500 cylinder swap and gear reduction questions - Honda Foreman Forums : Rubicon, Rincon, Rancher and Recon Forum
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post #1 of 4 (permalink) Old 10-07-2019, 09:59 AM Thread Starter
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500 cylinder swap and gear reduction questions

Hello all.
I have a few questions regarding my (new to me) 2012 Honda Rancher 420 AT 4x4.



1) I did my research and discovered that I can swap in a Honda Rubicon 500 cylinder and piston. Since the both models use the same fuel injector, is it absolutely required that I buy an aftermarket tuner? Reason I ask is because I once had a 2009 Suzuki Z400 with EFI. After I piped it and took the lid off, I was told to also purchase a fuel controller for fear it was running to lean even though it ran fine without it installed? To my surprise, the fuel maps downloaded from the internet actually leaned out the fuel curve rather then add it because the Z400s came from the factory with a rich map. Granted that the 500 piston is 6mm wider, will the fuel map from the 420 be sufficient or is a tuner necessary? Is there a noticable power increase running the 500 set-up?



2) I just installed 26'' Maxxis Zillas. The traction is amazing. The engine does turn them well but there is tiny loss in power going up steep hills. I've read that gears from a SRA Rancher 420 would bolt right in. How much reduction would it offer and what would be the overall result running it with 26'' tires?
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post #2 of 4 (permalink) Old 10-07-2019, 01:08 PM
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You will notice much more difference in the $55 SRA secondary than you will from the 500 top end.


I replied to your PM, but to put it here in case people ask in the future, the 475 top end is not worth the money unless your existing 420 cylinder is ruined. Miniscule power increase. I used a programmer but others have done with swap without a programmer and said it ran fine/ not lean without a programmer.


The new 520 top end will supposedly bolt on BUT you have to grind the cases to get the larger cylinder into the crankcases.


If you're doing a full rebuild might be worth doing while you have the cases split, but otherwise just have your 420 cylinder bored oversized and call it good.

2005 Foreman Rubicon Camo
Perfex, 27" Mudbugs
Heated grips and Thumb , HID's
5K Viper Max winch

2009 Foreman 500FM Green
Perfex with HL springs
27" Execs on Rubicon rims
Heated Grips and Thumb, HID's
4K Viper Max winch

2006 Foreman 500FM Green
28" Mugbugs, stretched, Perfex, HLsprings
3K Superwinch winch

2009 475 Rancher AT Tan
26" Mudbugs on Rincon rims
Warn winch. Foreman pod light with HID, SRA gear reduction
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post #3 of 4 (permalink) Old 10-07-2019, 02:21 PM Thread Starter
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Thank you for the quick reply. I see in your signature, you are running a rancher with 26'' tires and a SRA gear reduction. In your opinion how is the overall result? Is the gear reduction to much for 26'' tires? Do you know approximately how much reduction it is?
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post #4 of 4 (permalink) Old 10-09-2019, 12:10 PM
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I believe the SRA secondary is either 15 or 18%, depending on who you ask.


Given the low cost of the secondary GR (about $55 for the two gears) and the relative ease if install, I very much recommend it.


Keep in mind that you will have to shave the speed sensor down a bit to get the speedometer to work, and for the auto shifting to work after you do the GR.


In auto mode if you go WOT it will bounce off the rev limiter unless you add a shift module from Rapid Revolutions (another $175ish IF you can get one, they are rarely in stock). You can get a shift module or simply change your driving habits a bit, as simply letting off the throttle for a second will make the bike shift.


I think it would be perfect with light 27's (like a Zilla or Mudbug). 26's has no power issues in thick stuff at all. Good enough that I think a light 27 would work well.

2005 Foreman Rubicon Camo
Perfex, 27" Mudbugs
Heated grips and Thumb , HID's
5K Viper Max winch

2009 Foreman 500FM Green
Perfex with HL springs
27" Execs on Rubicon rims
Heated Grips and Thumb, HID's
4K Viper Max winch

2006 Foreman 500FM Green
28" Mugbugs, stretched, Perfex, HLsprings
3K Superwinch winch

2009 475 Rancher AT Tan
26" Mudbugs on Rincon rims
Warn winch. Foreman pod light with HID, SRA gear reduction
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