Car is SD tuned. Should have mentioned that, haha

 

All good articles that I havent read before.

 

A MAF is tuned for the air flow through the tube it's mounted in. If that doesn't change than neither does the calibration. Sometimes, in MAF mode, the vehicle will still reference the VE tables. And that's one (of a couple) reasons I tune the VE tables, then the MAF. I have noticed that if I tune the VE tables then return to MAF mode, and the MAF mounting has not changed (in location or the piping before and after it along with orientation) that I'll not need to re-calibrate the MAF.

Basically, if it is a MAF tune and all he changed was the exhaust, the MAF will not need adjusted again in the tune. In MAF mode, if there is less air moving through the engine it'll fuel less. It only cares about MAP and IAT to target AFR's. It doesn't look at RPMs. So it doesn't know that the engine is moving less air because it doesn't know it's RPMs.

In SD mode it doesn't know actual air intake and it uses the MAP, RPM, and IAT to calibrate the fueling.

The benefit of the new exhaust is less back pressure. It's pumping losses have been reduced, therefore the engine is more efficient at making power per drop of fuel (BSFC). So it doesn't NEED to flow more air because it has less resistance through the exhaust primaries.

So it lost exhaust scavenging, but gained efficiency, ending at the same power (maybe even a couple horsepower more). In the end, on this build, it was worth it IMO. He lost little low end torque, gained efficiency, and lost no high end power. But, it'll only gain exhaust gas velocities from here with future mods. So it'll show it's worth in the future with larger power gains than the 1-3/4" headers would've put out; especially since it only cost dyno time.

 

Uhhh, incorrect. Under WOT it is in open loop relying on a power enrichment and using the VE table to calculate incoming air. No MAF, No stock o2 sensors, straight up PE and VE.

What ever is in the stoich setting of the tune will get divided by the PE multiplier.
When PE multiplier is set to 1.148 it will shoot for 12.8afr assuming stoich is set to 14.7

14.7 / 1.148 = 12.8

VE is then adjusted to correct the actual airflow the motor is seeing through the MAP and RPM range.



I do agree that getting AFR in line could increase the power seen.

 

My stoich is set at 14.62 and your right about it using the VE table at WOT in conjunction with the PE table and thus the reason why it wont fix itself. The outcome in my opinion shows that the setup was damn near perfect with the 1 3/4. When I decide to go bigger the 1 7/8 should help out but not with this combination. I also agree it will pick up power but it wont be much after I lean it back out and nothing to write home about. Either way I learned a lot from this comparison and enjoyed doing it Plus the car sounds much better from the old exhaust setup. I am going back to the dyno in a few weeks with the 150 shot and purchased HP tuners and a wide band so we will see exactly what leaning her out does

 

I wrote that response before the op stated he was in SD. The PE table is just a multiplier as you stated and will reference whatever table from the tune its told to. I assume (because the op never stated differently) that he ran a maf in which case above 4000 at wot the PE would be jiving with the maf table to get proper fueling not the ve. The O2's are ignored because its open loop but the maf is referenced normally for wot assuming no SD tune

However since he is SD then then pe is referenced with ve. The PE doesnt care which table is being used its just an equation for proper fueling.

I agree though that without correcting afr the results are not valid

 

The results are valid if you can think outside the box and see what the 1 7/8 header did even without a retune and no one is arguing that the car wont pick up some power up top but its not going be much, plus it hurt the lowend a bit.

 

Trust me, my degree is mechanical engineering and fluid systems. I understand very well what they did. I'm merely stating in order to get a fair comparison the af needs to be corrected. There's sinply too many variable to say they may or may not et better the truth is that no one knows

 

LOL, I could tell you were an engineer by your responses (I work with a few) You guys have to have your empirical data and won't budge without it We will know for sure in a couple weeks though and what it does with a 150 shot to boot.

 

I think the 1-7/8 will shine more than the 1-3/4 on the juice.

 

Always interesting thread!
Wonder why any of our experieced sponsors havent never join the conversation.
I have experienced twice the power loss from going to bigger primary. Last time was when i changed stock manifolds to 1 7/8 in a stock LS1. I can feel the loss of torq but its not dynoed.
First time was when i did trackracing pretty seriously few years a go and did alot developemet to that race engine. I notice that in a 1800cc engine 2mm primary diameter grow i lost 10hp/10Nm. Length was all the same. At the dyno it went rich and it never came up when we corrected it, so i changed back to smaller primary. The bigger isnt always better. My LS1 street car what i have now, i really respect power under curve, so in a street use i think 1 3/4 is a best average shoot for every small cubic LS street engine.