M Danger

can anyone expound on using NA heads both 2.5 and 2.7?

RajDatta

2.7 has water jackets in different locations and mates to engines with 104mm bore. 2.5 is for standard 100mm bores with water jackets matching them..
Raj

M Danger

i thought i had read that the 2.7 had bigger valves?

RajDatta

Yes, they do.
Raj

Tom Carson

and bigger manifold ports

PCinDC

The idea behind using an NA head is that without the ceramic exhaust liner, you are free to port both the intake and exhaust ports. I am not sure how much there is to gain there, someone with more experience can comment on that.
The 2.7NA head is used for 3.0 turbo conversions for a number of reasons:
1) Bolts onto 104MM bore block with water passage in the right location - no modifications necessary to fit to a 3.0L block
2) 951 intake manifold bolts directly onto the 2.7L head - no modifcations required to run standard 951 intake plumbing. And yes, it has bigger intake valves.

hosrom_951

I have my 88 NA head off the car for a while now, i am keeping it for a 'future' upgrade, since i read in the archives that with the NA head, p&p is done to both exhaust and intake ports, this would have a greater increase than standard p&p on 951 cylinder heads. But the idea of runing without ceramic liners and real world proof of advantages/disadvantages is what i would like to see some time.