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Old 03-12-2012, 05:15 PM   #61
Vettrocious
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You're welcome, Mike, but my earlier post really does comprehend the issue.

It would be nice to come up with a fuel/air curve for E10 pump gas, but frankly E10 is not one mixture, it is a different mixture every time you purchase it. There are hundreds of hydrocarbons in pump gas and oil companies vary the components and their percentages, as they so choose. All they have to do is vary the percentage of one component for Winter and the volatility changes dramatically, as does performance in a FI engine.

My point is that maybe E10 sometimes works in FI engines, so more power to those of you who use it. In attempting to make that stuff work for everybody, every time, though, you're facing an impossible task. If you insist on trying, that's fine, I wish you luck, but the odds are stacked against you.

As it stands, though, I'd rather not stall at lights and have trouble re-starting, a situation I always see with E10 and never see with any racing fuel.
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Old 03-12-2012, 05:44 PM   #62
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As it stands, though, I'd rather not stall at lights and have trouble re-starting, a situation I always see with E10 and never see with any racing fuel.
This is taken from post #17 and this is what I have issue with:

"Calibrating the units with ethanol is almost a waste."


Stalling at stop lights and hot restart problems are not a calibration problem. That is a Reid vapor pressure problem.

This poster led us to believe that you can establish a linear fuel curve with racing gasoline but even with minor tweaking for the leaner E-10 mixture, the mixture would not be stable and run a parallel curve to the racing gas and saying that it's a waste of time to calibrate with E 10.

I disagree. The only way I know that could happen is if the specific weight of the fuel (whichever one you choose) would vary throughout an air/fuel calibration.

That could possibly happen on a chassis dyno where underhood airflow doesn't represent actual road conditions and could conceivably cause fuel to vaporize in the fuel spider while calibrating. Otherwise, once you establish a fuel curve with one fuel, an alternate fuel should run a parallel curve to the first fuel.

So ask yourself, if calibrating with E 10 is a waste of time, just how do these guys that fix these things for a living do it, knowing full well that many of their customers use E 10? Well, we know one that uses a chassis dyno, we know some use the Kent-Moore manometer method and I'm sure there's other ways to do it. You even have one guy that says racing gas is the only way to run these things. Others swear by 100 LL. Others like myself have little/no problem with E-10.

No argument from me that racing gas or AV gas will make a FI run smoother when they get warm or hot retarts. The reason is obvious and it has nothing to do with E 10, it has to do with fuel vapor pressure.

My only issue is the statement that "calibrating a Rochester FI with E 10 is a waste of time.
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Old 03-13-2012, 08:04 AM   #63
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I just read your original post stating this car sat for over 10 years. My 61 FI sat for over 25 years.
I did not want to take a chance and run the FI without rebuilding it and I didn't know how the engine was going to run. So I changed the fuel tank, replaced all rubber lines and the metal fuel line.
Then I removed the FI unit and installed an old manifold and carburetor that I knew was OK. This way I could set the engine up and drive it for a few months to get the ‘bugs’ out while I rebuilt the FI unit.
My thinking was if the engine ran good with the carb set-up and it didn’t when I installed the FI, then the trouble had to be in the unit not the engine.
This worked out perfect for me. I didn’t want two unknowns.
Joe
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Old 03-13-2012, 09:06 AM   #64
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my FI sat, on the car, for 17 years and was never started during that period; just drove it into the car and parked it... the FI gods must have been smiling on me as, when i finally got around to it, i figured the fuel pump would be corroded beyond all use. i had put a marine gasoline stabilizer in the gas and maybe that is what 'saved' me as i expected to see the same kind of mess one often sees when they take the top off a carb that has set with fuel in it...

well, i pulled the plugs, squirted WD40 into each cylinder and the fuel pump and let sit over night, changed oil, installed new plugs, and with a new battery started it right up WITH 17 YEAR OLD GAS....

but this was back when gas was leaded, the real thing..

not sure i would be so lucky today...

Bill

BTW, Joe, congratulations on your aircleaner fix...
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Old 03-13-2012, 09:41 AM   #65
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my FI sat, on the car, for 17 years and was never started during that period; just drove it into the car and parked it... the FI gods must have been smiling on me as, when i finally got around to it, i figured the fuel pump would be corroded beyond all use. i had put a marine gasoline stabilizer in the gas and maybe that is what 'saved' me as i expected to see the same kind of mess one often sees when they take the top off a carb that has set with fuel in it...

well, i pulled the plugs, squirted WD40 into each cylinder and the fuel pump and let sit over night, changed oil, installed new plugs, and with a new battery started it right up WITH 17 YEAR OLD GAS....

but this was back when gas was leaded, the real thing..

not sure i would be so lucky today...

Bill

BTW, Joe, congratulations on your aircleaner fix...
Bill-

Your story reminds me of a car that I looked at back in 89, really nice 70 LT1 4speed car. Pulled the gas cap, and it looked like grape jelly!
Yes Sir, would you like that on whole wheat or plain?
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Old 03-14-2012, 07:26 PM   #66
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Jim
if it wasn't for the summertime problems i'd still be using the Rochester; ...as dinosaurs go, it's a simplisticly beautiful beast...
Bill
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Old 03-14-2012, 09:38 PM   #67
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I bought a 63 fuelie 4 years ago that had been in storage since 1969. I sent the unit to Ken Hansen to have it restored. He rebuilt it and then installed it on his 63 and drove it 2 weeks. It has performed perfectly since then. His price was very reasonable and turn around time was 3 -4 weeks. His shop is in western Tenn. Shop phone num. is 731-783-0815. Good luck , Dave
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Old 03-15-2012, 11:04 AM   #68
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It has performed perfectly since then. Dave
What kind of gasoline do you run in it. Just curious.
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Old 03-15-2012, 04:28 PM   #69
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Thanks for the kind reply. That unit was calibrated with pump gas and yes it had the percolation problems at idle on a hot day. With all my units I recommend using racing fuel when ever possible, 100LL as a second choice. I also recommend fine tuning the unit with a dino. I too am amazed at Jerry's findings with the repeated dino testing with different fuels. In my opinion the only way to get a unit totally dialed in is with the use of a dino.

I also think its only fair to post Jerrys complete analysis which was posted on his web site:

Until November, 2011, I used pump premium gasoline for all my road testing and calibration work. Occasionally I'd get a bad tankful at some station and have to replace it with a different brand, but that happened only once or twice a year. Unfortunately, I consider those years the "good ol' days". Today the pump premium sold here in Mobile is unacceptable for use in Rochester injected Corvettes. Now I use undiluted racing gas exclusively in my test cars.

On a '57 - '62 unit, make sure there is an air gap between the top of the spider hub and the bottom surface of the plenum.


Modern pump gas can cause FI running problems throughout the RPM range. You're probably familiar with the poor idle caused by percolation (boiling) of pump gasoline in the distribution spider. You may not have heard about the problems it causes during cruising and at high rpm though. Those problems are a little tougher to detect.

It took four hours on the chassis dyno for me to understand the Air / Fuel ratio differences between running modern pump gas and true racing gas. I was in shock by the end of that test session. I found that pump gas burns much leaner at idle (below 1,000 rpm) and high rpm (above 4,000 rpm) during hot weather than racing gas. Oddly, pump gas burns richer than racing gas at legal cruising speeds (30 to 70 mph). This means that although your car will run on pump gas, it won't run its best. In the summer your idle will be rough after the engine is fully warm, and you'll foul spark plugs more frequently while cruising. This also means sustained engine operation (many minutes) at very high rpm (above 5,000 rpm) with pump gas could burn a hole in a piston or a head gasket on a hot day.

Here's my opinion why modern pump gas doesn't calibrate properly in old Rochester FI units. Gasoline is a mixture of many components. These components have different physical characteristics. Some are "light ends", and vaporize at relatively low temperatures at atmospheric pressure. This fact isn't apparent when you see the published vapor pressure of gasoline because it's an average for the entire mixture.

At idle, the distribution spider is only pressurized to 0.25 pounds per square inch. This is very near atmospheric pressure. A significant portion of modern pump gasoline will vaporize inside a hot spider hub at such a low pressure. This causes the Air / Fuel mixture at the nozzles to go lean. It may not be lean enough for your seat-of-the-pants gauge to detect, but I can certainly see it going lean using the dynamometer control panel instrumentation.

The high speed lean-out is caused by a similar, but different, vaporization problem. All pumps need a certain amount of feed pressure on the suction side to maintain liquid flow at the design pumping rate. If this feed pressure (called "Net Positive Suction Head") is less than required by the pump design, the incoming liquid will partially vaporize into bubbles. It's called "pump suction cavitation" when this happens. Bottom line: a pump that doesn't have enough Net Positive Suction Head will not flow as much liquid as it should.

The amount of Net Positive Suction Head is determined by the height of the liquid feeding the pump suction side and the physical properties of that liquid at pumping temperature. Hot modern pump gasoline less than 3" high in the fuel bowl doesn't provide squat for NPSH. I can see exactly when gear pump cavitation starts while watching the dyno control panel. On a hot day, it can occur as low as 4,000 rpm under full acceleration load. It only gets worse as the rpm's climb. By 5,000 rpm, cavitation can cause a mixture as lean as 18:1. That's lean enough under load to hurt some engine parts if you don't take your foot out of it.

Pump gas burning richer than racing gas while cruising is not a big shock to me. After all, octane rating is often indirectly related to volatility. Because it is more volatile, I believe modern pump gas burns more efficiently than racing gas at relatively low engine compression ratios. Running slightly rich while cruising won't cause any major problem. It may foul spark plugs a little sooner than running the right A/F ratio, however.

You can run 100LL Aviation gasoline, but it won't help much. Those special gasoline additives sold at auto parts stores don't have any significant effect either. Neither does the additive sold at swap meets that is 99% kerosene. I've tried the thick, one-piece, plenum to baseplate gasket too. It was no help. Insulating the gas line from the engine fuel pump to the FI fuel meter makes things worse. The best course is to just run 100% racing gas. I use the VP brand with a 110 octane rating, but other brands of racing gas would probably work just as well. I tried cutting it 50% with pump premium to save money, but the running problems were still there.


Regards
Ken Hansen

Last edited by OrinDales Rochester; 03-15-2012 at 04:35 PM.
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Old 03-15-2012, 05:26 PM   #70
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Originally Posted by OrinDales Rochester View Post
Thanks for the kind reply. That unit was calibrated with pump gas and yes it had the percolation problems at idle on a hot day. With all my units I recommend using racing fuel when ever possible, 100LL as a second choice. I also recommend fine tuning the unit with a dino. Regards
Ken Hansen
Rochester FI's had perc problems when they were new. No such thing as E 10 back then. That's what DeGregory said that E 10 was the problem. I think not. I think it's the reid vapor pressure of the fuel.

No question, racing gas will smooth one out for all the mentioned reasons. Racing gas isn't supposed to cause these problems, that's why it's called racing gas.

DeGregory says you can't properly calibrate a Rochester FI with E 10. I guess that's because of Jerry's dyno findings. On the other hand, I'm not sure that a chassis dyno comes close to duplicating airflow over the engine and keeping that fuel system cool opposed to running the car on the road.

How do you calibrate your FI units? Manometer? Dyno? Do you use racing gas? What does the customer use for fuel if you have it set up for some other fuel?

Not picking on you. Just curious.

PS. Haven't seen you on VH's in a couple of years.

Last edited by MikeM; 03-15-2012 at 05:28 PM.
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Old 03-15-2012, 06:29 PM   #71
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seeing how weather has a BIG influence on richness/leanness. considering that the rochester has no way adjusting the AFR like EFI does, humidity and temperature has a GREAT deal of influence on AFR and performance and only seasonal tuning will mitigate it... heck, even underhood temps at different driving scenarios will affect AFR..

i know for a fact that the FI ran/runs better in the winter than in the summer

Bill
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Old 03-15-2012, 07:19 PM   #72
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seeing how weather has a BIG influence on richness/leanness. considering that the rochester has no way adjusting the AFR like EFI does, humidity and temperature has a GREAT deal of influence on AFR and performance and only seasonal tuning will mitigate it... heck, even underhood temps at different driving scenarios will affect AFR..

i know for a fact that the FI ran/runs better in the winter than in the summer

Bill
I don't see how it affects a Rochester FI anymore than a carburetor and I agree that underhood temps can/do affect performance and that is one of my points.

An EFI system is completely oblivious to any of these conditions. Mostly!

I can understand that there can be differences in different batches of E 10 due to different concentrations of the ethanol. 8% vs 10% would make some difference. How much, I have no idea but I would speculate it would be on the order of 1%.

I DO understand that the FI high pressure pump cannot pump vapor and I understand that low vapor pressure fuel can vaporized in the spider lines. By the same token, I think these conditions can be heightened by lack of cooling airflow while using a stationary chassis dyno.

In other words, I don't believe what I'm reading here that you CANNOT calibrate a proper fuel curve on either a carburetor or Rochester FI using E 10 for a fuel. Maybe not on a chassis dyno but certainly on the road, using an O2 sensor.

I purchased an air/fuel meter for just such this purpose a few months ago. I tried it out on the highway with the O2 sensor in the tailpipe. Got some screwy readings I think because it was in the tailpipe. When I get to it, I'll put the bung in the exhaust pipe, just downstream from the manifold and look for more stable/accurate readings. If I can get these readings within reason, I think I'll try the chassis dyno just for s...s and giggles to see if the results are the same.

In any case, I can't believe the air/fuel mixtures would go that far out of bed.

One local chassis dyno operator (25 years experience) I consulted on this scoffed at the idea that a fuel curve for E 10 wouldn't run parrallel with any other fuel.

If I get ambitious, I guess I'll find out.

Last edited by MikeM; 03-15-2012 at 07:26 PM.
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Old 03-15-2012, 07:42 PM   #73
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Mike
i agree with you, my point was that there are things other than the formulation of gas that affect performance; temp & humidity being 2.. and they can be BIG factors. heck, even altitude.. none of which the rochester can accomodate
Bill
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Old 03-15-2012, 08:21 PM   #74
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My mistake...........I was just referenceing a similar problem with my 340 hp car that did not want to idle. Obviously, I need to brush up on my FI stuff....

Thanks for correcting me,
Boyan
Don't feel bad. Only a handfull have the fuel injection down.

If you have never had one? No need learn.Not exactly a common item now days.

I am just a bystander on this one.

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Old 03-15-2012, 08:26 PM   #75
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Mike
i agree with you, my point was that there are things other than the formulation of gas that affect performance; temp & humidity being 2.. and they can be BIG factors. heck, even altitude.. none of which the rochester can accomodate
Bill
You have strayed from my issue with this thread. DeGregory says that carbs and FI's can't be properly calibrated with E 10.

I just happen to think that' s a bunch of baloney.

Also lot's of hysteria over E 10 eating up fuel system components. I have a '65 Corvette that still have the original carb/fuel pump on it. Never touched and still working well.

'66 327/350 fuel pump original. Still working well.

63 Rochester FI. Ran on leaded gas until 1980. Switched to E 10 for another 10 years and was running okay until I tore it apart to find out why it was still running well.

Got two more Rochester FI's that have been running for 5-6 years, no latest rubber or anything. Runs fine. Plugs down't foul. Pistons don't burn. I mean, WTF is the problem?????????????
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Old 03-16-2012, 08:33 AM   #76
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i prefer 'ricocheted' rather than 'strayed'..

Bill
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Old 03-16-2012, 08:36 AM   #77
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63 Rochester FI. Ran on leaded gas until 1980. Switched to E 10 for another 10 years and was running okay until I tore it apart to find out why it was still running well.

Got two more Rochester FI's that have been running for 5-6 years, no latest rubber or anything. Runs fine. Plugs down't foul. Pistons don't burn. I mean, WTF is the problem?????????????

You have no commercial incentive to convince people that the sky is falling?
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Old 03-16-2012, 09:25 AM   #78
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WE have 93 oct. with no ethanol here in Greenville S.C. and i add an additive that i buy from Jack. It has been running great since I got it back from Ken Hensan 4 years ago. Dave
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Old 03-16-2012, 10:28 AM   #79
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You have no commercial incentive to convince people that the sky is falling?
Absolutely none. You mean that's why there could be a difference of opinion?

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Old 03-17-2012, 12:42 PM   #80
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Are we talking about what type of fuel can run smoothly on today's Ethanol fuel in an early performance engine or what's the best type of fuel that matches maximum performance of when our engines were new?

I totally agree it depends on ambient temperatures, altitude, and humidity. Here in Florida, June & July 98 to 100 degrees an 11.0:1 and higher compression ratio engines with the older Rochester fuel injection runs better on aviation, or racing fuel than any fuel containing Ethanol period.

If I could run Ethanol the performance would suffer without a doubt, so why use it! If you run your Corvette to achieve good gas mileage without any concerns to performance, I say sell it...... and buy a Honda!

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Old 03-17-2012, 12:42 PM
 
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