[Firebob]

There's a lot of talk about porting and air flow but I never hear anybody say what kind of a difference in performance it makes from before to after. Has anybody ever posted before and after results from dyno pulls with no other changes effecting the outcome?

[Rick Jones]

I don't have any first-hand info, but on the SD Performance website it states that the "Street Port" D port heads will see a 50 hp gain. That is porting to 250 cfm from stock 208 cfm. I would imagine a cam change to match the increased flow would add even more.

[steve25]

Do not forget that HP is a number durived from the torque and rpm numbers, so first you need a gain in torque to see a gain in HP even at the same rpm.
The porting of a head so that a good amount more air can pass in and out of the motor thru much the same size ports will make for a super responsive monster out of the motor at any rpm level up to the rpm of peak torque.
Once the rpm of peak torque has been hit the motor has tapped out the whole flow systems breathing ability.from that point on more Hp is made just do to the shear fact that higher rpm numbers are making the additional HP (remember the math), and this HP than peaks out when the motors internal friction losses equals the HP being made.

[PONTIAC DUDE]

I have seen 1/2 second plus gains with 13 second cars and mild port with intake match.

[ponjohn]

Too many variables.

One combo can be perfectly tuned and cammed and the additional airflow could in fact hurt the combo.

If the same combo is over cammed then the additional flow will be of benefit.

Ask the Dude about how BAD airflow can hurt a combo.

[steve25]

Sorry, but you seam to want to over look my point of the ports being relatively the same size as stock, let's say for the sake of this discussion about 20 CCs worth.
This would equal the difference between a stock 154 CC 6x head that flows no more than 210 CFM @28" and a stock 172 CC 455 71 or 72 HO that flows a stock 225 or so CFM.
With the right porting work the 6X head will out flow the HO head by 5 to 10 CFM,and only if the motor in this discussion was not re-jetted right for the additional airflow would the motor not perform better, even in the bottom end of the torque curve!
you can bank on it as long as the motor is over 350 CID!

[Firebob]

Still all just theory and conjecture except for PD's 1/2sec gain. I don't debate SD's numbers but they are in the business to sell what they do. Just wondered if anyone had verified for themselves?

[Skip Fix]

Steve gave you a good example.

Any HP formula(Superflow formulas, calculators) based on airflow will show the difference in potential HP but they all make the assumption you have fairly optimized the combination.

Look at the factory HP difference between the "plain" 455 and the HO or SD 455s-main difference in the increase in HP is airflow.

My first tweaked Pontiac motor was a RAIV headed 444 with some cleaned up ports. made right at 400 hp on a VERY conservative dyno with a lot of factory parts. Machinist liked it so much copied it with using some ported D ports that stil didn't have the same ariflow and it was 50 hp down.

[Firebob]

Skip, you gave the example of the 455 vs the HO or SD, the difference in HP being the air flow. Can you give me specifics like where the added flow came from and how much difference there actually was?
It would just be nice to know that after spending a ton of money on porting it's going to be worth it. Does added air flow equate to torque gain? Maybe higher flow only makes a big difference with higher cid engines.

[1971WARBIRD]

high performance Pontiac did a very good article on this back in the early 90's. it was a section called Indian Head, ran late 1990 to mid 1991. article was by Pete McCarthy and i think Dave Sizemore did the porting.
off the top of my head this is close.
67 400 670 heads, ran it stock on a dyno, then after porting ran it again and they LOST power.....after looking at each other they decided to try some things. add a torquer intake which used to cost power on a stock engine..... power came up. they went from there to tune the carb, distributer to optimize things. at lets say 5800 RPM( I can't remember where the stock one topped out) the ported one made about 50 hp more. but the big story was, at lets say 6500( can't remember rpm) it was like 150 hp more.
so like people have said before, the whole package has to work together, ported heads needed better flowing intake to take advantage of the new flow.

[Firebob]

I understand what everyone is saying, that to take advantage of porting you will also need to take advantage of some other supporting parts as well. So it seems that just a port job in and of itself is not going to show performance improvement and may very well be detrimental to performance because of the volume and different speeds of incoming air/fuel charge. So basically, unless you are prepared to build a completely different engine, porting is not where you would want to spend your hard earned dollar.

[rexs73gto]

That by itself is not true either. I had the heads worked on my 73 T/A. It was a stock 455. I took the 4X heads in & had the valves done with the 4 angle grind from Arnie's book with the 2 deg's back cut on the valves. I had the studs changed to screw in studs. I installed new springs with an open seat pressure at 145. The porting opened them up to the tune of about 20cfm per. I port matched at home the intake which was a 72 455 HO intake. All else was the same . The cam was A RAIV (Crane Blue print) with a tricked out Q-jet. I did change the piston from the stock cast to a set of TRW forged with nothing done to them at all. Porting the heads & putting all back together the way it came apart except for what I said the rear wheel HP went for 334. to 368. I don't tink the pistons would do anything, & everything else as far as parts were the same as what came out. The only thing different was really the heads. I gained 34 HP. It could be felt to. The timming did go up from 12 to 15 & the total timming went from 34 to 37. But thats it. It worked for me, a little bit.

[1971WARBIRD]

Hi Rex.
on your combo as you say you port matched the intake to the heads, not much, but every little helps.
but the big thing is the cam. you can see how much it was over cammed with the RA IV cam and those stock heads. that cam really wanted to breath and the porting let it. not trying to pick a fight here, just saying, in my opinion, the cam matched the ported heads a lot better.
total package makes the best all around performer.
by the way, I plan to use a ported 71 HO intake with a set of 197 heads I got that were ported to flow big numbers(don't have the flow sheets here with me but were close to 280-290 @. 650 if I remember right). hoping to get 500+ hp looking pretty stock in a 71 GTO.

[Cliff R]

A few years ago we built and dyno'd my old 455 engine with a well prepared set of 6X-4 heads. They were not "ported" in conventional terms, just nicely cleaned up and opened up for 1.77 exhaust valves. A port match was done exactly to a stock intake manifold gasket, and all casting flash removed from the runners, and gently smoothed with a sanding roll under the valves. On a flow bench they flowed 232cfm. The engine made close to 1hp/cid with those heads on the dyno with a Crower 60919 camshaft (RAIV clone), 455.4hp/540tq.

A swap to a stock unported set of KRE aluminum heads netted 494hp/467tq with no other changes. This was on a pretty "basic" 455 build using TRW flat top pistons, Crower rods, stock "N" crank, factory iron intake, 1977 Pontiac q-jet, and stock HEI distributor with a positive stop added for the advance.

We've also dyno'd 400 engines with unported heads, not touching them anyplace with a grinder or sanding roll.

A stock set of #48 or #62 heads (for example) will EASILY support a 400cid build to 1hp/cid without the first bit of port work anyplace.

On the dyno with a 60916 camshaft we made 419hp/453tq, and 424hp/465tq with a larger 60243 camshaft. Installing an unported set of KRE aluminum "D" port heads with 260cfm intake flow moved those numbers up to 440hp/450hp respectively.

As for porting heads, for most street engine builds extensive porting is not needed. In any and all cases, the valve/seat/bowl work should be excellent, to maximum flow numbers, especially low lift numbers. Working with 30 degree intake seats this pays big benefits with the stock Pontiac heads and relatively small camshafts designed for decent idle quality, strong low end power, and good street manners.

The camshaft is a big player with these things, and will effect the end result as much as if not more than the heads and work done to them.

It is a complete waste of time/funds to put out big money for CNC'd heads at or past 240cfm's unless you put enough camshaft in the engine to utilize the additional port flow. Even with that said, the end user may see some minor benefits with the larger heads if the work is excellent and picks up flow numbers at all valve lifts, as this would increase cylinder filling and engine efficiency in the "normal" rpm driving range. That deal could even be trumped if the larger heads were installed on small cid engine and port velocity fell off some. So in any and all cases, it's all about the combination of parts used, not specifically head flow and runner volume.

Anyhow, when it comes to this topic, when working with the Pontiac V-8 engines and factory heads, one must keep in mind that they are very conservative in both flow numbers and cross section for the size of these engines. Most flow no better if as good as a run of the mill SBC head, which in most cases sits on a much smaller engine.

This means that port velocity will be pretty high, and these engines will be sucking pretty hard on the runners at high rpm's, especially the larger 455cid engines. A side benefit of using conservative heads on big cid engines is that they will make loads of low rpm power and excellent mid-range power. To see strong upper mid-range and top end power, a pretty large cam is going to be required. There are simply no free lunches when it comes to this deal with the longer stroke engines. They are actually HORRIBLE by design, under square, heads too small, and internals too heavy. Doesn't mean for a second that they can't be quite successful at getting it done, and make great power, you just have to work within the limitations of the basic design, and do things to enhance the excellent qualities these engines possess.

As far as this topic goes, as mentioned someplace above, there are simply too many variables in the equation. Head flow is only a small part of a big plan when it comes to engine building, and making the HP/tq goals in the intended rpm range for the end user.......Cliff


BTW, WRONG name above, it is Dave Bisschop at SD Performance.

[scott70]

On my street car 70 gto when it had a auto trans and 3.73 gears,,,I was running a 455 with #62 heads,t2 intake and 800 DP,231/239 @ .050 UD flat tappet hyd.with rhoads.Ran a best of 7.8's at 87 and change. Took the heads off and sent them to butlers for a 250cfm port job.Put them back on, same headers,,same everything.Best after that was 7.42 at 92 and change.(11.70 at 115mph in 1/4.)

[Skip Fix]

Most HO heads flow around 230 stock, most D port heads maybe 210-similar cams on factory motors usually has 10-20 more HP for the HO motor. Mild motors more airflow.

If I remeber on Pete McCarthy's motor there were some other parameters to me that affected the outcome-been too many years to remeber the exact combination issues.

Kind of like with the comments we used to have here about "big 215cc E heads ports will kill bottom end torque", or even the bigger KRE D port would run slower as it did on Jim Hand's wagon compared to smaller iron heads. I think even Pete was suspicious the E head would do that. I think the many many strong mild streetable combination with no loss in bottom end that are faster than when all we had were iron D ports maybe 350 ported show airflow does make a difference, liek Scott just showed.

[zeebo]

question: what is the ballpark flow numbers of a standard D port head with big valves, say a #12 head vs like a round port #197 head? i have read that the round port intakes are 10% larger and the exhausts 36% larger than a comparable d port from the factory...???

[Skip Fix]

"Most HO heads flow around 230 stock, most D port heads maybe 210-similar cams on factory motors usually has 10-20 more HP for the HO motor. Mild motors more airflow."

RAIV and SD ports even a little more even in stock form. Valve jobs, back cuts on valves all can make an impact also even on a stock port-how the NHRA stocker guys run mid 11s with smogger 78 400s and RAIV 400s are in the 10s with fairly stock ports.

[Fast 68 GTO]

this probably won't help to much because I did flow them before and after but the second engine I ever did 20 some years ago my car ran 11.70s then all I did was port the heads myself they were d port heads first ones I ever did then the car ran 11.40s no other change.

[PAUL K]

In 2002 I was working on developing an LS1 CNC program. In early testing, I baselined a 1999 T/A with a mostly stock (just basic bolt-ons including headers) engine on a chassis dyno. Peak torque was 346 and peak power was 382. The heads were pulled off and ported, nothing else was done. When the car was dyno'd again, peak torque rose to 356 and peak power to 401. The car did lose a slight amount of torque (which was brought back later by improving the valve job) below 3500 rpm. Above 4500 rpm the ported heads blew away the factory heads. The rpm where the TQ & HP peaks occurred did not change much.
Something to think about here, this was on a 346 cid engine. Stock LS1 heads flow around 250ish, the ported versions were in the 270's.
Also around the same time, I ported a set of late model LT1 heads for a gentleman. He had been to the track several times and ran a best of 12.20. He pulled the heads off during the winter, I ported them (did not do anything else) and his car ran 11.8's next time out.