RMK 800 PRO Mods?

Well you certainly don't have too but I run stock arms and rails with a Fox rear suspension that has an the new 2011 Evol R rear shock and the Fox Zero Pro that Renton Coil Spring loaned me a prototype progressive rate Ti spring to test with. I make my own limiter straps normally after I've had an opportunity to try out a system. Once I got the pre-set tension correct on the Ti spring it turned out to be just right with the factory stock settings on the limiter. I had to search around with the Ti spring settings before I got it just right. Almost removed it and called it a no go but tried a very very loose almost no pre-load setting and BAM magically delicious! Those springs are expensive and they don't just make fifty to try so we were in a stretch but it's exactly what I would recommend for them if they want to go into production as this setup is sweet and very high performance. Fox OK'd the project and helped us with the parameters to attempt. The guess came out great using Fox's initial tensions and length ratios and then getting as close as we could with some of the existing prototype progressive rate Ti springs that RandD had available.

The PRO is so light and balanced that you definately don't get the instant and obvious impact of the track trim like the iq raw in bone stock form. This is another reason why I think there is some funny business going on with the stiffness that everyone is claiming. The PRO track does not seem to lay over and spin nearly as dramatically as the iq raw did. But once I got the combo of the head and the track trim that is when it got really exciting. The stocker at alt is pretty lethargic and I think it's a compression deal. Once we bumped up to 13.6 and had the track trimmed it became a completely new beast. Snap was right there and in all conditions not just packed drag racing. It's cool to hammer it and have the skis pack and hold steady only changing with throttle control not terrain. Probably why this sled rips so good in various conditions. Really good setup and balance. Also note it wasn't like that the entire season. I messed with a bunch of clutching, head, track, and shock setups throughout the season and alot of them weren't all that "special". Tons of rides on a mediocre running sled...but by the end we got it really right and especially in our home stomping grounds.

mountainhorse said:

Since the timing seems to play such a vital role in the DTR runs... I'm wondering what the results would be with stock exhaust, stock head, no shim BUT adding the timing key and the PC-5?? (no speculation.... just a real world test)

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I've been wondering the same. Makes sence, do the least expensive/invasive mod 1st.

So why does carls use the cat track instead of just cutting the 5.1 especiallyp on the turbo sleds???

F-Bomb said:

Well if you ask Polaris or Camoplast they will tell you the 5.1 is the same and I've always installed stiffening screws on the 5.1. BUT...when the PRO showed up last year studying it directly next to my 09 the track appears stiffer. So I simply trimmed it first but no screws to compare. It throws and feels identical to my old 5.1 with inset screws. Now the two sleds are totally different so you couldn't conclude anything against one another but they stood out similarly in their comparison to other like sleds in testing.

Windage and resistance are huge performance factors. It doesn't take much drag to have a significant effect on performance.

I trimmed a camo extreme on one of my sleds and it was outstanding as well. Once again same chassis situation on both the IQ RAW and the PRO..just not enough room and snort to efficiently spin that mass...as least not as good as the exact same track trimmed to 5.1 and what ever durometer or flex/throw you end up with on the old 5.1 with 1" inset screws or just trimmed on my PRO. Never did a direct comparison on a 5.1 155 versus a camo extreme trimmed (only non trimmed and the cut 5.1 was better). There is a snowest member from the midwest that bought a camo extreme 155 for an IQ and trimmed it...he liked the results or so he said.

I had such a good result from my trimmed stocker 5.1 on the PRO this past season that I consider it a done deal. I"m sure waiting for someone to come along and show me a significantly faster or better performing PRO with any kind of a track or track mod. It's gonna have to be something new because what was offered last year didn't do it.

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The PC track is very popular down at Carl's! Obviously Jack feels like that is the superior track system for their setups.

BugIto said:

Isn't the timing key relative to the shim?

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Yup, shim changes port timing so you adjust timing key to compensate... do both not just one or the other. Like I said before... poor man's port job. Was dissin on it as I'd rather get the real deal at FTX but currently being jobless has me reconsidering that age old '70's trick. Not sure if voiding the warranty would be worth it tho!

Have FUN!

G MAN

gman086 said:

Yup, shim changes port timing so you adjust timing key to compensate... do both not just one or the other. Like I said before... poor man's port job. Was dissin on it as I'd rather get the real deal at FTX but currently being jobless has me reconsidering that age old '70's trick. Not sure if voiding the warranty would be worth it tho!

Have FUN!

G MAN

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What is the "shim"? Is it as simple as a thicker gasket? This sounds like a cheap way to play with improvement. I like the "poor man's port". Porting will void warranty too. I suppose if you had to go that route you could get the sled back to stock with a shim/timing change.

has anyone not liked the results of trimming a 5.1? either on the pro or iq raw chassis?

still better in bottomless powder?

BugIto said:

What is the "shim"? Is it as simple as a thicker gasket? This sounds like a cheap way to play with improvement. I like the "poor man's port". Porting will void warranty too. I suppose if you had to go that route you could get the sled back to stock with a shim/timing change.

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Look at Dyno tech articles, there are some names and adresses, Donavon is in to it, he'll probably be doing some research with timing (valve and ignition) as well, to see if the gains at dyno tech will hold up at elevation. Sounds like the shim is more than just a gasket it's a spacer but the articale doesn't state any measurements.

how to trim track

any links/pix/or details on how to trim track as F-Bomb has suggested? Thanks for any help.

Anytime you are in Boise give me a shout and if I'm in town you can stop by for a look see.

simple stuff and here is what you need and how I do them:
$12 electric turkey knife from Walmart or any serrated blade hand knife
wd-40
low stool to sit on

Hoist the rear of the sled and suspend...lift the flat out of the way...spray with a generous amount of wd 40 on the lug row ( I usually hit two or three rows at a time) then trim just enough so that the nubs all stay together in one piece from each paddle. The net result is perfect! It's amazing the performance benefit from this tiny amount of rubber but it's 100% proven performance winner over the stock 5.1 on both the PRO and the IQ RAW in any snow conditions that you will encounter.

G Man,

Sincere question here... not trying to be a smart azz

I understand that the shimming of the cylinder also raises the ports slightly ... and this changes the character of the cylinder fill/scavenge.

The crank still reaches TDC in Stock and Shimmed setups at the same point in the rotation...

How does changing the port timing change point at which the fuel/air charge needs to be lit?

gman086 said:

Yup, shim changes port timing so you adjust timing key to compensate... do both not just one or the other. Like I said before... poor man's port job. Was dissin on it as I'd rather get the real deal at FTX but currently being jobless has me reconsidering that age old '70's trick. Not sure if voiding the warranty would be worth it tho!

Have FUN!

G MAN

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mountainhorse said:

G Man,

Sincere question here... not trying to be a smart azz

I understand that the shimming of the cylinder also raises the ports slightly ... and this changes the character of the cylinder fill/scavenge.

The crank still reaches TDC in Stock and Shimmed setups at the same point in the rotation...

How does changing the port timing change point at which the fuel/air charge needs to be lit?

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What changes is, as you say, port timing leaving the ports open longer (duration). This gives the engine more time to get exhaust out and fresh air/fuel charge in at high rpms, enhancing the filling of the cylinder.

The burning is fast but i does take time, so give it a bit more time to burn more fuel.

Ideally, to complete this you could also shorten your pipe a tad to give the pressure pulses less distance to travel and be more suited for the higher rpms you just helped.

On the PRO tho, this is something the average Joe might want to think twice about. The engine cuts ignition at 8500 so gaining on top and losing on the bottom end is a risky sport here (I imagine).

RS

The carls cycle clutch works the best by far from all the different ones ive rode!!

We are going to have a few power enhancers for the Pro for this season.. I need to get them installed on the 2012 Pro and finalize some testing.

Adding the shim, IMO is not a good idea for the higher elevation riders.. this will only work , somewhat well, at low alt.. too much case volume and performance suffers..

Stay tuned..

Norway said:

What changes is, as you say, port timing leaving the ports open longer (duration). This gives the engine more time to get exhaust out and fresh air/fuel charge in at high rpms, enhancing the filling of the cylinder.

The burning is fast but i does take time, so give it a bit more time to burn more fuel.

Ideally, to complete this you could also shorten your pipe a tad to give the pressure pulses less distance to travel and be more suited for the higher rpms you just helped.

On the PRO tho, this is something the average Joe might want to think twicw about. The engine cuts ignition at 8500 so gaining on top and losing on the bottom end is a risky sport here (I imagine).

RS

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Well said! And like Kelsey says... " a dyno has never passed me on the hill!" DT Jim's info has to be put into perspective, it's good info but may not apply to your needs!

Have FUN!

G MAN

F-Bomb: If I were to cut my track down to 2.1", what kind of screws would you recommend to screw into the lugs? And how many in each lug? And ive just mounted silber turbo on my pro, do you have any reference and recommendations on cutting the track on a turbo sled?

I would try your PRO as is first prior to putting in screws. I like mine without screws compared to my 09 track on my IQ RAW. If you run them heads up (which we do alot) they act and feel almost identical in bite and go.

I'm not at all sure that anyone other than me actually trimmed a PRO track last season. You'll have to be a pioneer like me on your turbo. I will say I never did run into a sled that made me sorry to have a trimmed track. I also didn't get stuck all the time or hate it in the over the hood stuff in Afton at 10,000ft. I've said it before and I'll say it again here...not one single time did I think "dang I shouldn't have done that".

Is this a new turbo for you? Take it out stock and stop time a 300 yard run. Go home and trim the thing and rerun...YOU"LL SEE (take another set of weights if she's dialed stock..trim usually equals 100rpm-150 depending on the sleds) 1 gram min most of the time we could use 2

Man I have got to figure out how to post these videos that I have taken all last season....it's very conclusive

Thanks, im very curious about this mod and im definatly considering doing this to my track also. Will it be a great improvement on hard snow? We have alot of hard snow in the middle of the season, and with the stock track im just spinning and cant get a grip, seems like the lugs are to soft and lay down to much and wont dig into the snow.

Wonder what the other guys are gone say when/if i do this Maybe it will shut them up

Im new to turbo yes, the kit are used and I have already mounted it, so stock testing is not possible

OK just do it...everything you have said SCREAMS "trim that track". You WILL love this modification. Based on your comments I am absolutely CERTAIN that you will like the results.

The bad thing is your buddies are all going to think your turbo is so magnificently powerful when a good portion of your performance is going to be hook up.

So now knowing what we know on your deal. Trim and test...then you might try one more additional deal. I put two hex headed 1" screws in each paddle lug of the center but not on the outside so that they don't tear up your cooler covers. I didn't want to install protective strips which is what you have to do if you run screws in every lug. Like I said in my last post that ate some RPM's but I had really good drag racing hook up...plus it still went up a good hill in deep heavy snow REALLY REALLY GOOD. I'm theorizing here for your application but I think that will be YOUR TICKET.

Put slp single pipe, and have slp head and carls clutch kit. Good improvement over stock. Had to run power commander with kit.