Effect of turbine size on ignition timing

[Logg]

I was just wondering what the general effect of turbine housing and turbine wheel have on possible ignition timing.

I've gone from a 48mm wheel size and an AR of .46 to a 58mm rear wheel and a AR of .64.
Will this mean my lil C1J would benefit from more advance or retard?

Thanks for your thoughts, opinions and knowlage in Advance.

[w35ty]

pretty sure advancing the timing will help with spool up on the turbo to help it come in sooner just loose abit of top end speed i think...

[Logg]

Thanks for the reply there's no problem with spool 0.5bar @3k 1bar@3.5k 1.3bar@3.8k.

Want I'm trying to find out is does having a bigger hot side to the turbo increase or decrease the tolerance of ignition once on boost. If at all.

[w35ty]

Not sure maybe someone else could shed some light on it.. But id say it decreases it slightly

[R5MJH]

welcome back logg matey

[Logg]

Not sure maybe someone else could shed some light on it.. But id say it decreases it slightly

For some reason in my head I thought I might increase due to the better flow of the bigger housing and wheel, lower EGT's and less back pressure.

[Logg]

welcome back logg matey

Sssssshhhhh

[Matt Cole]

Welcome back boss. Duly missed.

[Logg]

Welcome back boss. Duly missed.

Cheers big fella.

Have you any thoughts on this, knowledge or a direction to point me in.

[GTphil]

Welcome Back

I think your onto it with the smaller turbine and higher EGT's would give you less tolerance for advancing the timing.

I think

[Tutuur]

As you probably know yourself it's all much of a muchness without a dyno really, however if you had to get timing retarded because of the small turbine/high boost (knock limit) the odds are pretty big you can now advance it.

Although advancing it won't neccesarily mean you will gain hp unless you are far of mbt atm...

[Logg]

Welcome Back

I think your onto it with the smaller turbine and higher EGT's would give you less tolerance for advancing the timing.

I think

That was my thinking but trying to find good info about it is a little difficult.

bit like trying to find out what effect retarding a cam has on a engines ignition sweet spot if you will. Got to love my technical terms.

[Logg]

As you probably know yourself it's all much of a muchness without a dyno really, however if you had to get timing retarded because of the small turbine/high boost (knock limit) the odds are pretty big you can now advance it.

Although advancing it won't neccesarily mean you will gain hp unless you are far of mbt atm...

The car was mapped on the small turbo I've adjusted the fuelling already for the new set up but only up to 1.2-1.3 bar but want to push further to at least to the 1.6bar I run before the turbo swap. think i might leave the ignition alone unless I get pinking or the car feels gutless. But still quite interested in if there is a difference.

[Tutuur]

I'm guessing you had to add fuel?

[Tutuur]

Welcome Back

I think your onto it with the smaller turbine and higher EGT's would give you less tolerance for advancing the timing.

I think

Imho you're right regarding the tolerance, however it wouldn't mean you need more ignition to get at mbt. As when you make more boost, are filling the cylinders more, have higher swirl so need less timing to fully burn the fuel at 14* atdc (which iirc is the ideal moment)

[Logg]

I'm guessing you had to add fuel?

Well this is the odd thing I retarded the cam around the same time as I found it was timed up at 104 rather than 110 it should be. When it comes on boost ive had to add fuel but after that I had to take fuel out as it dropped to 10.5 rather than 11.5 it was before.

[Tutuur]

Hhhmmm that's odd indeed, you sure you've read the cam timing properly? As generaly when retarding the cam, the intake event would come later in the cycle resulting in higher ve on top of the rev range and less lower down....

[Logg]

Hhhmmm that's odd indeed, you sure you've read the cam timing properly? As generaly when retarding the cam, the intake event would come later in the cycle resulting in higher ve on top of the rev range and less lower down....

Yeah thats what I thought we checked it a quite a few times. If we got it wrong I'd now have close to ten degrees of advance on the engine. the car goes well just needs more boost as 1.3bar is barely tickling the turbo maybe the turbos not efficient at lower boost levels.

This is is why I was wondering if changing turbo size and cam timing has altered the ignition sweet spot massively.

[Tutuur]

Imo if you could put that much more fuel in with the previous setting and it didn't feel lazy off boost the other setting should work better

[HAndy]

dont gestimate get it on a rolling road and make sure100% whats going on afr/egt wise, word of mouth/ internet is worthless, rolling road data priceless

do it once do it right even

[Logg]

Just looked at the map I had to put more fuel in from 3.5k- 6k by 0.3-4 then had to take 0.2 out up to 7k.

[Logg]

dont gestimate get it on a rolling road and make sure100% whats going on afr/egt wise, word of mouth/ internet is worthless, rolling road data priceless

do it once do it right even

I know mate but dont have the spare cash for a trip to scoff at the mo so going pmt.

Obviously just cause the internet says put 10 degrees more advance in I wont do that but I like trying to understand why things happen. And det cans are pressent.

[Scoff]

You can sometimes squeeze a degree or two in after a reduction in turbine inlet pressure, since things are usually cooler, reversion is happening less. But don't gamble, you need to be measuring knock if nothing else.

[Logg]

Cool thanks for the reply Chirs.

in the end I just adjusted the fueling by following the trend set by my previous fuel map corrections which worked fine up to 2bar and just added an extra degree or two while listen for det which I couldn't hear. Seems to be holding together so far at 1.8 bar day to day.