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The Quest Continues

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1981 HD Suspension; ZN1 Option
Well folks,

I took the Vette again to the Dyno today. At least I had a plan, and I was able to leave work, complete 3 pulls, and return to work in about 2 hours.

I aimed to investigate what is causing the relatively rich air/fuel mixture in the engine.

So on the first run (identified as run 003 on the chart), we ran the Vette while in stock configuration (air cleaner assembly installed, computer harness verified connected, snorkel flap doors verified open, engine warm, base run). Illustrated in lime green, you'll notice how the air/fuel mixture ratio (A/F ratio) dips into the 10 to1 range. This run averaged 150 HP at the wheels.

Run 004 was my experiment of the distributor disconnected during the 2nd pull. The graph is illustrated in blue, and I was aiming at isolating the computer as a cause of the rich condition. The carburetor was still in closed loop though. As you can see, the A/F ratio dips into the 10 to 1 range as well. The lack of computer timing advance caused a drop of about 40 horsepower at the rear wheels. So it behaved about the same as the first run today as far as the A/F ratio is concerned.

On run 005, I removed the air cleaner assembly, and I reconnected the 4-pin wire to the distributor. The graph is illustrated in black, but you can see how much the A/F ratio improved!!!! It averaged 12.5 to 1.

NOT BAD AT ALL. On run 005, the HpRW breaks the 150 line at 73 MPH, and on the first run it did not break the 150 line until 80 MPH. Also the curve is nice and flat meaning that it could still pull steadily past 106 MPH.

So something is causing the rich A/F ratio while the air cleaner is on. I will continue investigating and I'll report back after the next test.

View attachment 13033
 

Peer81

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'81 Black
Hello Gerry,

The only thing that pops my mind is... are you running (the dyno pulls) with the hood open or closed? When I did my pulls (already 4 years ago...) everybody had there hood open to cool the engine better but the c3 hood opens in front of the air intake and blocking it off. I hoop it helps, good luck with this project :)

Groeten Peter.
 

Yoda

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1981 UL5
:w Gerry

Is the charcoal filter still glued to the base of the air cleaner? ;shrug

Bud
 
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1981 HD Suspension; ZN1 Option
Peter, in run 003, the hood was down, and the additional cooling fans were directed at the grill openings.

Bud, the charcoal cannister still is glued (funny, I didn't know that it was "glued"). I have always wondered if the charcoal filter is replaceable.

I have a replacement air scoop seal set, but it is not installed. I wonder if that would make that much of a difference.

Has anyone here taken their L81 to the dyno and what was your A/F ratio?:confused
 

Peer81

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Bud, could you explain what you mean with if the charcoal filter still glued to the base of the air cleaner? I don't know what you mean by this.

Gerry, I "dynoed" my vette 4 years ago. 172.4hp on the rear wheels and 351Nm all stock except for the dynomax mufflers. Sorry don't have any A/F ratio's.

Groeten Peter.
 

Yoda

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The 1980 and the 1981 came factory with a charcoal filter about an inch or so high glued to base of the inside of the Air Filter. The paper filter fits outside the charcoal one.

The charcoal does restrict air flow, how much I don't know, but after taking mine out, I actually could hear the quad opening and sucking air..

Some come out fairly easy, some you almost have to destroy to get out. 81 MAKO's came out fairly easy, mine was pretty stubborn and I ended up trashing it. If you can get a thin steal wire under it and work your way around, you might be able to save it ;shrug

Bud
 
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1981 HD Suspension; ZN1 Option
I'll try that, Bud.

What was its purpose, though?
 

Yoda

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I'll try that, Bud.

What was its purpose, though?

I don't seem to be able to find any *reference to the filter, other than it was discontined for the 1982 production model (crossfire).

My best guess and most educated would be as a flash barrier against carb backfire... fires. Jokingly I've heard it was to keep the hp down on the sharks due to insurance companies and Naders Raiders coming down on the big 3 for safety.

JohnZ or a few others may actually know the engineered reasons for the design...

Bud

*Reference: "The Complete Book of Corvette" Richard M. Langworth; page 216.
 

Peer81

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Gerry, could you take a photo of the charcoal filter? I only remember the filter that is inside the airfilter which is connected to the tube for valvecover ventilation. If that isn't it, I don't think I've ever seen one.
Thanks :)

Groeten Peter.
 
Joined
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1981 HD Suspension; ZN1 Option
Gerry, could you take a photo of the charcoal filter? I only remember the filter that is inside the air filter which is connected to the tube for valvecover ventilation. If that isn't it, I don't think I've ever seen one.
Thanks :)

Groeten Peter.

Peter,

The charcoal filter is that filter downstream from the paper air filter that is glued to the air filter housing assembly. The glue I pulled from my charcoal filter is some stubborn stuff -soft, blue colored, and a real pain to scrape off.

The best way to remove it was to use a scribe or pick (like the ones that dentists use), and dig from under the filter the glue out. The I used a large screw driver to pry the inner lower edge from the housing by rotating the screw driver blade 90 degrees. Go around the housing, but be careful with the temperature sensor. One hint is that all you'll need is patience and only part of the filter to separate from the housing. Once that happens, the glue looses its hold on the filter and it will come out.

I covered the carburetor throttle venturi with paper to prevent glue from dropping inside. Then use paint thinner or even perhaps Stoddard cleaning compound and clean-off the remaining glue.

Thanks go out to Bud for the hint on the gluing of the filter (for some reason, I thought that it was tack welded).

The charcoal filter is a whole another issue. I tried to force air with my mouth through the mesh, and I found a lot of resistance. Could it be causing the rich condition? We'll see, So I took it off.

View attachment 13039
 

Peer81

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Thanks, the charcoal filter is also still present in my assembly. Good to know it could be removed maybe a better airflow :)

Groeten Peter.
 

Peer81

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What does 172rwhp equate to at the flywheel?

-Tatortot

If I remember correctly with an automatic, the losses from the converter, automatic and diff are about 25% together.
For a C4 with handshift ZF6 its 19% together so for a c3 handshift arond 20 to 21% I think :)

Groeten Peter.
 
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1981 HD Suspension; ZN1 Option
What does 172rwhp equate to at the flywheel?

-Tatortot

That is hard to answer, but the true measure is what it will do at the track in the 1/4 mile (if that would be the goal).

These dyno numbers are perhaps only good for measuring progress to changes on an engine or driveline not to mention "bragging rights", but the true measure of my L81 when compared with a stock L81 would best be done at the track. If the drivers for both L81's have an "equal" ability or skill for drag racing, and both vehicles weigh approximately the same (+/- 50 lbs), and it is done under the same track conditions, then it follows that If a stock L81 does the 1/4 mile in 15 seconds flat, and my L81 does the 1/4 mile in 15.400, then the ability of the stock L81 to put the power to the ground when compared to my L81 would be better, and so the ability to do work is better.

Here is a good article to read on this subject: http://www.superstang.com/horsepower.htm

Perhaps the best way to measure the driveline loss in my Vette would be to dyno an engine prior to installation into the vehicle, and then dyno the out of the engine after installation into a vehicle, but that was not worth and additional $1,100 dollars in my part.

I say -Who cares![and by this I DO NOT mean an answer to your question, but to the question whether we should give that much importance to the dyno numbers themselves]... Except for what it can do while compared against another similarly powered vehicle at the track or deserted road, and besides, I would be dumb enough to still compete against a Z06, a Cobra, or even a Viper. My hope at least, in the competitive spirit, is that their driver may miss a gear change or overpower their ride, and I would still clean their clocks...:rotfl
 
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1981 white/blue interior automatic
Understood Gerry. Just wanted to see if our L81s are cranking out more than the advertised 190.

-Tatortot
 
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1981 HD Suspension; ZN1 Option
Understood Gerry. Just wanted to see if our L81s are cranking out more than the advertised 190.

-Tatortot

All things being equal, a good ball park figure for my L81 would be 210 Hp at the flywheel. Don't get me wrong, I am still on the quest to extract the most I can.

I will be returning to the Dyno soon. I removed that charcoal filter, and I reset the settings on the carb today as well. It is running real nice. I even got 20 miles per gallon in a 100 miles round-robin I did today. So not bad at all either. It seems I have the settings in the sweet spot.

I began owning my Vette with unlimited love, and then I began to treat it like "you are a Corvette, why can't you go faster". Almost as if I were to criticize someone for how bad they can't do something, instead of how well they can do many things.

And in a nutshell, if Bud allows me to paraphrase him, Bud's love for the L81 comes from admiring the many things the L81 can do, even though it may not have the output power of an LT-1, LS6, LT-5, or LS7.

For a while I lost that excitement that I used to have with my L81, and now I am beginning to appreciate "her" the way she is. Yoda's wisdom goes a long way.:BOW
 
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For a while I lost that excitement that I used to have with my L81, and now I am beginning to appreciate "her" the way she is. Yoda's wisdom goes a long way.:BOW



Agreed in every sense. The reliability of these low compression 350's are amazing. I have never, EVER failed to get her home, even when I broke a pushrod. But squeezing a few more ponies out of her, while maintaining her GM given gift of grace is also not a bad thing. A new hairstyle on a pretty girl is the way I look at it. Whatdoya think?

-Tatortot
 
Joined
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Messages
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Location
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1981 HD Suspension; ZN1 Option
Agreed in every sense. The reliability of these low compression 350's are amazing. I have never, EVER failed to get her home, even when I broke a pushrod. But squeezing a few more ponies out of her, while maintaining her GM given gift of grace is also not a bad thing. A new hairstyle on a pretty girl is the way I look at it. Whatdoya think?

-Tatortot

Or a nice dress (paint job)...You have come a long ways, Tator :beer
 
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1981 white/blue interior automatic
:beer To you too, my friend! Speaking off dresses (paint jobs), mine's wearing a mumu!


-Tatortot
 

Yoda

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Thanks Gerry ;)

It was ment to be... June 2001 Rain, Rain Storm or not, I could see you needed a refresher course and bit of encouragement... AND Rare kept nudging me to take you for a short spin, she said it was all you needed :lou :Steer ;)

THEN watching you and Gail in 2004 during our trip to Auburn, IN... was like watching a father and daughter enjoying each others company. Thank YOU for the memories :)

Bud
 

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