I'm going to be port matching a 52mm TB to my Plenum, my plenum to SLP runners, the SLP runners to an Accel base, and the Accel base to a set of AFR 190's.

I only plan on port matching since that's all I've ever done before but it appears to me that the only weak link in this setup that really may need to be hogged out is the stock plenum. All of this is only going on a 305 with a ZZ4 cam, considering that do I really need to port my plenum or will I be ok? I mean if I need to I want to do it while I have it off but then again if it's more trouble than what I'd be gaining. Not like it's a 383 or anything, would I really gain needed airflow from doing anything more than simply port matching everything?

Opinions?

Thanks!

 

Personally, I think a 52mm TB on a 305 is useless. The stock 48mm TB will flow enough air to make over 500 HP when bolted to the RamJet 502 BBC. A 305 almost certainly doesn't need the $400 part in lieu of something that would cost less and make a greater difference, like a camshaft or larger valves.

The plenum, however, does have some restrictions, both right behind the TB and frequently in the mismatch of the side ports to the runner sets. Factory and FelPro gaskets don't help, since they also align poorly with either part, further restricting flow through turbulence at the transitions. A little attention at the plenum and runners can help more than a larger TB>

 

Thanks but I didn't go with a larger TB looking for a performance gain now anyway. I did it because I broke off the TPS sensor bolts into the housing and I figure if I'm going to rebuild it and remove those bolts that at the same time by the same place I would go ahead and bore it to 52mm. It seemed stupid not to do it at the same time by the same place for just a little more money. BTW, it was no where near $400...

I bought the GM top end gasket set and it looks like they are a card board type material that once I port match, I can cut the gaskets to match with an xacto knife or something.

Where can I get info on what portions of the plenum need attention while I am port matching? Pics would be really great...

Thanks!

 

Looking at my plenum I can see the obvious that needs to be removed however I noticed something is off, I have no little triangular hole in the front between the TB openings

See this picture here (NOT my plenum but a pic posted on this board):



I don't have that hole between the TB passages. Am I suppossed to???????

 

I would think so?? That hole is for your IAC, and all TPI'ed thirds came with and IAC, at least I think they did??

 

The pic posted is from an 85-88 TPI plenum with IAC passage. The two other types of plenum used(1989 and 1990-1992) did not have the hole for the IAC, therefore you should not have one on your 1992.

 

I am also considering porting the plenum and runners of my 5.0 liter TPI. I have been doing a lot of research before I begin this project. Start by reading the two articles in the section entitled "Important/Useful: *EVERYONE READ* FAQ / Index for the TPI board" on porting the plenum. They are quite good articles. Soon I will obtain quotes from a few shops in my hometown on how much they will charge and then decide if I will get someone to do it, or do it myself. Also consider an adjustable fuel pressure regulator at this time. All the articles I have read indcates this procedure is worth it.

 

Thank for answering that you guys!

BTW, IMO you need an AFPR only for replacing the original to insure factory pressure is at a constant 43.5 all the time. Any changes you make should be in your PROM like tuning your VE and PE tables to get your BLM's in a good place. The only time you should ever deviate from the 43.5 psi setting is if you install injectors with a different psi requirement and even then you still need to update your tables.

 

GTA,

Well, that's a different thing altogether, and makes perfect sense. As long as you have to replace the TB, it might as well be a larger one (I didn't catch that in the original post, and thought I would spare you some money).

As for the gaskets, I've found that both GM and FelPro gaskets are poorly matched. After porting to match/size, I have used a conduit punch to open the gaskets. The gaskets I've used were a fiber/steel sandwich, and would be very difficult too cut cleanly with a knife or shears. A 1¼" (trade size) counduit punch will make a perfect 1.660" hole in the gaskets, which is just about right for the runner openings, and a lot closer than the 1.525" holes in the replacement gaskets.

This is what has worked for me:

Plenum Porting.pdf

 

Thanks!

 

Hey about that triangular hole for the IAC, I have a plenum with that so my plenum should be from 85-88 right, but I am installing slp runners for 89 and i am gonna go with a computer for an 89 as well so i dont have to use the cold start injector i shouldnt have any problems with this right?