Yep, that's how I do it. I'm not religious about it, but I do get each tank very full. And, I know there's quite a difference because once in a while my wife will fill up the Subie and she quits when the pump does. That tank shows MUCH better MPH than the others, but the next tank goes down when I fill it up.

 

From what I understand the issue is in newer vehicles with vapor recovery systems.

If you completely fill the tank raw fuel can back up into the vapor recovery/emission system. This can cause damage to certain components. Yet another reason to pass on all those new fangled smart cars that are too delicate! Give me an old truck with no emission system!

 

Ding! Ding! Ding!

This is correct plus...


<TABLE border=0 cellSpacing=1 cellPadding=3 width=530 align=center><TBODY><TR><TD vAlign=center width=303 align=left>HELP PROTECT THE ENVIRONMENT!
SAVE MONEY!


</TD><TD vAlign=center width=206></TD></TR></TBODY></TABLE>

• Do you top off your gas tank and overfill it?
• When the gas pump nozzle clicks off automatically, do you add a little more gas to round off your dollar sale?
• Topping off your gas tank is bad for the environment and your wallet.
  
  Here's why:

<TABLE border=0 cellSpacing=4 cellPadding=2 width=550 align=center><TBODY><TR><TD bgColor=#ffffcc vAlign=top width=263>Topping off the gas tank can result in your paying for gasoline that is fed back into the station's tanks because your gas tank is full. The gas nozzle automatically clicks off when your gas tank is full. In areas of ozone nonattainment, gas station pumps are equipped with vapor recovery systems that feed back gas vapors into their tanks to prevent vapors from escaping into the air and contributing to air pollution. Any additional gas you try to pump into your tank may be drawn into the vapor line and fed back into the station’s storage tanks.

</TD><TD bgColor=#ccffcc vAlign=top width=267>Gasoline vapors are harmful to breathe. Gasoline vapors contribute to bad ozone days and are a source of toxic air pollutants such as benzene. Evaporation from the spillage of gas from overfilling can occur, contributing to the air pollution problem. Remember you pay for the gas that evaporates or is spilled on the ground.

</TD></TR></TBODY></TABLE><TABLE border=0 cellSpacing=4 cellPadding=2 width=550 align=center><TBODY><TR><TD bgColor=#ccffcc vAlign=top width=263>You need extra room in your gas tank to allow the gasoline to expand. If you top off your tank, the extra gas may evaporate into your vehicle’s vapor collection system. That system may become fouled and will not work properly causing your vehicle to run poorly and have high gas emissions.

</TD><TD bgColor=#ebebeb vAlign=top width=267>Topping off your gas tank may foul the station's vapor recovery system. Adding more gas after the nozzle has automatically shut off can cause the station's vapor recovery system to operate improperly. This contributes to the air pollution problem and may cause the gas pump to fail to work for the next person.

</TD></TR></TBODY></TABLE>


<HR class=horizontalRule align=center SIZE=4 width=530 noShade>
I work in a vehicle emissions lab and we do tests called "purge and load". The process purges the charcoal canister in the vehicle then uses butane to load the system. I'll do some more research tonight when I go in before I comment anymore. I do not actually run the tests I fix the equipment the test operators use. But you sure do not want to saturate the canister with fuel.

Go here and click the link in the first post it will explain...

http://priuschat.com/forums/gen-ii-p...-believer.html

Jim

 

Passed my emissions test on the first try today:

Idle:

CO: 0.14 / 1.20
HC: 135 / 220

2500 RPM:

CO: 1.09 / 1.20
HC: 132 / 220


The look on the guy at the station's face was great as he popped the hood. Just this sarcastic "yeah right, kid, you're gonna pass with this" look.
Then finished up with, "Well, you passed. Even with your big @$$ carburetor."

 

Awesome. I know that look. Don't have to worry about it anymore, though, vehicles are exempt from emissions testing after 25 years in Texas. Even here in Dallas. So we've got that going for us.

 

A properly tuned vehicle with a carburetor burning with the correct fuel/air ratio is just as good as a fuel injected, emission tard.

What are the minimum requirements to pass in your state? What are the maximum too?

Thats pretty cool you passed emissions with those mods.

 

Yeah, I'm pleased. I'd passed with the 390 cfm and was pretty sure the 600 wouldn't be any different. But still, makes you a little nervous.

The numbers I posted were the requirements. The number on left is what I was putting out, the number on the right is what I had to be under.

 

Your truck was giggling pulling out of that lot. I just KNOW it was just giving the emissions laws the bird all the way home!



Kind of makes you wonder how wide the tolerances are for emissions testing.

 

I heard an old wives' tale that a few ounces of acetone in the gas tank will get a marginal vehicle through the sniff test.

 

I think next year, I'll be exempt here. I believe it's 30 years. We're in a flat valley right up against a mountain range, so air quality is really important because everything collects against the mountain side and sits right over the city.

The thing that makes me feel good is I didn't have to pull any tricks, it just passed. Even if I'm exempt next year, I'll still pass smog.


Heh, if the truck wasn't, I sure know I was.

There isn't a lot of room for tolerance. I think where I get off is they don't test for other things, such as CO/CO2 % (it's on the paper, I think I was around 14.5%), but that's about it. They just list it.
There's also a few other tests that are listed as "not performed", so who knows, I may fail those miserably.

It's the same tolerances that my '88 fuel injected LeBaron had to pass.

I remember when I was fighting with the stock 1bbl when it was failing emissions, it was failing them terribly. Like 1500 / 220 HC and 6.00 / 1.20 CO.

 

Hey AB,

Have you decided which Offy intake you like better? I've got the option of either manifold and just wondered what you've decided. I've already forgone the option of the 390 and will go with a 600cfm - I'm just on the fence about going with a Holley or an Edelbrock.

In any case, your Broncos and experience with hopping up the 300 have been quite helpful with my build planning; thank you!

 

Bumpin this from the cellar as I'm gonna be running a 600 Holley as well...

Hot Rod had an article on carbs being "too big" being BS....Bigger venturi meant slower air velocity which wouldn't bog out an engine or something to that effect.....it was awhile back and I didn't pay much attention

 

So, do you have a question? Or just a comment?

 

Oh neither, just brought it up top for future reference from page 52 or whatever so I can re-read thru the thread at my leisure!!

 

Carbs depend on a vacuum signal. Large engines draw more air through the carb than smaller ci engines, and can therefore use larger cfm carbs, carbs with larger bores, and still get a good amount of air through the bore to produce suction and produce good crisp quick throttle response. Putting a carb with a larger primary bore on a small ci engine produces a weaker vacuum signal and sluggish throttle response.

I noticed the difference between a 1.08 venturi 4100 Autolite (480 cfm) and my Summit 600 cfm. The throttle response is okay, but with the smaller 480 it was peppy, like the engine was just dying to leap forward. I don't get that with the 600. Larger primary, weaker signal. Is is liveable? Absolutely. Would, imo, a smaller cfm carb feel better? Absolutely.

I also noticed a difference between a Quadrajet, with tiny primaries, and an Edelbrock 500. Again, the difference felt like a dog dying to run and pulling at the leash, and just a dog who wants to walk.

Having drawn a good, imo, analogy, I'll move along to what I learned with the QJ, and hopefully readers can apply it to a carb selection. Every carb is designed to have a certain volume of air flowing through it to make meter fuel properly. If you change the application to an engine outside that range of air flow, you loose something. What I learned with the QJ, and it applies to most carbs, is that GM put that QJ on a vast number of different size engines. But with each change of engine ci, GM changed the internals, the metering restrictions, the air bleeds, the tiny passages designed to meter an exact amount of fuel to a range of air flow.

Now circling back to what I presume to be the basic question here: Can you use a large cfm carb on a small ci engine? Yes. But, ask yourself this: Are you willing to study that carb for months, understanding what each orifice and internal restriction does, and experiment by taking it on and off the vehicle 50+ times to dial it in? Or, would you rather buy a smaller carb and bolt it on and go, "holy cow, I guess the team of 50 engineers with masters degrees who designed this carb got it right for once."

I have run cabs of 480, 500, 600, 750, and 800 cfm. The most peppy and best mpg was the 480. Each was a different woman.