I'm glad Force is still running hard, he had a couple of difficult years and was getting all sorts of grief from the nay sayers about being too old - especially when drivers with the hunger to win, like Matt Hagan rising to the top. I'd expect him and the rest of the JFR cars to be top of the pile this year. Having Alan Johnson tuning the dragster is a match made in heaven - AJ is to dragsters what Austin Coil and Jimmy Prock are to Funny Cars.
Quite how the Greek is still racing at his age, I'll never know - I'm concerned enough about my ECG for my medical in a few weeks time, and I'm 54 years younger... data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
A quick trial assembly for the Racepak computer. All present and correct though I might swap out some of the cables to freshen it up a bit. In terms of the current layout and what's plugged in as you see it:
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From the Racepak out to the left, the braided hose will plumb into the fuel pump to measure fuel pressure.
The red leads which branch off to two junction boxes, lead to the 8 exhaust gas temperature sensors. These plumb into weldments in the headers and will see some quite high temperatures.
The black lead that runs to the bottom left branches off to the on/off switch for the data recorder, and to a split collar that sits around the driveshaft to measure rpm.
Lastly, the lead to the top right that ends in a rubberised cover, connects into the ignition system to collect engine rpm data.
The 3 remaining data collection sources, as shown in the previous post, pick up oil pressure, fuel nozzle pressure and supercharger boost. With everything plumbed in, it's possible to gather data on engine rpm vs driveshaft rpm to help calculate clutch slip and lock-up point, along with boost and fuel pressure that form the basis for fuel system tuning. The EGT sensors in a nitro application serve mainly to indicate if a cylinder has been dropped on a run (raw fuel exiting the cylinder will cool the sensor down noticeably).
The other side of this coming weekend should see a decent update with progress on the chassis. It's been a busy time despite the Easter break. The Easter weekend saw the first round of the Nostalgia Funny Car championship. Due to most of us still putting cars together, only one entry appeared, and despite the weather, good performances were had.
To keep things ticking over til the weekend, I figured it might be an idea to go through some of the more iconic parts that always associated with the sport but perhaps not understood. So, here's some waffle about mechanical fuel injection, in the way of a bugcatcher:
They're available in 3 sizes; bugcatcher, birdcatcher and buzzard catcher. The overall size increases with the size of what you wish to consume - butterfly diameter and therefore intake volume increase each time. This is the bugcatcher, the baby of the bunch, but with the fuel pump regs as they are, it's all we need for airflow.
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Throttle position, whilst adjustable, tends to be very much on or off due to the way the fuel system works. To the right of the injector is the barrel valve. This is the brain of the fuel system, but unlike an ECU, it's purely mechanical, using poppet valves, springs and carefully sized holes to direct fuel in certain directions at specific pressure.
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From top to bottom on the inlet (left) side of the barrel valve:
The top valve is the pump saver. This is sometimes called an anti-spike - the purpose is to free up the fuel pump from excess pressure in the event of the throttle being slammed shut - the fuel in the inlet line (second valve down) needs somewhere to go - the valve is set to around 160psi. The pipe plumbed into it will simply send fuel back to the tank.
As noted above, the second inlet is the inlet straight from the fuel pump. Inside the barrel valve is a spool with a hole that opens up as the throttle is engaged. The wider the throttle, the more the spool rotates. Idle pressure is quite low at 3-4psi. Fuel passes through the barrel valve towards the rear and out of the tubing seen to the right of the photo.
The bottom valve is the idle pressure valve. Again this is set low, at around 2-5psi. This works in tandem with the spool, and also the main jet, situated directly next to the marking 'Ret'. This is nothing more than a screw in fuel jet that has a hole in the middle (think of a polo mint). The larger the hole, the more fuel is returned to the tank. In this case, it's a blank jet, therefore nothing is returned and the whole let is fed into the engine in one fashion or another.
When fuel pressure rises above the 5psi needed to overcome the check valve, it flows to the forementioned line towards the rear of the injector. Here there's a distribution block that have 8 nozzles plumped into the injector.
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As you can see, 3 nozzles feed each side of the injector. This feeds fuel in above the supercharger and forms the basic idle / off throttle fuel air mixture. The back pair of nozzles have been replaced with air bleed screws - the screws themselves aren't in place.
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The purpose of the screws is to provide a start line tuning aid for idle rpm. By removing the plastic screw that sits within each air bleed, the extra opening helps adjust the rpm by increasing the air volume consumed.
The rubber hoses shown, lead to a pair of jets that would be in the injector if it wasn't for the air bleeds, instead they run to the supercharger. Importantly, these are right at the back of the supercharger casing (jets shown below at the top of the blower casing).
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The meat of the fuel system in terms of fuel flow is in the port nozzles. The outlet at the rear of the barrel valve angled downwards leads to the port nozzle distribution block which will be mounted on the manifold and feeding up to 16 individual nozzles (2 per cylinder). That's the mass of plumbing seen resting on the manifold above.
A check valve with a pressure of around 20psi is used. As the throttle is opened the pressure rises enough to overcome the spring and fuel flow rises from around 1.5-1.8 gallons per minute at idle, to around 20 gallons per minute at 8k rpm.
That's the bare bones of how the fuel system works in this application. Going right back to the beginning - the turnbuckle linkage connection the butterfly shaft to the spool in the barrel valve is adjustable - the purpose of which alters the idle mixture. A longer linkage richens the fuel mixture, a shorter linkage makes it more lean).
Hopefully on Sunday, there'll be an update on what's going on with the chassis, body, and some new bits - namely the rear tree that'll form the backbone of the body pivot system data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7.
Well at least I understand the individual words... data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
It might be time to grab a coffee and some chocolate hobnobs – here’s where we’re at.
Saturday was a useful day at the workshop. I’ll split this into 3 lumps, the chassis, the body and the ancillary kit.
The chassis work is into the stage where it gets complicated, intricate and time consuming. The rear tree behind the roll cage is being fabricated from scratch; this was always the intention as the previous tree on Chaos whilst being very neatly packaged given the space constraints, was too small for the Corvette body and there’s ways and means of making it lighter and easier to work with.
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With the Vette having such a large rear deck behind the cage, there’s acres of space to house all the kit required (oil catch can, 2 fire bottles, 1 air bottle for the transmission and 1 air bottle for the fresh air system).
It’s a two pronged approach to sorting out the rear of the chassis; a new roll cage will go on shortly but the seat needs remaking first – the previous seat is still mocked up in the chassis just to provide a guide as to where I’m located to calculate headroom but ensuring my feet aren’t somewhere they really don’t want to be. Having been rotated in the seat and moved down, the ergonomics around the normal area the pedals would be sat it, is somewhat cocked up.
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The whole reason for this was of course to get the body to sit correctly in its finished state. The mock-up of it place looks damn near perfect but has been a compromise in other areas.
With me sitting as low as possible and the body mounted as far forward as possible so the cage meets the body at the highest point in the roof, it was still coming up shy of where it needs to be, so a hole’s had to be cut in the roof – this allows the very top of the back hoops to protrude. In an ideal world, the rear section of the roof area would be fibre glassed over with a larger radius but done so as to be not visibly different from original. We’ll see how it goes, there’s bigger issues to tackle first, the body itself being one of them…
So…fibreglass race car bodies, there’s great ones, there’s good ones, there’s bad ones and there’s odd ones. There’s also original ones – those period correct ones from an original mould, with all their imperfections. This here Corvette lives in that last category. After dimensioning the body to calculate centrelines and check for general straightness, a few things became apparent, and these weren’t good.
The worst issue was the rear wing – it’s twisted in the middle and taller on one side. With the Vette being one of few bodies from back then with a cast-in wing, it’s a nuisance as the fix means re-fibre glassing an area of the car with compound curves and lines in multiple directions. While some of the issues sound quite minor and are only really noticed by those with a critical eye, the rear wing situation would pose a problem. Back in period, the Vette was a new style of body that whilst seemingly aerodynamic, had severe handling issues from around 900ft (speeds around 190-200mph at that point on the track). Instead of air running up and over the wing, it circled it and got around the back, into the dead zone, causing lift. Spill plates fixed this and helped channel the air – however, a wing that’s longer one side that the other will want to turn the car, much like a rudder on a boat. The upshot is that it’s fixable, it’s just a nuisance.
Next up, the front strakes in the hood. These are mostly straight but for some reason tail off to the right as the lines blend into the nose. An easy fix with some new glass, but again…nuisance. Lastly – and purely an aesthetic / accuracy issue; the front wheel arch line which is quite pronounced and a nice feature on a largely curvy body, stops far too short. Back in period this line was longer, almost running out to the ‘A’ pillar. More glass…
Lastly, some positive stuff – safety first, kids…
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One SFI-20 firesuit and HANS device. I’d previously worn an RJS firesuit which felt like wearing cardboard – Simpson on the other hand have always produced some of the nicest safety kit available and this one is very flexible and fits nicely. The HANS device is one of those safety innovations that make you wonder how we survived before it was a thing. The weight of it vanishes once you’re strapped into the car, and you never really feel constrained by its presence. It’s a requirement for racing at this level but I’d recommend it to anybody in any formula, they’re brilliant.
Lastly, the blower restraint – these vary from just a bag around the blower to a full works deal like this one (SFI 14.3 spec)
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From the bottom up:
- Bottom plate sits between the top of the manifold and underside of the blower.
- Ballistic bag wraps around the blower.
- Top plate sits between the top of the blower and underside of the injector spacer.
- Straps galore – the aluminized straps fix to the headers (2 per side) and one to the rear that fixes to the mid plate.
- The black straps wrap over the injector to prevent that ripping off if an explosion is severe enough to burst the threads on the injector bolts.
I’m hoping to get all the bits in one place in a few weeks to assemble it all, so it’ll make more sense thendata:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7.
Next update – body stuff, chassis stuff and the start of the engine disassembly for final checks before it goes back together.
Must be frustrating having so many niggles to deal with. What's the current ETA for race ready?
It hasn't helped my blood pressure data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7.
At present I don't honestly know. I'd like to be ready for Dragstalgia in July but that's unlikely. After that there's one more event at the end of September (UK National Finals). The way things are going though, that'll most likely slip and I wont be into the snagging list of small items to have it ready in time.
So...realistically, this year might be a non event completely, such is life though - I've done what I can to accelerate the build but the obstacles and delays have scuppered the original plan. If nothing else, it'll super shiny and polished by Easter next year...
There are so many tiny things that just have to go right and the law of Murphy (or Sod) that says they won't!!!
Fascinating build though - thanks for the thread and keep keep us posted of all ups and downs data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
A brief update following the weekend...
The chassis fabrication has reached a point where the body issues need addressing before any further bits are done internally. The rear wing issue has been resolved and will be getting re-glassed this week. The front end area is a bit of a pain - there'll be some fibreglass sectioning work to straighten out the lines, allowing the body mounting pads to sit symmetrically (with them being an external mount job, they're a bit more noticeable).
Hopefully in about a month, the glass work will be complete and it'll look like a car and should be rolling around.
Whilst all that goes on, I've started to get the engine hardware together and prepare a build schedule for the engine. The fuel pump arrived with the engine and transmission but I hadn't got around to unboxing it.
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From the bottom up, the inlet pipe sucks fuel from the tank - the outlet sits on top (that will pipe into the inlet on the barrel valve that I mentioned a few posts ago). A return inlet is visible on the right hand side; this enables excess fuel to pipe to go back through the motor and not back to the tank. The red lever is the shutoff that controls fuel flow. As the only way to turn off a nitro engine is by starving it of fuel, this is quite a critical part of the fuel system.
With the pump being driven off the camshaft, pressure is square to rpm, so at 8000rpm crank (4000rpm cam), it produces 21.0 gallons per minute. Job's a good'un data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7.
In other news, the spare pair of cylinder heads are being machined shortly to accept the larger head studs of the block, and a fresh rack is quickly being put together with new pistons, rods, bearings, pins, button & rings.
I mentioned previously that timescales and deadlines have become a bit of a moot point, but there's a plan in place and I'm working on getting some track time this year one way or another... data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
You could always take it to a "wrung what you brung event"
If you can't beat the chavvy modded VX Novas then you know the car needs more work.data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7