What would it take to get a 4.0l over to 10to1 compression?

[black_demon69]

And what would be the the PROS and CONS of doing it?

 

[RonD]

No more running on 87 octane regular gasoline, $$$

4.0l SOHC 2001 Rangers and up runs 9.7:1 compression ratio, needed a knock sensor added so it can run regular gasoline.

Compression = heat, octane is a heat rating so higher octane takes a higher heat before self-igniting, pinging/knocking.

Pros would be you could squeeze a bit more power out of the 4.0l OHV, but not like swapping in a V8

Cons are no more cheaper gasoline and a once reliable engine is now running above spec HP so things may break inside.

If you are racing in a 4 liter class, NA, then might be worth it, to gain an edge.
For a Daily driver go with V8 and regular gasoline

Just an opinion

You can shave the heads and use domed pistons to increase compression

 

[black_demon69]

assuming you were just shaving the heads just how far would you have to shave heads? also what other problems could be obtained by shaving heads?

 

[gw33gp]

I run almost 15:1 compression in my SCCA sports race car. I can tell some of the issues you can encounter with shaving the heads.

I don't think the 4.0 OHV engine is an interference engine but shaving the heads can make it one. I have to be very careful about changing cam timing or I can get the valves kissing the pistons. I doubt you will run into a problem with spark plugs but I have to index them to keep the electrode from being down or the piston will close the gap. You may also have to get a different length push rod to have it optimal. You should look at quenching to see if you get into a range that can create problems. At 10:1 compression, the stock head gasket should be OK but may be marginal. A V-6 (or any V engine) can also have problems with the intake fitting up after shaving the heads. This can be fixed by machining the intake or the head at the intake surface. Good luck.

 

[RonD]

4.0l OHV has a stroke of 3.31" so shaving the heads 0.037 would change 9.0CR to 10.0CR
Just over 1/32 of an inch

Yes, you have to change push rods and mill intake for best fit

That will net you about 15 horse power at high RPM, 8-10HP below 3,500RPM

 

[black_demon69]

4.0l OHV has a stroke of 3.31" so shaving the heads 0.037 would change 9.0CR to 10.0CR
Just over 1/32 of an inch

Yes, you have to change push rods and mill intake for best fit

That will net you about 15 horse power at high RPM, 8-10HP below 3,500RPM

Small return for the investment


And not looking into v8 swap at this time

Was curious because I currently have a burnt valve on cylinder 2 and I have have to tear it down to fix and figured it might be a good way to gain some extra power. However having to move to high octane fuel for just a few extra horse I will only mill heads if needed. Thanks for the information.

This is why I like this site good knowledgeable people without all of the bickering and a willingness to educate others. So here is a big thanks to RonD and others who contribute to that education of the TRS community and Jim oaks for starting and maintaining the site..