Hello. I have looked around and havent really found anything saying how to port the 2.8 intake manifold and 4.3 throttle body modification so i am going to try to make one. (First one for me)
Starting off you will need:
2.8 V6 Intake Manifold.
dremel and aluminum cutter attatchments and sander.
Micrometer (Electric or Analog)
I got a used intake from the local junk yard and used the marks left from the previous heads to mark where I needed to port/touch up around intake runners.
I used a 4.3 Throttle body 43mm put it on the intake and marked where it matched on the intake. I then proceeded to use the cutting bit on the dremel to port the holes to 39.5mm ( I didnt feel comfortable porting more then that because the egr and coolant passages are separated by that wall and I didnt want to make it too thin.) at the uppermost edge I rounded out to 41.2mm. you must make sure not to go more then 1-1.3" into the bore do to the rough aluminum is needed to create turbulence for the air/fuel mixture.
sorry for there being no pictures on here but I have them on my photobucket. for some reason my computer wont allow me to copy and paste the image URL's www.photobucket.com/DarkKnite2002
If you take to a qualified machine shop they'll chuck it up in a lathe and bore the bores out to the larger size professionally - it's pretty close to impossible to get good looking/proper circles freehanding - you can a stepped boring bit that's large enough but the extra length of the bit will have to be knocked off other wise the bit will hit the bottom before it will go in far enough - a bit like that will capitalize on the perfect circles you already have
true. anyway here is an update. I put in the intake and 4.3 throttle body with my 2.8 injectors. it appears that my injectors cant keep up with the bigger bore of the tb and intake (not surprised) Drove it to work today and it falls flat on its face in lower RPMs. tried advancing/ retarding the timing still does it. I think I will try for the 4.3 injectors this weekend and see if that makes a difference
The 2.8 injectors are too small even stock for the 3.4. Swapping to the 4.3 injectors should make a difference. I didn't port my intake, but I did put the 4.3 TBI and injectors on top of a bored intake.
So i woke to 28° outside and the injectors wouldnt run the engine at all. So put in the 4.3 injectors. Huge difference in throttle response and low end to mid range power howerever my top end power is almost non existant but thats expected since i didnt do a cam. Over all im satisfied with it for now till i can get parts together for a turbo build