I did some searching and found many answers that varied due to different engine internals and combinations.

I have a 91 305tpi that has a ram air intake, cat back, and a cutout before the cat. I can get an entire TPI plenum and intake setup from a buddy for nothing, so I am wondering how much of an HP gain will I see if I ported the intake, plenum,and removed the little excess material(flange?) on the runners?


I will continue to search, however answers to my exact situation will be greatly appreciated!

 

I have never seen a back to back test.

I'll say, there is a ton of room to open up the lower plenum. I'm finishing mine now.

Just a guess but from the looks of it, it's certianly worthwhile.

 

Ok cool, I have tons of time on my hands right now, so it looks like I will go ahead and pick up the system and start porting it over the next month or so.
You have any pics of your progess?


Anymore input?

 

Check out my build thread in the members camaros section for pics.

 

Theres plenty of room for improvement more than shown was just screwing around here.

Have a before and after for an 89 C4 i used to own would have to dig up the time slip. It wasnt much I can tell you that but the port job wasnt all that either.

 

I'm sure someone has done the before and after dyno runs. Maybe do a Google search.

Using the gaskets as a template for porting seems popular.

 

There was a thread about it last year??

 

There's a lot of info on here about porting, though not much of it gives good before/after dyno info. From what I've seen, I'd guess that a good port job will give you maybe 7-10 horsepower on a healthy 305 that has other supporting mods. You'll get a bit more on a 350 because the stock stuff is more of a restriction on the 350. Porting the stock hardware isn't going to add a lot of horsepower because the runner length stays the same, so even with a wider diameter tube, your power band isn't going to change because it's determined by the runner length. This gets compounded by the fact that there's really no way to open up the diameter of the factory runners, so you aren't really able to increase airflow that much. A ported base with ported SLP runners and ported plenum can allow you to shorten the runner length as well as increase the diameter of the ports, so you are likely to get more noticeable gains.

 

Yeah, I was gonna say the stock runners will be the biggest roadblock.

I am using 1 3/4" diameter gaskets to match. I'm using slp runners which need a ton of porting to match them as well.

Just like everything, one part change will not make a big difference, other mods must match. With other mods to take advantage of the porting will combine to make a greater gain.

That said, the stock base has a lot of room for porting and polishing. I think I have a bog enough pile of aluminum shavings to cast a new intake

Gasket matching the upper, and porting behind the tb will help as well.

 

 

Thanks for the info and pics guys! I have decided to go ahead and port the Intake,plenum, and runners that my buddy has. I will go ahead and make a documented thread on my gains. I don't have access to a dyno, but I do have an accurate way of 0-60 times.

So from what I have gathered from this thread aswell as other 10-15 hp is possible.