I was reading some tests about the Sierra Cosworth and noticed that most reported top speeds were quite down on Ford's own figures. Ford quoted 151,4 mph (242 km/h) for the 2wd sapphire. Autocar measured 143 mph and during the Top Gear trackday challenge it also got to exactly 143 mph (229 km/h). For the 4x4 Ford also quoted 150 mph (240 km/h), but it was measured by Autocar at 144 mph (232 km/h).

Last week I was re-installing the amalvalve and read that the ECU switches the boost level to 0.3 bar above 6000 rpm (at least for the 3dr). When looking at the speeds the cosworth does at 6k rpm in 5th I get 142 mph (228 km/h) for the 2wd and 138 mph (221 km/h) for the 4x4.

Now is the top speed simply limited by the fact that the amalvalve reduces the boost at 6000 rpm? If so, I don't understand why Ford quoted these high figures because they knew the engine wasn't making enough power above 6k rpm.

 

Where are you getting the info re the boost cut, I don't think it's true!

@ 7K you will activate a hard cut (This is information from the handbook, so factual)

Above 6,800 RPM every second FI pulse is missed and the boost pressure is reduced by 0.3 BAR (4.5 ibf/in) I think this is what you are referring to, it's certainly not 6000 RPM lol, they don't make peak power until then.

They were known for the official Ford quote, although they may be a little shy of this in some cases, also the acceleration figures vary depending on where you look.

Martin

 

I got it from the original Ford training manual that describes the 3dr. It indeed says it has a soft rpm limiter at 6800 rpm and a hard limiter at 7000 rpm. But it also says the boost is gradually reduced to 0.3 bar above 6000 rpm or with ACT's above 70 °C. I suppose when coming from the Ford manual it should be correct. I also asked Stu from MSD what my 320 bhp chip does, and apparently that still switches the amalvalve at 6000 rpm and 70 °C ACT.

 

It is true for a standard chip. Although the lowest value you will get depends on the waste gate and could be a little higher.
Look at the boost control table and the influence of the air temp in the software. (Amal Map and Amal ACT multiplier Map). See (almost at the bottom): http://bigturbo.co.uk/main3.htm

 

That's a really nice link. So the amalvalve isn't really an open/close valve, it can also be somewhere in between. That explains it a bit more.

The amal map for the L6 shows that the boost is slowly reduced over the whole rev range. It also says the L8 runs higher boost as the L6 and also more boost at higher rpm. This explains why the 4x4 makes max power at 6250 rpm and the 2wd at 6000 rpm. It's probably also the reason why the 4x4 got up to a higher top speed, although the Ford figures show it shouldn't have.

 

Not really dude as the 4x4 has more drive train power loss than a 2wd.

But i am more than likely wrong lol.

 

But more power to compensate

So in effect then, they make the power they do at lowish boost, OR are we saying it requires 70 degrees IAT AND 6K, or it will lower the boost at the those revs period?

Martin

 

Well, I now think the ECU drops the boost gradually. But on the 2wd the boost is dropped earlier than on the 4x4, that's probably the reason why the 2wd has max power at 6000 rpm and the 4x4 at 6250 rpm.

Still if the 2wd drops the boost at 6000 rpm, which is 142 mph in 5th gear, I don't think it's a coincidince that the top speed is measured at 143 mph. It probably can't pull past 6000 rpm, as it loses boost.

For the 4x4 that problem is less as the boost is dropped at a higher rpm (don't know what value though).

 

Hard to know what condition the Top Gear one was in with regard to fuelling/boost/actuator etc and also what the road wind conditions were like ( head wind/tail wind etc ) if it was the one down on the autobahn?

However, the British mags figures were done on the bowl at Millbrook in most cases (or occasionally Montlhery near Paris ) which is a small bowl compared to Nardo where the Ford official figures were done. The test facility at Lommel was used a lot by Ford but for top speed runs/max speed durability runs on the Cosworths, Nardo was usually preferred as it is an eight mile bowl and much kinder to tyres as the steering angle/heat build-up in the tyres is less than on a smaller bowl.
You can usually say that about another 3 or 4 mph can be added on to Millbrook bowl figures if the car were to run on the Nardo facility or a big straight test track
such as Ehra-Lessien that VW use