why does ski doo put 40mm carbs on the 600 trail sleds and 38mm carb on the RS???

long story short.....

The combination of intake parts they use works best.... I don't think 40mm will fit without hitting jackshat on RS cylinders with RS reeds.

can anyone elaborate more cause im kinda thinking that i wanna bored my 38's to 40mm and would like to know the pros and cons of it and y ski doo didnt???

im going to be running ported 700 cylinders for a sleeper sled

Hate to burst your bubble, but a ported 700 jugs on the rs will NOT be a sleeper. It will be basically the same as a 600rs, probably even a little DOWN on hp. Do a big bore, then youll have a sleeper. a ported 700 in the rs is like flushing money down the toilet.

It would be worth a try boring the 38s to 40mm if you are looking for max performance with the portred 700 jugs. Another thing you should do if you are running the 700cc jugs is remove the stinger choke in the stock 600RS pipe. Your 700 and any 600RS for trail riding on pump fuel needs a 40mm ID stinger. The stock 36.5mm stinger is way to tight, for wot runs on pump fuel, i can't stress this enough, it needs to be done.

Can i ask who ported you jugs and did the head work? If it is ported right your ported 700cc, should be in the 137-140 hp range and 91-92 trq. Stock 600RS 133-134hp and 86-87 trq.

What else are you doing to the motor, reeds and pipe? I ask because i am doing the same motor work as you.

well like i said im making it look like a sleeper using RS pipe, RS head with stock domes or maybe mod, cut for the 78 mm bore, maybe bored 38's, porting done by local guy that i take all my stuff to, maybe high tension reeds on the v-force cages, RS timing, RS clutch, doo 700 pistons(77.98mm), RS wrist pin bearings, and i got a RS top end kit that came with like 4 or 5 different size base gaskets.

as of right now the cylinders are being sent to be denikasiled, then he is going to port them, and then send them out to be renikasiled.

im going to dyno the sled as a 600, then put the ported cylinders on it with the cut domes, and set the squish around 50 thousandths, dyno it again, then we will decide if we wanna mess with the pipe choke, reeds, carbs, and stuff. and dyno again.

if i dont see a good improvement then i will just put the 700 motor back together in my summit and have a ported 700 summit, so the money wont go to waste, besides maybe bored carbs but all well.

Is porting really worth 10-15hp? Dont think so.


A stock 700 is anywhere from 122-127hp. I dont see how youll get anywhere NEAR 137, let alone 140 with porting alone. Maybe boring carbs, but that can't be much, not to mention the tuning headache.

gonna throw in a big bore next spring. rk tek 780.


But like you said, atleast your jugs/money wont got to waste!!!

If you would not mind, let us know the number. I would like to know how the dyno runs pan out. Thanks, Later Ski-B.

ya i will post the dynos numbers of before and after, im hoping to have it totally done by like 1st weekend in December


but can anyone elaborate more on y they use the 38s for racing and the 40's for trail?

ttt

I will take another stab at it. The 38mm non rack carbs? Better throttle response, easier to jet not being on the rack, lighter throttle pull maybe and more available tuning parts like needles vs the 40mm rack carbs.

Old rule of thumb, bored carbs net 2-3 hp vs stock bore carbs, what ever the size maybe.

Oh man, i wish it was Dec 1st to see the results on the dyno

How about Taper bored carbs?

Olav Aaen claims, 38mm flat slide = 100 cfm.
------- 38-44 Taper Bored flat sled = 136 cfm.
--- 44mm straight bore, round slide= 139 cfm.

Just another option for you in search for the max hp, RS.

stab in the dark

smaller carb = better initial bottom end performance vs bigger carb being more top end orienting?

WT F....760 not enuf PAH?

Calamari,

Throwin the 780 in my RS... the 760 is in my Rev chassis...

Think snow fellers!!!

How are things going? any Dyno numbers yet?

only got the stock 114hp and 75 ft/lb tourqe numbers with bad reeds

should be soon for the 700. fell alittle behind and things got in the way.

Has anyone removed this " 36.5mm stinger" from the stock rs pipe for a trail set up?

Is this the stock 600RS? If so would bad reeds rob that much HP? I've seen dyno numbers for a stock RS in the 134 HP range.

It could rob that much hp with a chipped reed paddle. I have had V-Force reeds chip the corner away on my 800HO and the sled would loose 300-400rpm on a full throttle pull, and have very poor throttle response.

Guess we can only wait and see what his healthy 600RS will make on this dyno.

ya the sled just seemed like it was running really fat we were getting low egt's it was hard starting. and pull the reeds and they were warped pretty bad and starting to crack and acting like they want to fold back into the cage.


v-force reeds are junk out of the box, i hate them, take any brand new set and look through them in the light and you will see a pretty good size air gap. then take and pull the pedals off and take a sanding block to the faces and notice how uneven the mold is.

call it obsessive or call it what you want but to me it would seem if those reeds cant seal that good then ur getting blow back through the carb and its playing with the carb signal.

and the reed tension isn't to the standards i like, think of it like a 4-stroke(i know totally different kinda) when you wanna spin the motor at higher rpms you gotta increase the valve spring tension to stop the valves from floating, well if the reeds start floating in a 2-stroke then your not getting the same amount of air/fuel mixture up into the cylinders, air is going to take a path of less resistance and maybe bleed through a bad sealing reed. aslo the better sealing the better air/fuel mixture is in the cases and can lead to better throttle response.

only good thing is they flow good air but i honestly dont think the stock ski doo ones have a problem with that at all

so v-forces are junk enless you spend a extra hour or more per cage and a extra $200 on custom pedals and thats my opinion

next time its on the dyno its going to be a 700 sleeper

rack 40's work better in a trail or a race app. i have gone on the dyno with both and i run rack carbs bored you can go up to 42.5mm and on my 800 thats still not enough..i did build a 700 trail mod once though 150 hp ported cyl. 800 dynoport pipe modified,head cut,v-force,bored carbs, w hooded neddle jet,timing in the mpem this thing ripped would kill stock 800's and run with 800 snox mods..