[BRYN-THOMAS]

Hi guys
Would increasing boost (roots) by a couple of lbs make a diffrence to air/fuel ratio.
Had car on chassis dyno all good 440hp at wheels uncorrected at 5lb boost so got room to play.
Three good runs last sunday 10.75 10.74 10.78 at 124 60ft down from 1.8s to high 1.5s mickey thompson sportsman pros seem to work at 9-10lbs
cheers

[johnta1]

Technically, no or depends.

What do you have for an induction system?

[ponchospidel]

to be safe, you should jet it up if you are going to increase boost levels.
then lean it out afterwards.

[Tom Vaught]

1) Buy a good air/fuel wide band ego sensor system.

2) Start rich, as was said, 11.5 and slowly move toward 12.2

You want the a/f to be a flat line at all rpm points under wot.

Tom Vaught

[baron_]

indeed on wideband
lm1 with XD gauge is quite nice

[ponjohn]

Curious where is the best place for the a/f sensor ?

[baron_]

best to have a heat sink or something...or bung extender
and put it 18" to two foot? past the turbos...so it doesn't overheat
The closer you go to the turbo, better chance of an error or overheating the sensor....


But needs to be in front the end of the exhaust at least a foot maybe two (or you'll read some of the reversion, on occasion)

And there's a whole discussion regarding the angle of the actual sensor, so it doesn't collect condensation

[GTOGreg]

Originally Posted by ponjohn

Curious where is the best place for the a/f sensor ?

I put mine at 9 o'clock (LH) and 3 o'clock (RH) about a foot past the elbow on the downpipes coming from my manifolds. You don't want them below this as condensation will shock the O2 sensors and ruin them quickly. 10 and 2 o'clock would be even better - somewhere in the top 180* of the pipe. Keep you wire run to the firewall in mind.
Wideband is a GREAT investment for peace of mind with your AFRs. You 'll want to wire your meter to the tach at a minium. Then, depending on your meter you can measure/map/monitor intake air temps, EGT, manifold air pressure, etc...(if desired) . I bought the LM2 from Innovate and it was the best $350 I've spent to date.

[BRYN-THOMAS]

Originally Posted by johnta1

Technically, no or depends.

What do you have for an induction system?

2 750 Mighty demon blower carbs 8/71 stage 2 bds blower and intake ported 87cc e heads, 15% underdriven.
was thinking of fitting some sort of data logger to get a/f, boost, rpm, any suggestions?
thanks

[Tom Vaught]

Check out this forum:

http://www.innovatemotorsports.com/f...isplay.php?f=3

They have good air fuel meters but what is even better a forum to discuss all parts of the system and the data logging.

Unit can log several things and display on a laptop easily.

Tom Vaught

[BRYN-THOMAS]

Thanks Tom exactly what i wanted

[Mr Twister]

Originally Posted by ponchospidel

to be safe, you should jet it up if you are going to increase boost levels.
then lean it out afterwards.

Thats what I did on my roots blown boat motor. I ended up back where I started at jet wise. Must be OK-It hasn't melted down yet (50ish hours since the boost increase) I only have plug readings and an EGT to go by, no wideband 02 sensor.

[Tom Vaught]

So Mr Twister, what was the original Boost Level vs the increased Boost Level of your boat engine?

Boat Engines typically run cool so they can be leaner vs a car engine and Carbs typically have a pretty wide range of Air/Fuel ratio vs the speed load.

Carbs can actually add more fuel with the same main jet size depending on signal to the jet.

Tom Vaught

[Torment]

I'd insure you found the optimum jet for the current drive % if you haven't already. I varied my OD % a good deal from street to strip driving - but the jet was setup for best performance with the greater OD in good air.

[Mr Twister]

Originally Posted by Tom Vaught

So Mr Twister, what was the original Boost Level vs the increased Boost Level of your boat engine?

Boat Engines typically run cool so they can be leaner vs a car engine and Carbs typically have a pretty wide range of Air/Fuel ratio vs the speed load.

Carbs can actually add more fuel with the same main jet size depending on signal to the jet.

Tom Vaught

5.5 no intercooler, to 6.5 BELOW the intercooler installed at the same time. I think you lose 1 pound of boost due to the intercooler on this application. The engine does run a steady 155 deg. I havent run a roots blower on a car, so this may not be apples to apples.