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With the fuel system bits and pieces back home, it's time to start assembling it all for the last time. Or at least it would be if some small parts had arrived... delays in the US. They're good enough to try and save the customer money by shipping everything in one lump, but when you're only waiting on some bolts, it's frustrating that the rest of the order hasn't been flown over.
In any case, to explain the fuel system further, upside down as it were - I talked about the role of the bugcatcher injector before. Many will have seen these before, if not at the race track, probably in films such as The Fast & The Furious etc.
These can carry up to 8 fuel injector nozzles and allow the motor to drink around 1.5 gallons per minute at idle. Lower down in the intake manifold is where the bulk of the fuel goes.
The number visible is the nozzle orifice, in thousandths of an inch. Typical numbers for these will something like 50-55 in the injector hat and a staggered arrangement in the manifold but with much larger numbers (low 70's up to high 80's).
When the poppet valve in the port line check valves (seen here with the orange blank off) exceeds 10psi, this opens and allows fuel to be distributed to 8 more injector nozzles, one per cylinder.
As this manifold was designed originally for big show cars, it has provision for 3 injectors per cylinder. If you had the pump volume these would be used, but with a baby fuel pump as dictated by the rules, one per cylinder is sufficient. These nozzles point at the intake valve and go a long toward providing the 21.0 gallon per minute target.
The burst panel at the front of the manifold is a safety feature, mandated by the rules (in nearly all blown classes nowadays). It allows a build up of pressure to be relieved by giving way before the manifold and blower assembly make an escape for low Earth orbit. The manifolds come either cast with the opening in them (like this one), or you'll see them be machined if it's aluminium and of Chevy / Ford / Chrysler application.
Onto the clutch. I'll perhaps do a comparison of this versus the first choice clutch in a few weeks. The differences are mostly cosmetic as the physical operation is similar but the lever locations are different.
This is the spare clutch which might well be sold on shortly - there's nothing wrong with it, I came to acquire it as a package deal and whilst it's a lovely bit of kit, there's no crossover for spare discs and floaters due to it being a 10.5" all titanium deal rather than the 10" part titanium one.
Much like a moped, it's a slider clutch that locks up under centrifugal forces. Adjustment is 3-fold. Firstly the air gap which decides with how much force the clutch is initially applied, is set by adjusting the stands you see in the photo below. A good track will allow you to get aggressive and open up the gap for it to hit harder. A poor track needs a softer transition. 0.040" is the typical figure that's a happy medium between the two.
The holes allow them to be spun up and down the threads. All of these clutches, without exception are a pain to adjust for air gap as the top cover needs to sit flush and you're often chasing your own tail to ensure each stand is the same height.
The 6 springs in the top photo control idle pressure i.e. how much the the clutch locks up when the car is stationary. These are set generally to allow the springs to turn but not freely. This is a rule of thumb that normally means the car can coast by itself, much like a torque converter road car. The difference in this instance being it'll want to coast at 30-40mph on occasion.
The 6 levers are what decide the rest. How quickly the clutch locks up depends on the weight on the fingers. More weight equals more mass turning and therefore it locks up quicker. The nut & bolt arrangement is where weight is added or subtracted. We adjust in grams, sometimes a little can make a lot of difference.
The goal is to have the clutch fully locked before the 1/8th mile. It also helps reduce wear - as the fingers rotate the radius on the heel of them pushes into the pressure plate, jamming the clutch pack together.
There's a whole science about this element, with different radius finger heels (compound curves, normal curves, you name it). I've never deviated from the standard fingers that the clutch comes with - maybe in the future.
Of everything that goes into a nitro burning race car, the clutch is what makes or breaks a run. The crowerglide type of clutch has been used in nitro racing since the 1960's, as technology moved on, the design didn't change all that much, it just (as most American things) got bigger and then electronics and control systems came in...
A current Top Fuel and Funny Car clutch looks like this:
18 levers, 10 stands. All titanium construction - these use a canon system where if you imagine the levers throw out (the fingers will throw toward you as you see it) the throw out bearing is controlled by a pneumatic or hydraulic system controls how quickly, and at what rate it locks up by restricting the lever movement.
This is perhaps the most critical difference between and old style and current Top Fuel clutch. When you're able to accelerate, pause or decelerate the lock-up action of the clutch, you have much more control over proceedings and can tune for track conditions - especially when you consider the amount of power available and that track conditions may vary down track and you have to be going a decent speed before aero kicks in and allows you traction over and above the mechanical traction the car naturally has.
With the old style clutch we use, track conditions are assessed (you walk to the start line, dig your heel in, wiggle it, cross your arms, squint, perhaps let out a small grunt) and decide what it'll take. It's really not very scientific. There are few things as rewarding as getting the call right and having a glide clutch lockup just right, with none of the modern day trickery. Old-skool!
In a few weeks once the SFI tags are sorted on the actual clutch I'll be using, I'll do a proper comparison, and also a weight check - I myself don't know how different they are in raw weight, but when such a mass is hanging off the back of the crank, the rear main bearing prefers to be abused as little as possible by a big titanium lump bobbing around  . |
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Author: Chevyonfuel
Author
24-11-2019 22:33:39
