This “logic” is in conflict with the oft quoted advice/reality that (a) you have to set the mixture with the air filters fitted, or you will end up too rich when you install them (as the filter restricts the air flow), and (b) when you go from the standard “canister” air filter to a less restrictive filter, such as K&N pancakes, or the ITG filter, you have to add richer needles, or you will run lean.
Then explain why the car apparently runs just fine with or without the airfilter fitted David. There’s evidence to show the car can achieve max performance with the filter in place or not. My car runs just fine in either case, up to 85mph at least as born out by my runs at least, and in either state the idle is smooth. I don’t call that anecdotal just reality.
As an adder to the discussion I removed the filter, as a test, based on information from a “highly regarded” expert from North of the border. I felt the car ran better, not a whole lot better but better, but that might have been due to it being distinctly cooler on the test day. Test was done over about 150 miles.
Of course there’s the notion of crap getting into the engine without the filter and I agree that is a big consideration.
Placebo effect, Les.
The added intake noise can possibly throw you off.
Many modifications result in changes so small one needs a way to measure (time to distance or a dyno) to really suss out what’s real.
I’ve always wanted to swap my OE distributor for my Mallory while on a dyno. That was a difference so large even my butt dyno felt it.
I think I’ll order some UE needles from Joe C. because of this thread.
I didn’t mean to question your experience, Les. My apologies if it came over that way. I’m just trying to understand it. In the end, I guess we need to remember that the mixture control in a 50+ year old car is not that precise, so as Jerry used to say, YMMV. My car is set up on the rich side, because I’m more afraid of the effects of running lean, than of the effects of running a little bit rich. If I removed my filter, I imagine it would lean out a bit and probably run a bit better - it certainly idles a bit faster when I do so.
That’s a good point. There was a tripple SU S2 sold on BaT last week with “rock guards” for air filters. The seller said that the compression was 160-180psi when he bought it a few years ago. A recent test, a few thousand miles later, showed 90-120psi per cylinder, but he says it still runs fine. I can just imagine what those cylinder walls look like…
So this whole issue has become a bit difficult to determine what really is going on. Some say that with filter in place there’s not enough, if any, restriction to impact performance. Others say the car runs better with filter removed. Then there’s info saying that jaguar themselves showed a power reduction caused by the filter. Then there’s the fact that jaguar put a different induction filter on the same carbs and manifold on the SII cars, putting into question that cooler air (from the low down snorkels) really means anything.
My bottom line point is that if the engine can suck as much air as possible with filter in place then there should be no change without it, as far as mixture dilution goes.
Placebo… possible but I drive with the windows open and along with that goes the wine if the box. I, annoyingly, couldn’t hear any change in the induction.
I do accept that historically removing an air filter on old cars meant leaner mixture, but in this case it’s not clear to me that it does, and if it turns out to be so then perhaps a 1/4 turn richer would cure the problem.
Signed…on the fence!
Just one LAST thought on this…isn’t the big joy of the constant depression carb’ that it will adjust to all kinds of air density/volume? If in fact a lot more air passes through to the engine without the filter in place, then surely this will lead to a greater depression (venturi effect) and thereby provide an enriched mixture.
That’s why the damper goes up and down Les. It keeps the airspeed over the jet at approximately the same speed. So suction stays about the same. More air? The damper rises. Air speed goes down. Another name for this style of carb is “constant velocity”.
By definition, an air cleaner has to have some resistance to air flow to catch the dirt. One just needs enough area not to cause a big power reduction over a reasonable service interval. (This is where Wiggy tells us about K&N’s). As an old dirt bike rider I would never run an engine without an air cleaner. Even if it went faster.
So if your car went actually faster taking the air cleaner off… the filter was dirty or your carb was too rich…I think. You can usually rely on the engineers not choking the engine too much with an air cleaner. Hey - was your car faster with the Webers on it way back when?
Dave
An explanation of the carb here:
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The statement is correct, but the degree to which it applies varies for the engine’s operating condition:
- At idle, I doubt if is presence or not would be measureable unless the air filter is seriously dirty;
- high RPM, overrun (0 or very little throttle), its presence or not would have little/negligible effect unless dirty;
- at mid to high RPM, mid to full throttle its presence or not would be most noticeable where removing it would result in LEANER mixture, not necessarily “lean” - unless the mixture was already marginally leanish (which is certainly not true in your case).
I agree with David that it seems your car is already running too rich and now you want to make it even richer?? I would recommend a ¼ turn LEANER.
Wrong, the car is at a very good mixture setting, based on idle quality and plug color.
If you noticed in my comment, I said “PERHAPS” a 1/4 turn richer and that was based on the notion that IF, repeat IF, the car was too lean when running without a filter then PERHAPS a 1/4 turn richer would cure the problem.
Then what about the comment, suggesting I suppose, that Jaguar said the filter setup caused the engine 16HP?
Webers…faster then it does with the twin Stroms…yes.
I maintain that with a CD type carb’ any issue of a leaning out of the mixture due to removal of an airfilter…on an engine whos filter and induction assy does NOT impact airflow…will NOT run too lean…IF repeat IF…the factory engineered/designed standard fuel moderating devices are still fitted and carbs are in good order, as mine are…YMMV.
Nice read on the carbs John, thanks for posting.
