C1 Fuel Injection Octane needs.

[Bruce B.]

Re: C1 Fuel Injection Octane needs.

My 57 FI 250 HP Powerglide runs fine on Shell 93 octane with ethanol.
I broke in the engine on 100LL ave gas but found it was a waste of money and if you drive a lot you it's not readily available.
The engine was a fresh rebuild with 9.5 compression and a L-79 cam.
I have put about 4000 miles on the car and runs fine, starts when cold or hot (90 * plus weather) and has never had a percolation problem.
I think the thick 1 piece gasket helps along with a great tuneup by Bob Williams in Sidney, Ohio.

[Michael W.]

Re: C1 Fuel Injection Octane needs.

I just find it a bit humorous that some folks that have never owned a car with a Rochester FI unit seem to have all the answers.

You're right, nor does one person's experience apply to everyone, everywhere.

[Richard S.]

Re: C1 Fuel Injection Octane needs.

Bruce, Do you recall the manifold vacuum at crank and 850 rpm with the L-79 cam?

[Duke W.]

Re: C1 Fuel Injection Octane needs.

The percolation and hot restart flooding issues on vintage cars that don't have pressurized fuel systems are not due to changes in Reid vapor pressure over the years. RVP is measured at 100F and is an issue with evaporative emissions from the fuel tank, which may be a greater source of HC emissions than the tailpipe on modern cars. So RVP has been going down over the years to reduce evaporative emissions. Lower RVP may affect cold starting on vintage cars due to the greater low end boililng points, but there don't seem to be many complaints.

Percolation symptoms are poor idle and driveability problems in hot weather, low speed driving and lengthy hot restart cranking. Both are due to a 10-40 degree reduction in the lower mid range (20-50 percent) boiling points, which is the result of ethanol that boils at 170F. This is not an issue with modern cars since they deliver fuel at 40 psi or more and the flow rate through the fuel rail is on the order of 40 GPH, so the fuel has little time to heat up because of the high circulation rate through the rail.

California summer blends are delivered to retailers beginning March 1, but there is a transistion period. The summer blends have lower RVP, but the mid range boiling point is about the same as winter fuel, so percolation is not effected, but is more likely in warm weather.

Within the last year there was a thread where one or more owners placed insulating sleeves over the fuel supply lines beginning with the frame pipe in the engine compartment. Before/after IR gun readings of various components showed clear reductions in temperatures from this point up to the fuel bowl, and the owners reported a reduction in percolation symptoms. The first thing to do is wire the heat riser valve open on carbureted engines.

Anyone who is experiencing significant percolation symptoms should search for this thread, and if you are having significant percolation symptoms use the flooded start procedure in the owner's manual if the car hot soaks for less than 30-60 minutes in warm to hot weather.

The vast majority of engines with the Flint-built compression ratios do not detonate on modern premium, and real compression ratios of these engines is typically half a point lower than advertised. The advertised compression ratios are as bogus as the advertised power ratings.

That leaves percolation as the primary issue, which can cause poor idle and other operational characteristics in low speed traffic in hot weather due to excessively rich mixtures and lengthly hot restorts due to flooding, but there are ways around this without having to buy $8-10/gallon race gas or 100LL avgas.

Finally, if you really want to understand why we have percolation problems with modern gasoline download and read Motor Gasolines Techical Review published by Chevron. This is a technical, not marketing document and one of the co-authors is Western Regional Rep Mike Ingham, who is also a fellow graduate of the U. of Wisconsin Engine Research Center and spent his career as a Chevron engineer.

https://www.chevronwithtechron.com/products/documents/69083_MotorGas_Tech_Review.pdf

You only have to get a couple of pages in before you see the distillation curve comparison of modern E10 versus traditional straight gasoline blends to understand the problem. Then it's a matter of implementing simple solutions that have been presented, tested, and discussed on the TDB.

Duke

[Richard S.]

Re: C1 Fuel Injection Octane needs.

Duke, You have addressed the issues of ethanol and lower octane contributing to percolation however, does the addition of tetraethyl lead provide needed additional lubrication for vintage FI systems that have not been upgraded for ethanol as suggested by John D?

[Bruce B.]

Re: C1 Fuel Injection Octane needs.

Richard,
I do not have the vacuum figures , but I choose the L79 cam due to a LSA of 114, which yields a good vacuum.
I also use the L79 cam in a 327 (0.060" over = 337") on which I am going to use a Hilborn injection I converted to EFI.
When using MAP for fueling a good vacuum signal is essential.
By the way I am not a expert in this area, just researched some specific info for my application.
Bruce B

[Michael W.]

Re: C1 Fuel Injection Octane needs.

Duke, You have addressed the issues of ethanol and lower octane contributing to percolation however, does the addition of tetraethyl lead provide needed additional lubrication for vintage FI systems that have not been upgraded for ethanol as suggested by John D?

People have been running FI systems on unleaded fuel since the 70s.

[Michael H.]

Re: C1 Fuel Injection Octane needs.

The percolation and hot restart flooding issues on vintage cars that don't have pressurized fuel systems are not due to changes in Reid vapor pressure over the years. RVP is measured at 100F and is an issue with evaporative emissions from the fuel tank, which may be a greater source of HC emissions than the tailpipe on modern cars. So RVP has been going down over the years to reduce evaporative emissions. Lower RVP may affect cold starting on vintage cars due to the greater low end boililng points, but there don't seem to be many complaints.

Percolation symptoms are poor idle and driveability problems in hot weather, low speed driving and lengthy hot restart cranking. Both are due to a 10-40 degree reduction in the lower mid range (20-50 percent) boiling points, which is the result of ethanol that boils at 170F. This is not an issue with modern cars since they deliver fuel at 40 psi or more and the flow rate through the fuel rail is on the order of 40 GPH, so the fuel has little time to heat up because of the high circulation rate through the rail.

California summer blends are delivered to retailers beginning March 1, but there is a transistion period. The summer blends have lower RVP, but the mid range boiling point is about the same as winter fuel, so percolation is not effected, but is more likely in warm weather.

Within the last year there was a thread where one or more owners placed insulating sleeves over the fuel supply lines beginning with the frame pipe in the engine compartment. Before/after IR gun readings of various components showed clear reductions in temperatures from this point up to the fuel bowl, and the owners reported a reduction in percolation symptoms. The first thing to do is wire the heat riser valve open on carbureted engines.

Anyone who is experiencing significant percolation symptoms should search for this thread, and if you are having significant percolation symptoms use the flooded start procedure in the owner's manual if the car hot soaks for less than 30-60 minutes in warm to hot weather.

The vast majority of engines with the Flint-built compression ratios do not detonate on modern premium, and real compression ratios of these engines is typically half a point lower than advertised. The advertised compression ratios are as bogus as the advertised power ratings.

That leaves percolation as the primary issue, which can cause poor idle and other operational characteristics in low speed traffic in hot weather due to excessively rich mixtures and lengthly hot restorts due to flooding, but there are ways around this without having to buy $8-10/gallon race gas or 100LL avgas.

Finally, if you really want to understand why we have percolation problems with modern gasoline download and read Motor Gasolines Techical Review published by Chevron. This is a technical, not marketing document and one of the co-authors is Western Regional Rep Mike Ingham, who is also a fellow graduate of the U. of Wisconsin Engine Research Center and spent his career as a Chevron engineer.

https://www.chevronwithtechron.com/products/documents/69083_MotorGas_Tech_Review.pdf

You only have to get a couple of pages in before you see the distillation curve comparison of modern E10 versus traditional straight gasoline blends to understand the problem. Then it's a matter of implementing simple solutions that have been presented, tested, and discussed on the TDB.

Duke

Well stated and I agree.

[Duke W.]

Re: C1 Fuel Injection Octane needs.

Duke, You have addressed the issues of ethanol and lower octane contributing to percolation however, does the addition of tetraethyl lead provide needed additional lubrication for vintage FI systems that have not been upgraded for ethanol as suggested by John D?

First of all it's not the marginally lower octane of today's E10 premiums (93 PON = 97-98 RON, and typical sixties vintage premiums were 97-99 RON. Few were actually 100.) that contribute to percolation. The percolation issue is ethanol, period. Today's marginally lower octane may contribute to detonation, but few owners with the actual as-built original compresssion ratio report significant detonation, even with more aggressive spark advance maps.

Gasoline has poor lubricity, and it's not clear to me if TEL improves the lubricity compared to not TEL gasoline.

Some FI owners add a few ounces of ATF or Marvel Mystery Oil every time they fill up. It's not clear to me if this helps lubricate the pump gears, but I doubt if it will do any harm.

Duke

[Jim L.]

Re: C1 Fuel Injection Octane needs.

California summer blends are delivered to retailers beginning March 1, but there is a transistion period. The summer blends have lower RVP, but the mid range boiling point is about the same as winter fuel, so percolation is not effected, but is more likely in warm weather.

I'm having trouble parsing your meaning. This reads as if you are saying that fuel perc tendencies are the same with winter and summer fuel. Surely, that's not what you mean to imply.

That leaves percolation as the primary issue, which can cause poor idle and other operational characteristics in low speed traffic in hot weather due to excessively rich mixtures and lengthly hot restorts due to flooding, but there are ways around this without having to buy $8-10/gallon race gas or 100LL avgas.

Must be a carburetor thing. Rochester FI goes full lean when fuel perc sets in.

Jim

[Timothy B.]

Re: C1 Fuel Injection Octane needs.

Jim,

I think with the fuel percolation in a carburetor the float drops because the liquid turns to a vapor and more gasoline gets pumped into the float bowl causing the rich mixture. The vapor gets sucked into the motor through the air cleaner.

[Jim L.]

Re: C1 Fuel Injection Octane needs.

Jim,

I think with the fuel percolation in a carburetor the float drops because the liquid turns to a vapor and more gasoline gets pumped into the float bowl causing the rich mixture. The vapor gets sucked into the motor through the air cleaner.

That explanation works for me. What I know about carburetors you could inscribe on the top of the "nail" of an FI spill valve.

OK, maybe that's too obscure. The top of the "nail" is just very small.

[Dan H.]

Re: C1 Fuel Injection Octane needs.

That explanation works for me. What I know about carburetors you could inscribe on the top of the "nail" of an FI spill valve.

OK, maybe that's too obscure. The top of the "nail" is just very small.

Jim, as always, agree with your FI information. Had the 64 out today, 80 degrees, ran fine on Mobil 91 octane. Let it sit for 45 minutes, stumbled upon restart, then smoothed out, typical FI behavior. I did install a shut off valve in the feed line to the spiders, only lose the fuel in the spider when shut off, helps alot. When restarting, the cool fuel is again sent into the spider and it then runs just fine. Also put a brass plug in the fuel bowl anti siphon valve, one less thing to leak fuel down to the spiders. Tried insulating the fuel lines and plenum, helped a bit with hot restarts, but will work without also.

[Michael G.]

Re: C1 Fuel Injection Octane needs.

Duke is correct about the effect of placing insulating sleeves on the fuel lines and filter of an FI engine. I was able to significantly lower the temperature of fuel entering the fuel bowl by insulating the lines all the way under the battery to the frame. Before insulation, the fuel was being heated to 170 degrees as it passed the exhaust manifold, so I had the typical problems with idle and hot starts when the ambient temperature exceeded 85 degrees. Those problems were significantly worse with E10.

Luckily there is a station that sells ethanol-free gas about a mile from my home, so I didn't have to use E10 much, unless I went on trips.

Since the insulation was added, I can put just about any gas in it without problem, even when its over 90 degrees outside. I still tend to use ethanol-free 91 octane when I am home, but I often drive that car 250 miles to Detroit, in the heat of Summer, refilling with E10, with no issues.

I have not yet altered the fuel system on my blue car. That car normally runs wonderfully, because I use only 110 racing fuel (or a mixture of 110 racing fuel and ethanol-free 91 octane) in it. Unfortunately, last summer I put 10 gallons of 93 octane E10 in it when I got to Detroit and couldn't find any racing fuel. It ran fine on a 90 degree day for a few miles, until the E10 got to the fuel unit, then the car stalled as I was making a left turn in front of traffic....I don't use E10 any more. That car's now finished its Duntov, so the insulation will be going on it in a few weeks.

[Jim L.]

Re: C1 Fuel Injection Octane needs.

Also put a brass plug in the fuel bowl anti siphon valve, one less thing to leak fuel down to the spiders.

Hi Dan, good to hear from you.

The brass plug is a good idea, in my opinion, for any unit that's been retrofitted with an external anti-siphon solenoid valve. One thing.... Be sure the top of the plug is flush with the top of the fuel bowl after it's fully seated. That will ensure that it can't possibly be blown out when fuel pressure builds.

Jim