[s346k]

i believe on NA motors it's widely accepted that one can consistently manipulate the map kpa with air intake modifications. ie if you see 100 kpa @ the start of a pull (2500 rpm) and 90 at the end (6500 rpm) there's a good chance you have a restriction, presuming the car has no other obvious issues.

my question is... is there an accepted horsepower value assigned to the kpa drop? i'm presuming it varies by engine and is a percentage based value.

i know it's not a one size fits all definition of scenario, but other cars i've had showing a drop like that really didn't gain much at all after correction. after comparing logs, my car now shows 96. im on the fence about a cai, as i am still using the stock one. it does very well with insulation and general function. the car picked ~67 whp / 73 wtq on the dyno with only a ported stock intake, full exhaust and e85. stock air box and stock tb still. the car runs hard, i hope to put a number on it at the track soon.

any of you guys with similar mods and rotofabs showing a similar kpa loss? i'm moving up to an msd/95 mm tb soon and don't want to leave 20 whp on the table by using the stock air box. but truth be told, i don't think there's much gain to be had at all with only bolt ons: rotofab vs stock.

fun fact: i saw kpa values as low as 93 before i cut the air box.

is this something anyone even looks at anymore on stockish cars?

[Snowblind]

Monitoring kpa is a thing and I watch it religiously. Their was a H/C car strapped to a dyno at my local shop, had a MSD and ported 87. I forget the numbers he put down but I saw his kpa was down to 94 (we are at sea level for reference) on a pull. I had the guys take my 95 off my car and swap it out while still on the dyno. 24 hp gain with no other changes.

[s346k]

that's what i'm trying to figure out. 94 on his car and 94 on mine have to be different. i know weather will affect density etc. ill find out soon enough, i think i'm going to swap the intake & tb while leaving the stock air box in place. see what i get. then swap out the stock air box for a rotofab while still on the dyno. hope the tuner is ready for a day of slow car bullshit haha.

i'm trying to get real person numbers. i am very skeptical of any numbers that shops and vendors post.

[s346k]

i've seen where i believe pray swapped a stock hacked box at the track for a rotofab. i want to say it picked up something like .5 mph. i also think an a8/10 car is going to be less sensitive to small changes like that.

[BDPhoto519]

You convinced me to go check my logs...

My 3 dyno pulls the other day show I started at 99KPA@2500 and finished at 97KPA@6400 right at the very end.

Pretty stock setup, just 2" TSP headers w/cat delete and RotoFab Dry, pump gas pulls on a hot and humid day. Baro(SAE) PID was reading 99KPA and flickered to 98KPA occasionally during the pull. The fan was tiny and not doing much in front of the car.

[BDPhoto519]

I checked a log from last weekend doing some 1/8th mile runs in Mexico.

They all started at 99KPA and ended around 97/98KPA

[cmitchell17]

Originally Posted by s346k

that's what i'm trying to figure out. 94 on his car and 94 on mine have to be different. i know weather will affect density etc. ill find out soon enough, i think i'm going to swap the intake & tb while leaving the stock air box in place. see what i get. then swap out the stock air box for a rotofab while still on the dyno. hope the tuner is ready for a day of slow car bullshit haha.

i'm trying to get real person numbers. i am very skeptical of any numbers that shops and vendors post.

I am really glad you are stepping up and saying you're not trusting vendors and "tuners". They are making a fortune as long as people keep taking their word for it and don't question and verify.

I have also asked around on the HP Tuners forum and elsewhere as to the best ways of doing what you are trying to do here. Unfortunately no one seems to be interested in trying to use the built in engine sensors we have at our disposal for free to gauge performance. I will say I have way more faith in these than I do some "tuners" dyno.

I have been using the APC (cylinder airmass, dyn airmass, etc.). GM has named the PID like a million different things over the years. I have given though to just using the MAP sensor as well, however my questions are the sensor is at the top of the manifold subject to the plenum pressure. Is there a significant pressure gradient in the manifold? Is the MAP sensor only indicating pressure drop of the throttle body? or is the intake runners included? I would think looking at the MAP sensor would only give us the restriction and pressure drop from the TB and everything upstream.

Here is mine, ill try to go back and get a log before heads/cam for comparison and add it to the graph as well:


Also in your logs does your barometric pressure increase at WOT? I always take my baro readings at a non WOT point in the log otherwise they get aritfically skewed or increased at WOT. I am guessing pressure is leaking into something somewhere. The thing is this happened even when stock so I'm not sure what's going on.

[s346k]

eh well i got impatient. wanted to see what the rotofab is all about. not sure what to think yet. iats and kpa are nearly identical to the stock air box i cut up. weather was about the same. i didn't see any evidence of a ram air effect when looking at the wot logs of the rf cai. kpa began steadily dropping at the same rpm the stock air box did. basically i couldn't tell any difference whatsoever between the 2. i noticed the factory intake tube looked like it would work with the rf box, so after fighting with the coupler for a bit, it went together. the rf tube is thinner and much lighter than the stock stuff, i wasn't trying to use it if i didn't have to.

at stockish power levels the air intake restriction isn't in the air box or the rf cai is no better than a hacked up stock one. im reserving an opinion until i can get more substantial info.

hopefully the msd intake manifold i ordered 2 weeks ago will show up soon. waiting sucks.

[cmitchell17]

Originally Posted by s346k

eh well i got impatient. wanted to see what the rotofab is all about. not sure what to think yet. iats and kpa are nearly identical to the stock air box i cut up. weather was about the same. i didn't see any evidence of a ram air effect when looking at the wot logs of the rf cai. kpa began steadily dropping at the same rpm the stock air box did. basically i couldn't tell any difference whatsoever between the 2. i noticed the factory intake tube looked like it would work with the rf box, so after fighting with the coupler for a bit, it went together. the rf tube is thinner and much lighter than the stock stuff, i wasn't trying to use it if i didn't have to.

at stockish power levels the air intake restriction isn't in the air box or the rf cai is no better than a hacked up stock one. im reserving an opinion until i can get more substantial info.

hopefully the msd intake manifold i ordered 2 weeks ago will show up soon. waiting sucks.

I tried to test my rotofab, heres what I got:

You can ignore the spikes since you have 2 different runs and there is no way to compare airmass at a common RPM unless I can figure out a better way to have excel interpolate between RPM points. It does look like the rotofab is increasing airmass above a certain RPM though.

[s346k]

what gear was that done in? interesting how there's a larger gap @ 5k than there is 7k.

[cmitchell17]

Originally Posted by s346k

what gear was that done in? interesting how there's a larger gap @ 5k than there is 7k.

I think it was second, I would have to go back and look at my logs to see. One of the problems is that between runs we don't have the same RPM points to compare, but we can look at similar RPM samples. I just can't think how to quickly do it in excel. You can just dump a raw data export from HP tuners into a pivot table and pretty quickly filter it out to see some useful data, but HP Tuners doesn't have an easy way of exporting data for analysis, I wish they would just build in a feature to compare log files easily instead of just dumping a huge CSV file with a bunch of unnecessary data.

Another thing we could do is compare the torque PID's from each run, then multiply them by their respective "Air Density Torque Multiplier" PID, I believe this would give you a "corrected" torque to compare between runs. Then the problem becomes which "torque" PID do you use, there are like at least 4 you can log on the GEN V E92's and I haven't been able to confirm each ones purpose (delivered engine torque, driver demand, driver demand pedal, etc.)

[s346k]

im not sure how accurate the torque pids really are. my delivered says 600 @ 4800 rpm. it said 425 when the car was stock.

[s346k]

also the laptop i'm using is 14 years old. i've removed everything i possibly could in order to run hpt as smoothly as possible, as that is the computers only purpose. the only time i ever had it on the internet was to download the cars stock file.

[cmitchell17]

Originally Posted by s346k

im not sure how accurate the torque pids really are. my delivered says 600 @ 4800 rpm. it said 425 when the car was stock.

Yes we need to figure out which torque PID is directly related to the airflow model. I don't think we should be concerned about its absolute accuracy, but more its accuracy from run to run. So we need to find out which torque PID the "Air Density Torque Multiplier" plays a factor in. With all the hassle in exporting data to excel in HP Tuners (EFI Live allows you to quickly highlight sections of data and displays average and MIN/MAX values and also tracks the reference cell back to the tune tool) I think this would be the quickest way to gauge performance.

We still won't be able to identify any improvements related to pumping or frictional losses but I would think those are very minimal compared to volumetric efficiency enhancements.