Mad Mart Posted September 30, 2009 Share Posted September 30, 2009 On my track Sprint I've been running my 45 DCOEs with no filters at all, for the last few years, just 60mm. trumpets. Various people have commented that I should really have something to stop the crap getting into the carbs/cylinders. I tend to agree with them but it does sound nice without. ;D Anyway, I've bought a pair of second hand 80mm. deep K&Ns from fleabay. Question is, having 60mm. trumpets only leaves 20mm. max. from the front plate of the K&Ns. Will this cause a problem with air flow? Should I get some shorter trumpets? Link to comment Share on other sites More sharing options...
JohnD Posted October 1, 2009 Share Posted October 1, 2009 Mart, The pictures of the Candy Box Vitesse that I recently recieved from Leon show slightly shorter stacks, with the inner side of the wheel arch cut off and replaced with a flat sheet. See below. I can only presume that this is to give gerater clearance at the inlet mouths. Feel like doing the same to your car? John Link to comment Share on other sites More sharing options...
mark spit Posted October 1, 2009 Share Posted October 1, 2009 Isn't the generally recommended maximum trumpet height to be half the available distance from filter backplate to cover, so in 80mm K&Ns you'd be limited to 40mm trunpets max. Mark Link to comment Share on other sites More sharing options...
RK Posted October 1, 2009 Share Posted October 1, 2009 well, usually it is recommended that you have trumpet diameter * 0.5 as minium distance between end and filter/airbox. A 60mm trumpet should work in an 80mm K&N Box, for 40mm carbs, and for 45mm carbs you might set the limit at (roughly) 55mm. Reinald Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted October 1, 2009 Share Posted October 1, 2009 Usual safe min distance is 35mm or so. I'd class 20mm as marginal. Link to comment Share on other sites More sharing options...
thegave Posted October 1, 2009 Share Posted October 1, 2009 Radiused trumpets! Do they make a difference? Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted October 2, 2009 Share Posted October 2, 2009 The general verdict is yes. But talking a few %. Link to comment Share on other sites More sharing options...
thegave Posted October 2, 2009 Share Posted October 2, 2009 But if they're cheaper than normal ones then I might as well right? Link to comment Share on other sites More sharing options...
JohnD Posted October 2, 2009 Share Posted October 2, 2009 I have an old article by Dave Walker, the tuning and rolling road guru, from good old CCC magazine, about flow benching. He took a 90 degree radiused trumpet, as seen above on Mart's car, and added a complete radius, as seen on the Candy Box but in modelling clay! He had observed that a loose trumpet would be drawn AWAY from the throttle body, as the pressure in the throat and on the outside of the bell fell at full suck, and the ambient, higher pressure behind pushed it away from the body. He thought that a complete radius could smooth the flow, improve flow and prevnt this happening. It didn't do either! John Link to comment Share on other sites More sharing options...
Mad Mart Posted October 6, 2009 Author Share Posted October 6, 2009 So what's your opinions of running without filters? Link to comment Share on other sites More sharing options...
GHR630 Posted October 6, 2009 Share Posted October 6, 2009 I stopped doing it after my throttle jammed in the paddock and we found a pebble stuck in one of the butterflies!! Link to comment Share on other sites More sharing options...
Nick Jones Posted October 6, 2009 Share Posted October 6, 2009 So what's your opinions of running without filters? Don't. Nick Link to comment Share on other sites More sharing options...
thegave Posted October 25, 2009 Share Posted October 25, 2009 On a semi-related note, is there much between running trumpets that are tapered/flared and say a simple length of hose with a filter stuck on the end, kind of like the one below? I saw it and thought it would be a good idea for a)lengthing the "trumpets"/rampipes, as I'm fairly space limited so need something that bends b)moving the intake source away from the top of the exhaust manifold and towards a cooler area of the engine bay with more airflow Will the pipe kill airflow because it's not tapered like the trumpets or is it more to do with the bell shaped lip? Link to comment Share on other sites More sharing options...
GT6Steve Posted October 25, 2009 Share Posted October 25, 2009 The curve itself won't impede airflow as long as there's a proper, ideally full radius, flared air horn at the front. Look for David Vizards "How To Modify Your Mini" for an excellent treatise on performance airflow. His illustratrations have been reproduced about a milloion times on the web so someone may have a link for you. BTW, I ran open stacks for years. See above, Don't! Link to comment Share on other sites More sharing options...
thegave Posted October 25, 2009 Share Posted October 25, 2009 So having a filter clamped straight onto the end of the hose (as in the picture) still wouldn't be as good as having the flared horn? What sort of difference are we talking about though, and why? Link to comment Share on other sites More sharing options...
GT6Steve Posted October 25, 2009 Share Posted October 25, 2009 Massive difference. I always picture the airflow like a crowd of people rushing into a train station. If you have a large smooth funnel they'll all shuffle in and squeeze together without much slowing. But stick a square corner in there and there will always be the buttheads who walk into and then try to push over into someone else to get in until there's a scuffe and restriction from said buttheads pushing in. I don't see the book anywhere near but I think a square cut pipe would only flow 67% of what a decent flare would do. Link to comment Share on other sites More sharing options...
thegave Posted October 25, 2009 Share Posted October 25, 2009 Thanks for the analogy. Well not the end of the world... I'll just have the curved horn part of the trumpets lopped off the stack, fix the hose to the stack and then fit the horns back on to the end of the stack.. Somehow. Yeesh. On a less related note, it is generally agreed that longer stacks provide more torque lower down the rev range compared to shorter ones, yes? Link to comment Share on other sites More sharing options...
thebrookster Posted October 25, 2009 Share Posted October 25, 2009 That is my understanding yes. Inlet is like exhaust, you can work it out with physics as to what length of runners you need. Adding longer/shorter stacks just lengthens/shortens the full length. Link to comment Share on other sites More sharing options...
JohnD Posted October 26, 2009 Share Posted October 26, 2009 Flow through a tube is governed by Poiseuille's Law: Resistance= (8 x Viscosity x length)/Pi x radius^4 Which says that Resistance to flow is proportional to viscosity and length, and inversely proportional to the fourth power of the radius of the tube. "8" is a constant. Not much you can do about viscosity, and a longer tube will increase the resistance. One twice as long will cause the resistance to double. But make the tube twice a wide and the resistance will go down SIXTEEN times! So always make intake tubes, esp. those from the open air to the filter, as wide as possible. There is an added advantage to wide hoses, in that the above applies to laminar flow. Make the flow too fast and the flow will go turbulent, whereupon resistance becomes proportional to density, rather than vsicosity, and much greater than while flow is laminar. The air flow through an engine can be very large! 1500cc at, say 6000 rpm, will drag through 4500 litres/minute (assuming perfect flow). A standard Spitfire has two hoses to the airbox, each about 4cms wide, so at those revs, air tries to get through those at 180kph (112mph)! It won't go so fast, due to the resistance elsewhere, but flow will certainly be turbulent! Increase the hose size, the velocity of the air will go down, laminar flow is more likely and resistance will be further minimised. On stack length, It is indeed true that resonance occurs, can benefit induction and that the higher the revs, the shorter the resonant stack. Just like an organ pipe. But sad to say, at the revs that Triumph engines can achieve, the resonant stack is unfeasibly long! Like, off the top of my head, 14" for 6K. I'll check that at home, and repost if necessary. On filters, how big is the smallest bit of grit you'll tolerate? The smaller that is, the finer the filter, and the finer the filter, the bigger the filter must be to minimise resistance. If all you are worried about is gravel that will jam a throttle, then coarse wire mesh will do - race engines will wear faster from what they do, rather than any fine grit they ingest. But even wire mesh will add resistance, so a good dome over each stack. John Link to comment Share on other sites More sharing options...
thegave Posted October 26, 2009 Share Posted October 26, 2009 Well I'm building a road car so unfortunately longevity is a fairly important concern, which I suppose will come at the cost of slightly restricted induction. 14" is huuge, would've thought it would bring peak power a bit lower thank 6k. So in any case, I should focus more on width than length? It'll be interesting trying to match super-wide hoses to the carb inlets Link to comment Share on other sites More sharing options...
lordleonusa Posted October 26, 2009 Share Posted October 26, 2009 Sorry to go off thread, just for a second, I see JohnD is alive and kicking... JohnD, please check your emails, I have sent you some quality photos of the Candybox also the owner Butch Gilbert, has not heard from you yet. Best Regards Léon normal thread resumed. Link to comment Share on other sites More sharing options...
RK Posted October 26, 2009 Share Posted October 26, 2009 Hi, I use following rule of thumb formula to calculate the length for my intake: Length = (((720 - InD) * 0.25 * 1300 * 2) / (rpm * rv)) - (dia/2) with InD: working Inlet Duration of the cam, i.e. for european seat timings you need to substract 20° to 30° rpm: RPM rv: reflective value, usually for our Triumphs we can tune to 3rd reflection, since there is no place to get it done for 2nd reflection dia: Inlet Diameter, for adjusting the length to open pipe reflection length and dia are given in inch remember, the figure for length is the total length from the valve seat to the trumpet end. formula is taken from David Vizards "how to build horsepower". Playing around with the numbers, you will realize some interesting things: - of course EVERY intake has resonances at first, second, third and forth pressure wave reflection. It is just a question if it is in a range, where you can actually benefit from it. - using a hotter cam, the inlet resonance for a given length moves DOWN in the RPM range. - The impact of changing the trumpet length from 30mm to 60mm might be smaller than you expect :-) have fun Reinald Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted October 26, 2009 Share Posted October 26, 2009 Tried 10-25-35-40-60mm trumpets... I liked the 10mm the best 60mm was "dead" by comparision... Link to comment Share on other sites More sharing options...
spitNL Posted October 27, 2009 Share Posted October 27, 2009 Hi, I use following rule of thumb formula to calculate the length for my intake: Length = (((720 - InD) * 0.25 * 1300 * 2) / (rpm * rv)) - (dia/2) with InD: working Inlet Duration of the cam, i.e. for european seat timings you need to substract 20� to 30� rpm: RPM rv: reflective value, usually for our Triumphs we can tune to 3rd reflection, since there is no place to get it done for 2nd reflection dia: Inlet Diameter, for adjusting the length to open pipe reflection length and dia are given in inch remember, the figure for length is the total length from the valve seat to the trumpet end. formula is taken from David Vizards "how to build horsepower". Playing around with the numbers, you will realize some interesting things: - of course EVERY intake has resonances at first, second, third and forth pressure wave reflection. It is just a question if it is in a range, where you can actually benefit from it. - using a hotter cam, the inlet resonance for a given length moves DOWN in the RPM range. - The impact of changing the trumpet length from 30mm to 60mm might be smaller than you expect :-) have fun Reinald Some clarification: -720 is 2 cycles (720 degrees of rotation) -1300 is the speed of sound in air (~1300ft/s @ intake temperatures) -rv; you can simply use "2" if you want to tune to the 2nd wave, "3" for 3rd wave, .... The dia/2 at the end is there because the reflection at an open pipe-end does not happen at the end of the pipe but actually occurs at an additional distance out, at half the pipe's diameter (L = l + 0.5Dia) F. Link to comment Share on other sites More sharing options...
JohnD Posted October 27, 2009 Share Posted October 27, 2009 Leon, Thank you, thnak you, thnak you, thnak you, thnak you! Pics downloaded, drooled over, and contact made with Butch Gilbert. (It's the Candy Box, before anyone gets any ideas) Leon has gone the the trouble to take loads of pics and to talk to Mr.Gilbert on my behalf. Deeply grateful. Mr.G is likewise very helpful, so one day.........................! John Link to comment Share on other sites More sharing options...
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