Throttle Bodies

April 13, 2008

With the Alfa finally booked in for paint (5th May!) and it going to the sodablasters next weekend, attention turns to how we’re going to build up the engine.

I’m really keen to keep the rorty carb “sound” of the old engine – its just a defining characteristic of an old sports car. There’s no way I was going to keep the fuel injection of the doner twin spark motor, so the Bosch Jetronic was one of the first things we binned after lifting the motor out of a Alfa 75 condemed to the scrapper by its rusty sills.

However, I’ve been coming round to the idea of throttle bodies, specifically Jenvy throttle bodies, which maintain the sound of old carbs (and look pretty similar) but use modern injectors and an ECU for very accurate fuel delivery, and mean you can get massive power and a well-behaved engine when pootling about in traffic.

Image © Jenvey Dynamics

Combined with an Emerald K3 from engine management guru Dave Walker, these puppies should be good for 200bhp and beyond.

I suppose I can get some of the not inconsiderable funds required to purchase them from selling my old Dell’orto 45 carbs on the ‘bay.


Eaton M45

April 6, 2008

Hmm, I wonder if this can be used in my Twin Spark rebuild?

Eaton M45 Supercharger

Alfa update

March 22, 2008

It’s been some months since I posted on the progress of my Alfa build. There’s been a fair bit more welding – rear panel and inner/outer arches plus middle and outer sill on the offside in addition to those on the nearside since my last report. Although its been a touch expensive at least I know the car is 100% steel and the repairs should be good for many years to come.

One positive to come out of this was an opportunity to sort out once and for all the fit of the driver’s door – the gap between the bottom edge and the sill was always too big (around a half inch) and it didn’t sit too well with the b-pillar. Now we’ve replaced the outer sill properly, the fit is much better, and Pete (aka weld-o-man) took to opportunity to roll back some metal out of the rear wing and butt-weld the seam back up to get the b-pillar to door gap looking just right.

Meanwhile, I was tasked with stripping everything from the car. Seeing as I’m never going to have the car in this many pieces ever again (engine and gearbox out, pretty much the bottom 6″ of the car replaced) I’m going to take the whole lot back to metal and respray it inside and out. This means I’ve spent about 3 weekends stripping the whole interior, wiring loom, hydraulic lines, exhaust and all the trim off the car so it is now a bare shell. The photo shows the car halfway through this process (you can see the brake servos are still in).

The loom came out in one piece and looks in pretty good condition – I’ve managed to keep the stalks and the buttons attached so re-fitting it shouldn’t be that difficult. The hydraulic lines, however, were a complete nightmare and I resorted to cutting them in places – so much corrosion where the lines enter under-floor master cylinder that trying to unfasten the unions resulted in them turning to brown dust. As the lines were all steel, they could do with complete replacement with copper items which won’t rust.

I also took the opportunity to ask Pete to weld in some proper seat mounts – the existing arrangement consisted of bolting the buckets to universal Sparco mounts bought from Demon Tweeks, and then bolting these in turn onto the captive nuts (mounted on the floor pans) that held the old runners. After a quick personal fitting, with the seat roughly in place thanks to two antique blocks of wood (Pete’s main business is restoring old French furniture) he welded two hefty cross members (per side) between the inner sills and the transmission tunnel. The universal mounts now sit on these instead. Much safer in the event of an “off”.

So, although it looks like complete shit at the moment, the project is actually coming together nicely. With just wheels still attached so the shell is mobile, the next step is getting all the paint and old filler blasted off and then it’s ready for a fresh skim of P38, prime and a very neat paint job inside and out. Then comes the tedious job of a re-fit.

Meanwhile, batman is having a tinker with the engine side of things. He’s making noises about throttle bodies and re-using the actuator from the doner engine that can alter the cam timing with revs – a primitive form of variable valve timing – we could end up with an engine pushing near or even over 200 ponies at this rate. Now the car’s got some metal in it making it nice and stiff, this is shaping up to be one cheeky little track weapon.

Full photoset of latest progress here.

One thing after another…

October 27, 2007

The problem with old cars is as soon as you start tinkering with one thing you find another thing that needs some attention. Having taken the old engine out of the Alfa (in preparation for the twin spark) we found some minor welding that was required to the front cross member. The grubby engine bay could then do with a spraying afterwards to make it look like it did 40 years ago.

Also, the interior (which has been stripped and caged) could do with a lick of paint. Ideally, I’d like to take the dash out (simple) and the seats + door trim and get a pro to give it a spray with the same matt grey that I used on the cage bars. Might as well have the (split!) dashtop re-trimmed whilst it’s out…

In addition, I’ve known for a couple of years that the rear arches will need doing on the car. Not only do the tyres rub, but the inners were full of filler and the replacement outers that were done back in 2002 weren’t the best job (before I owned the car). Might as well get it all tidied up whilst its out of action.

Plenty of stonechips on the front valance, too…

Bah! Might be as well to do a full lower half respray to keep things tidy. Do’h.

The front case and sump (35 years old) proved too much to clean using the degrease/brush/degrease/air cycle, so I’ve sent them to a media blasting expert… They’ll be finished tomorrow, I’ll pick them up friday and I’ll post some pics.

An hygenically clean base is so important at this stage of the build to ensure reliability – although we’re essentially rebuilding this engine as a race specimen, I’d expect ten year’s track day usage once we’re done…

I now need to find someone local to rebuild the starter motor and alternator – they’ve been rattling about in the back of the C43 for a couple of days now – I keep being reminded when I hit the loud pedal and hear a thump!

Actual lap where I lunched my engineHaving managed to blow up my Alfa’s engine at the Nurburgring back in August, I’ve been plotting a bigger (well, more powerful) and better (built) new motor for the GT Junior.I’ve decided to go for a transplant to a later, but similar Twin Spark engine from an Alfa 75. £300 secured me a running engine complete with loom an injection system from an MOT-failed 1991 car – just about as late as you can get. Despite my car being a 1972, and being originally designed in the early 60’s, the new engine will drop straight in on the same mounts and can use the same bell housing, mating up to the same transmission as my old Alfa Nord twin cam.Twin Spark engine in yellow, yesterday...

The new twin spark, twin cam engine has several advantages over its earlier single spark counterpart. With two spark plugs offset from the center of each cylinder (making a total of eight) comes potential for bigger valves (and more BHP). Also, 35 years of cylinder head development since the first Alfa twin cam engine appeared in 1954 means that the later twin spark variant breaths much better – hence 148bhp out of the factory, versus an optimistic 130bhp of its predecessor. Due to a shallower angle between the values, it’s got a lot more torque too. (Image: Jim Steck

Before throwing the new engine into the car, I’ve decided to rebuild the engine. My old engine had around 170bhp, pretty highly strung for a Nord – I’m aiming for 180bhp out of this one. I’m going to throw away the Bosch Motronic fuel injection that came with the donor engine and keep the car on carburettors to make sure I retain the sound and under-bonnet appearance of a classic. However I’m going to bring the car bang up to date by hiding a 3D mapped ECU under the dash (probably an Emerald) to handle the timing and fueling. I’m going to fit some JE forged pistons and expand the capacity subtly, and also fit some quite frankly ridiculous cams. Using the mapped ECU will let me vary the ignition advance, so it should still be tractable driving somewhere south of 7000rpm. This lot, with a little bit of head work and a decent exhaust should easily see me with 180 ponies.Batman to the rescue!

However, before getting any where near the exciting stuff, a strip, inspection and clean was in order. My slightly unhinged mechanic and friend batman a.k.a. Dave Hood, fastest pensioner older gentleman in the Midlands (sorry Dave) stripped the old lump down and gave me a bunch of parts to clean and another bunch of parts to send for machining.Knife-edged crank

The crank, rods, front pulley and flywheel were taken to Rob Walker of Rob Walker Engineering near Banbury for a damn good lightening and balancing. I’m determined with this engine to blue print and balance everything I can in a quest for smooth, reliable power. Rob knife edged, lightened and double doweled the crank (on Dave’s advice). He also took a huge chunk of material out of the flywheel to make sure the engine spins up quicker. The Alfa 75 front pulley was also chopped in half as I have no need to drive either an air conditioning compressor or a power steering pump, and besides which without the chop the pulley wouldn’t clear the radiator in my Junior’s engine bay. Rob bead blasted and balanced the con rods, I’m intending to have these shot peened for further protection against stress cracks that can occur – unfortunately, the company Rob normally outsources this to have recently stopped offering the service.Alfa 105 modified flywheelA fully balanced and lightened bottom end ensures the engines smoothness and helps reliability by reducing vibrations, but also gives the potential for higher revs. Higher revs bring the potential for more power – my old (unbalanced) Nord engine would rev to 7000rpm, I’m hoping to get 7500rpm out of this one.My next job was to degrease the block of the donor engine, and the front case and sump off my old Nord, these will be combined with the TS block and head in order to fit my car properly, the TS sump being discarded in the conversion process. I used a rather ridiculous amount of degreaser, plus electric drill with wire brush and a variety of used tooth brushes… and an air compressor kindly lent to me by my colleague Dave Whitehouse.It’s not looking too bad… Now time to start ordering the pistons from the US and getting my hands on the head for some cleaning, more machining and crazy cams!