Hi

Im building a GTX3071r 1.8T with 82mm pistons (9.25:1 CR), supertech valves, top mount manifold, 4" maf housing with tial 38mm wastegate.

Im looking at injectors and need some advice.  Ill be running a ME7.5 BAM ecu.

What size injectors do people recommend?  Ive heard 680cc's will do the job, but I want plenty headroom so they not running a high DC.  Also what make is the better ones?  Ive read a bit able misfires on idle, spray patterns etc so just wondering what people have had experience of on here and what they would recommend.

Chris

I have just reached 90% duty cycle on this turbo on 870cc injectors, so these are a bare minimum.

Rick

Ideally I will be on 3bar pressure, but my setup should take 4bar easily.

Fuel using will be UK Super unleaded (vpower  or equivilant (97 and 99RON))

Hmm, I was hoping pistons would be ok....THeres a few people here in UK that run 600bhp on 9.25 or 9.5 compression ratio.

Was hoping the 9.25:1 would give me a pretty quick spool but not cause too much knock up top end and eat power.  Only other option was 8.5:1.

We have 97-99RON fuel here so hoping my guy who does mapping can work something out.

Also be running water meth.

Water/meth will improve it quite a bit, but I have no idea why you went with that high compression ratio.
No, 9.25 will not give you better spool at all. 8.5:1 or 8.0:1 would give you much better spool.
This stupid myth of "the engine will be weaker down low with lower compression ratio" is making a lot of people choose their engine components incorrectly. You have a turbocharged engine, not a normally aspirated one!

This only starts to hold true when you go below 8.0:1... Until then, the lower, the better and more responsive the car will be in the entire rev range, because the engine is highly knock limited.
The only thing you will lose is low-load cruise efficiency, meaning slightly higher fuel consumption on the motorway.

This is of course if you are using gasoline as fuel. If using other fuels, such as LPG or E85, then the "break even" point arrives at a different ratio.

What made you think this?

Seems your research has failed and you have bought the wrong parts then.
Lowering CR would only ever hurt spool if you were not knock limited. Any time you go anywhere near WOT you are instantly knock limited even at 8.0:1 on this engine.

No idea where that "high CR is good for spool" myth comes from, but it sure as hell has nothing to do with a turbo engine on pump gas.

I read that the higher CR would give me more responsiveness off boost. Which is also more efficient. The lower CR turbos would need more boost and timing to reach the same figures of that from a higher CR engine.

If knock and hear can be mapped around,  then surely there's no reason for this setup not to work? More efficient engine using less boost to get same power figures.

There's are many guys running a big turbo over here in uk with an above 9:1 compression ratio and plenty in the USA.