running engine without filters
Discussion
Hi all, I am coming to the end of a tricky engine install and I am thinking of running the engine without air filters for a number of reasons, the engine is a rover k6 with jenvey throttle bodies, I have had to use dumpy air horns to get it all under the bonnet and I am having troble finding any filters to fit. Any suggestion.
Thanks Matt
Thanks Matt
If it's been quite tricky getting it all in and done, imagine how you'll feel when the engine's blowing blue smoke in 10K miles or less due to all the dust it's eaten. Is there no way of fitting some elaborate piping and remote mounting a filter? As said, trumpet socks, whilst normally a bad idea, may well be your best option.
Not at all uncommon to run bike engines without filters (excluding Japanese ones where it screws up the carburation 
). I haven't got a filter on my MZ and I've had it apart for experimental reasons a few times without seeing any undue wear. Mate of mine has never had filters on his bikes including running a Guzzi in the Israeli desert without filters with no ill effect, and currently runs an XK120 replica with no filters. The twin-carb 1275 A-series in my Morris Minor was quite happy with no filters too.
). I haven't got a filter on my MZ and I've had it apart for experimental reasons a few times without seeing any undue wear. Mate of mine has never had filters on his bikes including running a Guzzi in the Israeli desert without filters with no ill effect, and currently runs an XK120 replica with no filters. The twin-carb 1275 A-series in my Morris Minor was quite happy with no filters too.As someone who has stripped many engines run without filters and owned one myself I can be fairly definitive about what will happen. In normal road use you'll 'get away' with it for a long time but the damage is occuring even if you can't immediately notice it in engine performance. The first thing to suffer is the valve seats on both the valves and the seat inserts in the head. Constantly closing and rotating on a mixture of air and fine dust they abrade away gradually. Most of the debris then exits with the exhaust gases but what remains gets past the piston rings into the oil and starts wearing bores and crank bearings.
The wear rate accelerates exponentially with rpm. On road engines not much might happen for 30,000 miles but on race ones I've seen significant bore wear after just one season with the filter box lid lifted to get more air in. On properly filtered race engines there would be no measureable bore wear in a single season.
Nearly all engine wear, even in properly filtered engines, is actually because of inhaled debris. With state of the art oil and air filtration engines can run for half a million miles. Even OE filters on car engines are nothing like as good as those on high mileage truck diesel engines which have to last a long time. With no filtration at all I'd say you'll get 30k to 50k miles in road use before it's rebuild time although the engine will go longer than that before acually expiring in a cloud of steam. It all depends on how dusty the conditions are and where under the bonnet the air intake is.
On a race engine it'll probably mean a rebuild each year entailing a full rebore, crank grind and head recon instead of just replacing bearings, rings and service items.
Dave Baker
Puma Race Engines
The wear rate accelerates exponentially with rpm. On road engines not much might happen for 30,000 miles but on race ones I've seen significant bore wear after just one season with the filter box lid lifted to get more air in. On properly filtered race engines there would be no measureable bore wear in a single season.
Nearly all engine wear, even in properly filtered engines, is actually because of inhaled debris. With state of the art oil and air filtration engines can run for half a million miles. Even OE filters on car engines are nothing like as good as those on high mileage truck diesel engines which have to last a long time. With no filtration at all I'd say you'll get 30k to 50k miles in road use before it's rebuild time although the engine will go longer than that before acually expiring in a cloud of steam. It all depends on how dusty the conditions are and where under the bonnet the air intake is.
On a race engine it'll probably mean a rebuild each year entailing a full rebore, crank grind and head recon instead of just replacing bearings, rings and service items.
Dave Baker
Puma Race Engines
Daveuk9xx said:
As someone who has stripped many engines run without filters and owned one myself I can be fairly definitive about what will happen. In normal road use you'll 'get away' with it for a long time but the damage is occuring even if you can't immediately notice it in engine performance. The first thing to suffer is the valve seats on both the valves and the seat inserts in the head. Constantly closing and rotating on a mixture of air and fine dust they abrade away gradually. Most of the debris then exits with the exhaust gases but what remains gets past the piston rings into the oil and starts wearing bores and crank bearings.
The wear rate accelerates exponentially with rpm. On road engines not much might happen for 30,000 miles but on race ones I've seen significant bore wear after just one season with the filter box lid lifted to get more air in. On properly filtered race engines there would be no measureable bore wear in a single season.
Nearly all engine wear, even in properly filtered engines, is actually because of inhaled debris. With state of the art oil and air filtration engines can run for half a million miles. Even OE filters on car engines are nothing like as good as those on high mileage truck diesel engines which have to last a long time. With no filtration at all I'd say you'll get 30k to 50k miles in road use before it's rebuild time although the engine will go longer than that before acually expiring in a cloud of steam. It all depends on how dusty the conditions are and where under the bonnet the air intake is.
On a race engine it'll probably mean a rebuild each year entailing a full rebore, crank grind and head recon instead of just replacing bearings, rings and service items.
Dave Baker
Puma Race Engines
I have seen road tuned&modified engines make less than 10K(driven very hard of course) with no air filters and the usual thing to suffer 1st is the rings indicated by excess blow/by followed by using oil,i am not questioning your post more backing it up Daveuk9xx,i would never consider running any engine of worth on the road with no air filters The wear rate accelerates exponentially with rpm. On road engines not much might happen for 30,000 miles but on race ones I've seen significant bore wear after just one season with the filter box lid lifted to get more air in. On properly filtered race engines there would be no measureable bore wear in a single season.
Nearly all engine wear, even in properly filtered engines, is actually because of inhaled debris. With state of the art oil and air filtration engines can run for half a million miles. Even OE filters on car engines are nothing like as good as those on high mileage truck diesel engines which have to last a long time. With no filtration at all I'd say you'll get 30k to 50k miles in road use before it's rebuild time although the engine will go longer than that before acually expiring in a cloud of steam. It all depends on how dusty the conditions are and where under the bonnet the air intake is.
On a race engine it'll probably mean a rebuild each year entailing a full rebore, crank grind and head recon instead of just replacing bearings, rings and service items.
Dave Baker
Puma Race Engines
Edited by That Daddy on Wednesday 17th September 10:24
Your best solution would be to make some kind of airbox which allows you to run with either a ruddy great conical filter, or better still, a large panel filter.
To answer the question in words of one syllable though... NO.
I concur with all of the comments about engine damage. I've been in a position where I have had to run a car without filters (because there is no room to get anything in there within the rules), and I have, in the past, had the enjoyment and expense of regular engine rebuilding due to power falling off due to wear.
To answer the question in words of one syllable though... NO.
I concur with all of the comments about engine damage. I've been in a position where I have had to run a car without filters (because there is no room to get anything in there within the rules), and I have, in the past, had the enjoyment and expense of regular engine rebuilding due to power falling off due to wear.
I've just come across some notes I'd long since forgotten about on the Metro I ran on the road without air filters nearly 20 years ago. It ran a highly tuned 1380 engine with hot cam, big valve head and a single HIF SU. Power we ended up with was 85 bhp at the wheels (just over twice the stock figure of 41 at the wheels we recorded when I bought it as a standard 63 bhp flywheel 1275 Metro), about 110 bhp flywheel at a best estimate, maybe even a tad more. There's not many normally aspirated cars you can double the OE wheel bhp on and still have them completely road driveable. It certainly did go like that stuff off a shovel though with so much power and very little weight. I ran it for somewhere between 15 and 20 thousand miles without filters. I can't be certain if the first 5k miles had filtration but the last 15k definitely didn't after the final spec cylinder head was fitted.
It did get stripped down after that time but it's so long ago it's hard to remember every detail. The piston skirts were a bit scuffed but nothing to really worry about. Bore wear I simply can't recall and the head got reconditioned for another engine so it certainly wasn't beyond repair. Power was starting to drop off towards the end though and I must have been getting concerned about oil consumption because I've found an old log of it. There's no mention of what it was when the engine was new but after 13,000 miles it was only doing 500 miles per pint. Mind you big bore A series engines that get caned to within an inch of their life aren't reknowned for good oil consumption anyway. 500 mpp is perhaps not that unusual for them. Sadly there's no mention of what the oil consumption was right at the end of the 20k miles or whether it had got worse.
A friend ran a 1600 CVH in road use without filters for about 30k miles. That was also quite highly tuned with a big overbore and stroked crank taking it out to 1800cc, one of my ported heads, cam and twin DCOEs. It finally expired due to a crack in a bore wall because of the big overbore rather than any long term wear and because the crack was letting water in to the sump there wasn't much left of the bottom end anyway so it's not possible to say how it would have lasted without that. The valve seats were the worst I've ever seen though. The valves themselves were actually worn so concave they were beyond regrinding. The equivalent of well over 200,000 miles worth of wear in the 30k it actually ran for. The head just needed the seats recutting thoroughly but of course there's tons of meat on the seat inserts in cylinder heads so you can't really wear those out even without air filters.
On both those engines, which I guess on balance survived quite well for extended mileage, the intake faces the bulkhead so it's fairly well shielded from dust. It might be a different story with a front facing intake picking water and crap up straight through the radiator.
When you can do all your own engine building with parts at trade price like me or my mate we weren't that fussed about wearing the engines out. Rebuilding them is half the fun. It'd be time to try out the next stage of tune anyway after so many miles. For someone who's just paid a small fortune to an engine builder though it's suicide to run without filters.
If space is tight the best method is to make up a plenum from fibreglass or aluminium and use trunking to link that to a remote filter.
Dave Baker
Puma Race Engines
It did get stripped down after that time but it's so long ago it's hard to remember every detail. The piston skirts were a bit scuffed but nothing to really worry about. Bore wear I simply can't recall and the head got reconditioned for another engine so it certainly wasn't beyond repair. Power was starting to drop off towards the end though and I must have been getting concerned about oil consumption because I've found an old log of it. There's no mention of what it was when the engine was new but after 13,000 miles it was only doing 500 miles per pint. Mind you big bore A series engines that get caned to within an inch of their life aren't reknowned for good oil consumption anyway. 500 mpp is perhaps not that unusual for them. Sadly there's no mention of what the oil consumption was right at the end of the 20k miles or whether it had got worse.
A friend ran a 1600 CVH in road use without filters for about 30k miles. That was also quite highly tuned with a big overbore and stroked crank taking it out to 1800cc, one of my ported heads, cam and twin DCOEs. It finally expired due to a crack in a bore wall because of the big overbore rather than any long term wear and because the crack was letting water in to the sump there wasn't much left of the bottom end anyway so it's not possible to say how it would have lasted without that. The valve seats were the worst I've ever seen though. The valves themselves were actually worn so concave they were beyond regrinding. The equivalent of well over 200,000 miles worth of wear in the 30k it actually ran for. The head just needed the seats recutting thoroughly but of course there's tons of meat on the seat inserts in cylinder heads so you can't really wear those out even without air filters.
On both those engines, which I guess on balance survived quite well for extended mileage, the intake faces the bulkhead so it's fairly well shielded from dust. It might be a different story with a front facing intake picking water and crap up straight through the radiator.
When you can do all your own engine building with parts at trade price like me or my mate we weren't that fussed about wearing the engines out. Rebuilding them is half the fun. It'd be time to try out the next stage of tune anyway after so many miles. For someone who's just paid a small fortune to an engine builder though it's suicide to run without filters.
If space is tight the best method is to make up a plenum from fibreglass or aluminium and use trunking to link that to a remote filter.
Dave Baker
Puma Race Engines
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