Z32_5.3

Hey guys, I have a built 5.3(stock port 706 heads) with twin eBay .68 gt35s, 80lb injectors, 92mm TB, ls1 intake...hptuners

i am about to order my exhaust. The turbos are 3” vbands so I am going to run full 3” exhaust and the cat back will be name brand so will have resonators and mufflers. I’m hoping car makes 7-800whp and was told at that level the catback will hurt me and to run cutouts.

That is fine with me, however, how do I manage the tune? Someone else will tune it, not me. Should I have the car tuned with cutouts open or closed? Will one tune be ok for both situations? Will it be safe if I tune for max performance with cutouts open and the close it and still beat on it once in awhile without cutouts?

I dont plan to always beat on it with cutouts closed but in the event I do, I don’t wanna blow it up either.

turbolx

1) Ran a MAF so the PCM always has a correct airflow measurement at WOT. (Changing exhaust backpressure can shift VE by as much as 20%, depending on the application)
2) Tune it for worst case (Cutouts closed) so that you have the higher backpressure and residual heat in the cylinder for knock tolerance
3) Drive and enjoy.

Z32_5.3

Map , no maf sensor.

Do you think ill be losing out on a lot of power? I’ve read a lot before posting and seems it could really run different when the cutout opens. Could boost higher too.

turbolx

If you aren't going to use a MAF to detect the actual change in airflow between the two conditions, and you only have one active VE surface, then you will be forced to tune for one condition or the other. This means you'd likely calibrate to the highest flowing (dumps open) condition that results in higher VE. The engine would run pretty rich with them closed, depending on how much difference it actually makes in pumping efficiency.

A MAF sensor just directly reads the airflow and lets the ECU adjust fuel/spark accordingly when flow changes. Since the GM ECU already has capacity for a great MAF measurement, I don't see why you'd want to throw that away in this case.

Z32_5.3

I attached pic of the area. Running maf would be hard to plumb. Unless I can use a blow through maf with my meth. I mean, I’m not against a maf sensor as long as I can still reach my power goals and not get held back from it. The Nissan world I live in can’t use blow through and limit to 500hp on one. So we have to plumb 2 and use special box to split signal. Not sure how that works on the LS ecu

LSX Power Tuning

iTrader: (4)

We have seen 100rwhp difference with cutouts open vs closed on boosted setups with full exhaust. In those situations all you can do is have 2 tunes and switch between them.

Z32_5.3

Exactly. I’m hating the truth at this moment... anyone know a way to switch tunes on the fly? If I run the hptuners on a tablet or raspberry pi, can you switch tunes while car running or do you need to recycle key? Is there some way I can do this if hptuners cannot?

ddnspider

iTrader: (26)

I believe Frost or someone had a dual tune PCM that worked with a toggle switch, just need to google. Otherwise need to flash 1 at a time. I was tuned cutout open as the difference was 30 whp at 8 psi. Assuming you're not running full time OL, trims will account for normal driving. WOT will be rich with the cutout closed as said above.

LSX Power Tuning

iTrader: (4)

Wont be able to do it on the fly. The dual chip pcm that used to be out (might still be) I think you have to still shut off to switch.

Z32_5.3

I spent ALOT of time trying to find something like the frost setup. Thank you. I just messaged on his website but didn’t see it as an option under products anymore. That would be perfect, get max performance under low boost with exhaust and max performance with high boost and cutout.

Z32_5.3

That’s ok with me. Could easily shut off quick in neutral and restart before doing a pull on highway. Prob take 5seconds max.

DFORESI

My suggestion would be to trick the PCM into running two different spark maps.

I would tune the VE table with the dumps open, but as it was mentioned before, tune the spark table and knock sensitivity with the dumps closed (as this is worst case for heat and back pressure)

If you find that you are able to add more spark with the dumps open then you could send a false frequency into the flex-fuel sensor pin to trick the vehicle into thinking it is running E85. Your flex fuel AFR table should be calibrated to 14.5 across the board, but this will allow you to use the flex-fuel spark adder table.

Essentially, when you open the dumps you can flip a switch that will tell the pcm to use the spark adder for flex fuel.

gametech

iTrader: (1)

Your best solution is to use boost activated cutouts. That way, you only run one tune. You get the full exhaust when cruising, and wide open pipes under whatever level of boost you set them for. The only downside is some people have a bit of rattling exhaust leak sound with them.

ChopperDoc

I like where this is going. Great idea here. Would ECT cut switch be another thing to think of to get control of spark? Similar to the IAT cut switch for nitrous... For his case ECT would be better since he's SD. Also, wouldn't you be able to essentially change commanded fuel using the OL EQ table to get control of that area as desired? It wouldn't be perfect, but it could be like "cutout enrichment" essentially.

This is why I love this ****. So many possibilities.

It's almost like doing the 2 bar MAP sensor trick to an N/A nitrous car. It basically gives you 2 VE tables at the flip of a switch, by throwing an extra 5V at the MAP to give it 105-210 range instead of the normal range. Hell even that could work if this is a 2 bar, by throwing more voltage at it to make it think it's 3, and bam, you have an "extra" area of VE to play with.

ChopperDoc

Another good idea here. I've even seen people put the turbos after the cutouts... As in basically having boost on demand. Now that's yet another option to chew on. One routed "regular" exhaust with an N/A tune, but throwing the switch you now have boost and a rowdy sound since you could just dump the exhaust wherever at that point, and set VE accordingly above 105. My vote would be short pipes right in front of the tires lol. You will need 2 sets of cutouts for that, a set to open to the turbos and a set to close the "regular exhaust" off. Wire them up with a relay so one opens and one closes with one switch. But tuning that actually wouldn't be too difficult since the N/A area won't be of great concern with twins. Won't be in it long so any errors aren't going to be too bad in the N/A region.

More ideas... Not sure how well that would work, but if you want to be different, and run one tune, this is just another possibility.

DFORESI

Yea I've been toying with programming a small module to do this. I could probably use a small microprocessor to take the request and send out the appropriate frequencies. Could be a pet project over the winter, I'm just not sure if there would be the interest for it. Originally my thought would be to use it for guys who want to run pump and race gas without having to reflash.

ChopperDoc

You never know man. I'm sure there are some guys out there that would love to have an option like that. However, the other tune tricks I mentioned here might be your competition. Just doing the ECT chop switch can also be used to add timing too, for use with race gas. I have mine wired into the car, for use later when I get around to it, but literally for no other purpose than "fireball" mode because I think that's f'n cool. Also, for nitrous when I get around to adding that, but not before I have a freaking fireball switch (which can be used for nitrous retard obviously). Pull like 20* on decel and see how the neighbors like that. LOL. Ironically, I have cutouts too, and I'm pretty sure I'm going to need some heat shields under the car before I commit to this lol.

bubba2533

I've actually created a flex fuel simulator that you could easily remove the pots and add a switch to control the output. So then you could modify timing/fueling for race gas etc. There are values that I believe take into account how much the fuel level sensor has changed and how much fuel has been used, so you may also have to disconnect the battery when you want to switch between fuels as well.

Never thought of that use case, but I have tested it with a PCM and it works just fine. Just have to be careful how you wire the Arduino.

https://www.tinkercad.com/things/5Gu...nsor-simulator

Z32_5.3

Thanks for all responses.

i spoke finally with my tuner and he wants to use efi live anyways, he says he can tune a low boost setting with catback to its full potential and tune for high boost for its full potential on meth and cutouts open on the same map. He also tunes afew psi over the finished boost level as a safety restriction.

i guess efi live has no need for diff maps. Thought he was saying each psi he can use its own timing and fuel map. Could be wrong on that but it’s the way it seemed. Either way, works for me.

TrendSetter

efilive has nitrous tables in the COS5. i used to use them for my two step with a manual trans turbo 4.8. i bet you could find a clever way to get the 80% solution using that.