Boost Level and A/f Ratios
 

If you were running x boost and had a/f ratios of 11.6, then changed pulleys to add 2psi, what would you expect the a/f ratio to do? Go richer, go leaner or stay the same?

I would expect leaner, but that appears incorrect. They actually went richer to about 11.25-11.3. Is this normal?

BT

All depends on how the original mapping was set up.

It's sounds as though itis running in a different fuel table cell with the additonal boost, I would not question the accuracy, sounds reasonable.

Yes it depends on the mapping, provided it's EFI. My mapping outside of the normal ranges, is on the rich side. Its safer for the stort term.

Sorry, 1050 dominators. No Efi.

Who setup the carbs? There not box stock are they? Setup is the key.

The carbs are merc 525sc takeoffs. I am tuning them with an o2 sensor. I'm just curious if getting richer a/f readings is the norm when upping boost. I was expecting it to go leaner.

Is based on the vacum signal past the ventures. I would have guessed since you up boost the amount of air thru the carb goes up thus richer a/f or the same.

If your motor doesnt require more fuel.be its out of cam, cant flow enough air, load on motor is less(Less load
less fuel needed) ect.... can make this happen. On our 1000hp motor we had to take fuel away up top because the cam was to small and couldnt make enough power past a certain rpm. Also is your system boost regulated?
are you running the same rpm or are you pulling more due to power gain?

Interesting. I didn't seem to get hardly any rpm increase. I attributed this to it going richer, but you bring up some valid thoughts. No boost regulation.

Did you notice the need to pull jetting out after a boost change upward?

All the carbs "know" is more air is going through them. The amount of fuel delivered at this higher air flow depends on carb setup and could easily be a lower A/F.

Lots of possibilities for no RPM increase but one reason may be that the extra 2 psi is mostly due to heat and air density has not increased much.

Yes, I was afraid that may be the case tomcat. But I was hoping because the the relatively low rotor speed I am turning (even at the higher boost) that would not happen. I am at ~10k rpm and the stock 525sc I believe ran 12k rpm, both with no innercoolers. I'll have to try the larger pulleys again (9.3k rpm) to see if the rpm still remains unchanged. There are just so many variable when trying to water test this stuff, getting meaniful comparisons run to run can be a challenge.

Thanks for all the input.

BT

The stock 525SC runs the 177 blower at a 2:1 ratio. At 5200 engine rpms, the blower is at 10400rpms. Max recommended rpm for the Wieand blower is 12500 rpms(if I remember right). I was spinning mine at 2.5:1 (7.5#) for right around 13000rpms. Just change the lube often.

I bought some 525sc take off 177s and they came with 3.070" upper pulleys and 7" lowers. I assumed because the upper pulleys were splined that these must have been the originals. I can only find keyed pulleys in the aftermarket. Anyway, thanks for the correction. I did have 2:1 in my notes from winter research but guessed that must have been wrong.