Fun with needles

[okayfine]

EFI's great, but stock EFI is set up with compromises all its own. Once you get into modifying EFI, the learning curve is at best similar, and at worst a world more complex. There are results for that, of course, but I'm just saying that EFI isn't a magic bullet unless you leave it stock.

[Chickenman]

Yeah.. I hear ya Keith. I was just teasin' ya. I wouldn't change it either... but did I just hear a gauntlet being thrown in the direction of some of the new guys?

[Chickenman]

EFI's great, but stock EFI is set up with compromises all its own. Once you get into modifying EFI, the learning curve is at best similar, and at worst a world more complex. There are results for that, of course, but I'm just saying that EFI isn't a magic bullet unless you leave it stock.

Not quite following there.. particularly the last sentence. And not quite sure what you mean by Stock EFI is set up with compromises all it's own. Modern EFI is a big part of why we now have 600 HP Corvettes and Muscle Cars that idle smoothly, have great drive-ability, pass stringent emissions standards and still get decent MPG on the HWY. I don't see where the compromise is... but maybe we should start another thread as we've kind of High Jacked this one.

Edit: I've started a new thread to continue EFI vs Carbs discussion:

http://www.the510realm.com/viewtopic.php?f=30&t=28414

[SteveEdmonton]

Busy week at work-- a lot of words have been spilled since I checked in. Again, very helpful input. As you "regular contributors" can tell, my thinking has evolved 8 levels in 10 directions since I started this thread. I had no idea at the beginning how much I didn't know!

BTW, to answer one of your questions. Underhood temperature variations affect AF mixture a LOT!! Especially with the exhaust manifold right underneath the Intake manifold as on an L-Series engine. Heat soak can easily raise Underhood temperatures by close to 100 F when sitting in Traffic on some cars. You're never going to get that wild of a fluctuation in ambient temperature. And underhood heating of the the air changes the air density much more than what you would see in normal atmospheric Barometric changes....in our Climate.

One of the things I noticed on your car is that you do not have a factory Air Cleaner system like the SS 510 or a 240Z. You are using Open element air filters. That is not a good plan. L series engines with the are a very bad design with regards to Heat soak and the Induction system. Regardless of whether or not hood vents are used , Under-hood open element air cleaners are a bad, bad design for maintaining stable fuel mixtures.

Recent posts, including Richard's, are giving me a clearer vision for where to go. Cutting a vent in the hood?-- nah, not any more. How October 7th that was!

Even more, I'm coming to see air pressure as my friend. My backyard manometer is giving me really interesting readings-- from 15mm of underhood pressure at about 50 MPH up to a high of 35mm at 85 MPH, with levels fluctuating at all points in between, at all speeds in between. The most constant figure is that once the pressure reaches more than about 10mm, my mixture starts to go lean-- regardless where on the needle I'm running. It's purely speed related, which of course doesn't correlate very closely at all with piston position.

I get it, though, that those pressure spikes can be a good thing. Nature's "ram air" effect. Harness it and away we go!

In order to harness it, I'm inclining now (though ask me again in 5 minutes) toward a closed air-box, as several of you have suggested. In fact I would have done that right from the get-go with this motor except for two things: (1) the fact that the SSS air-box apparently doesn't fit on our LHD vehicles due to the intrusion of the brake master cylinder in exactly the wrong spot, and (2) the "coolness factor" of pancake-style open air filters, which I've always had a soft-spot for. I know they're inefficient (sigh)... but honestly, aren't they just awesome looking?

I can bodge sheet-metal in simple forms when I need to, but given the level of finish that I'm aiming at on this car and so far, I think, mostly achieving), I want something a little nicer looking than I can probably make myself. IIRC, Bikepapa was one of the guys who modified a stock SSS air cleaner to fit, namely by shortening its profile-- but I don't think he turned it back into a closed box. Does anyone have experience doing so? How hard would it be to tackle this? (I realize that's like asking how hard it would be to learn Greek, or water-ski backwards-- how are any of you supposed to know how hard that would be for me? But if anyone cares to comment, I'm all ears.)

Given a decent-looking enclosed air cleaner, I'm thinking of routing an external air supply to it, maybe through one of the headlight sockets. The coolness of that look would, on reflection, compensate for the loss of my pancake air filters... And a steady supply of ambient-temperature air sounds like the ticket. Especially since the "ram" aspect would tend to be more progressive and linear than the rather erratic "wham" effect of the current situation, where the underhood pressure seems to come on all at once and then oscillate a fair bit more than I would have anticipated.

I think we all spend nights dreaming of ways to get our carbs to behave nicely in all situations and different ways to adjust them as needs arise and conditions change.

I've dreamed of using fuel injectors in the bowls to fill them with complex level detectors to control them, ways to adjust the bowl fuel level by raising or lowering the entire bowl, gear and chain mechanisms with stepper motors to adjust jet heights from the driver seat, setting them rich then controling additional AIR instead of Fuel to tweek mixtures, and other madness I don't care to share..... Now I'm afraid all I've done is give you-all more crazy ideas!

Jim, I'd love to hear more about some of those crazy ideas-- though you're right, you've stoked the fire now for sure!

[Chickenman]

Carbon Fiber airbox's are really cool. Fiberglass less so, but cheaper. Actually, single weave CF is pretty cheap now. I'd make some in FG first until you get the hang of it.

There are also pre-fabbed Airbox's made out of aluminium sheet that you can buy. Then have your Friendly neighbor hood Tig specialist weld it together. Or make the whole thing.

[okayfine]

Steve, whatever amount of higher pressure you're seeing at the carb filters versus in cabin (which you haven't quantified, so while present it may be minuscule in inches of mercury terms), "ram air" is mostly a myth. And on cars that do achieve a ram air effect, it's limited to a couple of percent of total HP and achieved near Vmax.

Moreover, creating an air filter box will close your carb mouths from that area of high pressure. The impetus for a closed/cold air box is to shield the carb mouths from exhaust heat by drawing air from a colder part of the engine bay or, preferably, from a duct to the front of the car (missing headlight, the cutout near the factory horn, etc.). Also keep in mind that whatever heat convection from the exhaust that happens at a stoplight (and there's plenty), it's vastly reduced once the car is moving, which is most of the time and all of the time that you're going to be concerned with mixtures. In fact, the How To Modify book suggests more of a cold air duct to the carbs than a box, directing to leave the back of the "box" open to prevent turbulence. But that's also on a race car that sees more speed than less the entire time the car's running. Again, compromise.

[Chickenman]

The How To Modify Book is 40 years old. In regards to the open back air box, the book contains many, many sections sections that are out dated due to technology upgrades and Computational testing. Have a look at current Race day air boxes for correct designs. It's all been documented. None use an open back... From GT4 racers to LMP1 cars. Same with factory designs. An open back lets Hot air in which defeats the purpose. Dyno's don't lie and CFD is " mostly " correct. In the mid 70's when How To Modify was written, they didn't have CFD or the computational power that we have these days.

Ram air is NOT a myth.. I don't know how you can possibly state that. It may be incorrectly named as a convention ... but it is not a Myth. That's why the term Cold Air Intake is more relevant ( or the term " High pressure Zone " intake ). The the cool outside air ingress is the most important part of the equation. Whether or not you call it CAI or Ram intake, proper design is important. One of the design criteria s is that the air inlet is always positioned in a High pressure zone. The Head Lite area on a 510 should be a good high pressure area.

Note: Neither Keith nor I used the term " Ram Air" . We both referred to a Cold Air Intake and I specifically said that the Inlet should be positioned in a High Pressure zone. OKFine ( what's your real name please ) used the term " Ram Air" and I think that is misleading. . A High pressure Zone is any area that has a air pressure HIGHER than atmospheric. And those develop in the Bow wake of the car at speeds as low as 30MPH. It's a lot different than " Ram Air " which takes around 100 MPH to develop . One is a product of a Bow wake from a LARGE moving object ( an High pressure zone ) and the other ( Ram Air ) is the result of compressive forces created in a semi closed chamber. There's a big difference and the two often get confused.

Moreover, creating an air filter box will close your carb mouths from that area of high pressure.

I disagree strongly with that statement. Without correlation, you have NO idea if what he is seeing is the result of a high pressure zone with the hood on or if that pressure is normal and what you are actually seeing is a low pressure zone at that point with the hood off. I suspect that he is actually seeing a Low pressure zone ( due to " Bleed off ) with the hood off and the area at carbs is not seeing a " High pressure"zone ... only ambient or close to it. There is a difference. An Air Box PREVENTS the bleed off of higher pressure air by containment, so you should maintain a more stable level of air density with less turbulence.

[okayfine]

Steve used "ram air," I was correcting. I did not say you used the term, or that that is what we were talking about. Ram air as generally claimed on the Intertubes is a myth. People claim it, it's almost a genericized term, but it's very rarely reality. And then, as you and I both state, it's at MPH so high it's meaningless in the real world.

As to my last statement you disagree with, a closed air box will eliminate the area of HP that he's currently measuring, which is what he stated he wanted to harness.

[Chickenman]

As to my last statement you disagree with, a closed air box will eliminate the area of HP that he's currently measuring, which is what he stated he wanted to harness.

Read my reply over again. An air box won't eliminate ANY high pressure area.. it can only enhance it if designed properly.

And you said it yourself, that he has not compared the area in question to see if it actually IS a High Pressure area... as compared to outside air pressure.
Without calibrating the homemade Manometer and calibrating it against absolute atmo pressure you really don't know what is going on.

Hood off scenario is more likely creating a LOW pressure zone in that area due to no containment, as compared to Hood on. Pressure gradients are always are compared to absolute atmospheric pressures. Pressure always flows from High side to Low side.

And a manometer test on a closed Air Box fed from a high pressure zone ( H/Lite ) area will likely show even Higher pressures than the maximum that he is now seeing. Only testing will tell.. but there are tens of thousands o Hours of R&D from hundreds of Race Teams that support that Datum. Proper design is the key. No need to re-invent the wheel.

[okayfine]

I think we're arguing semantics at this point. Steve knows he has a high-pressure area between his carbs when compared to his cabin - he's measured this. Whether or not high-pressure relative to his cabin exists anywhere else under the hood (and it does, quite obviously), that area he's measuring will no longer have an effect on his carbs if he switches to a closed air box drawing air from a different point of the engine compartment.

Relative to race team R&D, what race teams are concerned with is generally not what DD/relatively low performance applications need to worry about. Again, a different set of compromises.

What is a relatively straight-forward cure (needle reprofiling) has turned into a whole lot of mission creep. Regardless of what happens relative to the air box vs. open filters, the needles need reprofiling. Done correctly, the same needles should be able to be used if/when he switches from open filters to an air box, or any other air modification, by using jet height to adjust the AFRs. IMO that's the first step, but however you see it is has to happen at some point.

[Chickenman]

Yes, I agree. Eventually you have to try something. Regardless of the air cleaner setup he decides to use, he has to adjust the tune to what the engine wants under the condition it runs at. If those conditions change down the road, then naturally you have to change the tune again. Time to move forward.

[SteveEdmonton]

Time to move forward.

So finally, five and a half months later, I am....

I'm all ready to make an air box. Here's a sketch of the plan.

Air-box sketch Mar2016.jpg (182.64 KiB) Viewed 3695 times

As you can see, my creative juices have been working. A cardboard mockup suggests that this is workable in terms of space requirements and also some of the smaller fabrication details that this sketch omits for the sake of clarity. But let me point out a few things that are, I think, a little unusual.

1: I'm not using a single large air filter that's the same height as the air box itself. The box will be about 60mm in height but my existing pancake-type filters work just fine and are only 50mm tall. By continuing to use them, inside the air box, I save money-- and have a much straighter path for the feed, as noted below, than the usual "snorkel" feed on the front end of the air box. Both the distributor and the rad are in the way, making some sort of zig-zag feed necessary if I were to have designed this in the conventional way.

2. The air feed comes through a headlight bucket and is a pretty straight shot via 4-inch semi-rigid aluminum ducting to a sheet-metal transitional piece that converts it from round to rectangular. The air dumps between the two air cleaners and (because they're shorter than the air box) on top of them as well. This will create turbulence, I realize, but it should also help a good supply of air to reach all sides of the air cleaners, not just one section of them. Or so my logic suggests, anyway.

3. The detachable part of this air box is simply the outermost flat surface, the plane to which the sheet-metal transitional piece is attached. This will make it easy to get at the smaller internal air cleaners, and/or the carbs, without having to disturb the brake master cylinder. I'm using a 7/8 BMC from a 280Z that has the bleed screws on the outboard side, so they're not an issue. But even so, clearance is relatively tight, and this should make the whole thing very user-friendly.

Here's my question. As Chickenman noted in a post last fall, the air pressure within this closed air-box system is likely to become quite high under some conditions due to two factors: the size of the intake pipe (4 inch = 100mm diameter = 78.5 cm2 surface area) plus the lack (at present) of any other "destination" for all of that air, except for the carburettors (2 x 38mm @ 11.3 cm2 apiece = 22.6 cm2 surface area). The venturi effect creates a relatively high airspeed through the carb throats, I know-- I guesstimated it, after some crude calculations, at something like 150 km/h-- but even so, I think there will be quite a bit "more air than needed" under some conditions.

At low speed I can see this abundance as a good thing: the carbs will be able to "suck" as hard and fast as they want too, plenty of nice cold(ish) air from outside. However, as speeds increase I imagine that the two lines on the graph will cross: more air will be pushed into the carbs by the car's forward motion than they really want to handle.

As Julian and others have noted, everything is a trade-off. My AFR gauge was showing me, last fall, that my carbs were too lean at speed with the hood on. My homemade manometer then suggested that this leanness was due to a (relative) high pressure area around the carbs. It's because that lean condition came on quite quickly but also quite unpredictably, that the idea of an air box came to mind-- if nothing else, simply to make the pressure gain more linear. My thinking was, and is, that the more predictable the changes to pressure (and thus AFR) are, the easier it will be to modify my SU needles to get the right AFR.

Obviously I won't know for sure what effect(s) this air box will have until I make it. But already now I'm wondering if there's a conventional or standard way to accommodate the rather significant pressure increase that this design seems likely to create. Two options spring to mind.

Option One: Should I change the plan and use a smaller intake tube? Four inch just happens to be the size of the headlight bucket, and pipe and fittings are very readily available in that size so the whole thing would be a snap to create. Otherwise, though, a smaller diameter is quite possible.

Option Two: I wonder about adding some "exit holes" to the sides and/or the base plate of the air box itself, so that instead of cramming so much down the carb throats at higher speeds I'd be giving it another place to go-- an alternative escape route.

As you can tell, I love thinking this all through-- despite my obvious lack of engineering experience. When the snow is gone and all the gravel is picked up from the roads in a couple of weeks, I'll be enjoying the testing / trial-and-error phase too. For now, I just want to fabricate this airbox as smart as I can.

[Chickenman]

I think you should just run it first and see what happens before drilling holes in things. I ran a Cowl induction Airbox on my Camaro for many years. The Airbox completely sealed against the bottom of the hood and air came in from the high pressure area at the base of the windshield. It was VERY effective and definitely added some Ponies at Knox. Had to jet up on the Secondaries 1 - 2 sizes richer to maintain AFR, but that is a good thing as it shows engine is pulling in more air and denser air and making More HP. After the initial re-jetting I never really had to change it again.

Then the DA I sold the car to took off the Airbox and a custom heat shield under the Carb because he thought they looked ugly....

[okayfine]

I think you should just run it first and see what happens before drilling holes in things.

Concur. Given your propensity to quantify, you'll know whether you have a problem you need to fix once you get the new box up and running. No sense creating more variables. Run the box, adjust as necessary.