Best location for AFR Sensor Bosch LSU 4.9
 

The Bosch LSU 4.9 AFR sensor install instructions say to place the sensor at the hottest location.

1706°F is the acceptable running temp.
1886°F max peak for short intervals.

I have dry exhaust Stainless Marine Gen 1 with collector mounted O2 bungs.

I've heard on here to mount the O2s 6-10"s past the collector.

Though technically, the gen1 Stainless manifolds have a large open area where the collection happens...and the joint is above that.

I have CMI ETops - the O2 sensors are in the tailpipes about 5 or 6 inches away from the flange and clocked at the 10-o'clock position.

Not sure it helps with your SM exhaust but the concept is the same.

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Heat kills , I moved mine further back .. not sure if it helped thou ..I always change too much at once lol


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Thanks Dan. Good info on the Holley system install manual.

Probably the hottest location is a few inches past the actual tube merge point.

Adding another concept...should I place the O2 sensors on the same sides of the twin engines...or 1 port man...other engine stb man?

B&M 420 Blower fed.

Ive done it both ways and really didn`t find much difference.

Check, the 420 doesn't load up one side at lower rpm like the Whipple.

I'm thinking maybe the reason for the angled down sensor is to shed condensation?

The 8.3l whipple loads to one side ? Which one?
The condensation question is above my pay grade but I would think it has something to do with the exhaust flow.

Edit: why point o2 down ?
Water.
Lots in vehicles exhaust now too.

Not specifically the 8.3 Whipple per say, just a factor of how they want to spin fast. If they're slowed down, having a factor of poor distribution left/right.

Tried to find the links. Eddie Young may have been the source.

You're running injectors in your tunnel ram if I'm not mistaken, so wouldn't affect your setup.

If I'm off the ball here please tune me up. This is speaking more to the carb'd or pre-rotor injection systems.

Round table talk…..Pretty sure the whipple thing is frt to rear issue, not left to right, as the discharge , on most , is at the end of the of the supercharger.And because of packaging, the discharge is not placed in the middle of the lower intake the sc is bolted too. It is placed at the very end.

The advantage with the roots , in this topic, is the rotors don’t pull air in from one end and discharge at the other. It pulls from the top and discharges to the bottom.

I really never noticed a difference in fuel distribution between the Whipple and 10-71 . That being said all the fuel comes in the front so I have ( 8) 100lbs injectors in the blower and (8) 43# injectors in the ports since i would think the fuel distribution is leaner in the back
Should probably be reversed but it is what it is for now.


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Correct, this is an issue on any screw blower with a male/female rotor. The blower will usually pull the heavy fuel through the female rotor and then throw it into the opposite bank and rear cylinders. (By a couple of percentage points.) That is until you hit a certain amount of boost, then it all starts to even out. The physics of this I do not understand, I just know I have seen several motors with 400* EGT deltas until the boost gets up to that magic number. If I didn't have individual widebands, I would think the inverse, that all the fuel was going to the colder cylinders. The AFR spread has been almost 3 points on some engines. It may be more related to blower RPM than actual boost, but I haven't tried the same blower set up on different head and cam combos to define the catalyst.

Port injection corrects a lot of this, and that's why (I think) the port injection manifolds are becoming more popular.

It would be interesting to test a 454 at 10PSI and then bolt the whole top end on a 540 or 572 and retest at 10psi. Keeping all things relative that would help tell the story about what causes the phenomenon.

PSI makes a defuser or turtle that goes directly under the discharge of the blower for that reason.

There is a video of a clear intake I wish I could find ..

I’m in for $50 for rotor speed too. :)

Precision, thanks for the good info, I was trying to find where I read that..and just couldn't find it.

O2 sensor locarion info, seems to also have a factor if distance from the exh port. 24" for NA, 36" for Supercharged. Turbos want the O2 post turbo.

Assuming this is to allown the FA combustion to finish up in the pipes if over fuelled or late ign timing. So the O2 sensor gets the mostly combusted FA mixture to analyze, and keep out of flame.

The angled down position is to shed condensation. Especially when hot.