Idle gearhead question

DanicaFreak

DanicaFreak

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@BobbyFord

Need your input. Was driving taxi the other day and a old chevelle SS pulled up beside me. We were at the light, and the engine revved and drop back. Revved and dropped back. If the rear end gearing and torque is set up a certain way does it cause this? Guy was not on the throttle.

when the light turned green he squawked the tires as he saw me admiring his ride. Was beautiful.
 
Revved how high?
If it was only a couple or three hundred RPMs it could have just been surging.
My truck will do it if I don’t have the carb set exactly right.
 
BobbyFord said:
Revved how high?
If it was only a couple or three hundred RPMs it could have just been surging.
My truck will do it if I don’t have the carb set exactly right.
Click to expand...

AHHHH. not very high. prob just 300 rpm.It was kinda impressive.

as an aside bobby, my dream muscle car would be either a 442 or a mustang GT500
 
DanicaFreak said:
AHHHH. not very high. prob just 300 rpm.It was kinda impressive.

as an aside bobby, my dream muscle car would be either a 442 or a mustang GT500
Click to expand...
Two very nice cars.
I was Paul’s last week and the 66 Chevelle is just about finished. I’ll try to get some pics. The owner and his wife picked Tesla Titanium metallic. Not the color I would have chose but it came out nice.
 
BobbyFord said:
Revved how high?
If it was only a couple or three hundred RPMs it could have just been surging.
My truck will do it if I don’t have the carb set exactly right.
Click to expand...
In the 60s and early 70s the hotrodders and wannabe's set the timing to do that.
 
BobbyFord said:
It drives me crazy. Setting the timing, idle and mixture has to all be done at once. Changing one affects the other two.
Click to expand...
Most of'em just set the idle and timing. It was 50 years ago so I'm not sure but I think that they "advanced" the timing until they got the result they wanted. Lots of burned up parts doing that also. I was happy with mine just the way it was.
 
Johali said:
In the 60s and early 70s the hotrodders and wannabe's set the timing to do that.
Click to expand...

On purpose johali?

I have seen vids where the engine surges so much that it squeals the tires with each surge....
 
Thanks so much @Johali and @BobbyFord

this thread has made me smile.....


12-1971-oldsmobile-442-driving.jpg



a-67-shelby-mustang-gt500-and-the-joy-of-aimlessness-column-car-and-driver-photo-674179-s-original.jpg
 
You wanna hear some surge? I'll get you some surge.

Now that we know better, we have two 1/4" holes, an 1/8" hole, and a quarter turn valve with 1/4" hole for controlling the air bleed into the supercharger. Right before dad stages I'll reach over and turn the valve until there's enough air going in to stop the surge.

The surge is lean-rich-lean-rich-lean-rich going back and forth. On a blown car, it is caused by the vacuum being pulled on the intake side of the blower. It is particularly worse as blade area increases, as that typically indicates a more flexible blade element.

Essentially what is happening is that the vacuum pulls the blades shut, this makes engine go rich, RPM comes down, engine goes lean, RPM goes up, this sucks the blades closed, engine goes rich, RPM comes down, engine goes lean, RPM comes up, sucks the blades closed........ you get the idea.

Same general rule applies with carbs, but the blades usually aren't flexing, it's more of a mechanical vacuum advance which does the same thing in affect, but rather than the blades being pulsed shut, it's pulsing the timing in and out by a couple degrees.

 
Magnethead said:
You wanna hear some surge? I'll get you some surge.

Now that we know better, we have two 1/4" holes, an 1/8" hole, and a quarter turn valve with 1/4" hole for controlling the air bleed into the supercharger. Right before dad stages I'll reach over and turn the valve until there's enough air going in to stop the surge.

The surge is lean-rich-lean-rich-lean-rich going back and forth. On a blown car, it is caused by the vacuum being pulled on the intake side of the blower. It is particularly worse as blade area increases, as that typically indicates a more flexible blade element.

Essentially what is happening is that the vacuum pulls the blades shut, this makes engine go rich, RPM comes down, engine goes lean, RPM goes up, this sucks the blades closed, engine goes rich, RPM comes down, engine goes lean, RPM comes up, sucks the blades closed........ you get the idea.

Same general rule applies with carbs, but the blades usually aren't flexing, it's more of a mechanical vacuum advance which does the same thing in affect, but rather than the blades being pulsed shut, it's pulsing the timing in and out by a couple degrees.

Click to expand...

That's too technical for me. You lost me at "now that we know better". I barely knew how they made the street rods lope 50 years ago. :confused:
 
There are obviously some new mufflers out or some type of new exhaust bypass. They absolutely sound like crap. I hear them a lot in the city. Usually on Dodges or import crap. I’m not sure what they are but they sound terrible.
 
BobbyFord said:
There are obviously some new mufflers out or some type of new exhaust bypass. They absolutely sound like crap. I hear them a lot in the city. Usually on Dodges or import crap. I’m not sure what they are but they sound terrible.
Click to expand...
The manufacturers are using variable pressure resonators to control the sound of the multiple displacement engines. Dodge was first to do it, now everybody else is catching on to make a 4 or 6 cylinder or MDS engine always sound like a V8....sickeningly
 
Magnethead said:
The manufacturers are using variable pressure resonators to control the sound of the multiple displacement engines. Dodge was first to do it, now everybody else is catching on to make a 4 or 6 cylinder or MDS engine always sound like a V8....sickeningly
Click to expand...
It’s really terrible
 
I was gonna say 'Blower motors be blower motors'. I like Magnethead's response better lol.
 
Advancing the timing will increase rpm, it won't cause a ''lope''.
We used to roll thru the cruising spots with the choke pulled out to get the desired 'lope'. Hey anyone here remember manual chokes besides me?
Who else put a spark plug in the exhaust pipe and wired it to the battery? Roll through with the choke out loading the exhaust with unburned fuel, hit the switch and instant flame thrower. Worked great until ya blow the muffler off your Mom's car. DAMHIKT:rolleyes:

Now they make kits, wussies.
 
Bobw said:
Advancing the timing will increase rpm, it won't cause a ''lope''.
We used to roll thru the cruising spots with the choke pulled out to get the desired 'lope'. Hey anyone here remember manual chokes besides me?
Who else put a spark plug in the exhaust pipe and wired it to the battery? Roll through with the choke out loading the exhaust with unburned fuel, hit the switch and instant flame thrower. Worked great until ya blow the muffler off your Mom's car. DAMHIKT:rolleyes:

Now they make kits, wussies.
Click to expand...

Increase timing = RPM rise
Reduce timing = RPM drop

Now imagine how vacuum advance is behaving and RPM goes up and down, making manifold vacuum go up and down. It could make a lope depending on how the hydraulic lifters load up and the cam profile.
 
Magnethead said:
Increase timing = RPM rise
Reduce timing = RPM drop

Now imagine how vacuum advance is behaving and RPM goes up and down, making manifold vacuum go up and down. It could make a lope depending on how the hydraulic lifters load up and the cam profile.
Click to expand...
Yep. It's been 50 rears so I forgot to mention the oversize cam shaft.
 
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