duckvett

Tom,
I am asking you to "educate" some of us who are still old-school. In my earlier days I built many small-block (carbureted) Chevy's and did some weekend drag racing. But performance enhancements on the new generation, computer-controlled LS series engines leave me puzzled and bewildered.

What does a "tune" consist of?

If I want to leave my 2000 LS1 basically stock (ZO6 airbox, K&N filter, smooth coupler, and Corsa exhaust) what gains would I see from just a tune?

Are there any longevity issues regarding internal components with a tune?

What, if any, fuel mileage changes are normally seen?

Thank you for your expertise.

randy814u

tjwong

A dyno typically will optimize the fuel and timing maps in a given efi application. When a modifcation changes the incoming air flow, this includes mods such as headers, and Cold Air Intakes otherwise known as the infamous CAI. These mods often will change the incoming air flow into the MAF meter. When this happens the fuel trims can skew one way or the other, more often they will skew the fuel trims to the negative side which means the PCM sees more air flow than before. What happens now is that the o2 sensors which are the final control element in the process, sees this rich trend, this in turn causes the PCM to "trim" back the fuel. It does this by two means, one is known as the short term fuel trims and the other is the long term fuel trims.

Short term fuel trims are for immediate changes, long term just as the name implies is a change that is made because the PCM "predicts" based on the short term trims that a change is more permanent, it is a adaptive strategy as we controls guys call it. The PCM can make a long term change of plus or minus 25%, meaning that it can take out or add up to 25% fuel. However usually if it goes beyond 17% it will throw a DTC to warn the owner that there is something wrong.


During the part throttle portion of the tuning work is when I make the corrections to correct the fuel tables so that the PCM neither adds nor takes out fuel. A negative 1 to 2 % is acceptable, as I try to make it so that it errors on the rich side meaning that the PCM has to take out a bit of fuel. On most stock applications I can get them as close as 0, with cams its the negative 1 to 2% numbers that I target. I also adjust the timing tables at this time.

The next part of the tuning job is to adjust for proper WOT fueling and timing. I target a air fuel ratio of 12 to 12.5:1, this is a safe AFR to target that is on the rich side of the MAP. Also one has to know that during the summer months when its hot and a little humid, a tuner should not lean out the PE or WOT fueling leaner than 12.1:1. Because on a nice cold winter day, that same PE fuel table can be as lean as 13.5:1! The reason is that on a hot and humid day, the air density is much lower than a cold day. I will probably get a lot of flack for making that statement but I have seen it and its NOT a rare occasion. In the old school days, this would be the same as setting up the secondary jetting in a Holley and setting up total timing curve so that we can get a total of 36 degs of timing in a small block. Which was done by a combination of different weights, springs and initial timing settings.

A typical stock cal may have a AFR as rich as 10.5:1, which that is where my new Z was set up from the general. There are a few ponies that can be found when the AFR is leaned out to 12.5:1, some tuners will target 13:1 or a little leaner but for me its 12.5, the difference between going to 13 or leaner is minimal, and at say 375 RWHP and up, one or two Hp isn't going to be missed or noticed.

I try not to gurantee fuel economy numbers but I can honestly say that I have never had any complaints of lost mileage and often many will see an increase of fuel economy. One customer after a head and cam job on his 2003 Vert told me he got 32 MPG on one cruise up the Gorge, another local head and cam customer with a 02 Z06 got 30 going to California.

There should not be any changes to life span of the engine with a dyno tune. Not unless I totally screw up (not likely) and lean your engine out or give it wayyy to much timing where it will detonate itself apart
A tune will realize improved throttle response and greater acceleration under WOT conditions, overal gains in measured power varies from car to car, on average on bone stock car 10 to 15hp can be realized. My personal Z netted nearly 50hp gains with just bolting on headers, cold air intake, ported TB and Intake manifold. This was on a very conservative tune that I just "threw" together. On another customer car with the exact same parts, he made 9 more Hp on a relatively conservative tune, he is sitting right at 500rwhp! I hope to gain another 75+ with the heads and cam that I have sitting in my living room

HOMERLIKEBEER

VERY IMFORMATIVE, THANKS

C5 Dawg

How long do you need the car to do this?

tjwong

On average 2 to 3 hours, cammed up engines, blowers and such require much more time.

duckvett

Tom - Thank you, your reply was very informative and concise. I'm sure a lot of people gained some insight into what can be done.

So, basically it is a lot like we used to do by timing, idle, etc. but a lot more technical and much more precise. I have a much better perspective of the tuning process now. I'll save my pennies and probably talk to you about doing our 2000 next spring.

nwc6

Not to hijack the OP's thread, but I have a question about ported intake and TB. I just had the car tuned, and want to send my intake/TB off to Cory after the holidays. Will the car be drivable, and will it require a retune post port work?

tjwong

It should be minor if needed, drop by after you get it on. We can take it on a test drive to see if it affected the fuel trims, if not you are good to go, the PE fueling and timing should be fine for that mod.

tjwong

Yes, its quite involved when comparing to the old days. Mainly because I can add or take away timing in specific load areas. Lets say I detected some knock between 3500 and 4000 RPM under X load points, I can go in and edit those specific load points and remove a bit of timing to take care of it. In many situations when knock occurs, imagine a snowball that starts down the hill and how it gets bigger and bigger.

With knock its a similar issue, when it happens the chamber temperatures skyrockets, and if the knock sensors don't take it out, it will perpetuate at an exponential rate. So if I take care of it before it happens, your engine makes more power and does it safely. It is with these advanced controls that allows GM to design our LSx engines to live on pump gas and yet run 11:1 compression ratios and higher. The old muscle cars of yesterday such as my old Dodge SuperBee with a 440 6 pac and 10.5:1 compression will knock like an old steam radiator gone nuts on our unleaded 92 Octane premium fuel.

Herringchoker

Thanks Tom, much easier to understand when you see it in print. JOE

C5 Dawg

Forgot to ask: Approximate cost for a stock C5 except for the Vararam?

Maui

I've noticed that one of the "forum" tuners, whose name rhymes with bovine, states the only way to accurately tune is by driving the car. What's your take on that? How would driving differ from the dyno?

Also, the same tuner talks up the ability to tune automatic transmissions. What about manual transmissions? How is the tuning different for AT as opposed to MN's?

OCCOMSRAZOR

I've always been dubious of "so-called" seat of the pants gains, or tuning.

I suppose tuning while driving the car could be accurate if one is viewing or collecting data in real time. But to have that significant of an improvement over a DYNO you would have to drive in a variety of different conditions. Not really practical.

IMO, since the tuner you are refering to does onsite tuning without a dyno always available, maybe he must tune while driving. However, it's just hypothetical on my part since I don't have alot of information on his practices or procedures.

Rogue C6

What my question would be is HoW does the A/F ratio get checked? I would imagine that is an important part to making the most power while not starving the engine and detonating.

As I understand, with a dyno, you can monitor A/F all the way threw the power band.

tjwong

That is because the bovine street tunes them by the SOTP method, beacuse most of the time a load bearing chassis dyno is not avaiable to him. I normally test drive the car after the fact, to make sure that the tune is spot on. With my Mustang dyno, I can load the car down just as if it was driving down the road at any speed, I can also simulate different gradients and add load to simulate you pulling a heavy load. With the advanced software I can do this safely without drving your car on the highway and make all changes in the shop. A final test drive validates the new calibration, or lets me know if I have to tweak it again.

As far as tuning a Automatic transmission goes, it depends on which tranny he is talking about. With the earlier A4 transmissions there was several tables and variables that can be changed, from shift points at normal part throttle conditions to WOT shift points both via road speed and engine RPM. Also shift firmness was another variable that could be changed by raising pressure in the transmission. Here is where some "tuners" can get into trouble, which may or may not show up immediately. Tweaking the pressure tables to get a firmer shift often means raising line pressure, and changing the force motor current tables to the raise line pressure. Also some will tweak the actual shift timing of the transmission. In my books this can be done but VERY carefully, this is an area where the wrong key stroke will end up frying a customer transmission. I always advise if you want a A4 to shift like an old TH400 with a -2 shift kit, then the way to do it and do it correctly is via a REAL SHIFT kit. That is what I had done to my 4L80e in my 3/4T suburban with a blown 8.1L big block. If a tuner tweaks the pressure tables, on top of a tranny with a shift kit, in my opinion you are flirting with danger.

With the new A6 tranmission we can change the shift points and pressure setting. Where there used to be a force motor current table, in the new TCM there is no such tables. So basically all we can do presently with HPT is to have the ability to change the speeds at which the tranny will shift based on Throttle position and engine speed. Also there are a few TQM paramethers in the newer calibrations that I so far have not verified if they have an adverse action on measureable power and torque. That is about it unless they have a version of HPT that I don't have which I highly doubt.

As for a manual transmission, there is only the torque managament tables vs gear range.

The actual tuning process is virtually the same as far as optimizing timing and fuel goes. The only difference is that with a A4 or A6, I just move a lever to get into the desired gear, with a M6 I have to push in a clutch before I shift into a desired gear I still load the car and run it up and down at various speed, gear and load points.

Patrick on the dyno, I can monitor AFR, I can also monitor both banks if I desire. However on the street to really do it right one needs to weld a sensor bung into the exhaust stream preferably before the CATs to get an accurate measurement. Just sampling from the tail pipe is not always the best because there is a good chance for dilution there and therefore an inaccurate reading.

Maui

Thank you, Dr. Wong. S0 the car doesn't have to be moooooving

C5 Dawg

???

tjwong

If may add, , many tuners out there use a generic tune sort of on size fits all deal. That is basically what you get with these hand held tuners, or some shops uses SCT which gives you what they refer to as a "value tune" its basically generic. Years ago I looked into the SCT software, but when I saw their "value tune" and their sales rep says "hey you can load the customer up with a quickie value tune and charge for it!" Well personally I didn't like that and I didn't feel comfortable with selling a value tune, for me its all about doing it right and customer satisfaction.

As for myself, when a customer comes to me and I dyno his car, the customer gets a taylored tune for his car, Patricks car may get a tune close to Joes car, but neither will be identical. Every engine irregardless if they are both LS1's or LS2's are always slightly different. Generic tunes work, but a real on the dyno tune is a better tune. Also generic tunes cover a broad spectrum, this is because they can load it in Joes and and Patricks car, and not worry about being too lean or detonatiing because it will be on the conservative side of things.

duckvett

This is turning out to be a great thread! I am learning so much just by reading these replies. We are lucky to have such a craftsman in our PNW backyard.

Tom - with your permission I would like to reprint some of your technical advise in our club newsletter (Cascade Corvette Club - Eugene). Thank you!