Jeep Strokers

Assuming the compression ratio remains unchanged, how much of an improvement in performance results from increasing cylinder bore?

That is... How much more HP & Torque will you get from a 4.6L, 4.7L, 4.8L over a 4.5L if they are all at, for example, 8.3 DCR?

From what I understand, without improving head flow, the biggest change will be in torque rather than HP, right? But either way, I'd like to be able to quantify any changes.

Thanks

Personally I would go with the smaller over bore you can get away with. Stronger walls and more meat to do another bore job. Unless you are going for every HP you can get.

Well, I'm familiar with the saying, "There's no replacement for displacement." But I've also read that over-boring doesn't usually add much power, increases friction, and can make detonation more likely for a given octane.
If going from 4.0 to 4.5 is a big deal, what about increasing the extra displacement by an additional 40% by going to 4.7?
And if I'm not going to beat on the thing like it's a track car, why worry about the ability to over-bore again?

Thanks

Gristleheart wrote:And if I'm not going to beat on the thing like it's a track car, why worry about the ability to over-bore again?

Because shit happens even if treated well.

Worry about having extra over bore available if the vehicle is your daily driver. Otherwise, get ridiculous. My truck does truck things for hauling stuff around, but I do not drive it to work every day. Since I do not have to worry about it being broken for an extended period and especially wanting the extra horsepower for hauling it made sense to get ridiculous with it.

The is one way of looking at it. If you happen to have to a good supply of 4.0L blocks laying around for cheap then does it does not matter. For me the local machine shop is going to charge the exact same price for over boring a 4.5 to 4.7 to fix a screw up as it would to bore a 4.0 to a 4.7 in the first place.

OK, thanks. But I suppose my question is really about output. When one of these engines gets stroked from 4.0 to 4.5, does the additional power and torque come primarily from the extra displacement, or from the increased compression?

Thanks

The extra power comes primarily from the increased displacement but a higher compression and better breathing (ported head, cam, high-flow CAI, bigger TB, header, exhaust) also contribute.

Gristleheart wrote:OK, thanks. But I suppose my question is really about output. When one of these engines gets stroked from 4.0 to 4.5, does the additional power and torque come primarily from the extra displacement, or from the increased compression?

Thanks

This isn't necessarily accurate, but gives a rough idea....if hp was proportional to the engine size, a 4 liter producing 200 hp (50 hp per liter) would make 225 hp at 4.5 liters and 235 hp at 4.7 liters.