Engine loses power around 5000RPM

[Jacksboys]

I took the Challenger out this morning for a short drive.  In the process, I decided to give it a hard run and at about 5000RPM I noticed it losing power.  I also noticed the tach started to get erratic at the same RPM.  I built this 360 to have plenty of power until at least 5500 RPM so I know something is not right.  Other than that the engine runs great, idles great, and has plenty of power.

I know it has to be in the ignition (electronic), so what do you think I should look at first?

[ntstlgl1970]

Plugs and plug wires

[HP2]

Have you run it up at that rpm ever before? If so, is it different now than before? Just verifying because stock mopar small block heads usually aren't worth much power over 5000 rpm because of lousy airflow. If you've never had it buzzing that high before, you may not have an accurate point of reference simply based on build specifications.

[moparclown]

Sorry about jumping in here,but where did you hear that small block heads don't flow good?I am just curious is all?

[Super Blue 72]

Plugs and plug wires

Cover the bases:  then cap/rotor/coil.  Make sure your control module has a good ground too.

[MEK-Dangerfield]

Your tach gets it's feed from the "-" side of the coil. That might be at fault here. I once had a coil that was fine until I got close to 2000RPM, then the engine would miss, and the tach would go bonkers. 


  Mike

[Bullitt-]

Don't overlook running out of fuel....pump/filter/small lines....
add a couple of degrees of advance, even if it doesn't like it at low rpms, & see if that helps top end, if so an advance recurve would help.

[MEK-Dangerfield]

If your tach is going nuts, the problem is electronical.   

[ChallengerHK]

 

[Oldschool]

If your tach is going nuts, the problem is electronical.   

Prolly, but not neccessarily....  It depends on HOW erratic it is getting.  If it is going wild, then I agree with you entirely.  But, if it is only recording what the engine rpm's are doing, it COULD be fuel.  Eg:  if it has fuel problems, the engine will stumble and the rpm's will drop, and when it picks the fuel back up, the rpm's will rise again and the tach could be seeing that.  Thus the tach would fluctuate and it would be fuel related.  Just my old 0.02......          

[Jacksboys]

I am pretty sure it has nothing to due with the fuel because I have an O2 sensor and I did not see a lean spot.
I have the Edelbrock heads, so airflow is not a problem, and 5500RPM should be a breeze.

This was only the second time I have spun it up that high while I was watching the tach.  The first time (about a month ago) I thought it was just my imagination, so I did not worry about it. 

The tach does not fluctuate up and down, it  shakes erratically until I shift into 2nd, then it is fine again until it gets near 5000RPM again.  I can still feel the engine trying to increase in RPM past the 5000 mark but it is very weak.

I forgot to mention that this happened once before with a different distributor that I tried to refurbish, but the problems started at 3000RPM.  Then I got the Mopar Performance dist. and I thought that solved the problem...I guess not. 

I am 99% sure it has to due with the electronic ignition.  I might borrow my father's coil and see if it makes a difference, since that would be the cheapest route first.

[Chryco Psycho]

what intake / carb / exhaust ?

[Jacksboys]

what intake / carb / exhaust ?

RPM intake (port matched)
600cfm edelbrock carb.....I know it is small, but should be enough for 5500 RPM
Dual 2 1/4" exhaust

other info:
XE268H cam


I built the engine to be a torquer   

[HP2]

Sorry about jumping in here,but where did you hear that small block heads don't flow good?I am just curious is all?

First hand experience. The stock heads I've used would spin past 5000, but I can feel them flatten out at that point. Ported and Magnum heads don't have the same issue. I['ve enver tried any aftermarket heads. It isn't that they don't flow good, they just don't flow great. With the pushrod pinch point on the stock small block heads, flow over 5000 rpm isn't sufficient to maintain the % of horsepower increase as below 5000. This is why the T/A and W series heads all used offset rockers to match the reconfigured port and the later magnum heads were revised as well.

With Ebrock heads, this isn't the problem being discussed here.

[Bullitt-]

I'll put my   experience re: heads...I'm taking bone stock '73 back in the day, at 120 MPH I'd be turning 6000 rpm & still pulling reasonably well, later changed to ported cc'd early model O heads & while I have never ran them for top end speed they are even stronger & rev. well past 5G.
  Can anyone give any specifics of O heads? ... I think their pretty rare.