'65 FI Mixture question

[Blake W.]

I've got a '65 FI car with the original 380 unit. The car runs very strong, Idles well, doesn't breakup at high rpm's (I don't run it to redline though). I installed new plugs about 250 miles ago, pulled 4 out yesterday and to my surprise the insulators were still white. I would think that if this motor was running that lean it wouldn't run like it does. So my question: Does the economy stop
position or adjustment affect the running mixture of this motor? If so then what direction do I need to go to richen this thing up? If this isn't the issue then suggestions.

Thanks, Blake

[William C.]

Re: '65 FI Mixture question

White insulators are not uncommon with today's unleaded gas.

[Blake W.]

Re: '65 FI Mixture question

That's interesting; however I run a blend of 110 leaded and 91 alcohol free pump gas (ratio of leaded/pump approx 2:1). If indeed this is normal for the plug to burn this way then I won't get too worried about burning up something.
Thanks Blake

[William C.]

Re: '65 FI Mixture question

How many miles have you run it? Have you examined the upper regions of the insulator (up inside the threaded area) for signs of color? What is your blend ratio?

[Dan H.]

Re: '65 FI Mixture question

Blake, what plug/heat range are you running? I use AC 45R in my 64 380 with the pop up pistons etc. Come out with white center insulators all the time. Running 91 unleaded with alchohol etc. My unit was set up with the Kent Moore Manometer, 1" of mercury setting on the economy stop.

[Blake W.]

Re: '65 FI Mixture question

Dan, I too run 45's. the non resistor ones. Have even run autolite (equivalent to 45's; forget the plug number). same exact plug coloration after a few hundred miles. Maybe it's the unleaded portion that keeps the plugs clean?

Thank for the reply, Blake

[Joe R.]

Re: '65 FI Mixture question

Blake,

Sounds like your engine is runniing exactly like Mr. Duntov designed the camshaft to run.
Enjoy your Corvette and quit fretting over nothing!

JR

[Blake W.]

Re: '65 FI Mixture question

'ur probably right! I would like someone who knows these FI units to answer the question reguarding the economy stop and its relationship to the overall running mixture. The books I have don't really explain this. Even if it's not an issue with my car I'd really like to know. Just what does happen when that stop is either turned in or out in respect to how the engine responds?

thanks so far for everyones imput, Blake

[Dan H.]

Re: '65 FI Mixture question

Blake, JR is right, if it runs well for you, then that's great. To check/set the economy stop you would need a Kent Moore set up or go to a dyno shop with an exhaust analyzer and check it out. Otherwise, do not start twisting things!!!
Dan

[Jerry G.]

Re: '65 FI Mixture question

I can tell you but then I'll have to kill you. If you screw the economy stop in so that the end of the screw goes back toward the firewall then you are richening it. I run 114 leaded race gas in the race car and I monitor the A/F ratio continually. It runs an A/F of around 13.8 to 14 on idle and 12.5 to 12.8 under load. My plugs don't get very much discoloration even in race conditions. My FI unit has been modified for racing but yours will do the same. They are very reliable and steady when set up properly. I would resist the urge to twiddle.
If you really want to do it right take your car to someone who can measure A/F ratio and see what it is, or invest $500 and get your own A/F meter and then you'll always know.
Using a monometer is an approximation at best. Therre is no reason to use monometers given the low cost of A/F monitoring equipment today.

[Duke W.]

Re: '65 FI Mixture question

Because the FI system fuel distribution is very even compared to a carburetor/manifold they can run very lean at cruise, which is why they get better than equivalent SHP engine fuel economy with the same gearing.

To get the best fuel economy, lean out the economy stop until you detect a little steady speed surge, then richen it just enough to eliminate the surge.

That's how the economy stop should be set for best fuel efficiency, and as long as you are running unleaded gasoline and oil consumption is not excessive there should be no deposit buildup on the plugs. That's how it should be if everything is right.

Duke

[George J.]

Re: '65 FI Mixture question

Duke,
I finally got around to using your's and John's technique for setting the valves. I am embarrassed to say that the clearances were well above .030". The car ran well and idled well, though. Once I set the valves the engine ran very smooth mechanically. I did need to richen up the economy stop by at least two full turns, and I may need more, to get it to cruise without surging. I am doing the adjusting at a quarter turn at a time, doing both the economy and power stops. I am surprised as how much richer it needs to be.
That said, it starts easier, even in 90 degree plus conditions. It really made the engine come alive over 2500 rpm, too. I did loose some lower end torque, though. All in all, very happy with the proceedure. Thanks.

George
31887

[Clem Z.]

Re: '65 FI Mixture question

I've got a '65 FI car with the original 380 unit. The car runs very strong, Idles well, doesn't breakup at high rpm's (I don't run it to redline though). I installed new plugs about 250 miles ago, pulled 4 out yesterday and to my surprise the insulators were still white. I would think that if this motor was running that lean it wouldn't run like it does. So my question: Does the economy stop
position or adjustment affect the running mixture of this motor? If so then what direction do I need to go to richen this thing up? If this isn't the issue then suggestions.

Thanks, Blake

you should compare your plugs to a brand new one when looking for color. cigarette ash white is the correct color

[Duke W.]

Re: '65 FI Mixture question

Duke,
I finally got around to using your's and John's technique for setting the valves. I am embarrassed to say that the clearances were well above .030". The car ran well and idled well, though. Once I set the valves the engine ran very smooth mechanically. I did need to richen up the economy stop by at least two full turns, and I may need more, to get it to cruise without surging. I am doing the adjusting at a quarter turn at a time, doing both the economy and power stops. I am surprised as how much richer it needs to be.
That said, it starts easier, even in 90 degree plus conditions. It really made the engine come alive over 2500 rpm, too. I did loose some lower end torque, though. All in all, very happy with the proceedure. Thanks.

George
31887

Setting the lash at my recommended specs increases effective overlap, so there is usually some loss of low end torque depending on how loose they were before the adjustment.

On the other hand, loose clearance shock loads the valve train because the valves are jerked off the seat and slammed back down at greater than clearance ramp velocity. That's why the valvetrain is noisy if clearance it too loose. If the valves are lifted off and set down on the seat at clearance ramp velocity, the valve train should be virtually "hydraulic lifter" quiet.

The greater effective overlap may require a richer mixture and slightly higher idle speed, so my recommendation is to adjust the idle speed and mixture when the engine is first started, and with FI and the 30-30 cam start with a target idle speed of about 1100. Depending on the engine it may have an acceptable idle as low as 900, which is what the 365 HP engine will usually accept.

The greater effective overlap may also require a slightly richer cruise mixture, so once idle is acceptable, the economy stop may need some tweaking to eliminate any cruise surge.

The WOT throttle mixture should not be effected to any significant degree, so the power stop should not require adjustment, and it's tough to do "by ear". You really need to run the car on a chassis dyno with a wide band O2 sensor, and you want the WOT mixture to be in the range of 12.5-13.5:1 and no leaner than 13.5:1 at peak revs even if the low rev mixture goes below 12.5:1.

Once everything is set up properly, the engine should really "sing" in the upper rev range, and the valves and valve seats will lead an easier life.

I'd be interested to see if you find any decline in fuel economy. Theoretically it may decline slightly, but most probably don't drive their cars enough or maintain sufficiently accurate fuel consumption records to notice any difference.

Duke

[George J.]

Re: '65 FI Mixture question

Duke,
Yes, the car is much more willing to rev. I have needed to increase the economy stop by a fair amount. More than I thought. I have been increasing the power stop the same amount each time, thinking that there should be a corresponding need for richening the wot mixture, as well. Why do you say there shouldn't be, or am I misunderstanding. I surely don't want to make a wot mixture too lean, right?

George
31887