Hey all, hoping some of you can help me out with picking the right specs for my first engine build. I have a little understanding, but theres a lot that I still dont know.

I have 2 possible paths to go down and was hoping for some help deciding which makes the most sense for me. I have an 85 F150 with the 4.9 and ZF5 swapped in. Currently has an Offenhauser C series with an Edelbrock 500cfm on it. Im happy with how the truck performs, but I know that I have leaky valves and have been chasing a high Idle for a while. I know the bottom end is bored .020 over, and I feel like head work is my next move. I have a freshly cleaned and resurfaced EFI head that is bare, no valves or anything. Would I be better off sending this head out to get machined? I was originally looking at the Promaxx CNC head, but am wondering if Im better off just using the Stock one I have now. Depending on answer Ill probably do some deeper searching into what valve size and spring rates to look at as well as cams, but open to hearing opinion on those here as well! Im looking to make a torquey truck that I can have fun with.

Thanks in advance!

 

Your meaning of a " torquey truck that I can have fun with" and mine are 2 different things.
Note when you start going with larger valves, bigger ports on the head and larger cam and higher rate springs moves the RPM where this all happens into a higher RPM range.
Higher RPM range to me means more wear & tear on the motor. How long do high RPM car motors last nowhere as long as a normal everyday motor does.
So that is something to keep in mind to start with.

The other is the RPM range this motor will run in with the final gear ratio with the over drive the motor will run in.
If the speed you use the truck at most of the time is say 65 MPH and the RMP now is 1700 and the motor pulls good at that RPM.
Now you go and do all that work and the motor now will not pull good till 2000 RPM you will need to change the rear gear ratio.

The 300 six is a low RPM torque motor and IIRC that comes in at about 1800 RPM.
From the factory my truck runs at 1800 RPM in 4th gear @ 55 MPH.
Now in over drive I can run 70 MPH and the same 1800 RPM.
Same wear & tear at a faster speed limit of 70 MPH

So it is not just the motor you have to think about.
Also look through the performance section on what others have done for motor builds to see what works and not work.
You will also want to talk to cam people and Summit Racing / Jeggs to see what they say on cams but I would go with matching springs.
Dave ----

 

Im not looking for anything too crazy, just something I can comfortably pull a 5k lbs camper with, but still have some fun on weekend cruises with. I was looking into the Comp 252 cams, since they claim to kept the power range lower. I dont want it to be high revving or crazy HP, but something more than stock. I just found an EFI block that was bored and freshly machined on marketplace for a good price since posting this and I am planning to pick that up.

I know right now I have a super low rear gear which I like for highway driving. From the factory my truck would do about 80 at 1700-180mph (Stripper model with the T170 OD and 2.47 rear end) so adding the ZF5 kept the highway rpm, but gave me the low gear which I use like 1st.

I know that these motors benefit from increased flow, and I already have the EFI exhaust and a 4 barrel, but I feel like I wont see their full benefit without some head work. I can always just put together my fresh EFI head with stock components, but I figured since it was bare I would look into either machining it, or buying a pre-machined one.

I looked through the performance section a little, but Ill have to go back and dig a little deeper. Thanks!

 

Its not sinking in yet. You are correct, larger manifolds/carbs and head work mean more flow. But the only way to take advantage of more flow is higher rpm like Fuzz said. You can modify the engine and have more power, but you will have to wind it up higher to take advantage of it. And you will start sacrificing low end grunt.

What you are trying to achieve has been sought after for years. The foreign cars and the later model OEM's have started figuring it out. Like multiple valve engines. Why does a little 4 cylinder engine have 16 valves, it only needs 8? Because they can turn off 8 of them at lower rpm, and it makes the intake and the cylinder head look like a small engine with good low end. Then at higher rpm they turn on all 16 valves. That promotes good flow and lots of horsepower at higher rpms.

Then you talk about camshafts. What are all those solenoids and variable valve timing camshafts on newer engines? You know the ones that give everyone trouble when they do not change their oil like they should? They are changing the camshaft profile on the fly. Changing it for low end power or changing it for high end full output horsepower.

Your engine is old school, it will be a compromise, anything you do to it. What doesn't help matters, you have the same 4 inch bore as a 5.0, but you have a very long stroke. The 300 is 4.9 liter engine, much the same as the 5.0 or 302. That long stroke makes it very powerful at low rpms, but it's not naturally going to want to snap up in rpms and rev like the shorter stroke 302 will. It's a truck engine, best for pulling loads.

Just keep all this in mind when modifying it. Keep on with your plans, and change the rear gear to something with a higher number so the engine revs higher, and you will be making progress.

 

Okay, I think Im starting to understand a little better. I should change my rear gear to put my OD in a more usable RPM range on the highway (around 2200 rpm at 80mph with a 3.27 vs 1600 rpm with my current 2.47) then leave the valves alone unless I want to move the power band up? Which the more I think about the more in line with what Im thinking. I keep forgetting that this is such a low RPM engine. I think when I said "Low End torque" I was comparing to my cars, which isnt a clean comparison. After reading other threads I think I understand a bit better how all this works together.
I appreciate all the help and patience!

 

I think you are getting it now that the 300 is a low RPM work horse not a high RPM sports motor.
You may find the 302 in F100 / F150pickup trucks but you will not find it in a F250 or F350 or larger truck like the 300 will be seen.
I think if you do a rear gear change to something that works well with the ZF5 unlike the 2.47 gear you got now that will put the zip back into the truck more than a larger cam and high flowing ports in the head.
I got a 2.75 gear in my truck and it could use a little more gear but for the work and money it takes to do that and what I use my truck for mostly I will keep the 2.75 unless something happens to it and I cant see that happening.
I also dont know why Ford put a 2.47 gear with their over drive manual transmission trucks with a 300? Yes my parts truck came that way from the factory it puts the 300 below it's TQ range and that does no help MPG either.

If you can find it maybe on YouTube, Horse Power TV did a Ford 300 build and ran dyno pulls from stock to intake / header up to a full blown turbo build so you get to see how the power & RPM go up with the changes.
BTW I am running the factory intake / carb but EFI exhaust manifolds and factory 1994 F150 exhaust system without cat and a welded muffler and am happy with it for what I do with the truck.
I do pull a 20' enclosed trailer at times so I do work the truck. If I come across a Offy intake cheap I may swap it on with a Holley 2300 350 CFM v2 carb as I dont want to loose the low end TQ.
Dave ----

 

Do you think going to the 3.27 would be enough? I dont want to go too high due to my driveshaft. I cant have it spinning too fast because of its length, so going with too high of a rear gear makes me nervous. If I could start using my 1st as an actual granny gear, and start out in second unlike what Im doing now, that might be nice to have. I agree on not knowing why Ford would do that though. I didnt do enough research and didnt know enough when I bought the truck, I had no idea they even sold them with the 2.47!

 

It was Ford's early attempt at a fuel miser. Most cars of that era came with a mid 2ish rear gear, usually with a 3 speed automatic that slipped all the time.

I looked up a zf 2wd gear ratios and this came up. 1st: 5.72:1, 2nd: 2.94:1, 3rd: 1.61:1, 4th: 1.00:1, 5th: 0.76:1, and Reverse: 5.24:1.

If you use a 3.27 gear with a overdrive 5th of .76, your final ratio in 5th will be 2.48 to 1. So if you want to know instantly what it would be like with a 3.27 gear in overdrive, drive around in 4th, that is what it will be like in 5th with a 3.27 rear gear. Take it out on the highway and leave it in 4th gear at high speed, that is what you will have.

 

Thats true, I didnt even think of that! Thanks!

 

I love playing with the numbers like DaveF did and dont know why I did not think of it.
I have done it when I dropped a WC T5 into a 70's car that had a T10 4 speed where the T10 first gear ratio was too tall.
I als did it with my truck when I was thinking of adding a over drive unit of either a Gear Vender or Advance Adapter units
I went with the Advance over drive because I could split all gears turning my 4 speed into a 8 speed transmission.

Some good auto math calculators here I have used too http://www.wallaceracing.com/Calcula...oogle_vignette
Dave ----