Turbocharging a 2 litre BF18 engine

[funkihamsta]

You know that engine in the renault 19, volvo400 series etc... well it comes in a variety of flavours 1.6 to 2.0 turbo1.7only, na and diesel.

Attempts to use the turbo set up head and 2 litre bottom have been thwarted due to heat build up. Allegedly (JuTu) the space between the cylinders is insufficient to dissipate the heat on 0.75bar forced induction and pop! (although nature of said pop is unclear, l am assuming a warped head rather than detonation damage)

Any suggestions that might ameliorate/avoid this?

[funkihamsta]

Thanks for all your replies given l have provided so little info. I'm still waiting for some response to some Q's. (This is not my project but it was something l was hoping to pursue in the near future)

The 2 litre head would have been a 10.5:1 CR but l would have expected that this was lowered! CR on these engines under forced induction are typically 8.5. Also the boost would definitely not have been running above 11psi. From what little info l have so far, it appears the problem arises after sustained bouts of hard driving (racing?).

Will add more when l hear more. Thanks again.

[funkihamsta]

Well bollox to them, guess they only respond if you going to buy something. I am going ahead with the 2.0 conversion. I have sourced a bottom end and have asked an engine builder if he would entertain the experiment.

So far l know the following:
1.7 turbo head fits straight on the 2 ltr bottom. Cambelt is the same, engine mounts, gearbox connection are the same. Oil return pipe may need drilling into the sump for the turbo.

I want the engine rebuilt, so:
Compression lowered from 10 to 8.5 (Will this essentially also increase the capacity or is it measured only by swept volume?)

Rings, what type?
Pistons. Eutectic pistons? Ceramic coating? (Good thread that)
Crank. The crank has a larger rotational circumference than the 1.7. I am trying to work out how that will affect torque and power curves, but l am totally unsure!
The injection system is LH2 jetronic, with an air MASS meter so it should be fairly adaptable.

So apart from the usual strengthening, lightening, balancing and tolerances etc... What do l need to consider, have l missed something critical?

At this point anything specific or general would be extremely welcome.
Dan

[funkihamsta]

I can't for the life of me remember what they call it, but the head is flat. There is not combustion chamber formed by the head itself only by the tops of the piston.
CR for 2.ltr is 9.8
CR for 1.7turbo is 8.1

Throw (presume stroke)
83.5mm Vs 93.0mm.

Could l not use piston head shape to get some nice proven combustion chamber form whilst reducing CR? Seen pistons with depressions expressly for the valves to fit into. (perhaps these are non-interference only and are pants performance-wise)

The airflow is a hotwire air mass sensor. I shouldn't think it'll have any real problems as it IS already turbocharged. Fuelling could be an issue coupled with other modifications. Though about upping fuel pressure and larger injectors, bringing the whole lot back to earth with a fuel chip remap (seperate chips on this engine) so l don't run rich all the time when not on full throttle.

How do l go about finding some custom pistons chumrade?

[funkihamsta]

Can someone please tell me the best way to reduce CR other than thicker gaskets.

Different pistons perhaps, but what if the current pistons are already dished?

Reducing the throw with a different crank, would also reduce the capacity though wouldn't it? Do l have any real choices here?

[funkihamsta]

The bore is wider by a good couple of mm between the 1.7 and 2ltr engines: 81mm Vs 82.7mm so unless l use the 1.7 block, 1.7 pistons, with the 1.7 crank... hang on that's the stock set up!

Go on, just tell me l haven't got a hope, l can take it.

Can l assume that because the pistons are already dished to create the combustion chamber l am much less likely to be able to bring CR down by piston choice alone?