engine idle/noise

[KlsCuda]

Hi everyone,

As always, I appreciate everyone's help. This community has been great as I work through the many issues with my Cuda.

What I have here is a mystery 440 6 pack. The guy I bought it from had no clue about the engine, so I have no idea is it has a big cam or anything done internally. What I do know is that it has a MSD6al and a holley electric fuel pump pushing 7psi, Hooker Comp headers, vacuum advance on the distributor is plugged off (as well as the carb port for it)


When I got the car it would fire up but not idle at less than 1200 rpm and even then, it was so rough the whole car would shake

I've replaced plugs, wires, cap, rotor, rebuilt the center carb (I plan to do the outboard carbs this fall). i've adjust float levels on all 3 carbs and set fuel mixture screws on center and front carb ( can't do the rear without taking it off the car, so that'll happen when I do the rebuild).
I've adjusted timing to what I think is about 15 degrees BTDC.

It will now idle around 900 RPM but there is a bit of surging when driving and some hesitation.

I can't tell if there is a miss but it's not very smooth and this engine/exhaust combination is so loud it's really hard to hear anything when driving over the exhaust(it's setup AAR style with side exhaust) and i'm pretty sure a big exhaust leak


I have a video of it idling so you all can hear what it sounds like: VLIX

 

[Challenger RTA]

Post the video on you tube. Then copy and past link hear.

 

[KlsCuda]

i edited my original post and put a link at the bottom.

 

[Challenger RTA]

Not that this is correct it just came to mind. Timing chain. More diagnosis is needed. Like vacuum reading, timing,compression test, leak down test, distributor wore? Check fuel pressure steady.

 

[KlsCuda]

I was concerned about timing chain, vacuum reading is around 8 at idle. no matter where I set timing or adjust fuel mixture I can't get it over 8-9. I haven't done a leak down test... i have no idea how to do this.

sucks working on mystery engine. I think it's been cammed.. but I have no idea what it is.

 

[Challenger RTA]

A leak down test requires an air compressor.https://www.motortrend.com/how-to/cylinder-leak-down-test/ A leak down test will show if the rings or valves are sealed . There are a number of good builders here. Get the results from other tests, and they more than likely can figure it out.

 

[Xcudame]

Just going by what I heard, it sounds like it has been over cammed and your response of 8-9 inches of vacuum supports this. Leak down test and compression test will definitely help diagnose the problem. Depending on what camshaft is in there, the mechanical advance most likely needs adjusting. When people unplug the vacuum advance, it's usually because the distributor hasn't been modified to work with the high lift high duration camshaft. No vacuum advance helps the problem, but if it's driven a lot on the street (is that your intention?) you're wasting fuel mileage and causing pre-mature engine wear. If you wind up getting into the timing chain, I'd go ahead and remove the intake and carbs and try and determine the camshaft lobe lifts are.
You're right, trying to tune an unknown engine combo is harder.

 

[KlsCuda]

Thanks for the info. Yes my intention is street driving.. hard and fast lol but street driving. I might take it to the local drag strip just for fun once in a while, but nothing serious.

I'll probably pull it all apart at some point

 

[pschlosser]

A few thoughts:

In the video, the engine does sound as if it has a longer duration camshaft than what was factory original. This may mean the engine is not entirely original inside, and may have been rebuilt at least once.

I am often dubious of a someone selling a performance car, and having amnesia about the status and condition of the engine. For someone who both doesn't want to lie or tell you bad news, they may develop... amnesia.

With patience and help from this forum, I am confident you can discover what needs to be done.

Your vacuum at idle seems pretty low to me, but then, with longer duration cams, this is a common side effect. A smallish vacuum leak might effect the surging and stumble you're seeing when driving. There are several ways to test for vacuum leaks, and some methods are pretty easy.

Is your exhaust so loud you cannot hear the engine when driving? If so, this will make some things harder to hear and diagnose, like a spun rod bearing.

 

[KlsCuda]

A few thoughts:

In the video, the engine does sound as if it has a longer duration camshaft than what was factory original. This may mean the engine is not entirely original inside, and may have been rebuilt at least once.

I am often dubious of a someone selling a performance car, and having amnesia about the status and condition of the engine. For someone who both doesn't want to lie or tell you bad news, they may develop... amnesia.

With patience and help from this forum, I am confident you can discover what needs to be done.

Your vacuum at idle seems pretty low to me, but then, with longer duration cams, this is a common side effect. A smallish vacuum leak might effect the surging and stumble you're seeing when driving. There are several ways to test for vacuum leaks, and some methods are pretty easy.

Is your exhaust so loud you cannot hear the engine when driving? If so, this will make some things harder to hear and diagnose, like a spun rod bearing.

The "mystery engine" was a good negotiation point and I was able to talk him down on the price of the car significantly, so that's something .

The seller claimed that he bought the car this way several years ago, so he was not the one that did the work and doesn't know much about it. I have my doubts but either way I'm having a lot of fun working on it and driving it.

I've been searching for vacuum leaks but haven't been able to identify any yet... but I'll keep going at it.

The exhaust is quite loud and makes it hard to identify what other noises I'm hearing. I may have to quiet it down just to help diagnose things.

as always I appreciate all the feedback!

 

[Challenger RTA]

I'll save you some time. To find a vacuum leak use brake cleaner. I seen other use gasoline but I think brake cleaner is a bit safer. Here is someones video. .

 

[Chryco Psycho]

SO what is the question ?
Vacuum reading at idle in gear will give you a idea of the cam size , the power valve probably needs to be changed so it stay closed at idle in gear so if you have 6" at idle you need a 3.5 PV , , you also need smaller air bleeds on the idle & probably the jet circuit which cannot be changed on 6 Pack carbs but inserting a wire & trapping it behind the squirter can help