Mtntk full mod vs Rktek 858

[snobyrd]

I'm running the bikeman durable kit, low ele head, low ele pipe at 4000 and pulling 82-8350 with 67.4 grms with gold star weights, only issue is , I'm fouling plugs at very low throttle positions, due to I'm thinking a cool pipe, no plug issues at higher rs and hotter pipe.

 

[TUFFPOLARIS]

I went with MTNTK full mod. Sending out cylinders today. They seem like the best guys to deal with and iv heard of a couple people with the kit that really like it. Hoping to have everything back in 3 weeks or so

 

[tdblakes]

Pulling 6g more weight for pretty much the same alt says a lot!

Not all weights are created equal. This is straight from SLP's site...
"To order, add 4 grams to the amount of weight that you are currently using to choose the correct SLP MTX™ (ie: if you are using a 10-64 Polaris Weight, you should use a 68 gram MTX™ Weight)."

Just an FYI

 

[Reddragon800]

Ya, I agree. Those MTX weights are lot different. Put so 10-66's in there and see if you will hold RPM. Doubt it. The MTNTK full mod kit makes more power than the SLP stage 4! t also depends on his helix and spring. Im running a lighter primary spring and more helix angle as well.... so you cant compare the 2!!

 

[Scott]

Anyone have a dyno graph of the RKT 858? I'd like to look at the torque curve.

 

[gunnerthesnowman]

I ride between 5-7000 feet. This is the set up im running and so far its working well. 10-66 weights with the Team white spring (120-310) in the primary. And a 73-57.46 helix with the team red/black spring. ( 140-240). When your running the lower elevation turn the helix to the other angle. 73-59.46. Give this a try!!

Same topic, different kit: CALL FASTRAX! I'm running their "stage 4" equivalent and it runs very well!

Riding 55-6500 ft and pulling 72.5 gram MTX weights with similar stock clutching otherwise. It spins 8250-8300 with their kit. And I'm running a 3" 156 track as well. Very nice setup!!

Just comparing some clutching in some of the pro BB kits - Bikeman , RKtec etc.
I run a 870 BB , 12.7 : 1 compression on pump gas , I run the sled from 3000-6500 FT , 163 2.5" CE stock gearing 20/42 , i had a hard time loading the engine up as it pulls so hard , but with help from Al ( Sled Shed - turbo Al on here ) got it clutched : primary -red/white (100 / 220 )
- 11-70.5 grams
secondary -- red/green ( 120/ 220 )
Helix --- 62 - 42 .4
I also set my exhuast valves to open at 5000 rpm,s , develops a lot of torque a low rpm,s , top rpm,s set for 7700-7800

 

[Reddragon800]

Just comparing some clutching in some of the pro BB kits - Bikeman , RKtec etc.
I run a 870 BB , 12.7 : 1 compression on pump gas , I run the sled from 3000-6500 FT , 163 2.5" CE stock gearing 20/42 , i had a hard time loading the engine up as it pulls so hard , but with help from Al ( Sled Shed - turbo Al on here ) got it clutched : primary -red/white (100 / 220 )
- 11-70.5 grams
secondary -- red/green ( 120/ 220 )
Helix --- 62 - 42 .4
I also set my exhuast valves to open at 5000 rpm,s , develops a lot of torque a low rpm,s , top rpm,s set for 7700-7800

Thats alot of weight in the primary... but still running the same final angle on the helix as stock. probably pulls hard off the bottom.

 

[gunnerthesnowman]

Thats alot of weight in the primary... but still running the same final angle on the helix as stock. probably pulls hard off the bottom.

Ya , tryed doing as much of the tuning with the springs ( cheaper ) I was thinking about playing around with the helix more , but i don,t see many options ??? i just checked and i do have a 66/44 .46 OR 66/46 .46

 

[tdbaugha]

Ya, I agree. Those MTX weights are lot different. Put so 10-66's in there and see if you will hold RPM. Doubt it. The MTNTK full mod kit makes more power than the SLP stage 4! t also depends on his helix and spring. Im running a lighter primary spring and more helix angle as well.... so you cant compare the 2!!

Well based straight off SLP's information, it will pull 10-68.5's... And that's to 8250-8300rpm with a 3" track.

Fastrax claims 20-25 hp over stock and that's without the new v force 3R reeds which I'm also running. Butt dyno says it's making all of that if not more.

 

[Reddragon800]

Ok. But what springs are they running. I could spin more weight to if I had stiff springs too. The MTNTK kit is more involved than the SLP kit and they claim 19 hp on the top and 21 hp in mid range. This is with proven Dyno runs!! It does really matter, as long as you are happy with it.... more power is always more fun!!

 

[tdbaugha]

Ok. But what springs are they running. I could spin more weight to if I had stiff springs too. The MTNTK kit is more involved than the SLP kit and they claim 19 hp on the top and 21 hp in mid range. This is with proven Dyno runs!! It does really matter, as long as you are happy with it.... more power is always more fun!!

140/330 primary spring

160/240 secondary spring w/ 1 delrin washer

58/40 .46 helix

Very happy with it! For an 800 on pump gas it runs great!!

 

[Reddragon800]

So your using a stiff primary spring, stiffer secondary spring and less final angle on your helix. All im saying is that you cant just look at the primary weight. im sure yours rips and it should...
I should come down to MT and go riding with you!! ive always wanted to ride down there!!

 

[tdbaugha]

So your using a stiff primary spring, stiffer secondary spring and less final angle on your helix. All im saying is that you cant just look at the primary weight. im sure yours rips and it should...
I should come down to MT and go riding with you!! ive always wanted to ride down there!!

Stock primary, dang near stock secondary (if I were higher alt that would be Polaris recommended), and steeper and longer initial rate than stock (.46 vs the .36) so dang near oem clutching for comparison sake which is what I stated.

And then basing off the 10-62 stock vs my equivalent 10-68.5 weights, it's a 6.5 gram increase which is what AZ800 stated in the first place! That's not even counting the ~200 rpm increase...

Come on down! It's fun to take visitors out and show them around!

 

[Reddragon800]

Sorry, i was comparing to what im running!!

 

[Scott]

Nobody has a RKT858 Dyno sheet?

 

[gunnerthesnowman]

Thats alot of weight in the primary... but still running the same final angle on the helix as stock. probably pulls hard off the bottom.

Yes , but running a 100/220 in primary compared to 140/310 and a 120/220 in the secondary compared to 140/240 , the softer spring rates load hard and i started with 11-74 lighten on the tip to get 70.5 g ( base heavy ) to load hard at low rpm,s.
Opening the exhaust valve sooner really wakes things up.

 

[gmustangt]

Comparing clutching for horsepower , best form of bench racing... To many variables , snow type , rider weight bla bla.

Best to compare duty cycle (mapping) at equivalent afr. Even then many variables.

 

[tdbaugha]

best form of bench racing...

Oh come on! Isn't that why we're all on this site anyways? That and make up fictional problems?

 

[gmustangt]

Oh come on! Isn't that why we're all on this site anyways? That and make up fictional problems?

Of course , but with DC we can have winners and losers , and really hurt some feelings.

 

[SnoHunter]

I am currently running a RK TEK 858 kit on my Polaris Pro. So far it has added alot to the bottom end and a lot to the midrange power. The top end I'm disappointed in. I just installed a new helix and springs and have the clutching figured out. Everything is good but the top end RPM and power. I'm currently just testing a set of twin pipes on this kit to see if it will add what I'm missing. It sounds awesome and we turned up the fuel. I'm excited to see if it runs like I hoped it would when I installed the big bore initially! My guess is that if you run stock intake, and stock exhaust you won't see huge gains with most of the big bore kits. Unless you do an exhaust with them. First ride will be in a few days. I'm hoping the twin pipes are it! Turbo was the way to go but I'm too far into my project. It sounded mean as heck in my yard. It's like a modified turbo on a diesel pickup. If the intake air and exhaust pipe aren't modified to match maximum power and flow cannot be achieved. I'll post this week what I have found out.