I would like to know your reaction and what fuel are you using to keep your FI units working properly. What in the hell has these gas companies done to us? The only way I can keep mine running perfectly without hard starts and poor idling is to use 108 or better. I have not tried Av gas yet, but I may if there are succesfull users out there using Av gas. I was low on gas and put less than 2 gallons of Sunco 94 with some 108 left over to may sure I wouldn`t run out and it nearly quit. I personally have horrible drivability with this junk pump gas.

 

Union 76 112 Octane @ Sears Point

I am only running 11:1, altho my competition all runs 13:1 and a carb.

 

You can effectively raise the octane rating by blending racing gas with pump gas. You can't realistically do this using over-the-counter additives, however. Also, additives and blending will not raise the boiling temperature of pump gas significantly. If you have a problem with percolation (gas boiling), your only practical fix is to lower the temperature of your engine or run undiluted racing gas. Avaition gasoline doesn't have a much higher boiling temperature than pump gas.

Jerry Bramlett
www.jerrybramlett.net

 

put FIVE gallons CAM 2 with each fill-up of 93 octane unleaded on my 1963 Z06 - runs like a scalded dog!!!!!!!!!!!!!!!!

 

Wally, a couple of years ago when I built the 355 for mine I also traded my stock (non vac. adv. distributor) to Jerry for a 65 distributor with vac advance can. I recurved it and run the VC1810 can and it runs much cooler especially at idle than the old 283 motor ever did. I am running 10:1 compression but it runs strong on 93 octane without problems. It idles good hot or cold and only occasionally runs rough on a hot start and then only momentarily. I have noticed the percolation problem is more pronounced when "winter gas" is being pedeled by the stations. I had tried various methods of insulation but they made no difference at all. In an earlier post regarding percolation, a member related that he had installed a bilge blower to add cooling air to the spider area, with good success. I thought this was a brilliant idea and installed one on mine and although I have not had to use it since the stations switched to summer gas it does seem to be effective. Its a simple and clean installation and most folks don't even know it is not a stock item. In addition it boosts air throughput to your heater when the heater cowl butterfly is open.

My thinking is that your centrifugal advance only distributor limits advance at idle and cruise which makes it run hotter and exacerbates the percolation problem with the junk gas we get today.

Hope this information helps with the discussion as it would be sad to see all the fuelies get dumped because of the gasoline mutations.

 

And where are you finding this in our area these days, Rick?

 

Union 76 Racegas, in any racetrack paddock area.

 

I'm not sure it is necessarily the octane rating that is causing the problem...

i'm having (had) the same issues as Wally... and it isn't octane.. becasue ther is no spark knock or ping..

its the boiling point of the pump gas today. something that they either put in, or took out of gas... i had to put a spacer on my vette last summer becasue when it got hot, it would boil over into the carb... now that I have the FI on it, the fuel gets hot in the fuel line and breaks down... seems like if you have any less than a 50-50 mix of leaded race gas and pump gas, it is gonna cause problems... i got my FI all setup and ran beautifully (of course had a tank of 110 in it) i drove it about 50 miles and was in heaven, put 10 gals of Sunoco 94 in and it wasn't 10 minutes before it was surging and just wouldn't idle at all...

i sufferred through 4 or 5 gallons on the highway, just to burn it out, and put more turbo blue in and almost instantly, it cleared right up...

i also noticed that if I popped the hood, and it got a couple breaths of fresh cooler air, it cleaned up a bit... so it is clearly the temp that is causing the issue... it my car gets hotter than 180 ( on the temp guage) thats when I start to have these issues with anything but 110 in the tank..

Aaron

 

I want to thank everone for their responses. It now appears that this is national issue with FI Vettes. What a sorry state the gas companies have placed us in.

Aaron, since your only a few miles away, tell me where you found the turbo blue.

 

110 was the answer for me...

 

Stay away from Avgas. You'll end up with some serious seal/gasket problems. It's a common misconception that modern 100LL Avgas is a "better" fuel for an auto appplication. It is not. Most aircraft piston engines are less than 9:1 compression, esp. the turbocharged ones. The type of aromatics used and vapor pressure is different than auto gas as are most other characteristics. Remember, an aircraft engine is designed to run at less than 3000 rpm, (usually about 2400-2500) and with very low air densities. Not good car gas.

 

Av gas also runs 'drier' than auto gas. In my racing days, I witnessed more than one engine go tango uniform running Av gas. Apparently, it's also more oxygenated than auto gas.

 

Wally,

Dave

 

as a 'newbie' to this forum, i can only offer my 2 cents worth of input based on my experiences......

i have driven Rochester fuel-injected Corvettes for 35 years; a 65 for 5years and my present 62 for the past 30 years and have never had a problem with fuel vaporization while driving, at idle or in traffic, even with today's gas. i drive my 62 'every day it doesn't snow'....

to put things into perspective: my 62 is presently outfitted with a stock 1970 LT-1, 30 year old, crate engine (solid lifters, 11:1 comp, 2.02 heads, etc), a New Process MY-6 overdrive trans, and a 3.36 rearend. (just completed a 1750 mile trip and AVERAGED over 22 mpg... ) but i digress....

the only problem that i have is with pre-ignition as the only gas available here, that i know of other than racing fuel at $6+/gal, is 93 octane.

FI's run differently depending on the ambient temperature. even here in Florida i have to lean it out in the summer in the 95+ heat and richen it in the winter (to avoid lean surge) when the air is cooler. i use a 160 thermostat and the 'normal' idle rpm is approx 1000. i tried the B22 vacuum advance can and noticed an immediate 'seat of the pants' boost, BUT pre-ignition became so severe that the car was basically undriveable without placing an egg between my foot and the accelerator pedal. i have gone back to the original B28 and find it to be an all-around better choice for everyday driving. timing is set at about 4 degrees in order to mitigate pre-ignition, but that is becoming a losing battle and is ultimately going to cause a switch to a lower compression ratio, etc...

as previously stated in one of the replies, octane isn't the problem (except for pre-ignition). maybe some of you have fuel formulation mixes that are easily vaporized, but still 300 pound fuel pressure in the spider lines shouldn't vaporize that easily unless they are touching some hot surface of the engine, especially when being driven.

my suggestions: run a 160 thermostat (and check the fan if it's a viscous drive, i use a stainless steel flex-flite; noiser, but reliable) , raise the idle to about 1000, richen the economy stop a half turn at a time until the lean surge goes away, and use a B28 vacuum advance if pre-ignition is a problem.

Bill

 

Bill, it sounds like you're running a '64-5 7017380 series injection on your '62 since you have a vacuum advance distributor with a B-28 (clone of GM "236") canister. If you are, remember that all '63 - '65 injection units use a different spider that is designed to minimize idle percolation. If you were running a stock '62 7360 series injection in the Florida heat (with a hood on your car), you'd probably be having hot idle percolation problems with pump gas too. Most '63 - '65 unit owners just see idle percolation for about 5 to 10 seconds after a very hot restart.

The gasoline pressure in all '57 - '65 Rochester FI spiders is about .2 psi at an 800 rpm idle speed. Yes, that number is point two pounds per square inch pressure. I believe modern Rochester electronic injection units do have a much higher gas pressure at the nozzles and do not have the percolation plague.


Jerry Bramlett
www.jerrybramlett.net

 

Thanks Dave, the Duece is back to normal. The SOB runs great again just like new except 44+ years later. I printed a couple of the site locations and found one a mile away at Van Born and Middlebelt. With all those sites I can now go anywhere. Once again with a perfect 800 RPM idle and the 4.56 I can still pull away from a light in 4th as I occasionally do my being so damn lazy.

I also thank eveyone for the interesting discussion and intelligent comments,
Wally Knoch

 

Jerry
my unit is a 7017360, not the later removal plenum cover unit of the 63-65 era.

and, while memory did not serve me correctly (shame on me for not checking), the Rochester Fuel Injection manual (Form 1474, page 3) states that "nominal fuel pressures vary from near zero psi to 200 psi, depending on engine speed". depending on the effectiveness of the spill valve, my perspective is that the spider could see a considerably higher pressure than 0.2 psi at anything other than an idle and should not be a percolation problem during driving.

and , i do believe my car will idle satifactorily, with or without the hood, for as long as necessary as evidenced during my 30 years of ownership.
Bill