Kinda dumb engine tuning question

[loco340cuda]

Ok, I feel kinda stupid asking this question but I will anyway.

I had my 340 stroked to 417 and it now has a Mopar 484 cam in it (108lsa). Now I asked for a cam that idles rough and I believe I got what I wanted and I do like it.

But the thing that I'm trying to figure out is how can I tell if the the engine is tuned properly. Before I had the motor rebuilt the engine had a mild cam in it that idled fairly smooth. It was easy to tell if the engine was in tune. But this engine idles rough so I'm not sure how to tell if something is wrong.

I have checked the timing, vacuum, and idle, as well as made sure all the plugs were firing (checked this with the timing light) what else can I check to verify the engine is running properly? In other words I just want to verify the rough idle is from the cam and not do to engine issues.

-Thanks

[MEK-Dangerfield]

The only thing I could suggest is take it for a ride, and see how it behaves. Just driving easy and getting on it a bit should tell you if it is happy. My car has a big cam, and it always seems like it is ready to die idling at a red light.

  Mike

[loco340cuda]

MEK, does your car really shake when you are at a stop light to the point you almost want to hit the gas to smooth it out a little?  I have never had a car with a big cam so I don't what to expect, I really like the way it sounds and that it shakes the car, but I want to make sure that the shake is normal.  I have checked the motor mounts and they are good.

As a point of reference, when I drive the car it it seems fine it is just when I get to a stop light and let it idle the car really shakes, it just got me to wondering.   

[HP2]

The 484 is a decent cam that will lope fairly hard, but so long as it idles without dying you should be okay. If you have a problem you will always need to fiddle with it to get it to idle or you'll need ot turn the idle up to get it to run. You could always do the old propane torch around the intake trick to see if you have a vacuum leak. Leaks will cause a very rough idle that will smooth out on accelleration. Other option is to hook it to a scope or a dyno. It is usually worth the $100 or so to have someone do a dyno tune just to get the a/f ratio, timing, and output maximized. Could net you an additional 20-50 horses over a shade tree tune up depending on your skill level.

[MEK-Dangerfield]

MEK, does your car really shake when you are at a stop light to the point you almost want to hit the gas to smooth it out a little?  I have never had a car with a big cam so I don't what to expect, I really like the way it sounds and that it shakes the car, but I want to make sure that the shake is normal.  I have checked the motor mounts and they are good.

As a point of reference, when I drive the car it it seems fine it is just when I get to a stop light and let it idle the car really shakes, it just got me to wondering.   

I'm not really feeling the shakes with mine, but at a stop light, I always feel I need to give it some gas, or it will die out. It lumps, lumps, lumps, at about 700 RPM, or so, but feels like it wants to die. How is your car running otherwise? Is the engine responsive and such? Is the idle your only concern?



  Mike

[ntstlgl1970]

What are you setting your idle speed to? Once you change a bunch of stuff (cam, exhaust, carb, intake and so on) stock specs -idle speed, initial advance, idle mixture- go out the window. What carb/intake/exhaust are you running? Is it an automatic?
Trying to make a 484 cam idle at a low speed might be a stretch, maybe try it at 800 or 850 and see what it is like. Or take a video on a cell phone or a buddies camera and post it so we can check it out.

[422STROKER]

I think a 484 cam in a 417 should be small.

Tom

Make sure there are no vacuum leaks.

[loco340cuda]

What are you setting your idle speed to? Once you change a bunch of stuff (cam, exhaust, carb, intake and so on) stock specs -idle speed, initial advance, idle mixture- go out the window. What carb/intake/exhaust are you running? Is it an automatic?
Trying to make a 484 cam idle at a low speed might be a stretch, maybe try it at 800 or 850 and see what it is like. Or take a video on a cell phone or a buddies camera and post it so we can check it out.

Thanks for the replies everyone.  Here is my setup:-

-340 stroked to 417
-MP 484 cam (108lsa)
-stock 'X' heads (unported)
-Holley Street Avenger 770 carb with electric choke
-Edelbrock RPM Airgap intake with a K&N dropdown base and 2.25" aircleaner with the K&N high flow filter top
-TTI headers out to a TTI 3" exhaust system through Flowmaster Super 40 mufflers
-FBO electronic ignition with curved distributor (initial timing is set to 18deg per FBO spec's)
-4 speed with 3.23 gears and 27" tires, (going to 3.91 gears in a few weeks)

Last time I checked the idle RPM it was 850-900, and once the car warms up it seems to idle ok, in that it doesn't stall.  Also I'm a little suspicous that the low profile air cleaner might be interfering with the choke door a little (i.e. not enought room between the top of the choke door and the bottom of the inside of the airclearner lid.  Anyone had or seen that problem before?

Where can I buy a small propane torch to do the propane test?  Also the car has power brakes (which I am going to convert to manual in the near future) is it possible there could be a vacuum leak in the brake booster? 

I'm going to mess with the car on Saturday so I'll try to take a short video and let you long distance mechanics give your opinions on how you think the car is running.     

[Chryco Psycho]

yes the vacuum booster can leak , cap the port to the booster & see fi it runs differently What is your manifold vacuum at idle ?? You may need tro change the power valve to a 4.5 " to clean the idle up , I assume you have set float levels up?

[HP2]

Boosters are a great palce for leaks to hide.

The small propane bottles can be found at any hardware store. Open the valve, direct it around the intake manifold, carb base, hoses, booster, etc and as it sucks in the propane, your idle will increase. You can do the same thing using spray carb cleaner only it will drop your idle. The propane does tend to work a little easier since it is a gas instead of a liquid.

[loco340cuda]

yes the vacuum booster can leak , cap the port to the booster & see fi it runs differently What is your manifold vacuum at idle ?? You may need tro change the power valve to a 4.5 " to clean the idle up , I assume you have set float levels up?

Chryco, the mainfold vaccum was around 9-10" at idle, I'll double check it on Saturday.  I'm new to the holley carb world so bear with me as I come up to speed on these carbs.  I checked the float level for the front bowl which I believe is the one for idle and it was right at the bottom of the window when the car was running.  I did not check the back float level.

Where can I find some documentation about how to change the power valve as well as find out what I currently have in the carb now?

[moper]

If that's a 417 with the MP 484, and it has 9-10" of vaccum in gear and shakes, you have issues. It should idle rock smooth and pull more vaccum than that. The 770 Avenger should be fine for that setup. Can you get a cylinder pressure reading from it?

[loco340cuda]

I do have a cylinder pressure guage.  If I get time on Saturday I try to check the cylinders. 

[422STROKER]

If that's a 417 with the MP 484, and it has 9-10" of vaccum in gear and shakes, you have issues. It should idle rock smooth and pull more vaccum than that. The 770 Avenger should be fine for that setup. Can you get a cylinder pressure reading from it?

I agree, I wonder why....

Tom

[Chryco Psycho]

if you have 9+ " of vacuum the power valve that is in htere  is ok