I was fortunate a few months ago and ran across someone selling a TPI setup that uses the larger SLP runners and a Holley 62mm(?) throttle body. I got the whole setup pretty cheap. But, they raised a few questions.

First, I noticed that the runners are ported at the top. I've searched and read about others are doing additional porting to both the top of the runners and the plenum to improve the flow. QUESTION: how much will this move the peak power up into the RPM band.

Second, I've also read that some are porting the base and the bottom of the runners. QUESTION: What is the purpose and how moch more will it move the powerband.

Third, If I do both, will it improve my air flow for a larger displacement motor?

I'm looking into building a 377 motor. I've read LOTS of pro and cons on this motor but since I'm planning on putting this into a light vehicle coupled to a weak transmission, I don't want gobs of torque off the line but I do want more top end horsepower.

So I guess my overall question is: If I build a 377 and port the top AND bottom of the intake system, will this be enough to let the motor breath up to at least 6500 RPM?

Thanks in advance,
Roy

 

I am also interested in trying to port my own plenum.(sp) Any advice?

 

Probally wont flow well to 6500rpm. You would be better of with a holley stealth ram. Yes it will raise the rpm peak a little. You will probally be around 5200-5400 rpm peak for a well ported TPI system including aftermarket base. What sort of questions do you have about porting? Use a dremel or die grinder with an aluminum cutting bit to remove the metal. Then use sanding drums to get it all smooth. Start by removing the little walls right behind the TB in the plenum. Then for SLP runners match the runners and plenum to the TPIS big mouth or similar gaskets.

 

I am going to get a stealthram eventually, I just want a little more power for almost free. I know how to port and how it works perfectly, I also have done some of it, mostly polishing heads. I want to know the best places to port it out. What should I go by? How far should I port it?

 

Here is one good set of instruction for SLP runners and base.
https://www.thirdgen.org/newdesign/t...meseport.shtml
I know there are other good articles, try doing a search on porting plenum.

 

"QUESTION: how much will this move the peak power up into the RPM band."

Hundred or two RPM. Maybe.

"QUESTION: What is the purpose and how much more will it move the powerband."

Increase the amount of air the engine can suck through a straw. Shouldnt move the powerband much, if any. More like a power increase at the same RPM.

"Third, If I do both, will it improve my air flow for a larger displacement motor?"

Yes.

"So I guess my overall question is: If I build a 377 and port the top AND bottom of the intake system, will this be enough to let the motor breath up to at least 6500 RPM?"

377 as in what? Destroked 400? If so... thats not what a TPI would prefer, it'd like a 383 better.

I dont think you're going to see much by porting the plenum aside of the EGR walls. Its just an air storage tank.

 

The motor I'm considering is a 400 block w/ 350 crank. I already have a crank-less block and a block-less crank.


I suppose you're referring to grinding through the bases runner walls into the EGR cavity? I was looking at the link listed above as an example of base porting.

Roy

 

Thank-you for posting that thread. I ran across it before while searching for info and forgot to mark it as one of my favorites. And, actuall, that was the thread that got me thinking about air flow when I started looking in to de-stroking a 400cid.

Roy

 

By egr walls he means the walls just behind the tb in the plenum. They are a useless part of the egr system.

 

Thank-you for clearing that up for me.

Roy

 

Here is another good tech article. Made by Vader
http://216.121.161.76/files/PlenumPorting.pdf

 

Just a bump to see if anyone else has an opinion about the flow of ported SLP runners and base.

I seems to me that porting at the base would dramatically change the peak of the motor... more than just a couple of hundred RPM. Since the motor would be sharing the air from two ports right near the intake port, would it have the same effect of a miniram?

Roy

 

tpi will never have top end... if you port them, yeah, you get a LITTLE bit more, but to be honest, it's better to just get a mini ram. what, you loose a few lbs of low end torque and you gain sooooo much more top end it isnt even funny. i've heard 3rd gear with a MR or HSR pulls better than the third gear of an LS1 ... well worth the $$$ you invested in the intake, after propper tuning and messing with the timing and fp.

 

Of course it depends on the setup. You could stick a Miniram on top of a stock L98 and have dog.

 

porting the base is almost a waste of time,not to diss those that have but the gains are so minimal its worth it to save the money to get an aftermarket base,porting the plenum is well worth the effort it has many obstructions inside...

 

The way I understand it is, the reason the stock TPI gets such good low RPM torque is because of the long runners and the speed of the incomming air (a factor of the diameter of the runners vs motor size). I have the larger SLP runners so the air speed is slower which raises the peak RPM of the motor. Now:

By porting the plenum and the top of the runners, I'll shorten the runners which will move the peak RPM up, again.

If I port the base and the lower portion of the runners like shown in the link above, the intake charge shares two runners all the way to the base, which now has only a short distance before entering into the combustion chamber, say 6" long.

It seems to me that by doing the above, you've basically created the same situation as you would by replacing the whole setup with a miniram. Lots of air to very short runners.

Are you saying that the base ports, when fully ported like in the link above would still be so restrictive, no matter how much porting is done, that the peak would only be raised a couple hundred RPM?

Not trying to argue, just trying to understand.
Roy

 

i undrestand where you are headed with this but the stock base does not have enough material to port enough to make a worthwhile gain,aftermarket has solved that problem.

 

Who makes a better flowing aftermarket base?

Roy

 

www.tpis.com

they make the big mouth base for tpi, and the mini ram intake if you want to sacrifice about 10 lbs of low end torque for almost 100+hp at 6500 rpms, over tpi.

 

edelbrock has the best price on a base and flow is the same as the big mouth,accel,so to save a few bucks i would get the edelbrock.

 

Maybe you haven't seen mad max's dyno he did on siamesing his intake. 20hp is not minimal, especially if it is free. 15lb/ft of torque is not minimal either. Read the article.

https://www.thirdgen.org/techbb2/sho...antituning+TPI

 

Did'nt he along with a few other base siamisers burn up the #7 or #8 piston from it being too lean, while the opposite was too rich?

 

Nope. Car has about 10k miles on the current setup. Its fine.