My friend had his dad bore the cylinders out in his Beretta GTZ and he now has a damn quick GTZ. He said he can do the same to my Mustang but I'll need bigger pistons (which obviously makes since). I'm wondering how many people have done this, and what would be a safe volume to bore to (my car is a DD for 6 months of the year). Also, where do you buy the larger pistons, and how much are they? I'm assuming the pistons from a 5.0 Mustang would work if you bored to 5.0? Is there anything else that needs to be purchased for this? Is the power increase substantial?

 

Pistons from the Windsor engines will not work in modular engines since they are almost 1/2" bigger than the modular versions. Usually .03" is what most people do and is the max recommended. Just make sure you check what plant your engine came from since Windsor pistons are different from the Romeo version. If you want the 302ci displacement, you will also have to increase your stroke too.

 

Pretty much every shop wont go past .020" because then the walls are to thin in our motors, which already dont have thick walls as it is.

 

Anyone know the gains if I go for the 302?

 

almost no power increase for a straight displacement increase. The intake flow is kinda restricted by the heads and cams so you don't gain that much. Cams would be WAY WAY WAY cheaper and easier and give you better gains in practice.

If you have a hardon for an overbore (which should be reserved for the rebuild of your motor later on down the line) I would stay at .020 or less on modular motors. There've been way way too many heat issues with .030 and up. If you're going to spend that kind of money, go .020 over, slap some 10:1 pistons in it, and H beam rods and a cobra crank. It'll cost about 2500 bucks to do all that and you'll get a little power increase out of it. You could buy a BUILT short block from CHP or DSS for about that much and not have to buy bearings, pay for assembly, or worry about someone knowing the idiosyncratic nature of the modular motor when they're assembling it and you ending up with a possibly bad engine from the get-go.