Effect of inlet manifold choice on ignition advance

Hi,

Hoping someone can point me in the right direction, I have a GQ (Y60) Patrol with an N/A Barra in it. Had it tuned at a local shop when it was first converted, just pulled the tune out recently and all it has is 2* added to the borderline knock table from about 0.6 load upwards.

I'm going to give it a bit of a tweak up myself, however I've fitted the engine with an FG inlet manifold (plastic, much better flow than the old BF alloy one), 20% underdrives, extractors and a good intake.

Checking out the spark maps for the FG falcon, standard it has the same compression ratio as the BF, very similar combustion chamber (only a small difference), the same cam specs, same exhaust manifold, almost the exact same VCT maps etc. The FG seems to have much more timing at cruise and low loads (up to about 0.7 load, ) than the BF.

Would the inlet manifold make that much difference?

The software I'm using is PCMTec if that helps, but I have full access to the (BF) Falcon PCM tables and config. Not going to go all ham fisted about adding timing (have knock ears), but was just interested to see the difference between the two. I added a couple of degrees in notable part throttle flat spots and it helped smooth it out so far.

Thanks!

I guess what I'm asking, can changing an inlet manifold make an engine more or less prone to knock?

You gotta help us out with these acronyms man. We don't have half this stuff in the USA. So you have a Patrol and you swapped a Ford Falcon engine into it? Which engine? Can you explain the mods with the acronyms? Can you post screenshots of the maps you are looking at in the software?

Sure!

- BF / FG are Falcon model designations in Aus

- N/A = Naturally Aspirated (non-turbo)

- VCT = Variable Cam Timing

- PCM = Powertrain Control Management (ECU)

Yep, I basically swapped a Ford Falcon engine into a Nissan Patrol. I'm mainly asking from a theory perspective, as I'm trying to find some more economy from it, and the stock FG falcon tune has at least 5* more timing in some areas. Similar timing at wide open throttle (WOT) though.

I'll grab some screenshots of the spark maps.

Do you know if the BF and FG are both advertised for the same octane fuel? For example, is one "premium required" and another "premium recommended" or "regular" ?

They are probably 'Flexi-fuel', designed to run on a range of fuels from pure RON 91 (your 87, I think?) through RON 98 (your 93?) to E90?

Back to original poster, yes, intake manifolds can make a small, but significant different - runner lengths, diameters and shape will affect flow and plastic will be expected to keep the charge cooler than aluminium. Which one is 'best' may change under the different operating conditions, and as you alter other parts of the inlet and exhaust.

In the end, the engine will tell you what it wants but, if you're doing some hard slogging in the outback with 45+C temperatures, you may want to leave a little on the conservative side.