In 1986, Ford was participating in the World Rally Championship (WRC) and the IMSA GT Championship (IGC), in both instances at the top level, respectively Group B and GTP (writes Ian Bamsey).
The 1986 Group B Ford was the mid-engined four-wheel-drive RS200, designed by Tony Southgate as a pure rally car. Campaigned since 1984, it was powered by a turbo-supercharged 1.8 litre I4 derived from the Cosworth-designed BDA and known as the BDT.
Mountune has reclaimed this BDT-E following serious damage in action
Group B permitted engines up to 2500 cc naturally aspirated or 1785 cc if blown, with the car then running at a minimum of 890 kg and also permitted 3000 cc/2142.8 cc at 960 kg. For 1987, Ford planned an evolution of the RS200 with the single turbo engine using a new block and head, paving the way to exploit the permitted 2142.8 cc.
The IGC had comparable weight breaks to the WRC. The 1986 Ford GTP was a radial front-engined ‘Mustang’ Prototype that had been introduced in 1984 using a 1.7 litre Zakspeed I4 turbo. It ran a 2.1 litre Zakspeed I4 turbo in 1985 and 1986, exploiting IMSA’s 2.1 litre weight break. Norbert Kreyer designed this before he designed the 1.5 litre I4 turbo for the Zakspeed Formula One car.
The 2.1 litre Zakspeed unit was a pure race engine pretending to be a modified Mustang street car engine. However, by 1986 it was not considered to be ideal. Terry Hoyle was therefore commissioned by Ford to produce a de-stroked, 2.1 litre Cosworth DFX (IndyCar V8 turbo) for the IGC; the Ford Mustang GTP car raced that engine towards the end of 1986.
It is possible that the 2.1 litre BDT-E produced by Brian Hart in 1986 could have been used in the 1987 Mustang, but Ford abruptly decided to pull out of GTP at the end of the 1986 season. At the same time, the FIA shelved Group B. By that stage it is understood that Hart had produced two batches of BDT-E engines for a total of 50. The only place left for them to go was Rallycross, powering RS200-Evolutions.
BDT to BDT-E
Mountune is expert in Ford engines and in Rallycross, and has a newly created Classic division within its Racing department. As Mountune managing director David Mountain says, “Most BDT-Es ended up in Rallycross cars but Ford wouldn’t have commissioned the engine as a Rallycross engine.
“Brian Hart had been commissioned to produce the BDT-E, because the standard BDT was an 1800 – it was almost a BDA with a turbo bolted onto it. Most RS200s had the standard BDT; the Evolution cars had the BDT-E engine, one of which we’ve just rebuilt.”
The Mountune-fettled BDT-E powers Harris’ RS200 Retro Rallycross car
There was a 2.0 litre version of the BDA, the BDG (RET 129 February 2021) ,which had a 90.4 mm bore, but as Mountain puts it, “The cylinders were then wafer thin.” The BDA had a 96 mm bore spacing, and structurally a 90.4 mm bore was considered too much of a risk given the cylinder pressures associated with turbocharging. As such, the BDT had an 86 mm bore, which was married to a 77.6 mm stroke for 1803 cc.
The BDT-E block had its bore spacing increased to 106 mm, which allowed for a 90 mm bore with structural integrity considered commensurate with the anticipated level of boost. That was married to an 84 mm stroke for 2137.5 cc.
It was another aluminium alloy engine, and Mountain remarks, “The BDT-E was a longer engine, so Brian had to do his own block and his own head, cam carrier, the whole thing. It was a completely different engine from the BDT: for instance, it’s got four-bolt main bearing fixing. Since he made only 50 they are rare nowadays, and RS200-Evolutions are valuable – I am told that the car we have been working on is worth about £500,000!”
The BDT-E has a longer block than other members of the BDA family
The car in question is the RS200-Evolution of Steve Harris. This is a genuine Evolution that has been outfitted to resemble the example with which Mark Rennison won British Rallycross titles in 1987 and 1988. Today’s British Rallycross Championship has classes for what are termed Retro Rallycross cars, including 1980s Group B cars, and Rennison runs in that category.
Rennison has been campaigning the car for a few years, and approached Mountune Classic when the engine failed. “He had been having ongoing problems with his engine builder,” Mountain reports. “The engine had blown up in a pretty big way; it dropped a valve and that made a hell of a mess. We had known him for some years and he said he’d like us to fix it.
“So we pulled it apart. The block was absolutely wrecked and the cylinder head was completely destroyed – it was just like a hand grenade had gone off in one chamber.
“I don’t know who did the original block and head castings for Brian but they were nice castings, and I know Brian sent the [linerless] block to Mahle to have the cylinders Nikasil-coated. You can’t just go and get a new block. So I went to Capricorn, had a meeting with them and we decided the only way to reclaim the block was to put some thin-wall aluminium liners into it.
The charge-air supply to the BDT-E is controlled by a single throttle
“So we did that and managed to find another cylinder head, which was amazing because really there are no parts for the BDT-E anywhere. Through a third party we found a guy in Australia who had a couple of cylinder heads. They needed to be re-inserted but they could be reclaimed, so at least we had a cylinder head to work from.
“So, it was a matter of us reclaiming and rebuilding the engine. We had rods and pistons made, we rebuilt the engine and it gave 650 bhp at 2 bar [gauge] boost.”
Engine internals
Mountain relates, “Back in the 1970s I was working on an engine at Ford Motorsport in Boreham [England] and we kept having piston trouble. [Ford Motorsport director] Peter Ashcroft said, ‘Pop over and see my old mate Brian Hart’. So I went over to see Brian with an example of one of the pistons we were using [made by a UK specialist], and he looked it and said, ‘Let me tell you, we use those pistons in lawnmowers. In race engines, we use Mahle pistons.
“So Brian reached out to his mates at Mahle and they produced pistons that totally transformed the engine – cut the blow-by down by about 50%. Since then, I have always tried to use Mahle pistons, but they can be a lot more expensive [than modern alternatives]. The original BDT-E had Mahle pistons, as you’d expect from Brian. We are now using Omega pistons. It’s just a conventional forged piston. Nothing trick.”
Mountain confirms these are not oil gallery pistons. “There is just a pair of cooling oil jets [spraying the underside of each piston]. It is pretty traditional in that respect.”
The piston rings have a titanium nitride coating – “to bed in with the [nickel silicon carbide-coated] liners. The original engines were all Nikasil-coated direct to block by Mahle, and it was bulletproof. But Mahle aren’t really interested anymore so we tend to use Capricorn these days. Their [nickel silicon carbide] coating works fine but there’s something a bit different about it [compared with Mahle Nikasil] and if you’re not careful, the rings pick up. So we get them titanium-nitrided to avoid that.”
The piston crown is designed for a compression ratio of 8:1 versus the original 7.2:1. The engine runs a 102 RON octane control fuel. “Nothing special, but it’s a decent quality fuel,” as Mountain puts it.
Engine management
Explaining the increase in compression ratio, Mountain remarks, “In the day, they ran the old Bosch MP1.2 Motronic engine management system. What we have found with a number of engines – including Rob Gravett’s [1980s Ford] RS500 [2.0 litre I4 turbo], which we rebuilt recently for Zak Brown – is that putting them onto a modern management system transforms them. We have found that you can raise the knock limit, just because the modern engine management system is so precise and so fast to operate.”
This is without additional sensors, although Mountain notes, “Motronic MP1.2 had only two triggers on the trigger desk and, of course, now we run 36 minus one. So in terms of accuracy, I think the 1.2 was always behind where the engine was!
“When running a contemporary management system, we have found that you get a lot more control of the engine. Not only does that give you more power, but the engine starts nicely and is much more driveable. Obviously, you’ve got all the data-logging capability too.”
Mountune has fitted the BDT-E with a Life F88 engine management system. “Life is local to us and we get good support from them. I think the Life electronics is superb and the F88 is good value for money.
“People can get a bit emotional about wanting to keep stuff as per the original, but you can’t get any level of support for 1980s management systems. There’s no way to repair or service them, or even map them anymore. So if you’re really paranoid about it, we can even fit a Life ECU inside an original box.”
Mountain reports that this BDT-E is running closed-loop lambda. “We are not running closed-loop knock control though. We have knock sensors that we are using for logging purposes only. I’ve found that, particularly with rallycross, you get so many false knock readings as you’ve got all the stones flying up and the noise and vibration.
“We would rather just look at knock in terms of the data logging, and then we’ll decide if we think it’s real or not. The fact is, because we’re running control fuel, as long as we map it on the dyno, we know where we are. We tend to run about three degrees off of knock; you are safe at that point. We’d certainly rather not have a knock control that’s adding spark, put it that way.”
The turbo system
This BDT-E’s induction and exhaust systems follow the original layout, complete with characteristic roof-mounted charge-air cooler. The intake manifold is as per original, with a single throttle, while the turbo has an external wastegate, as it did in the day, with pneumatic controllers top and bottom. However, those controllers are electronically controlled. “So it is full electronic boost control, operating on the original external wastegate,” Mountain notes.
The turbo itself is a BorgWarner unit, whereas the original had a Garrett turbo. “They were OK in the day but, one, you can’t get them now and, two, they weren’t terribly reliable,” explains Mountain. “If it was money no object we would go for a modern Garrett racing turbo imported from the USA but they are horrendously expensive. So we’ve got this BorgWarner turbo that works extremely well and is a lot less expensive.”
Engine control includes an anti-lag strategy. “However, we’re not running [a] fresh air [bypass anti-lag system] on this, we’re just running with the throttle stacked open a bit. So we’re basically flowing a fair bit of air to avoid having the turbine slow down.
“If you have an anti-lag system that causes pops and bangs then you have a problem. If the engine is popping and banging a lot they [the officials] will just tell you to turn the system off. It is all the noise issues around all the circuits, even though it’s what people go for and want to hear. I think it’s the local residents kicking off – although the cars do sound like machine guns if they really get going!”
Mountain reports that the BorgWarner turbo offers similar flow rates to the original. However, it is different in that it is twin scroll, having a divided-entry turbine housing, “which does tend to help boost response. The original engine was very laggy because, one, it had a bloody great turbo that was single entry and, two, it was low compression.
“I remember testing back in the day with the likes of Stig Blomqvist and how they found it was like being hit in the back with a sledgehammer when it all happens, high up in the rpm range, whereas now they’re much more driveable. That comes from going up on compression, having a good modern management system including an anti-lag strategy and the twin-scroll turbo. It all makes it a lot more driveable.”
Performance
The BDT-E is run to 8000 rpm. Mountain reports that the BDT-E engines that Hart delivered produced 550 bhp, given 1.5 bar gauge pressure (2.5 bar absolute). “We ran our rebuilt engine to 2.0 bar gauge and it gave 650 bhp, which we thought was pretty impressive. In competition it tends to be to run between 1.5 and 1.8 bar, and then it can be turned up to 2.0 bar if it needs to be.
“Obviously you could run more boost and get more power but it's a very rare piece of kit, and we’re trying to keep it in one piece!
“It’s an old engine but you have to say Brian did a bloody good job with it. He always did fabulous work, often with very limited money. The BDT-E was a really solid engine and it is still a great engine. It's an exciting project for us.”
DATASHEET
BDT-E
Mountune 2021 Classic Rallycross
I4
90 x 84 mm = 2137.5 cc
Single turbocharger
102 RON octane gasoline [control fuel]
Aluminium block and aluminium head
Aluminium liners
Five main bearings, plain
Steel crankshaft, four pins
Steel con rods
Light alloy pistons, three rings
Double overhead camshafts, belt-driven
Four valves/cylinder, 1 plug
40º included valve angle
37.1 mm intake valve, 31.8 mm exhaust
Electronic ignition
Sequential port injection
Compression ratio, 8:1
Maximum rpm, 8000