Just the other day Joe Beninca of Beninca Motors called to tell us about an engine he was in the process of bolting up to their engine dyno. He said it was a genuine Sierra Cosworth RS500 race engine and asked if we would be interested in having a look.
You'd better believe it! I mean, not ever having seen the genuine article before in the flesh, we felt that you too may be in the same position and be interested in finding out a little more about them. Further to this, we also called on Simon Gishus at Nizpro for a description of how the turbo engine has changed since Cosworth developed their engine in mid 80's. We'll cover this a little later.
In the meantime, let's look at a genuine Bathurst race engine. The unit photographed is one of many built for Colin Bond's Sierra by the Caltex Race Team between 1987 and 1991. Engine builders/tuners involved with the radical engines included Nigel Bolling from Autodelta, Simon Negus from Negus Autotech Perth, Mick Mitchell from Corse, Joe Beninca from Beninca Motors, Jim Hatfield, John Skola from Skola Developments and finally Brad King. Some big names for a serious engine!
Historically Speaking
The RS500 was based on a standard RS Cosworth 3-door but with the YBB engine replaced by a stronger YBD engine, specifically to qualify for evolution homologation into the 1987 Group A category. Additionally, the RS500 was fitted with a body kit providing significantly more downforce as well as an additional rear suspension mount for racing applications. The overall effect of these modifications was negligible - providing only 20hp over the original car - however the potential for tuning was vast with race spec cars running as much as 550hp.
The main differences of the Cosworth competition engine revolved around a thick-walled block; larger turbocharger and intercooler; a second set of injectors; an uprated fuel pump, oil and cooling systems; and the cylinder head had hardened valve seat inserts.
Factory Specs
| Capacity: |
1993cc |
| Bore & Stroke: |
90.82mm by 76.95mm |
| Block: |
Cast Iron utilising special "thick wall" production technique |
| Cylinder Head: |
Aluminium with 65mm diameter inlet tracts, pentroof combustion chambers, 35mm inlet and 31mm (sodium cooled) exhaust valves, bucket tappets. Four valve head Red colour cam cover |
| Inlet Manifold: |
Short runners for high RPM tuning |
| Pistons: |
8.0:1 Mahle forged pistons with oil squirters under piston from oil pump relief pressure dump. Ball bearing at the front of camshafts with plain bearings in the middle of 2 inlet or exhaust valves |
| Camshafts: |
Inlet opens 8 Deg BTDC, Inlet closes 52 Deg ABDC, Exhaust opens 52 Deg BBDC, Exhaust closes 8 Deg ATDC running in five bearings |
| Crank: |
Heat treated with four counter weights only |
| Turbocharger: |
T3 with S4 compressor, A/R 0.63 turbine case. 9 psi boost |
| Intercooler: |
60cm x 40cm x 4cm air to air |
| Oil Cooler: |
Water to oil heat exchanger mounted on the side of the block |
| Max Power: |
224hp at 6,000 rpm |
| Max Torque: |
206 ft-lb at 4,500 rpm |
The turbocharger used a dump valve to allow it to continue spinning when the throttle was released. The TO3 turbo was mounted on a high nickel content exhaust manifold with a special mounting plate that allowed the turbo to grow as it got hotter without cracking or causing undue stress. Cosworth chose Uniroyal rubber belts to drive the oil pump, distributor and camshafts. The RS500 Cosworth engine, like its turbocharged stable mate the MK3 Escort Series 1 Turbo, used a relatively sophisticated engine management system that controlled ignition timing, injection, fuel pressure and turbo boost.
Race Engine Development
Never let it be said that the Aussies are backwards in coming forwards with engine development. In fact, many of the modifications made on our homegrown racers were later employed in English race cars. The development process continued unabated for the five years the Ford Sierra was raced in this country, as follows.
The Cosworth suffered from a design resulting in poor oil drainback from the cylinder head and high blow-by. In alleviating the problem, a breather package of four half-inch tubes leading to a large catch tank and two half-inch almost straight down drain tubes to the extra large aluminium sump was developed. Amazingly the engine ran only a wet sump with a splash tray under main bearing caps.
In standard trim, excessive vibration quickly killed the alternator. A cure came with soft mountings which in itself meant that correct alignment was impossible. So the single pulley was replaced with deep grooved double pulleys with one driving the water pump and the other the alternator. This method allowed the alternator to be twisted and mis-aligned without running the risk of "throwing" a belt. You could easily flex the alternator 10mm - it was that loose!
In overcoming significant vibration problems, other cures were necessary. One example is a tricky damper that connects the turbo to cylinder head.
Fortunately this was a simple one with the guys making a double-pass radiator whilst ensuring all air that entered the front grille passed through it.
- Thrust Bearing Turbo Failure
As the boost levels increased, the load on the little internal 270-degree thrust surpassed its rating. So a "full circle" Berillium/copper alloy material thrust was devised.
Running relative low boost up to 1 Bar was fine, however as soon as the boost level rose, the wastegate exit couldn't pass enough exhaust gas which resulted in over-boosting. Race teams employed many variations of porting in the turbine housing to reduce this problem, but then as development moved forward and boost levels kept climbing, the problem of excessive waste gate flow disappeared because you needed an almost closed waste gate to achieve the high boost pressures.
The engine was fitted with two injectors per cylinder; one in the inlet runner and one close to the valve. However, when both sets were employed, it resulted in a mixture imbalance of up to 10% - with detonation the result. Clever flow porting was tried below the throttle butterfly but this only slightly reduced the imbalance problem. Ultimately, one large injector was used which minimized the imbalance and with the later ECU's having individual cylinder trims, the problem was solved.
Due to high bolt tension, high expansion of the cylinder head and stiff short studs, blocks would crack around the tapped stud hole in the top of the block. In resolving this problem, long Alfa Romeo cylinder studs were tried, and the blocks carefully drilled and tapped (an extremely delicate operation). The long studs allowed for expansion of the cylinder head without a dramatic increase in clamping force.
Engine builders were forced to go to Cooper Rings, using a cutout standard outer section.
Whereas a copper tube mounted to the engine mount bolts and connected to "ear plugs" worked for the lower budget teams, the more professional operations fitted pressure transducers under the sparkplugs to monitor the combustion pressure and therefore knock. This made for much more confident mapping of the advance curve for boost pressure and inlet manifold temperature.
Initially, solid cam followers and tappet shims on top of the valve stems were used but adjustment was found to be very time-consuming. Then it was found that by dismantling the standard cam followers and chroming the top surface, reliability improved. Numerous cam profiles were tried, however as the boost pressures rose it was found that an almost standard profile was the best.
The engines continued to suffer significant piston failure until the compression ratio was lowered from standard to 7.0:1 and piston to bore clearances were increased. Gapless rings were also tried with the locally made pistons but were found to require many hours of running in.
The engines used one of the earliest available sequential systems, the popular Zytek ECU, however few teams had the software to reprogram them. Conversely, budgetary constraints meant that all most could afford was the "screwdriver" adjustable Autronic ECU along with a mechanical advance in the distributor. Later, the first sequential Autronic was fitted with spark and closed loop boost control.
Note that the engine seen here was in fact tuned with a current version SM2 Autronic.
It was also found that CDI ignition was necessary to ensure proper burn and the Autronic system incorporated a high insulated Capacitor Discharge ignition coil. Amazingly, the engines ran with only a very small distributor cap.
- Compressor Outlet Pipe Connection
The factory silicon compressor outlet pipe joiner "cooked" with the heat from compressed air (250 Deg C). This was replaced with an aluminium pipe bend incorporating a vee clamp join and a machined mating flange, whilst the factory silicon connection at the intercooler was retained.
- Blow Off Valve (used to reduce compressor wheel failure).
Due to the radically high boost pressures being employed, the compressor blades had a tendency to break. In fact when Longhurst won Bathurst, the turbo only just limped home as the compressor blade tips had started to tear off. You could hear the vehicle whistling as the Great Race was ending. In an attempt to reduce the problems, teams polished and glass bead blasted the compressor wheels for a compressive stress on the surface. Also a reheat treatment was tried on the aluminium compressor wheel. Incredibly, before turbo cars were banished from competing in the Australian Touring Car Championship, boost levels of an amazing 2.6 Bar ( ~38 psi) were typical and used for the duration of a race.
Thanks to Beninca Motors for providing much of the tech information used in this article.
http://www.beninca.com.au
FORD SIERRA
Beninca Engine Dyno 22/12/2000
| RPM |
HP |
KW |
Nm |
Boost Bar |
Air Temp |
| 3000 |
78 |
58 |
184 |
1.3 |
30 |
| 3500 |
130 |
97 |
264 |
1.5 |
30 |
| 4000 |
253 |
189 |
451 |
1.5 |
30 |
| 4500 |
289 |
216 |
458 |
1.5 |
30.5 |
| 5000 |
335 |
250 |
478 |
1.5 |
30.5 |
| 5500 |
352 |
263 |
455 |
1.6 |
31 |
| 6000 |
433 |
323 |
514 |
1.6 |
36 |
| 6500 |
445 |
332 |
487 |
1.6 |
43 |
| 7000 |
490 |
366 |
499 |
1.6 |
44 |
| 7500 |
498 |
372 |
473 |
1.6 |
47 |
Note maximum boost was set at 1.6 bar or ~23 psi.
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The New!
We approached Nizpro's Simon Gishus for his thoughts on how engines have changed since the introduction of the Sierra Cosworth way back in 1986. Simon offered the opinion that, "in reality, cylinder head development hasn't improved over the past decade or so, and I would have to say that as the Cosworth was a little ahead of its time, it is certainly the equal of today's hi-tech four cylinder engines". Simon continued, "Back then DOHC was relatively new, however that didn't mean it wasn't done well." [Well DOHC has been around since the '20's, but we know what he means! - Ed] "The way I see it is that there are two categories with current and recent engines. One is the average 'family' engine which is engineered to merely get by while offering good fuel consumption. These engines don't like to be modified and are prone to failure when they are. The other is a heavier and more bullet proof engine that while less efficient, is happy to accept modification." "Either engine can be compared to the Cosworth in engineering terms. But of course there have been some technological advancements. For example, there's variable valve timing, and of course VTEC which is quite sensational. Then there's the electronics." "That is to say, back in 1989 Nissan released the GT-R with an electronics package that hasn't really been superseded. It's still a brilliant system with the only difference in contemporary cars being the inclusion of controls for other things such as active suspension systems." "I guess what I am really saying is that Ford and Cosworth got it right 15 years ago and all we're doing today is fine tuning things."
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