I was going through some old and new logs, (various injector setups) looking at my front and rear egt's. I noticed that my egt's front to rear have never really varied that much from each other. I am a stickler for flow testing and cleaning injectors and have never had any that didn't balance with a percent or two. Based off what everyone says the stock UIM has uneven to the rear rotor. Those that can record it (my assumption is egt only) has this uneven flow been seen or recorded with the stock FD LIM? Not sure it matters but this is using block off plates.

If you see my post on lopey idle egt's and get confused, my egt's are not equal at idle but as soon as I get above idle they track together through WOT.

 

Upper intake is pretty close in flow, but having an elbo right before the trottle body tends to make the rear get more air. The lower intake manifold seems to be the main problem, as there is a significant difference in secondary runner lengths from front to rear, hense the Xcessive manifolds being manufactured to cure this problem.

~Mike..........

 

most people see uneven EGT's from front to rear at least somewhat. I personally don't think it has that much to do with the stock FD LIM. I say this because my stock Series 5 Turbo II LIM has no flow imbalance and I see 100-150F higher temps on the rear rotor.



One theory someone has mentioned on here is that the rear rotor runs hotter because the coolant hits the front rotor first and heats up before going to the rear. Possible uneven placement of exhaust temperature probes doesn't help with the precision of the measurements either.

here is a pic of my series 5 LIM, it's not the best pic but to me it looks like the flow is pretty balanced.

 

I understand why they made the manifold but I just have not experienced uneven egt's which I believe would show the imbalance of the stock lim. I do have the Greddy elbow though but if it really was an issue the elbow i would not think would make a lot of difference.

 

I pointed out the LIM having a bigger difference in flow because YOUR post implied people were seeing differences in the UIM, not the lower. Maybe you have your acronyms mixed up. I also find that using EGT's very difficult to get front a rear differences. They need to be placed in the EXACT same spot, and most exhaust/turbo manifolds have different bends from front to rear which would skew the data even if the probes were placed the same distance from the port. You'd probably see better data using wideband sensors again, placed the same distance from front to rear in the same type of bends, even after that you'd probably still need to swap the sensor with one another and take the same data again to have any kind of comparison.

~Mike...........

 

Sorry meant LIM no UIM. I have actually swapped sensor to determine how far off they are. They are actually a lot closer than I expected. My EGT's are placed 1.5 inches from the outlet in very close to the same place. So I believe my setup is accurate for temperature readings. That's why I wonder who determined the flow was off. Physically the runners are different but in the real world sometimes items like this make a much smaller difference that what they appear.

AFR would probably be better but I"m not sure how long a WBO2 would survive at that temp. I get overheat codes with my WBO2 sensor in the downpipe with a heatsink can't image what would happen at the port.

I would think the coolant temperature difference front to rear would cause a difference as well how much would be an interesting topic. I have seen some threads pondering temperature as the problem with more rear rotors blowing which would make sense.

 

my thoughts exactly

 

You can see a SIGNIFICANT difference in temperatures from placing the sensor on the inside OR the outside of a bend radius withen a manifold!

~Mike...........

 

Here is a drag run i did, I am not 100% done with my tune, still rough

The Pre Turbo EGT's have the same sensor 1in from the flange

The Post Turbo EGT's have the sensor 3in from the turbo.

I have the Stock lower and upper intake with a Greddy elbow.

 

Interesting seeing the 300 deg difference in temperature between port and after turbo. Looks fairly even to me.

 

I guess the question would be then whether these significant differences in intake temps are the main reason for an observed difference in exhaust temps.

 

Also, this is only at about 16psi, and my turbo is barely in its efficiency range there.

I cant wait to run 25+ pounds on it, I think I am going to break something down stream.

 

A lot of it has to do with the uneven runners on the lim because of the emissions ports cast in. The ground zero lower evens them out significantly.

 

Just because they are uneven doesn't mean they are actually an issue though. That's why I started this thread. I couldn't see the any issues based on the EGT's that the runners could have been causing. Do you have data showing they cause uneven flow?

 

The rear rotor always tends to run leaner because of this and that is why compression is usually a little higher on the front rotor. I would say about 90 percent of cars I compression test are higher on the front rotor than the rear.

 

That's actually one thing I have never understood, if the rear rotor flow less why would it run lean. Wouldn't it run fat. If your egt's are similar wouldn't you say that the afr's must be close though?

Same idea if you had the EGR working it would increase the temperature in the rear runners giving less flow and therefore would be running richer, not leaner.

Running richer on the rear rotor might also cause the oil lubrication (if using the OMP) to wash away some of the lubricant allowing the rear chamber to wear more and read lower over time.

I don't doubt the compression being lower in the rear what I do doubt is that its running leaner, but this is based off EGT's and not AFR.

 

Wait are you talking about the FD or FC lower?

 

I am pretty sure he is talking about the FD LIM.

I am pretty sure the rear runs leaner b/c it not only is shorter, but also has a more direct flow of air as it comes through the elbow, tb, uim, lim and then the rear rotor housing. This would theoretically result in leaner mixture as compared to the front rotor.

It is interesting you are not picking up any differences in egt from front to rear rotors. Maybe this is just not as significant as once thought (and I know that is the point of this thread).

 

FD Lim.... The rear runner though has 2 distinct dents due to the EGR casting (I recently milled off the EGR chamber to see what's underneath). Maybe this was done to inhibit flow?

 

I do have the lag set just a bit different because of the lower intake runners. Maybe this is the reason why my EGT's are not that far off.

 

I don't have any injection trims on mine setup and don't see a difference.

 

Cool photos, Fritz.

 

Maybe you're not flowing enough air to see a issue with the stock LIM.

 

I'm pretty sure those dents are there to clear the stock turbos.

 

Need some Air movement


I agree