Plenum & IH Pull

[Paul Workman]

[QUOTE=32valvZ;302776]

Originally Posted by jss06c6

Im guessing Pauls gains of 70-75 hp was because he had his heads ported as well?

Below are two Dynojet "before and after" my porting and then final tuning by Marc Haibeck, prior to some later minor improvements to the IH/Head junction.

I don't have a Dyno graph of my motor with only top end* porting. I wish I did**. Instead, I have to derive an estimate of rwhp by subtracting the known gain achieved by others after the heads too were ported (that being between 25-35 rwhp) to approximate what my top end only porting was.

The Dyno graphs show the before (stock) peak starting point, and peak after that establishes the full porting (and cam phasing) improvement - the bulk of improvements up to that time: starting at 336 avg rwhp and ending with 432 rwhp with HEAD porting included. So, est. of "400" rwhp before porting the heads is reasonably accurate, in my estimation.

Dyno graphs and HP numbers and estimates are popular for most - salesmen especially. But, where rubber meets the road means more to me than HP bragging rights, and actual force at the wheels, i.e., TORQUE over the entire rpm range, or POWER UNDER THE CURVE gives a better indication of the worth of any modifications - to me, anyway.

*TOP END included the plenum and IH brought out to 36mm, and later 37.5mm

** Port matching into the heads was a lot more than just matching the junction diameters only.

Instead, I took to heart the recommendations of many knowledgeable people and good ol' physics and extended the port matching in the heads from the IH junction tapering all the way down to the valve bosses (to achieve a taper that was no more than ~ 2% (think of a the velocity stack design on a Webber single bore carburetor)

Unfortunately, I didn't dyno the motor before proceeding to finish porting the heads too, because the "seat of the pants" improvement after finishing the heads was very disappointing, compared to the improvement over the top-end only achievement. And, based on experience and study witnessed by others too with even minor improvements to porting, I'm certain doing the long taper has significant benefit over merely grinding the opening of the smaller runner to match and little more. And too, I suspect the longer taper mitigates (somewhat) any anticipated gains from pulling the heads to complete the tunnels. (I'll put it this way: Given the same circumsances as I had at the time, I don't think bothering to port the heads justifies the trouble or expense UNLESS the heads have to come off for some other mod or reason [my reason was a burnt valve]).

[jss06c6]

[QUOTE=32valvZ;302776]

Originally Posted by jss06c6

Are you port matching the primaries on the heads as well? If not, your gains will be limited since the primary intake port on the head will be much smaller than your freshly ported Injector Housing primary runner.. see pic atrached..Attachment 11052


No, I'm not doing the heads. What you say makes sense. How "limited" will I be? Ive heard/read my gains would be anywhere from 20-35 hp Im guessing Pauls gains of 70-75 hp was because he had his heads ported as well?

Paul, thanks for the detailed summary!

From a fluid mechanics perspective, sharp upsets, especially when fluid flow direction is such that a sharp reduction in diameter is encountered, causes significant turbulence and reduces laminar flow velocity (volume reduction). So, having a beautifully ported plenum and injector housing will deliver reduced volume by presenting the fluid stream with a sharp restriction like the stock primary runner on the head.

Gasses can be compressed, so a smooth reduction in crossection, especially when extended over a reasonable distance, allows most of the fluid volume (air) to "get through". The fluid is moving at a higher velocity..

I've not done a top end port without port matching the heads, so I can't provide actual hp/tq numbers or cfm data. I do know that my experience before and after top end port with port matched primaries, headers and tune yields a consistent 50 rwhp on our Mustang Dyno. Headers and tune deliver about 20 rwhp, port another 30 rwhp. This is with stock DM Flywheel as well as stock diff ratio.

Using 15% loss, that would be 24 crank hp for headers and tune and another 35 crank hp for top end port and tune. Total engine hp gain 59 hp.20191114_060111.jpg

Sent from my SM-G950U using ZR-1 Net Registry mobile app

[Ccmano]

If I remember correctly,LGAFF, one of the long time members had several ZR-1s and did porting with and without port matching to the heads. He found the difference to be negligible. +-~5hp or something like that. Let’s see if he chimes in on the one.
H

[32valvZ]

Well, Im sure there are a few ponies left on the table by not port matching the heads... It does make sense that necking down a passageway will interrupt flow of fluid or air... similar to exhaust.... BUT, Im pretty happy with the results of only the plenum and IH's. Give me some time... Ill catch up!!

[Paul Workman]

[/ATTACH]

Originally Posted by Ccmano

If I remember correctly,LGAFF, one of the long time members had several ZR-1s and did porting with and without port matching to the heads. He found the difference to be negligible. +-~5hp or something like that. Let’s see if he chimes in on the one.
H

Yes, I'm aware. But, what exactly did his "port matching" amount to? Was it just the expedient removal of the sharp angle and reduction, tapering only 1/4 to 1/2" as is so often seen (even in factory port matching)? Or, does he have data on the long (laminar-flow) porting? It would be very interesting to see.

This is a conceptual picture of a carbide porting tool I sent to a tool and die maker (10 years ago) that would facilitate the rapid porting matching of the head with respect to something closer to ideal laminar flow. The idea was to not only expedite the porting process, but to also mitigate the chance of breaching into either the coolant or oil areas. (But, since I had already completely ported my heads by that time, the couple hundred bucks for a tool no longer needed (by me) ended my pursuit of the bit. And, too, there was the question of being able to secure/position and power the bit if the head was not first removed from the motor - a step unnecessary if only doing a "top-end" port job.)

[Paul Workman]

And, another diagram derived via trial and (expensive!) errors! (in case anyone is interested...)

[Paul Workman]

AND....

One more, as long as we're on the subject of porting (yes?), supporting the LONG TAPER theory, one of the examples is this set of Webber VELOCITY STACKS mounted on single throat carbs. Check it out.