Port-matching 4.2 head
- Thread starter Bob Stockum
- Start date
The ports were first cut on the mill, with a
1 1/16" ball end mill.
Then blending and rounding all sharp edges came next.
Not a race engine, so polishing the ports is not "on the table"
3 angle valve job and light mill, (to clean up)
Ready to put together. 👍
1 1/16" ball end mill.
Then blending and rounding all sharp edges came next.
Not a race engine, so polishing the ports is not "on the table"
3 angle valve job and light mill, (to clean up)
Ready to put together. 👍
Attachments
Mooseman
Moderator
It can be worth it to do this little extra work just to make the engine more efficient. With gas prices nowadays, a little extra work can help to eek out that extra MPG.
If you have some before and after MPG data, what would be nice to know.
If you have some before and after MPG data, what would be nice to know.
Just got this TB, with a bad motor.
Hole in block/ #2.
Got a good deal on 03 Envoy motor.
This is the 05 head.
I was surprised at how small the exhaust port exit was. Chose to "match" to gasket for better flow. GM may have kept ex side small for some reason, but I want them all matched-up.
Using the 05 head, because some earlier models had soft-seat problems.
Hole in block/ #2.
Got a good deal on 03 Envoy motor.
This is the 05 head.
I was surprised at how small the exhaust port exit was. Chose to "match" to gasket for better flow. GM may have kept ex side small for some reason, but I want them all matched-up.
Using the 05 head, because some earlier models had soft-seat problems.
Mooseman
Moderator
...and now... all that remains to be done is to obtain a Brand New Dorman Exhaust Manifold Model # 674-777 and after giving it a "Splash of Dykem Blue" across the EM smooth mating surfaces ... Precisely Scribe out that Same, New OEM MLS Gasket you used on the Aluminum Head and then ...Well...You know what to do... :>)
Last edited:
It all looks good. This should improve the exh flow by 50 cfm to 210 cfm based on my prior flow testing.
