Ok so in short the motor was an old 305 tbi and is now a 400 bored .40 for a 408 expected hp is supposed to be near 600. At first the motor will run ok but after runnin it Hard like 20mins it will have issues but my TEMP are ALWAYS BELOW 160!! I have done everything from using :
the factory fuel pump and holley fpr with return style using both lines set to 7psi and still had fuel jumping from 3-15psi...got one fuel filter and had same issue...added another fuel filter after the fpr and before the carb...same issue...fuel bowls are correct and have been cleaned.
got rid of old pump and replaced with an high hp loud *** electric fuel pump mounted near the rearend after we dropped the tank and removed the old and got new holley fpr...same issue...changed filters again and got new FPR and same issue...cleaned carb just in case and the shop said its gotta be trash in the tank....
SO i got a new tank, checked the carb for trash, new filter again to 100 microns and SAME FUKN ISSUE....
Switched to mech holley fuel pump and same fukn issue just now the fuel drops to 1 and doesnt rise above 3psi.....
now i know the factory fuel line are near the headers about 1inch apart......im running hooker Lt's 1 3/4 coated as well and heard of vapor heating issues as the gas heats up causing bubbles but were can i relocate the lines now on both sides of the engine bay to where the lines are not close to the headers???
I also opened the gas tank to see if there was maybe a leak or vacum issue in the fuel lines but it did not help...was a lil better for normal driving but fuked up if i got on it...temps during all this are the same...Ive already bought a new tank, fpr's, 2 new differ kinds of fuel pumps and nothing fixes **** and $1k on parts and labor plus 9 trips from home to the shop and them towing it back..................
Ive never seen anyone run the fuel around the front of the motor for it'll look gay as hell and not professional but i can only think its vapor rash or w/e its called or new fuel lines but For *** SAKE.....ANY SUGGESTIONS FELLAS?????????????????????????

 

It's easy enough to test. Just shield the lines from the heat and see if the symptoms change.

If you're worried the tank isn't being vented right then just loosen the gas cap and test again.

You didn't really describe your symptoms other than the fuel pressure jumping from 3 to 15 PSI.

 

If it is a return style system and you are running a high pressure pump (especially a fuel injection pump), your problem could be the return line. If the AFPR can't bleed off gas fast enough and send it back tot he tank, your pressure will jump around.

I have the stock lines (original TPI car) feeding my Holley and I have never had vapor issues. I have the same headers too. I guess it could be that, but I would first check the return line for kinks, sharp bends or trash in the line.