How much can you safely shave 4.0 OHV heads?
How much does that raise compression ?

 

depends who you ask..Ford tells you do not machine heads

 

The 4.0l OHV is a non-interference engine, so you can probably shave heads down alot, making it an interference engine
The 4.0l SOHC is an interference engine, runs.9.7:1 compression

The 4.0l OHV heads are prone to cracking when over heated, they WILL crack between valve seats if over heated, not a maybe
So just a heads up, when you remove metal from the heads AND increase compression you will increase the heat in the head...................so have extra heads available

Shaving the heads increases compression, when compression gets to 9.5:1 and up you will need to up the Octane of the fuel you use
Ford got around that by adding a Knock sensor to the SOHC computer so it could run 87 Octane fuel, but with less power

On the OHV you will need to change pushrods if heads are shaved, you will need to do the math for max valve open and piston height at TDC to keep from bending valves

Good read here on 4.0l OHV modifications: https://www.therangerstation.com/tec...-0l-for-power/

 

Great information, so to be safe sound like I should even consider shaving the heads a little to raise compression?
So could possibly it be safe to shave the heads (stock 9.0:1) to get the compression to say 9.4:1?

So far my plans are:
To purchase a refurbished engine, my current engine has 226 miles on it with the Comps CAM 49-410-8 200/210
I'm trying to spec out a refurbished engine (any recommendations, Powertrain?)

Once the engine is received, maybe send the Heads to SupperSixMotorsports, to have a Stage 3 setup $1,9500):
Stage 3: Fully ported intake & exhaust orts, complete bowl work, unshrouded & polished chambers, stainless steel valves, 3-angle valve job, dual valve springs & retainers, new valve seals, surfaced completely assembled & ready to install

A Comps CAM 49-422-8 Cam (on the way)215/224 Duration at .050″. 112 Degree Lobe Separation Angle
Push rods to support the CAM at 5.550″ length for the CAM, unless heads get shaved, then I'll need a different length

And also purchase an upper & lower intake to send to SupperSixMotorsports to have those ported/matched to the heads
$350 porting for upper intake manifold
$450 porting for lower intake manifold

I'm not sure what additional HP to expect the Comps CAM upgrade with just the CAM upgrade?
I thought shaving the heads might help with raising the compression, but I don't want to worry about replacing/repairing them.

I supposed it might not be worth getting the Stage 3 head upgrade/work though unless I can raise compression?
I know the peak HP for the 1998 4.0L OHV is only about 160HP, I'd like to at lest get to around 210.

I already have the shorty headers, BBK throttle body, cold air induction, custom exhaust, Diablo chip, Throttle body spacer

Any advice would be much appreciated

 

What size throttle body do you have and do you have the part # off of it? I'm rebuilding the top end on my 4.0 with new heads I will be porting/polishing ,headers, free flowing exhaust.I may need a bigger throttle body..

 

A BBK 66mm throttle body,
Part # 1580
https://www.bbkperformance.com/ford-...ody-89-00.html

 

"Free flowing" exhaust will cause you to lose power
Exhaust manifolds(headers) are designed to create a LOWER Pressure at the exhaust valves to PULL OUT exhaust from a cylinder so piston doesn't have to push it out, this leaves more power on the crank shaft

This lower pressure happens at a specific RPM which is determined by the diameter and length of pipe at the head
Rangers come with mid-RPM manifolds, lowest pressure at around 2,700rpms
You can get lower RPM manifolds so lowest pressure happens at 2,200rpms
Or high RPM manifolds often called Racing headers with lowest pressure at 3,500rpms
Its FREE extra power, so it has been used since the late 1950s by most vehicle makers

You can do anything you want with larger pipe diameter AFTER the manifold/header, won't matter to the power


Just FYI, the MYTH of an engine needing back pressure comes from Factory manifold designs
People would remove factory exhaust manifolds and put on larger diameter pipe headers, "free flow"
Then go for a drive................
"WTF, I LOST power!!!!????", "this engine must need back pressure"
No it doesn't, they LOST the lower pressure created by the factory exhaust manifold, so lost the free power it provided
And a MYTH was born

Even straight pipes, one pipe per cylinder, sticking up or down, can be made with a diameter and length to create a lower pressure at a specific RPM, its just math
Exhaust design is an interest subject and beyond my pay grade I just know a bit on how it works not what makes it work, lol

In later years "X" or "H" pipes have been added to Dual exhaust to take advantage of the lowering of pressure in the exhaust system, some say it doesn't do much, but most agree it does do something to increase power

 

Since the 98TM heads in stock form don’t flow as well as the 1990-1997 (95TM) due to the smaller exhaust port, but the round exhaust port allows for better port work to be done to the exhaust port & can be configured to outflow the earlier style heads. With some port work using the later 98TM’s, I should use aftermarket castings. They are thicker and stronger then the Ford castings, are less prone to cracking, and come with new guides. Where could I get 98TM's aftermarket casting Heads?

 

I got mine from Jegs. The heads are from Promaxx and they are aftermarket castings.Were around $560 for the pair and they have much better reviews than all of the other company's that sell these heads.