a question asked on the psooc forum is ..why is the mi16 engine flat until after 4000 rpm ??? any suggestions on here ??

Which one?

The XU9J4 as fitted to the Mi16 isn't. It's got more torque everywhere compared to an 8V. The XU9J4Z is a bit down on torque due to less CR.

The XU9J4 as fitted to the Mi16x4 has a bit less due to slightly bigger cams., which allow it to rev hard to 7400. You don't get something for nothing!

but if i accelerate from , say , 30 mph in fifth gear in my 309 gti it would leave my mi16x4 standing , because of the torque( and less weight ) , so why make a flagship car so inflexable , as it is a fast road car , not a racing car ?? ..( just curious )

I'd don't think my 4bie would accelerate from 30 in fifth! To drive a 4bie fast all you need to do is keep the revs high, it has no disadvantage over other similarly powered cars as long as your in the right gear (but i'm sure you know this). Tbh the fact the torque comes high up the rev range makes it even more fun, and you get to hear that beautiful engine note when you plant it!

Try it after a longer workout on the autobahn, it reacts immediately in all regimes.

Volumetric efficiency. It's just basic physics. At low revs the air being drawn into the engine gets sucked in alot quicker if you have a narrow inlet. But the Mi has a big inlet and ports so the vacuum at low revs aint that great. You can either have high air intake at low revs or high revs but not both unless you have variable valve timing. I'm crap at describing this but there's some good websites out there on this stuff.

Engine condition makes a difference too. Worn piston rings just don't suck lol. My first 405 Mi16 was quite worn and just hated low revs in any gear. Yet on my current engine, which was rebuilt by Miles, I can accelerate from 30mph in 5th on the flat, albeit very slowly. V-Power seems to help alot a bit but then my pre-knock sensor engine isn't suited to 95 octane anyway.

Another thing is that 160bhp from just 1905cc is quite alot really. Most other manufacturers of the time opted for getting only 150bhp from a 2 litre engine so obviously they were gonna be more torquey. I think they should have had a 1.9 Mi16 engine for the 205 crowd and given the 405 a few hundred more ccs.

Personally I think it doesn't really matter because the Mi was designed for enthusiastic driving so you aren't supposed to be pottering around at 2000rpm.

Actually there is an advantage to crap air intake at low revs - good fuel economy.

Google search on volumetric efficiency

thanks Kris , thats the kind of answer/explaination i was looking for

my 4bie will sit at 30 in fifth all day and accelarate away no problem

some new ford v6 engine have long and short intakes for low and high revs to get the best of both worlds

Well so will mine, the point is what are you doing at 30 mph in fifth? Thats no way to drive an Mi16. I raced an Audi A3 2.0 TDi on the way home tonight and I kept with it off the line and above 40 mph i hammered it. The Audi had way more torque down the rev range than me but once I got the revs up it couldn't out accelerate me. I also beat my mates Golf TDi quite comfortably. torque isn't everything it seems.

im at 30 mph in fifth because i like my licence ..and do my racing at track days and on hillclimbs

Yeah the Jap V6 in the Probe had that as did the V6 duratec lump in the Mondeo - thrashed the v6 Cavalier in the 50-70mph test in 5th. It's not necessary though, the V6 406 hasn't got it and does ok.

I've handwritten all the torque/power figures from the French XU9 pdf thingy, must put them all into a graph at some point, unless anyone else wants to do it?

Link to pic: The official power figures for 1.9 XU engines
And the torqueNot as much difference as I thought.

Peter

So what impact does your stage 1 intake cam and/or an offset camshaft key have on the XU9J4 Mi16x4?

Would it give you back the lost low end torque without losing the top end advantage?

Tony

Everything is a compromise when it comes to cam timing, but it is possible to find a "sweet spot". It's generally not necessary to use an offset key with the Stage I cam, if you're using a #3 pulley. But it is necessary with a #2 pulley, or if you deck the block. I personally think that using these setups gets it in the "sweet spot" that gives the best possible broad power range, whilst still working with the standard internals and ECU. Ideally, you should verify the timing by measuring the lift @ TDC, but not everyone has the tools/expertese. So to answer your question. Yes, mostly.