Lm420 / late boost 4200rpm
 

Hi peeps, after some tech support :)

I'm by no means a expert in this field so need some answers hopfully in relation to the lm420 turbo im currently using. The spec c is up and running with the above turbo and has been for a month or two But have a issue I need to get to the bottom of...

The long and short of it is I'm not hitting full boost approx 4200rpm, I would be interested to no what other people using the same turbo are achieving full boost at, I have the billet version and was expecting to see full boost by 3600-3700 but that is guess work and ideally need to no what other people are achieving.

I understand all cars are different due to set up but I'm just trying to see Aprox what I should be achieving on this turbo as 4200 is just way to late...

I have a avcr in place but need a degree to work it which was set up during mapping, also I'm still on the Sti tmic as I wanted to see how that performed first prior to going fmic.

Any help would be appreciated :thumb:

Who mapped it pal?

I'm the same mate got a sc42 reworked by owen developments into a 30/76


about 4200 before I am on boost,


Mine is single scroll however so thought yours would be better,


I also have gt spec headers and Harvey uppipe,


Most turbos that make a real 400bhp on a 2.0 don't make any real power below 3500 (If there is show me :))

3600rpm 1.6 bar on Owens version of lm450
I insisted on them using the litchfield housing it even says litchfield turbo dynamics on it

Is this still on a 2.0

You got a power/torque curve for that ?


What numbers it make at that 3600rpm ?

Hi Raggy, see that's what I'm talking about ! Do
You have a Dyno graph ?

What boost and gear?
Top mount still?

Why using an avcr and not a proper map?

I'll dig graph out hks fmic 3 gear

So is this on a 2.0 ?? :wonder:

Ya

Get this graph dug out then,

Really wanna know what it's making and when :thumb:

Sounds like all you would need on the road,

Can you remember the peaks at least if can't find the graph ?

So is 4200rmp approx the norm then, I was sort of expecting
To be hitting it around 3700 :(.... I mean the sub is performing excellently
Just would be nice for it to around 500rpm lower....

At least yours is JDM and Revs out to 8k,

Some of us have to change at 7500 :(

The "usual" test for spool point is to do a run, in top gear, from low rpm. Note the point that you see 1 bar, and the point you see full boost. The 1 bar point is used as a comparison.

For example, my 500bhp 2.5 twinscroll, on an LM500, hit 1 bar at around 3400, and full boost at 3800/3900.

On the road, in lower gears, not a lot happened below 4000 rpm, but that's why you have a gearbox ;) And the JDM close ratio box assist this.

Main thing with mine was once you were going there was negligible lag during gear changes so acceleration was a brutal experience!!

Hi Tim

Thanks for that explanation :) in which case something is Definaltly not right I think, sooo here are my figures

1st gear, 1 bar @ 6500rpm approx
2nd gear 1 bar @ 5500rpm approx / full boost achieved around 6500rpm


I'm not sure where I got my original 4200rpm figure from now :wonder: but the figures above are there or there about.


I hardly see boost in first unless I'm giving it some :/

Any thoughts

Don't worry about 1st and 2nd gear for the moment - do a pull in top gear and report back.

My car is mapped to hit 1.7 bar,

I will do a few runs and log at which point i reach 1bar,

I do find that in 1st & 2nd due to how fast the car revs it doesnt read 1.7 on the gauge, i would guess this is because it starts boosting at 4000/4500 but revs out quicker than boost builds if you can understand what i mean.

You're very unlikely to see full boost in the lower gears. My map actually lowered the boost target in lower gears so as not to break traction.

So is it normal not to achieve the full 1.7 bar in 1st & 2nd on a 2.0 if using a larger turbo ?

I'm also still on stock ECU if this isn't helping

In my experience, yes, that's right.

Stock ECU, *properly* mapped won't be an issue.

Thanks man, :thumb:

I'm waiting on bob Rawls to resend me the graph I get 1.6 bar early in every gear

Hi Tim, thanks for all this advise :) I took the sub out for a spin see if I could get the figures in 5th and 6th although I'm doing this by myself so a little tricky but these are the figures that are approx there or there abouts

5th gear @ 1 bar 3500rpm
Full boost at approx 1.6/1.7 bar @ 4100

6th gear @ 1 bar 3200
Full boost at approx 4000 rpm



Dose that sound about correct or am I gonna need to get a second person in the car with me to make it more accurate ?

Thanks :)

That's accurate enough for this purpose :thumb:

I would say the 1 bar point, at 3200 rpm in 6th, is spot on.

Full boost is a little late though, in my opinion - I'd be hoping for 3600-3700 in 6th I think (although I am not a mapper, nor did I have a 2.0l). It might be possible to improve this in the map - maybe AVCS needs a tweak, or the wastegate duty/timing/fuelling/etc. adjusted to improve spool.

But it's not a million miles off what you would expect for this turbo on a 2.0l I would say.

Ok thanks Tim, tbh the car dose drive very well I just wanted to be sure that everything is as it should be so really happy :) it may have been 3800- 4000 in 6th.

When I next go for a spin with someone I will look for a more accurate figure in 6th at full boost, but thanks again for all your input :)

Who mapped it bud