As I have stated before, I have recently acquired a l26 intake manifold set. (Upper and lower) im considering getting the lowerr manifold ported/polished before installation. I am planning a turbo setup and thusly getting the heads port/polished along with new exhaust/ headers and all of that after a new trans.


Any thoughts?

 

I wouldnt get TOO carried away with the porting. It will sure help but isnt necessary. I would smooth it out a little without taking a huge chunk of material out. I dont know if L26 is prone to intake manifold leaks like the l36 but I wouldnt want to take alot of material out and cause one.

 

I smoothed and polished the LIM and called it a day. Keep in mind that the work is a total PITA! I must have lost about a pound of knuckle skin.

 

Most people don't port the LIM at all unless thry are porting the heads (and then gasket matching the LIM), otherwise you can end up with turbulence when the air transfers from the LIM into the head. Also, you generally don't want to completely smooth out your intake runners, as a slightly rough surface will actually increase velocity on the intake side.

To sum that all up, I wouldn't bother touching the LIM unless I was porting the heads as well, but would seriously consider an HV3 insert to go along with the turbo either way.

 

X2

Beat me to it. General rule of thumb is to port and polish the exhaust, and only port the intake.

 

I think you mean to port and polish the exhaust, but only port the intake.

 

I don't know so much about the L26 LIM (but I believe it's identical to the L36, or has minor differences), but in regards to the L36, there is some room for improvement. If you are not porting the heads as well, you can still port-match the LIM (NOT gasket match, otherwise, this will create the wrong type of turbulance by forming a "step" in the flow). Also, as I understand, you do not want to polish the intake runners, you DO want the air somewhat turbulant as it enters the cylinder so it mixes with the fuel properly.

The Bonneville guys seem to be the bigger crowd on this topic. Here's a post I submitted on the Bonnie forum for info on the subject (they also have other ones of good value):
View topic - Port Matching L36 LIMs : PontiacBonnevilleClub.com

Per WillWren on the forum:
The corner radius should match that of the cylinder heads, and the ports should measure 0.9x1.9" when done (with an exception for the injector boss bumpout).

I have a donor LIM in my garage all cleaned up and waiting for me to have some time, but I plan to port match it.

Below is a pic someone on the Bonnie forum submitted showing 2 of the 3 ports after they were port matched:

 

Whoops

That is indeed what I meant. Edited for obvious reasons, lol.

 

Yes it's for sure port and polish exhaust in the head and just a rough port and no polish on intake for heads or intake, for the exact reason of air/fuel atomization. But realistically where the injector sprays in it doesn't matter it would just be a waste of time to highly polish the intake either way.

 

The L26 & L36 LIM are identical, polishing the runners is fine, because the injectors are on an angle and spray into the cylinder head runners. Port-matching is also fine because there is a step where the larger gasket opening is sandwiched. The port openings on an HV3 are larger than the stock runners, so port-match the gasket under the HV3 to allow the greater air-flow to pass. Yes, I have done this (shiny as a mirror) and currently hold the stock cam NA record (without bigger valves or raised compression). This is just one trick and it's cheap, however it IS necessary for both NA & turbo record holding with a L36\L26 style intake manifold, more AIR+FUEL= MORE POWER(!).