Honda GX35 Power Increase

A. Devlin

New Member
Joined
Sep 27, 2017
Messages
6
Hi all,

Sorry if this has been covered before but I am new to this site and have not been able to find the exact information I have been looking for.

I am currently in my last year of a Mechanical & Manufacturing Engineering degree and my final project is titled as follows;

"To improve the efficiency and power output of a Honda GX35 engine"

I was wondering if any of you could point me in the right direction regarding this topic and the different methods of how I could squeeze more power from this little engine. I have been told the engine I will be working with has been converted to EFI in the past.

All help is greatly appreciated! - Thanks in advance,

Aran
 
Last edited:


6blueoval9

Well-Known Member
Joined
Aug 28, 2017
Messages
1,120
Do you have to use the parts the motor comes with meaning carburetor and exhaust etc..?
 
A

Aran

Guest
Do you have to use the parts the motor comes with meaning carburetor and exhaust etc..?
No, I can use whatever parts I feel is necessary to achieve the objective but I've been told that is preferred that any new parts are designed and machined by myself. I can modify and replace as many parts of the system as I like as long as I can justify a reason for doing it.
 

A. Devlin

New Member
Joined
Sep 27, 2017
Messages
6
Do you have to use the parts the motor comes with meaning carburetor and exhaust etc..?
No, I can use whatever parts I feel is necessary to achieve the objective but I've been told that it is preferred that any new parts are designed and machined by myself rather than just bought in and bolted on. I can modify and replace as many parts of the system as I like as long as I can justify a reason and explain the science and engineering behind it.
 

6blueoval9

Well-Known Member
Joined
Aug 28, 2017
Messages
1,120
No, I can use whatever parts I feel is necessary to achieve the objective but I've been told that it is preferred that any new parts are designed and machined by myself rather than just bought in and bolted on. I can modify and replace as many parts of the system as I like as long as I can justify a reason and explain the science and engineering behind it.
Sounds like fun project...i can suggest quite a few modifications that will improve power and efficiency...Im sure many others on here could as well.

Im not sure what you might be able to fabricate other than maybe a steel tube intake manifold and maybe part of an exhaust system.

Typical bolt on performance parts would be:

1. High flow air filter
2. Upgraded carburetor
3. Intake manifold.
4. Exhaust system
5. Ignition system

You can take things even further with cylinder head porting and compression increases, valvetrain upgrades to go along with a more performance oriented camshaft and in some cases big bore kits which increases cubic inches.

This can be a costly adventure but if you just want to do some simple basic modifications and describe how a particular change increased power and efficiency then you can do these simple but effective changes

1.High performance air filter replacement.
2. Upgrade exhaust system
3. Carburetor tuning.

Im not familiar with what the aftermarket is providing for this particular motor but performance is somewhat universal and im sure something is available to help you reach your goals.
 

A. Devlin

New Member
Joined
Sep 27, 2017
Messages
6
Sounds like fun project...i can suggest quite a few modifications that will improve power and efficiency...Im sure many others on here could as well.

Im not sure what you might be able to fabricate other than maybe a steel tube intake manifold and maybe part of an exhaust system.

Typical bolt on performance parts would be:

1. High flow air filter
2. Upgraded carburetor
3. Intake manifold.
4. Exhaust system
5. Ignition system

You can take things even further with cylinder head porting and compression increases, valvetrain upgrades to go along with a more performance oriented camshaft and in some cases big bore kits which increases cubic inches.

This can be a costly adventure but if you just want to do some simple basic modifications and describe how a particular change increased power and efficiency then you can do these simple but effective changes

1.High performance air filter replacement.
2. Upgrade exhaust system
3. Carburetor tuning.

Im not familiar with what the aftermarket is providing for this particular motor but performance is somewhat universal and im sure something is available to help you reach your goals.
This project has a timespan of around 24 weeks so I will have to go down the route of a more significant method of increasing power such as boring the cylinder and either finding a piston to suit or machining a new piston along with the upgrades you mentioned above (Air Filter, Exhaust & Carburetor). I have read that the GX35 piston can be replaced to that of a gx31 with some minor machining to increase the Compression Ratio to around 10:1 ?

Seeing as the carburetor has been replaced with an Electronic Fuel Injection system I may also be able to fine tune the injection timing and stuff like that.

Thanks for your help, its much appreciated.
 

Old Bob

Member
Joined
Dec 28, 2008
Messages
472
I have a chart somewhere on how much to remove from a GX31 piston to get 10:1 in a GX35, if you don't do anything to the top of it the CR is 12.5:1 too high for pump gas.
 

Old Bob

Member
Joined
Dec 28, 2008
Messages
472
You really need to improve cam timing, you can't do anything worthwhile with the stock cam, such as regrind, because of the geometry you need to add material to the flanks of the lobe not take it off the base circle. With a base circle regrind you only gain a marginal amount of lift, you don't change overlap at all and duration change is a small amount on top of messing up the valve tip contact point. Its not like a pushrod engine where you can do a base circle regrind and put a longer pushrod in t0 restore valve tip contact point.
Stock is around 250° duration and .105" lift. Not enough for max power.

Change to an electronic ignition, so you can change timing.

I don't have any GX35 cams left.I don't plan on making more.
 

A. Devlin

New Member
Joined
Sep 27, 2017
Messages
6
You really need to improve cam timing, you can't do anything worthwhile with the stock cam, such as regrind, because of the geometry you need to add material to the flanks of the lobe not take it off the base circle. With a base circle regrind you only gain a marginal amount of lift, you don't change overlap at all and duration change is a small amount on top of messing up the valve tip contact point. Its not like a pushrod engine where you can do a base circle regrind and put a longer pushrod in t0 restore valve tip contact point.
Stock is around 250° duration and .105" lift. Not enough for max power.

Change to an electronic ignition, so you can change timing.

I don't have any GX35 cams left.I don't plan on making more.
The engine I'm working has already been converted to electronic fuel injection so i'm just in the process of learning how to use the remapping software . Can you foresee any problems if I were to directly swap in a GX31 piston as long as I run super unleaded to cope with the 12.5:1 CR?
 
Top