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600RS- DMAX 770 vs RKTEK 734/738

600rs 770 dmax rktek 738 mod

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#1 MrClaus

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Posted 15 February 2021 - 09:26 AM

Hey guys!

Had a little too much fun in WNY last week with my 13 pro open mod chassis 600rs.
Melted down the PTO side after a WOT pull across a field. Too cold to tear down yet but,
Obviously when your junk blows up you add more power... because that solves everything.

Questions- 770 DMAX vs 738 RKTEK vs 600RS RKTEK ported?
What’s the better setup? I can source 700/800 cylinders no problem and will do all of my own work other then porting and plating.

Lots of info about the DMAX 770 out there and everyone seems to love it but the mileage sucks. Are the quiet twin pipes trailable? Here in NY it’s a death sentence to trails with anything loud.

Does anyone have the 738/734 setup? I couldn’t find much at all about people running them in an xp/xs chassis sled.I know the pistons and jug work are unique thus harder on rebuilds. Lighter dual ring piston is supposed to rev like the cats meow and carry 155hp.

Has anyone run an RKTEK 600rs (newer like 2013 up) ported jug with their dual ring pistons and custom domes? Any luck with that setup and is it really worth it over a stock 6hundey?

Is one better off just picking up an 800r and dumping that into a trail ridden sled?

Is one better than the other as far as reliability tune-ability etc?

Any input is appreciated guys! I couldn’t find much that directly compared the options in any recent posts!

This is the crap box I’ll be strapping the new motor into. Lots of cash already into it so I’d hate to part ways with her at this time.

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Edited by MrClaus, 15 February 2021 - 09:28 AM.


#2 MrClaus

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Posted 21 February 2021 - 07:41 AM

Anyone?

#3 djm

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Posted 21 February 2021 - 10:49 AM

Hey guys!

Had a little too much fun in WNY last week with my 13 pro open mod chassis 600rs.
Melted down the PTO side after a WOT pull across a field. Too cold to tear down yet but,
Obviously when your junk blows up you add more power... because that solves everything.

Questions- 770 DMAX vs 738 RKTEK vs 600RS RKTEK ported?
What’s the better setup? I can source 700/800 cylinders no problem and will do all of my own work other then porting and plating.

Lots of info about the DMAX 770 out there and everyone seems to love it but the mileage sucks. Are the quiet twin pipes trailable? Here in NY it’s a death sentence to trails with anything loud.

Does anyone have the 738/734 setup? I couldn’t find much at all about people running them in an xp/xs chassis sled.I know the pistons and jug work are unique thus harder on rebuilds. Lighter dual ring piston is supposed to rev like the cats meow and carry 155hp.

Has anyone run an RKTEK 600rs (newer like 2013 up) ported jug with their dual ring pistons and custom domes? Any luck with that setup and is it really worth it over a stock 6hundey?

Is one better off just picking up an 800r and dumping that into a trail ridden sled?

Is one better than the other as far as reliability tune-ability etc?

Any input is appreciated guys! I couldn’t find much that directly compared the options in any recent posts!

This is the crap box I’ll be strapping the new motor into. Lots of cash already into it so I’d hate to part ways with her at this time.

 

Why does the mileage suck on a 770; it doesn't on my two.  Use TM40's off 800R or 600HO and jet accordingly. Don't use the 600RS TMX carbs. Run a single 800 ETEC Summit pipe and muffler,  A Big John ported 770 will out run an 800ETEC no problem, spools instantly. decent fuel economy and great reliability. What's not to love. 



#4 MrClaus

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Posted 21 February 2021 - 02:41 PM

Awesome thanks Djm, your vote would be a 770 over a 734/8 then?
I currently have a spare set of 700 jugs and a matching rkt head so was thinking of going that way. Otherwise I will be going with a ported Dmax 770 with his single pipe. I know there’s tons of reviews on the 770 and people seem to love them but the rkt motor seems to put out 155+.

#5 revx440HO

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Posted 21 February 2021 - 03:03 PM

I would recommend talking to both. As far as choosing one over the other.... flip a coin.
Having had both. And setup numerous others. I dont feel either is bad decision. When all said and done Setup as a whole will determine how it runs.
Djm's sled runs well. He has his preferences. For a 770. I feel Rktek 800 porting is top notch.
As I would also go with a 800r ptek pipe. The tmx will make a few more hp. The tm40s are less finicky and easier if you add oil injection. Plus you have to factor in additional price for carb boots. The fuel consumption with tmx is more of a setup issue I feel.
Low gearing. Larger lug track. Clutching it like a 440/600 I think contributed to the excessive fuel use.

#6 Jcstacey8

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Posted 23 February 2021 - 05:30 PM

i loved my 770 once the jetting and clutching was right. idk what the mpg was as i built it to make power and be fun not to save fuel. if i was to build another i would just go ported 700. verly nice liner power and still a blast to ride



#7 MrClaus

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Posted 24 February 2021 - 10:44 AM

Going 734/738! Already have sourced a set of jugs and raves with an rkt head. Hopefully the head design for the shell hasn't changed and I can get a set of new domes cut. Thanks for all the info and spec guys. I'll put together a post about my build! 



#8 djm

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Posted 24 February 2021 - 03:40 PM

Awesome thanks Djm, your vote would be a 770 over a 734/8 then?
I currently have a spare set of 700 jugs and a matching rkt head so was thinking of going that way. Otherwise I will be going with a ported Dmax 770 with his single pipe. I know there’s tons of reviews on the 770 and people seem to love them but the rkt motor seems to put out 155+.

 

I have run RKT's stuff before.   And I replaced two ported 700's that ran great, with the 770s and would not go back.  I have had doo's ported by just about everyone, and their is a reason my current stuff is done at BJ's.  As 440HO mentioned, the TMX's might make a touch more power; but easier to be out in left field with them and they are less fuel efficient.  Why live with problems, just use the production TM40's and go with the single Doo pipe.  Should be lots of them around. The summit pipe on the 800 in those days was tighter than the MXZ pipe, and works super.  As mentioned I have two XP's with them and they both run well. Never had a lick of troubles with either one from day one.  You just need to send off a pair of 8000HO cylinders to get ported.   I don't want to say too much, but if they go to BJ, they will get done right and they might be cut to help out..  He can set you up head wise for what ever octane fuel you want to run.

 

Darn, just read your last post, sorry to hear it but I wish you the best of luck with your efforts!   A 770 will run closer to 15+ horsepower than a 738 every t time.  The 800HO ports stock are better than ported 700's and when they are ported they are equivalent to 800 Etec ports; just saying.  if you looked at all the pieces before assembly you could make the better decision.  Don't get me wrong, I loved and rode ported 700's for a number of years.  Still love them, but there is not enough room in the 700 cylinders for the ports you want to make that kind of horsepower every time on different dynos.  

 

Again I wish you the best of luck with your 738/700.   


Edited by djm, 24 February 2021 - 03:55 PM.


#9 MrClaus

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Posted 26 February 2021 - 10:26 AM

DJM, I haven't sent my stuff out yet so there's still time to switch directions and, the info you gave me is exactly what I was looking for!!

 

I'll sell the 700 parts then and go with a 770. I'll talk with Big John and have him do the job I spoke with him when I blew up the 600 and he seemed like an awesome guy as well as being super knowledgeable. He definitely did not like the TMX race carbs and said run TM40's. 

I'll cut my own case half on a drill press as the sleds coming apart anyways.... I burnt a pto ring at 500 miles on the RS motor.

Can you clarify some specifics on your setup as you obviously know what works...

 

-I know to pick up a set of 800ho cylinders and, I'll have them fully ported by BJ.

-What head are you running or does BJ take care of that side of things? RKT unit DMAX? 

-What year/model summit pipe are you talking about that you're running? Any reason to not get an SPI pipe or DMAX unit or is it just not worthwhile when compared to an OEM?

-With the TM40 carbs (I'm assuming 800r units) what reeds and boots are you running and did you swap to oil injection? Any concerns with the 600rs airbox and TM's? I'm running a custom MOD half aluminum airbox on a summit dual intake side hood for max air flow. I'm pretty sure I can swap out the rubber carb necks in the box to fit the larger units if need be but. (Not sure if the OD on the inlet neck is the same). 

 

My sleds being completely redone and made more trail friendly/ setup for the area I ride-

Swapping out a 1.75 paddle and 25/49 gears for a 1.5/1.25 Storm track with 90 studs and 25/45 gearing. Looking to redo clutching as well to be a little softer on launch as it just trenches like a mofo with the setup I have. 

 

Once again thanks for all of the info it's appreciated! 



#10 adamadam

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Posted 26 February 2021 - 06:06 PM

I wouldn't run a dmax 770 if he paid me.

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2020 GMC 1500 AT4 std bed

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2015 Summit SP 146
2012 MXZ 550f
2014 Yamaha YZ250
2013 Honda CB1000R, 2012 Ninja 250, 2015 CB500

2016 Can am Maverick XXC

 


#11 MrClaus

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Posted 26 February 2021 - 06:43 PM

Care to elaborate?
Big John would be doing the work not DMAX I’ve heard great things about Sled head racing!

#12 adamadam

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Posted 26 February 2021 - 09:21 PM

Care to elaborate?
Big John would be doing the work not DMAX I’ve heard great things about Sled head racing!

 

customer service is non existent and i'm pretty sure he doesn't even care.. a few people here have had bad experience with him. took me a while to get my 770 running but when it did it felt like an 850! but motor stopped very abruptly, and when i opened it up it looked ok only for both pistons in the same spot.. the one side snapped a rod. couldn't get any kind of response from Dmax (he built the engine complete) I've heard a few people complain about Dmax product.

 

then i went 800etec.. was a little heavier but i sure did like the added reliability and it ran all the time every time.

 

i'd like to build an XP RS again, i loved those 120's and make it a 700 or 770 from someone else. 


2020 GMC 1500 AT4 std bed

2020 Jeep GC SRT8

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2015 MXZ RS with 800ETEC
2015 Summit SP 146
2012 MXZ 550f
2014 Yamaha YZ250
2013 Honda CB1000R, 2012 Ninja 250, 2015 CB500

2016 Can am Maverick XXC

 


#13 MrClaus

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Posted 26 February 2021 - 09:43 PM

customer service is non existent and i'm pretty sure he doesn't even care.. a few people here have had bad experience with him. took me a while to get my 770 running but when it did it felt like an 850! but motor stopped very abruptly, and when i opened it up it looked ok only for both pistons in the same spot.. the one side snapped a rod. couldn't get any kind of response from Dmax (he built the engine complete) I've heard a few people complain about Dmax product.

then i went 800etec.. was a little heavier but i sure did like the added reliability and it ran all the time every time.

i'd like to build an XP RS again, i loved those 120's and make it a 700 or 770 from someone else.


Hey thanks for replying. Good to know I’ll steer clear of Dmax then. So It’s either my own 770 build or doing an rkt 738. I’m still waiting for djm to reply with his opinion as he’s run both setups. I’m super happy with the sled.. reliability is kinda meh probably my fault for the meltdown.
With the worked shocks from monster performance and all the other trick stuff this thing handles the nastiest trail I can hang on through.
Likely building this new motor to ride for a year or two until I get a house and then it’s a new doo for sure! This sled will stay as a trail machine for my local stuff where it’s a short tow back to the house/trailer haha!

#14 djm

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Posted 28 February 2021 - 01:19 PM

DJM, I haven't sent my stuff out yet so there's still time to switch directions and, the info you gave me is exactly what I was looking for!!

 

I'll sell the 700 parts then and go with a 770. I'll talk with Big John and have him do the job I spoke with him when I blew up the 600 and he seemed like an awesome guy as well as being super knowledgeable. He definitely did not like the TMX race carbs and said run TM40's. 

I'll cut my own case half on a drill press as the sleds coming apart anyways.... I burnt a pto ring at 500 miles on the RS motor.

Can you clarify some specifics on your setup as you obviously know what works...

 

-I know to pick up a set of 800ho cylinders and, I'll have them fully ported by BJ.

-What head are you running or does BJ take care of that side of things? RKT unit DMAX? 

xxx I never used a DMAX part.  As I recall, have an RKT head on one of them and Big John used an 800HO head with the domes cut out and new domes inserted. It has been so long ago that this was done, I will have to go look at both sleds to be sure. 

 

-What year/model summit pipe are you talking about that you're running? Any reason to not get an SPI pipe or DMAX unit or is it just not worthwhile when compared to an OEM?

xxxx  Duramax pipes are hard to find.  TT670 had one, he is he one that got me going on the 770 as he had built one.  I believe it was a 2013 but I will have to check, see if I can find the old thread on the subject as I detailed everything we did and used. 

 

-With the TM40 carbs (I'm assuming 800r units) what reeds and boots are you running and did you swap to oil injection? Any concerns with the 600rs airbox and TM's? I'm running a custom MOD half aluminum airbox on a summit dual intake side hood for max air flow. I'm pretty sure I can swap out the rubber carb necks in the box to fit the larger units if need be but. (Not sure if the OD on the inlet neck is the same). 

xxxx I used TM40's and Vforce reeds and manifolds (bought some Boeysens and still have them in a box in the garage.  Just couldn't install them. Too much aluminum for heat pickup and essentially solid mounting the carbs with needles and seats didn't seem like a good idea to me.  Know lots of guys use them.  I have oil injection on one sled and premix on the other.  Kind of wanted to see if the results would be the same and how much trouble it was using premix.  Had equal success with both.  I would use non 600 RS stuff for airbox and inlet.to match with the TM40's.  I don't remember why AdamAdam had so much trouble and bad memories as mine have all been good.  And these two engines have been super reliable. I will have to go back and look at some of his threads. Don't remember if he use TMX or TM carbs.  

 

xxxx I do know Big John won't steer you wrong.and his engines will be reliable.  When I did mine, I bought two 600RS crankcases, one with crank and one without. from Twinpower on here Rene and his dad are super. Big John happened to have a super 600RS crank at the time that had come out of Trgystad engine that he used in the second one.  I was so happy with the first one, I could not wait to get a second one.  Anyway my old thread on the the subject had the exact pipes I used with ID of the stinger outlets. if I can find them.  Jetting as I recall is within a jet size of what I was 

running on the ported 700's 

 

My sleds being completely redone and made more trail friendly/ setup for the area I ride-

Swapping out a 1.75 paddle and 25/49 gears for a 1.5/1.25 Storm track with 90 studs and 25/45 gearing. Looking to redo clutching as well to be a little softer on launch as it just trenches like a mofo with the setup I have. 

 

xxx If I can't find where I have the info written down, I can pull my clutches apart and tell you what I am running for clutching,  I know I have Joey's helixes in both sleds, with DooDoctors floaters and I want to think the ramps are 412's but I would have to check to be sure. seems to me pin weight was in the 21 gram range and I typically don't like high engagement speeds but would have to look to find what primary springs I was running.  Ha ha.. know you can run a RS flywheel with the standard twin pickup so you can have RER as I tried that initially and for some reason it limits you 

to 7200 engine speed.  That was my biggest hurdle when I got the first one built. I thought the two 180 degree short pickups on the RS fly wheels would work for RER and then did, but as mentioned it limited the sled to 7200 rpm.  Just changed the flywheels to production engine flywheels and walla I could run whatever max rpms I clutched for.  Memps were XP 800R with Ski-Doo installed hot 700HO curves in them. But the production 899R memp curve works just fine. 

 

Once again thanks for all of the info it's appreciated! 

xxx Based on some of the DMax 770 stories, I am glad I went with Big John.  Oh should add with the 700's I had cylinders ported by BJ, Trygstad, RKT, Chuck Walthers and one or two others

There is a reason why I keep going back to BJ.  Not sure who the guy is that ports for him, but he is good!   

 

Sorry, I didn't follow up here.  Assumed  you were off getting the 738 done.  



#15 djm

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Posted 28 February 2021 - 01:21 PM

I wouldn't run a dmax 770 if he paid me.

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Remind me who's pipe and which carbs you ran on your 770, I believe I knew at the time when we were all building them but I don't remember now. 

And sorry to hear you snapped a rod!  Fortunately I have not had that experience. 

 

Also what engine speeds were you running?  With BJ porting/port timing 8000 works perfectly. and it matched the 800 Etec summit pipes I am using. 


Edited by djm, 28 February 2021 - 01:26 PM.






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