pressure on the piston throughout the stroke that is required to sustain the level of horse power. BMEP = (indicated torque x 150.8) / displacement, so you can see that stroke DOES NOT equal into the equation."

The power curves

Small Cam, long stroke: Pk Tq @ 3500 and 3600 of 592, Pk HP @ 5300 of 547. Avg. of 551 TQ and 455 HP

Small cam, big bore: Pk Tq @ 3600, 3700, 3900, and 4000 of 589. Pk HP @ 5400 and 5500 of 549. Avg. of 550 TQ and 455 HP.

Big Cam, long stroke: PK TQ @ 4600 and 5500 of 643, Pk HP @ 6,600 of 717. Avg. of 612 TQ and 578 HP.

Big cam, big bore: Pk Tq @ 5400 and 5500 of 636, Pk HP @ 6,300 of 727. Avg. of 609 TQ and 576 HP.

One thing that they did discover was the ring tention may have caused a slightly more frictional loss in the big bore motor, but these are the basics of the article and I'll leave it to the rest of you gear heads to read it yourself and come to your own conclusions. Now...do keep in mind that both motors were built to be nearly identical in every aspect and they did go some what against normal conventions of engine building. One other thing of interest is that Pro Stockers and NASCAR motors tend to lean towards the Big Bore, long rod, short stroke method but this is due in part to valve size, bearing speed (assicated with piston speed for longevity) and the constraints of the rule books. Hope this was informative. Again. This is in the June 05 (titled The Great Bore vs. Stroke Showdown on page 98 and copyrighted 2005) issue of HotRod and was excerpted from author David Freiburger's article. I am in no way associated with HotRod, Primeda, or it's staff. This was for educational purposes only.

Originally Posted by sb427f-car

The following has EXCERPTS (paraphrasing) from HotRod Mag's June 2005 issue. A premedia publication. Article by David Freiburger and photography (which I don't have sorry fells) by author.


First of all...we've all heard for years the above mentioned "theories" but where have we all seen them? Various magazines and or discussing with various gear heads, ect. Stop and think for a second, have you ever challenged the idea that Bore > Stroke or vise versa? I know that I had even bought into most of these ideas, until last evening so...without further adue.

First, the motors:

Two, for all intensive purposes, equal cubic inches, big block chevy's. The big bore motor measures up @ 4.560x3.766, displacing 492. The big stroke motor measures up @ 4.280x4.250 for 489 cubes. The variance is .60%, or really negligable. Strokes for the math challenged are different by nearly half an inch (.484) and the bore is over a quater inch (@ .280). The other decently significant difference between the motors was the rod ratio. This was to keep the engines as "close to practical" for the experiment in the rod ratio. The short stroke used a rod shoter than typical that measured 6.135". The long-stroke was 6.535". This put the rod ratios at 1.63:1 and 1.54:1. Finishing out the short block were identical fasteners, head studs, Scat cranks and rods, a custom set of J&E pistons made specifically for the test. Both motors were topped off with AFR's 335 CNC-ported heads and the bottom end was buttoned up with a Milodon pan for Gen V BBC filled with Royal Purple 5w30.

When the motors were tested two different cams were used. One cam was a tame hydro roller, the other a more perf. oriented solid roller. Hydro roller was speced @ 218/224 @ .050 on 110 LDA with .510/.510 lift, which is pretty mild for a BB. The solid roller speced out at a more normal hi po cam for a big block (though still decently mild) @ 253/260 @ .050 ground on a 111 LDA with .734/.732 lift. Both the cams were run on a 1.7 rocker. The only difference was the lash seetings were moved around to alter the duration to effectively find the best AVGERAGE power in both motors. (I'm not going to get into this...read the article ).

Inconjunction with the cams...Cometic custom-mad MLS head gaskets were used to alter the comp. ratio. For the small cam, a monster thick .125" gasket was used on the big bore, to yield a 9.076:1 comp. ratio and on the big stroke a 9.039:1 comp ratio. For the big cam, a .040" gasket was used yielding 10.87/10.83:1 respecitively.

Induction was through a 975-cfm race demond carb atop an Edelbrock Performer RPM for the small cam. Same carb but a Weiand Team G single-plane was swapped in for the big cam. The set up exhaled through Hooker headers with 2" primaries and 18" extentions with Flowmasters (small cam only).


The test results

As most stated...we'd think that the big bore motor will make more HP with more RPM and the long stroke motor will make more TQ, especially down low.

Out of the box NO difference was really noticed. After some tuning, only minimal "wiggle was seen in the curves that supported the traditional theories: The long stroke made more low end and the short stroke made more top end, but not nearly the margin you've been lead to believe all these years. We're talking about differences of 7lb-ft and 12hp @ most." The author points out that even this much difference could be attributed to the very negligible difference of 4ci.

Upon further examintation of the short blocks...

The common theory is that a longer stroke acts as a longer lever arm on the crank and therefore offers better torque than a short block. Though this is not what the test discovered. What factors into this purhaps? A little thing called piston speed. Piston speed = (STROKE x RPM) / 6. So...@ 7000 RPM, the 4.250" stroke has a mean piston speed of 4,958 feet per min. The short stroke has a mean piston speed of 4,393 fpm. "That's a 11.4% reduction. Long-storkes with increased mean piston speed diossipates combustion press. more quickly than the slower piston speed of the shorter stroke, and is there fore less effective @ power production, but the concerpt of Brake Mean Effective Pressure (BMEP) conflicts with that argument. BMEP is the theoretical average pressure on the piston throughout the stroke that is required to sustain the level of horse power. BMEP = (indicated torque x 150.8) / displacement, so you can see that stroke DOES NOT equal into the equation."

The power curves

Small Cam, long stroke: Pk Tq @ 3500 and 3600 of 592, Pk HP @ 5300 of 547. Avg. of 551 TQ and 455 HP

Small cam, big bore: Pk Tq @ 3600, 3700, 3900, and 4000 of 589. Pk HP @ 5400 and 5500 of 549. Avg. of 550 TQ and 455 HP.

Big Cam, long stroke: PK TQ @ 4600 and 5500 of 643, Pk HP @ 6,600 of 717. Avg. of 612 TQ and 578 HP.

Big cam, big bore: Pk Tq @ 5400 and 5500 of 636, Pk HP @ 6,300 of 727. Avg. of 609 TQ and 576 HP.

One thing that they did discover was the ring tention may have caused a slightly more frictional loss in the big bore motor, but these are the basics of the article and I'll leave it to the rest of you gear heads to read it yourself and come to your own conclusions. Now...do keep in mind that both motors were built to be nearly identical in every aspect and they did go some what against normal conventions of engine building. One other thing of interest is that Pro Stockers and NASCAR motors tend to lean towards the Big Bore, long rod, short stroke method but this is due in part to valve size, bearing speed (assicated with piston speed for longevity) and the constraints of the rule books. Hope this was informative. Again. This is in the June 05 (titled The Great Bore vs. Stroke Showdown on page 98 and copyrighted 2005) issue of HotRod and was excerpted from author David Freiburger's article. I am in no way associated with HotRod, Primeda, or it's staff. This was for educational purposes only.