BDX 56mm throttle bodies
- Thread starter Qreiff
- Start date
No experience, but I think there would be more difference on a NA sled than a turbo because boost pressure would not change.
The reason why I disagree with the n/a motor benefiting more is that bigger doesn't always mean more air. The velocity of the air can have a very important effect on performance. For example, I've read on here by many people saying that on a stock M7 motor the stock air box produces the most power because when you increase the size of the air horn or mod the box in other ways, it is a bigger opening but the smaller one moves the air faster and in turn getting more into the combustion chamber. The bigger opening makes it easier to breathe but slows down the movement of the air also. I put bigger throttle bodies on my cpc 1-litre and it did give me a little more power, but I think that was because I had increased the displacement of the motor enough to justify the bigger bodies. On a stock M1000 going from 50mm to 56mm is a HUGE jump in size with the same displacement, which again is why I don't think it would help much. The bigger bodies (like carbs) will hurt throttle response on the bottom because of the velocity I've been talking about, on top end when the motor is really sucking hard it might help to have bigger bodies but THAT much bigger might actually hurt it. Think of your garden hose on full, if you want to increase the pressure you put a small holed sprayer on the end and the result is a smaller diameter stream of water but a lot more pressure (or velocity). It works the same with the movement of air into the combustion chamber. This is just my opinion so take that for what it is but scientifically looking at it is what makes my opinion what it is. I have NO experience with turbos but know that companies like cpc make larger throttle bodies specifically for turbo applications so I assume they would help more. If the turbo boost were the same on a larger throttle body as a smaller one, because of the larger diameter you would get more air and thus could add more fuel and get more power. AGAIN JUST MY OPINIONS AND TO ME IT MAKES MORE SENSE THIS WAY.
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Use your example of the hose, the hose has pressure, like a turbo would, the NA does not it sucks so your example is bust.
The reason the m7 and most stock sleds don't do all that well with intake mods has more to do with the fuel and timing mapping than the air intake. AC maps these sleds with a stock setup and the mapping tools we use are no where near as refined as what the ecu has programmed into it.
I am one of the ones that says sometimes smaller is better for air speed (I was prob one of the first to bring up that point) But I doubt anyone is going to throw 56mm on a stock m1000, but rather a full mod 1000 or bigger. The m1000 needs air and likes air, after that its a matter of tuning. Hopefully there will be some options for timing adjustment this coming season as well. Also at low rpm there is hardly any air speed moving through the intake so larger doesn't change air speed a whole lot off bottom anyway and on the m1000 being a stroker motor you can dump more fuel to increase the response. Even when I added a bdx intake with the right tuning gave it quite a bit of off bottom response. I feel on the m1000 it helped all the way across and required quite a bit of fuel to be added.
On a turbo it might help a little but if you are running say 6lbs of boost that means you are forcing 6lbs of boost into the cylinder and even with the 56mm it will still be 6lbs of boost and it will have to be retuned. It may help a little but on the top end I can't see it doing as much as turbo porting would, i e changing the port timing.
The reason the m7 and most stock sleds don't do all that well with intake mods has more to do with the fuel and timing mapping than the air intake. AC maps these sleds with a stock setup and the mapping tools we use are no where near as refined as what the ecu has programmed into it.
I am one of the ones that says sometimes smaller is better for air speed (I was prob one of the first to bring up that point) But I doubt anyone is going to throw 56mm on a stock m1000, but rather a full mod 1000 or bigger. The m1000 needs air and likes air, after that its a matter of tuning. Hopefully there will be some options for timing adjustment this coming season as well. Also at low rpm there is hardly any air speed moving through the intake so larger doesn't change air speed a whole lot off bottom anyway and on the m1000 being a stroker motor you can dump more fuel to increase the response. Even when I added a bdx intake with the right tuning gave it quite a bit of off bottom response. I feel on the m1000 it helped all the way across and required quite a bit of fuel to be added.
On a turbo it might help a little but if you are running say 6lbs of boost that means you are forcing 6lbs of boost into the cylinder and even with the 56mm it will still be 6lbs of boost and it will have to be retuned. It may help a little but on the top end I can't see it doing as much as turbo porting would, i e changing the port timing.
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blownsilver
Member
Well I run the 56s with dual injectors on my built rgt M1000 and there's a big difference still runs the same psi on the gauge as that's only a measure of restriction. The engine is now just seeing more cfm of air thrifts larger throttle bodies thus making way more power but still at same psi.
Who's kit, do you have porting done???
Thanks, I knew it was just a matter of time before someone with turbo experience and larger throttle bodies would chime in.
I guess I didn't explain very well the experience I had with my n/a big bore. I turned my 700 motor into a 1000 and ran both the 700 and the 1000 for several seasons with the stock 48mm bodies. Then on the 1000 I put 50mm bodies on and re-tuned, and yes I had to add quite a bit of fuel at almost all my boondocker rpm settings to get the wash back to where it needed to be. On the top end I noticed a little bit more power but not a ton but it also hurt the bottom end throttle response somewhat. My motor had the 4-degree timing key with both throttle bodies so whether changing that may have changed the decreased throttle response or not I don't know. That was just my experience, and that influenced obviously my OPINION on this subject.
The garden hose thing was just to explain increased velocity thru a smaller hole (throttle body). And yes I understand that a turbo uses pressure but if you think a n/a motor does not you are wrong. A n/a motor uses atmospheric pressure to breathe. There really is no such thing as sucking. When the n/a motor "sucks", what it really is doing is creating a void where atmosperic pressure can fill that void. The atmospheric pressure is lower than what a turbo produces and that is why a turbo puts more air into the combustion chamber and why you can add more fuel and get more power.
the 700 is a short stroke and the mapping was way different, I'm not completely disagreeing, on a turbo there are lots of factors also. I can see how it may make a difference but I can't see it being a huge difference with some turbo kits, some turbo kits I could see it making a much larger difference. Lots of variables.
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blownsilver
Member
My setup is a full port and cut head from arctic edge performance running the boondocker non intercooled rgt. I had to change the throttle bodies to dual injector setup to get more fuel to it over 8psi I think she responded better thru out the entire rpm band with the larger throttle bodies and just comes alive now that it has the fuel for hard top end pulls. I also thru a 101mm throttle body on my procharged mustang a few weeks ago and it runs so much better over the 78mm one I had to get it retuned for the extra air but still same 16psi on the gauge
The porting is going to change things, also I don't know what size charge tube and turbo you are running vs other kits. I think some use a larger charge tube with a 3176 turbo that will flow a lot more air. These are all variables on how well it will work.
I'm not sure porting will make any difference either. On a 2-stroke, as the piston goes up the reeds open and allow the air/oil/fuel mixture in the crankcase. There really isn't an intake "port", just the reeds. When the piston fires and comes back down it pressurizes the crankcase pushing the already air/oil/fuel in there thru the transfer ports up above the piston for the next firing. The exhaust port can be changed to evacuate the exhaust faster or better but I don't see how it would change the intake at all. Crankcase blueprinting can change things since you are enlarging the holes of the intake under the piston, but I also think that it could actually hurt for the same reason I'm contesting if not done by someone who has done some solid calculations on air flow.
The idea behind the bigger bodies is to increase the volume of air going in the combustion chamber but on a n/a you are limited by the non-changing displacement, and the RELATIVELY non-changing atmospheric pressure. Time is a factor since a motor turning 8,000 rpm has to have some fast moving air to get in there in time to do any good. We're talking probably millionths of a second. On a turbo it is like opening the water faucet another couple of turns and now you can have the same speed water (air) stream with a bigger opening (body) and get much more volume going in in the same required time it needs to get in there. That's how I see it anyway.
The idea behind the bigger bodies is to increase the volume of air going in the combustion chamber but on a n/a you are limited by the non-changing displacement, and the RELATIVELY non-changing atmospheric pressure. Time is a factor since a motor turning 8,000 rpm has to have some fast moving air to get in there in time to do any good. We're talking probably millionths of a second. On a turbo it is like opening the water faucet another couple of turns and now you can have the same speed water (air) stream with a bigger opening (body) and get much more volume going in in the same required time it needs to get in there. That's how I see it anyway.
Not that anyone asked but I did some math on the calculator to help visualize just how fast the air needs to travel to keep up with a WOT 2-stroke motor. If the motor is turning 8,000 rpm that means that every second it turns 133.33 revolutions. That means the piston travels from top dead center down to the end of it's stroke and all the way back up to top dead center just over 133 times every second. That means that each revolution takes just under one hundredth of a second, and since the motor is only "sucking" roughly about 1/4 of that time (I roughly figure that since about 1/4 of the revolution it is rotating over top dead center, 1/4 of the time it is rotating down it's stroke, and 1/4 of the time it is rotating across it's full lower position), that means if my math isn't wrong it is only "sucking" .00325 of a second per revolution. So I was wrong, not millionth of a second but thousandths of a second. I think that shows how important air velocity thru the throttle bodies is. If the air doesn't move fast enough to get in, the reeds will shut and you will actually have less air inside because it wasn't fast enough to make it in time.
In a fuel injected application I don't see how it can hurt, it isn't like you're having to pull a vacuum like you would on a carb to get fuel ... All you're doing is making the throttle body portion of your air intake tract less restrictive than it would be with the smaller bore. I don't know what the reduction in pressure drop across a stock throttle body vs. say 56mm throttle body would be, but perhaps they have some data from a flow bench test they publish?
I'm planning on upgrading to the CPC dual injector TB's for my turbo here before too much longer ... not so much for a performance increase, as I just don't really like how the additional injectors with the BD setup inject upstream of the TB blades.
Guess everyone will experiment with this and see what happens, but I can't for the life of me see how it will result in any negative performance gain.
I'm planning on upgrading to the CPC dual injector TB's for my turbo here before too much longer ... not so much for a performance increase, as I just don't really like how the additional injectors with the BD setup inject upstream of the TB blades.
Guess everyone will experiment with this and see what happens, but I can't for the life of me see how it will result in any negative performance gain.
The velocity going through the reeds is going to be the same, if not greater, with the larger TB's. You don't have a vacuum in between the TB's and the reeds eating mass (unless you have a TB boot leak
) ....Larger TB diameter means less restriction through that portion of the air intake tract, therefore less pressure drop across that portion.
Yes, you do slow the velocity down going through the TB, but by taking less pressure drop across that portion, you actually have denser air "available" right in front of your reeds to feed the motor ... the geometry of the reeds doesn't change at all, so by having a higher pressure on the upstream side of the reed, you have more potential to flow more air through the reeds than with the smaller more restrictive throttle bodies.
If bigger is always better (which is what it sounds like everyone else seems to suggest) why doesn't every fuel injected snowmobile motor out there come stock with 3 inch diameter throttle bodies? Heck, why not 5"? And if bigger were always better, why did it take aftermarket companies so long to make bigger throttle bodies when fuel injection has been on sleds for so long now? It seems to me I didn't start seeing them until turbos became so popular.
Why don't they all come with turbos?
It's simple cost vs. necessity.
If you don't need a 56mm throttle body on a stock 150 horse sled, why build it that big?
I don't think these bigger throttle bodies are netting people huge horsepower gains on their own, I think its mainly something to complement other mods ...
I'm planning on the CPC ones mainly just because I want a more uniform injector spray from my secondary set of injectors, I'm not expecting any huge performance gain out of it ....
But then again I don't know, if people start using these and have good results, maybe they're worth it *shrug*
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polemite.productions
Well-known member
i'm not a turbo expert, or a 2 stroke expert, but here it goes...
larger bore for an NA motor is going to slow down intake air velocity. this can be a problem, unless your engine mods cause your motor to demand more air, and your stock tb's have now become a restriction to the increased demand. so i'd say that in the case of a big bore, or if you are revving way higher than stock, the bigger tb's could work.
for a boosted motor, your turbo is only going to supply compressed air at the rate that the smallest bore diameter in your intake tract will allow. so if your tb's wont flow the same volume as your charge tubes, you should see a gain up to the point where they can flow the same volume as the charge tubes.
if the tb's get increased beyond the volume rate of the charge tubes, your charge tubes become the restriction and the tb's aren't going to help.
if your tb's and charge tubes get way too big, your turbo wont be able to supply enough charge to the motor, or you would have lots of lag, cuz it's trying to fill so much more volume.
i have a pressure washer that makes 1800psi at the nozzle, through a 1/4" hose. think it would still make 1800psi if i upped the hose and nozzle size? nope. even just a nozzle change would drop pressure.
but speaking of throttle bodies...
our tb's have coolant lines that run to them to warm up the intake charge, which helps warm up the motor quicker. bypassing the tb coolant connection would keep the tb's cooler, and in turn keep the intake charge cooler. something we used to do in our cars to prevent power fade as the motor heated up. haven't done it on my sled yet, but its food for though. something i've been thinking about doing. anyone here try it already?
larger bore for an NA motor is going to slow down intake air velocity. this can be a problem, unless your engine mods cause your motor to demand more air, and your stock tb's have now become a restriction to the increased demand. so i'd say that in the case of a big bore, or if you are revving way higher than stock, the bigger tb's could work.
for a boosted motor, your turbo is only going to supply compressed air at the rate that the smallest bore diameter in your intake tract will allow. so if your tb's wont flow the same volume as your charge tubes, you should see a gain up to the point where they can flow the same volume as the charge tubes.
if the tb's get increased beyond the volume rate of the charge tubes, your charge tubes become the restriction and the tb's aren't going to help.
if your tb's and charge tubes get way too big, your turbo wont be able to supply enough charge to the motor, or you would have lots of lag, cuz it's trying to fill so much more volume.
i have a pressure washer that makes 1800psi at the nozzle, through a 1/4" hose. think it would still make 1800psi if i upped the hose and nozzle size? nope. even just a nozzle change would drop pressure.
but speaking of throttle bodies...
our tb's have coolant lines that run to them to warm up the intake charge, which helps warm up the motor quicker. bypassing the tb coolant connection would keep the tb's cooler, and in turn keep the intake charge cooler. something we used to do in our cars to prevent power fade as the motor heated up. haven't done it on my sled yet, but its food for though. something i've been thinking about doing. anyone here try it already?
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