318 rpm drops to 400 in gear WHY???

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EV270CUDA

EV270CUDA

EV270CUDA
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Posting for friend who's 72 318 dart just rebuilt motor and it idles perfect @ 1000 rpms until you drop it in gear and falls on its face to 400 rmps . Things we have checked ,vacuum leaks, cant find any . Vacuum check say 8 pounds Timing at 32 brand new Holley 650 the second one we tried still does the same thing things done in rebuild include msd ign 6al distributor, performer intake 4 barrel, hooker header ,484 lift cam , ported iron heads, 2500 stall converter . Blocked the power brake booster off and no difference ?? So what should we check next ?? New fuel pump and line also .Any ideas or help please will be appreciated. Thanks
 
had the same problem with my 360. I put the 484 purple shaft cam in it.
I think they cut the key way wrong for the cam gear. I sold the car recently and never did get it figured out. i let it idle at 1200rpm and it helped alittle while in gear. engine had a bad shake to it at idle. let me know when you figure it out. i had a 2600 stall b&m convertor. i am curious.best of luck to you
 
32 degrees total or sitting at idle? Whats the compression ratio? 8lbs of vacuum is too low, it should be 10-12 if you want it to hold a decent idle. How did you set the idle mixture?
 
Does it run rich and stumble when in gear? 8lbs of vaccuum would require a 35-45 power valve (in most holley's) to avoid dumping fuel and idleing horrible.

I would check carb and ignition tuning and once they are ruled out you can dig deeper.
 
not enough converter? that 284/484 like atleast 3000 stahl if i remember correctly. had that cam in a 340 and it had to idle at like 1300 to make it idle in gear. had a small converter like your in it.
 
I ran my 318 with similar components (same cam) in a 68 cuda using stock 340 converter and had no idle issues (once I solved the fuel loading problems). Only other difference was I used rhoades lifters... they worked pretty well to help idel quality by bleeding off at idle and reducing cam profile but coming back in quickly when rpms increased.

If you are using the larger 318 converter it may not be enough but stock 340 or better should work (of course "should" means "no gurantees")
 
I hope you've got a good compression ratio going with that cam. I made that mistake once and won't do it again. Also, as someone else mentioned.....32 degrees @ idle? I've actually heard about people drilling small holes in their primary throttle plates to get more air flowing through (because of the low vacuum) so they wouldn't have to crack the throttle open so wide and start getting the booster venturis dribbling. Maybe you could research that.
 
cudavert said:
I hope you've got a good compression ratio going with that cam. I made that mistake once and won't do it again. Also, as someone else mentioned.....32 degrees @ idle? I've actually heard about people drilling small holes in their primary throttle plates to get more air flowing through (because of the low vacuum) so they wouldn't have to crack the throttle open so wide and start getting the booster venturis dribbling. Maybe you could research that.
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I tried that on my 340 with the 292 hydraulic cam, and it didn't work. I ended up swapping the Holley for a new Speed Demon, and out of the box the car ran great like it never did with the Holley.
 
I've got the .474 cam in my car, those MP purple cams need a lot of initial timing to idle well. i had to put in about 18* initial to idle good and draw good vacuum. if i had to do it over again i would not use a purple shaft cam.
 
compression is 9.5 to 1 timing @32 deg at idle runs smooth not rich . Drops to 400 in gear .It has a 2500 stall tci converter recommended by cam card.
 
32 degrees btdc is way too muchtiming from what I have learned here. You want about 15-18 btdc at idle with the vacuum advance and carb ports plugged.
 
abodyjoe said:
not enough converter? that 284/484 like atleast 3000 stahl if i remember correctly. had that cam in a 340 and it had to idle at like 1300 to make it idle in gear. had a small converter like your in it.
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Crane cams is who he got the cam from recomened the tci 2500 stall converter . We tried run the idle up to 1200 rpm and does the same thing when droped in gear .
 
EV270CUDA said:
Crane cams is who he got the cam from recomened the tci 2500 stall converter . We tried run the idle up to 1200 rpm and does the same thing when droped in gear .
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We just switched back to the first holley 650 that he had on the car before the rebuild that ran perfect to see if that would change and boy it did cant turn the idle below 2,000 rpms or it will die. So looks like were going back to the new carb . ???????????
 
Did you try messing with the idle mixture screws? Even with that big cam I think you chould have more vacume than that.
 
distributor feeding mechanical advance in at idle, because its 1200rpm, and when it pulls into gear that mechanical disappears when idle speed drops. Possible?

Need to sort out the timing first before worrying about anything else. It will likely need at least 18* initial is my guess. Setting total timing is an absolute waste of time at this point.

484 cams need lots of convertor and initial timing. They aren't particularly friendly in smaller LA engines.

Vacuum leaks?
 
I had the same problem when my converter was to tight for the rest of the rig.
 
If its idleing ok until you put it into gear THEN the idle drops that much its a tranny or torque converter problem, not engine. Doesn't have a lockup TC by chance does it? If its bad it will do that. Stock, the car was set up to idle at 650 RPM in drive. With a stock converter that means it would idle around 750 in neutral. By running the idle up to 1000, it just means that the low stall TC is pulling the engine RPM down to where it was designed to be....
 
All good points and Most likely both timing and the convertor draging it down.
Sad to say but the Mopar cams today are not the Mopar cams from the 70's
I have a "509" cam in a Duster Im working on for a friend and maybe going to buy,and that cam is just junk.
Has a Mopar conv too and it's a joke.
The cam and the conv are comming out if I buy the car!
 
If you need 1200 at idle, out of gear; the carb is the first place to start. I'v run that set-up @ 700 rpm. Carb.
 
I think Crackedback has a good point that at 1200 rpm at idle the centrifugal advance is probably coming in and when you drop it in gear the rpm's go down so the centrifugal advance goes away and the timing drops. You can verify that by checking the timing with it in gear idling making sure to disconnect the vacuum advance. I doubt seriously that it would even start if the timing is truly 32 degrees before initial. Mine kicks back on the starter at 22 degrees before. It's probably more like 12 degrees initial and by the time it's idling at 1200 rpm it's advanced to 32 degrees. If this is the case you'll have to install a heavier spring on one side of the centrifugal advance to slow the centrifugal advance coming in. It shouldn't come in before 1500 rpm.

Also 8 INCHES of vacuum is decent for that cam in a 318. I say INCHES because vacuum is measured in inches, not lbs.
 
The cam is too large for the compression ratio and stall converter your friend is using. What gear ratio is in the car? with that cam you should be in the 3.90-1 ratio. The stall converter should be at least 3000 rpm, preferably 3500. Even with that cam, there should be at least 10-12 inches of vacuum at idle in neutral. The engine idle should be about 1000 rpm in drive with vacuum around 10 inches. The ignition timing should be about 10 degrees BTDC at idle in gear at 1000 RPM. 32 degrees advance is for total advance at 3000 to 3500 RPM. USe a set-back timing light to do this setting. The power valve in the carb should be at least three inches of vacuum less than the vacuum the engine draws when in gear. Carb primary jet for that small engine size should be 72 for a start, then do a plug check after a hard run and adjust the jet size from those readings. Now I hope that your friend is NOT using a double pumper carb, because that will kill off any throttle response you might hope to have when just off idle.
 
Though the converter/cam combo is not optimal... I will +1 for carb/vaccum checks and explain more what happened on my 318 setup with a 484 purple shaft/X Heads, 340 converter (in 1985 :-?)...

Car ran and idle'd fine at 900-1000 with carter AVS, but had similar vaccum to yours at around 10-11" at 1000rpm. Switched to a Holley 750 vaccum secondary and engine lugged and struggled to hold an idle in gear. Tried a friends Holley off his running 340 (stock cam) and same issue. Found that the carb had a #65 powervalve in it stock which was designed to open below 12" of vaccum (power valve delivers extra fuel flow when throttle is cracked/vaccum drops before plenum vaccum allows gas through carb venturi). At 10" of vaccum the valve was fluttering and loading up the car so it struggled at idle and when the car was in gear the 200rpm drop also dropped vaccum more which dumped more fuel hurting the idle speed and vaccum even more. The car would run but lugged and even shuttered sometimes. Switching to a #35 power valve (opens at <7" of vaccum)cleaned up the fuel issue and allowed for reasonable idle of around 1000rpm in gear. Since you had worse results with another Holley I feel like your problem is carb (+timing) related.

Mine took a while to diagnose since it was only when the converter drag took the vaccum below 10" that the car really suffered. Any Holley-type carb will have to be tuned to work with a lower than normal vaccum signal.

A looser converter will definatley help the issue by allowing the RPM's to stay higher and vaccum to stay up but I would think you should be able to get it to idle with a 2000+ stall converter.. at least mine did. As I mentioned in my earlier post, I also ran Rhoades vari-duration lifters. They bled down at low RPMs effectively giving me a smaller cam profile which gave me 1-2" more vaccum. This helped my idle and throttle response a tad.​
 
I've got a similar issue with the 318 in my Duster. I've recently rebuilt the 318 to below specs..

*302* casting heads
Weiand Dual Plane High Rise Intake
Comp Cam 224@050
Stock rebuilt bottom end
Hooker Headers
Holley 600 Vac Sec (NEW)

Having the same issue where it idles fine and then as soon as I put into Drive it stalls.. I have to re-look at the timing and vacuum levels which I havent done yet and also check for vacuum leaks as well... Damn frustrating...
 
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