P500 Big Bore Kit

[Duckhunt]

Okay I gotta ask now: Anyone else get a big bore kit from Hormell Xtreme ATV? Last year this time I considered it but decided it was too much $$$. This year is different, and with my Camso tracks I ordered I need all the power I can get, called them later last week and put a deposit for the kit, cam, and I already have a power commander but got their base program. I got #7 of the 8 kits they're having made, supposed to ship next week. They are very helpful and intelligent, they have been tinkering with this kit and are getting 9-10 hp with 11.5:1 compression. I don't care anything about the $$$, I love my P5 and need more power. Any other P500 guys get in on it?

 

[906UP]

Awesome, I can't wait to hear your thoughts. I will probably have to put rings in the Donkey in the spring at a minimum, it's starting to smoke a little.

 

[Russ989]

Awesome, I can't wait to hear your thoughts. I will probably have to put rings in the Donkey in the spring at a minimum, it's starting to smoke a little.

What did you do to Donkey?

 

[Duckhunt]

Awesome, I can't wait to hear your thoughts. I will probably have to put rings in the Donkey in the spring at a minimum, it's starting to smoke a little.

10-4. I cannot wait to see what this engine mod does with your gear mod. To pull hard all the way to 48?!? "I can picture it in my mind, and it's breathtaking!" - N.L. Christmas Vacation.

 

[906UP]

What did you do to Donkey?

I may have ran it a bit too hard a few times

 

[Russ989]

I may have ran it a bit too hard a few times

Hmmmmmmm.... surely not.

 

[906UP]

10-4. I cannot wait to see what this engine mod does with your gear mod. To pull hard all the way to 48?!? "I can picture it in my mind, and it's breathtaking!" - N.L. Christmas Vacation.

So they have 1 more available?........hmmmm

 

[Duckhunt]

So they have 1 more available?........hmmmm

Do it!! So when I called they said they were having 8 kits made they had the pistons and cams in, waiting for the cylinders to get done Tuesday or Wednesday next week. They had 5 deposits and another name on the list (no deposit) before me.

The only negative could be for some people is they recommend 93 octane, sounded like they could detune for 91 non-oxy which is what we got here in MN, however I can't remember the last time I got gas at the pump for the P500, and also there's a VP race fuel shop 35 miles from me so I'll just keep 6 gallons of 110 and mix 1 gallon of that to 4 gal 91 in the 5 gallon can I reserve for the P500 anyway. They said that's exactly what most guys do running this big bore kit. Point being a little pre-planning but not much will change for me in terms of refueling.

Did you ever get a Power Commander V?

 

[906UP]

.....
Did you ever get a Power Commander V?

No, I bought a Talon instead

 

[BenBusenitz]

Just saw that Honda increased their 2020 Foreman/Rubicon quads to 520cc. I have checked the oem parts schematics and they are still using much of the same parts from the 475cc engine. The 475 is 92mm bore and 71.5mm stroke. New 520cc is 96mm bore and 71.5mm stroke. The cam, pushrods, valves, and head bolts are the same part numbers for both engines. But thats about where it stops. Case halves and heads are different. I was hoping that we could just drop oem jugs and cylinders from the new 520cc engines onto our P500s (or any older trx500 quad.) So.... it could be possible if the head/cylinder bolt spacing is the same, but my guess is that one would need the newer head to match the 4mm larger bore. Anyone know how to find out the head bolt spacing?

Edit:
I came across a youtube video of a guy doing this to his quad. From reading the comments, it sounds like the case or the jug has to be trimmed to fit each other.
watch

 

[Duckhunt]

Just saw that Honda increased their 2020 Foreman/Rubicon quads to 520cc. I have checked the oem parts schematics and they are still using much of the same parts from the 475cc engine. The 475 is 92mm bore and 71.5mm stroke. New 520cc is 96mm bore and 71.5mm stroke. The cam, pushrods, valves, and head bolts are the same part numbers for both engines. But thats about where it stops. Case halves and heads are different. I was hoping that we could just drop oem jugs and cylinders from the new 520cc engines onto our P500s (or any older trx500 quad.) So.... it could be possible if the head/cylinder bolt spacing is the same, but my guess is that one would need the newer head to match the 4mm larger bore. Anyone know how to find out the head bolt spacing?

Edit:
I came across a youtube video of a guy doing this to his quad. From reading the comments, it sounds like the case or the jug has to be trimmed to fit each other.
watch

Yes there's been some topics on the new 520!!! You probably could drop the new 520 jug/slug into the old crankcase and be fine mechanical wise. The difference is they probably increased head combustion chamber volume to keep up 9.5:1 compression. My new 99mm piston has a .082" dish (stock is flat) and I will be getting 11.5:1 comp with stock head. I literally just got the motor on the bench and tore apart tonight! Yes, I decided to pull entire motor, just easier for me to change stuff on bench. Also, the new cylinder protrudes less into crank. Hold on a second bud, I got pics if I can figure out that stupid IPhone I'll post em up.

 

[Duckhunt]

Here's some images obviously new jug and piston on left. I will also mention it ALMOST brought a tear to my eye the stock 2600 mile jug still had fine cross hatch and no ridge or scoring.

 

[906UP]

View attachment 173339
View attachment 173340

Hell yes!!!! Tear it up!!

 

[Duckhunt]

Hell yes!!!! Tear it up!!

LOL. Yeah, I got that same sickness, you get something stuck in your head and you just do it!

I'm also afraid that this will push Hector with your @906UP gears all the way to 48mph with ease.... and we'll need a 6th gear!!!! She'll be wrapped up by Sunday.

 

[906UP]

LOL. Yeah, I got that same sickness, you get something stuck in your head and you just do it!

I'm also afraid that this will push Hector with your @906UP gears all the way to 48mph with ease.... and we'll need a 6th gear!!!! She'll be wrapped up by Sunday.

Awesome, can't wait to hear about the results

 

[BenBusenitz]

Way to go, Duckhunt! Where did you find a 99mm jug and piston? That will put you right at 550cc. How much extra displacement can the stock 2-valve head handle before it starts limiting air flow? Or are you replacing the head as well? I assume the 36mm throttle body will handle the extra displacement no problem. I have hit 50 mph on my phone gps speed app running 27 radials and with the gearing change but it took all it had. I think it was down hill too. Any chance the oem 475cc cylinder could be bored to 96mm?

 

[Duckhunt]

Way to go, Duckhunt! Where did you find a 99mm jug and piston? That will put you right at 550cc. How much extra displacement can the stock 2-valve head handle before it starts limiting air flow? Or are you replacing the head as well? I assume the 36mm throttle body will handle the extra displacement no problem. I have hit 50 mph on my phone gps speed app running 27 radials and with the gearing change but it took all it had. I think it was down hill too. Any chance the oem 475cc cylinder could be bored to 96mm?

Thanks! Hormell's Xtreme ATV in Louisiana is the place. If you go to their facebook page in November posts they discuss them. The head is a limiter for power I'm sure but I also got their camshaft which gives more lift and duration. I also have an opened no cat straighten exhaust, K&N w/ short MN snorkel (snorkels over 6" illegal in MN), and a Power Commander V and got their program. The most fuel difference over stock is +24%. I'll probably run a little less with 1400' elevation compared to sea level and they're program is for HMF exhaust.

Also, They said it was a 550cc so I figured it was 99mm bore for math to work out like you found, but measuring this morning before assembly it was 100mm, and the CP piston sheet even states 3.937" bore which is 100mm so it's 561cc!

 

[BenBusenitz]

Thanks! Hormell's Xtreme ATV in Louisiana is the place. If you go to their facebook page in November posts they discuss them. The head is a limiter for power I'm sure but I also got their camshaft which gives more lift and duration. I also have an opened no cat straighten exhaust, K&N w/ short MN snorkel (snorkels over 6" illegal in MN), and a Power Commander V and got their program. The most fuel difference over stock is +24%. I'll probably run a little less with 1400' elevation compared to sea level and they're program is for HMF exhaust.

Also, They said it was a 550cc so I figured it was 99mm bore for math to work out like you found, but measuring this morning before assembly it was 100mm, and the CP piston sheet even states 3.937" bore which is 100mm so it's 561cc!

Ok, I will have to check Hormells out. I also removed the cat when I had the back end apart to do the gear change. My brother had an FMF dirt bike pipe laying around so I threw it on and got rid of the stock muffler. Sounds like a thumper now. It was burning a little oil when I got it, so I have already rebuilt the top end with a wiseco piston .....wish I had known about this big bore stuff. I remember doing a search for rubicon/pioneer big bore kits, maybe they just started making them. I think removing the restrictive exhaust definitely helped some, but it still needs 5-10 more ponies. Have you been running the power commander before the rebuild? Did it give noticeable power increase?

 

[Duckhunt]

Ok, I will have to check Hormells out. I also removed the cat when I had the back end apart to do the gear change. My brother had an FMF dirt bike pipe laying around so I threw it on and got rid of the stock muffler. Sounds like a thumper now. It was burning a little oil when I got it, so I have already rebuilt the top end with a wiseco piston .....wish I had known about this big bore stuff. I remember doing a search for rubicon/pioneer big bore kits, maybe they just started making them. I think removing the restrictive exhaust definitely helped some, but it still needs 5-10 more ponies. Have you been running the power commander before the rebuild? Did it give noticeable power increase?

Yup I ran the power commander all summer. It did help. The main thing I noticed is I was hitting the rev limiter more, because it pulled harder through the entire rpm range. I was running 5 degrees ignition advance at top end, never ever had any sign of detonation or anything running 91 octane. I still say the biggest improvement in all was removing the CAT!

I tried a MBRP Sport universal ATV muffler and I literally threw it in the scrap iron bin after 30 miles. Except for the outlet - I put that on my stock muffler when I opened it up. But on the speedo I could just barely hit 35mph with it! Just a dog. Unfortunate because it sounded awesome. Not loud but very low.

 

[Tstover]

I just want to say you guys are impressing the hell out of me. Your skills and knowledge are impressive(yeah, I said that twice). Thanks for sharing.