Porting 3800 heads
- Thread starter smug
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HUGE improvements to be made in the bowl and chamber, on of the largest things is to correct for core shift...try to keep em as "matched" as possible will mean airflow and power will be more even.
shoot for the higher mold heads
the numbers 1-20 are horrible as the tooling was reworked so much...start with good heads and your job will be easier
i normally kill inj boss, cleanup and square intake (preferably to the lim too), check roof and outboard wall of intake port for sand flaws (see em there alot) intake guide narrowed and pockets widened around valve and the shortside blended into the seat. there tends to be a notch on the inboard intake wall from the throat machining tool clean that up and kill the lump as it passes next to the intake valve (youll feel the "notch" that your aiming to remove metal from the high spots to make it a nice radius)
exhaust, more machining blending really, narrow guide, open the bowl roof up stream of the exhaust valve guide. downstream of the guide raise the roof from approx 1/4inch to 3/4inches into the exhaust port from the header flange face, this is only ~ 7mm thick so only hit it as much as you feel comfortable, the left and right of center is a bit thicker.
exhaust floor i blend the shortside to the valve seat and aside from "cleaning" it i dont hit the floor till the last 1/8th inch of the port (from flange) where i widen it out and radius the exit to more of a D shape. the walls of the exhaust ports also tend to show core shift here so do you best to grind the highs and try to match em.
the chambers i knock down the high spots on the machining to casting transitions and outboard of the valves where they are shrouded a bit
use your fingers, remember..... yer gonna fing so many holes that the old lady's gonna get jealous...you a dust monkey so im sure ya know what a high spot feels like
shoot for the higher mold heads
the numbers 1-20 are horrible as the tooling was reworked so much...start with good heads and your job will be easier
i normally kill inj boss, cleanup and square intake (preferably to the lim too), check roof and outboard wall of intake port for sand flaws (see em there alot) intake guide narrowed and pockets widened around valve and the shortside blended into the seat. there tends to be a notch on the inboard intake wall from the throat machining tool clean that up and kill the lump as it passes next to the intake valve (youll feel the "notch" that your aiming to remove metal from the high spots to make it a nice radius)
exhaust, more machining blending really, narrow guide, open the bowl roof up stream of the exhaust valve guide. downstream of the guide raise the roof from approx 1/4inch to 3/4inches into the exhaust port from the header flange face, this is only ~ 7mm thick so only hit it as much as you feel comfortable, the left and right of center is a bit thicker.
exhaust floor i blend the shortside to the valve seat and aside from "cleaning" it i dont hit the floor till the last 1/8th inch of the port (from flange) where i widen it out and radius the exit to more of a D shape. the walls of the exhaust ports also tend to show core shift here so do you best to grind the highs and try to match em.
the chambers i knock down the high spots on the machining to casting transitions and outboard of the valves where they are shrouded a bit
use your fingers, remember..... yer gonna fing so many holes that the old lady's gonna get jealous...you a dust monkey so im sure ya know what a high spot feels like
IDK smug, your car trapped 110mph with 18" wheels right? Why ruin something good before you even have a chance to show it's true performance. Lightly porting the heads with stock valves won't do much if anything IMO. Taking the heads to a shop and have the valves back cut and a really nice valve job to go along with it would do more. M@ had some hella ported heads with bigger valves, 1.7 rockers on an S1X cam, lots of weight reduction, and trapped 115. I'm sure with some weight reduction, lighter wheels with some sticky tires, your car will do 112+ just the way it is.
backcutting the valves helps but isnt necessary as removing some of the far more horrible machining to as cast transitions and casting flaws
since the smugness has a bit of hayseed in 'im he can backcut the valves with a variable speed drill and a dremel...easy as fuck.
"wont do much of anything" lol helluva alotta room for improvement on mass produced heads bud
since the smugness has a bit of hayseed in 'im he can backcut the valves with a variable speed drill and a dremel...easy as fuck.
"wont do much of anything" lol helluva alotta room for improvement on mass produced heads bud
Money says he doesn't pick up more than 1mph for all that work. The castings aren't that bad, it's a supercharged 3800. You're not going to flow a significant amount more with just cleaning up the castings.
I vote leave it the hell alone as it's probably one of the more reliable modified 3800's on this forum.
I vote leave it the hell alone as it's probably one of the more reliable modified 3800's on this forum.
whats silly about alllll of this.
I trapped 114.x on my 18s. on a stock engine at 13psi.
dont do your heads smug. i don't think it'd be worth it...
what cam do you have again?
if it was a stock/rockered short duration setup you can logically have a reason to not port the heads...but up the duration and airflow... and pulling the heads to make improvements is not an unworthy endeavor
go a step further and notch the bores if you wanna eeek out a little bit moar flow by unshrouding the valves by a crapload
go a step further and notch the bores if you wanna eeek out a little bit moar flow by unshrouding the valves by a crapload
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