Have a 98 and thinking of adding headers. Heard you need a tune but what exactly does the tune do? Does the cars computer do any learning and compensates for the better flow? And what happens if you don't tune it? Thanks.

 

just richens it up, leave it stock and it will run lean

 

Tune will make more power on even a stock C5. With headers, without a tune you'll be too lean, even dangerously lean, as posted. LT headers and a tune should pick up close to 50hp@crank/35hp@wheels. Well worth it, imho.....

 

Tube headers drastically change the volumetric efficiency of the engine and they can also change the distance between the oxygen sensors and the exhaust valves. All this is critically important to how the PCM manages fueling, especially for rapid throttle angle changes.

That said, my base coupe has longtubes and nothing whatsoever has been done (yet) to either the VE table or the O2 delays (typical things a tuner will need to modify for headers). It smells pig rich at idle but a previous owner had it dynoed and it put 349hp/366tq to the wheels. But, it also has cnc ported 241 heads.

 

Best to make sure you carefully assess any such change. Doing anything to a car is a domino effect. The tune up may be your least headache.

 

I mean yeah it changes VE, but with a MAF, it could compensate the fueling side. Add more ign timing. Also since you're going thru the hassle of tuning, good idea to tune fuel/MAF/VE, and you can set target AFR to something a bit leaner at WOT.

 

So the PCM wont or cant make the changes and rich up the mixture?

 

It can make some small adjustments, but its range is limited. Its range of compensation is there for possible production variations, and altitude changes. But it's outside its range to expect it to compensate for cams, headers, etc. You should get it tuned, if nothing more than protecting the engine from overly lean conditions. Hope this helps......

 

I love how folks are more than willing to open their wallets for headers, yet are so averse to making sure their tune is optimized. Especially when so many vehicles pick up a chunk with just a tune otherwise mechanically stock.

 

The trims can adjust for an awful lot of error in the fueling. If the PCM is going closed loop and the upstream O2s are healthy the trims are able to compensate for +/-30% fueling error. So there's no reason to worry anyone by saying they could damage their engine with a dangerously lean condition. If the MAF is working correctly, it's always used as the primary A/F calculation input for WOT conditions so there really shouldn't be anything close to a dangerously lean condition. It's the only way (having a MAF) the ding-dongs on youtube can get away with putting dual turbos on the C8s their channel subscibers paid for.

Yep. Yet I have receipts from previous owners for "1 x Tune NA HP Tuners 650.00", a new set of name brand plug wires, and two Bosch O2 sensors that I have no doubt did absolutely nothing. I would post an image of the receipt but don't want to trash the shop since I would never have done business with them in a million years. The tune I dumped off it when I first got it matched the factory MM6 calibration with the exception of some ridiculously large spark advance numbers in load cells the engine will never operate in, a MAF calibration that was blindly increased by around 10% over stock, and the cylinder volume constant being adjusted (probably by a previous tuner for another $650) due to having overbored cylinders.

Long story short, not everyone who claims to be able to "tune" your LS is actually capable of doing so. Certainly no-one offering mail-order services. I just shake my head...

 

You're absolutely right and without doing your homework, they can convince the uninitiated that they're the best there ever was. In fact I just wiped out what I suspect was a canned tune today on a competitor's car. What I saw made no sense. Our series requires a stock tune anyway, hopefully that was a significant contributing factor in his overheating. OP look around and talk to folks who've used any shops you're considering. Even that can only do so much good, for most folks if the car seems to work that's proof enough that the shop did their due diligence regardless of what lurks beneath.

 

Like mentioned above your car is safe without a tune but without you could be leaving power on the table. A tune can also set your fans to turn on earlier, turn off cel for codes caused by headers, and make the car run better.

 

Its different when you know how to tune an engine, whether the engine needs a tune or not.
For example on some cars you can install a wideband and adjust the fuel pressure to compensate if I don't like the a/f ratio for minor changes.

The ECU has an airflow model so if the VE of the engine changes and power changes it should provide the necessary fuel adjustment automatically in open loop assuming it relies on a MAF sensor.
IF the ECU is looking at MAP however the VE change won't influence MAP and so it could run rich or lean in open loop without having any idea what is going on "ecu is dumb".


End of the day only two things the ECU really do: Fuel and Timing. In general the timing is already too much I usually remove timing for performance engines that had stock tunes. Stock engines from various vehicles typically run more timing at WOT as rpms rise due to anemic cam profiles which limit cylinder VE and pressure. If you modify the engine with a serious cam/head then the VE and cylinder pressure is too high for stock timing it needs to be reduced timing. This affects almost all cars from Supras to Skylines to whatever.
The fuel aspect is simply wideband display. You look at the wideband and compare to dynojet wideband for accuracy and to validate the wideband (never trust in-car wideband without validation) and if you don't like what you see there are shortcut ways to adjust without tuning per-sey, for example air-flow converter (SAFC) piggy back can adjust MAP or MAF voltage up and down as needed to adjust fueling. This was popular in the 90's before stand-alone and OEM ecu tuning got ramped up where it is now. You can adjust fuel pressure but the stock car of your kind may run 60psi which is awful and leaves no headroom for adjustment upwards. I always run 38psi base fuel pressure just like Supra/Skyline/Silvia/older return style systems for many reasons (fuel system stress, lifespan, pump flow rate, fuel heating, voltage/current heating & resistance) but you would need to change the regulation method and fuel components as injectors and re-tune anyways to do that way. Another option is adjust ethanol content, a drop from 10% to 0% ethanol at 93 octane fuel it will richen up some. Inconvenient as hell but I am just giving some ideas to show that tuning isn't the only way to play around with a/f ratio. End of the day the right way to setup a performance fuel system IMO is Install a real fuel pump(s), install a return style regulator and set to 38psi base with vacuum reference, install at least 800-1200cc injectors and enable flex content for over-valve injection, Now the engine will support 600 800 1000rwhp depending how you play it and with flex fuel you can adjust boost and fuel content to match, and of course you should learn to tune it yourself because you can't trust anybody to do it for the way you would do it.

 

Thanks all, I learned a lot from you guys. Problem is I live in Calif now but moving to Idaho next year and that's when I'd add the headers, no smog checks there. My big concern is finding a tuner there. I wonder if there are even any in Calif left?

 

CA is a problem for long tubes, but not for a tune on a C5. Those slip under the radar, so no reason you can't have it done there after you re-up your plates the last time. Unless there's something even more evil about CA emissions regs that I'm not tracking.

 

I obviously don't know a lot about tuning computers. Carbs, yes. But redundant here. The computer does have a limited range of compensation for tuning. Even if trims can adjust some, so engine damage wont occur (with a good MAF and 02 sensors), a tune would still be better, certainly better for power, and sometimes it even helps fuel mileage, which doesn't hurt anyone's wallet....

 

I've run headers on a stock tune and helped friends with heads and cam builds who had headers on a stock tune. We didn't see any signs of detonation.

However, the car will make more power and have better throttle response if you do get the car tuned properly. The problem is most tuners focus on wide open throttle and don't dial in VE and MAF as well as they could. If you are interested in tuning there are many resources out there. Setting up the histograms and tuning the VE and MAF would be a good first step into tuning.

 

My thoughts exactly. On my old 99, I did a tune with Chuck at Corvettes of Westchester with just a CAI and Z06 exhaust, definitely picked up lots of power and feel with a tune; we didn’t dyno, but we estimated about 20HP to the wheels, again on a pretty much stock car.