I've been roaming these forums for the last 10 years (since I bought my 89 formula) and haven't done any kind of performance mods until now. If there's already a sticky on the subject I'd appreciate a link. This is my first time posting so apologize if this has been mulled over. I'd just like to know how far I can go until computer tuning is required. It's a stock engine with headers, full exhaust, open air element, air pump delete, and a tbi riser.

 

Have you datalogged to see how it’s running?

 

The air pump delete may want a change to the calibration.

I think the ECM adjusts the R/L threshold voltage by 100mV on the O2 sensor to account for the extra O2 being introduced by the AIR system when it's activated.

But if you're not noticing any performance issues from seat of the pants, I think those mods could probably be absorbed by the stock calibration.

 

I don't have any way of doing anything with the ecm. It's running all this on the factory tune. It seems to run fine and it's certainly drivable. So maybe I'm in the clear for this. Any idea what it would take to swap to an lt1 cam? All the threads I've seen are from 2003ish and I don't recognize any of the software they refer to.

 

Until you go to changing cam or heads... You will probably be ok

 

A tune would certainly help maximize what you've currently done but more importantly give you the confidence and experience to tune when you do a cam swap. If you totally botch it now, you can resort back to the stock tune and be ok. This is much harder to do when you are learning and tuning a new combo. I agree with TPI above about starting to data log and studying those. The old swap threads you mention are indeed more mechanically focused, as the EBL system didn't exist at that time and tuning was way more laborious.

 

So what software would I need to try my hand at it? I would need a wide band 02 sensor too correct?

 

As someone who ran a SBC 400 with cam/headers/intake/exhaust and other stuff, on the stock tune for a 305 CFI, you can go as far as you have....and a lot further. A tune is definitely not required for the mods that you've done so far. As you proceed further down the modding path, other tuning tactics may be necessary; such as fuel pressure adjustments, injector sizing (for more extreme changes) and base timing. But as long as you keep the shape of the torque curve close to stock, then it's pretty easy to add power and not NEED to do ECM tuning. That means no radical cams. Keep the cam conservative, gain power in other ways. I would consider an LT1 cam to be quite conservative.

How far you can go until computer tuning is REQUIRED, really boils down to, what can YOU tolerate? -with regard to driveability, fuel economy, power that may be missing? What is O.K. or good enough, for you? If the car runs basically fine, you've picked up good power from your hard-part changes, and so on...then nothing is required. Run the wee out of it and enjoy. It's no different than if you did the same changes on a carb'd engine; "how far can you go until you have to re-jet"? It's the same, ECM tuning or carb tuning. When symptoms start to show that annoy you. Or whatever that line is, for you. That's when it's "required".

Some day, if you feel like getting into ECM tuning, buy the stuff and try it out.

 

It is something I'd like to try out. I just don't know what all I would need. I can do just about anything mechanical but I'm not too proficient with computer stuff.

 

The AIR system will not put air (oxygen) into the exhaust system ahead of the O2 sensor in closed-loop. In open-loop, the computer ignores the O2 sensor anyway.

On my '88 K1500 5.7L, the AIR solenoid controlling the diverter valve causes the AIR pump to blow the air into the air cleaner assembly instead of the exhaust manifolds by the time the computer is switching to closed-loop. The AIR system is effectively non-functional at that point.





As for computer tuning, the "stock" tune stinks. You'd have power gains (and emissions failure) with a custom tune on a stock engine. My '88 K1500 is running an aftermarket intake manifold, aftermarket aluminum cylinder heads, and a Vortec camshaft/1.6 rocker arms on the stock tune with some additional fuel pressure. I have a stumble in cold weather as the engine warms-up, otherwise it's running acceptably well but underpowered.

 

Needed to be tuned when it was stock. I never got less than +2-3 mpg, 20 whp and 30 wtq gains tuning a stock engine. With tri-y headers, high flow 3-way cats, LT4 roller cam, 1.6 rockers, RPM intake manifold without EGR and a 2" bore 454 TBI my L05 actually ran cleaner tuned than it did stock. It also made 250 whp and 310 wtq with the stock heads and 8.75:1 compression ratio. The emissions standards on that were for the non-catalyst equipped non-feedback carbureted stock engine with dual air pumps. One of the nice things about using the later TBI truck engine, no air pumps needed. That was using the emissions dyno in training mode to see what the emissions output was like after dialing the tuning in. Anybody causing failing emissions from tuning needs to learn how to tune. EGR was always a joke too, GM did away with it on pretty much everything that had it in 2003 without changing the engines just altering tuning. The 4.3L, 350, 4.8, 5.3, 6.0L, 8100 and others all dropped EGR in 2003 and most had factory block off plates. The factory GM block off plates actually had a smog guy arguing that I had deleted the EGR on the stock 2003 L31 350 powered Tahoe I owned later on in the 2014 time frame.


Factory GM EGR block off plate on a 2005 Silverado 3500 L31 350 for example.