Camshaft changes or not with stroke increased.

[blackflag]

Im curious if you had an engine with 4.185” bore X 3.280 stroke with a 2.100 intake valve to help with larger bore (361ci) that is cammed close enough, and a good enough combo to win on a consistent basis. Then built a 3.915” bore X 3.75 stroke with a 2.055 intake valve to help with shrouding (361ci) and tried to cam the engine to be competitive against the short stroke engine. How much would you have to change the duration and LSA, or would it want the same cam because it’s the same cubic inches? Thanks

[CamKing]

You would need to make a huge change in duration, and lobe centerlines

[Stan Weiss]

What is the rod length for each combination?

Stan

[Walter R. Malik]

Im curious if you had an engine with 4.185” bore X 3.280 stroke with a 2.100 intake valve to help with larger bore (361ci) that is cammed close enough, and a good enough combo to win on a consistent basis. Then built a 3.915” bore X 3.75 stroke with a 2.055 intake valve to help with shrouding (361ci) and tried to cam the engine to be competitive against the short stroke engine. How much would you have to change the duration and LSA, or would it want the same cam because it’s the same cubic inches? Thanks

I would use a few degrees more duration and a slightly wider separation if all the lobe profiles are from the same family.

[gruntguru]

Can we assume the longer stroke engine turns lower revs?

[blackflag]

Mike that’s good to know. The long stroke must need more time to get cylinders filled even though they are the same cubic inch. Stan both engines have 6” rods. We have 7 different 360s (3.280” 3.285” 3.268” 3.480” 3.50” 3.625” 3.75 strokes) with anything from 5.7” to 6.125” rods and are new to the 2 longest strokes. Have run the other combos for a very long time. Just wanted to try out a couple new combos to gain an edge at certain tracks. Thanks

[Stan Weiss]

The cam's duration is related to the FPM of the piston, not the RPM of the crank. The lift rate of the profile is related to the rod to stroke ratio.

Hi Rick,
Hope all is well

Good to see you posting here.

Stan

[PRH]

Since the displacement between the long and short stroke combos is the same, the area of the bores are the same.
In the 180* crank rotation from TDC to BDC they both expose the same sized hole.

Anyone have a program to chart the difference in displacement for each degree of crankshaft rotation?

Almost seems like this is an expanded variation of the rod ratio thing.

The thing that stuck out the most to me was the smaller bore using a smaller intake valve, which seems like that might end up needing a little head start on the timing event.

[Stan Weiss]

Since the displacement between the long and short stroke combos is the same, the area of the bores are the same.
In the 180* crank rotation from TDC to BDC they both expose the same sized hole.

Anyone have a program to chart the difference in displacement for each degree of crankshaft rotation?

Almost seems like this is an expanded variation of the rod ratio thing.

The thing that stuck out the most to me was the smaller bore using a smaller intake valve, which seems like that might end up needing a little head start on the timing event.

If the rod stroke ratio is the same for both engines then the displacement for each degree of crankshaft rotation is the same.

Stan

Code: Select all

Bore_=_4.185___Stroke_=_3.28___Rod_Length_=_6.0

Crank______Piston_____Crank_______Rod____Cylinder___Cylinder
Angle______Travel______Rod_______Bore_____Volume_____Volume
Degree_____Inches_____Angle______Angle______CI_________cc
-ATDC_
___.0000___.000000__180.00000___0.00000___0.00000____0.00000
__5.0000___.007943__173.63494___1.36506___0.10927____1.79058
_10.0000___.031678__167.27950___2.72050___0.43574____7.14058
_15.0000___.070915__160.94329___4.05671___0.97548___15.98517
_20.0000___.125180__154.63584___5.36416___1.72193___28.21745
_25.0000___.193821__148.36663___6.63337___2.66614___43.69014
_30.0000___.276016__142.14499___7.85501___3.79677___62.21798
_35.0000___.370787__135.98010___9.01990___5.10041___83.58079
_40.0000___.477020__129.88088__10.11912___6.56171__107.52714
_45.0000___.593478__123.85598__11.14402___8.16367__133.77861
_50.0000___.718829__117.91366__12.08634___9.88796__162.03458
_55.0000___.851664__112.06171__12.93829__11.71518__191.97747
_60.0000___.990523__106.30734__13.69266__13.62528__223.27834
_65.0000__1.133922__100.65712__14.34288__15.59783__255.60261
_70.0000__1.280378___95.11681__14.88319__17.61242__288.61588
_75.0000__1.428433___89.69129__15.30871__19.64901__321.98961
_80.0000__1.576679___84.38448__15.61552__21.68823__355.40639
_85.0000__1.723779___79.19923__15.80077__23.71168__388.56480
_90.0000__1.868484___74.13728__15.86272__25.70219__421.18343


Bore_=_3.915___Stroke_=_3.75___Rod_Length_=_6.0

Crank______Piston_____Crank_______Rod____Cylinder___Cylinder
Angle______Travel______Rod_______Bore_____Volume_____Volume
Degree_____Inches_____Angle______Angle______CI_________cc
-ATDC_
___.0000___.000000__180.00000___0.00000___0.00000____0.00000
__5.0000___.009361__173.43929___1.56071___0.11268____1.84657
_10.0000___.037326__166.88931___3.11069___0.44933____7.36320
_15.0000___.083546__160.36080___4.63920___1.00573___16.48096
_20.0000___.147446__153.86443___6.13557___1.77495___29.08616
_25.0000___.228229__147.41088___7.58912___2.74742___45.02209
_30.0000___.324897__141.01070___8.98930___3.91110___64.09150
_35.0000___.436261__134.67435__10.32565___5.25169___86.05983
_40.0000___.560961__128.41210__11.58790___6.75283__110.65905
_45.0000___.697492__122.23394__12.76606___8.39639__137.59226
_50.0000___.844231__116.14953__13.85047__10.16283__166.53889
_55.0000___.999460__110.16804__14.83196__12.03147__197.16047
_60.0000__1.161404__104.29807__15.70193__13.98096__229.10681
_65.0000__1.328263___98.54745__16.45255__15.98960__262.02254
_70.0000__1.498241___92.92316__17.07684__18.03579__295.55368
_75.0000__1.669585___87.43114__17.56886__20.09842__329.35415
_80.0000__1.840611___82.07617__17.92383__22.15723__363.09188
_85.0000__2.009734___76.86175__18.13825__24.19313__396.45434
_90.0000__2.175493___71.79004__18.20996__26.18853__429.15319

[Stan Weiss]

Hi Rick,
Hope all is well

Good to see you posting here.

Stan

Hi Stan,

I'm doing fine. Thank you for asking.
And I hope everything is good with you.

I foresee nothing but pleasant discussion.....

Rick

Rick,
I am doing well. Thanks.

For the most part they should be pleasant discussion. But this is the internet and some strange things do happen.

Stan

[CamKing]

For the most part they should be pleasant discussion. But this is the internet and some strange things do happen.
Stan

Rick will be a perfect gentleman. He promised his little brother.

[Stan Weiss]

For the most part they should be pleasant discussion. But this is the internet and some strange things do happen.
Stan

Rick will be a perfect gentleman. He promised his little brother.

Mike,
I have had a number of personal exchanges with Rick and they have all been very pleasant. I was just referring to the nature of the internet.

Stan

[PRH]

If the RR stayed the same, and the displaced area per degree of crank rotation was the same........ why would the longer stroke need a different cam?

The OP hasn’t filled in the details of the rods used for both combos, but I suspect the RR between the two combos is different.

Maybe when that gets revealed, we can see how the two combos compare in displaced volume in that first 90* of rotation.

Edit: I see where Stan used 6” rods for both combos in his sim.

I’ll have to look that over.

[digger]

If the RR stayed the same, and the displaced area per degree of crank rotation was the same........ why would the longer stroke need a different cam?

The OP hasn’t filled in the details of the rods used for both combos, but I suspect the RR between the two combos is different.

Maybe when that gets revealed, we can see how the two combos compare in displaced volume in that first 90* of rotation.

Edit: I see where Stan used 6” rods for both combos in his sim.

I’ll have to look that over.

theres a different inlet valve right? the smaller bore has smaller valve

also its unlikely the rod stroke ratio is going to be the same so whjy assume that in some hypothetical way when we can disuss something real and practical

[6.50camaro]

I'm here to observe and learn ,so please don't shoot me if i ask a dumb question .
the OP stated in his second post that they both would be using 6" rods . So they can't have the same rod to stroke ratio the short stroke is 1.82 and the long stroke is 1.60 if my math is correct. looking at Stan's chart at 90 * the long stroke is around 8cc larger in volume and had more volume at every 5* increment . now if they are the exact same displacement the volumes with be the same at BDC . So the short stroke will gain more volume than the long stroke motor for ever 5* increment from 90* to 180* to equal out at BDC is this correct ? Dan