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MG MGB Technical - Timing with K&Ns

Hi Guys

My newly acquired 76 B had completely rotten air filter housings so I am going to fit K&Ns and richer needles to the HIF carbs. Do I need to consider the timing once these have all been fitted please?

Cheers

Dave
D Dunlop

It will be second order thing. The vacumn kicks in at small throttle openings, but down there you wont have changed things much anyway. If you choose the right needles the mixture will be much the same at high outputs as well.(so it will take the same time to burn)
Stan Best

Dave. As Stan notes, ignition timing is not a function of what air filter, nor what carb(s) are being used.

The first thing to do is to set the timing as per the factory specification (assuming you have the original distributor--if not, set it as per the instructions received with the dizzy). Set the mechanical advance with the vacuum line disconnected from the vacuum advance can and the line plugged, then, reattach the vacuum line to the can.

Install the new air filters and tune the carbs. I found that the AAA needles worked fine with both the factory air cleaners and with the K&N filters.

There has been some discussion, which should be available in the archives, about what value the K&N filters really provide. On my 68GT, I could detect no performance improvement when I switched from the factory system to the K&N. But, my cars are mainly used as daily drivers, not race cars.

Les
Les Bengtson

Thanks for the info guys. I'll let you know the outcome.

Cheers

David
David Dunlop

I have never seen any direct comparison between K&N and OE air filters.
R J Collier

I have never seen any direct comparison between K&N and OE air filters. Air filters efficiency does not just depend on the voulme of air to the carbs but also its temperature which is why the OE filter air intakes are directed towards the cooler engine bay air.

For me the benefits of K&N filters over OE filters are:-

1/ Improved looks
2/ Smaller and therefore easier to work on carbs
3/ Long life and no need to renew paper filters

If you do fit K&N Filters I would recommend you fit K&N stub stacks. K&N claim another 3bhp, but I found that the car idled smoother and quicker from cold.
Rob
R J Collier

"OE filter air intakes are directed towards the cooler engine bay air"

Can't really see that in my roadster. On the roadster the front intake is sort of pointing at a hole in the radiator mounting panel it's true, but the back intake is tucked right behind the engine. However I'm convinced from previous experience of using cold air ducting that it *is* beneficial to performance. Hot air is less dense and will carry less mixture into the cylinders for a given throttle opening, steam injection 'improved' mpg by doing precisely that, although all it does is effectively reduce the throttle opening, which any driver can do for themselves, but have the extra performance available for when they need it. OTOH jet aircraft engines use (or used) injection of distilled water into the intake at take-off to cool the charge and so deliver more power. I remember one failure to take-off in Germany many years ago that was put down to contamination in the distilled water, and this was enough to cause it to crash (I *knew* flying iffy). For the same reason turbo bosted engines use intercoolers, to cool the charge back down after it having been heated by compression, again to give more power.
Paul Hunt 2

Paul

Perhaps I should have said that the OE filters are directed away from the hot manifolds and engine?

Cant really remember the exact place the OE filters do point since Ive had K&N filters fitted for several years!!

Rob
R J Collier

Hi Rob

We reckon K&Ns add 4 to 4.5 bhp you might not feel it but it is better than losing 4 bhp. The best setup seems to be the MG plate system that utilises the OE radiused filter base plates. The OE filters flow the same as K&N cotton gauze, it is the cannisters which reduce air flow (and noise!).

Peter
peter burgess

A jet engine's thrust depends on two things: the volume of air moved, and the difference between inlet and exhaust temperatures. Although the air at higher altitudes is less dense, the outside air temperature is -55 degrees Centigrade (Celsius) at the tropopause, so the loss in thrust with altitude is modulated.

The fuel controller in a jet mixes air and fuel on the basis of weight; whereas a reciprocating engine is based on volume. Thus at high altitudes, fuel consumption is reduced.

Water injection on takeoff increased the density and thus the quantity of air moved (but not by much, relative to fan engines).

Reciprocating engines (such as the R-3350) also used water injection for brief periods, permitting higher manifold pressures and a bit more speed.

The government looked the other way when Boeing or Douglas certified takeoff and landing weights that were overly optimistic and some airlines carried this even further to keep from limiting payload. Probably this had much to do with the German aircraft having such marginal performance that it had to rely on water.

About 15 years ago, management at United caved in to the pilots' safety committee and petitioned the FAA to include a more realistic performance evaluation. I don't know what came of it, but hopefully is was passed into regulation. (rant, rant)



Dan Robinson

Peter

I have the pancake style K&Ns and the optional stub stacks as you will know are similar to the OE radiused venturi. i dont know how these compare with the thicker K&N filters availiable.

Going back to the original question, I did not alter my timing when I fitted K&Ns. I have one of your excellent Burgess unleaded heads fitted to my 3 bearing engine which runs superbly with no pinking or running on.

Rob
R J Collier

I thought that water injection was to cool the charge to suppress detonation. Denser air has more air/fuel per unit volume. The more air/fuel in the cyliner, the bigger the bang. Cooling it once inside the cylinder would decrease the volume not increase the mass and therefore the bang will not be any bigger. You'll get more power because detonation is avoided, not because the air is more dense. Getting cooler air in the first place (by routing it from somewhere cold) on the other hand, does increase density and hence power.

David Vizard's book on A series tuning has loads about the benefits (and otherwise) of various air filters. The benefit of a 'better' filter is more power, which you'll only feel at maximum power at high revs. SOme of use this power, some of us don;t. If you don't, you'll not notice the difference!

Peter - I know it's a long time since I came in to buy that 285, but it's fitted, and after careful measurement the compression ratio raised to 10.5 plus I cleaned up the valves as they were a bit sticky. Goes like a train!!! I mean, noticeably faster, 0-60mph in the 8s territory. Thanks! And it's not even been on the rolling road yet.

Neil
Neil22

Hi Rob

Your K&N filters are fine. The stub stacks are getting difficult to obtain so the one plate two filter-type is easier to supply and fit.


Neil

Maybe a dyno session would slow it down :)


Peter
peter burgess

Water sprayed into the intake cools the charge as it is going in, which reduces its volume/increases its mass or density, which takes in more fuel with it, which gives a bigger bang. You could only get water into a cylinder separate from the charge and after it had been drawn in if you had a separate injector. A cooler charge, from whatever source, will also reduce the likelyhood of pinking, as can opening the throttle *wider*. This might seem paradoxical, but part of this will be due to the increased cooling effect of the bigger charge and part due to a reduction in vacuum advance.
Paul Hunt 2

Interesting posts on this topic lads! The K&N pancakes and richer needles have been fitted, the jets centred, the mixture corrected and the carbs balanced and what a difference! I reckon an increase in 4 to 5 bhp is an understatement (mind you the original set up was dreadfull).

The timing was out too but there is no pinking and no running on now and using Colortune on each cylinder shows a nice bunsen blue flame at idle moving to a nice yellowish flame on accelaration.

Interesting comments on the use of water as I always thought my Bs and Cambridges ran better with moisture in the air.
D Dunlop

This thread was discussed between 28/06/2007 and 10/07/2007

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