I was curious as to how high some of your guys' 390 raps out to?
Mine is a remanufactured unit with a rv cam and edelbrock manifold and 600 carb and it will only go up to about 3400 rpm. What all would determine how far it goes? Is there something the matter with my motor? What can i do to get it to go higher? When it gets to 3400 it just sits they and misses sort of like the valve springs are to weak and not closing good enough and floatng or something. At first I figure the carb was to small or something but we put it on my bros car that has a 396 (fricken chevy) and it goes clear up to 6500 rpm. Is it my cam or something? I'm clueless. Be great if somebody could help out a poor old boy.
Richard

 

I'd start looking at the ign. If your running points i'd convert it over to the Pertronix setup for about $60. Check the coil and wires.

Run the engine with the timming light and see what the advance is and try different starting points from about 6 btdc to 14 btdc and see if that make a difference.

Check the fuel supply, a bend in the line can cause low volume as well as a clog in the tank. You can remove the line and blow thru it to remove any rust in the path then run the tank dry and replace the filter.

Stock springs are good for about 5000 to 6000 with a stock or near stock cam so I'd really focus on the tune up and fuel system.

I assume you talking about free reving not freeway revs under load.

 

I would have to lay my money on the valve springs. The cheap way to fix this is to put some shims under the spring but be careful that the springs don't bind with the shims under them. The right way to do it is to buy a new set of springs. You can have your springs pressure checked at a machine shop to determine if they are wore out. First check your timing at about 2500 rpms. It should be in the 34 - 36 degree range.

 

beat me to it karljay

 

Check your points, your timing, your fuel filter if you have a external one. You said it's remanufactured, I'd try to check to see how well the cam was degreed if at all. Did you put new plugs in it and new plug wires on it, is your positive and negative reversed on your coil? How wide is the gap set on the plugs? try putting a fuel pressure gauge on it and tape it to yoru windshield and go for a drive, get on it and make sure you have at the very least 4psi of fuel pressure after the second shift your tranny makes.

 

My first 390 had an Edelbrock Performer Manifold and 600cfm Edelbrock carb w/ Crane XR700 electronic ignition and Comp Cams 268H cam. The heads were worked over at a machine shop. It stopped making power about 3200 Rpm. I ended up tearing it down and found that as I suspected one oil ring was gone and I had a broken piston. This engine also had the stock exhaust manifolds going through 2" dual exhaust which I think is rather restrictive. It's on and engine stand now waiting for a rebuild. While discussing options w/ one machine shop I got disdain for the Comp Cam 268H cam in a 390, they think they work ok in other engines but don't recomend it for the 390. They also were suspicious of valve springs and certainly I was getting lots of blowby and bad cylinder pressure. I now have another 390 I got at junkyard and am using in my truck now. It's had a rebuild by evidence of machinists stamps on the block and heads, so I don't know what cam it has, but it's got a stock iron 2V manifold and motorcraft carb. I'm using the Crane electronic ignition to trigger an MSD 6a w/ Blaster coil. It seems to have somewhat higher rev potential although I haven't tried to find the upper limit, I've had it to around 3400 under a load. I have 3.25 gears and 31 inch tires and a Manual tranny so it does have a load to overcome. And it has the same exhaust on it. It does have much better oil pressure though. I've heard of others likeing dual pattern cam grinds w/ more exhaust duration, and also ppl using BB Chevy valve springs. Certainly if they could race 427's at high rpms.... you should get a 390 (w/ the same stroke) up higher than 3200.

BBT

 

I would not suspect the valve springs. I'm running stock heads and valve-train. I've been brave enough to see 5500 RPM in 1st and 2nd gear. It could probably approach 6000, but I'm not that brave yet. I do have a reasonably high duration cam (Crower Power Beats 292H), Performer RPM intake, 750 carb and upgraded ignition and headers with 2.5" duals. I suspect I'll easily see 6000 after upgrading the heads and valve train.

Greg

 

Hey BBT, was there a reason they didn't like the 268H? Other than ignition and the intake, thats what I have in mine. I don't like it mainly because I don't build any power until about 2200 RPM, then it takes off. I hit over 4,000 RPM last winter when I was stuck in a blizzard. I always thought top engine speed was determined by cam and springs more than anything.

Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.

 

In answer to the machine shop telling me they didn't like the Comp 268H in FE motor, they didn't get technical with me as to cam science, they just said it seems to work well in other kinds of motors but not the FE. I guess I was suppose to respect their years of expirience in these matters, they had some ego, and made fun of "HotRod" type magazine writers and their "technical" advice. Unfortunately most of us have to trust an expert for advise, not haveing the ability to try many combinations out. I do know they had a bias against Comp Cams because they said they'd' gotten some in the box new that were bent. I've heard many suggest dual pattern grinds w/ more exhaust duration for Fords, and the Comp 268H isn't. I'd venture that the main reasons my engine wouldn't make power past 3200 was the poor ringseal and restrictive exhaust. I had a fresh dual row timeing chain installed straight up btw.

BBT

 

 

i have a 1970 250 custom camper special w/390 4-spd it redlines at 4100 and goes to 6500 probaly .stock 2bbl autolite carb, everthing else is also stock .. the 390 likes some good ol lead foot driving every once in awhile or it gets kinda lazy..



Fe power

 

I'd look at point gap first. I have a 351M that used to melt the plastic block on the points where it met the dist shaft when I was in 29 Palms, Cal. The ambient air temp was around 110 deg or so.

Trail Rider