63Corvette

VP Racing fuel or Union 76 Race gas works for me.......one of the benefits of living just 10 miles from MSR Cresson

wmf62

John
Frank was the guy that taught me what i know about FI, is he still alive?
Bill

MikeM

I have been hoping someone will explain this one to me. What does E-10 have to do with it?

genejockey

Well, I got some new hose, and did the pinch thing, and it made no difference. A re-build is the next step. Had a nice chat with John DeGregory. I'll see him, and maybe some of you all at the Spring Carlisle show.

MikeM

Next time you talk to him, have him explain post #19 to you and then pass it on to me.

PS, I'm sure he'll do a good job on your FI unit!

MikeM

Somebody? Anybody?

jim lockwood

John's a good man. You won't regret having him work on your FI.

Jim

vettsplit 63

Well Mike,
I'm not an FI expert, got one that I can make run OK, but I surmise that it would'nt make any difference whether we are talking about FI or a carburetor-- Anytime you are running a fuel that has a different gram weight /cu ml., which ethanol contains, for instance, .789 grams / cu ml. versus gasoline, which has only .680 gr./ml., you can see that alcohol (ethanol) is much denser. Without going into a (very) lengthy discussion on the properties, advantages/disadvantages of ethanol, a simple explanation would be that it takes a lot more ethanol to do the same job an equal amount of gasoline will do. That is why cars set up to run straight methanol/and or ethanol for that matter, require jets larger on the order of half again as large. Since there are only a few selections for nozzle sizes available on the Rochester FI units, I think that is probably what John meant.

MikeM

Thanks but John indicated that a proper air/fuel ratio curve could not be maintained over the operating range of the engine because the fuel was E-10 instead of straight gasoline.

That would imply it could be maintained at certain rpm but not all rpm.

I don't believe nozzle size is the issue here, if there is an issue? Fuel delivery is controlled by nozzle size, spill valve and pump output.

He also implied that the fuel curve couldn't be maintained with E 10 but could be with other fuels. What's up with that?

Thanks for your answer and I am no expert on the stuff either.

Mike Ward

This is true- but the fuel being discussed is E10, only 10% ethanol.

MikeM

How can you be 15% lean when you only have 10% ethanol? Does this mean the ethanol is totally inert, plus some?

wmf62

Mike
here's my .02...the liquid output of the Rochester is going to be the same whether it is water or gasoline or alcohol; and, given that it takes more ethanol to generate the same energy as gasoline; and, if the power stop is not changed, then the ethanol fuel would be leaner across the range. mechanical FI doesn't have an O2 sensor to adjust mixture, it just senses air flow which tells the spill valve what to allow to the nozzles.

BUT, if the power stop AND the rod length to the diaphragm is adjusted to allow more fuel in relationship to air flow AND a O2 analyzer is used to do the setup, then i would think the original stoichiometry could be attained. the standard tuning methods are out the window...

Bill

MikeM

I think you are agreeing that there should be no problem getting a correct fuel curve, across the board with E-10?

wmf62

, i think it will take an O2 analyzer to dial it in; a Kent Moore manometer wouldn't have a prayer....
Bill

jim lockwood

Instinctively, this would seem to be true. Adjust the ratio lever stops as Bill describes and you'd expect the leaning effect of ethanol would be negated.

I think what John D. was referencing is related to a discovery Jerry Bramlett has recently made about the difference between pump gas and racing gas.

The following is a quote lifted from Jerry's excellent and comprehensive web page which addresses the issue:

Before Jerry drew this conclusion he did very good science to repeatedly verify the results he was getting. While I can't explain what's going on, I do believe Jerry's conclusions.

Jim

jim lockwood

I'm seeing more and more FI units that have had inexplicable nozzle changes.... a recent 283 unit with 327 "X" nozzles was one, a '62 unit with un-marked, sewer-pipe Z+++ nozzles was another.

A Kent-Moore manometer wouldn't have any way to detect or to deal with such inappropriate changes. Neither would anyone's Seat-Of-The-Pants-O-Meter.

These days, regardless of fuel, the ONLY way to accurately dial in an FI unit is to use a wide band O2 gauge.

Jim

wmf62

Jim
not only the lever stops but i think also the position the lever floats at between the stops. getting it to 'float' in a slightly richer position will richen the mixture at light load conditions and across the range. the economy stop and the power stop are the extremes.

Bill

Jerry's findings puzzle me too....

MikeM

I read Jerry's conclusions, I just don't know how he got there and I want someone to explain how he drew those conclusions. Besides, his remarks just draw a differenece between racing gas and E-10. Doesn't say you can't adjust for one or the other and that is the issue as far as I'm concerned. John D and others thinks the sun rises and sets on 100 LL. Jerry B says if you don't want to put racing gas in your car, he doesn't need your business and 100 LL makes little difference.

Nothing against Jerry. Smart, meticulous guy.

WTF?

I don't have any of the problems Jerry and John mentions mentions. No more so than what was normal in 1963. I haven't burnt any pistons, fouled any plugs, etc., etc.

So, somebody tell me why you can't get a linear fuel curve with E-10?

wmf62

dumb old me had no problem at all with E10 in the winter, i just used the old seat of the pants 'lean it til it surges, then back it off til it goes away; then read the plugs', but come summer no amount of tinkering would keep it from stalling... the only thing that made it civilized was a mix of 112 racing gas and 93 E10 (boy, did it ever smell goooood; i had forgotten that sweet exhaust smell...)

but, it was too expensive; so the Rochester went in a box and y'all know the rest of the story.
Bill

ps: now have a smooth top doghouse, another thing i had forgotten was how much smaller the runners were in the ribbed top plenum...

jim lockwood

Bill,

Under all normal driving conditions, the ratio lever rides firmly against the economy stop. The manifold vacuum "window" within which it can float between the two stops is very small.

On my '60, for example, which has the correct enrichment diaphragm spring, the transition to the power stop begins when manifold vacuum drops to 9" Hg and is complete before the vacuum has reached 6" Hg.

I might be able to float the ratio lever if I were pulling a fairly steep grade in 4th gear at moderately slow speed and if I had a sensitive throttle foot. It'd be an effort, though.

Jim