i'm not sure but somone told me that if you put 2.8 heads on a 3.1 that it will raise the compression ratio has anyone tried this or know if this is true????????????

 

same cc heads, but depending on the type/year of the 2.8 heads, you might end up w/smaller valves. for higher comp have heads machined on the block side & intake side to keep manifold allignment. Do not have too much removed or you will need custom legnth push rods.

 

Yep, the 82-84 2.8 heads have smaller valves.

 

i could be wrong, but carbed 2.8 (82-84 as tomp said) have small valves.. the mpfi 2.8 and 3.1 got bigger valves (85-92).. and the sfi 3.4 valves have the biggest (93-95) stock valves..
bigger valves = bigger cc = smaller compresion ratio..
smaller valves = smaller cc = higher compression ratio..

 

so higher compression will give me horse power?

and how much power will i get from a new high performance cam and timing chain?

 

depending on the age of the motor, a little bit more than stock. improve the tranny & suspension, lighten the weight of the vehicle & it will scoot & handle much better.

bigger valves do not neccessarily mean bigger comp ratios, just better flowing heads.

 

i'm pretty sure that the valve size doesn't effect the compression ratio, but the combustion chamber size can. This is the reason that if you shave a few thousands off the bottom of your heads you can raise that compression up w/o buying new pistons and whatnot, because it'll make the combustion chamber smaller, and therefore raise the compression, so you can have super high compression while still running large valves. The problem that can be encountered is if things are matched up right, a cam with super intensive lift, with great valve overlap, what would end up hitting the piston when it is approaching TDC (top dead center). Because of that youv'e gotta be careful on your lift, and the pistons you run. I'm thinking that the 3.4L's had dished pistons to clear the valves, but i'm not 100% on that, would have to look into it, i am pretty srue that atleast the DOHC version does. not to sure though. gotta check.

 

yeah and for these motors, better flow is probably more important

 

that's definately true enough, if you've got heads that have a valve job including a three angle. Once sayroller rockers are done too, and eh, hmmmmmmmmmmm maybe some porting work on the rest of the head. Then think about decking it to raise the compression up. Running 10.1 won't have much effect on Hp when ur running a very very stock valvetrain.