K&N Air Filters

[Pettifordo]

I’m hopefully starting to get close to getting my Spitfire back on the road.

I bought the car as a failed resto project and it had a sports exhaust on the car (sports manifold and twin pipes), however the air in take to the carbs is the factory standard.

Shoild I upgrade to the K&N Air Filters which look nice - but not sure if they make too much difference

[Stratton Jimmer]

I wouldn't bother with K&Ns. The PO of the GT6 had fitted them to the HS4 SUs but they looked to be in poor condition. I replaced them with a cheap pair from Mini Spares as a temporary measure and the engine runs really well. The Sixfire had K&Ns on its HS6 SUs but the Strombergs now fitted use a conventional Triumph original air filter box and filters and it runs better than it did with the SU K&N fit. 

[PeteH]

Assuming your Engine is standard, the Makers System will likely be the most efficient?. I know folk do fit aftermarket items, we all do somewhere, But manifolding and fueling will have been reasonably well calculated by the designers. IMHO.

Pete

[Neil Clark]

I met the K&N people at a trade show and their logic of air flow improvement is good but they themselves said that the real benefit only comes if all else is adjusted to suit, perhaps needles etc etc.  On the MG forum the consensus seems to be that unless outright performance is needed, the cost isn't really worth it and a rolling road session with someone who knows what they are doing is apparently a better use of funds initially.  On my MGB I've stuck with the original air filters since the car runs fine.

[Pete Lewis]

whilst KN are lifetime use with some cleaning they cost a fortune the std paper filters last many many miles 

having  free flowing is going to upset the fueling and you will have to play with metering needles to compensate for the filters reduction in intake vacuum  so 

instead of making better now gives you a serious headache with weak mixtures as less fuel will be sucked from the carb jetting 

unless you have access to a dynamometer to set up whats going on you cannot replicate what Triumph spent months of testing 

fitting SU to replace Strombergs has never worked well  lost count of how many i have reverted and returned cars to run far nicer 

sorry  silly expensive must haves just give you a Headache    stick to std  unless you have the where withall to play for days and get the ache 

most of all you dont want hot underbonnet air for an intake   you need good cool air from outside the engine bay is best 

Pete

[Clive]

If you consider what a free flow filter does for a moment, most people will realise they are a waste.

Teh only place they will add to a cars performance is at maximum airflow, above what the paper filters will flow. So we are talking 6000rpm? With teh added complication that the fuelling is altered right the way across the rev range, which is not great for the vast majority of people.

And the bigger downside is you are loosing the cold air intake....

So yes, I run a K+N  cone filter on my injected car. But I also have an AFR gauge, so it is tuned appropriately, and automatically tweaks the fuelling as I drive. Setting a carb car up on a rolling road is rather harder, and requires somebody with lots of experience. 

[johny]

11 minutes ago, clive said:

If you consider what a free flow filter does for a moment, most people will realise they are a waste.

Teh only place they will add to a cars performance is at maximum airflow, above what the paper filters will flow. So we are talking 6000rpm? With teh added complication that the fuelling is altered right the way across the rev range, which is not great for the vast majority of people.

Wait a minute though, surely a K&N cant do both? Change fuelling across the rev range but only change airflow at max revs...

[NonMember]

They change the "vacuum" across the range but only increase air flow at full flow. It's the change in pre-throttle depression ("vacuum") that throws the fuelling off.

[johny]

Surely the two are connected less vacuum (K&N) = more air flow and vice versa?

[Clive]

16 minutes ago, johny said:

Wait a minute though, surely a K&N cant do both? Change fuelling across the rev range but only change airflow at max revs...

No, it allows more airflow across the entire range, but the paper filter can match that right up until the paper filter is maxxed out, at which point the K+N has the advantage. But because the K+N does allow more airflow across teh range, it needs a different needle. 

So the only time the K+N has the advantage is at very high rpm and going for max power. Which precisely 3% of triumph drivers actually try.

 

 

(I made the 3% up, but it probably isn't far off accurate)

[johny]

If a different (richer) needle is needed to match the increased airflow then there must be more power being produced as doesnt more fuel + air = bigger bang?

I would have thought the power curve would proportionally increase over standard across the complete rev range...

[Clive]

2 minutes ago, johny said:

If a different (richer) needle is needed to match the increased airflow then there must be more power being produced as doesnt more fuel + air = bigger bang?

I would have thought the power curve would proportionally increase over standard across the complete rev range...

The same power and mixture can be achieved with the std filter. At 3000rpm on the open road a spitfire may be making 30bhp. The filter will make no difference at all. The throttle will be a little more open with a paper filter, but the power and economy will be identical (as long as the needle profiles are spot on). The same applies right up until the paper filter reaches its limit. The paper filter just needs a little more pedal. 

[johny]

Yes ok I get it as the airflow restriction at partial opening is the carb butterfly not the filter but when fully open its down to filter/porting/valves👍Those power curves are a bit confusing then as dont they show an increase at all revs?

[Clive]

1 minute ago, johny said:

Yes ok I get it as the airflow restriction at partial opening is the carb butterfly not the filter but when fully open its down to filter/porting/valves👍Those power curves are a bit confusing then as dont they show an increase at all revs?

It is extremely rare t find a set of proper comparison power/torque curves. 

They do a before, chuck filters/manifolds etc on, tune it to perfection then show the difference. Really you want to see is the car fully tuned in std form, then add things one at a time, but tuning to match. Then you could see where the improvements happen. Of course, that is expensive top do and may not help sell as much tat.

There were proper articles years ago by John Thomason. He tuned a spit in std spec, put a sports exhaust on and retuned, then added a manifold and tuned again, showing where the benefits were. He did the same for a single HS4 vs a pair on a spitfire (tiny difference in power). Years ago I took part in a magazine article for one of teh magazines. My "thrown together" 2.5 engine made 2bhp less but a little more torque than a jigsaw 2.5 "bells and whistles" engine with triple strombergs. All a tad embarassing for the owner who had spent a fortune with jigsaw. 

[johny]

So really you can never see an improvement in power at partial revs because you could just open the throttle a bit more on the standard engine to equal the output from the tuned one! The curves should be identical until the throttle is full open on the standard engine at which point the tuned one will hopefully still have some power left to give...  

[68vitesse]

1 hour ago, Pete Lewis said:

most of all you dont want hot underbonnet air for an intake   you need good cool air from outside the engine bay is best.

Added pipes to air box on my Mk1 Vitesse, standard on Mk2, but air box has holes in the bottom presumably for water drain, but wonder how much air is drawn in that way.

Regards

Paul.

 

 

[PeteH]

It is rare, that just altering one parameter, makes a decided difference, it is all but certain that it will alter the overall balance of the Engine at some point.

"Tuning" per-se, only really works IF the Whole engine is looked at. "We" tried enhancing the performance of Ford Crossflow engines back in the day. In the end we came to the conclusion the the easiest/cheapest option was to use the Pinto Engines, in virtual bog standard form.

Pete

Edited November 1, 2022 by PeteH
Spelling Dylsexia.

[Pete Lewis]

there is little change in air flow on any normal driving what you really loose with a pancake is the drop in inlet vacuum which pulls /sucks fuel from the jet 

thats where the weak mixture comes from .

so then you start messing with damper springs and needles to attempt correction by guess work and more headaches 

loading the damper spring lowers the piston and increases air flow over the jet     

Pete

[Ian Foster]

I think Triumph struggled with their twin carb airbox design, as there are many iterations from the early cars to later Spitfire and Dolomite boxes. The late saloon box has an enlarged box with a centre bottom feed.

My GT6 Mk2 already had 175 CD2s on it when I bought it in 1977, but with an empty original airbox. Clearly a case of someone just slapping bigger carbs on. In my ignorant youth I put on a pair of wire gauze pancakes, which probably didn't filter or flow well, but made a lot of sucky noise. I subsequently bought a pair of K&Ns which I still have to this day which actually work well giving decent power and economy, but I am troubled by the fact that they are probably drawing hot air when the car is not moving.

The early GT6 box had a pair of open tubes in the front and by the time they got to the MK3 Triumph had added the feed pipes. This arrangement seems to favour the front carb and there is a rectangular hole in the bottom of the box under the rear carb which is perhaps intended to compensate for this (or to let water out). The later Spitfire and Dolomite boxes have indentations in the cover (and presumably unequal length tubes internally) to distribute more air to the rear carb. There isn't space on my GT6 to do this. The TR(250) boxes seem to have various slots on the sides of the box, perhaps to address this issue, but surely this then also allows in hot air in when stationary.

I have made a mock up of a new airbox to enclose my K&N filter elements, which flares out forward of the front filter (making use of the shape of the wheelarch) in order to accept a larger diameter single air duct into the radiator cowl. I have yet to commit the design to metal/glass fibre/carbon fibre, but it might just happen this winter.

Ian

PS Paul you have some very nice shiny bits.

[Iain T]

9 hours ago, Pete Lewis said:

so then you start messing with damper springs and needles to attempt correction by guess work and more headaches 

Been there! It took me over a year of peeing about with damper oil, springs, needles to get it right and that's with the aid of an AFR meter. 

Iain 

[ed.h]

I've seen at least a couple of more or less scientific tests of various air filters, includIng K&N.  One common finding was that  K&N filters are among the most free-flowing, but this is at the expense of filtering efficiency.  They let more particulates through than other filters.

This is a tradeoff I'm personally not willing to make, especially for the small potential gains in fairly extreme situations.

I also avoid the disagreeable feeling of being gouged on price.

Ed

[John Harris]

Lets just deal with some facts.

To get the most out of a standard engine ignition timing must be fully optimised, carbs set optimised, this assumes everything else as per the specification. The first statement - ignition timing fully optimised cannot be achieved with a standard set of points, with standard weights and springs. 

So the first point of performance improvement should be ignition timing. ( I won't enter the debate, but I use a programable 123 - other solutions are available )

Second step to performance is get more fuel and air into the engine - K&N filter do do this, side by side rolling road test show this, it is modest perhaps 5 %, little bit more if the exhaust is optimised for flow - up to 10%. Torque a little bit more perhaps getting on for 7%. Yes you have to change the needle - AAQ/AAT for a 1500 would be the richer needle. 

I accept the cost/performance argument but K&N will provide an improvement assuming all the other steps are done first. 

If I was to spend money, I would always start with the ignition before anything else. You can see an improvement on a rolling road throughout the rev range immediately. 

[Pete Lewis]

theres some other facts

most have no idea how to calibrate a 123 to suit what they have

fitting electronic in the main aftermarket is just a electronic points using the same good or worn Dizzy advance mechanisms 

and to test dizzy data needs some very careful work and understanding 

Triumph like all makers spent days and weeks setting data to do what it says on the tin  50yrs on it still works well 

most members have no means of using or even finding a dynomometer to get the best out of  whats fitted 

they have to rely on the base specification costs and abilities which gives a good reliable performance for peanuts 

All  "Must  Have's "   are all down to personal  preferences and the ongoing attack on the wallet often for no real advantage to the general driving 

to so many they gain a headache  and   thats not any fun anymore 

each to there own 

Pete

 

 

 

[John Harris]

Apologies in advance for the long post.

A set of points, with a fully reconditioned dizzy, using standard weights and springs and properly timed is not optimised ignition. 

It is a manufactures operating envelope that will work well in most conditions and allows for the fact that most garages back in the day could not or not be bothered to set dwell angles and timing accurately from a work shop manual. Anything set just statically to BTC or dynamically at BTC will not be accurate, the tick over of the engine will not allow very accurate measurement. That is why in a good work shop manual the measurement is given at RPM points and must be measured coming down the rev range and should be checked at the point from maximum advance down. Most garages would not do this. 

You can find the advance graph for a dizzy online, with the advance at set rpm through the range. Indeed many of them have a +/- 2 degrees or so at each point and you can plot the envelope. To optimise for this you would still need to know what you are doing with at least a programmable strobe.  With this technique, you could optimise for the advance for the particular weights and springs. This would not be the optimised advance curve for the engine. That's why racing engines were set up on a dyno with the tuner testing different weights and springs. A conventional dizzy can never be optimised in a production car, the graph alone is governed by the weights and then the point at which the secondary spring comes into operation and the cut off point for maximum advance. Elegant in its day, but when fuel efficiency was needed mapped ignition came to the rescue. They are not curves put two straight lines as the first springs takes precedent before the second one comes into operation. 

Fuel injection and engine management overcame this problem.

Taking a programable ignition, entering the advance graph for the conventional dizzy and timing on the engine in the conventional way is not complex or difficult. It will of itself be an improvement on a conventional dizzy because its frequency of spark operation is far more consistent. Anyone who has seen even a new dizzy on a test bed under a strobe will know their variability in comparison with an electronic system.

I completely agree that fitting an electronic pick up to a convention dizzy brings no advantage other than not needing to change points. If properly timed as above, then at least it should relatively be fit and forget and remain accurate. Having bought classic cars with these fitted - my current spitfire included, I find that most of them have not been properly timed. If you added an electronic pick up you have to ask yourself did you properly time it or just set it at static or dynamic BTC. If that is all you did it is not running optimally for the weights and springs in the dizzy. 

To optimise for a conventional dizzy then every time points are changed the correct timing procedure must be gone through. With an electronic pick up this only needs to be done once. With a programable ignition, the torque and bhp can be properly optimised, and this will enhance the driving experience. I accept the cost issue, but before fiddling with fuel or filters etc then at least properly time a conventional dizzy. 

A programable ignition is not a must have. 

To get a car operating properly a must do is to have a properly operating conventional dizzy timed properly, which is more work than setting it  statically or dynamically at BTC. 

Lots of members will have a strobe light, so having got data for the graph,  could measure at a set rpm ( probably no more than 1800 rpm ) against a timing mark, this will be more accurate than just setting dynamic timing. The strobe light/timing mark will be steadier.

Those that have a programmable strobe can test the curve all the way from maximum advance down. Those that are capable of doing this will manage a programable ignition easily. 

A conventional dizzy, points or electronic pick will make a car run well, provided it is truly properly timed and in good condition. Anything with old springs and weights is unlikely still to be following the ignition graph well. 

 

[Pete Lewis]

you missed out pretty much all dizzy test data is in the triumph WSM and dizzy test data is decelerating 

which complicates most members conception of dizzy testing 

pete