Frankenstein engine?

[Brighouse-gti]

So its like this, I want to build an engine up, and am pondering this;

Mk3 1.9 tdi bottom end(1Y)
Mk3 1.9 tdi gearbox(1Y CHC)
Mk2 1.8 gti top end(digi of PB engine) big valves, gasflowed, uprated cam
KO3 turbo intercooler bla bla bla

.... to someday fit into my mk2. My thinking is it should marry up together, (top n bottom) and will just fit straight in (mountings wise), but that's pretty much as far as my amateur knowledge goes! Just looking for some advice, as always, or for someone in the know to say, hold on a minute, that won't work! Or of it does, yeah but you'll have to do a + b or it won't work.
Ta for any info!

[Waspy]

What fuel?! Deisel? Why?

[Brighouse-gti]

Diesel, what's that?
Petrol my good man!!

[Waspy]

Unless you know something I don't, you cant run petrol through a diesel bottom end, they work in completely different ways... Hence why people who stick the wrong fuel in their car end up at the side of the road.

Petrol needs a spark, your diesel bottom end has no way of providing a spark. Thats my (possibly very wrong) take on the matter.

[Santiago]

Waspy: sparkplugs (or glowplugs for CI engines) are in the head, not block.

Brighouse-gti: are you sure the diseasel bottom end will physically line up with a PB head? I don't really know why, but my gut feeling is that it probably won't. Spacing of bore centres, headbolt holes etc?

[Brighouse-gti]

I'm pretty sure it should work, or there is a combination that should, although I think the combination I've said is correct.... reason being I met a lad a while back who had done such a conversion, and I almost certain he said he'd used the mk3 diesel bottom end combined with the mk2 head, and what he'd done was use the turbo setup from a cosworth. He also said something about it being like s**t of a stick and putting a big smile on your face when you put foot down!!

[jezza16v]

Even if it did fit, you would have to put a big spacer between the diesel block and PB head with two head gaskets. Diesels run a 20:1 compression ratio, normal PB is about 10:1 otherwise pistons would hit the valves. Turbo'd engines need compression ratio reduced to about 8:1 as when turbo'd the compression is increased to around 10:1 (you can't get high enough octane fuel to run more than about 10:1 unless you use Avgas) otherwise the fuel pre-ignites (self detonates). You need to reduce the compression ratio for a turbo so using a diesel block would be counter-productive unless you change the pistons & con rods. I think Turbo Technics used a head spacer and double gasket on their PB turbo conversions.......?

[Waspy]

lol my bad.

On another point, why, other than something different?

Sounds like a complex way of getting bhp. A boring old 20vt is also like sh!t off a stick (and is tried and tested)

[Brighouse-gti]

The mk3 1Y block is a tdi block so surely it would have a low compression ratio anyway no? Part of the reason behind such a conversion is that I cant see it needing a loom swap, which would be the absolute bonus as when it comes to the electrics side of things with cars I'm almost useless. Maybe a remap or something or very little in the way of electrics but you can see where I'm trying to go with this..

[jezza16v]

The tdi block only has the compression reduced to about 18:1, so still very high. Tdi wiring/ecu would have no control for the spark & timing and Tdi diesel injectors are way different to petrol. I'm not saying its impossible but it does not seem a logical way to go, also petrol turbo gasses burn at much higher temperature than diesel so you need special oil cooled pistons to get the heat away.