I have a 1984 F250 extended cab 4x4. Factory driveline 351W, NP435 Transmission, NP 208F transfer case, and 3.55 gears, 8,600 lb GVWR. All that to say that I rebuilt my engine and driveline with my elderly dad back in 2018. It stayed as a running but non-driving project until June of 2024 when I got it on the road.



So my issue is I don’t think the engine is where it needs to be. Truck lugs way too much and lacks power and torque than I expect, and is getting 8-9 MPG putting around locally at no more than 50 MPH. My guess is key things not upgraded, most likely heads, and overall tuning can’t be accomplished. Looking for pointers or confirmation on thoughts. Below is the current build.



351W that was factory 2 barrel. Fully rebuilt and had to bore .040 over. Went with Lunati Voodoo tow/RV cam, spec sheet attached. That included new dual coil valve springs. Rest of valve train and heads are factory for 84' (note that heads are from 6,600 GVWR truck if it matters). Heads have 1.78 intake/1.48 exhaust valves, and I suspect 69cc chambers. I do have a lifter and valve train tap, which I suspect is clearance beyond spec. Running MSD 6AL with a factory Duraspark II distributor. Mechanical advance is already allowing too much advance. Base is set for 8° BTDC, lower mechanical arm setting is 16, which gives me 32° of mechanical advance, for a total of about 40°. Changed springs to bring my all in RPM from 3,200 to about 2,500, but stopped when I couldn’t get the total down. My best option to resolve the advance is aftermarket distributor, but all seem to lack vacuum advance, which I seem to really need with a manual transmission that is low geared and downshifting is not always best.



Failed to mention that I am running an Edelbrock Performer intake, and Edelbrock AVS2 Carb, and quality Hedman long tube headers that I had all new 2 1/2 dual exhaust ran with some simple turbo style mufflers for controlled sound.



I know timing needs addressed and I look for pointers. I know I could benefit from adjustable rocker arms as I know my clearances are too great. But does any of that matter if I don’t upgrade heads? I feel like I lack flow and compression ratio for what is already done. Truck is my put around vehicle that I want to focus on its capability to pull and tow. But it is weak for what it should be. Also note that when you drive it fully warmed up and park it for 20 minutes or more, starting is rough like it has boiled all the fuel out of the bowls.



If heads are my best bet, with adjustable rockers, looking for guidance and chamber cc, runner cc, and 1.6 vs 1.7 rockers. And thoughts on distributors with vacuum advance. This seems way underpowered vs my 1979 F100 with a 302 automatic that I had when I was much younger. This heavy duty driveline should make this thing just want to pull, but it lacks the power and falls way back on hills. Would love input, knowledge, and guidance in getting it where it needs to be.



I grew up in teens and early 20’s knowing more than I know today, and my dad helped with this build that was too old and forgot majority of what he knew and is not around to help me work through the issues with the build we started. All help greatly appreciated.

 

Personally I think a 80's F250 with the 235/80 16 tires, or taller need to be running a 4:11 gear. The mods that have been done so far have raised your power range some, and lugging around at 50 I think just is running the engine out of that power band. As for the build? Ya your right that the heads are junk. Earler 351 heads are nice, but the cost of rebuilding them with adding hardened seats makes them a bad choice. Just about any aftermarket head is world better then what you have. Stocke early heads had 1.84 intake, and those or the chevy size 1.94 are a good size for a truck 351. I would not go too small with the chambers... 58-60cc would be what I would be shooting for. All this depends on the pistons also. Im assuming you went with stock tyle cast pistons. Most replacement cast pistons seem to ride a little lower in the bore making lower compression. You might find some GT40 heads cheap. Im not a fan of the GT40P heads because of the header fitment issues, but if you don't mind dealing with that, thats a good affordable choice also. Remember if you go with a 302/5.0L head you will need to drill out the head bolt holes. Your cam has a fair amount of lift also, so make sure your check piston to valve clearance if you start going with bigger valves, and smaller chambers. As for your dist? There are so many good choices, and a lot have the vac advance. A replacement DS II unit, MSD or other company ready to run, even the GM style that I hate, but they work fine.

 

Disconnect the vacuum advance and plug the hose with a screw. Then set the timing at 12 degrees initial with the timing light. I think you will be surprised at the results, and that will give you a direction to go.

On the noisy lifters, as you know the Ford valvetrain is none adjustable. That aftermarket cam has most likely thrown things off. But you can check it to make sure. Not sure you have ever done any other engines, but treat the Ford the same, even though you can't adjust it. Run the engine around to #1 TDC. Pull the valve covers off, make sure you are at #1 TDC and then loosen both rockers on #1 cylinder. Then grab the pushrod and move it up and down till you just get the play out of the pushrod, and then looking at your ratchet, count the number of turns till the rocker bolt stops. You can't adjust it, but you can see where you are at.

If the bolt is tight and you still have play in the pushrod, the pushrods are too short. If you can get a1/2 turn out of the bolt before it gets tight, that is about perfect. 3/4 turn is ok, even 1 turn will work. More than 1 turn you are getting borderline too tight.

You can then do the exhaust on #1, then turn the engine 1/4 turn and do the next cylinder in the firing order, checking the lash on all the cylinders. If you find them a little tight, sometimes you can fudge it and put shims under the pedastel of the rocker to move the rocker arm up a little bit and still be able to tighten it down. And you can get different length pushrods also.

 

There is no need to replace the distributor as you gain nothing and lose money what you paid for it. I have seen a DSII system in a drag car run in the 11 sec 1/4 and faster on spray.
On the MSD 6AL all you really get is the RPM limiter and a multi spark if that even dose anything.

Do as Franklin said and remove the vacuum hose and plug and bump the timing up.
Now at 12* BTDC you may get some starter kick back when warm or even pinging just bump the timing back a few degrease till it will start and no pining.
What is the idle RPM and the vacuum reading at idle? How did it change after the above change?

What is the RPM & vacuum at that 55 MPH?
I have a F100 with a 300 six that pulls at a lower RPM than a v8 dose, a NP435 trans, 2.75 gear and 235/75/15 tiers I am at 1800 RPM @ 55 MPH.
Your v8 I would think should be up around 2300 - 2500 RPM to make any kind of power and not lug the motor.
I also have over drive and can run as low as 1200 @ 45 MPH in over drive and it will still pull, that is the difference between the 2 motors cant do that with a v8.

On the valve train noise if you did not check where the rockers ride on the valve tips and using the factory push rods you may need to get new pushrods, thinking longer.
The other thing I think of is cam break in. If this was not done right and with the right oil, even now on the oil, the cam may have a flat lobe or 2.
Only way to know a flat cam is to check the lift on each lifter or rocker. If one or two are less the lobe has or is going flat and the motor pulled, gone through and cleaned to remove all the metal then put back together with new bearing.
Opening the oil filter looking for metal flakes will also tell you if something is wrong.

If you do go for a head change I would not waste my time / money on any old cast iron used heads and go right foe ALUM ones.
In my book in the end for the money you end up with a much better head design / flow and it can keep the pinging down too.

What plugs you running and have you pulled them to see if it is running rich or lean?
I have a AFR gauge (air fuel ratio) in my truck and it runs between 14.5:1 to 16:1 yes it is lean but it is mostly at the 15:1 and I avg 15 MPH.

Lastly you say "lacks power" what are you comparing it to?
Dave ----

ps who put the motor together you / dad or a shop? Could the timing chain been installed 1 tooth off?

 

I suspect the primary problem is your expectations. The 3.55 gear is great for towing. But its not going to help your seat of the pants feel for the truck above 2nd gear. And im not sure what you are referring to with the timing. A base of 8 and mechanicle of 16 will give you a total of 24’ advance. You probably want a total in the 30-34’ btdc range. I would start there. I dont think you need more parts just yet.

 

He is adding the vacuum advance too.
I know they dont count it but they should as it advances the timing even higher.
I know the TV shows alway say 32* to 34* BTDC but if you look they are not using vacuum advance and it is always on a dyno stand as they are looking for top numbers.
I wonder how good the motors do in a real world driving car or truck?
Dave ----

 

As i understood it vacuum advance does not get added to mechanicle advance for the total advance calculation. Because its generally considered an either/or situation as vacuum comes in as you go off throttle and visa versa. 🤔 Setting the timing for that is done by seat of the pants testing. Test, adjustest, test again. Take it up till it tings back at you then back off.

 

How many miles on the rebuild? When did the tap begin? Immediately on the first startup? That would imply an adjustment out of spec during assembly. Or did the noise begin after some miles? That is likely something failing, such as a collapsed lifter or worse.

Under the "worse" scenario, here's my tale of woe, which leads me to ask about the break-in procedure and oil used:

https://www.ford-trucks.com/forums/1...brication.html

As a quick check, inspect the oil immediately after an engine run.. Pull the dipstick and put a few drops on white paper. If as glittery as Liberace's piano, that's a bad sign.




That sounds like a separate problem, with underhood heat affecting fuel sitting in the carb. This is a fairly common issue with our old trucks. But for now, I'd suggest concentrating on the ticking noise and seemingly low power. Once that is resolved, we can come back to the hot restart problem.

 

Thing is there is no easy way to limit vacuum amount of timing.
The adjustment is at what HG the timing starts to advance, I know as I have tried to adjust it on my 300 and from what I have see are the only motors to come with adjustable vacuum from the factory.
With out finding my records to give numbers at what HG mine started at and what it is at now and I still get pinging, I just back out of the throttle a little and it goes away.
I am on ported vacuum advance if anyone wants to know.
I really need to get back inside the distributor to see if I can limit the vacuum side as the motor runs great otherwise.
Dave ----

 

This project truck started with a regular cab 1984 F250 with extract drive train, but was only 6,600 GVWR with lighter axles. However it did have the 4.11 gears. Had this extended cab given to me so just moved my rebuilt engine/tranny/transfer case over to it.

What are the header issues with the GT40 heads? Is it straight spark plug holes?

 

This is far from my first engine, but may have gotten some “good enough” teaching and guidance growing up over the years doing them. I will say my 302/C4 combo in my 79 F100 just seemed so much hotter than this. Both were smog engines, but I am sure the 84 was toned down even more.

I was running 12° timing but did not see more power or pickup, and was only compounding total timing issue, as that had me at 44° at about 2,800 RPM. Even back at 8°, I can’t run down the interstate as it is pinging with the lightest load, because I am running 2,000-2,500 RPM. Crappy gas these days don’t help, but premium gas is not going to help it run with that timing.

I had not done the checking of how tight the rocker arms are, that is a good tip and something I can check.

 

The only reason to replace the distributor would be to get a more adjustable mechanical advance. You can’t find the smaller arms for the DS II to get the advance within range.

Cam break-in should have been good, and was running ZDDP additive and continue to do so. Engine was built by me and my dad, but I have considered pulling the cover to check. I seem to remember it having 2 sets of marks, one of those being for a 2° advancement. Would like to verify that didn’t occurred. I believe it is a Melling double roller chain setup that we went with.

I am running factory pushrods. Vacuum is right at 19 at idle. Was running about 750 RPM for idle, but last tuning I couldn’t get it down below about 850. I don’t suspect a vacuum leak so need to explore that further.

 

I don’t expect it to set me back. Running on a local backroads around me, it just falls back more than it should in 4th gear, and that downshift to 3rd is a large change in ratio. Not looking for setback power, just doesn’t have the grunt power.

The 16L arms actually give you 32° of advance. I have done deep thorough research on that side. I really need a set of 10L arms to give me 20°, and then set my base to 12°. Can’t seem to get there without going with an aftermarket distributor, which I don’t want to lose vacuum advance since that helps a lot on my manual transmission setup.

 

You are correct, doesn’t get added, just helps get to that total sooner at low RPM under load. I find that is much needed on manual transmission since your not always downshifting and just putting around back roads.

 

Noticed ticking after getting it on the road finally and getting a few miles on it. Ticking has not gotten worse. I now have 2,500 miles on it. Again, it was a driveway runner from 2018 until June 2024. I was leaning towards a collapsed lifter as well. I am pretty sure we used regular Castrol oil with Lucas ZDDP additive for break-in.