then please tell me some information... i am searching some information about changing engine heads from st220 in to a 2.5 v6 engine, this modification gives some diferent or not. if there is anything about this, then i go to pay money and read.
He's right though I know a little. And Pardon my english. Im american and it's wayyyy different then pretty much everyone.
So here goes. And those ST numbers mess me up but here ST220 is a 3.0L and I believe the 2.5 is a ST200?? Anyway to your question, 3.0L heads on a 2.5L I think will actually cause you to loose compression. What you're referring to doing we call a Hybrid V6. Don't worry about those threads I didn't do it. There is some interesting stuff but nothing that would help you with this.
I forgot the actual numbers, and Im to lazy to google at the moment but, the main difference between the 2.5 and the ST220 Is the bore size. That meaning the hole the piston fits in. The rods and crank I believe are the same. I know for a fact the rods are. I had ST220 rods from a noble in Luci's 2.5L engine.
So for sake of arguement we'll say the bore for the 2.5 is 86mm wide. The circular indention in the head should also be 86mm wide. Now the ST220 being a larger bore, lets say 94mm, the circle in the head is also sized to match.
If you take the ST220 heads and put them on a 2.5L they will bolt on just fine, but you now have a 94mm circle on an 86mm hole. This basically makes the cylinder hold the same amount of air for a larger container. Think of it as taking a cup of water and dumping it into a larger cup.
To add to how engines work, Ford made various changes throughout the years to our engines. They moved oil ports and water passages. Added and deleted them as well. We even have a version here of the engine that doesnt have the water pump running off the camshaft i believe. You have to double and triple check all the openings in the heads to make sure they all match up correctly.
The main question here would be, why do you want to do it?
If you're trying to gain horsepower, that alone wont do it unless the difference in intakes might be able to pull it off. I don't think so because your compression ratio is going down.
If you're purposely trying to lower it so you can for instance add forced induction then sure maybe.
Another thing you have to look at. The 2.5 we have has the IMRC in it. The little butterflies in the lower intake. Unless you get old split port 3.0L heads you're going to loose that and the mounting points for the control box. The ST220 didn't have that. If your engine computer is set up for that system then its going to throw a fault code unless you can get with these fine chaps over there that have figured it out.
You're also either going to need an ST220 intake manifold setup, or fabricate an adaptor to make the 2.5 intake fit the ST220 heads. The ports are different. The ST220 heads are oval port, the 2.5 is split port. Totally different set up all around.
If you're doing this to try and gain power and its a because I want to and not because I have to situation staying naturally aspirated, you need to reverse what you're doing. You need 2.5L heads on an ST220 engine. It gives you the larger bore of the ST220 engine but using the 2.5L heads leaves it totally stock looking for our cars as well as raises the compression ratio.
Im going to apologize now if you made it this far, for me taking up the last 30 minutes of your life with this super long post. I hope it helped though and good luck.
