Front case and sump off for blasting

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!

Alfa Twin Spark engine rebuild (part 1)

Having 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.

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 http://www.autocomponenti.com/)

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.

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.

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.A 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!

New LSD

I sent a spare Alfa rear axle up to Charlie Skinner at Cloverleaf Transmissions in Cumbria today to have it fitted with a “Gripper” LSD (Limited Slip Differential).

A differential allows driven wheels on the same axle to rotate at different speeds – this is essential for proper handling going round corners – the inside wheel always travels less distance than the outside one. The characteristics of a normal diff detnote that power will be transmitted to the wheel with the least mechanical resistance to motion. This means under hard cornering, it is possible to “spin up” the inside wheel (which is subject to less weight transfer) than the outside one, meaning it is more difficult to get the power down out of tight corners, as it is wasted driving (and thus spinning) the inside wheel which has the least grip.

Conversely, a limited slip differential can sense the wheel with the most mechanical resistance (and hence grip) and transfer power to this wheel instead. Indeed, it was possible to specify an Alfa GT with a LSD from the factory way back in the early 70’s – and I’ve had one fitted to my GT Junior for a couple of years now. Seeing as it’s a rear wheel drive car, fitting an LSD means it’s possible to powerslide the car out of corners (see photo taken on the way home from Le Mans 2005

The original Alfa diff created its locking effect using clutch plates – these eventually wear out, and the diff needs rebuilding – and this happens even more quickly when you increase the engine power. With the track use my GTJ gets, the diff is now pretty much toast and has lost its locking effect – out of Goddards at Donnington I was spinning up the inside wheel again.

The gripper diff I’ve bought doesn’t rely on friction plates for its locking effect – it’s a geared mechanism that requires no maintenance. The other advantage is that it has two different “ramps” depending if you’re on the power (up to 70% lockup) or on the over-run (up to 40%). The standard Alfa unit was just 25% from the factory regardless. This allows more precise positioning of the car on the approach to corners, reducing the tenancy of LSD diffs which can feel like they are pushing the car straight on into corners on initial turn in.

I’m also taking the oppertunity of reducing the final drive whilst having my diff rebuilt from the long 4.1:1 of my current setup (great for motorways, but barely get into 4th gear on the track) to 4.55:1 (max top speed of about 120, but much better acceleration). This should work much better on the track – I’ll let you know how I get on.

Donnington

Yesterday I had the pleasure of driving round Donnington for the very first time, quite how it took me so long to do a trackday at a venue less than 20 miles from where the Alfa is garaged escapes me.

One of the advantages of being just 20 miles from home was that at lunch, with my 35-year old Alfa’s brakes fading (poor fluid and air in the system) and front wheel bearings wobbling (already bought some heavy duty ones for the run to the ‘ring) I took the old girl home for a well-earned rest and picked up the C43 (pictured with Ian Pleeth’s silver GT Junior step-front, below).

The Merc is a complete contrast to the Alfa, much much quieter but with a more sophisticated V8 rumble, so much quicker on the back straights (100 vs. nearly 125mph) and much, much more sideways. But was it any quicker? Certainly up the hills, the Merc with nearly double the torque of the bertie was sensational, and you actually found you had to brake before the Craner Curves, unless you fancy taking them at 110mph in a car weighing over one and a half tonnes (the Alfa, in contrast is well under 1000kg, and probably bearly more than a modern Elise). Through the slower corners, though, the Alfa was undoubtedly quicker, thanks to its better balance and the inability of the Merc’s slushbox to work out what you’re doing, dumping you down a couple of gears at wholely unappropriate moments causing ridiculous oversteer!

Overall I think the Merc was somewhere in the order of 3 seconds a lap quicker. That doesn’t sound a lot and it isn’t – and I think all of that is probably gained on the straight. In addition, the Merc used £10 of petrol for a 15 minute session (around 8mpg – frankly ridiculous) if you regularly tracked it, replacing those SL600 brakes would cost you a packet (they smoked after 3 hard laps) and the cost of the tyres would be prohibitive.

The Alfa on the hand (a not insubstantial 35 years old) uses about £40 of fuel for 6-7 20 minute sessions, my last set of tyres lasted about 7 or 8 trackdays plus road use, excusing today the brakes normally stand up well to repeated abuse (only just replaced the discs after 3 years) and is just as much fun if not more. Plus people come over and talk to you in the pits with comments such as “just beatiful” and “goes well, what engine?” (quote from a Caterham Superlight driver to both me and Ian who we were both barely slower than – driver error).

I’d say on track, Classic Alfa-Modern Merc 1-0.

Photos from Castle Combe

Couple of photos of me from my trip to Castle Combe early last month. First one is me in the passenger seat of Seb Greenwood’s Maserati Quattroporte Evolution V8:

…and this one of me driving (BFU 800K) trying to overtake a GTA into quarry: