That idiot just has it idling too low or it isn't warmed up enough to idle properly (or be revved on it like at the end of the clip).

tom

 

I was curious, because we recently had a car show downtown and some blown cars were there and they were doing that radical, but "surgin" type of idle, where the back tires would chirp as it idles. Sounds wild......So that isn't normal though. Correct?

 

You are correct, in a way. Many people like the sound of the rolling or surging idle though if the engine is tuned properly, it will have a normal idle. When diesel engines equipped with blowers idle like this, it's called the "Detroit Roll" because the roots style superchargers are found most often on Detroit diesels. Here is what is happening when a supercharged engine idles this way.
The supercharger roll is caused by the superchargers vacuum signal to the power valve not being the actual engine vacuum, but the vacuum created by the supercharger. The power valve reads the higher vacuum created by the supercharger, this vacuum closes the power valve, causing the fuel mixture to go lean, the engine then slows down due to the lean air/fuel mixture so the vacuum signal from the supercharger causes the power valve to open as the superchargers vacuum drops, so again the engine again speeds up due to the richer air/fuel mixture, rolling from rich to lean causing the engine to speed up then slow down.
I hope this answers your question.

Barry

 

I was curious, because we recently had a car show downtown and some blown cars were there and they were doing that radical, but "surgin" type of idle, where the back tires would chirp as it idles. Sounds wild......So that isn't normal though. Correct?

Correct. The guys I know with blowers (they know what they are doing) know how to make them idle right.

tom

 

So the blower is just messing with the carb....."need more, no I don't"..."need more, no I don't" ......In fuel language, that is.......LOL Thanks guys!!

 

and, if it doesn't really hurt anything, I think it sounds wicked that way..........

 

Also, just noticed the one in the video I had linked here looks injected and not carbed...........dunno....

 

Machine Shop Tom,glad I found you.Can you get tools to install K-lines?
Paulo

 

Topfuel, the power valve isn't in the idle circuit.
It's in the main, full throttle circuit.
Try again.

 

If their isn't any vacuum to hold the valve shut it will be open and will dump fuel at idle. Thats what I am getting from topfuel's response. I tend to agree with that as well. When I blew out a couple power valves the exhaust, at idle would make your eyes water. I have run a couple times without a power valve and the same thing happens, rich idle, fouled plugs. When I run functional valves the idle is good and A/F mix is normal.

Just from personal experience (not that much compared to others here) I can see what topfuel is talking about.

 

Machine Shop Tom,glad I found you.Can you get tools to install K-lines?
Paulo

Yes I can. PM me with your K-line needs.

tom

 

Topfuel, the power valve isn't in the idle circuit.
It's in the main, full throttle circuit.
Try again.

Ok, I'll slow down so you can understand. The power valve reacts to engine vacuum. Engine vacuum is effected by many variables. When you open the throttle blades, engine vacuum drops and a power valve opens. Full throttle does not need to be achieved to activate a power valve as you erroneously stated. While it is not in the idle circuit, try putting a low value (ex. 3.5, 4.5) in a carburetor on an engine that has moderate vacuum (ex. 12" or higher) and see how it effects the idle. It will idle pig rich and drivability will be in the toilet.
I can only guess that you don't have or have ever tuned an engine with a supercharger, I do and I have.

 

But how does that explain the same condition on an injected motor???

 

But how does that explain the same condition on an injected motor???

Psssst, tdkkart, it doesn't.

 

actually its running on alcohol or methanol... our mud bogger jeep idles the same way as well as the alky burning cars on the nhra circuit... gas will idle smooth... runs sweet though... :thumbup:

 

The car is injected, so no carb. The idle air control valve is either mis adjusted or it's in the wrong place to be effective. Chances are it's mis adjusted. I have seen plenty of blower engines that idled normally, it should not be doing that, and it in no way sounds cool. Actually it makes driving it a pain.

Vince

 

hmmm... sounds like a monster truck in the show... seems like the pro monster truck mechanics would tune it right

 

Topfuel, the power valve isn't in the idle circuit.
It's in the main, full throttle circuit.
Try again.

This is a 100% true statement... I have been into the carb deal for many years... You cannot effect the idle circut with the power valve... they are 2 entirely different carb functions....

Keith

 

hmmm... sounds like a monster truck in the show... seems like the pro monster truck mechanics would tune it right

some i guess have never heard a motor running off alcohol/methanol...
and ur right, they would.

 

Rough idle

Good day could it also be the cam that is being run ? Tony :thumbup: R

 

Then some have never heard a properly set up blown engine....I guess .

Vince

 

I work with an IHRA Pro-Modified team here in Alaska, and our car is blown on alcohol. The surge from the idle is that it's lean. Our car only surges for a few seconds after startup, then stabilizes. Our tune-up is only slightly lean at idle so we can build heat in the motor prior to the run. Also, depending on how the setup is, fuel distribution might not be right. For a blown alcohol motor to run right, it needs injector nozzles both below the hat and in the port runners. Blowers don't discharge evenly across the manifold, so that's where the port nozzles come in at. At idle, we run only off the nozzles under the hat (scoop). None of the port nozzles are active until there is throttle opening. I've heard motors that surge, and motors that don't. Just depends on what the tuner has it set up to do. Not that big of a deal as long at it's right when it's under load going down the track!!! Pistons melt real quick when it's too lean...................................

 

It is NOT the power valves causing this. My blower motor does it. It has Edelbrock carbs on it. No power valves. Now I have only got about 30 minutes run time and I have not timed it or tried to tune it. But it does roll at idle.

 

From what I thought, maybe wrong, is that the blower surge is caused by exactly the vacuum. Again, I thought that the blower surge is caused by the power valve opening and closing at idle due to vacuum drop & increases (surge). If you pick your vacuum up above the blower it will surge. If you pick your vacuum up from the manifold, no surge. ?????

I am researching too, putting a blower on my 502, just do not have all details yet. Put the money aside. I like the surge too, but do not want it if it is at all harmful.

Jason

 

I have heard blower motors do that also, mostly at car shows I might add, and I thought they were off the tune. I would have never guessed that someone would purposely tune for that. To my ears it does not make a car sound powerful, not a motor that sounds like it is about to lay down. I like the sound of the power you will here at the drags, and at the staging I do not believe I have heard the blower motors surging and chirping the tires, must be a car show, pretend racer thing.