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Help 390 Dog
I have a rebuilt 390 That does not run strong/pull any help would be appreciated this is were I'm at bore is .080 Silv-o-lite pistons PN# 1138 Comp.Height 1.66 compression ratio(s) 10.3 crane cam 941 Edelbrock performer manifold holley 650 DP headers Mallory unilite dist. At 750 rpm idle vacuums 14 Compression tested 140 low 150 high my question is that enough compression? also if not what is the best way to raise compression?This is the cam spec. Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration Intake 1 BTDC 35 ABDC 107 216 ° Exhaust 51 BBDC (3) BTDC 117 228 ° Lift: Intake @Cam 3027 @Valve 533 All Lifts are based on zero lash and theoretical rocker arm ratios. Exhaust @ Cam 3200 @Valve 563 Rocker Arm Ratio 1.76 Cam Timing: TAPPET @.004 Lift: Opens Closes ADV Duration Intake 25 BTDC 67 ABDC 272 ° Exhaust 75 BBDC 29 ATDC 284 ° Also I decreed the cam and it is right on the numbers |
Some suggestions
I'm no expert but I'll tell you a few things to try...
Easiest and cheapest is to work in your timing curve. I like to try 20 initial with 38 total in by 3000 rpm. Work up to that until you hear detonation. That will probably perk you right up. I would recommend a Performer RPM intake instead of the regular performer. You might want a bigger cam. I had picked that cam for my pickup truck, but in a cobra you can use more. Here is a desktop dyno plot of my isky cam vs the crane in my 390 build. Chuck http://www.chuckbrandt.com/cranevsisky.gif |
Makre sure you have good fuel pressure. I have seen performance problems related to this that stump the best of them. What is your carburetion and fuel pump setup?
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Do not confuse cranking pressure with compression. Compression is determined by piston configuration and head size (chamber shape and size) that you have limited power may or may not be related to low compression.
I'd look at ignition timing and carburation. 140-150 is pretty normal cranking pressure for a standard FE. |
390 Dog
The previous replies are right on but you didn't say what your rear-end ratio is. If it is too close to 3.00, that and your cam effective rpm range, might be contributors to the doggy performance. Also, a 390 can benefit from a lighter flywheel such as a Centerforce billet steel (not alum.) at 29#. Helps it spin up faster.
Paul |
I would check the timing too. Even a stock 2v 390 would pull hard and smoke the tires.
I had a Galaxie with a 427 2x4v that wouldn't do a burn out and no low end power due to a timing issue. Tony |
EVERYONE IS RIGHT ON ABOUT TIMING. FE'S LIKE A LOT OF INITIAL LIKE CHUCK ADVISED. ALSO, TODAYS CAMS LIKE INITIAL AS WELL. QUESTION, WHATS TOUR JETTING AND HOW FAST ARE YOUR SECONDARYS OPENING? TOO SOON AND THEY WILL BOG AND NOT PULL HARD. GOOD LUCK
BYRON W. |
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