I'm thinking about lowering my turbo transition about 500-1000RPMs. I have a datalogit(although I've never hooked it up) and I was wondering if anyone's done this? I'm sure someone will ask why I want to do this so I guess I better say it now. The BNRs I'm running don't produce a lot of boost on the primary(less than stock actually). Even with the prespool duty cycle at 90%, I still only get 10-11 PSI and that's right before transition. But once the secondary kicks in, the car pulls hard. I'm thinking if I lower the transition, I might be able to get better boost from 3500-4500RPMs and a smoother transition.

thanks
Hoody

 

I never tried it, but it seems like it could be a great feature for highly modded sequential cars. It seems like the primary runs out of flow/efficiency by 4500 RPM on cars with very free-flowing systems (intake/IC/exhaust). It seems like lowering the transition point might give a smoother power curve by brining in the second turbo earlier to handle the flow. My car jumped by like 100-125 RWHP in 500 RPM at the turbo transition when I was sequential.

However, since you have higher-flowing BNR turbos, I am not sure that will be true for your setup. It would certainly be worth experimenting, though. Perhaps one of those G-Tech Pro units with the "dyno graphing" feature would be a useful companion for the tests.

The settings for the turbo transition RPM are on the Settings 1 tab of the FC-Edit software for the Datalogit.

Anyone who has fooled around with this, please share your experiences.

-Max

 

The stock PFC setting already lowers the transition to about 4200 rpm. If you lower the transition point in the datalogit, you will also lower the rpm that the PFC keeps the twins in non-sequential mode. The default is 3k rpm, which is already too low IMO.

 

Well, I have a G-tech competition so when I mess around with transition, I'll see what kind of difference in power it makes. Seems like it should help transition a bit smoother.

 

Qoute " just do it, do it , do it now, do it good...suck that ..." Oh, forget the last part. D:

Do it and let us all know. Can't we also adjust the rpm in non-sequential mode of PFC too (what rynberg said)

 

The Settings 1 tab appears to have separate settings for the switch-to-both and switch-back-to-primary turbo transitions.

-Max

 

I've run mine another 200 rpm lower with good results. I also raise my back to primary to about 3400. The back to primary is preference. The initial switch works very well with no dip in boost response. You almost can't tell that the second turbo comes online, except that the car is pulling harder. It is really nice.

 

I have played around with mine also with very good results. I raised the 3000 rpm to 3300 to close the gap there where it will return to single operation. and right now with stock twins and all the flow mods and ported motor Im switching to 2 turbo's at 4050RPM. this helped the smooth feel when transitioning. and also smothed out teh verall boost curve. the way I adjusted was with feel (accelaration) and logging the boost curve. the smoothest of each was my target.

 

aaah...very good information, thank you

 

oh this one...ck ck...how could I overlook this thread...
Anyway, Houdini, did you have any success? I think it is annoying in autocross to suddenly come out of turn then your boost not there...

 

not yet, going to give it a try this weekend probably. As far as AutoX goes, the real advantage is not that you get more low end boost(although you might), the advantage would be a smoother transition. The abrupt jump in boost during transition can really unsettle the car, especially around turns.

 

This is great information. Please keep updating. This may help those of us who live at altitude and thus transition late. I may just be tempted to spring for the PFC.

 

I set mine to:
TPS% low high
60% 3760 4080
40% 35xx 42xx
20% 33xx 45xx

Now it switch to secondary at about 4000rpm, then switch back to primary by about 3800rpm. So the window where the secondary not spool up and primary out of breath is much narrow...

 

I think the low values could be determined by butt dyno, but a real dyno might be best. This debate could get real interesting with some non-seq guys in the mix.

 

you can plot boost versus RPM by recording it on the datalogit using Excel.

 

the low value is when it switch back from both online to only primary online... Really help with getting back on throtle between 3K and 4.5Krpm...