machanic
Active Member
A question for OTTO, I have the Chinese copy GX35 crankcase, been looking at the intake and exhaust ports and they are clean of casting flash but are a crude 90 deg. angle, is this the same as with a true Honda case?
Honda GX35 Power Increase
Otto Neumann
Active Member
Hello Machanic,I really can't tell,until now I haven't opened up my Gx-35 and I can't tell, as the clone engines generally are 95% perfect copies,I assume that it should be right; but double check by asking to more people
-Otto
machanic
Active Member
Thanks for the reply Otto, I have project planned for one of these engines and wouldn't mind getting a little more out of it.
Otto Neumann
Active Member
No worries,I'm making a lil video about making a gasbike on a really cheap budget,basically everything that I'm getting takes a lot of time to arrive and it's really inexpensive,and I'm managing to get my bike motorized for 180 bucks
Steve Best
Well-Known Member
These are the traditional generic "quick fix" route to more power, mainly pushed by the performance parts manufacturers.
I believe Devon was asking for how "To improve the efficiency and power output of a Honda GX35 engine" for a research paper.
A better route, especially for a paper, would be to scientifically determine where the loses are and where the gains could be had.
For example:
1) Determine the air pressure drop across the air filter to see if an improvement is possible.
2) Determine the air pressure drop across the carb (or FI system) to see if an improvement is possible.
3) etc
4) Determine the back pressure in the exhaust system to see if an improvement is possible.
5) Determine burn efficiency to see if better ignition is required.
I would add to that:
- Dyno the engine to baseline performance and document gains
- install O2 (Lambda) sensors to read the mixture ratio for adjustments
- add detonation detection microphones to map out ignition timing needs and prevent destruction
- add a plug and exhaust temperature thermocouple to prevent destruction
Power comes from:
1) Pressure average across the piston
2) Length of stroke
3) Area of the piston
4) Number of power pulses per minute
5) minimizing power loses (mainly friction, but also heat loses)
Efficiency is how much of the energy in the fuel is used to perform useful work.
Many times we sacrifice efficiency (and reliability) to maximize power, ie: overly rich mixture or large cam overlap.
Some tricks to enhance both would be to maximize many engine parameters (compression, timing, mixture) to the limits of their safety margins. This mainly increases average cylinder pressure. Also improved combustion will do this, with a different chamber shape or squish gap. No squish gap or a very hot cylinder head may reduce unburnt fuel. More combustion turbulence may speed up burn time allowing less timing lead and greater average pressure because the burn is still going on during the power cycle. Venturi generated exhaust vacuum could be applied to the underside of the piston. Low overlap cam timing. Dry sump. low viscosity oil, minimal cooling fan blades. Longer connecting rod minimizing piston side thrust. Heat insulation on the piston top and cylinder chamber. Better bearings.
machanic
Active Member
The FI system for these engines also replaces the ignition and is adjustable and comes with a huge (for the engine) air cleaner very low restriction, the stock exhaust is restrictive, the intake and exhaust ports are restrictive and the upper case/ head should spend some time on a flow bench, the compression ratio should be upped, piston crown ceramic coated along with valves, the head which is the whole upper case half probably wouldn't survive the 700 degree F. cure temperature without warping, and a low friction coating on all metal to metal contact surfaces. Anyway that is what I am doing with my project with the exception of the FI which is outside my budget.
Just an update on this thread, the project has taken a slightly different direction where I now have to modify the engine so that it can be used to propel a vehicle competing in the Shell Eco-Marathon rather than just generically increasing the power and fuel economy. The SEM is a competition to find the most fuel efficient vehicle so I will now have to make this engine (Honda GX35) as fuel efficient as possible. I have installed an Ecotrons Electronic Fuel Injection kit so I will be able to vary ignition timing and other parameters when I learn how to use the software properly. My next step is to test the engine to find its original performance figures for power, fuel economy, etc as a base point before carrying out physical modifications.
After initial testing I plan on increasing the CR by swapping the standard piston out to replace with a taller piston. However, ive read many different conflicting stories regarding swapping a GX31 piston into the GX35, some people say this pistons can be swapped in without any work and other people say material needs to be removed from the top of the GX31 pistons before it can be installed. Can somebody clear this up for me as I will be looking to purchase the GX31 piston in the near future?
After initial testing I plan on increasing the CR by swapping the standard piston out to replace with a taller piston. However, ive read many different conflicting stories regarding swapping a GX31 piston into the GX35, some people say this pistons can be swapped in without any work and other people say material needs to be removed from the top of the GX31 pistons before it can be installed. Can somebody clear this up for me as I will be looking to purchase the GX31 piston in the near future?
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CrazyDan
Well-Known Member
I didn't know about that mod and did a little research. Looks like you gotta shave the top of the piston down .024" to clear the valves. It'll give you around a 10:1 cr.
machanic
Active Member
Not a power increase project it is a MPG project the post is about improving efficiency, HP increase is a bonus.
