87hellbird

I am porting my engine and read that if you port the heads to much that it can create to little of resistance and reduce air speed. On a tpi air speed is a good thing, so how much is to much where is loses tuned intake force that tpi is known for. And I had it in another post with no reply, where not to port on the tpi base intake?

Abubaca

iTrader: (3)

There's no official black and white answer. What heads are you porting? ....on a purpose built, performance engine where parts are generally matched together,intake, heads, cam, you're correct in that you can over port the heads and have a mismatched system. On a stock TPI though, ANYTHING that increases airflow will be beneficial. Fully ported heads, intake, aftermarket runners, cam, headers, tuning, etc. etc. would really be a HUGE step forward, and yes, at THAT point, slightly over-porting may potentially cost a few ponies, but you'd still be WAY ahead of the stock TPI. My buddy just put a set of Etec 200 heads he had lying around on an old 70's era 350. Heads are way bigger than the cam, displacement and carb can use, (think over ported) but it was still a big bump in performance. 10 steps forward, 2 steps back kinda thing.

87hellbird

It's the 305 tpi so 081 heads I believe. They flow really well on the intake side not so much on exhaust, but I'll be porting both, I already have everything else done you possibly can to these cars down to modified shaved spark plugs. Decided to start porting, I just know that the way this intake is set up because it's a tuned intake that it can actully create up to 5 psi of boost in the powerband because of the wave lengths, and just dont want that to go away haha

Abubaca

iTrader: (3)

Yeahhhhh um I dunno about 5psi. ....but....I have no data, so I won't say no. Keep in mind that the more velocity you're getting (5psi or not) directly relates to less RPM and lower HP. blower/turbo boost is pushed by the head unit itself, but in this case with TPI....it's only there for a split second where is DOES help, and then only costs power farther up the powerband.
Don't think of it as creating boost, thinking of it limiting potential airflow.....and as a biproduct of that, it does happen to create a "boost" in a specific and small part of the powerband. LOTS of threads about people not wanting to lose "all that torque" the TPI is famous for....until they ditch the whole thing in favor of a better intake, and they never look back, and never miss the torque.

Don't get me wrong, your logic is spot on, but be careful not to over think it. I think ANY porting will help. As you say, at SOME point, you could probably over do it, but you'd still be so far ahead of the game, I wouldn't lose sleep over it.

87hellbird

Another question is the heads are stated to create 195 cfm on the intake and 110 on exhaust, should I be paying more attention to the exhaust? 195 on the intake using the equation of multiplying intake cfm by 1.7-2.2 these heads would be able to flow up to over 400hp. I understand the intake is a restrictor but every where says the exhaust should be about 70-75% of the intake which would be around 140-150 not 110.

Abubaca

iTrader: (3)

I don't know enough about the 305 heads to really say. What size valves are they? ...and how do they flow at various RPMs?

87hellbird

I believe1.84 intake and 1.5 exhaust

Abubaca

iTrader: (3)

Ya know, I spend so much time reading about aftermarket heads, and on occasion, my old stock L98 heads, but not much on the stock 305/LB9 heads. I know small block chevy heads often need a little help on the exhaust side, so it makes sense. That being said, I am by no means the person to offer specific advice on how to custom port those heads. ...but...I agree with your thoughts thus far.

cuisinartvette

If I can help you out on the heads pm me.
A great place to lurk and learn if you havent dove in is speedtalk.com
There are some big name builders that if youre nice will break loose with some info so you dont turn those old heads into boat anchors. Heads are a funny animal, not the same as porting a TPI base.