NefMoto

Hey guys,

So my 1.8t engine is running lowered compression ratio, 8.5:1 CR and I am currently seeing high EGTs on cruise. Fast cruise of 90-95mph around 3.5-4k RPM, my EGT gauge is reading constant 780-820°C, with load varying between about 50 and 100 depending on incline etc. This is resulting in ignition angle of 30-35 degrees based on the stock timing in the low load areas. The MPG also seems low as I guess high EGTs mean that a lot of the energy is wasted in the exhaust.
This was the same on my old setup with a hybrid K04, factory log manifold and relentless 3" downpipe/exhaust, and now I'm running GTX30 with a custom tubular manifold and custom 3" downpipe/exhaust, which leads me to believe that the problem is in the spark timing rather than poor exhaust design. The IATs are good, maximum of 5 degrees above ambient
The engine is a APX/BAM hybrid, so there is no VVT or EGR.

Has anyone with lowered compression ratio tuned these low load areas for better economy? From what I could find online on this subject, lowered compression ratio results in slower burn, hence timing should be advanced but I could not find any concrete information on how much advance I should be aiming for.
Anybody willing to share some wisdom on the subject?

Well, best thing is to put it on dyno, but you can do it on street as well. Add couple of degrees in those areas,  go out and drive, look for timing corrections. GL.

Are you sure that I will get knock before reaching MBT at low load areas?
What you said is what I have done for WOT tuning...

You will not reach MBT in low load areas, only way is on dyno with real time torque output, torque control off and pedal mapped 1:1 to throttle plate.
You also need emulator. The way I did it is find MBT then manually set the max throttle angle, so it's always at max throttle and a shaky foot can not affect it.

I mean you can try to do it on road off of EGT, but to get stable conditions on road is almost impossible, even slight wind will affect it. I can't imagine doing it without a dyno.

Thanks for the info; unfortunately I do not have easy access to a dyno so I will have to just get it "close enough" for now.
I am also playing around with lean AFR on cruise (closed loop wideband) so hopefully together with advanced timing I will be able to lower EGTs and improve economy.
I will add 5 degrees across the low load areas as a starting point and go from there.

Prj, are you willing to share the approximate resulting advance you found for MBT on a 1.8T in low load (say 50 load, 3.5k RPM)? stock maps puts this at around 35 degrees and reading online regarding lean burn and lowered compression I have seen numbers >50 degrees thrown around for vacuum conditions (not 1.8t specific).
Even this online estimator https://forum.autosportlabs.com/viewtopic.php?t=2210&view=next&sid=755264c325a797de117453405c425699 puts the timing in this region somewhere between 35 and 42 depending on how it's filled out for a 1.8T engine and this is for "safe values" at lambda = 1.

Is the stock map overly conservative even in low load areas and assumes worst fuel, desert IATs, high altitude and "most compliant" emissions?

Waste of time, dyno is needed.
If you don't have access to one, you have no business tuning timing maps on low CR engines - you will never get it right.

It's just how it is unfortunately.

Yes alright, well I will try to lower EGTs at the very least, my EGT gauge is quite consistent when using cruise control at high speed and I normally use this fun car for the weekend journeys so as long as I log the drives then not much time is actually wasted. At the very worst case I will learn something new from it.
Presumably tuning WOT is fine using knock corrections? Attached is my resulting WOT timing curve from not too long ago, think it is consistent with some other curves I've seen for a 1.8T BT at high psi.

WOT is fine if you are knock limited.
For example on E85 it is often impossible to find correct timing without dyno.

And yes you can put it on cruise control and adjust for EGT's...But that does not get you the whole map filled.

No e85 across this side of the pond, just premium UK fuel, which is definitely knock limited...
Once I get my WMI system sorted, then a dyno visit will be first on the to do list. But that won't be until the 5120 hack is sorted and a whole load of other maps fixed.

I have 5120 and meth map switch sorted (useful if you are fitting a proper system such as aquamist, which has a failsafe). If you want to buy your way forward some...
I have dyno tuned quite a few different low CR 1.8T and have lots of timing maps, but they are all different. Hell, even small and big port head makes a huge amount of difference in the timing the engine makes and what timing makes best power, due to burn rates being different.
Don't even get me started on cam switching...