I want to start some intake mods on my '90 L 98 (auto. - 55K miles).
The car is set up with the usual minor mods, K&N, open lid, AFR, Taylor wires, TB vane, TB by pass - no frisbee - Hypertech Street runner, magna flows

With the stock TB, will a ported plenum provide any increased air flow/ performance improvements? Or would I really need to go the whole route ...... 52mm TB, port the runners, intake manifold and heads to see any improvements?


Flatbush862

 

You could keep the 48mm TB, get some Accell runners, port the base youd see a difference. Just doing the plenum by itslefyou may pick up something but probably not SOTP noticeable.

 

port the base, or buy a bigger one like Accel or TPiS
buy some AS&M Runners or siamese your own as you port them
port the plenum

keep the stock TB, a bigger one isnt going to help you

buying the aftermarket parts will do better than porting your own because theyre capable of flowing more, but if you have to keep anything port the hell out of it

 

The stock TB flows enough for a TPI 350 engine (it isn't until you get into bigger cubes that a larger TB is necessary). But just porting the plenum without doing anything else downstream will be waste of time. Larger runners (TPiS, AS&M, SLP, etc...) and a larger manifold (Big Mouth, Accel, Edebrock, etc...) will result in a slight bump in power (I'd estimate between 10-12bhp). Adding a set of 1.6:1 roller rocker arms will help too. But don't expect big numbers here. TPiS claims something like a 30hp increase using their Big Mouth intake, which is very misleading. Without some heavy-duty porting of not only the manifold but also the heads (AND maybe even a ZZ4 or 219 cam?), expecting a 30hp from just changing the intake is wildly optimistic at best.

The only way I would suggest porting the plenum without doing the runners and manifold is if you have it off the car for some reason, and you plan on doing this stuff later anyway. TPiS will port your plenum for $100+s/h. So if you have the plenum off the car, then it might be worth the $100. Otherwise, save the cash and do everything at once.

But that's just my $0.02.

 

CorvetteKid has a good point, but I have seen in person with just an intake swap 22rwhp/22rwtq and no tune. This was an accel base/as&m runner/ported plenuem on a 88-90 vette. i forget the exact year. one would think the air/fuel might of been of a tad, so he might of seen a tad more. But keep in mind the tq/hp curves were very close to stock meaning it gave the same TPI characteristics, but there was more jam under the hood. If you can find these parts at a great price, It wouldnt be a bad idea. The TPI feeling on the street is fun. Throw in some 1.6's, and a set of pulleys, and 30rwhp would be the number.

Dont believe what TPIS says either!

 

 

http://www.gmtips.com/3rd-degree/dox...-port/port.htm

 

Porting the plenum is important in that it becomes kind of a retsrictor plate if you've done the other mods. (base, runners, TB)

I would pull it apart and do it all at once. While your in there-Cam?

The LPE 219 is my favorite for a street driven 350.

Also consider the runners, I like the SLP because they are siamesed and let you rev a bit higher before you hit the "TPI Wall" In addition you can port them for even greater performance.

I mention this because I do this. Mike from corvetteplenum.com

 

I asked TPIS in person at their shop before I bought their Big Mouth base and LT runners and I received what I thaught was a honest answer. 15HP and 15TQ on a stock 350ci motor. Their numbers in their catalog and on their web site are what you would see if you put together something like I did all together at once.

 

Hi Mike, you did a plenum for me (1991 vette) & was very happy w/ your work! I reccomend your work to all.... Keep it up! Welcome to the forum.......