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Part 1.

Porting an F2T head for an member, decided to measure and CC the ports, valve openings before starting and will measure them again when done.

I have ported many F2 heads but never bothered measuring any of the ports because it kind of doesn't matter, no matter what the final numbers and % increases are no more can be done to the F2 head, if the port mouths are any bigger they wont seal to the manifolds, if the ports are made any bigger the aluminum would be too thin to handle boost or coolant pressure, if the valve seats get cut back any farther the valves wont seal. So no matter what the numbers are it's as good as it gets with the F2 head.

After taking measurements I was surprised just how small everything is, granted the intake and exhaust ports are very short.

.................. . . . . . . .. ...Exhaust: . . . . . . . . . . . . . . . . . . . . .Intake
Port at manifold. . . . . . 1.299" . . . . . . . . . . . . . . . . . . . . . . Dual
Valve port opening. . . . 1.1005" . . . . . . . . . . . . . . . . . . . . . 1.098"
Port CC volume (ML) . .50CC . . . . . . . . . . . . . . . . . . . . . . .84CC (42CC each)

The head was measured as it was, used with carbon build up. At most there is 2cc/ml of carbon in the exhaust ports.
The valve port openings where measure just past the edge of the valve seat where the head aluminum is.


Part 2.

A while ago I watched an episode of Engine Masters, season 6 episode 80, Do cylinder heads matter under boost?

On this episode "The crew dives into head flow and boost affect horsepower. They run their 363 Windsor once with 195cc and 225cc heads and declare once and for all if cylinder heads actually matter under boost."

Usually Engine Masters results are pretty conclusive and answer questions and myths.
They felt the episode was but here is what they did and what they missed.

They ran the 363 with a belt drive pro charger. They first tested the cast 195cc head, then the cnc 225cc head.

*Note: when running a belt driven supercharge, pro charger, blower... or an internally wastegated turbo taking boost sourced at the compressor housing, the amount of air delivered by the forced induction device is fixed. You can improve engine flow, port size, exhaust size, piping size and throttle size, this will all improve parts of the power band but the maximum amount of air the forced induction device will deliver will remain the same. The only way to increase it is to change belt gear ratio's or wastegate tension.

On the second pull with the large 225cc port heads the dyno showed a few small increases in certain parts of the power-band but peak numbers remained very similar.

When checking and comparing the intake manifold boost pressure between both runs the 195cc ran 11 psi boost and the 225cc head ran 9psi boost (well boost wasn't steady but the boost gap between the two heads was). Steve Brule said he expected the boost drop due to less resistance/better flow at the intake valves causing lower boost.

The "crew" decided that head flow doesn't matter with forced induction and Freiburger stated just run more boost.

I will say this is a decisive result if you are running fixed flow forced induction (*see note).

Here is what I noticed:
-The 225CC head was a 15% increase in port volume size.
-The boost difference between the two heads was about 20% so the 225CC head flowed 20% better than the 195cc head.
(port size yields better result with forced induction).

Here is what they missed:
-Most people running forced induction run some form of boost control and it is based on intake manifold readings, boost control set-ups and boost gauges... don't monitor or care about boost pressure at the compressor housing, they make up for all pressure losses between the turbo and intake manifold.
-Most forms of boost control on forced induction motors will maintain intake manifold boost pressure despite engine flow/performance upgrades.
-If anyone dyno's their car/engine at 15psi before and after mods they will want to run 15psi to compare before and after mod results.
-The larger port heads flow enough to make the same power on a better curve at 20% less boost, at 11psi they would have made lots more power than the 195CC heads at 11psi.
-The episode should have been called "Can a fixed air flow forced induction device flow more peak air on a better flowing or bigger engine at a fixed compressor RPM", the answer to that would be no (unless the stock engine couldn't consume all the supplied air).
-Fixed flow forced induction can run boost control (bleeds boost pressure from the compressor before the throttle. It works the opposite of a wastegate boost control, to maintain or increase boost less air gets bled off, with a wastegate more air is bled off).

As someone who runs boost control forced induction I feel any modification tested fro improvement must be tested ate the same pressure to answer anything once and for all.
Test something in a pressurized environment for comparison the pressure should be the same.


Part 3.

How does any of this apply to the F2T, the VJ-11 and Ported heads?

-Well I have always said it's not worth doing huge flow mods on the F2T when running the VJ-11 turbo because the turbo is limited by how much air and exhaust it can flow before the shaft snaps.
-I always said the heads I port and polish will flow so much that they spool the small turbo faster than the wastegate can control it and kills the turbo.
-I still believe that is the major cause of vj-11 turbo failure when running one of my ported heads but only after measuring and starting porting this head did everything connect, three things I know combining it to one moment of clarity and everything is explained.
1- With a sufficient turbo 1psi boost is one psi boost on the same motor no mater what the turbo's flow charts says as long as the turbo is in it's efficiency zone. A 400cfm turbo and a 600cfm turbo will make the same power at the same boost putting out 300cfm, the 400cfm turbo will spool quicker. If pressure is delivered at the same temp through the same size pipe at the same pressure it = the same amount of air despite the size of the pump or available cfm/lbs/min.
2- A boost leak will cause the turbo to work harder to maintain boost in the intake manifold, if it took 17.5psi at the compressor housing to deliver 15psi boost after the intercooler, pipes and throttle body with a boost leak it could take 19 or 21+ psi compressor housing boost to make 15psi intake manifold boost (boost gauge).
3- Making the head flow better lowers intake boost pressure but the boost controller corrects that.

Up until now I always assumed what killed vj-11 turbos was all exhaust related and in a way it is but that's just 50% of the reality or equation, I know there is a boost pressure drop after the the intercooler because cooler air takes up less space therefore pressure drop ratings across the intercooler your looking at say almost nothing, is it free flowing but deliver hot air or is it efficient and causing a pressure drop because it cooled the air?

When my mind puts all this bullshit together reality slaps me in the face.
Although I said it and thought I completely know why, I didn't. Every air and exhaust upgrade brings you one step closer to killing the VJ-11 turbo.
Reality: Every engine flow mod causes the turbo to generate more boost at the compressor housing to maintain manifold pressure. Engine flow mods have the same effect on the turbo as boost leaks so just because intake manifold pressure/boost stays the same, boost at the turbo is higher with mods. So the turbo is running more boost at the same intake manifold/gauge boost.

If running a lager turbo who cares or this isn't an issue but engine flow performance upgrades aside from intecooler can clearly be measured by boost changes at the compressor housing, the greater the difference between manifold and comp the better the engine is flowing. The air being deliver to the engine is fixed to the amount of boost psi at the compressor housing.

The port work I do on the F2T head, as a conservative estimate will yield over 75cc exhaust ports and 126 cc intake ports (50% volume increase), 15+ % exhaust an intake port mouth and 10% valve seat increase.
What psi this will cause the turbo to boost to maintain manifold boost? but I am sure it's a bigger difference than the engine master 195 and 225 cc heads cause.

After port work F2T/F2 head numbers still to come.

The more I learn about combustion engines the more the sparkle and shine fades and it all becomes math, ignorance is bliss but when it come to cars bliss = swapping parts.

Taking away the magic of the F2T is understanding it.
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Discussion Starter · #2 ·
My shattered illusion was that porting the trubine and compressor housings, running larger mandrel bent intercooler pipes, modified or ported throttle body, ported intake and exhaust manifold, larger mandrel exhaust and extremely ported head made the engine more efficient and yielded more power per PSI boost. This is still true but only in intake manifold psi, the turbo has to make more boost at the compressor to make the same manifold boost after all my air/exhaust flow work. I feel the turbo and reality have stolen my thunder, on the stock VJ-11 none of this work is necessary because the turbo can be killed on the stock set-up when boost is high enough. It will always result in more power per intake psi, faster longer boost and less heat. Any flow performance gains can be measured by the compressor boost change required to maintain manifold boost. Any boost increases at the compressor when running the same intake manifold boost with modifications is exactly the amount of extra air being flowed.

Finished porting the exhaust side of the head.
Some of my estimated numbers where optimistic, but the flow path and port shape is so much better than factory.
The valve seats can not be ported more than 1.1920", that is cut to the very edge of the valve grind angle, the port now opens up right after the seat (tapered inward after the valve seat before porting).

.................. . . . . . . .. ...Exhaust: . . . . . . . . . . . . . . . . . . . . .Ported..............% Increase
Port at manifold. . . . . . 1.299" . . . . . . . . . . . . . . . . . . . . . . .1.5002"...............15.488%
Valve port opening. . . . 1.1005" . . . . . . . . . . . . . . . . . . . . . .1.1920"...............8.314%
Port CC volume (ML) . .50CC . . . . . . . . . . . . . . . . . . . . . . .62.5CC ..............25%

Measuring the port CC is a real pain in the ass, I have to keep reinstalling and removing the valves.

Ported the openings on an exhaust manifold to go with this head, opened the mouth of each port to 1.554" then I resurfaced the exhaust flanges until they where clean and had to port the mouths some more to get them back to 1.55+".

The reason I have to measure the head ports before finishing the heads is because I will resurface the heads exhaust and intake manifold flange mounting surfaces, I won't have to take much off but any amount will reduce the port mouth size and CC of the ports. Although the Port mouth and CC will be slightly reduced, the ports will flow the same they will just be a tiny bit shorter.
This is where everyone can call bullshit on the numbers, if I don't surface the head flanges the numbers will be higher but I want the manifolds to seat perfectly (they have to there is a lot less gasket surface to hold a seal).
Besides I figure these numbers reflect how much can be done to the F2 head and not the final number CC and port size.

Exhaust ports stock:

(With 3 broken studs).

Stock exhaust valve seats:

Exhaust ports after porting:

Valve seats after porting:

Exhaust manifold after porting (ports are round):

After resurfacing the flange:

Not so round anymore, Oh well.

Conclusion, even if you run custom forged lower comp pistons, stronger rods, E85, the right cam timing or an adjustable cam gear or any other combination of mods peak performance, throttle performance, redline performance and max performance potential are all increased with a ported head.

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The more I learn about combustion engines the more the sparkle and shine fades and it all becomes math, ignorance is bliss but when it come to cars bliss = swapping parts.

Taking away the magic of the F2T is understanding it.
Great information. I totally get what you mean. I started playing with these cars over 20 years ago. I've been working at an OEM for nearly 10 years, with the last few being spent dyno testing engines.

There is no magic, just numbers and variables.

I'll have to think on your observations about compressor pressure some more. It makes me want to spring for a turbo with provisions for a shaft RPM pickup. That would answer some interesting questions.

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Discussion Starter · #5 ·
Great information. I totally get what you mean. I started playing with these cars over 20 years ago. I've been working at an OEM for nearly 10 years, with the last few being spent dyno testing engines.

There is no magic, just numbers and variables.

I'll have to think on your observations about compressor pressure some more. It makes me want to spring for a turbo with provisions for a shaft RPM pickup. That would answer some interesting questions.
Well there is something about the fact the F2T is faster at the same "power" as other inline 4 cylinders.

The Garrett G25-660 turbo can run a compressor speed sensor, this would be the only true accurate way of measuring the effects on turbo deliver by flow changes at the engine.

Here is what I am thinking.
I do understand PSI is not a direct reflection of how much air a turbo is flowing but how much resistance the engine causes, if a turbo that flows 400cfm is bolted to a big block motor that flows 650 N/A, at that turbo's peak flow manifold PSI would be zero, the turbo would actually be chocking the engine, the engine would be trying to suck up more air than the turbo can deliver and without an intercooller compressor PSI would be 0, with an intercooler maybe 2psi.

There is always a pressure drop after the intercooler, some of it is caused by the intercoolers flow resistance and some by the fact cooler air occupies less space.
How is the pressure drop mapped out is the big question. Does it take a certain amount of extra boost to fill the space of the intercooler? would comp pressure be 5 psi if manifold demand was 2psi and as boost is increase the numbers get closer up to the point the intercooler starts restricting flow and above that boost the numbers get further apart?.
Intercoolers have so many variables affecting them, pressure drop and cooling capabilities will very based on engine size and flow, turbo efficiency and heat generated, ambient temperature, installation...

If at a manifold pressure of 15psi the pressure at the compressor is 17psi there is an 11.76% pressure drop between the compressor and intake.

If manifold boost was increased 1 psi at a time and compressor psi was recorded again at 16, 17, 18, 19 PSI (intake).
(Once complete having comp pressure readings for 15, 16, 17, 18, 19 psi manifold, it could be charted out in 1/4 psi or 1/10th psi increments.).
Then a better flowing throttle body or intake or cam, head, exhaust manifold.. is installed, intake manifold boost is set back to 15psi and compressor PSI is measured. This would give a rough idea of how much better the modification flows/ it's equivalent manifold PSI based on it's new compressor PSI.

Having a compressor speed sensor and running the car on a dyno and safely running 1,2,3,4 psi above the boost the engine will run, recording power, torque and compressor speed at each PSI and mapping that out on a chart would give a future performance modification chart that would show exactly how much peak power was gained from a flow related mod without having to dyno the car again.
If compressor speed was mapped across the entire rpm band for each extra psi then after a mod the compressor speed maps where compared it would show all gains across the powerband under boost.
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