Having had a 67 427 tri-pwer 435 hp back in the days, know what the wrong jets and air fuel mixutre can led to in a very short period of time, burned valves which is a costly mistake.

Car Configuration: 23,000K miles, 2001 Coupe, Brembo Brakes, Goodrich stainless lines, Z-06 front and rear brake coolers:

My C5 has the blackwing induction, the removed MAP screen, the very large snorkle from West Coast, the solid rubber coupler (no accordian) the 90 mm throttle body and FAST intake, running Corsa Indy mufflers with the Corsa X-pipe. Using the Diablo Predator.

Here is the question: In Corvette Magazine, Feb 2/07 issue, they state they upgraded the pushrods, cam and new roller bearings, FAST intake and 90 mm throttle body and on the dyno got a substantial HP increase at the rear wheels. They also stated that they reduced the air fuel mizture 5% and got an additional 12 rear horsepower by this simple change. That sounds too good to be true. Before experimenting, need to know what the best Air to Fuel Mixture should be for the LS1 with the mods I specified, free breathing and clear exhaust, cannot touch the exhaust manifold due to California regualtions on smog testing even though this car produced .01 when the limit was .5.

In the old days it was 14.25 to 1, using the predator diablo sport the Af was 14.85 to 1. The car pulls strong at 14 58 but do not wish to go lower if that will burn valves and therefore leave it to the experts as I am a novice in this area. 14.58 gave me an average of 20.2 mpg, 14.85 was 16.9-17.2 mpg with no real noticeable change in performance leaving all the other options constant, shift points, rpm limiter, performance shift curves etc.

The Sevice manuals are of little help on this issue as I want the car tuned for the best performance and then drive accordingly with a soft foot giving me the best of both worlds, high performanance when desired and maximum fuel economy. The rear axel is 2.73, 2000 rpm = 75 mph using Eagle 1 factory profile tires.

Any help is greatly appreciated, thanks gutys.

grandpa bear

 

I heard 12.7 AFR is best to be safe.
Good luck
But here is what I got in reply from a tuner:
Quote:
Originally Posted by SleeperC5
Hi Rick,
I've been told that the recommended AFR is 12.7, but recently I've seen this number bumped up to 12.9-13.0.
So my question is. What do you think of this thread and the recommendation in it?
Will these number be bad for the life of your engine?
Thanks for your input.
Check this thread:
http://forums.corvetteforum.com/show....php?t=1621556

SLPRC5

I dont think there is a certain number to go off of. When I am tuning, i try and look for things like timing and AFR to see which make a difference the most. Sometimes you can keep adding timing till you are blue in the face and nothing happens. And if you only gain a few hp with timing, then whats the point. You might find you make more hp and TQ with a leaner AFR. But only to the point where you stop making power. And if she dont rattle, then you are ok. But dont get carried away with it either. Lean is mean, but there is too mean. There is alot more to it, but we keep that to ourselves.

RIck

 

There has all ways be a lot of debate on this subject. The first problem is where you are getting your reading. The stock O2 sensors are only accurate at 14.7 to 1. When tuning a wide band O2 sensor is used to give you an accurate AF ratio. Once you have an accurate reading then you will be able to make changes based on an accurate reading. At crusing and idle, you want AF ratios in the high 14's and 15's for gas mileage. At WOT a mid to upper 12's will give great performance.

 

They way my car is setup right now is it run between 15.3 to 14.0 cruising. When I get on the car the A/F is set to around 12.5 to 13.0. I know all this from recent tuning and I have an air fuel wideband in the car. I watch both the wide band and fuel pressure while driving.

 

Rich is almost always safer than too lean.

 

but are we talking street AFR... or dyno AFR???

12.7 dyno AFR will become 12.9 AFR once off the dyno and out on the street.

 

That depends on the dyno. Typically, load bearing dynos such as Dyno Dynamics and Mustang dynos will be spot on with the street. Dynojets are typically, from my experience, leaner on the street than the dyno.

A good number to shoot for as WOT with a naturally aspirated engine is 13.0:1 (give or take a few tenths). Nitrous and forced induction need to run a bit richer due to the extra air flow, in the 11.5:1 to 12.5:1 range depending on the type of power adder.

 

Totally agree.

Keith

 

you're too caught up in the claims spewed in the sales literature, and believing the sales rep.

Although loading dynos are more accurate, there will still be a differential between dyno and street AFR. Because; it has little to do with "loading" and a lot more to do with air temp and the delivery of air into the intake.

But the sales rep and operators manual want you to believe their more-expensive load dyno mimics the street accurately (to try and justify the added expense).

I wouldn't want my car dyno-tuned by someone thats been fooled into believing there is no need to add a "street factor" because they bought the "expensive" loading dyno.

 

ttt

 

Your intake mods will really throw your tune out of whack. A predator can't fix it. You'll really notice a difference if you do a proper tune, with a w/b, to adjust the VE and MAF tables to deliver what you are telling it to. Non PE, the engine will attempt to maintain stoich. I use 14.681, and the values from my PE table are:

Labels 0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 6800 7200
EQ Ratio 1.07910 1.08496 1.08984 1.09570 1.10156 1.10645 1.11230 1.11816 1.12305 1.12891 1.15625 1.15625 1.15625 1.12891 1.12891 1.12891 1.12891 1.12891 1.12891

With a tuned VE table, my car delivers what is commanded, the throttle is crisp, and my gas mileage is awesome.

 

Cool Post!

 

Well Gpa, I'm VERY familiar with the days of your old 67. But these machines are VERY different.

If you are going to run in Closed Loop, the PCM will force you to run at 14.7 afr. You have little choice. (And there is no real reason to desire something different.)

If you elect to run in Open Loop (OL) then you can set the afr anywhere you want. You just need a wideband and a decent tuning software package. NOT the Predator.

Now if you are running in Closed Loop, you do have the opportunity to set the afr in PE mode, where the PCM will command any afr you desire. Take a browse around www.hptuners.com and see what the option are.

I am running a BIG cam in CL, and it works really well. SO I only monkey around with afr in Power Enrichment mode.

Bottom line: you do have some control over aft, but its limited.

Good luck.

 

Since I have witnessed this first hand on a Mustang Dyno, I'm not caught up in any literature or sales rep's claims.

I can agree that there will be a difference in AFR from a dyno to the street regardless of the dyno. However, I have witnessed first hand a tune from a Mustang Dyno and a tune from a Dyno Jet.

The car that was on the Mustang Dyno was within one tenth of the AFR on the dyno when going down the road. This was with the same wideband that was in his car while on the dyno.

The car that was tuned on the Dyno Jet was nearly a full point leaner in AFR on the road than on the dyno.

I know tuners with both dynos, and they both do a street tune just to get everything dialed in as best they can. I never said that a load bearing dyno could be used in place of street tune, I just said that from an AFR standpoint, they're nearly spot on every time. Again, as I have seen both with my own eyes, I can speak from a bit of experience.

 

Just wanted to say thank you for the advise and guidance.

Grandpa Bear