Gen 1 LIM / Runners / Plenum porting, do's/don'ts

[82-T/A]

Hey guys,

I'm going to be pulling apart the gen 1 v6/60 in my Fiero in the next month or so, and I figured I would go back over all the parts again to get everything absolutely as perfect as I can.


So, when I rebuilt the motor years ago, I had a larger throttle body installed and had the plenum port-matched to the TB. Then, I did some light port-matching between the plenum and the runners, and did some SIGNIFICANT port-matching between the runners and the lower intake manifold (shocked to say the least at how badly they matched up).

Now, I just wanted to ask... what do you guys recommend in terms of porting and polishing? I assume that I can try to hog out some more space in the plenum to gain some additional volume, as well as polishing everything all the way down, UP until the point at which the injectors go in. Is that correct? Can I polish everything up to that point?


Thanks guys!!!

Todd
1987 Pontiac Fiero SE / V6 5-Speed

[2.8/3400 1985 Camaro]

Polishing is pointless imo, it was been discussed to death, with no clear victor, polishing vs. "roughing up/texturing" on intakes and cylinder heads, generally they are about even in effectiveness, the texture tends to promote better atomization of the fuel and air, polishing tends to make it less resistant because the air has nothing to grab onto, but I may be wrong but I THINK that that actually tends to cause a static air layer that doesn't really move, its counterintuitive but I think I recall that it happens. But either way, its no more effective than a rough texture.
As far as what areas to work over, I do not recall offhand, but I think with the intake manifolds you generally want to just bore out the LIM, the middle intake you want to work on the transition to the upper, its a really sharp U-bend, you basically want to make it less sharp by grinding away material on the inside side of the bend if memory serves, Idk if you are doing the heads or not, but if you do, do NOT touch the vane in the ports, removing or altering it will actuall decrease flow velocity by as much as 15%, last but not least, wait for someone to chime in before porting the intake, as I am not 100% sure thats the way to do it, I am fairly sure its the most effective thing to do there though, also if you do the heads make sure to deshroud the valves.

[pocket-rocket]

I wouldn't polish anything in between the injectors and intake valves because fuel can drop out of suspension in the air on a smooth surface, hence the texture talk.

[85erbirdie]

polishing can be a waste of time if ur on the street. i recintly went through my 2,8 top end gasket matched everything and mild port just to help flow and transition and yes i did go through the heads as well and yes be very carefull of the diverter the little pointy thingy in the intake port of the head i cleaned mine up a little smoothing and transition but kept it just remember think like a air molicule they are dumb and dont know how to drive lol

[geoffinbc]

Do an 80 grit finish on everything. Are you doing the heads or just intake manifold?