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Vauxhall C20XE and LN engine It's been out of production for over ten years, but Vauxhall's C20 XE/LN motor is a tuneable classic, as SBD Motorsport's Steve Broughton explained to Peter Knivett.
Photography: Peter Knivett
Last month TRC showcased a brace of powerplants well suited to budget motorsport applications and Vauxhall's 1998cc C20XE 16-valve motor came right near the top of the list. With 150bhp and 144lb ft of torque as standard, tuners quickly realised the power potential of the C20XE, which could be readily unlocked affordably and reliably if carried out correctly. Even today the motor is very popular in a huge variety of motorsport disciplines from single-seaters, to Westfields, to MK2 Escort rally cars and track day Astras and Novas, where its reliable, torquey power delivery and affordable nature are much in demand. But how do you extract the best from this engine on a budget? To find out some answers, TRC paid a visit to one of the companies at the forefront of tuning the C20XE engine - SBD Motorsport Ltd to chat to its founder Steve Broughton.
What makes the C20XE engine so good?
Over to you Steve. "It's one of the last production engines with a massive in-built tolerance for being tuned up. Most of the components are good for 250bhp. The rods can cope with that - the only reason we advise against it is that if the engine is over-revved it can cause problems. Even the pistons are fantastic. The original piston is a forged item - it's beautiful."
The entire bottom end of the C20XE is very strong, especially the crankshaft. "It's bomb proof," says Steve. "I've never seen one break. Even with an engine has run out of oil and the con-rod has disappeared out to the side of the block the crank is still in one piece!" Such strength would be useless if the C20XE couldn't produce the power and torque to exploit it, but the cylinder head is something of a mass-produced masterpiece, being designed by Cosworth engineering for GM/Opel's requirements. Packing decent-sized valves and ports and a highly efficient combustion chamber shape, the alloy 16-valve head will flow enough air to reach 230bhp before modifications are required.
History and the Cosworth connection
The iron block C20XE motor made its debut in 1988, being based on the highly successful GM 2.0-litre 8-valve, J-series Family One motor. Once Cosworth's engineers had finished with their design, the new 16-valve engine was churning out a smooth, torquey 150bhp, complete with a upgraded bottom end, designed with an eye on Group A and Group N rallying and touring car racing. Interestingly, Steve highlights the fact that the GM/Cosworth connection goes far deeper than just designing the cylinder heads, because Cosworth cast and machined the early 16-valve units. Therefore any C20XE built up to about 1990 will use a Coscast cylinder head, whereas beyond this point GM switched to a production item, cast and machined by Karl Schmidt in Germany.
Distributorless ignition arrived in 1992, while internally there were a number of changes, which make the later engines less attractive, as Steve explains. "They put a big heavy flywheel on and added mass to the crankshaft so that when they leaned the engine off for emissions (which they from the 1992 model cars) the heavier flywheel helps keep everything moving." Meanwhile the cylinder head port shape was revised on emissions grounds and the forged pistons were dropped in favour of inferior cast items. Finally the bearing size and material was reduced in size and quality. These final engines gained a C20XE-LN label, highlighting the 'Low Noise' requirements as dictated by EU regulation. During the redesign the block was given a makeover, so ironically (given the downspeccing of the rest of the design,) the later engine blocks are actually stronger than the early ones.
The final C20XE-LN engines were built in 1993/1994 for the UK market for fitment into a 'run-out' Cavalier SRi model. "The last batch had 'Ecotech' on the cam cover and Vauxhall did this because they wanted to keep running the older engine in the BRCC for as long as possible," says Steve. That wasn't quite the end of the C20XE-LN, because the engine was still being produced in 1996 and 1997 for overseas markets, including Turkey.
Track & Race Car June 2005 What should you look for when buying the engine?
These engines will be at least 11 years old, but Steve reckons that's not a reason to walk away, because these motors are tough. "There are a lot of cars out there that have gone rotten but the en ignes are good," says Broughton. "We had one recently that had done 130,000 miles and it was really dirty, but the engine was fine." If high mileage shouldn't put you off, neither should a clatter from the top end when cold, because the hydraulic followers have a habit of making a horrible racket if the engine has stood idle for some time. "That's because the valve spring slowly squeezes the oil out of the follower. so when you come to fire it up, it takes ages for it to stop rattling," says Steve.
For an easy overhaul Steve recommends the following. "If you're going to drive it hard and use it for track days, then I'd replace the followers, drop the big-ends out and replace them and put a new set of rod-bolts in. I'd possibly replace the oil pump, plus change the cambelt and pulley idlers. You don't have to take the engine out of the car to do this, you can do it all in situ." Interestingly Broughton advises against digging further into even high-mileage engines, preferring to leave well alone.
That said, the C20XE engine didn't have a problem-free life, courtesy of the well-documented porous cylinder head issue which afflicted engines from around 1990-1991 onwards. This coincided with the switch from a Cosworth-produced cylinder head to a production GM item made by Karl Schmidt in Germany, which compromised the original design, particularly in the oil gallery area.
Symptoms of this problem are similar to those of head gasket failure - a film of oil in the water and a milky liquid in the sump - but curing it is difficult. some firms offer to bypass the gallery with external pipes, but Steve's not a fan of this as a cure, preferring to use only Coscast heads on his engines. these are identified by a lack of core plug style casting on either end of the head, plus they have an oval-shaped Coscast logo embossed onto the front. Finally, don't dismiss the very late engine that ran 'Ecotech' badging, because it may still be worth a punt. "The way to tell is the trademark L-shaped spark plug cover," say Steve. "If it's that shape it doesn't matter what's written on it, it's a C20XE/LN engine underneath."
Certainly the earlier distributor-equipped engine is the one to go for, because it's more likely to have a Cosworth head, plus the better bearing and pistons, even though it may have covered more miles. Interestingly, Steve reckons his ideal combination for an engine that he'd run in near standard trim would be to run an early crankshaft, in a later block (which was stronger), with a Coscast head.
General performance pointers on the C20XE and LN exhaust manifolds
So, how do you set about tuning C20XE and LN engines? Well, step number one is replacing the standard exhaust manifold, as the standard item was designed to maximise low-end torque. At high revs this becomes a restriction, so it's critical that it's upgraded at the earliest opportunity. Steve explains - "Apparently the first pre-production engines from Cosworth produced 170bhp as standard but they wanted more torque for the road which they got by making the manifold's pipes smaller. This also helped reduce emissions by keeping the gas speed up, but when you get up to the top end it becomes a restriction."
Happily, SBD has a huge range of manifolds for a wide variety of applications, whether front-wheel drive Astra, Westfield, Caterham or rear-wheel drive Escort or Manta. Prices range from £229.70 to £586.91 depending on applications, but if you don't attend to this early on, you're not going to produce the quoted power outputs as outlined here. Bear in mind that even on a standard engine a 6-8bhp gain can be expected when used with an efficient exhaust system.
Oil Systems
When the XE engine is used in front-wheel drive applications it's common to see the cars puffing smoke during hard cornering on circuit use. this looks worrying and can cause problems, as Steve explains. "There's a breather pipe coming out the front of the block which allows pressures between the top and bottom of the engine to be equalised. Sometimes on track use under heavy cornering the oil goes up that pipe and into the cam cover and it can't get out. This can detonate the engine where the oil mixes with the fuel in the cylinder head, but there's an easy modification to the baffle so that it dumps the oil back in again and cures the problem."
When the engine is transplanted into rear-wheel drive cars, more work is needed on the oil system - SBD advises using a hard-to-find Manta sump - while they produce a sump for the rear-wheel drive Sunbeam. "But if you can afford it, dry sumping is the way to go," says Steve, and that's certainly true when the motor is fitted into a Caterham, Westfield or similar. Expect to pay from £799.00 for this setup.
Carbs or not?
Steve makes the point that these days switching to carbs' may be a false economy, particularly as the Weber DCOE is no longer available. "You need to change your fuel pumps and fuel lines. Yes, it's a good, quick way of getting the engine to run, but if you go to throttle bodies you've got all the fuel lines you need already." Also, if you choose that you'll either need to run SBD's mapped ignition system of fit a distributor from an early eight-valve engine, but then you'll need new HT leads and caps. "It seems cheaper, but then you take the car to the rolling road and spend £200 on jets and chokes and then you find out that actually your carbs' are worn. Then when people start to tune them up they have to go back to the rolling road, so it's a false economy." These days, he message is clear, sticking with injection will save you money in the long run.
Track & Race Car June 2005
Group N replacement ECU 170bhp/173lb ft Unavailable wef June 2009
Given that we're sticking with fuel injection, our first port of call is a replacement ECU. These kits were designed for group N racing and rallying applications, where a standard under bonnet appearance was mandatory. Ultimately, almost all the works Group N cars ended up using this kit. Along with the power increase the biggest improvement these kits offer is a much quicker throttle response, courtesy of the MBE ECU that runs ten times faster than the stock unit and uses a throttle angle control rather than relying on the readout from the airflow meter.
Happily, the MBE ECU is the same unit that's run on SBD's throttle body kits which makes it easy to upgrade at a later day. Downsides? Well, for road applications a lack of idle valve control means you need to keep the revs up until the engine is warm enough to tick over. Given the price, it's no surprise that SBD Motorsport is still a popular choice. "It's still got its place, because a lot of people come to me and say I've got an engine but I can't afford throttle bodies, so this is the most affordable option. Then later on, they can easily upgrade to the throttle body kit and all you throw away is the throttle pot and the idle control valve, that's it," says Steve.
196bhp/170lb ft
MT196 Multi-throttle injection kit. This was the original twin throttle body kit developed by SBD in the mid 1990s as an upgrade for customers running Weber carbs. Featuring a pair of 45mm throttle bodies and an MBE 967EF ECU it gives a big upgrade at a price that's £300 cheaper than the taper throttle kits that superseded it on both packaging and power output. Peak power is around 6500rpm, but it'll happily rev much higher, which is why SBD advises fitting uprated con-rod bolts as a precautionary measure. "The standard rod bolts are really horrible, so we think it's a wise safety precaution to fit these," says Steve and the result is a bomb proof engine that produces a good spread or torque and power.
208bhp/172lb ft
TP 208 Taper throttle injection kit. For those with more to spend, SBD's most popular kit takes all the advantages of the MT196 a step further. Individual tapered throttle bodies (measuring just 66mm long and with a 45mm butterfly in the middle) allow more room around the inlet side of the engine, making this kit a viable proposition in just about any application. "It's just a straight bolt-on kit, plus the rod bolts," says Steve, so it's testimony to the brilliant design of the original engine that so much extra performance can be extracted from bolt-on tuning components. Peak power is again around 6500rpm, and the kit is designed to use Bosch Cream injectors as fitted to C20XE engine.
225bhp/172lb ft
Given that we're looking at budget horsepower, this is our cut-off point; beyond this stage tuning the C20XE & LN engines gets expensive. That said, between 225 and 230bhp allied to 177lb ft of torque is a lot of performance and it's produced by taking TP208 kit a stage further, adding a set of hydraulic cam profiles that add lift and duration. this extra valve lift requires pocketing the pistons, which gives customers a choice - they have SBD machine their original items or fit purpose-designed Omega piston. Fitting the Omegas helps keep the compressions up, which unleashes more torque and power, to the point where 230bhp is a distinct possibility. This also makes sense on a high-mileage engine, because the pistons can be used as part of a rebore. With TP225 the standard valve springs and caps replaced, while SBD includes a pair of vernier pulleys, to help get the cam timing spot on. The results: an engine that loses 8bhp at 2500rpm compared to TP208, but "after that gains torque and power everywhere and keeps going, peaking at 7200rpm and can rev to 7750rpm," says Steve.
For TRC readers on a reasonable budget that's probably as far as we would go; the next stage gets much pricier, according to Broughton. Even so, with up to 230bhp available, that's enough to make any road or motorsport car move in style!
