Hey man I'm hoping for some personal advice. I'm parking my 87 trans am 305 for a few months and will be doing some more work to it. I cannot find a definitive answer on the boards as to whether its worth the time to port the stock plenum and intake runners (siamese, bore out, etc) or not. I will certainly be polishing the plenum and attempting to polish the stock runners but don't want to flip the bill yet for an aftermarket setup (doesn't seem worth the reported gains). F.Y.I. I have some basic air/fuel/exhaust mods that might compliment a porting job hence my question....will I see any gains in performance at all or improved throttle response this way or is it generally a waste of time to port the stock intake? Thanks for the help.

 

If I was takeing my plenum or intake off I would go ahead and do it.From what Ive read it`s not that hard.As far as gains I dont think you will feel the differance but it does help a little.It cant hurt.

 

On an LB9 with stock heads, I don't believe that you'd see any gain.

 

bump. anything to gain?

 

Use the search feature.Try ported plenum or something or ported manifold.All I was saying is if you have the stuff off why not go ahead and make it flow as good as possible.If you`re going to build the motor up or add other mods or do a larger engine swap it will benifit you more.An aftermarket base and runners would be better but much more expensive.I doubt there is a enough material to port or do anything other than polish the ruunners.A good ported and gasket matched intake will improve air flow,Every little bit helps

 

I dont think you will get a noticable gain except maybe at wide open throttle

 

 

i think u sent me and email/msg but i cant open it.

to reply to this post its pretty simple. the TPI setup is and was originally designed for GM's flagship motor which was gona be the 305, this intake isnt all that restrictive on a stock 305, unlike the 350 which it chokes stock. by porting the intake which all i would personally do would be the plenum...EGR walls etc unless aftermarket runners would be used, the kind of improvements you would see from aftermarket larger runners/base would be not nearly as much as on a 350 stock, but if the 305 recieves upgrades such as HEADS!!!! and a CAM and a good exhuast then the intake would become more of a restriciton where it would benifit from larger runners/base etc. 305 heads are horrible even if u port and polish them intake mods would make minimal difference. u cant really port much on the plenum except the EGR walls bc u havent upgraded the runners, the stock runners can not be ported since they are made of super thin wall tubing. polishing them would be pain and prob not worth the trouble. removing the EGR walls will help increase top end flow slightly. the base can be ported but that is extrememly time consuming and if your gona upgrade it anway a ported stock base will not flow as much as a good aftermarket base without porting. aftermarket bases/runners are larger already and offer alot more material for lots of porting... so why would u port something that wont make a big diff if u might upgrade it and port it later... u dont want to do it twice believe me.

so if u want, port the plenum by removing the EGR walls and clean up around the runners if u want to smooth things out but thats all i would do as far as porting. a good exhaust will really wake your motor up, reports of normally gaining .4-.5 in the 1/4 is a mod u can really feel expect 25 hp at the wheels. other mods would be to do a coolant body bypass, install an adjustable fuel regulator, complete tuneup, upgraded ignition(coil, module, wires, new plugs) a simple home made 3" cold air with cone filter is worth alil more HP. bump the fuel pressure to 48-50psi is worth alil HP. these mods will give u way better throttle response and noticable power increases.

a nice set of heads for the 305 that are extrememly affordable and flow well for a 305 are the 305 SR torquers by world. set that up with a ZZ4 cam or a nice performance roller for 305s and u can get nice power from that lil 305. the heads are like 700$ complete ready to bolt on and u could prob pick up the cam for 100-150$ from someone. u do those 2 and ur intake will need to be upgraded.

hope this helped

 

oh also... since i have the HSR ready to go on my 383... i should have a fully ported plenum, EGR etc, and completely ported and port matched to SLP siamesed runners, very lightly ported slp runners usually only at the siamesed part, motorvation spiral spacer between TB and plenum, and 48mm TB with SLP air foil, also fuel rails with good 22lb injectors and BBK adjustable fuel pressure regulator... prob gona be selling this soon, like the spring when i drop the motor in.