Carbs, Cams or 904?
- Thread starter Pete R
- Start date
ivar
TT Racer
was in the same boat, now I'm in the process of doing all 3.
If I had to choose, I'd maybe do the carbs first - just to start somewhere. Then save up to do both cams and 904 at the same time
Also depends a little where you want most gains, e.g going 904 only should give you a nice boost in low/midrange torque, but be restricted at top end b/c of the restriction now being carbs and cams.
If I had to choose, I'd maybe do the carbs first - just to start somewhere. Then save up to do both cams and 904 at the same time
Also depends a little where you want most gains, e.g going 904 only should give you a nice boost in low/midrange torque, but be restricted at top end b/c of the restriction now being carbs and cams.
mikenva
Rocker
Do the carbs first .then you can do the cams next .When you get around to the 904 get a tpusa kit and think about getting the head done with os valves at the same time a 904 needs the extra head flow to get the hp out of it. You allso need a pieman box rework and pod fliters with all of the above you should have 80to85hp and mid 60s ft/lbs.
That will wake the bike up alot.
That will wake the bike up alot.
em_dot
Street Tracker
I'm in the same boat, so I've decided to wait until I can do everything all at once. Later this fall I'll do a proper TPUSA 904 BB, 813 Cams, 39mm FCR, Headwork w/ 2mm+ valves, Pieman ignitor. I just ordered a brake up grade from Carlos last week, so we talked BB options too.
Right now I'll just run the stock 865. The airbox will be out and the pods will be in by this weekend. That'll have to due for the duration.
I was on the fence about doing a bigger motor until last weekend when my daughter took her first horse riding lesson. She is 5 years old and she was utterly amazing her frst time out. I was just blown away at how well she did. She has been on me since she was 3 to start riding horses and now she is ready. Regardless, I have my ride, and now she will have hers. For me a 904 will do...
Right now I'll just run the stock 865. The airbox will be out and the pods will be in by this weekend. That'll have to due for the duration.
I was on the fence about doing a bigger motor until last weekend when my daughter took her first horse riding lesson. She is 5 years old and she was utterly amazing her frst time out. I was just blown away at how well she did. She has been on me since she was 3 to start riding horses and now she is ready. Regardless, I have my ride, and now she will have hers. For me a 904 will do...
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Ninja K
Two Stroke
What do you think the performance difference over stock will be once all that is done?
Aussie_T100
Banned
I can't really offer you any advice on which to do first because in my opinion the easiest way is to do all at once. Why? Because you'll only have to tune the carbies once that's why. If you do this in three stages you'll have to tune the carbs three times, that's a lot of time and/or dyno runs which can add to the cost substantially.
Also I cannot recommend going with a 904 kit on an 865 despite the entrenched opinions held by others in this regard. Why? Very poor bang for buck as well as a few other reasons. If you really must go 904 at least sell your 865 barells & pistons to a 790 owner in exchange for his barells and use the 790 barells as core exchange on the 904 kit, that will reduce you cost a little and save one more set of 865 barells from being bored out to the maximum oversize.
At least consider using a TPUSA 865 performance kit instead of the 904 as it is much better bang for buck and you can put the money saved towards headwork if you wish. The 904 kit plus a set of 813's is double the cost of the 865 high performance kit ($1,830 verses $920), in fact you can buy an 865 high performance kit plus a street head for virtually the same money as a 904 kit & a set of 813's. $910 is a lot of money to pay for just 39cc's and a 0.8 to 1 increase in compression in my opinion.
Personally I would just do an 865 high performance kit and a set of FCR's along with a Pieman ignitor at $2,100 total and be happy with the 75Hp+ you would get from those mods. Those mods would give you a 15Hp+ boost for your $2,100. The $2,500 extra cost to get to 85Hp with a 904 plus headwork is not worth it in my opinion as you are paying $2,500 for less than 10Hp.
Others will disagree I'm sure but the figures speak for themselves.
Another complication is that like me you are an Aussie so you won't get the 904 kit through customs without paying brokerage, import duty & GST so you can add a considerable amount ($1,000?) to the figures I have quoted. Unfortunately the 904 kit is exceptionally poor value for us Aussies because of this. If you buy the FCR's and the 865 high performance kit separately you will get them through customs without any additional charges.
Also I cannot recommend going with a 904 kit on an 865 despite the entrenched opinions held by others in this regard. Why? Very poor bang for buck as well as a few other reasons. If you really must go 904 at least sell your 865 barells & pistons to a 790 owner in exchange for his barells and use the 790 barells as core exchange on the 904 kit, that will reduce you cost a little and save one more set of 865 barells from being bored out to the maximum oversize.
At least consider using a TPUSA 865 performance kit instead of the 904 as it is much better bang for buck and you can put the money saved towards headwork if you wish. The 904 kit plus a set of 813's is double the cost of the 865 high performance kit ($1,830 verses $920), in fact you can buy an 865 high performance kit plus a street head for virtually the same money as a 904 kit & a set of 813's. $910 is a lot of money to pay for just 39cc's and a 0.8 to 1 increase in compression in my opinion.
Personally I would just do an 865 high performance kit and a set of FCR's along with a Pieman ignitor at $2,100 total and be happy with the 75Hp+ you would get from those mods. Those mods would give you a 15Hp+ boost for your $2,100. The $2,500 extra cost to get to 85Hp with a 904 plus headwork is not worth it in my opinion as you are paying $2,500 for less than 10Hp.
Others will disagree I'm sure but the figures speak for themselves.
Another complication is that like me you are an Aussie so you won't get the 904 kit through customs without paying brokerage, import duty & GST so you can add a considerable amount ($1,000?) to the figures I have quoted. Unfortunately the 904 kit is exceptionally poor value for us Aussies because of this. If you buy the FCR's and the 865 high performance kit separately you will get them through customs without any additional charges.
RumRunner
Street Tracker
Aussie,
You make some really good points, and I’ll both agree and disagree with you. I’ve actually been looking at this to determine what direction I want to go with my Thruxton. I’ve been thinking of going with carbs (still up in the air on FCR vs. Mikuni but that’s another story) then cams, at that point I’m up in the air on whether I go with High Compression 865 & Head work or going 904… I’ve been leaning more towards the 865 route myself. For me I’d actually rather go in steps. Carbs → Cam → Head & Pistons or 904 kit. My reasoning is that I actually want to tune my bike so I can learn how it works, and I like to tune. I’m actually hoping to get an Wide Band O2 setup so I can see how she’s running now with the stock setup.
Doug
mikenva
Rocker
The 904 will give you more torque then any 865 kit 5 ft/lbs can make the motor feel alot stronger.Its well worth the extra money if you are pulling the jugs off.
I have mikuni carbs go with the fcr carbs you can dial them in closer in low and mid range then the mikuni.Allso the fcr kit you can use your stock throttle and cables.You can balnace the throttle opening alot easyer on the fcr kit allso.I may switch mine to fcrs soon.
I have mikuni carbs go with the fcr carbs you can dial them in closer in low and mid range then the mikuni.Allso the fcr kit you can use your stock throttle and cables.You can balnace the throttle opening alot easyer on the fcr kit allso.I may switch mine to fcrs soon.
mikenva
Rocker
a few have got near 80hp with out head work most get more like 75hp.It all depends on how good your stock head is .A os valve head done right like the tpusa or the ones fast freddy did pick you up a bunch .Some of the others out there that dont know what they are doing dont show as much gain.
RumRunner
Street Tracker
Agreed TQ really helps. Just toying with different ideas for now. What's the difference between the Mikuni ad FCR that you can't tune the Mikuni's in properly? I thought the Mikuni carburetors were actually more tunable?
em_dot
Street Tracker
When that 865 kit first came out two years ago I was kind of interested, but the thought of puting new pistons in a bore with even a few thousand miles on them never really sat well with me. For me, the extra money for a clean bore and new pistons is worth it. The extra torque will be nice too.
If I were on a tighter budget I'd do a 904, 813s, FCRs, and Pieman without the headwork.
mikenva
Rocker
The Mikuni has way less adj then the fcr .There for you can tune the fcr in much closer. Mikuni are just as good for wot raceing though.But a street bike dont stay wot that much lol.
Allso the fcr kits are cheaper.
RumRunner
Street Tracker
Well not if you sell me your used Mikuni's when you buy a set of FCR's
Thanks for the info.
strokerlmt
Moderator
Which one do you reckon I should do first? (it's an '05 Thrux, preds, K&N pods.) I'm going either 39mm FCRs or 813/T-Bike cams or the 904 bore kit. I can only afford one of these mods at this time.
Decisions decisions decisions!
Thanks for any advice guys,
Pete
Carbs first.....then break the engine down once for 904 and cams.
LMT
Aussie_T100
Banned
So are you saying here that a TPUSA 904 kit would make 5ft/lbs more torque than a TPUSA 865 high performance kit if all other modifications are equal?
I've been wondering if the extra 39cc and a tad more comp would make that much difference. Then I found Aussiebiker's posts in the sticky dyno thread at rat.net...
http://www.triumphrat.net/twins-technical-talk/97729-twins-dyno-results-thread-5.html#post1540235
It seems that is does!
That's a good one and I'd love to know the answer - then we'd know whether Dave's above results were soley due to 39cc or due to increased compression.
http://www.triumphrat.net/twins-technical-talk/97729-twins-dyno-results-thread-5.html#post1540235
It seems that is does!
That's a good one and I'd love to know the answer - then we'd know whether Dave's above results were soley due to 39cc or due to increased compression.
mikenva
Rocker
if you do all the good the stuff you can do to both yes .I have never seen a 865 motor make mid 60 torque.904s do that all the time.The 865 kit was made as a cheap way to get more power it wont do what a good 904 will.If you dont have bores in like new shape the 865 kit is not a good idea in the first place.