Looking at the Honda specs there is a discrepancy.
Honda Engines - Small Engine Models, Manuals, Parts, & Resources
Specs:
36mm bore
41.8mm stroke
Capacity 49.4cc
comp ratio 8.0:1
OK, the bore & stroke gives us a Sv(swept volume) of 42.55cc, therefor if 49.4cc is correct we have a Cv(clearance volume) of 6.95.
CR=Sv/Cv + 1
= 42.55/6.95 + 1 = 7.12, So if the Bore, stroke & displacement specs are the correct then the 8.0:1 is wrong and the real ratio is 7.12:1
If we assume the bore stroke & CR are correct then the displacement of 49.4 is wrong.
Cv=Sv/(CR-1)
= 42.55/(8-1) = 6.08cc
Displacement = Sv+Cv = 42.55+6.08 = 48.63cc NOT 49.4
I am inclined to think that the error is in the CR calculation & the real world CR of the GXH50 is 7.1:1.
Please chime in and correct me if the above is incorrect.
I really like the idea of a stroker crank, it would deliver a higher CR, a longer leaver about the crank & little more displacement. Higher CR will also yield benefits to the performance cam as they work better with higher CR.
By my calculations with 2mm stroker crank would yield:
stroke = 45.8mm
Sv = 46.62cc
Cv = 4.91cc
displacement = 51.53cc
CR = 10.5:1
Looking around various sources suggest 4-5% increase in torque for every 1.0 increase in CR. So an increase of about 3.4 x 4% is about 13% more torque. the longer leaver of the stroker is 11% longer so 11% more torque there. additional 2.1cc is about a 4% increase in volume. So it may be possible to achieve something around 25% increase with a stroker.
1.25 x 1.6 = 2kW & 3.3Nm sounds like a good starting point before the addition of main stream add-ons like carb, filter exhaust & cam.
Question
does anyone know the clearance between the piston and valves, my Honda is on the way, otherwise i would pull it apart myself & put some clay on the piston and check myself.
In the mean time i will be looking to a couple of workshops that weld & regrind crankshafts. assuming they can tool up small enough, it should not be that expensive going by charges to do full V8 cranks.
Honda Engines - Small Engine Models, Manuals, Parts, & Resources
Specs:
36mm bore
41.8mm stroke
Capacity 49.4cc
comp ratio 8.0:1
OK, the bore & stroke gives us a Sv(swept volume) of 42.55cc, therefor if 49.4cc is correct we have a Cv(clearance volume) of 6.95.
CR=Sv/Cv + 1
= 42.55/6.95 + 1 = 7.12, So if the Bore, stroke & displacement specs are the correct then the 8.0:1 is wrong and the real ratio is 7.12:1
If we assume the bore stroke & CR are correct then the displacement of 49.4 is wrong.
Cv=Sv/(CR-1)
= 42.55/(8-1) = 6.08cc
Displacement = Sv+Cv = 42.55+6.08 = 48.63cc NOT 49.4
I am inclined to think that the error is in the CR calculation & the real world CR of the GXH50 is 7.1:1.
Please chime in and correct me if the above is incorrect.
I really like the idea of a stroker crank, it would deliver a higher CR, a longer leaver about the crank & little more displacement. Higher CR will also yield benefits to the performance cam as they work better with higher CR.
By my calculations with 2mm stroker crank would yield:
stroke = 45.8mm
Sv = 46.62cc
Cv = 4.91cc
displacement = 51.53cc
CR = 10.5:1
Looking around various sources suggest 4-5% increase in torque for every 1.0 increase in CR. So an increase of about 3.4 x 4% is about 13% more torque. the longer leaver of the stroker is 11% longer so 11% more torque there. additional 2.1cc is about a 4% increase in volume. So it may be possible to achieve something around 25% increase with a stroker.
1.25 x 1.6 = 2kW & 3.3Nm sounds like a good starting point before the addition of main stream add-ons like carb, filter exhaust & cam.
Question
does anyone know the clearance between the piston and valves, my Honda is on the way, otherwise i would pull it apart myself & put some clay on the piston and check myself.
In the mean time i will be looking to a couple of workshops that weld & regrind crankshafts. assuming they can tool up small enough, it should not be that expensive going by charges to do full V8 cranks.
