What is the LOWEST Idle speed your Generator will Charge at??

[Dan B.]

Here's a question I'd like to throw out there to all the C-1 guys, at what engine idle speed will your Generator produce enough juice to show a charge with all the lights ect... on (under load) assuming you have a healthy electrical system?????

I have been running some tests with the newly converted Solid State Voltage regulator and it seems I need a minimum of 850 RPM with the lights on and 700 RPM (daytime) no load to keep the Ammeter at "0". At 1000 RPM, I can run everything the car has and show a positive charge until the battery tops off.

Also, according to the specs, they call for 450RPM idle speed which I have NEVER been able to achieve a decent rate of charge at. Does anyone know why that number is so low??? Did GM mean for these cars to run at a discharge at idle?? TIA Dan

[Domenic T.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Dan,
Don't beat yourself up with this.

Pulley size makes a difference as you know.

I am using the same generators you have on LOW RPM equipment and I can use pulleys to get enough RPM to get a charg at Idle.

Nature of the beast, after using altinators it's hard to look at the gage.

DOM

[Dan B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Dom, thanks for the reply. Unfortunately one thing always leads to another with these cars. If I try to go with a smaller diameter pulley, then the Tach (Generator driven) is reading too high. I hope someone can provide an explanation of the 450 RPM setting the book calls for. I never met anyone who was able to run their car at that low an idle.

[Terry D.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Dan
What year car and which engine are you referring to? Most C1 cars do not charge at an idle, as you were already told, it is the nature of the beast.
Terry

[Dan B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Terry, A 59 with base motor and 30Amp Generator. What I was really wondering is if anyone actually operates these cars at 450 RPM like the specs say. I could never figure out the reasoning why the book calls for such a low idle speed and was hoping someone could explain why they would not use say 650 - 750 which is what seems to work best. Thanks for the reply. Dan

[John H.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Terry, A 59 with base motor and 30Amp Generator. What I was really wondering is if anyone actually operates these cars at 450 RPM like the specs say. I could never figure out the reasoning why the book calls for such a low idle speed and was hoping someone could explain why they would not use say 650 - 750 which is what seems to work best. Thanks for the reply. Dan

Dan -

It's been my experience that the "specified" idle speeds shown in carbureted Corvette owner's manuals are unrealistically low. Why? I don't know.

[Dan B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Thanks John, I guess published low idle speed will be one of those ongoing unsolved Corvette mysteries. Cheers!

[Timothy B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Dan,

This low idle speed has been of interest to me also but not for the reasons of generator charging as you state.

IMO think the 500 rpm is achievable but with todays gasoline you need to make some minor changes to the engine timing and A/F ratio. My 67 327/300hp w/Holley will idle down easily to this rpm and run fine but it always seems happy at 600+-..

[Dan B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Tim, aside form the charging issue on Generator models, my 64 with Alternator and high compression engine runs best above 600 RPM as well. Today's gas is most certainly a factor as well with the ethanol and percolation issues in the Summer months here in the Northeast. I recently spoke to a retired mechanic who said they never followed the published RPM settings even back in the day when better gas was available, "most people did not like the sound of 450 RPM idle speed" according to him. Cooling is another factor that was aggravated by the low specs as well. Dan

[Domenic T.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Tim, aside form the charging issue on Generator models, my 64 with Alternator and high compression engine runs best above 600 RPM as well. Today's gas is most certainly a factor as well with the ethanol and percolation issues in the Summer months here in the Northeast. I recently spoke to a retired mechanic who said they never followed the published RPM settings even back in the day when better gas was available, "most people did not like the sound of 450 RPM idle speed" according to him. Cooling is another factor that was aggravated by the low specs as well. Dan

Dan,
be careful when you say better gas was available!

I got bashed for saying that from the guys that bought these cars in the70's or later that never ran them on the BETTER GAS. They are oblivious to that fact. I was one of those older mechanics.

Seriously,
The old fuel that we had burned at a slower and more even rate which made that possible.

All the experts on the NEW gas say different but back then GM spent millions on engine design and now the 2 bit engineers now better.

They were only a gleem in there fathers eye then and are experts on old fuel now.

Another thing that they are oblivious to is the combustion pressure that different gas explodes at. This was proven with dual plug applications using a gage and a one way valve in the other spark plug hole.

I asked in class "what is the pressure is on the top of a piston during combustion?

I was told 16 to 2,000 lbs. I am sure that was the total, not PSI.

Thats why they could idle that low, the experts never saw that fuel.

Premium back then burned at a slower, more even rate as where regular burned Quickly and pounded the piston. thats one reason for lower compression with regular.

I saw a 348/250 HP idle smothly at 300 rpm back then and stay running at 250 RPM.

The engines won't do what they were engineered to do on todays gas .....

DOM

They may call you a pea brain or a thick skull as they did me.

[Timothy B.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Hi Dom,

I am not a expert but have read that todays gasoline because of the additives takes longer to gas (vaporize) than old regular or premium but the energy content in the gas is the same.

Tuning a particular engine requires knowledge of compression pressure, engine vacuum and ignition timing. That's why I posted that slight changes in the factory tuning specs can make the engine run better.

In my situation with the 300hp cars, I have found that reducing the inital timing some will let the engine idle lower and by richening the mixture some will give more stable idle so when put under load it's not too lean.

I don't understand how the NCRS can be so picky over some items but let others like engine curb idle fall in a range like 7-750rpm (300hp engine) as others have reported. I agree that 500 RPM idle is slow but it can be done.

[Domenic T.]

Re: What is the LOWEST Idle speed your Generator will Charge at??

Tim,

I remember the automatic transmission cars without power brakes.

We had to get the idle low so the car would not creep.

There were lots of complaints (especially women that had to push the brake pedal harder than they felt comfy with and they were right.

It was funny that they would ask if the transmission could be adjusted because they had to push the brake to hard.

I thought they were being picky untill I drove one for a few hours, it was not comfy to raise your head at a stop light and see your car inching forward.

There were actually different idle speeds (with the same engine) for automatic and manual shift in the tune up section.

DOM