MG-Cars.com
MG Midget and Sprite Technical Which air filter? BBS discussion at MG-Cars.net
MG-Cars.net
Welcome to our resource for MG Car Information.
Recommendations
Parts
MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.
|
|
MG Midget and Sprite Technical - Which air filter?
| I am going to change my air filter but which is best; K&N ITG Pipercross Also, I assume I will need to change the carb needle (Mk2 Sprite, 948cc, twin 1.25" SU), it is currently standard V3. What needle should I use, V2? Thanks for your help. Les |
| Les Robinson |
| it is a bit of a believe question. non of them are bad. the most important part is how do you use them rampipes, substacks? so it is more of a question how does you complete intake look? that usualy dictates the filter example i run a 45weber on a long manifold. it is fitted with medium ram pipes. and i do not want to cut the inner part of my wing to fit a big k&n filter. so i ended up with 2 pipercross socks over the ram pipes. |
| Onno Könemann |
| If like me you are a touch over weight. You will get the same performance increase as it will give at best by loosing a stone in weight. Saving on cakes, chocolate, biscuits, crisps and about £70 for the air filter. If you are not over weight you will only save on the filter by not buying one. I have used them and did not notice any speed increase on a number of more modern cars. eddie eddie |
| Eddie Cairns |
| Colin Dodds has done back to back testing on the flow bench and reports no difference from factory filters. |
| Mike Allen |
| http://www.max-boost.co.uk/max-boost/intake/intake.htm#highflowreplacementairfilters Take a look at this site. They are not very enthousiast about k&n. I too have piper cross filter socks on my weber, found sand in my ram pipes and venturis.... |
| Alex G Matla |
| Hi Les Nice meeting you yesterday. As I said the mechanical integrity of the K&N filter is way superior to the foam based filters which seem to become shabby very rapidly.Many years ago I worked on developing a twin foam and steel mesh air filter setup for the 'donkey' engines in tanks. It was found pleated (big surface area)paper filter flows the same rate as K&N pleated filters but no strength. The paper filters with reinforcing steel drilled plate had poorer flow chracteristics. The foam material required an area some 2.5 times the paper/K&N area to flow the same. Under 'working conditions' adding a specific grade dust the foam filter clogged much quicker than either paper or K&N elements. With the greater strength of K&N elements my first choice would be K&N (not some cheap replica that seems to pervade the VW world). Peter |
| peter burgess |
| Agree with the comments about the quality of the socks - on my Weber they lasted less than a season before cracking up. I have done back to back rolling road tests with ITG filters on both SU's and Webers and there was no difference in power without the filters. I cannot imagine the others are much different. |
| John Collinson |
| In general confirmation of what Peter says - when I used to have a bit to do with the running of FIA Rally Mini Cooper S's back in the 90's with Bill Richards Racing, we did some relatively inscientific back to back tests on K&N filters and foam filters (ITG and Pipercross IIRC). Power was similar regardless of filter used - but we put smears of grease on the inside of the filter cases before various Minis went off on long European stage rallies - when the foam filter Minis came back, the foam filters were clogged, and the backplates on the inside of the filter were coated in a fine paste of grease and grit (and the valve seats on the heads had taken a hammering). On the K&N cars the filters were similarly clogged, but the insides of the filter cases were coated with clean grease (and the valve seats were largely undamaged)... Guess which filters we sent the cars out with from then on - and guess which filters I have always used on my race cars... |
| James Bilsland |
| Les I run K&Ns with V3s |
| Alan Anstead |
| Another question, which is preferable 2 single filters or 1 double. Or dosn't it make any difference. Thanks Les |
| Les Robinson |
| Eddie you are wrong. An increase in power may increase top speed. Whereas a reduction in weight will not increase top speed but will improve acceleration, handling and braking. There are books with this stuff in... |
| Daniel Thirteen-Twelve |
| Daniel, no picture? 8^P |
| Alex G Matla |
| >>Eddie you are wrong. >>An increase in power may increase top speed. >>Whereas a reduction in weight will not increase top >>speed but will improve acceleration, handling and >>braking. Daniel I still say that the filter will only empty the mans wallet without giving anything other than a warm feeling and a bit more intake noise. eddie |
| Eddie Cairns |
| K&N for me, i could live wiveout the induction roar on a DHLA45, but prefer the noise :-) |
| Brad (Sprite IV 1380) |
| I got 2 bits to add... Well here is an interesting question...When I converted to K&Ns I Maxed out lean on the carb needles. thus need richer needles. If K&Ns are not flowing more air, then why do I need a richer needles? if for no other reason they are good to 1,000,000 miles just clean/wash (see special instructions) and re-oil ever 60,000 miles...thats alot of money saved on filters. Not to mention a meater throater carb music thur the exhauste Prop |
| Prop |
| Prop, did you only change the paper filter for a k&n or did you discard the original set-up and replace it with just an open filter? |
| Alex G Matla |
| Hi Alex If prop had to richen needles he will have fitted stand alone filters, it tends to be the casing which causes the restriction to flow. It is this restriction to flow which creates a slightly greater pressure drop between filter and inlet valve, nature abhoring a vacuum does its best to equalise pressures, easiest place is to lift more fuel from jet. reducing pressure drop across jet reduces fuel lifted, therefore need more fuel via slimmer needle. Peter |
| peter burgess |
| just to settle the weight issue, I can confirm that Les is not overweight. In fact, I have seen more fat on a butcher's pencil. Bernie. |
| b higginson |
| So, question remains: does a k&n really flow more air? I don't think so, its more due to the restrictions being cleared. Also see the link I posted before. |
| Alex G Matla |
| Or are the questions: How long does it take for a standard air filter to clog such that its performance is degraded and power suffers? Is there an aftermarket filter case I can put standard filters into that doesn't restrict airflow as much as the standard air filter casing? |
| Daniel Thirteen-Twelve |
| """nature abhoring a vacuum"" What a beautiful use of the English language, I like that Peter... Yes I am not a big fan of the flows 10% more air school but there are a number of issues here of great interest. As Peter alludes too a number of effects contribute to the size of jet/needle. Take the simple case of sidedraught Weber (DCOE 45) Tuners of this carburettor can change the size of the throat inside the carb. (Venturi) Naturally this could cause less air to flow but lets assume for one moment that the same amount of air passes through the throat as there was before with a larger throat. If the jet remained the same for the same amount of airflow he smaller throat would become very rich! Why? Because the air would be accelerated more with the smaller throat (has to travel faster becuse the hole is smaller) Thus the depression (Suction) above the jet will be lower and as Peter described more fuel will be spewed into the engine and thus the mixture will become rich even for the same air flow. |
| Robert (Bob) Midget Turbo |
| Vary cool Peter ...thanks yes... I replaced th whole filter system ... its a pancake type set up...basically 2) 1 gallon paint can lids with the filter sandwhiched between and mounted on the front of the carbs |
| Prop |
| Just because its prop.....I now have visions of actual paint can lids in a DIY pancake filter setup. |
| Dean Smith ('73 RWA) |
| Just to clarify things a bit, K&N's reusable cotton element air filters have an airflow capacity of 6.5 Cubic Feet per Minute while some air filtering elements that are made with paper filtering media have an airflow capacity as little as 3.2 Cubic Feet per Minute. However, switching from the Original Equipment airfilter elements to the same size K&N airfilter elements will have no effect on performance if you retain the use of any of the variations of the Original Equipment airfilter housings. The purpose of the inlet tubes on the airfilter housings is first to accelerate the airflow so that intake noise is literally sucked into the engine. This occurs because the air goes in faster than the sound goes out (sound only travels in air). This is a big issue since the advent of noise regulations, and it is illegal under US Federal law to alter or modify the air intakes on modern vehicles for this reason. |
| Stephen Strange |
| Stephen, I remember you quoting those filter flow rates once before. At the time, I asked if you had the correct units right or had the decimals in the right place, but I never saw that you answered. If I did the math right, an MGB at 3000 RPM at 100% volumetric efficiency would take in about 1146 cu ft / min. (110/2/144x3000)=1146 So, is my math wrong or is it your figures? Charley |
| C R Huff |
| Hi Charley Flow will depend on pressure drop when tested so can be very difficult, if not impossible, to compare. It is standard practice to quote the pressure drop test pressure in inches of mercury or inches of water. I think you also have a cubic foot as 144cu in but it is 12x12x12=1728 cu in. Peter |
| peter burgess |
| Right you are, Peter. It is 1728 for the cube. That still comes out to 95 cuft/min. I realize that the volumetric efficiency isn't 100%, but 95 is still a long way 6.5. Is a Spridget only taking in 6.5 cuft/min per carb? Charley |
| C R Huff |
| I think Stephen's figures on airflow need to be be appended with an additional number, such as "per square inch" or "per 100 square cemtimeters" to make sense. It's impossible to state all K&N's flow XX cubic feet per minute, as they come in different sizes. Richard |
| R J Reeves |
| Hi All The problem is stating at what pressure drop and what fluid the flow figures are given. carbs are often quoted in inches of mercury, atmospheric pressure is approx 15 psi which is 33 feet of water or 760 mm (30 inches) mercury, all three are the same thing just different ways of stating the pressure, the water and mercury comparison is a factor of 10 ie pressure drop at 1"Hg is the same as 10" H2O. Charley, you are working sort of actual cfm used whereas the air filter flow is given at a specific pressure drop across the air filter for test measurement purposes. As I said comparisons are difficult :) My flow bench measures the actual air flow and then we calculate what the flow would be at 25" H2O at standard atmospheric conditions so we can make comparisons with the various mods we do, our adjusted figures are not dependant on temperature, pressure or humidity.They can be compared from day to day and year to year and still be accurate. It is like your car going quicker when the weather is cool and damp or slower when hot and dry, the conditions obtaining on the day can be related to theoretical standard conditions and a correction factor applied which would give the same corrected bhp amount whether the bhp was corrected up on the hot day or down on the cool day . Peter |
| peter burgess |
| Peter, Actually, I wasn't thinking in terms of actual cubic feet per minute (acfm). I was thinking in terms of standard cubic feet per minute (scfm). Stephens figures didn't state which, and without being clarified, I would think the figures would be scfm, that is, cubic feet per minute at standard temperature and pressure (at STP), which is something like 68F and 14.7 psi. It has been too long since I actually did any math with these figures, so I would have to go back to the books to do any. Therefore, I may be way off on the concept. But, the possible error I am questioning is greater than the difference between acfm and scfm. It seems to me that there is an error in orders of magnitude, not just the differences between acfm and scfm. Don't get me wrong, Peter. I know who you are, I own your book, and I used it to build my MGBGT engine. I am thinking that if you put a filter on a carb on a midget that could only flow 6.5 cfm (acfm or scfm), you wouldn't make it to the bus stop. Just to see if I was wildly off base, I grabbed up my Vizard (1996 edition) book that I used for my Midget engine. On page 76 in the carburetion chapter, it says that about 2 to 2.2 cfm is needed per potential HP. So, at 6.5 cfm, you could have about 6.5 HP (assuming twin carbs). So, if there is some point that I'm totally missing, let me know. Thanks, Charley |
| C R Huff |
| Peter, Actually, I wasn't thinking in terms of actual cubic feet per minute (acfm). I was thinking in terms of standard cubic feet per minute (scfm). Stephens figures didn't state which, and without being clarified, I would think the figures would be scfm, that is, cubic feet per minute at standard temperature and pressure (at STP), which is something like 68F and 14.7 psi. It has been too long since I actually did any math with these figures, so I would have to go back to the books to do any. Therefore, I may be way off on the concept. But, the possible error I am questioning is greater than the difference between acfm and scfm. It seems to me that there is an error in orders of magnitude, not just the differences between acfm and scfm. Don't get me wrong, Peter. I know who you are, I own your book, and I used it to build my MGBGT engine. I am thinking that if you put a filter on a carb on a midget that could only flow 6.5 cfm (acfm or scfm), you wouldn't make it to the bus stop. Just to see if I was wildly off base, I grabbed up my Vizard (1996 edition) book that I used for my Midget engine. On page 76 in the carburetion chapter, it says that about 2 to 2.2 cfm is needed per potential HP. So, at 6.5 cfm, you could have about 6.5 HP (assuming twin carbs). So, if there is some point that I'm totally missing, let me know. Thanks, Charley |
| C R Huff |
| Peter, Actually, I wasn't thinking in terms of actual cubic feet per minute (acfm). I was thinking in terms of standard cubic feet per minute (scfm). Stephens figures didn't state which, and without being clarified, I would think the figures would be scfm, that is, cubic feet per minute at standard temperature and pressure (at STP), which is something like 68F and 14.7 psi. It has been too long since I actually did any math with these figures, so I would have to go back to the books to do any. Therefore, I may be way off on the concept. But, the possible error I am questioning is greater than the difference between acfm and scfm. It seems to me that there is an error in orders of magnitude, not just the differences between acfm and scfm. Don't get me wrong, Peter. I know who you are, I own your book, and I used it to build my MGBGT engine. I am thinking that if you put a filter on a carb on a midget that could only flow 6.5 cfm (acfm or scfm), you wouldn't make it to the bus stop. Just to see if I was wildly off base, I grabbed up my Vizard (1996 edition) book that I used for my Midget engine. On page 76 in the carburetion chapter, it says that about 2 to 2.2 cfm is needed per potential HP. So, at 6.5 cfm, you could have about 6.5 HP (assuming twin carbs). So, if there is some point that I'm totally missing, let me know. Thanks, Charley |
| C R Huff |
| Sorry, Don't know what happend there. When I posted the message, the scren started flashing, and by the time I pulled the plug and signed back on, the message was posted three times with a bunch of blank space below each post, and the edit feature was gone. Charley |
| C R Huff |
| I was wondering, maybe posting many times in a row can be like typing all in caps or something. "Look, guys, I really really mean it!" Perhaps the website manager can delete the extras? Or we can just keep them for curiosity sake. ":o) Norm |
| Norm Kerr |
| Vizard 1st edition gives a couple of charts for various filter elements. Range is 4.5-5.5 CFM/insq for new paper, 4.0 for average paper at 5000 mi, 4.2-5.5 for various wire/wire-wool mesh, 4.5 for thick foam that actually filters, 5.5 for thin foam, and 6.5 for K&N. The K&N was still as good as the best new paper elements when covered with 3/16" of dirt after a Baja 500 race. All for overall element dimensions, CFM/insq at 1.5" water drop. FRM |
| FR Millmore |
| Hi FRM thanks for info Mind you the declared pressure drop still isn't there so it is still difficult to equate the flow to anything. It is like saying to someone take a piece of string 15.756 long, the first thing they will say is 15.756 what! Charley, the cfm used by the engine is based on engine size, whether 2 or 4 stroke, rpm and vol efficiency at some point. The filter flow is given by applying a pressure drop across the test piece and measuring the resulting flow. Not the same thing at all. As an example of actual flow a 14 cfm theoretical cfm compressor is only say 75% efficient so actual air delivery will be 10.5 cfm not enough to supply a 12 cfm air tool continuously...I mention this as compressor sales tends to promote theoretical cfm whereas the tool makers tend to state actual cfm consumption. Peter |
| peter burgess |
| Hi Peter, look again! "All for overall element dimensions, CFM/insq at << 1.5" water drop>>." FRM |
| FR Millmore |
| Must go to the opticians :) I was trying to get over that the air filter scenario is a rate of flow and the engine scenario is consumption of air. Peter |
| peter burgess |
| Aha. So it looks like the spec that Stephen quoted was probably per square inch as Richard surmised. I can make sense out of that. Norm, I really don't quite know what happened to that post. The screen started flashing and I think it was filling in the post with blanks until it reached a maximum message link, and then it apparently posted it three times. I suppose I might have inadvertently hit some key that did it, but I have no idea what it was. I'll hope I don't do it again. Charley |
| C R Huff |
| Hi Charley Adds to the anticipation scrolling down the screen :) Peter |
| peter burgess |
| I figured charly just got a call from "E.F. Hutton" .....WHAT......??? LOL. you had to know who the 6 million dollar man was to get that old referance. Prop |
| Prop |
| Well, at least we now know the maximum message length. And to think ... I could have said so much more. Charley |
| C R Huff |
| Charley. It once did that to me when I was trying to put my other car on the vehicle profile bit and I never did find out what happened. It just started repeating all the way down the page and now I can't get rid of it. Just view my vehicle profile and you'll see what I mean. Bernie. |
| b higginson |
This thread was discussed between 21/01/2010 and 28/01/2010
MG Midget and Sprite Technical index
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.