Carb Sizes Larger Than Stock Don't Work Well.

[jayzx10r]

Here is some info I pulled from the Toomey Website regarding carb sizing. They claim that the stock carbs are best and that larger carbs are ineffective because of the poorly designed too small reed cage. Since a lot of people consider T5s to be the best pipes, wouldn't this probably be accurate as well?

I mean, I agree that the smallest carb that will allow you minimal restriction at WOT (Wide Open Throttle) would be the best choice for the reasons they expound, but are we truly limited primarily by the reed cages? Personally, I've always been skeptical of those anemic transfer ports... What changes can be done to the cages to flow better? Does it offer significant improvement?

I've got Boyesen reeds on a 4mil dune port.

I'm running 33PWKs...a lot of us are running 35s...some larger.

 

Here is a cut and paste from the Toomey site about RZ carbs...same motor:

 

Carburation

 

The most frequently asked question is: What about bigger carbs? I would like to take a moment and talk about that. You must remember that your RZ is being transformed from a strangled, asthmatic, EPA special to nearly road race specifications with just the installation of Toomey Racing Pipes. Obviously, the carburetion requirements are at opposite ends of the spectrum.

 

Since there is a power increase of some 50% when using your new Toomey Pipes, you might think this is quite a demand on your stock carbs, huh? Not really.

 

What we have to remember is that a carburetor is an airflow / velocity device; therefore you would want the highest volume flow AND the highest speed through the carb at the same time. It is a balance. Personally, I would like to see the smallest possible carb on your bike, not the biggest! Emotions aside, the facts are, that the stock carb can out flow the stock reed valve almost two to one, so why make the carb bigger? All that happens, when you do, is the air flow slows, and it makes it much harder to atomize the fuel droplets nearly as fine as with a high speed flow, making them harder to burn therefore contributing less to power. The net result is less power and range. So you can see that there is really no need for bigger carbs when they are not the thing holding you back. The reeds are.

 

Boyeson reeds help quite a bit and are definitely the best thing we have found for the stock engine. The reason is, they have better flow characteristics from bottom to top, and have better reed control than anything else on the market, including those six petal reeds that some people offer. (Boyesen Reeds are available from us for only $49.95. Ask for Part # 603.)

 

Unless you are willing to spend nearly $1,000.00 on bigger reeds, and the accompanying extensive port work to get them in there (and I mean BIG, like YZ 125 reeds) you have no need for bigger carbs. We have the dyno tests to prove it.

 

We tested 28, 30, 32 and 34mm carbs on the dyno and the best combination for peak power, as well as power range, was the stock carbs with our jet kit. The reason is simple. The air volume being drawn into the engine is a fixed amount determined by the pipe and ports, and does not exceed the maximum flow capacity of the stock carbs. You will get slower air-speed through bigger carbs with a proportional rise in air pressure due to the Venturi effect. Fuel atomization is not as efficient as in a smaller, lower pressure, high speed air flow . The poorer atomization burns less efficiently producing less power.

 

>>>>Back to me<<<<

Are we just wasting money on bigger carbs??

Thanks, Jay.

Edited September 17, 2007 by jayzx750

[Bansh-eman]

well i know for a fact that the dyno will show thier statement to be false.

 

on a 421 cub changing from 35 pwk to 39 pwk with no other changes the dyno has shown up to 6 hp differance. so if the limiting factor was the reeds this power increase would have not happened.

 

although reeds are the "choking point" of the intake. companies have found ways to get better flow. like the vf3 reeds. yes the open less then stockers or other brands, how ever they have double the amount of reed surface. allowing better flow.

Edited September 17, 2007 by Bansh-eman

[dajogejr]

To be 100% honest, Toomey makes a fine pipe, there is no doubt to that at all.

 

Outside of his little world of stock motor bikes....he doesn't know much IMO.

 

Before I had my 35's and Shearers for my 4 mil cub, I asked him via email about his needle (dynojet needle) and where I should start the clip for my 4 mil cub.

 

He said he doesn't know what a cub is....

 

So...that was a quick phone call.

[jayzx10r]

He said he doesn't know what a cub is....

:yelrotflmao: :yelrotflmao: :yelrotflmao:

 

Thanks for the info, guys. That's kinda what I figured. Even a YZ125 is running a 38MM carb!!

[RZBansheeMan]

My understanding of it is "stock cylinders, stock porting, stock reed cage" with only the addition of "toomey pipes, boysen reed petals, dynojet needle" They're probably right you wouldn't need anything more than stock carbs.

 

As for the 50% increase in power on an RZ enigne with just those few mods I highly doubt it, that would be almost a 90 - 95 hp bike with stock carbs, very unlikely.

[sredish]

I usually have a little different philosophy on this than others in this group, probably more so because I'm not a dragger. While I do believe a bigger than stock carb is helpful in a lot of applications, I personally think it's often overdone. In a stock bike with pipes, stockers work well actually and bigger is unnecessary. In a ported 350 to 370 cc application, I don't see the need for any bigger than 28s or 30s. True, if you were to step up from 30s to 35s, you might see a 4 or 5 horse difference but usually at the expense of torque or low end power. There's a certain trade off where upper hp, narrowing the powerband will result in negative overall effects. A smooth, more linear powerband is more important to me than that extra handful of ponies. Perfect example of this is how a torquey 52hp 4 stroke can hang with a 60 hp narrow powerband Banshee. The peak hp number is not aways the very most important factor in motor modifications, that is, unless your strictly a 300' straight line dragger who has one ultimate goal, a 7.5 second shot of power. Time and time again on these boards, years worth, I've seen people set their quads up with a dune/drag port, throw a set of CPIs on and mount some 35mm's and then a few months later complain that they have no lowend or it comes out of the hole bad. I've also been a big promotor of the 2-1 carb setup and ran it against some potent quads with dual 33s and drag pipes or Toomeys and hung right in with them. It's all in the setup.

 

Along with that theory, I think that drag pipes are often overused, as it sounds good to say, "yea, I have some CPI drag pipes" but often times something a little more broad would be more fun and easier to ride without a lot of power loss, it's just that the people haven't given it the chance. I've had quite a few different setups, however never a full drag setup but I've had stock 350cc ported motors that have ran with some pretty tough competition and all without drag pipes, drag carbs and nasty porting. It's more of an overall package, synergy you can call it. There's an art or special touch to building motors, it's usually not a buy this and buy that and throw all this together. Its more of a goal in mind, then do one step, do some testing, see what works best, a lot of buying, testing and selling to get where your goal ends up.

 

I haven't read the Toomey stuff, I'm not familiar with their motor theories, I'm just speaking from my personal experience and for the record, I'm not a fan of Toomey pipes at all and I dislike the T5s, even though they're considered gold by many.

 

EDIT: and for the record part 2, I know what cubs are.... :biggrin:

Edited September 17, 2007 by sredish

[RadarRacing]

A stock stroke,4 mil,7 mil and 10 mil cub run stock banshee sized cages and the cheetah cylinders run the much larger cages from a 250 R honda however the bikes have very similar hp numbers till you get up into the really good running 10 mil or 130 hp and up bikes. A really good drag ported oem cyl or cub will not run very well with stock carbs. Theres also a factor that a larger carb will in some ways force a smaller reedcage to flow more and make more power. I do definately agree though that many people want to run huge carbs on a motor and dont really need them. I know of very fast 350 triple exh ported bikes with bored stock carbs bored to 28mms. Small carbs= good snappy motor.

Edited September 17, 2007 by RadarRacing

[sredish]

Man 1: Hey, that's a nice bike you have there, she run fast?

 

Man 2: Yea, it's really quick once we finally got it jetted.

 

Man 1: Jeez, was it hard to jet?

 

Man 2: Yea, after we got those 35mm carbs on there.

 

Man 1: Dang, I need to get some 35mm's, maybe some 39mm's. If 35's are good, the 39's must be really good.

 

Man 2: Yea, those are some big carbs.

 

Man 1: By the way, what size is that motor?

 

Man 2: Oh, it's just a plain stock motor with some FMFs and Vforce reeds.

 

Man 1: Uuuuuhhh.. cool.

Edited September 17, 2007 by sredish

[dajogejr]

EDIT: and for the record part 2, I know what cubs are.... :biggrin:

 

They are a trail and MX motor...LOL...

I agree with you, in the fact it's all about your particular needs and setup.

Every motor combo and it's needs are different.

Bigger carbs don't always equal big performance...you need a motor that needs bigger carbs for them to work right, no doubt about it....

[John]

I haven't read the Toomey stuff, I'm not familiar with their motor theories, I'm just speaking from my personal experience and for the record, I'm not a fan of Toomey pipes at all and I dislike the T5s, even though they're considered gold by many.

 

EDIT: and for the record part 2, I know what cubs are.... :biggrin:

 

Just out of curiosity, why don't you like Toomey pipes? I am fairly new to Banshee's and their workings but aside from my bike being totally stock, and researching on the site, it seemed like the T5s were almost a unanimous choice for pipe upgrade? You appear to be very knowledgeable and have sound theory I was just curious to know why you don't like Toomey? I just bought a set of T5s but have not put them on yet, waiting for the jet kit, air filter and air lid, along with cascade hangers.

[letsgetthisdone]

Just out of curiosity, why don't you like Toomey pipes? I am fairly new to Banshee's and their workings but aside from my bike being totally stock, and researching on the site, it seemed like the T5s were almost a unanimous choice for pipe upgrade? You appear to be very knowledgeable and have sound theory I was just curious to know why you don't like Toomey? I just bought a set of T5s but have not put them on yet, waiting for the jet kit, air filter and air lid, along with cascade hangers.

 

he doesn't like them cuz they hit hard in the middle, sredish favors a smoother powerband, hence the very nice 450r in his sig..

[sredish]

pretty much what he said. and, not that anybody is saying i did, I never said they don't produce good power because they do, as many have proved. I just don't personally like the narrow powerband they seem to produce. IMO, the hit is hard, it's blah blah then Bam into the midrange / top end. I don't have a problem clutching and riding properly and if I rode strictly dunes, it'd probably be fine but I just like a little more smoothness and a little wider powerband. Many people have just succumbed to the idea Banshees have an on/off narrow powerband but that's not totally true, with a proper setup, you can have a machine with a smooth midrange and still have a killer top end. You also have to take my background which is mx and xc, not dunes and drag. I rarely make it to the dunes so I tend to opt for a machine that was equally at home here in xc trails of texas and in the dunes.

 

There's nothing wrong with T5's so don't let my negativity ruin it for you. You may absolutely love them, as a good friend of mine does. He had PT mids and I tried to keep him away from T5's and couldn't. Now he has them and loves them. So, pipes are like tires which is like colors, everyone has they're favorites and opinions and that's what makes us individuals....

 

For the record, Paul Turner Hi Revs for midrange / topend pipes. They are super smooth with broad power. The topend is similar to the T5s but they come on sooner and smoother. I have no use for drag-specific pipes and to me the T5's are caught in the middle, not quite drag pipes but then not quite smooth enough for me to consider for a midrange top end pipe.

 

John, you'll probably love the T5'S, especially if you haven't experimented with a lot of Banshee pipes. If your switching from stockers to the T5's, your bike will just come alove. I've just had about every kind short of the drag specific pipes. You'll find the PT Hi Revs are uncommon. The high price new and the fact that there aren't very many out there make for a pipe that very few are really familiar with.

 

Hope that makes sense, doesn't run on and doesn't bore everyone. Its true that once I rode a 4 stroke at a xc race, I was hooked. So so much easier to race, so much less work and after an hour of racing, I was in much better condition to continue the add'l 30 minutes. I've now spent way more than I'd care to admit on the motor of my 450, got it in the upper 50s in hp and it's a super strong runner but for the same money, I could've built a 75hp stock bore banshee.

Edited September 18, 2007 by sredish

[Snopczynski]

Toomey did two good things in their history span. They made T5 pipes cause they copied the fmf gold series, and they made some good needles for stock carbs. Other than that they suck. I called the tech department there about 4 weeks ago and the young kid on the phone didn't sound sure of the advice he gave me at all.

[dajogejr]

I'm pretty sure dynojet made the needles to "Toomey" specs...

 

Well...that's what Stuart Toomey told me, anyways....

[sredish]

I'm actually not a fan of the Toomey needles at all. Back in the past when I was on a lot, there were quite a few peeps having trouble with jetting their machines and Toomey needles were often times the culprit. And, unless somethings changed, the Toomey needle is nothing more than a Blaster needle.