[AngryInch]

I have a 21 comp, JB4 map two with 94 oct pump fuel, running good. I just ordered dps and mids, catless.

Does the ecu have enough capacity to auto tune the AFR for the increased flow?? Has anyone run this exact setup?

Typically, most cars require a retune for cat removal due to increased flow and fuel requirements...

[AngryInch]

This is exactly what I was thinking... Fuel trims typically do 25% +/- before a code is popped and or they lean out with no further compensation... Im not sure the ecu can add enough fuel to cover the extra flow of the downpipes...

I seen there was a tech on here that did DP with no tune, I msg'd him but no reply yet. He is stock tuning however, which will be less fuel.

Since the JB4 is piggy back, the ECU would be adding extra fuel via the trims to compensate for the extra air, I guess I could do a log and see where the trims are... Do the trims work in a percentage of their baseline? IE, if it said 10, that is 10% extra?

Thanks for your reply.

[pbonsalb]

You would want a flash tune with revised vanos mapping to take advantage of the reduced back pressure.

[AngryInch]

One day, once they release a tune for these...

I talked to a couple friends and DME, they said it should be fine. I’ll run it easy, check logs and put it on the dyno..

[apsuard]

I have this same setup on my M5 but I haven’t been able to test and log since it is so hot and humid now. I will say the car “feels strong “ on Map 2 but I haven’t pushed it hard until I can test and log.

Terry said the car will adjust and I shouldn’t see any issues but I need to test and confirm that. I’m out of town for a few weeks but will test some different fuels and maps when I get back

[AngryInch]

Only thing is... testing on the street, by full throttle blast without knowing how the afr and trims are till after a run is not the smartest idea... if it runs lean, you won’t know till after and that could lead to engine issues...

I’m going to hook an afr gauge to the secondary o2 bung and see how it goes. I might out it in the dyno after install and start small first...

[Mcc420]

Originally Posted by AngryInch

Only thing is... testing on the street, by full throttle blast without knowing how the afr and trims are till after a run is not the smartest idea... if it runs lean, you won’t know till after and that could lead to engine issues...

I’m going to hook an afr gauge to the secondary o2 bung and see how it goes. I might out it in the dyno after install and start small first...

If you watch live data you should see it right away. No need to hook up a wire. Just use the app. Plus Jb4 has fail safes for that.

[AngryInch]

I did some reading and talked to tech at VP fuels. As I suspected, ms109 will cause your tune to run lean as the stoich value is 13.3. VP recommends adding 5-7% additional fuel to the tune to compensate for the difference in stoich vs pump gas.

Browsing their website, I seen ms103. It has 1 lower octane, however, the stoich is 14.2, which is much closer to pump gas and a better solution for race gas without tune changes. I just ordered a couple pails and will test it out shortly.

[apsuard]

Originally Posted by AngryInch

I did some reading and talked to tech at VP fuels. As I suspected, ms109 will cause your tune to run lean as the stoich value is 13.3. VP recommends adding 5-7% additional fuel to the tune to compensate for the difference in stoich vs pump gas.

Browsing their website, I seen ms103. It has 1 lower octane, however, the stoich is 14.2, which is much closer to pump gas and a better solution for race gas without tune changes. I just ordered a couple pails and will test it out shortly.

I will also do some testing with 93, 93/102 mixed (~100), E30 (93/E85) and will report back and post some logs.

My car ran so strong and with clean logs with stock downpipes I’m hoping I didn’t mess up a good thing. The car sounds wicked but I want to ensure it doesn’t blow up also

[AngryInch]

I think DPs are way better for the engine, all that boost and flow from upgraded tunes, slamming into the cats, must create some decent back pressure... Letting this engine breathe is likely a positive thing. Report back, I think your results will be good. My DPs go on soon...