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Ignition Timing for boost. How much to pull per psi?


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Posted (edited)

Getting to the stage where I am able to start testing and dialing in the set up.

I have a 1316cc slabby with efi.  Fully built engine with 10:1 comp. and stock head aside from springs etc.

I've seen info stating to pull 1* per psi of boost, and have also read on a thread in the archives to pull 1* for each 20KPA which equates to 1* for every 3psi.

What is a good starting point for retarding the timing on boost for these engines and where did you end up with the engine being the happiest?

 

Edited by TiZiK
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As you are running moderately high CR i'd start with 1 Deg. per psi! You won't be able to run a lot of boost anyway so once you find it's ok you can wind it back slowly. High CR will get detonation earlier unless you have significant intercooling or other anti-det methods available!

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I have no intercooler but will be using meth-injection to help cool and curb knock.  Should also add its drag only.  May plate it to cruise to a bikenight here and there but not at all concerning myself with a street friendly tune.

So you think 1*/psi is a good starting point?  At what psi would you suggest to start pulling timing?  I've read to wait until 3-4psi before pulling timing. 

Its a rather large turbo if that matters.  Holset HY35. Similar compressor size to the HX but a smaller 9cm^2 single scroll turbine house instead of the twin scroll 12cm^2

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Difficult to give definitive answer as turbo response will influence ie. could be real slow starter then bam - 20psi or nice a linear climb to wherever the WG is set to.

First one is dead tricky due to rate of change - ecu would maybe have to drop 20 degree's in less than a few engine revolutions.

A dyno is the best place for evaluation - if in doubt, take more out than you think as its easier to put back into a running engine as opposed to one with holes in the pistons LOL!

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Oil cooled engines that I have tuned have usually liked about 28-30° timing at 1 bar boost. And if the stock N/A timing is around 34-36° then that would be close to degree per 20kPa that you mentioned. 1 degree per psi sounds excessive in any case.

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Posted (edited)
3 hours ago, Arttu said:

Oil cooled engines that I have tuned have usually liked about 28-30° timing at 1 bar boost. And if the stock N/A timing is around 34-36° then that would be close to degree per 20kPa that you mentioned. 1 degree per psi sounds excessive in any case.

Thanks Arttu.  I thought 1* per psi was a bit much as well.  From your experience, hows this table look for a starting point?

 

Slabby IGN Table.png

Edited by TiZiK
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19 hours ago, TiZiK said:

Thanks Arttu.  I thought 1* per psi was a bit much as well.  From your experience, hows this table look for a starting point?

 

Slabby IGN Table.png

Looks quite ok, I think. Just few notes:

  • If you want to start safe I would take out a couple of degrees from 140kPa and above.
  • I would ramp up timing with rpm a bit slower. 2000rpm column around 20° and 1500rpm around 15°. Although I haven't done much experimenting with this area, this is just how it seems to be on stock timing curves.
  • As extra trick you can try to stabilize idle with timing: Move the lowest column just below the idle rpm, like 900rpm. Set the next column at your target idle rpm. Add few degrees on the lowest column. This way the timing advances if the rpm drops below your idle target and that tends to drive rpm back up.
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