rebuilt 390

[390owner]

Now that I have 390 broken in or at least I think I do. I have driven it about 1200 miles. I am a little disappointed with the power. It has the comp cam 33-234-4. This engine does not want to pull as good down low as my old 390. It is bored 60 with stock heads and balanced. Why did my old worn out 390 seem to have more power. It was also bored 60 over stock heads with a rv type cam. The new engine has almost stopped burning oil but still has a slight smell of an old lawn mower that smokes. Maybe I just need to drive it some more miles. Also I have a hei dist. Can I do something it so it does not advance so much. I have it adjusted all the way out and am still getting some pinging at light throttle at highway speed. I set the timing again today to 34 total then test drove it it pinged a little at wide open throttle pulling a hill with the spark advance unplugged and plugged. So I backed off the timing 2 degrees but have not drove it yet.

[cammerfe]

I would look into the actual timing you are using. Using a Ford distributor, the old rule-of-thumb was to set the centrifugal advance mechanism to the "10 degree" position which gives 20 degrees of engine advance and then try for 18 degrees of initial dialed in for a total of 38. It took good gas (Sunoco 260) to use this much initial. Performance Ford engines didn't use any vacuum advance.

Not enough advance at the right time will definitely make your engine 'lazy'.

You may have some sort of internal engine sealing problem. With today's rings, you should be all run-in within about 15 minutes of fast idle.

Good Luck!

KS

[rockhouse66]

I was very unhappy with the Comp H cam I had in my 428.  The one you have is 212/218 so it is very mild and has extra exhaust duration.  I always suspected that this cam needed a high CR to work right or it would just bleed off the compression at low RPM.  But....camshafts remain a mystery to me.

[Falcon67]

Some thoughts -
- Looking at the cam specs, I have more duration in my street 302.  So you should have plenty of cylinder pressure - may want to take some actual cranking compression readings. The LSA is lower than I thought it would be, that's what makes it "Xtreme".  That's not necessarily an "RV" cam.  But it's still small for that displacement.
This would be their "RV" cam - http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=941&sb=2
Not sure about FEs, but I never stick a shaft in a 351C without doing a full degree in.  Too many little things tend to be off.  Like crank keyways, balancer markings, etc.

- Timing - you should run as much initial as you can, then limit total.  If you keep twisting it back to reduce total, you're killing low end.  Vacuum advance should be adjusted separately if it's a decent distributor.  "HEI" - that's a GM term, hope it's not one of those "ProComp" units. 

- Oil use - If you used good quality moly faced rings and had the cylinders finished appropriately. your rings should have seated before you left the driveway.  No way it needs 1200 miles.  Not even 12 if done right.

[machoneman]

Did you degree the cam? If it's retarded, it will lack low end power. Smokey could be flooded cylinder heads (blocked drains), no drip tins, shafts installed upside down.

[e philpott]

not enough total timing and a turd cam is my bet

[WerbyFord]

Now that I have 390 broken in or at least I think I do. I have driven it about 1200 miles. I am a little disappointed with the power. It has the comp cam 33-234-4. This engine does not want to pull as good down low as my old 390. It is bored 60 with stock heads and balanced. Why did my old worn out 390 seem to have more power. It was also bored 60 over stock heads with a rv type cam. The new engine has almost stopped burning oil but still has a slight smell of an old lawn mower that smokes. Maybe I just need to drive it some more miles. Also I have a hei dist. Can I do something it so it does not advance so much. I have it adjusted all the way out and am still getting some pinging at light throttle at highway speed. I set the timing again today to 34 total then test drove it it pinged a little at wide open throttle pulling a hill with the spark advance unplugged and plugged. So I backed off the timing 2 degrees but have not drove it yet.

IN GENERAL:
Well yes I've seen it. If the engine was built "tight" you can be down 10-20 ponies across the board so it may seem about the same as your old one. It will "loosen up" (ie stuff will wear until it's looser) with time. Not ideal but many are built that way. And if you'r eafter a 200,000 mile cruiser, a tight build is not so bad. What were the main, rod, piston clearances when you built it? With just the crank in & mains torqued, did the crank spin free? How much torque did it take to turn the whole short block over?

TO HELP MORE:
What car combo is this? Car, weight, trans, gears, pipes, mufflers, exhaust manifolds or headers, which intake & carb.
Any idea of the specs on the "old" cam?

WHERE is it slower? Below 3000? Not surprising. Around 3000-5000 that cam should be happy, after that it will fade out.

TIMING:
WHERE is it knocking in terms of RPM? You want to cut the timing back right in THERE, not necessarily initial or even total. I like a curve that's in full by 3000rpm too, but sometimes a stockish engine wont take that. It will take 36 total but not at 2800rpm!
How hot is it running? If new & "tight", it will run hotter & knock more.

The old engine was probably loose as a goose, sometimes they run really good that way, until something lets go.

[Faron]

The HEI cheapo Dists that are out there usually have a min of 12 to 15 in the dist that will only allow a initial of 8-12 initial in a best case deal , being able to run 16-20 initial really brings in the bottom end with a bigger cam, also they usually have a vacuum advance that brings in MORE timing way too early and way Too much  , your HEI can be modified to allow that but it will take more than a spring change I can do it if interested

[Falcon67]

X2 on send to Faron or get him to supply you a debugged unit. 

[390owner]

Thanks everyone. A machine shop that has been in business over 35 years built this engine and the last one that I replaced. He said about 34 total was all it would take.