I rebuilt my father's 400 for his 78 f150 while i was in high school. The crank was turned 10/10 and it was bored out .030..Since I could not find any performance pistons I ran stock .030 over.. I put a comp cam 268H kit in it as well as edelbrook intake and 600cfm carb..I also put hedman headers on it as well..

Now to the Problem

After I moved away he always said he oil presure problems but I never had time to look at it..Now that I own it I relized the problem...At startup it has 80 all the time which is fine..As it warms up it drops bad..At highway speed at 3000rpm it will keep dropping to about 25 psi...When I accelrate it will drop 40 to 20 then back to 35 and back to 25 within 5 secs..Yes the oil is full..This is with a mechanical oil pressure guage and I have tried another. I have switched the oil pump and pickup allready but no fix.Using a stock oil pump. I checked all the clearances during assembly and did everything but install the cam bearnings. This motor has less than 10000 miiles on it..

I am going to take it back apart and go through everything to see what is going on.. Since it will be apart I was going to get the KB 177 pistons because I understand they will get me to around 9.5 to 1 compression ratio. If I am wrong please tell me. I was also thinking about taking my 268H cam out and putting in a dual pattern like a 255 or 265..Not sure still need some input..I was also going to install adjustable roller rockers

Any advice would be great on the oil pressure problem or the perfarmance mods I want to do...

 

Do you have a baffle in the pan to keep the oil in the right place during acceleration? Are the oil drainback passages clear or are they full of silicone junk? Did you set the bearing clearances loose or tight? You might want to get tighter bearings or shim them to reduce clearances.

A 255/265 cam would be a good choice, it will give you a little better fuel economy and more low end torque than the 268. The compressoin should be about 9.0:1 or a hair higher but 9.5 is too much for efficient operation on pump gas. You can make it run at 9.5 by detuning the engine but you loose power and torque. Remember that combustion deposits will raise the compression over time and they also provide hot spots which will agravate any preignition or detonation problems.

 

The block was completely cleaned and the clearances were in the middle of the recommended..the crank was turned 10/10...The oil pan is in the rear so I don't believe that there were and baffles..

So KB 177 will give me about 9 to 1...And I want a daily driver with performance

 

If you put bushings in the rods, 351C piston fit.
use a campcams 255DEH or 265DEH cam. stock heads love the extra exhaust duration.

 

Welcome to FTE.

For the oil pressure problem, check the wear on the main bearings and look for any premature failure. If you see any sign of abnormal wear, then re-check all of the main bearing clearances before you remove the existing bearings. There could be a weird crank journal defect (out-of-round or taper).

Check the oil pump for a sticky pressure relief valve. Sometimes they hang up and bleed too much pressure.

Check the clearances downstream from the main bearings, especially the lifter bores.

If you deck the block or heads at all, the KB177 pistons will probably push you over 9.5:1.

Before making any decision on the pistons, get the cylinder heads off the engine and measure the volume of all the chambers. Last time I used the KB177s, I had to relieve the chambers to get the comp down under 9.5:1.

Polishing the chamber surface is a good way to prevent pinging with the 400's poor quench and large clearance volume. Polishing eliminates "hot spot" bumps, reduces the radiant heat transfer into the heads, and deters the accumulation of carbon.

With CR anywhere near 9.5:1, you'll need the 265DEH to reduce dynamic compression at low rpm. Compared to the 255DEH, the 265 will cost you some mpg efficiency and an insignificant amount of low-rpm torque. If you're concerned about that, keep the CR close to 9.0:1 (or a little less) and get the 255DEH.

With about 9.5:1 CR, the 265DEH can give you awesome torque and power up to over 5K rpm (450+ ft-lbs and 350+ hp).

I'd suggest using pedestal-mounted rollers instead of stud-mounted (adjustable). The valve lift with the cams you mentioned is still pretty mild, so you should be fine with a pedestal-mount rocker, like the FRPP #M-6564-C351. To get any more strength, you need to get the heads machined for 7/16" studs.

 

Thanks for the input bubba, I did change the oil pump out to rule that out but no change..I heard that that the cam bearings could be install wrong and could affect the oil pressure.

I had the block and head both milled to give me a square surface but don't know how much was taken off..What would be the next piston below the KB 177 that i could use that would get me closer to stock but not that low

The reason I want to run adjustable rocker is because mine tick, not because of oil pressure, they tick all the time no matter what oil pressure..I would use the stocks if I knew the proper way to set them up since the block was decked

I was