Dynomation Enthusiasts?

[RevTheory]

Any of you guys with a good sym program bored this weekend and feel like running a comparison? I'm curious to see how the torque curves overlay between a 350 SBC and a 340 SBC, all else being equal. Both at 10.5:1 compression.

4.03 in bore
3.48 stroke
5.7 rod

vs.

3.8 in bore
3.75 stroke
5.7 rod

RPM Air-Gap intake
750 vacuum secondary carb
1 5/8, long-tube primaries, 2.5 in collectors, 18 inch collector length
1.94 x 1.5 valves- I have a good guestimate on flowz but I don't know how many inputs are available.
Hyd/roller: 276/278 at .006, 223/225 at .050, 142/146 at .200, .557/.536 valve lift with 1.65/1.52 rockers, 107 LSA, 103 ICL
2,500 to 6,500 rpm?

If interested, let me know what other parameters are needed for a test and I'll give you what I can.

Many thanks!

[jacksoni]

I ran it in EAPro. 350 better by 13lbsft peak, 8 lbsft avg; 4hp peak, 6 hp avg. Above 5600 essentially the same and dropping fast. How long are "long tubes" and not being a V8 guy, I am thinking the RPM airgap is a single plane (sorry)? EAPro uses some generic manifold specs if I don't enter port lengths, manifold tube lengths etc. I might be able to attach the graph if you want.

[RevTheory]

I'm having a hard time finding accurate runner dimensions for that intake but it's a dual-plane with a notched divider. IIRC, the primaries average ~36 inches in length. Estimated head flowz are as follows with 1.94 x 1.5 valves:

.100- 67/56
.200- 134/108
.300- 184/140
.400- 216/175
.500- 237/186
.600- 244/188

This is really just an experiment to see if the torque curve changed much and if swinging a little more stroke with a lower rod/stroke ratio would be beneficial to turning 35 inch tires with a 4-speed stick. Being down 15 cubic inches right out of the gate probably doesn't help much.

Hp was dropping like a rock, huh?

Edit: I lost Engine Analyzer after a computer crash and a subsequent Windows 8 platform

[jacksoni]

Minor input mods done. Upper curve is the short stroke motor.

[RevTheory]

Wow- that's not what I was expecting. I appreciate you doing that for me. Thank you!

[jacksoni]

Gotta remember this is just computer HP. Real world may be different......

It may be the program is seeing the bore size as shrouding valves or something; the engine builders here may be able to point at other issues.

I just ran it in Pipemax 3.7. It predicted virtually the same HP peak as EAPro and a similar but slightly larger drop in peak HP with the long stroke engine. I did not look at other parameters. They don't seem to like the small bore is my impression. Then again, 10ci is 10ci and at 1.2hp/ci or so is 12 hp which is about the difference.

[jacksoni]

Along the lines of the displacement issue, I just re ran it adjusting the bore up to 3.88 so the displacement is pretty much the same. Then the curves virtually overlay with the short stroke engine still winning by a hp or two. Six of one, half dozen of other. Goes to the argument, of which there is a lot, that a long stroke engine will make more torque with same CI ( long arm= more torque.)

[RevTheory]

Gotta remember this is just computer HP. Real world may be different......

It may be the program is seeing the bore size as shrouding valves or something; the engine builders here may be able to point at other issues.

I just ran it in Pipemax 3.7. It predicted virtually the same HP peak as EAPro and a similar but slightly larger drop in peak HP with the long stroke engine. I did not look at other parameters. They don't seem to like the small bore is my impression. Then again, 10ci is 10ci and at 1.2hp/ci or so is 12 hp which is about the difference.

Very true! It's not looking so bueno from a "proof of concept" standpoint, though. Maybe some of the guys who've hopefully dynoed this stroked 305 combo before can chime in when they get done with the EMC final stretch.

Another strike against the smaller-bore stroker is that if I just did a 355, the 4.03 bore opens up my cylinder head options so I'm not stuck with 1.94/1.5 valves.

Then again, everyone and their brother-in-law as done 350s and 383s to death. What to do, what to do...?

Thanks again.

[maxracesoftware]

Any of you guys with a good sym program bored this weekend and feel like running a comparison? I'm curious to see how the torque curves overlay between a 350 SBC and a 340 SBC, all else being equal. Both at 10.5:1 compression.

4.03 in bore
3.48 stroke
5.7 rod

vs.

3.8 in bore
3.75 stroke
5.7 rod

RPM Air-Gap intake
750 vacuum secondary carb
1 5/8, long-tube primaries, 2.5 in collectors, 18 inch collector length
1.94 x 1.5 valves- I have a good guestimate on flowz but I don't know how many inputs are available.
Hyd/roller: 276/278 at .006, 223/225 at .050, 142/146 at .200, .557/.536 valve lift with 1.65/1.52 rockers, 107 LSA, 103 ICL
2,500 to 6,500 rpm?

If interested, let me know what other parameters are needed for a test and I'll give you what I can.

Many thanks!

I'm having a hard time finding accurate runner dimensions for that intake but it's a dual-plane with a notched divider. IIRC, the primaries average ~36 inches in length. Estimated head flowz are as follows with 1.94 x 1.5 valves:

.100- 67/56
.200- 134/108
.300- 184/140
.400- 216/175
.500- 237/186
.600- 244/188

PipeMax v4.00 results :

Code: Select all

355.11515321 Cubic Inches
4.03 in bore
3.48 stroke
5.7 rod

600 RPM/Sec Dyno Test             Minimum        Average         Normal        Maximum
Peak HorsePower    @  5600 RPM      423.6          429.0          434.4          439.9
Peak Torque Lbs-Ft @  4200 RPM      448.9          458.4          464.2          470.1

HorsePower per CID                  1.193          1.208          1.223          1.239
Torque per Cubic Inch               1.264          1.291          1.307          1.324
Peak Torque BMEP in psi             190.6          194.7          197.1          199.6
Carb CFM at 1.5 in Hg.                575            640            673            705

========================================================================================


340.23448438 Cubic Inches
3.8 in bore
3.75 stroke
5.7 rod

600 RPM/Sec Dyno Test             Minimum        Average         Normal        Maximum
Peak HorsePower    @  5600 RPM      402.7          407.8          412.9          418.1
Peak Torque Lbs-Ft @  4200 RPM      426.7          435.7          441.2          446.8

HorsePower per CID                  1.183          1.198          1.214          1.229
Torque per Cubic Inch               1.254          1.281          1.297          1.313
Peak Torque BMEP in psi             189.1          193.1          195.6          198.0
Carb CFM at 1.5 in Hg.                551            613            644            675

[englertracing]

Gotta remember this is just computer HP. Real world may be different......

It may be the program is seeing the bore size as shrouding valves or something; the engine builders here may be able to point at other issues.

I just ran it in Pipemax 3.7. It predicted virtually the same HP peak as EAPro and a similar but slightly larger drop in peak HP with the long stroke engine. I did not look at other parameters. They don't seem to like the small bore is my impression. Then again, 10ci is 10ci and at 1.2hp/ci or so is 12 hp which is about the difference.

Very true! It's not looking so bueno from a "proof of concept" standpoint, though. Maybe some of the guys who've hopefully dynoed this stroked 305 combo before can chime in when they get done with the EMC final stretch.

Another strike against the smaller-bore stroker is that if I just did a 355, the 4.03 bore opens up my cylinder head options so I'm not stuck with 1.94/1.5 valves.

Then again, everyone and their brother-in-law as done 350s and 383s to death. What to do, what to do...?

Thanks again.

4.125 x 3.25

[RevTheory]

Sure sounds like these programs care less about the bore/stroke combo than they care about total cubic inches. They also seem a little more generous than I would expect to see on the dyno.

I appreciate your input

[jacksoni]

Larry has said that Pipemax is pretty good if EVERYTHING is right. See my prior about computer HP. Folks will argue interminably about how an engine propels a car down or around a track and its behavior that may be different than what is seen on the dyno (which generate its own set of arguments- "happy dyno", "conservative dyno" etc). Maybe the bore/stroke ratio doesn't make as much difference as many people think. Of course every time a parameter changes, something else is affected-cam timing, port sizes etc etc etc. Hard to truly make an apples to apples comparison. Like you said, bigger bore opens up head choices. Performance/race engine will have different specs than similar displacement street/emissions/mileage engine. Build what works for you.

[RevTheory]

Maybe this will help with my conundrum:

The engine is for a Jeep Cj-7 with 35 inch tires so it's not a rig that needs a rompin' stompin' 383+ engine. A well-prepped 350 is plenty adequate but I just wanted to see if a different bore/stroke combo would be more favorable for those tires.

I think 425 hp, 425 ft. lbs. is easily doable and won't be overkill; just wondering if the stroker version (although a little smaller) would fatten up the torque curve below peak. It doesn't appear that's going to be the case.

And then there's this article from Reher-Morrison http://rehermorrison.com/tech-talk-66-g ... /#more-381 and I belive Vizard always goes for bore for the same reasons stated in the article.

But there are some EMC teams that go for at least a squared bore/stroke combo so I'm still stuck at

I'm getting pretty close to "shut the hell up and build 350", lol.

[maxracesoftware]

Maybe this will help with my conundrum:

The engine is for a Jeep Cj-7 with 35 inch tires so it's not a rig that needs a rompin' stompin' 383+ engine. A well-prepped 350 is plenty adequate but I just wanted to see if a different bore/stroke combo would be more favorable for those tires.

I think 425 hp, 425 ft. lbs. is easily doable and won't be overkill; just wondering if the stroker version (although a little smaller) would fatten up the torque curve below peak. It doesn't appear that's going to be the case.

And then there's this article from Reher-Morrison http://rehermorrison.com/tech-talk-66-g ... /#more-381 and I belive Vizard always goes for bore for the same reasons stated in the article.

But there are some EMC teams that go for at least a squared bore/stroke combo so I'm still stuck at

I'm getting pretty close to "shut the hell up and build 350", lol.

for EMC , go with nearly squared bore/stroke combo for highest Points is usually a good choice

in PipeMax , i'm using same sets of RPM points that Peak TQ and Peak HP occur at
but in real-world, these 3 Engine Combos will be different

4.125" Bore x 3.250" Stroke

Code: Select all

347.46505623 Cubic Inches
4.125
3.250
5.7 rod

600 RPM/Sec Dyno Test             Minimum        Average         Normal        Maximum
Peak HorsePower    @  5600 RPM      416.6          421.9          427.2          432.6
Peak Torque Lbs-Ft @  4200 RPM      441.5          450.8          456.5          462.3

HorsePower per CID                  1.199          1.214          1.230          1.245
Torque per Cubic Inch               1.271          1.297          1.314          1.331
Peak Torque BMEP in psi             191.6          195.7          198.1          200.6
Carb CFM at 1.5 in Hg.                563            626            658            690


========================================================================================

355.11515321 Cubic Inches
4.03 in bore
3.48 stroke
5.7 rod

600 RPM/Sec Dyno Test             Minimum        Average         Normal        Maximum
Peak HorsePower    @  5600 RPM      423.6          429.0          434.4          439.9
Peak Torque Lbs-Ft @  4200 RPM      448.9          458.4          464.2          470.1

HorsePower per CID                  1.193          1.208          1.223          1.239
Torque per Cubic Inch               1.264          1.291          1.307          1.324
Peak Torque BMEP in psi             190.6          194.7          197.1          199.6
Carb CFM at 1.5 in Hg.                575            640            673            705

========================================================================================


340.23448438 Cubic Inches
3.8 in bore
3.75 stroke
5.7 rod

600 RPM/Sec Dyno Test             Minimum        Average         Normal        Maximum
Peak HorsePower    @  5600 RPM      402.7          407.8          412.9          418.1
Peak Torque Lbs-Ft @  4200 RPM      426.7          435.7          441.2          446.8

HorsePower per CID                  1.183          1.198          1.214          1.229
Torque per Cubic Inch               1.254          1.281          1.297          1.313
Peak Torque BMEP in psi             189.1          193.1          195.6          198.0
Carb CFM at 1.5 in Hg.                551            613            644            675

[MadBill]

I've posted it before, but here's a bore/stroke dyno comparison by Chevrolet Engineering, circa 1965. The solid line is a 4.25" x 3.46" 392 with 11.3:1 CR and the dotted one is a 4.09" x 3.76" 396 with 12.1:1 CR. Both used the same cam, heads, etc. Note the significant difference in HP, as much as ~30 HP, and friction torque, as much as 20 lb-ft.

BBC bore & stroke.jpg