65 L84 Idle Speed.

[Tim S.]

Can someone provide me with the spec idle speed at temprature as well as on cold-high idle? I am getting ready for Bloomington and would like to have it set properly. I has read Duke's revised article on valve lash and it made mention of 1000-1200 rpm. Is that correct? I agree it runs a lot nicer there but I want to set it up correctly. In advance, thanks.

Tim

[Michael H.]

Re: 65 L84 Idle Speed.

Can someone provide me with the spec idle speed at temprature as well as on cold-high idle? I am getting ready for Bloomington and would like to have it set properly. I has read Duke's revised article on valve lash and it made mention of 1000-1200 rpm. Is that correct? I agree it runs a lot nicer there but I want to set it up correctly. In advance, thanks.

Tim

Your 65 FI car should idle at around 800-900 RPM when at or near normal operating temp.

There's no such thing as a specification for cold/choke on idle speed RPM.

[Duke W.]

Re: 65 L84 Idle Speed.

FI idle speed is problematic. I don't know what Bloomington rules require, but I have stated that up to 1200 may be required on a 30-30 cam FI engine to achieve acceptable stability.

Look at your AMA Specs and '65 Corvette Shop Manual Supplement to see if a specfic idle speed or range is stated. For '63 a 700 RPM idle speed was implied based on the initial timing recommendation at 700, but there's no way a Duntov cam will idle reasonably at that speed, and the 30-30 cam's greater overlap means that it should idle a bit higher than a Duntov cam to get reasonable stability. (My spec is about 850-900 on a 327/340.)

I believe your engine has a recommended fast idle speed. For example, on a '63 340 HP the spec is 1750 (hot) with the fast idle cam set to the proper cold start position, and this yields about 1500 on a cold start.

The '65 Supplement should have a similar spec for your engine.

For judging you may want to set the lash at .030/.030" as specified in most service documents. This is certainly looser than the .025/.025" called out on the 30-30 cam drawing, which is based on the "theoretical" 1.5:1 rocker ratio times the .017" clearance ramp height. My .023/.023" lash recommendation is based on the 1.37:1 lash point rocker ratio that I measured on a typical production machined engine.

The origin of the very loose .030"/.030" lash recommendation in service literature is unknown, but as stated in the paper, it may have been to achieve better idle stability, especially on FI engines, even though it beats the hell out of the valve train and seats. The looser the lash, the less effective valve overlap, and running .023" lash will likely require 100-200 revs higher idle speed than with the lash set at .030".

Duke

[Michael H.]

Re: 65 L84 Idle Speed.

Look at your AMA Specs and '65 Corvette Shop Manual Supplement to see if a specfic idle speed
I believe your engine has a recommended fast idle speed. For example, on a '63 340 HP the spec is 1750 (hot) with the fast idle cam set to the proper cold start position, and this yields about 1500 on a cold start.

The GM recommended hot idle speed IS 800-900 RPM. That's why I posted it. (and a 65 FI that is set up properly will run well at that idle speed)

The reason I also stated that there was no such thing as a "cold idle RPM spec" is because... there isn't.
The only specification given for 65 FI fast idle speed is 2600 RPM with the engine fully warmed up to normal operating temperature.
That setting would produce a cold idle speed that is quite different.

I wouldn't attempt to go through judging with a 65 FI with the valve lash set at numbers less than the factory recommended .030".

[John D.]

Re: 65 L84 Idle Speed.

Tim, Back in 1965 I used to complain that the 65 fuel car idled much too high when the engine was cold. I mean it was really racing at the factory set 2600 RPM. I have my original 65 supplement and looked up what Hanson quoted from the manual. Fast idle Speed (engine hot) is 2600 RPM. I guess it's too early for me but I don't understand what that means??? Fast idle speed is attained witht the engine cold.
Anyhow not too many 30-30 FI cars will idle very good at 850 RPM. But give it a try. Then after judging turn the idle screw up a tad to better enjoy the car. When my 65 was new my father gave me strict orders not to take the car apart or tinker with it. (I didn't listen). I remember turning the idle screw up to about 1000 and the car was a 100% better for everyday driving in the hills of PA.
My 63 FI car idles at 950 and 2200. Went thru ops with no problem. JD

[Joe C.]

Re: 65 L84 Idle Speed.

Tim, Back in 1965 I used to complain that the 65 fuel car idled much too high when the engine was cold. I mean it was really racing at the factory set 2600 RPM. I have my original 65 supplement and looked up what Hanson quoted from the manual. Fast idle Speed (engine hot) is 2600 RPM. I guess it's too early for me but I don't understand what that means??? Fast idle speed is attained witht the engine cold.
Anyhow not too many 30-30 FI cars will idle very good at 850 RPM. But give it a try. Then after judging turn the idle screw up a tad to better enjoy the car. When my 65 was new my father gave me strict orders not to take the car apart or tinker with it. (I didn't listen). I remember turning the idle screw up to about 1000 and the car was a 100% better for everyday driving in the hills of PA.
My 63 FI car idles at 950 and 2200. Went thru ops with no problem. JD

That is only a method for setting fast idle speed, and it's done the same way with carburetors. When engine is at op temp, manually place the fast idle cam in position and set the engine speed. Of course, this means that when the car cools, and upon restart, it will idle considerably slower than 2600. Probably around 1800.

This was probably one of yer wacko jokes..............and I just got "sucked in".

Joe

[Stuart F.]

Re: 65 L84 Idle Speed.

Setting the fast idle on an AFB equipped L-76 63 while the engine is running is not easy. To get at the screw requires you open the throttle near full - not too cool. I prefer to set and test until I get close. As it is, mine wants to run at around 1500 for the first few seconds or until kicked (live in Florida) and that's good enough for me. Actually, with a stock manual choke at normal setting, it wouldn't even close the choke full or get the screw to the high idle step. Now with my electric choke, that's a different story; It closes it full for starting and brings it off at a much more suitable rate for warm up. It ain't as pretty w/o the chrome tube, but for every day driving it is the best aftermarket upgrade I ever made. I could change it back in a few minutes, but why bother.

As for my normal full warm idle speed, I set for 750 rpm on the car tach to allow for the needle hysteresis. Even with my electric tach, it normally bounces around at least 50 rpm - always has regardless of which carb I have had on it.

Stu Fox

[Michael H.]

Re: 65 L84 Idle Speed.

Actually, with a stock manual choke at normal setting, it wouldn't even close the choke full or get the screw to the high idle step. Stu Fox

Ok, sounds like Joe and Stu get it.

The reason there is no such thing as a "cold engine fast idle speed specification" is because the term "COLD" can have a much different meaning in florida in July than it does in Minnesota in January. GM understood this so they supplied a setting for this speed using the only condition that would be constant for any condition. That condition is called "normal operating temperature".
With the engine thoroughly warmed up to normal operating temperature, adjust the fast idle speed to the specifications shown in a manual for the car. For the 65 FI engine, that RPM is 2600. (2200 for 63 and 64 with FI)

If a cold 65 FI engine is started at -15* in minnesota in January with engine oil that is more like grease than oil, it will NOT idle at the 2600 RPM that it was set at while at normal op temperature.
If that same cold engine is started when the air temp is 95*, the choke may not even come on, as Stu mentioned.

There is no constant for cold engine fast idle speed and because there isn't, it would not be possible to include it in any JG for any year Corvette.

This was discussed here a few years ago for the 67 cars and I suggested that the fast idle speed section of the JG be changed or deleted. I think John Hinckley mentioned that he sent the suggestion to the 67 TL.

I've owned quite a few FI 375 HP 64's and 65's over the years and I've never had any problem trying to get one to idle at the factory recommended 800-900 RPM. (well, there was that black/silver interior 64 conv that refused to idle properly but...)
If an FI unit is calibrated correctly and the engine is right, it will idle at factory specs. Unfortunately, though, very few FI units are calibrated correctly.

[James G.]

Re: 65 L84 Idle Speed.

Tim, make sure you have a tank full of good 'leaded' racing fuel so the car idles as it should. At least five gallons added to 91 octane street fuel, non ethnol.

Rochester Fuel Injection Corvettes have had great problems with todays fuels that have been discussed elsewhere in great detail.

[Tim S.]

Re: 65 L84 Idle Speed.

Thanks everyone! I apologize for all the confusion about the cold idle speed. I know realize it was a vauge question.This being the first time I am going to take a car through Certification / Flight judging myself, I just wanted the car to be in the "desired range" after the choke was set and after the car warmed.

Thanks again,
Tim

[Tim S.]

Re: 65 L84 Idle Speed.

When my 65 was new my father gave me strict orders not to take the car apart or tinker with it. (I didn't listen).

Boy John, can I relate to that!

[George J.]

Re: 65 L84 Idle Speed.

If I remember correctly, there was later information from Chevrolet that stated the idle speed should be "at least 900rpm". One thing that compounds some people's problems with idle speed is the lack of accuracy of the tach on the dash. I was at a Corvette repair shop and personally checked three or four different mid years against an analyzer and found some reading two to three hundred rpm high and some reading the same on the low side. Set it up at what it likes to idle at. If someone is judging a '65 fuel injected car, they should understand the concept.

George