Peter_Reinhard

Hello all
I just had my car tested on a Dynojet. It is a base 08 coupe, manual, z51, stock but with a Borla S-type and K&N intake. I wanted to baseline the car as I bought it last year and the after market mods were done by the previous owner who I never met. For a base 'vette I think the car screams. So the dyno ran 397.49/387.02 first pull, and 393.21/385.08 second pull. The technician said my car was not tuned because of the curve shape, and the air/fuel was lower than the 12.5 baseline he said was optimum. Basically running rich throughout the whole test band. So, I was glad that the motor appeared to be putting out to spec, but he said he could get more out of it by tuning it. That is $450 and a few hours. What do you guys think? Should I do it? How much of an increase would you expect? I am normally reluctant to change stuff, but he explained that from the factory it is tuned to pass in all 50 states and he can do better. Your advice is greatly appreciated. Thanks.

corvetteflier

Leaning the AFR makes a big difference. Between the Halltech Superbee and the Intune, my car has leaned out quite a bit. Anyway you can get it into the mid 12s is performance that was left on the table by Chevy.

Peter_Reinhard

Thanks corvetteflier for the reply. I wish I had the pdf of the dyno results to share, but it looked like the AFR was 8-ish, as opposed to 12.5 which he said is optimum for the LS3. So, since the car runs real well as is, is tuning it for $450 worth it? Would it gain 5 hp? Or more? (Just trying to justify the cost. I like the idea of it being optimized)
Thanks again
Pete

tennblkc6

I find it hard to believe your afr was in the 8s in any range of the rpms...especially with the dyno numbers you posted. that said..you will usually benefit from a tune all across the rpm range. you should also pick up a nice hp/tq gain.

corvetteflier

8s would be so rich your eyes would water. Generally, at wot, the AFR will run in the upper 10s, low 11s at richest. Rich protects the engine. That's why the manufacturers dial it in that way. Leaner is more power to the point where detonation occurs. 12.5 would be ideal as a baseline and would drop to the mid 11s at wot nicely. Tunes can definitely dial it in. Although I take some claims with a grain of salt, I would think 25+rwhp would be a good number to expect. Your car has good power now, but a tune would lean it up, advance the spark and give some worthwhile gains. The price seems a bit high, but not out of line for a dyno tune. Low restriction exhaust and better, especially cooler airflow are the best places to start, imo, and you have them going in.

Mike's LS3

That's rich! My stock LS3 A/F ratio ran between 11.25 and 11.75. If the catalytic converters got hot, the A/F ratio would drop into the 10's to protect the converters from over heating and preserve their efficiency on emissions.

tennblkc6

i am new to these lsx engines but 11.60-11.90 is the afr I used to run at wot in my forced induction 347 mustang. never thought these engines ran that rich.

jim2092

Gentlemen,

An LS3 without a blower/supercharger should have an AFR of about 14.2 on E10 gas at idle or normal cruising and 14.7 on regular 92/93 octane gas. Then around 12.5 at WOT. All after being tuned. Some of the numbers mentioned about are not good.

tennblkc6

yeah...i thought so. thanks for clearing this up.

Peter_Reinhard

Thanks for the replies. I feel stupid because I reported incorrect AFR numbers. The tech has not sent me the .pdf of the runs, and my hard copy is not with me. I'll follow-up with the correct AFR just to close this topic out as soon as I can. (It was rich, quite a bit below the red dotted 12.5 optimum line under WOT, but I realize I must have read the scale wrong. Sorry for the confustion.)

Given all I've read and all of your replies, I'm going to spend the money and get the car tuned (optimized) for where I live, the gas I use, etc. Makes sense. Thanks.

tennblkc6

nice...keep us posted. you should feel a noticeable improvement.

corvetteflier

14.7 is stoich. In a lab, it may be perfect, but it is way too lean for pump gas. I'm far from an expert, but the goal I've always heard for normal cruise speeds on pump gas is ~ 12.6. Leaner = more power, until you reach detonation levels and anything above 13-13.3 is certainly getting to that level. Piston burn is a definite possibility which is why the ECU dials it richer at WOT. Lean also = hot.

tennblkc6

have you ever driven a car that had a wide band 02 or with a dashhawk showing the wideband afr? the range of 14:2-14:7 is great for cruise.

Peter_Reinhard

Ok, here is the data carefully read from the dyno chart, but the scale makes some of the numbers approximate, but close enough.
RPM Air/Fuel
2500 15
3000 11.8
3500 11.5
4000 11.5
4500 11.1
5000 10.5
5500 10.5
6000 11.8
6300 12.0

So I will never post numbers 'off the top of my head' again.

Also, I have read hours of posts on changing the thermostat. And the dyno tech said a new thermostat would be a good thing. I'm pretty much against it for now.
If drag racing more than once in a while, then it really makes sense to cool the motor down quicker, and start a bit cooler. But for my typical driving, my engine temp is 190 to 195. The ECU won't start to retard timing untill 199 (some people have posted). If it sits stopped in traffic, it goes up to 220. When driving, it quickly comes down. I like to wot pulling onto the highway or going from 50 to 120, etc, but don't plan to sit a a light and let it heat up and then need to race someone. If I DID, maybe a 180 degree thermostat vs.160 would be less radical.

By the way, I'm new to this car (1 year now) and its engine temp is different from all other cars I've driven. Every other car I have driven in the last 35 or so years gets to a temp, and stays there, rock solid. Maybe in very hot traffic, it runs hotter. The Vette, on the other hand, seems to run hotter than the thermostat can control, and has to rely on fans to save its a$$. Maybe thats why people beef up the radiator. I have heard that most automobile engines are designed to run their oil at 100C/212F. xW-30 will thin down to a viscosity that the engineers specifically designed the engine for (cooling, lubrication, etc). I'd be worried that the 160 thermostat guys who run at 180 degrees might not have their oil hot enough. Just something to consider. Maybe its not big deal either.

When I get the tune I'll post the new dyno results for more dyno data points.

Thanks for the replies.

tennblkc6

wow...does anyone know if these numbers are typical for a stock ls3? those are very rich numbers for a normally aspirated engine. they are actually a little rich even for forced induction between 4500-5500. your engine will definitely benefit from a tune.

Mike's LS3

You will definitely benefit from a tune. The following are just some of the benefits.

1. Leaning out your air/fuel ratio at WOT is part of it.

2. Adjusting the duty fan cycle will help keep the engine coolant temperature lower at city driving, this is without changing the thermostat. At about 213*F coolant temperature, the ECM will start to pull timing.

3. When installing some of these CAI's, the air intakes can lean the A/F ratio at cruise speeds. The ECM will adjust the fuel trims by adding more fuel at cruise speeds. However, positive long term fuel trims will carry over to open loop (WOT) further richening the PE (power enrichment) values. These PE values do not adjust, but are programmed values in the tune. So your adding more fuel to an already rich condition.
A tuner can adjust this overly rich condition by reprograming the values at WOT and rescale the MAF tables so that the long term fuel trims do not need to adjust as much.

4. Knock sensors may trigger at a specific rpm. The tuner can back off the timing or add a little fuel to prevent knock retard in a targeted rpm range.

5. Remove CAGS, reduce Torque management, adjust TCM for automatics, timing, etc.

A properly tuned car will make a car more enjoyable to drive. Good luck!

Mike's LS3

Look at post #6. My stock 2008, Z51, NPP, manual, ranged from 11.25 to 11.75 A/F ratio at WOT. This is typical for the stock LS3.

tennblkc6

thanks...i see. there is a lot left on the table on these cars in stock configuration.

Peter_Reinhard

Ok, I did the dyno-tune and am happy with it. The car just feels better all around.
I don't have the sheet with me, but I can summarize.
The A/F ratio is now a perfect 12.5 throughout the band. +10 hp, +15 torque over baseline.
He modified/lowered the fan turn-on temperature, adjusted the advance, and the throttle response, and maybe other stuff. It was worth doing.

When he did the baseline pull, it read approx 390 rwhp. The previous best was 397, but he said it was warmer and more humid this day.
So we finished with 400 rwhp for a delta of 10 hp. But he was disappointed he could not get more. The timing was +20 degrees. He said the car was just running too hot (over 200 degrees) and wants me to replace the thermostat with a 160 degree and he will re-tweak it, possibly advance to 25. He thinks there is 10 more hp in there.

So, after reading the 24 page discussion on the thermostat topic, with the best information coming from the Lingenfelter guy, I've decided to put in a 180 degree instead. I don't want to discuss this here but after reading all, and considering my application (wot here and there on the highway, some autocross), 180 is my choice. Part of my reasoning is the car is 1 year old to me but being an 08, it would be good to change the Dex Cool anyway, not knowing the car's past. Good excuse to change the coolant at the same time. So, whenever I get back to the Dyno, I'll be sure to publish the finding.

Does anyone know what thermostat is used in the base 08 coupe z51 manual? I've heard people quote, "187, 190, 194, and 197". My car typically runs at 195 - 197 on the highway, and heats up to 220 or so in traffic. The oil typically gets to 220. I haven't monitored it since the tune but I assume the fans are cycling more often. (I know, it may shorten their life)

tennblkc6

congrats...nice gains with the tune. as far as the stock thermostat I've read different temps. you can put yours in a pot of water with a thermometer and bring it to a boil while watching it start to open. and yeah...if you can get those ect lower you can run more timing until the pcm starts to pull it again due to rising temps. I'm at ~23-24.