Controversial Topic

[Steve G.]

Re: Controversial Topic

Here is Jerrys advice.....http://www.jerrybramlett.net/faq.html#gas

And even that is somewhat misleading. All of the high compression engines intended to run on high octane fuel will run best on high octane fuel. But it's more about being able to run the ign advance where it was intended to be.

Octane rating is a measurement of ability to resist knocking not a measurement of boiling point.

Steve

[Mark E.]

Re: Controversial Topic

I have to ask - does your car run 4.56 or higher rear gears, or did you complete the 50 mile legs in less than 30 minutes? Or do you have a hole in the gas tank? 10 mpg would be simply unacceptable, especially when paying a premium for fuel. Something is wrong.

70 MPH with 3.70 gears translates to over 3,200 RPM. I don't know... a V8 engine running continuously at this speed just might drink 10 MPG of fuel, even if tuned well.

[G B.]

Re: Controversial Topic

Here is Jerrys advice.....http://www.jerrybramlett.net/faq.html#gas

Thank you for referencing my Q&A section, but this is actually what I have to say about using modern pump gas in Rochester injections during hot weather: http://www.jerrybramlett.net/tips.html#nogood

[Steve G.]

Re: Controversial Topic

Thank you for referencing my Q&A section, but this is actually what I have to say about using modern pump gas in Rochester injections during hot weather: http://www.jerrybramlett.net/tips.html#nogood

With all due respect Jerry, your use of the term percolation is not consistent with how that word has been used over about the last 100 years.
Percolation has always been known as the vigorous boiling of fuel in the carb bowl. The term percolating was borrowed from the coffee makers that did just that, vigorously boiled the water, bubbling and churning as it did so. The consequence of that in a carb is an overly rich mixture at idle when the vapours leave the bowl and enter the airstream through the bowl vent. This is fuel that is introduced outside the fuel metering system. That has historically been known as percolation.

Fuel vaporizing off the end of the nozzles, if that is indeed what's happening, is not percolation. It would be closer to what is happening in vapor lock, which both the automotive and fuel industry identify as two separate issues, albeit happening at temps close to one another. In vapour lock it is the low pressure caused by the fuel pump that draws the vapour off instead of liquid.

The fuel temp that this becomes an issue, according to the fuel industry, starts about 200 degrees F.

fuel chart.jpg

As I said earlier, I don't have experience with this particular injection system. However, your theory about what is happening in the spider certainly leaves me puzzled. The fuel vapour in the carb example is a problem because it is fuel introduced outside the metering system. The carb metered out an appropriate amount of fuel for the conditions then the vapour was added resulting in an overly rich mixture.

In the case of the injector and spider, the fuel that is vaporizing in the spider is fuel that had been appropriately metered out. It should be the correct amount of fuel. After it's been metered the next step is to vaporize it as completely as possible. After it's metered, why does it matter where it vaporizes? It all needs to be vapour before it can burn. It's the right amount of fuel and it all needs to be turned into vapour. The purpose of the pressure pump and the nozzle is to turn it into vapour.

That is the advantage the fuel injection system has over a carb. It is better at turning liquid fuel into vapors. Spraying it under pressure atomized it better which resulted in better vaporization of the fuel. So much better than they did not need to heat the charge air with an exhaust crossover and a heat riser. And this cooler charge air contained more oxygen, which resulted in a bigger bang for the buck.

Steve

[G B.]

Re: Controversial Topic

Fuel boils in the Rochester injection system upstream of the nozzle discharge inside the spider. The nozzles don't discharge at high pressure like a modern system. At idle the discharge pressure is barely above atmospheric pressure, yet the flow must remain a very thin stream of liquid to make it all the way into the intake manifold. This is also true at high rpm when the fuel pressure is over 200 psi. It must stay liquid for the nozzle to work properly.

The point of nozzle discharge in the Rochester FI is inside the nozzle block. The fuel flow stream must first pass through a chamber that is kept near atmospheric pressure through a breather system called "idle air tubing" before it reaches the intake manifold passage. If the fuel vaporizes inside the spider, it doesn't form the tiny liquid stream (not spray pattern) needed to pass all the way through the nozzle block idle air chamber to reach the bottom end of the nozzle.

[Steve G.]

Re: Controversial Topic

Fuel boils in the Rochester injection system upstream of the nozzle discharge inside the spider. The nozzles don't discharge at high pressure like a modern system. At idle the discharge pressure is barely above atmospheric pressure, yet the flow must remain a very thin stream of liquid to make it all the way into the intake manifold. This is also true at high rpm when the fuel pressure is over 200 psi. It must stay liquid for the nozzle to work properly.

The point of nozzle discharge in the Rochester FI is inside the nozzle block. The fuel flow stream must first pass through a chamber that is kept near atmospheric pressure through a breather system called "idle air tubing" before it reaches the intake manifold passage. If the fuel vaporizes inside the spider, it doesn't form the tiny liquid stream (not spray pattern) needed to pass all the way through the nozzle block idle air chamber to reach the bottom end of the nozzle.

Once the fuel has been metered and it is pushed into whatever passages and chambers it goes to it must keep moving. The positive displacement pump behind it keeps forcing more fuel in. Whatever goes in one end has to come out the other end. Why would it matter what it pushes through the other end, vapour or liquid? Whatever it is, it's coming out the other end.

The whole purpose of the nozzles is to break down the fuel into the smallest particles possible so that it can easily vaporize. If it comes through the nozzle as vapour, so much the better. Ensuring it's a liquid so the nozzle can help turn it into vapour doesn't seem right.

How do you know it's boiling in the spider? What tests are performed to determine this? It seems to me that it would be unlikely for an fi engine, with no heat riser or crossover to reach the 200 F threshold required for the fuel to boil, given that measurements taken on lines and fuel bowls sitting on engines with heat risers and crossovers were only recorded in the 150-180 range. And that's the temp of the containers, not the fuel in them.

I don't doubt for a moment that your dyno tests recorded differences with the fuel. But I'd be inclined to suspect other fuel characteristics besides volatility. This systems bears no resemblance to any of the common rail injection system, but they share some things with the older distribution style mechanical systems used in older diesels in that both use a positive displacement pump behind the fuel. In these systems we do see performance changes with hot fuel. It has to do with viscosity of the fuel. Start and run great when the fuel is cold, hard to start when hot. Idle speeds slow to almost stalling on a 100 degree day.

Another thing I would want to explore further is your findings of lean conditions, particularly at idle/low speeds. An appropriate amount of fuel that fails to completely vapourize will not burn completely. The unburnt fuel may as well not be there. It manifests itself as a lean condition. The unburnt fuel tends to fowl plugs and collect in the combustion chanbers. Is it possible that your lean idle is in fact not fuel vapourizeing, but rather failing to vapourize?

Steve

[G B.]

Re: Controversial Topic

The whole purpose of the nozzles is to break down the fuel into the smallest particles possible so that it can easily vaporize. If it comes through the nozzle as vapour, so much the better. Ensuring it's a liquid so the nozzle can help turn it into vapour doesn't seem right.
The nozzle is what it is in a Rochester fuel injection unit. It does not vaporize or atomize the fuel. It must shoot it out in a steady liquid stream for the unit to function properly, especially at idle.

How do you know it's boiling in the spider? What tests are performed to determine this?
I use compressed CO2 to instantly cool the hub and stop the boiling so the engine will idle. I've also used spray liquid brake cleaner to cool the hub from evaporation but that gets messy.

It seems to me that it would be unlikely for an fi engine, with no heat riser or crossover to reach the 200 F threshold required for the fuel to boil...
Gasoline doesn't boil at one uniform temperature. The distillation curve for a particular gasoline blend will show the boil-off temperatures for volume percentages of that gasoline. For pump gasoline, the 10% boil-off point may be reached at much less than 140 degrees. For 30% to be boiling it may only require 160 degrees.

[Steve G.]

Re: Controversial Topic

The whole purpose of the nozzles is to break down the fuel into the smallest particles possible so that it can easily vaporize. If it comes through the nozzle as vapour, so much the better. Ensuring it's a liquid so the nozzle can help turn it into vapour doesn't seem right.
The nozzle is what it is in a Rochester fuel injection unit. It does not vaporize or atomize the fuel. It must shoot it out in a steady liquid stream for the unit to function properly, especially at idle.

How do you know it's boiling in the spider? What tests are performed to determine this?
I use compressed CO2 to instantly cool the hub and stop the boiling so the engine will idle. I've also used spray liquid brake cleaner to cool the hub from evaporation but that gets messy.

It seems to me that it would be unlikely for an fi engine, with no heat riser or crossover to reach the 200 F threshold required for the fuel to boil...
Gasoline doesn't boil at one uniform temperature. The distillation curve for a particular gasoline blend will show the boil-off temperatures for volume percentages of that gasoline. For pump gasoline, the 10% boil-off point may be reached at much less than 140 degrees. For 30% to be boiling it may only require 160 degrees.

We'll have to agree to disagree. Something has to vapourize the fuel. In carburated, it's the discharge nozzles and the heated air charge, heat from the crossover forced back by the heat risers. If the injection nozzles don't atomize and you don't have the heat, what vapourizes the fuel? Liquid fuel does not burn.

You cooled the fuel in the spider. You do not know if you stopped it boiling or changed it's viscosity, or changed any other characteristic of the fuel that is affected by heat. You are assuming it's the boiling you stopped.

We've been around the block several times with the fuel distillation charts and temps. Search out the two threads titled Gasoline Distillation charts, there are two. You might want to read them both.

In addition to this theory about the about the distillation curve and perc being inconsistent with what the fuel industry has published, it is contrary to what is seen in the field. In a carb you can identify percing by the steam pouring out the vent. Additionally, with a Holley, you can pull the plug and look for boiling fuel. Where people have been relying on the charts and infrared heat guns to determine percing, it appears they have never actually seen the smoking gun. If that fuelie with no heatriser and no crossover is still hot enough to boil the fuel us guys with working heat systems would have our fuel boiling by the time we got out of the driveway. That just isn't the case.

But the biggest puzzle has to be how do you keep pumping fuel into one end of a closed circuit and not have the same amount come out the other end.



Steve

[John D.]

Re: Controversial Topic

Jerry Bramlett, Well written my friend. I agree with you 100%. Although we can make the old fuel injection run on todays ethanol we all know it's crap. John

[G B.]

Re: Controversial Topic

But the biggest puzzle has to be how do you keep pumping fuel into one end of a closed circuit and not have the same amount come out the other end.

Because it's not a closed circuit, Steve. In a Rochester nozzle, the stream initially discharges into a chamber that is vented to the air meter. It must pass through this chamber and through a second (much larger) orifice as a liquid stream in order to reach the intake passage.

It's now time for me to bow out of this thread. Those of you who can use any of the info on my website are welcome to it. Those who think I'm full of beans should definitely ignore everything I've said in this thread and on my site. I am just a simple, one-celled mechanic who works in his back yard.

[G B.]

Re: Controversial Topic

Jerry Bramlett, Well written my friend. I agree with you 100%. Although we can make the old fuel injection run on todays ethanol we all know it's crap. John

I appreciate your support, but you may want to distance yourself from my weak BS. This is a tough room to work. I'm going to leave the remaining discussion to you. After all, you're officially recognized within the NCRS as a Technical Advisor for Fuel Injection, and I am, to date, not.

[Steve G.]

Re: Controversial Topic

But the biggest puzzle has to be how do you keep pumping fuel into one end of a closed circuit and not have the same amount come out the other end.

Because it's not a closed circuit, Steve. In a Rochester nozzle, the stream initially discharges into a chamber that is vented to the air meter. It must pass through this chamber and through a second (much larger) orifice as a liquid stream in order to reach the intake passage.

It's now time for me to bow out of this thread. Those of you who can use any of the info on my website are welcome to it. Those who think I'm full of beans should definitely ignore everything I've said in this thread and on my site. I am just a simple, one-celled mechanic who works in his back yard.

Jerry, we're not so different. I am a simple mechanic as well. I went to trade school and apprenticed 40 years ago, before we became known as technicians. I went into it because it was my passion, not to make a living. In fact I left the trade for a period when making a decent living was more important than my passions. Now that money's not as important anymore, I'm up to my elbows in it again. I'm also a one man show.

I'm convinced that you are onto something with the fuel, I'm just pretty certain it's not boiling. And if it's not boiling fuel there may be a better solution than having to stay close to a racing fuel outlet.

I will have to dig out my 63 service manual and read up on the system to get my head around this nozzle thing. Would seem to me that you'd have a lot of fuel flowing out that open ended vent when pressure at's 250 psi. I'm sure it will all make sense when I see the diagrams.

Thanks for the conversation.
Steve

[Jim D.]

Re: Controversial Topic

Although we can make the old fuel injection run on todays ethanol we all know it's crap. John

While ethanol may not work with an antiquated induction system, I wouldn't call it crap. We've had it in my area for many decades. I've never had an issue using it in anything from my lawnmower to my 1970 LS-6 Chevelle. In fact, my buddy's modified Z06 just dyno'd in excess of 650HP at the rear wheels. Not bad for 91 octane ethanol "crap". Lots of "stories" about ethanol issues on the internet but I've never personally known of anyone that has had a problem with it.

[Gary C.]

Re: Controversial Topic

Personal experience while living in Nebraska in 1971. Nebraska and Iowa IIRC during that period those two States mandated ethanol in gas sold in their States. I bought a new 1971 Honda. Within two weeks the new Honda was towed back to the dealership because it wouldn't start. All the fuel hoses and carb were totally eaten up by the ethanol gas.

That was my first experience with ethanol.

Gary
....

[Richard S.]

Re: Controversial Topic

Again, my original post was just a reflection of observed differences between 110 octane and Ethanol blend fuel in a single FI C1. I have way to many "hot day" stories about 60' dying or failing to restart when I was using 91-93 Ethanol blend. All I am saying is that when I got rid of the Ethanol and started the VP fuel my operation reliability went to 100% and that has been over the past 1 & 1/2 years. I am not trying to convince anyone to use hi-octane leaded fuel in a C1 however, for those of you who are experiencing operation difficulty in the Summer this might be a solution worth considering.