Boring out a 4.0 ohv

[shaggsta]

Well, after many long weeks I finally have a new engine in my X. But I am left with a very interesting situation. I now have an engine, laing around begging to be rebuilt and built up. I was wondering if anyone has done an overbore onto the ohv, what is required and costs are like. Are the performance gains worth it? Or should I easically rebuild it stock. It is a daily driver that I would like to have a little more fun with. Thanks

 

[briwayjones]

I'm not so sure you can bore out a 4.0. A 4.0 is already a bored out 2.8L from what I've heard and the cylinder walls are kind of thin already.

 

[Doug904]

Well, after many long weeks I finally have a new engine in my X. But I am left with a very interesting situation. I now have an engine, laing around begging to be rebuilt and built up. I was wondering if anyone has done an overbore onto the ohv, what is required and costs are like. Are the performance gains worth it? Or should I easically rebuild it stock. It is a daily driver that I would like to have a little more fun with. Thanks

Yes, a 4.0 block is a completely different casting then the 2.8 block. They are the same design but nothing even close in castings. The 4.0 block can be bore out safely .040 but don't do this expecting power gains. You'll gain more HP from a air intake then a overbore. This is just something every redneck likes to throw in their list of mods.

You wanna know why a .030 engine runs better then a standard bore? Because the standard bore engine usually has 100K mile plus so the new sealing of the fresh rings and bore surface of the cylinder walls will give it the the same power as if you had purchased it new.

In short, rebuild it, put a 410 or 422 Comp cam in it and have the heads ported and you'll gain more then if you simply bore it and put it back together.

Later Doug.

 

[Josh]

Doug,
What about stroking the motor similar to the 302 to 347. Is that possible? Does that make any sense?

 

[Creager]

if yr gonna go as far as porting and new cams, you might aswell put a rocker thats a little more, approperate? the stock rockers are stiff. full floating rockers will help the top of the motor "work easier"