Moparts
440 engine tuning help
Posted By: PJ68RT
440 engine tuning help - 07/16/08 03:08 PM
68 charger 440 all stock (10.1 CR) I put in a comp XE268 cam and have been having rough idle and low vacuum issues. Degreed the cam in and all was as it should be.
I had previously been running 10deg spark advance which resulted in about 9-10" of vacuum at 850rpm. I recently set the timing by vacuum gage and seeing where it had the most vacuum. This brought my vacuum up to 14", but i have to advance the timing to 35-40deg initial at 850rpm to get this much vacuum...???? This seems way too high. I thought maybe the balancer had slipped so i checked top dead on #1 and timing mark is right at 0 where it should be.
Anyone have any ideas what might be the problem??
Posted By: GomangoCuda
Re: 440 engine tuning help - 07/16/08 04:15 PM
Are you disconnecting the vacuum advance and plugging the vacuum when you are setting the timing?
You probably need to shorten the mechanical advance curve in your distributor so that you can have about 18-20 degrees at idle and about 36 degrees total. These numbers are without the vacuum advance connected. How you do that depends on what distributor you have. Afterwards you can try with and without the vacuum advance connected to see which works best for you.
(edit) I just noticed you are in Denver. That might affect how much timing you need and how much vacuum you are going to get. I don't know but maybe someone else that lives at high altitude can expand on that issue.
Posted By: lewtot184
Re: 440 engine tuning help - 07/16/08 04:38 PM
thats very low vacuum for that camshaft profile. i'd look for maybe a vacuum leak (rough idling a symptom), or maybe some trash in the carb.
Posted By: PJ68RT
Re: 440 engine tuning help - 07/16/08 05:10 PM
I have checked everything...no leaks. Read somewhere that every 1000' drops vacuum 1". So im at 5000' = -5". I'm getting 14" max @ 35deg initial. 14" is pretty decent at this altitude i think. Something is not right. Was just looking for some opinions before i tear the whole thing down.
Posted By: moper
Re: 440 engine tuning help - 07/16/08 08:02 PM
Timing lights were invented to set timing. Vacuum gages set carbs. Sounds stupid, but truth is truth. You need maximum effciency at cruise, not idle. Make sure the vacuum advance is disconnected. Make sure that it is normally connected to ported (no signal at idle) vacuum. What carb is it? When you changed the cam... did you re-install the same intake? It sounds like it's not tuned right, but it could be a vacuum leak. That cam should idle lower, and still give decent vaccum. Was this engine ever rebuilt?
Posted By: PJ68RT
Re: 440 engine tuning help - 07/16/08 09:16 PM
I should clearify...The max vacuum i get at idle is 14" and this is with timing set to 35deg initial. I get higher vacuum if i rev it a bit.
This was done with vacuum advance unhooked and hose plugged. This seems like way too much initial timing to get decent vacuum.
It was suggested to me previously by the forum members that i set the timing by using vacuum gage and seeing where i get the most vacuum at idle. Along with the low vacuum and rough idle (motor shakes) the bottom end performance is poor..comes on at about 3000rpm.
Posted By: PJ68RT
Re: 440 engine tuning help - 07/16/08 09:20 PM
I should also say that the engine ran great with stock cam..good smooth idle, good vacuum, lots of low end. Its just now that i switched to the comp that i have started to have these problems.
Posted By: BSB67
Re: 440 engine tuning help - 07/17/08 12:09 AM
Quote:
I should also say that the engine ran great with stock cam..good smooth idle, good vacuum, lots of low end. Its just now that i switched to the comp that i have started to have these problems.
First, that cam should idle much like the stock cam. Second, focus on the things that you changed. If you only removed and reinstalled the distributor and carb, I would not mess with them other than to make sure that you reinstalled them correctly. Challange and recheck your work that you have convinced yourself to be okay. I would start with looking for a vacuum leak. How did you check that the first time?
Posted By: RapidRobert
Re: 440 engine tuning help - 07/17/08 03:25 AM
vac leak.
Posted By: MikeyT
Re: 440 engine tuning help - 07/17/08 03:26 AM
I got the same exact cam and it runs very smooth when in the car and this is t stock. I would look and make sure everything is set and no leaks.
Mike
Posted By: thecarfarmer
Re: 440 engine tuning help - 07/17/08 04:04 AM
Propane boost test will spot a lean condition.
If you haven't done anything 'funny' with the idle mixture screws, and IF idle mix had been adjusted correctly before pulling intake... then a vacuum leak would be the likely culprit.
Check tops of manifold to heads with water stream; also see if brake vac booster and other vac hoses are in good condition.
Good luck!
-bill
Posted By: SomeCarGuy
Re: 440 engine tuning help - 07/18/08 05:07 AM
Look for somethig stupid, like a vaccum cap knocked or left off. I've had a few engines that ran poorly after some work and found I had left a cap off when I was done testing it with the vaccum gauge
Posted By: SomeCarGuy
Re: 440 engine tuning help - 07/18/08 05:10 AM
Also I see you are saying that the timing is set to 35 degrees initial.
I'm guessing that you mean total. If it is 35 initial I would think that is so much it would run real funky...
Posted By: PJ68RT
Re: 440 engine tuning help - 07/18/08 01:15 PM
That is what is causing me the most confusion. The initial timing is set to 35 deg to get the 14" of vacuum. This is just idling in the garage...i haven't drove it with the timing that high. Anything lower than this and i get low vacuum readings. I wouldn't think the motor would run at all with the initial this high but it does. I checked to see if balancer had slipped but the timing mark is at zero with #1 at TDC.
Posted By: Mopar_Mike
Re: 440 engine tuning help - 07/18/08 01:20 PM
Quote:
68 charger 440 all stock (10.1 CR) I put in a comp XE268 cam and have been having rough idle and low vacuum issues. Degreed the cam in and all was as it should be.
I had previously been running 10deg spark advance which resulted in about 9-10" of vacuum at 850rpm. I recently set the timing by vacuum gage and seeing where it had the most vacuum. This brought my vacuum up to 14", but i have to advance the timing to 35-40deg initial at 850rpm to get this much vacuum...???? This seems way too high. I thought maybe the balancer had slipped so i checked top dead on #1 and timing mark is right at 0 where it should be.
Anyone have any ideas what might be the problem??
Here is my two cents on this... I had this same came in my 66 440 and I really did not like it.. It has a rough idle and I believe on the Comp Cams spec sheet it says the cam is a rough idle cam. I chased down everything, leaks, timing, etc. etc.. (much like your doing) to smooth it out. It has a rough idle and that is just the way it is.. IMO I would swap it out for a lunati voodoo series or a Crane..
Posted By: Anonymous
Re: 440 engine tuning help - 07/18/08 01:29 PM
Quote:
Timing lights were invented to set timing. Vacuum gages set carbs. Sounds stupid, but truth is truth...
more people should use that advice. 
with those two tools,
one can prolly solve 99% of engine problems. welcome back.
Posted By: PJ68RT
Re: 440 engine tuning help - 07/18/08 04:46 PM
i wouldn't mind the idle if it ran good. I have lost bottom end performance. All in all this cam is .2-.3 slower then stock cam in E.T.
Posted By: Anonymous
Re: 440 engine tuning help - 07/19/08 02:27 AM
I run that cam in a 69 B body with a 440 and Holley Street Dominator (single plane intk) with a carter TQ.
At 650 idle rpm in neutral (Detroit area) it generates about 13" of Hg. The cam does have an idle to it. You will know there is a cam in there. 18 degrees initial and 36 total by 2000 rpm. Idle feed restrictions opened to .037".
That cam rocks. Good low end response and good pwr up to 5700 rpm.
Posted By: SomeCarGuy
Re: 440 engine tuning help - 07/19/08 08:05 AM
Maybe that cam is looking for some ported heads to be on top to make it run strong...