daveo1

Does anyone know the stock compression ratio of a 1999 7.4mpi (L29) motor? What is the volume/CC of the heads? any info would be appreciated.

Pat McPherson

Heads are 100cc.
Compression 9:1.

Adding a little punch to one myself...

daveo1

Pat, are you using the stock heads or are you going aftermarket? I have decided to go with some Merlin oval ports, 119 cc. I need to figure out what machining I need to do to stay around 9:1 CR.

Pat McPherson

Dave,
I am staying with the stock heads.

To get 9:1 with the 119cc heads you will need to change out the flat top pistons.
I did the swap on my old 330.
$250 will get you a set of Kieth Blacks or Speed Pro Hypos...

daveo1

How about milling the head a bit?

bago Baja

I'm interested in this question also. Bought some used large oval 781 heads on e-bay. Want to increase compression ratio from stock 8:1 up to ~ 9:1. 118cc chambers. What are the relative merits of domed pistons vs milling heads? How much can you mill before you get into trouble?

homan

i think if .040 is taken from the head that will raise you to 9:1

Pat McPherson

Not sure if you can mill that much on a Gen V or VI head, but I think the older heads have more meat...

I needed new pistons on my 330 so I used domed.