Koolguyson Posted May 4, 2005 Report Share Posted May 4, 2005 Answer me this...do you think that running a carb that was designed for a 350cc engine that produces 30hp should be ran on a 400cc motor that produces almost 2.5x more power? What is the purpose of building up a stock air pump (30hp) into a bigger, stronger, more efficient air pump (80hp) if you cant feed air into it. Remember more air in=more air out=more power. Builder may be a great guy to you. But 75hp is pretty easily attainable out of a 4mm. heck i got 71hp out of my gf's bike i did for her and its still stock reeds, and t-5 pipes and on nobbie tires. And there isnt anything fancy or drag related on how i ported it. Add for VF3 reeds(3-5hp over stock), some CPI pipes (claimed 5hp over t-5s), and a more suitable dyno tire (3-4hp) and im in the 85hp range easily. But for the guy who asked the question. A set of 33-34mm carbs is what you are going to want. Expect to spend 150 on a set and another 20-30 on a throttle cable. Dont forget you'll need 80-100 in filters and outterwears. Stock carbs will work fine for you though, they will have good bottom end repsonse and good top end pull. A set of 34s will still have good throttle response but the mid to top end will pick up more power. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted May 4, 2005 Report Share Posted May 4, 2005 heck i got 71hp out of my gf's bike i did for her and its still stock reeds, and t-5 pipes and on nobbie tires. And there isnt anything fancy or drag related on how i ported it. 364216[/snapback] Stock reeds, T5 Pipes and a port job to 71HP? I'd like to see a dyno sheet on that. NOTHING else but T5's and a port job? 71HP is attainable....but I think you'd need more than a simple port jobs and pipes... From what I've read, reeds, a good port job and pipes will put you more like in the 55 to 60HP range. Again, I'm not saying your wrong...or maybe I'm missing a mod or two...but that's pretty high based on the two mods you stated... Quote Link to comment Share on other sites More sharing options...
Koolguyson Posted May 4, 2005 Report Share Posted May 4, 2005 Stock reeds, T5 Pipes and a port job to 71HP? I'd like to see a dyno sheet on that. NOTHING else but T5's and a port job? 71HP is attainable....but I think you'd need more than a simple port jobs and pipes... From what I've read, reeds, a good port job and pipes will put you more like in the 55 to 60HP range. Again, I'm not saying your wrong...or maybe I'm missing a mod or two...but that's pretty high based on the two mods you stated... 364245[/snapback] that and carbs homie. I can give you dyno sheets all day long. Hell i own the dyno. But in fairness to me i made that number after the 3rd pass BTW its sikgirl's motor just in case you want to give her a "hell ya" Quote Link to comment Share on other sites More sharing options...
dajogejr Posted May 4, 2005 Report Share Posted May 4, 2005 Ah...that's what I was missing... I'm not knocking you...so don't take it this way when I say this. But...have you had it calibrated or tested your shee elsewhere? Like I said...don't take that the wrong way. I'm just asking... Hell yeah...nothing better than a girl on a ripping shee!! Ok, well...maybe a girl on a ripping shee roosting a four stroke... Quote Link to comment Share on other sites More sharing options...
thegreatestever Posted May 4, 2005 Report Share Posted May 4, 2005 Very interesting Topic What is the best kind "company" of carbs i should go with when i am ready to buy? and how much you think it will cost me? Quote Link to comment Share on other sites More sharing options...
RNBRAD Posted May 4, 2005 Report Share Posted May 4, 2005 I said there was a trade off between volume and velocity odaen, your right about there being a trade off between volume and velocity. Though the key is a good balance of the two. One without the other is nothing. You can talk velocity all you want but without volume your going no where and vice versa. Velocity is only beneficial to a certain point and without an increase in volume you will have a drop in power. Quote Link to comment Share on other sites More sharing options...
RNBRAD Posted May 4, 2005 Report Share Posted May 4, 2005 Very interesting Topic What is the best kind "company" of carbs i should go with when i am ready to buy? and how much you think it will cost me? 364251[/snapback] From looking at your mods, really depends on your type of porting whether trail to drag. For trail I'd look at the 28mm Keihin pwk oval bored to a 30mm, 33's for an mx style port and 35's for tt to drag porting. They will run you anywhere from 150 to 180 each. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted May 4, 2005 Report Share Posted May 4, 2005 Okay, I read most but not all of this. I had a 4mm with 28mm carbs. I then went to 35mm carbs and swore I gained bottom and top end. People said no way in hell. Banchetta tried his stock carbs on a dyno with a 4mm and switched to 35mm pwk's and proved it to be true. He gained through the whole pwr curve. You have to take into consideration the porting too. Something else no one has brought up is the length of the carbs. Most larger diameter carbs are longer which helps bottom end too. The shape of the bore is a biggy too. Short carbs help top end. There's more to a carb than the size of the bore. Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted May 4, 2005 Report Share Posted May 4, 2005 Here is the equation you need to use to find your flow-rates and velocities for those of you who want to put numbers into the argument. P = pressure at points one and two. Point one would be on the back of the carb and two would be at the engine intake g=gravity constant z = height above selected datum (if you choose your datum right allt he z's will cancel out) rho = specific gravity of the fluid you are using for the calculations hl = head loss due to friction (could probably consider this close to zero for this type of system) hp = if you had an accelerator pump you would add the head produced by the pump here q = flow rate v = velocity a = cross sectional area of fluid body those two equations will give you everything you need to figure out the velocity of the fuel/air mixture anywhere in the system with any size of carbs. I have to go take a couple finals, so I'm outta here for today. Peace Quote Link to comment Share on other sites More sharing options...
fixitrod Posted May 4, 2005 Report Share Posted May 4, 2005 (edited) To get most of that info you'd need more calculations that include rpm, bore sizes, jetting diameters or surface area fuel is being pulled from, angles.... the list goes on. ***EDIT*** That's why we just try it. If we don't like it we try something else... lmao Edited May 4, 2005 by fixitrod Quote Link to comment Share on other sites More sharing options...
twinzr900 Posted May 4, 2005 Author Report Share Posted May 4, 2005 wow thanks for all the info guys. no1 has said wether or not i need to adjust my timing though. i think i might try the 33 PWks for my trail bike.. i think it will be good enough for low end and top end. if u think i will loose top en then please tell me... maybe i have misssed soemthing and should go w. 28 pwks. thanks. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted May 4, 2005 Report Share Posted May 4, 2005 I'd adjust the timing, anyways... An adjustable stator plate from Rickystator.com is 35 bucks plus shipping. Should have mine on Friday, I'm planning on going a very, very mild +4 and be happy. Quote Link to comment Share on other sites More sharing options...
white trash Posted May 4, 2005 Report Share Posted May 4, 2005 33's should do you fine in the trails..... thats what i have on my bike, and i still have plenty of bottom end power. Im still running stock stroke as well. With the added tourqe your getting from your 4mm, the 33's will do you well. At most your going to be bitching about a sore thumb Quote Link to comment Share on other sites More sharing options...
hops Posted May 4, 2005 Report Share Posted May 4, 2005 I have stockers bored to "28". Don't bother. They work, but not very well. Just something that I have heard, but some say the 33's are the problem child of the PWK line, as in harder to tune. Get them there, your good to go, but you may lose some hair in the process. Since I'm a duner, I will be going 35's with my 4mm. The other choices recomended to me, by a reputible builder, was 28's, or 28's bored to 30, depending on port work and riding style. just my useless $.02. hops Quote Link to comment Share on other sites More sharing options...
BdBanshee Posted May 5, 2005 Report Share Posted May 5, 2005 I have a friend with a stock stroke and dune porting, he ran 28mm Keihins bored to 30mm for years, and it ran very good. He finally bought a set of 35mm Keihins and it woke it up from the bottom on up to the top end, way more pull on top. I liked it the way it was, used to always easily smoke him when we would drag! Quote Link to comment Share on other sites More sharing options...
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