Low Dyno Numbers, Need Help

X cam and GT40p intake and small diameter shorty headers? If you change just this you'll pick up big time.

My 347 runs a Holley Systemax with ported elbow, Comp custom grind cam and 1-3/4" Long Tubes with 3" Collector. If I ran an X cam, GT40P intake and shorty 1.5" headers without a tune I'd make under 300HP too.

Explorer intakes are great upgrades on stock 302 blocks but once you graduate into the big time w/ a 331 or a 347 stroker you should ditch the factory upgrade mods and go pure aftermarket for the best HP increase.

Did you buy the engine this way or did you build it this way? Like other have mentioned your intake and headers are choke points. Long tubes all the way!

On top of what @84Ttop asked, what MAF and TB are you running?

Junk intake junk cam junk headers. What rpm was it at? What compression? What kind of dyno? What was the correction factor? What were the conditions?

Ditto on all the above. Like Nick said give us the whole run down. As for intakes I agree with the systemax, eddy rpm II would also be a great choice.

The numbers are still too low. 1 1/2 headers doesn't sound right at all. They're probably 1 5/8". I'm not sure I've even seen 1 1/2" aftermarket headers. I had a 302 with a cobra intake, mild OTS cam, and GT40X heads, and a shorty 1 5/8" headers that made 270 rwhp on a Dynojet 248c through the stock 5-spd. You've essentially got the same combo except with much better heads and more cubes. Maybe this would make sense through an automatic on a mustang dyno, but I still would think there should be more.

The others are right, though. There is a ton of power waiting to be unlocked with a better intake (systemax II would be my pick with the RPM II close at hand), better cam (I prefer FTI customs), and long tube headers @ 1 3/4. That combo with good compression through a manual should reach the kind of numbers you've been told about. Your intake is not going much over 330rwhp in ideal circumstances, IMO.