Ported plenum..
 

I see there are a few members that do porting work on the plenum..
I believe I have emailed back and forth to them and have gotten some nice feedback....

I know bigger is not always better and don't want to lose any low end torque..Looking for more " usable" power in the rev range...Car has OBX Headers, exhaust,Haibeck chip, Intake temp relocation wire and hurst short throw shifter...

Maybe some members can chime in how effective there cars were after porting the plenum..

Thnx....

Re: Ported plenum..
 

Don't hesitate doing it. These motors are gasping for breath in stock form. You will need to re-tune in order to optimize results. Headers w top end port netted me ~400rwhp. And don't think twice about "losing" torque.

Re: Ported plenum..
 

Your setup is similar to mine. I have OBX headers, B&B 3", custom 3" x pipe, cut air filter lid, Pete's chip, lightweight p/s pulley and lightweight and under-drive water pump pulley, and his top end porting of the plenum and injector housing.

If I ever get time to go to the dyno I will. Car did 342 stock and I have noticed no loss anywhere in power.

Good luck!

Re: Ported plenum..
 

According to Heibeck you do not lose any low end torque with the ported plenum john. You gain power and torque so there is no sacrifice. he has a dyno tune chart on his website with ported plenum and corsa exhaust.

Re: Ported plenum..
 

First off, I'm guessing you're referring to ported top-end, including the Injector Housings (IH) and port-matching the heads to the IHs - not simply porting the plenum alone, yes? I've not seen dyno results for porting ONLY the plenum, and am guessing that is why this thread has gone begging.

Second, the evidence clearly demonstrates that top end porting of the LT5 does not fit the 'mold' when it comes to low end torque, post porting performance. Apples n oranges = 2-valve vs. 4-valve dynamics (or so it would seem in the SBC vs. LT5 anyway!), especially when comparing HP results! The power made by the DOHC, 32 valve LT5 is such that low speed drivability and performance is not sacrificed in spite of making just over 500 chp.

Stock bottom 350 LT5, stock cams, stock Throttle Body, secondary throttle plates deleted, fully ported primary and secondary runners "somewhere above 36mm", headers, X-pipe, 3" exhaust...all with a stock idle!

http://i185.photobucket.com/albums/x...ps723fdad7.jpg

I do so wish I had dyno'ed the car, prior to porting the heads; just for the sake of having recorded it for reference. But, I can tell you it added significant seat of the pants grunt in the mid range too - just the opposite of all the :blahblah: one reads in car rags - (I'm guessing wheel HP around 400ish, which compares with similar known examples.)

Here in FBI land you've several sources for top end porting, e.g., Marc, Pete, Lee Gaffgahn. OR, you can do it yourself (I and others that have done their own can put you onto the source for the tooling you'll need: just say the word!)

IMO, the ported version of the LT5 is how they should have come from the factory!! It completely transforms the demeanor of the car...for the better. And, the best part of all...without sacrificing reliability, :thumbsup:driveability!

Re: Ported plenum..
 

Yes.....Not just porting the plenum but everything else that goes along with it...From what I have read the LT-5 in its stock form is " starving for air".....Many members have said its a no brainer to have this done...

Thnx for all the input....

Re: Ported plenum..
 

Do the heads need to come off to match them to ported IH's? Or do people do it with the heads in place, and maybe stuffing greased rags into the ports to catch the swarf?

Re: Ported plenum..
 

yep, rags and blue paper towels...also I rotated the engine to ensure the intake was closed on the primary port that was being worked on. I left the secondary ports alone.

recently results have been posted that port matching the head isn't really all that much better just so long as you open up the plenum and injector housings. I suspect the head porting helps more when the entire head is ported. Anyhow my observation is that you will lose nothing and all hp gains are all top end over 5000 rpm. Additionally if your exhaust system is stock or generally restricted, this mod doesn't help nearly as much as it does with the other mods in place.

Re: Ported plenum..
 

Can you port the injector housings and plenum, but keep the secondaries in place?

Re: Ported plenum..
 

2ndrys are in the head....no need to port match the 2ndry as they are already 35-36mm