Just installed a set of 1600 secondaries, still running 550 primaries, stock sequential turbos, streetported motor, walbro fuel pump, automotive fpr with 38psi base pressure.

I've got a stumble as the secondaries come online. Currently I'm running Chuck Westbrook's settings for 1600's, namely

inj size 1600
lag 0.20
pri/sec transition(%) 20
Sec transition (ms) 0.100
Overlap 7 7 4

During transition the engine goes very "lumpy" (best way to describe it!) and I see momentary hits of up to 19 on the wideband. It's worse on part throttle, a heavy throttle run goes straight through with no stumbling, although there's still a brief lean spot.

I was running with Sec transition (ms) of 1.0 but it was much worse.

My question is where do I start adjusting next, I can't go much lower with the transition ms so do I play with lag settings or overlap?

Any help you guys can give me would be much appreciated. I've got a couple of logs if anyone has time to look through them.

thanks,

Steve

 

My transistion is 30%.
Try 7 7 5 or 9 7 5.

Is it consistant enough in recognizable areas where it might just be too lean in those areas?

Post your dat file.

 

I don't think it's a lean map problem as it moves about depending on throttle position. I also had no problems at all previously with the original 850's.

I thought I'd read you were on 20% transition. Did you try that and move back up to 30?

Dat file attached. I've changed the extension to txt to allow me to upload it.

thanks Chuck.

Steve

 

Go check your TPS voltages to see if they are in range and do not have any flat or uneven spots while slowly going from close throttle to full open.

 

Yo are running richer than me up through P 10 and I run richer beyond there.

See my dat(some stuff removed because it isn't for free).

 

thanks for the advice Chuck, much appreciated.

Had a spare half hour this evening so I went out for a bit of tweaking. Set the pri/sec transition to 30% and already it's 100 times better. Part throttle hesitation is mostly gone, in fact it only noticably happened once, a second gear part/mid throttle run. I'll try 7 7 5 when I'm next out, see if that cures it completely.

Still not happy with the afr's though but that should be sorted with a tune.

Checked the TPS voltages and they're fine, very smooth all the way through.

Are my mixtures different to yours because I'm still running seq twins?
Richer low down as I'm boosting on the primary, leaner high up as I'm not running as much boost as your single? I'm new to all this so please set me right if I'm way off here.

 

I have leaned out the idle and cruise areas to improve mileage, vacuum to 0 boost. Above that I have tuned for max power. From 0 boost to about 7psi, I run close to 12.1AFR with my single.

With non-seq twins, I taperd from 14.7 at 0 to 11.7 at 12psi.

 

thanks Chuck, it's good to have some numbers to aim for. Hoping to get out this weekend and get rid of this stumble, then the hard work begins!

 

This is handy information as I will be needing to do the same sort of thing in the next couple of weeks once my car comes back to me.

Fish