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840 Big Bore W/stage Iii Cams, Done!

32K views 95 replies 28 participants last post by  stroker0836 
#1 · (Edited)
Finished with it today and am still breaking in the new top end. but i can tell you that this thing is a beast. haven't given it more than half throttle and my vdi has not come back from Velocity yet, so there is a lot more power coming still. The low end torque is crazy and the top end is supposed to be even better. I will post some pics of the crank case breather setup that is required with this motor and if anyone has any questions on the install you can pm me.More to come!

just to clarify, this kit is from Four Stroke Tech and i don't do motor work, except my own. so if you are a do it yourselfer and have questions on this i may be able to answer them. by the way Mickey Dunlap at FST was great to do buiseness with both before and after the sale, i would recomend him to anyone, on top of that he usually has these kits in stock ready to ship!
 
#2 ·
Good to hear Chase!! What are you running for exhaust, did you make a custom one? These kits are awesome, once setup right with a VDI and good exhaust, it will most likely double your horsepower. Im trying to decide between the standard bore kit with stage II's or the 840 with stage III's. I do all woods riding so I think the standard bore with II's may be the way to go for me. Keep us posted on the beast.
 
#3 ·
I fabbed up a 2" stainless flowmaster hushpower II for now and made mounts that use the stock frame mounts, it sounds real good. will get something else as soon as something good becomes available. my vdi will be back from Lyle this week sometime, so for now i'm using the stock cdi
 
#6 · (Edited)
here are some pics, the first one shows were you have to drill a hole in the rear cylinder for a return line for the new crank case breather setup. i used a 1/2" brass nipple, JBed it in place then drill a hole through the cylinder. the hose is from a yfz 450 it is the perfect length and has a 90 on the other side just were you need it. the second picture shows the box you have to use for the crank case breather, it also is off of a yfz 450. i fabbed a mount for it that attaches to the shifter frame and it fits perfectly inside the engine cover like this, you can also see were i extended the hose coming from the crank case, it then gos into the second nipple on the yfz box. the top hose on the yfz box is the open air vent it just go's down to the bottom of the skid. i may end up rerouting it up and putting a small filter on it, we'll see. the third and fourth pics are of the exhaust i made, it mounts in the stock locations and there was no need to cut off the stock head pipes either. it seems to work very well for now. the merge collector was made from a piece of 2" stainless and a couple of bent 1.5" stainless, shaped and tigged together. then the inside was cleaned up with a die grinder to remove all edges and smooth out as best as possible. the last is of my teryx for those who have not seen it yet.
 
#7 ·
Man looks neat,how close are you too glamis? There is a fellow bench racer named michealtom401 that loves to outrun Teryx's.. He is in the dune reports thread. If you close please go and ride with this dude and show him how the teryx performs...LOL
 
#8 ·
I like where and how you mounted the breather should work good. For those of you getting ready to build a V-Twin motor this is something you want to make sure you do or you will end up with oil in your air box. Even if you start reving the stock motor with a VDI this can be a problem.

One thing I seen with these motors is you need to warm them up a good 15min. before you run them hard or you will damage the rings seal by blowing hot gases past the rings washing the cyl. Ring seal is the main problem we see with these motor from not taking your time warming them up and breaking them in.

As of today we will be building some new high compression 800 kits for the close course racers on the west coast for their cc rule limits.
 
#9 ·
How would you suggest break in on a new engine? In the past I have rode them pretty hard from the get go and mine have all ran strong.
Hopefully I'll get my teryx this week and I can practice it again just want your opionion.
 
#10 ·
The key is get it warm so the rings seal. It's OK to run them somewhat hard, just be on and off the gas, this is what seats the rings. Holding it wide open down the road is hard on them if the rings are not seated yet.:rm_thumbdown: You only get one chance to do it right or you will be calling me for a big bore before it's time:doh:lol
 
#13 · (Edited)
So following Mickey Dunlaps recomendations on building exhaust headers that would work good with this motor, i finished them today. I used mandrel bent mild steel that i will end up having ceramic coated when all finished and tested. I started with vw exhaust flanges and gaskets cause they are an exact fit, then came of the head with about 12" of 1.5" tubing then steped it up to 1.625" tubing. the front header i made go over the flywheel instead of under like stock, to make it as short as possible. finished header length is
40.5" and both front and rear are exactly the same length ( some said it would be impossible). I don't believe the front one can be made any shorter than this i did every thing i could to try. Tomarrow i will fab the merge collector and the pipe mounts and give a report on how it runs. the pipe i am using is a hushpower II shorty with 2.25" in and out. here are some pics of the headers, you can see the difference between the stock one and the ones i made.
 
#14 ·
Excellent work Chase, that should free up HP on that beast! Keep us posted on the results.
 
#22 · (Edited)
Not really, its been dynoed several times that equal length Muzzy headers make more hp than any other pipe on a built kawie V-Twin. The only comparable true duals are the LTE's, but there twice as much as Muzzy!

How about some infoe on motor kit like price,what comes with it, hp you are makeing now, stock weights in clutch still?
The FST 840 kit is right around $1500, includes Hi-Comp pistons, sleeves or possible cylinder exchange, custom grind FST cams of choice, heavy duty valve springs and I believe the head gaskets. The FST standard bore kit, includes everything above execpt the sleeves or cylinder exchange and is right around $800. I believe he has the kits in stock ready to ship. Check with Mickey at FST to be sure. He hasnt dynoed this setup in a Teryx yet, but it should be about double the stock output. Dont forget you still need a good exhuast and cdi. As far as clutching, I think Chase is still stock but will be experimenting in the very near future.
 
#16 · (Edited)
have not been able to get on this site since friday sometime, it seems to happen about every other day, i'm about ready to give up on this place if something doesn't get fixed around here. there are other sites that never go down.
got the pipe and headers finished, vdi installed, nine 1" holes drilled in the top of the lid, the main jets that i had to drill out to 3/32" cause they don't make them any larger than 200's, turned the fuel screws out two turns stock is one, and it hauls. on flat ground i hit the rev limiter in under 500', gps says 58.3mph. it pulls hard all the way, in fact once the belt has reached the top of the primary and it starts to rev higher it feels like it accelerates even faster, its still pulling hard when it bounces off the limiter. a higher clutch engagement rpm will greatly improve the acceleration. the full exhaust system i built made a huge difference, the top end power is amazing. earlier today we shot some video of my teryx drag racing a friends rzr, its no contest the teryx pulls away from the start and keeps pulling all the way. we marked out 550' and at the end its a huge gap. the video was supposed to be up today but we had some issues, we should have it taken care of tomarrow though. i will post a link when its ready, we filmed several races!
 
#18 ·



in the first one the camera is about 500' away, as i pass the camera you can here me hit the rev limiter, gps read 58.3mph.
the second one we are on a driveway that is only about 300' long so we had to brake quick.
the rest are still loading
 
#23 ·
i am going to send the primary drive off next week for mods and machine work, need to figure out what is available for the clutch to raise the engagement rpm also. this thing should be capable of 67-68 mph by the end of next week.
 
#27 · (Edited)
yes

I talk to VFORCEJOHNNY and he said that his stage three clutch
mod would really help a stock teryx go, I wonder how this would do
on this monster??!!!!
i talked to him today also, after seeing the video he posted on one of the other sites telling me i need the clutch work. i ordered the primary puller bolt and the primary spring today that he instructed me to. monday i will next day him my clutch and will have it back on thursday. he says it will accelerate much harder, he actually said it will pull the front tires off the ground. the machine work he does will give it 20% more overdrive, that translates to about 75mph. i also order the programer for the VDI so that i can up the rev limiter, cause its just starting to get into the power at 9200rpm. next week i will post more drag videos and film the speed on the gps if i can find someone to ride along. maybe even race my own 523YFZ on the street just for fun, might be a good one!
 
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