Discussion
A few of the guys I race with have been trying different things over the years to try and get that extra bit of performance without either pushing them over the class horsepower limit or jeopardising reliability. The latest thing they have been playing with is Ram Air. Not wanting to miss the boat or rely on others efforts (too much anyway) I want to have a bash at doing some close season ‘development’ work. The bike is a ’89 TZR 250 1KT, currently pushing out 53bhp on a dynojet, which is about 50/51 on the dynopro. Class limit is 53 on the dynapro.
So far the results have been negligible, with the only positive report coming from Snetterton where the rider felt a sudden increase in power down the back straight. Unfortunately this was happening too far down the straight for it to have any real benefit as it kicked in just as they were approaching the 150 marker. This was using nothing more than a hoover tube cable tied under the nose of the fairing and being fed in to the back of the air box. No mechanical force whatsoever, relying on momentum only to force the air.
So …ideas wise…I would like to run something small either side of the bike, say 38mm, as space is tight. Anything bigger could be squeezed in, but could suffer from being kinked which could hinder its operation. Termination would be a heath robinson affair into the back of the box, with the ‘funnel’ being in the same place as other bikes would have.
Fairings come off very regularly, so the ‘funnel’ needs to be easily detachable.
Does anybody have any ideas where (a) I can get bits from, like a funnel or bellow, whatever you would call it, and (b) and how can you get it to kick in earlier using the results from Snett as the model?
So far the results have been negligible, with the only positive report coming from Snetterton where the rider felt a sudden increase in power down the back straight. Unfortunately this was happening too far down the straight for it to have any real benefit as it kicked in just as they were approaching the 150 marker. This was using nothing more than a hoover tube cable tied under the nose of the fairing and being fed in to the back of the air box. No mechanical force whatsoever, relying on momentum only to force the air.
So …ideas wise…I would like to run something small either side of the bike, say 38mm, as space is tight. Anything bigger could be squeezed in, but could suffer from being kinked which could hinder its operation. Termination would be a heath robinson affair into the back of the box, with the ‘funnel’ being in the same place as other bikes would have.
Fairings come off very regularly, so the ‘funnel’ needs to be easily detachable.
Does anybody have any ideas where (a) I can get bits from, like a funnel or bellow, whatever you would call it, and (b) and how can you get it to kick in earlier using the results from Snett as the model?
Tony,
First consideration is sealing the airbox. Ram air is only relevant over 100mph, and needs the airbox to be sealed to maintain the pressure differential.
As for parts, without seeing pictures of the bike sans fairings, try looking at Ducati parts. The 999 series has a vet box like airbox, with detachable air tubes. If you fitted these with rivnut type fixings to the stock airbox, it might work.
But now we come to jetting. FI bikes have a pressure sensor to detect the airbox pressure, thus allowing them to add fuel to compensate for the increase in air pressure. This will be a non started with carbs. So you might see that while she is fuelled spot on at 100+, other than that she's dog rough. So that would be the first thing to overcome, high speed fuelling or ram air enrichment.
Steve
First consideration is sealing the airbox. Ram air is only relevant over 100mph, and needs the airbox to be sealed to maintain the pressure differential.
As for parts, without seeing pictures of the bike sans fairings, try looking at Ducati parts. The 999 series has a vet box like airbox, with detachable air tubes. If you fitted these with rivnut type fixings to the stock airbox, it might work.
But now we come to jetting. FI bikes have a pressure sensor to detect the airbox pressure, thus allowing them to add fuel to compensate for the increase in air pressure. This will be a non started with carbs. So you might see that while she is fuelled spot on at 100+, other than that she's dog rough. So that would be the first thing to overcome, high speed fuelling or ram air enrichment.
Steve
Your best bet would be make a wood buck / mould and then vac form your air box - feed system over it.
On the topic of ram air, the greatest air pressure will be at the point/nose of the fairing, so it may be worth taking your air from an intake in the nose rather than at the sides - something like a NACA duct as these are designed to flow air with very little aero drag.
The other issue you need to be careful with is the F/A mixture as you may find the ram air cause the engine to run lean at high speeds, and a TZ will not adjust to compensate like a 4pot will it?
On the topic of ram air, the greatest air pressure will be at the point/nose of the fairing, so it may be worth taking your air from an intake in the nose rather than at the sides - something like a NACA duct as these are designed to flow air with very little aero drag.
The other issue you need to be careful with is the F/A mixture as you may find the ram air cause the engine to run lean at high speeds, and a TZ will not adjust to compensate like a 4pot will it?
Played with this a bit on the race car
To kick in earlier you need to maximise the air intake funnel, have a look if demon tweeks or some other have something you can adapt, the as you say hoover pipes down to the air box, glass fibre is probably going to be your best friend for mating it all together
is it possible to mount say 6" scoops in the sides of the fairing?
To kick in earlier you need to maximise the air intake funnel, have a look if demon tweeks or some other have something you can adapt, the as you say hoover pipes down to the air box, glass fibre is probably going to be your best friend for mating it all together
is it possible to mount say 6" scoops in the sides of the fairing?
1. On the bits front. hoover (corogated tube) will be awful as its got ridges all the way down it creating turbulence and reducing flow and pressure to the airbox.
you need something with smooth walls. D tweeks do a smooth wall tube length that's flexible. shorter the run the better. not ideal, but better than hoover tube.
You also need to 'belmouth' the front face of the air intact (like the ram tube on a carb/T body), or again, the mouth will create a bunch of dirty air at the edges reducing pressure gains in the airbox.
2. Obvious I guess, but if you are upping the airbox pressure which you will eventually acheive with the ram air intake, you need to consider fueling. Total guess here, but the 'Snett' effect could have been a function of the speed finally creating 'some' effect matched with the bike then heading a bit lean.
Unless done really well and optimised the effect of RAM air on the figures will I expect be very small. IME, with Bike engined car stuff, Big cc, high speeds, clean intake tracks using bespoke formed devices with smooth surfaces, the effect was minimal under 90-100mph and didn't have a HUGE impact on power, although, when the system leaked, it did mess the fueling up, so was having SOME effect.
3. getting the air intake from a cooler source (outside of the fairing in front of the radiators) will improve charge temperature and could improve performance a little. Would have more effect I suspect than a home made ram tube.
Isn't winter great!? garages full of cold racers looking for the edge.
you need something with smooth walls. D tweeks do a smooth wall tube length that's flexible. shorter the run the better. not ideal, but better than hoover tube.
You also need to 'belmouth' the front face of the air intact (like the ram tube on a carb/T body), or again, the mouth will create a bunch of dirty air at the edges reducing pressure gains in the airbox.
2. Obvious I guess, but if you are upping the airbox pressure which you will eventually acheive with the ram air intake, you need to consider fueling. Total guess here, but the 'Snett' effect could have been a function of the speed finally creating 'some' effect matched with the bike then heading a bit lean.
Unless done really well and optimised the effect of RAM air on the figures will I expect be very small. IME, with Bike engined car stuff, Big cc, high speeds, clean intake tracks using bespoke formed devices with smooth surfaces, the effect was minimal under 90-100mph and didn't have a HUGE impact on power, although, when the system leaked, it did mess the fueling up, so was having SOME effect.
3. getting the air intake from a cooler source (outside of the fairing in front of the radiators) will improve charge temperature and could improve performance a little. Would have more effect I suspect than a home made ram tube.
Isn't winter great!? garages full of cold racers looking for the edge.
Airbox has to remain the same.
I had always expected it to be in the nose rather than the sides.
Mixture - hadn't considered this. Currently there is only one circuit this would concern me, Snett
Steve...why does it only come in at 100mph? Is there any way of forcing it below that speed?
I had always expected it to be in the nose rather than the sides.
Mixture - hadn't considered this. Currently there is only one circuit this would concern me, Snett
Steve...why does it only come in at 100mph? Is there any way of forcing it below that speed?
Fleegle said:
why does it only come in at 100mph? Is there any way of forcing it below that speed?
The pressure drops from intake to airbox and the fact you need to build up pressure at the intake limit the speed below which this will work. I'm sure someone will be along in aminute to explain the formula, but essentially the effect is minimal any hoo, so needs a lot of pressure.consider the effort a turbo makes in order to create a doubling of intake pressure, the losses are very substantial. you are trying to get this extra pressure for free.
The 'cleaner' the run the airbox & the optimisation of intake (which you won't be able to do in a shed, so to speak) might drop it a little, but not much.
Fleegle said:
Steve...why does it only come in at 100mph? Is there any way of forcing it below that speed?
It's all about fiziks mate. Below a ton, there isn't enough pressure differential to really make a difference. You need to factor in ambient air temps, ambient barometric pressure, all sorts. The amount of air an engine ingests is huge, so you have a huge pumping effect going on. So your airbox is possibly in reduced pressure/partial vacuum, and to raise this above that to positive pressure requires a ton of air. Look at howmuch air a turbo moves, eeven for modest boost values of 0.6bar. But what has been raised here is the posibility of a good cold air intake. Depending on where the current airbox takes is breath from, you could see good gains by feeding it with air that is forward of any heat device.
So this opens up some options. Cool air is all around you, so if ram air is not the aim, a NACA duct on the side(s) of the fairing would be very helpful. If possible, the front of the bike is the ideal spot to mount the feed pipes, but as was said earlier, NOT the corrugated stuff!! Wrecks airflow.
Another question is how are your carbs? Do the filters fot straight over the back? Are there bellmouths fitted? Do the filters sit over these bell mouths? Anything that doesn't promote good flow into the fuelling device will hurt power. Did you know that 90% of the air entering a carb/throttle body does so from the sides, not directly from the bore line!!! Hence why belmouths are so critical. And then fitting a filter over the bell mouth wrecks it's flow again, so make sure the bell mouth has as much free space around it as possible, preferably over an inch all round.
Also, you can tune the induction length to change the power characteristics of the engine, but thats properly serious stuff!!
See the pic of these Keihnins as a reference. Bellmouths are not just for show!!
Steve
Edited by bass gt3 on Monday 25th October 10:18
Tony,
Where does the OE airbox draw from? What is on the carbs for the transition of the air into the carb? How are the filters arranged? Answering these 3 questions will help you optimise the set up. And yesm, you can presurise below 100 mph, but it needs a turbo/supercharger, and i don't think you'll be allowed to play!!
Where does the OE airbox draw from? What is on the carbs for the transition of the air into the carb? How are the filters arranged? Answering these 3 questions will help you optimise the set up. And yesm, you can presurise below 100 mph, but it needs a turbo/supercharger, and i don't think you'll be allowed to play!!
Fleegle said:
sprinter1050 said:
Ride with you gob open then when a boost is needed "let it out" the other end for a turbo effect.
I have nothing left to let out.How do you think I get down to race weight on a race day???
dP = 0.5 x rho x V^2
rho(air density) is about 1.224 kg/m3, and assuming atmospheric pressure of 101325Pa means that at 100mph you could in theory get about 5.8% pressure increase.
However you're going to get pressure loss down the duct, which will be relative to she speed of the airflow down it, so the shorter, wider and straigher the duct the better. As already mentioned the whole path from duct entry to needs to be sealed to prevent losses.
The actual aerodynamics gets very confusing, as you're really looking at static pressure recovery rather than increased ram air pressure. Local static pressure will have dropped by up to that 5.8% if the airbox isn't already getting a clean airflow, and you're trying to claw as much of it back as possible. True ram air needs a large enough air flow to get stationary air at the inlet, which you're very unlikely to be able to achieve.
rho(air density) is about 1.224 kg/m3, and assuming atmospheric pressure of 101325Pa means that at 100mph you could in theory get about 5.8% pressure increase.
However you're going to get pressure loss down the duct, which will be relative to she speed of the airflow down it, so the shorter, wider and straigher the duct the better. As already mentioned the whole path from duct entry to needs to be sealed to prevent losses.
The actual aerodynamics gets very confusing, as you're really looking at static pressure recovery rather than increased ram air pressure. Local static pressure will have dropped by up to that 5.8% if the airbox isn't already getting a clean airflow, and you're trying to claw as much of it back as possible. True ram air needs a large enough air flow to get stationary air at the inlet, which you're very unlikely to be able to achieve.
The airbox draws air from a opening approx. 70mm x 40mm that on the standard bike would have a trumpet on it. We run without these. It faces towards the rear, close to the battery but it is not ‘fed’ air it is just freeflow. It has a decent amount of free area around this.
The filter is your normal road affair, fitting flat, suspended in the airbox. The carbs are connected to the airbus via the rubber inlets which are in good condition and make a good seal
The filter is your normal road affair, fitting flat, suspended in the airbox. The carbs are connected to the airbus via the rubber inlets which are in good condition and make a good seal
Fleegle said:
The airbox draws air from a opening approx. 70mm x 40mm that on the standard bike would have a trumpet on it. We run without these. It faces towards the rear, close to the battery but it is not ‘fed’ air it is just freeflow. It has a decent amount of free area around this.
The filter is your normal road affair, fitting flat, suspended in the airbox. The carbs are connected to the airbus via the rubber inlets which are in good condition and make a good seal
But how does the air transition into the carb?? The trumpet on the airbox is pointless if the carbs sit in free air inside the box but with no transition device(bellmouth)The filter is your normal road affair, fitting flat, suspended in the airbox. The carbs are connected to the airbus via the rubber inlets which are in good condition and make a good seal
Can you run a T arrangement pipe(s) from the airbox inlet to the front of the bike to feed cool air into the box, where you fit trumpets onto the carbs. Also look to ensure the inlet tracts/rubbers are as smooth as can be, with no defects, protrusions, casting edges. Even look to have them polished.
As it's rear facing you're going to be getting the majority of that dynamic pressure loss. Dunno if you can easily get anything to monitor the tempterature and static pressure at the inlet which might help show how much benefit you can get. I don't think bikes tend to suffer as much from the inlet temperature issue as cars which tend to have the intake under the bonet and behind the radiator, but it's worth checking.
Pressure is pretty much directly proportional to temperature (in Kelvin, so 273 + Celcius)so you're looking at about 0.5% pressure difference per degree.
Pressure is pretty much directly proportional to temperature (in Kelvin, so 273 + Celcius)so you're looking at about 0.5% pressure difference per degree.
Didn't think forced induction works on a two stroke - you'll end up pressuring the crankcase, the crankcase volume will need 'pumping' up the transfer ports which will be pointless as the exhaust port is open at the same time.
Surely flowing/filling the bottom end would have better scavenging results in getting all of the mixture already there into the combustion chamber.
I would imagine any power gains are simply by having the air intake in such an area that it's taking in more colder air than the warm air which is behind the motor, above the gearbox between the fram spars etc. You just need something that will get cold air towards the air intake.
Surely flowing/filling the bottom end would have better scavenging results in getting all of the mixture already there into the combustion chamber.
I would imagine any power gains are simply by having the air intake in such an area that it's taking in more colder air than the warm air which is behind the motor, above the gearbox between the fram spars etc. You just need something that will get cold air towards the air intake.
Edited by graham22 on Monday 25th October 11:22
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