Just wondering on which big boreto go with, I was looking into the bender 838. Has anyone on this site ever own one. I was also told by a bender rep that their custom bigbore pipes made power on the srx700. He told me 170hp, pipes, porting and v-force. I also just got into asphalt racing and really enjoy it, but now i'm looking for more power.
cacsrx1
New member
Have Don build a 780.
bufalobob
Member
gates:
below is a copy of a thread i posted this past spring. i believe this will answer your question on which big bore to buy.
bob
"today i took my 835 bender srx to dynotech for fine tuning. every sled i have owned in the last 20 years has been dyno tuned. if you have a high performance sled & have not had your sled on a reputable dyno operators dyno than you are definately leaving performance on the table. my srx is a trail sled with reverse, stock compression, stock timing, bender pipes, tunnel cooling kit & a cold air kit. i left my winter jets in & did not hook up to the dynos cooling system.
the motor made 185.9 hp @ 8400 rpm & 117.7 lbs. ft. torque @ 8200 rpm. jim said if i jetted it down for the days conditions it would be over 190 hp & if i added timing & increased compression it would be around 200 hp.
we then checked the accuracy of my tach to the dynos tach & found it to be spot on, as has been every other yamaha tach i have had checked.
jim also ran a test to simulate trail riding between 6000 & 7200 rpm & i found that the primary circut was jetted too rich, even for winter conditions. jim will be posting the results on his web site @ dynotechresearch.com soon.
by the way this motor has 2000 miles on it."
below is a copy of a thread i posted this past spring. i believe this will answer your question on which big bore to buy.
bob
"today i took my 835 bender srx to dynotech for fine tuning. every sled i have owned in the last 20 years has been dyno tuned. if you have a high performance sled & have not had your sled on a reputable dyno operators dyno than you are definately leaving performance on the table. my srx is a trail sled with reverse, stock compression, stock timing, bender pipes, tunnel cooling kit & a cold air kit. i left my winter jets in & did not hook up to the dynos cooling system.
the motor made 185.9 hp @ 8400 rpm & 117.7 lbs. ft. torque @ 8200 rpm. jim said if i jetted it down for the days conditions it would be over 190 hp & if i added timing & increased compression it would be around 200 hp.
we then checked the accuracy of my tach to the dynos tach & found it to be spot on, as has been every other yamaha tach i have had checked.
jim also ran a test to simulate trail riding between 6000 & 7200 rpm & i found that the primary circut was jetted too rich, even for winter conditions. jim will be posting the results on his web site @ dynotechresearch.com soon.
by the way this motor has 2000 miles on it."
Junior
New member
I'd recommend an 835. It's more expensive with the pipes and porting, but that also makes it a more complete system with every important part designed to work with the others. Rather than pipes and base porting designed to work with a 700 at 8500rpm.
BufaloBob's dyno results speak for themselves really.
BufaloBob's dyno results speak for themselves really.
yammiman
Member
I think before you decide "who" you should decide "how much" - bufalobob's sled put up some impressive numbers but it came at a price - the last I looked, the pipes needed to complete Bender's kit are in the $1000.00 range - (is that about right Bob?) - that would buy alot of engine work that could result in the same numbers - figure out how much you have to spend, and go from there and talk and look at them all - also do research on this website - don't think that just because someone's work is being recommended that it is just because they are a member or vendor on this forum - there is ALOT of experience on this site that you can use to your advantage that will save you money in the long run - good luck and let us know and see what you end up with!! 
Thanks for the info guys.
Junior
New member
you're correct Yammiman, there's alot more too it than just hp. But that goes beyond just pricetag aswell, longevity, and midrange power also come into it, especially for a trail motor. Doesn't take many sets of pistons to come up to the $1200 for a set of bigbore pipes.
bufalobob
Member
i will be taking another 835 to dynotech soon. this one will have stock carbs, pipes, timing, compression & no case porting. will post results.
bob
bob
Junior
New member
That'd be awesome, thanks bob.
yammiman
Member
I would love to see those numbers also - I didn't know the 835 would even work with stock pipes - is that a different design?
....Doesn't take many sets of pistons to come up to the $1200 for a set of bigbore pipes.....
Junior - I agree, but that is where the experience and knowledge of people on this site that would help avoid that from happening!!
....Doesn't take many sets of pistons to come up to the $1200 for a set of bigbore pipes.....
Junior - I agree, but that is where the experience and knowledge of people on this site that would help avoid that from happening!!
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bufalobob
Member
yammi:
same design.
bob
same design.
bob
Junior
New member
yea it's the same design, the pipes aren't necessary, but they sure help!
yea, we can help people prevent burndowns, but there's only so much that can be done. Whenever you're modifying, it's a risk, and frankly.. bound to happen. I mean anyone that's seriously played with these engines has been thru a number of pistons that they'll be embarrassed to admit to, usually for STUPID reasons too.
yea, we can help people prevent burndowns, but there's only so much that can be done. Whenever you're modifying, it's a risk, and frankly.. bound to happen. I mean anyone that's seriously played with these engines has been thru a number of pistons that they'll be embarrassed to admit to, usually for STUPID reasons too.
Please do tell us junior all about your 780 building expertise and your findings, I would like to learn more about how a 835 out does a 780, It sure sounds like youve owned and built both and can tell us all the gains and losses between the two.
What did you do with the timing?
what about the carbs, mods, jetting?
what about the skirt clearances/and piston clearances?
what rpm range did you run the 835 at if the 780 only runs at 8500rpm?
most importantly the headwork, what did you find?
be a great benefit for all of us to learn.
What did you do with the timing?
what about the carbs, mods, jetting?
what about the skirt clearances/and piston clearances?
what rpm range did you run the 835 at if the 780 only runs at 8500rpm?
most importantly the headwork, what did you find?
be a great benefit for all of us to learn.
Junior
New member
intentionally instigating conflict, particularly with a moderator isn't acceptable. Have a nice vacation.
now, in response to the questions. Timing I wouldn't advise playing with on a trail sled, on a race sled you'll be using your EGT to calibrate it same as always.
Carb mods I would advise bored carbs or bigger ones, IF they're within the price range of the purchaser, they'll wake the motor up, far moreso than with a stock engine. It will hurt your charge velocity, but help the flow, meaning that it'll hurt you in the midrange, but when she's open there'll be a gain.
Skirts I wouldn't EVER advise modifying, because in the past I've experimented with it and found no hp on the dyno, just a shortened piston life before it folds the skirts, something that the Yamaha 696's are already pretty fast at, and I am loathe to aggrivate the problem.
headwork; I've found that a 16.5-17* squish angle works best, squish height will have to go by the intended use, and what fuel is available, same as always. I generally will gently radius the squish zone into the dome where they meet, I honestly couldn't say exactly what radius it is 'cause I generally cut it by hand.
As far as what I like better about the 835? for starters, it uses cast pistons, which makes it better for the average trail rider in terms of warm-up times, tighter piston clearances, no piston slap on start up. For people after abit more, it's got the potential there, with the pipes that are set up for it, and possibly with a higher revving CDI box, to really haul. I've never had a race CDI on one myself, but with appropriate porting, the belly is deep. BuffaloBob's dyno results are a fantastic example of this, and that was with a stock CDI.
A downside is the steel sleeves, however it's not nearly the issue that people think it is, against a hot steel object, the layer of heated air will enlarge, reducing the transfer of heat, it's a self balancing thing. Nomatter what the material in the liner is, they will all gravitate towards each other, despite vast differences in rates of thermal conductivity. The larger air buffer actually helps to keep more heat in the cylinder, pressing the piston down. Meaning the energy goes to moving the sled, not heating up the heat exchanger. Furthermore, any machine shop can replace a steel sleeve in the event of a burndown, it's a trickier matter to re-NiCaSil a jug. This isn't so much just money, but downtime. If you fry a cylinder on an 835, you're talking same day service at the machine shop if you have a spare sleeve (which is a good idea, given what they cost) or same day service plus the wait for shipping 1 way on it. With NiCaSil you're into 2 ways shipping and usually atleast a weeks turnaround, even if you do it in the off-season, if you send it in in January, it'll be late February before you're rolling again. While that might be acceptable to me, who only puts on a couple of hundred trail miles a year, to the AVERAGE guy, that's not acceptable.
Truthfully, it's been 5 years since I've played with an 835, could be that stuff has changed since then, but at the time I was very impressed with it.
now, in response to the questions. Timing I wouldn't advise playing with on a trail sled, on a race sled you'll be using your EGT to calibrate it same as always.
Carb mods I would advise bored carbs or bigger ones, IF they're within the price range of the purchaser, they'll wake the motor up, far moreso than with a stock engine. It will hurt your charge velocity, but help the flow, meaning that it'll hurt you in the midrange, but when she's open there'll be a gain.
Skirts I wouldn't EVER advise modifying, because in the past I've experimented with it and found no hp on the dyno, just a shortened piston life before it folds the skirts, something that the Yamaha 696's are already pretty fast at, and I am loathe to aggrivate the problem.
headwork; I've found that a 16.5-17* squish angle works best, squish height will have to go by the intended use, and what fuel is available, same as always. I generally will gently radius the squish zone into the dome where they meet, I honestly couldn't say exactly what radius it is 'cause I generally cut it by hand.
As far as what I like better about the 835? for starters, it uses cast pistons, which makes it better for the average trail rider in terms of warm-up times, tighter piston clearances, no piston slap on start up. For people after abit more, it's got the potential there, with the pipes that are set up for it, and possibly with a higher revving CDI box, to really haul. I've never had a race CDI on one myself, but with appropriate porting, the belly is deep. BuffaloBob's dyno results are a fantastic example of this, and that was with a stock CDI.
A downside is the steel sleeves, however it's not nearly the issue that people think it is, against a hot steel object, the layer of heated air will enlarge, reducing the transfer of heat, it's a self balancing thing. Nomatter what the material in the liner is, they will all gravitate towards each other, despite vast differences in rates of thermal conductivity. The larger air buffer actually helps to keep more heat in the cylinder, pressing the piston down. Meaning the energy goes to moving the sled, not heating up the heat exchanger. Furthermore, any machine shop can replace a steel sleeve in the event of a burndown, it's a trickier matter to re-NiCaSil a jug. This isn't so much just money, but downtime. If you fry a cylinder on an 835, you're talking same day service at the machine shop if you have a spare sleeve (which is a good idea, given what they cost) or same day service plus the wait for shipping 1 way on it. With NiCaSil you're into 2 ways shipping and usually atleast a weeks turnaround, even if you do it in the off-season, if you send it in in January, it'll be late February before you're rolling again. While that might be acceptable to me, who only puts on a couple of hundred trail miles a year, to the AVERAGE guy, that's not acceptable.
Truthfully, it's been 5 years since I've played with an 835, could be that stuff has changed since then, but at the time I was very impressed with it.
I have always had cylinders back within a week and everyone else I know gpoing through millenium performance.Us chrome now that's a different story.
The thing that sucks about using bender pipes is there illegal here there too loud for wil trails or lakes unless your on a closed race track.
The thing that sucks about using bender pipes is there illegal here there too loud for wil trails or lakes unless your on a closed race track.
yammiman
Member
.....intentionally instigating conflict, particularly with a moderator isn't acceptable. Have a nice vacation.....
Junior - are you serious about this? - I guess I didn't see where his questions "intentionally instigating conflict" -
Junior - are you serious about this? - I guess I didn't see where his questions "intentionally instigating conflict" -
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cacsrx1
New member
yammiman said:.....intentionally instigating conflict, particularly with a moderator isn't acceptable. Have a nice vacation.....
Pro - are you serious about this? - I guess I didn't see where his questions "intentionally instigating conflict" -
X2...kicking off one of the most helpful guys on the site for instigating conflict and then answering his question????
Play nice
Well, looks like Junior finally got a chance to give Don a "nice vacation". Thanks so much Junior, the site will really benefit from Don not being around for a while. Thanks too Junor for the insight on your real world experiments with the 835. Real factual data there. Would you be willing to sponsor a free 835 contest here to benefit all of the users from all of your experience? You know, kind of like what Don offered with the free porting contest? Lastly, I have never heard anyone say that more heat in a 2 stroke motor makes more power. First you said that the cast cylinders are a downfall, then you explained how they transfer the excess heat into more power? I don't get it. Could you please explain that again? Thanks in advance.
Madmatt
Well, looks like Junior finally got a chance to give Don a "nice vacation". Thanks so much Junior, the site will really benefit from Don not being around for a while. Thanks too Junor for the insight on your real world experiments with the 835. Real factual data there. Would you be willing to sponsor a free 835 contest here to benefit all of the users from all of your experience? You know, kind of like what Don offered with the free porting contest? Lastly, I have never heard anyone say that more heat in a 2 stroke motor makes more power. First you said that the cast cylinders are a downfall, then you explained how they transfer the excess heat into more power? I don't get it. Could you please explain that again? Thanks in advance.
Madmatt
relax guys all is well.