Intake porting vs not porting

[gumba]

Does anyone have a dyno number showing the h.p./torque difference between stock intake 32mm vs 36mm? Where the ONLY change was enlarging the intake ports, injector blocks, and the cis manifold.
One school of thought I'm hearing is since the turbo is pushing air by increasing the port size the air is moving at a slower speed (his words not mine). It's all so confusing.
This is on a mildly modded 3.3, sc cams, k27, headers, stock cis & ignition. The dyno number doesn't need to be specific to a 3.3, but more to a slightly modded motor.

[mark houghton]

Originally Posted by gumba

Does anyone have a dyno number showing the h.p./torque difference between stock intake 32mm vs 36mm? Where the ONLY change was enlarging the intake ports, injector blocks, and the cis manifold.
One school of thought I'm hearing is since the turbo is pushing air by increasing the port size the air is moving at a slower speed (his words not mine). It's all so confusing.
This is on a mildly modded 3.3, sc cams, k27, headers, stock cis & ignition. The dyno number doesn't need to be specific to a 3.3, but more to a slightly modded motor.

Of course, increasing the port size would reduce the velocity or speed of the air (put a nozzle on a garden hose, see the velocity increase as a result).
But isn't the real benefit of larger ports, the delivery of more air volume even though it may be flowing slower? Just my thoughts, I'm not a wizzard on this topic. There must be hp and/or torque benefits, or people wouldn't be doing it. Would indeed be interesting to see dyno numbers.

[tailwind22]

My guess is Chris Carroll of Turbo Kraft would be well versed in these specific numbers.

[911nut]

Increasing port size is a tradeoff. Theoretically, low engine speed performance will suffer due to low port velocity and inefficient fuel atomization but more mass is delivered at high engine speeds, increasing power. I say theoretically because every time I drive a early big port 911 SC, for instance, it seems to has better low end power than my old small port SC did.
I've never driven a big port 930 but Chris Carroll told me that the 3.3 really responds to big ports (Carrera size ports: 41 mm),

[gumba]

His opinion was based on a turbo pushing air, vs a n/a motor pulling air. Big ports on a n/a motor pull more air/fuel in, where a turbo pushing would deliver fuel faster through a smaller opening.

[RarlyL8]

Velocity is more important in the turbocharged exhaust while volume is important in the turbocharged intake. This is not dissimilar to how bigger turbos make more power than smaller turbos at the same boost level.

[9Thirty]

More air is always good.

[gumba]

Still no proof?

[gsxrken]

I think your guy has it reversed. A normally aspirated car likes the small ports to speed up the air column rushing into the cylinder. The better engines can best 100% efficiency in their sweet spot because the momentum of the air column causes it to keep moving into the cylinder even as the piston is rising. Bigger ports kill this effect- see the Ford Cleveland 4V cylinder heads as example.

Whereas the turbo is creating another atmosphere of pressure, so the pressurized air is going to want to go anyway, as the delta between the vacuum in the cylinder and the pressure in the manifold is greater than in a N/A situation. Bigger ports mean more volume, and less heat as the fan can move more into the cylinders without it packing up in the intake system waiting to get in. The more air, the more fuel... this is more important than the pressure or speed of less air and fuel.

But's that's all bench racing. Can't help you with the dyno proofs and I doubt you'll find a guy that had enough willpower to ONLY widen his ports and do nothing else while he was in there. Maybe Chuck Norris could.

[kenikh]

I decided not to port my heads. I'm going for off the line perf, where velocity is everything. Also went 98mm 8.5:1 pistons, mod-SC cams, k27-7006, euro exhaust, twin plugs, stock ports, Andial IC, Andial 8:39 R&P. Not 100% ideal...Rarlyl8 headers and a GT35 would probably be ideal, but close enough to rip out your eyeballs off the line and still get close enough to 400CHP to make me happy. My other cars are early 2L, so needed to go entirely in the opposite direction.

Will know for sure in the coming weeks. The motor is going right as I type this.

[gumba]

Yes, wishful thinking that someone would do the one mod, then dyno it. I was curious as a best bang for the buck mod.
kenikh: So by not porting your getting better off the line performance because the a/f is moving faster into the heads?
gsxrken: Porting gets you less heat, and more a/f in the higher rpm range?

[911nut]

Originally Posted by gumba

His opinion was based on a turbo pushing air, vs a n/a motor pulling air. Big ports on a n/a motor pull more air/fuel in, where a turbo pushing would deliver fuel faster through a smaller opening.

Yeah, but until enough boost is developed, the turbo engine is running in n/a mode and not as efficiently as a n/a engine with a typically higher compression ratio. When there is enough boost then you have to worry about the choke point of the small intake ports.

[kenikh]

This is best as a long chat, had over many beers. Lots of nuance. For example, I've built a 2.0L 911S with intake port apertures measuring a nominal 39mm. Kicked ass over 2.7s throughout the power band. It was a cubic dollar motor...made 230HP @ 8000 RPM and mad torque down low, especially for a tiny motor.

There are many ways to increase intake velocity. Smaller ports are just the cheapest. As an example, CNC work for said motor above was north of $5K.

[RarlyL8]

We are machining injector blocks now so I will be porting my heads when the engine comes apart for a refresh, however it won't be just to port the intakes. I cannot imagine going to all that trouble and not opening up the exhaust. Velocity builds as the headers approach the turbo so porting the exhaust will allow more power out. Make the air pump bigger then match with a bigger turbo = huge gains. If all you want is a quick squirt of power then keep all the ports small and the turbo small.

[JFairman]

you can also think of it as.. lightening your cylinder heads





opened up to 40mm and port matched.
i donno, it seems to work

[gumba]

Back to my bang for the buck question. Is this a worthwhile mod to have done while having a valve job? Are the benefits worth the $1000,(less if you have the stock injector blocks bored out) porting, aluminum injector blocks , match porting the intake. Or, as Brian suggests, you shouldn't do one without doing the other.
I'm not after a quick squirt (too many beers), or big h.p. Since the motor is apart, and while your in there, this offers some kind of improvement?

[TurboKraft]

I'll look through dynos tomorrow, probably have something illustrative and quantitative. In the meantime, here's my $0.02 on the topic.

Bad port work = not worth the money, better to stick with stock tiny port heads.
Good port work = transformational.
So for the purpose of comparison, we'll say the port work is high quality.

Put SC heads on a Turbo, port match the intake, and it wakes up.

Put 3.2L heads on, port match intake & exhaust, and it's a better driver still.

I've never seen any loss in performance and/or drivability from porting open the heads. 36mm seems to be the go-to size thanks to Ruf doing it to his BTR engines, and Bruce Anderson recommending it in his book. But in my opinion, this size was determined because it's the practical limit of the factory plastic injector blocks. Port them further to 38mm, and they deform when you torque the intake manifold to spec. No bueno, so stop at 36mm, right?

We routinely open the heads to between 38mm - 41.5mm. Never looked back at a build with regret and thought, "Gee, I wish I'd run smaller ports on that engine..."

[RarlyL8]

Excellent point about the quality of the port work.
I have read here of a few folks who had their intake manifolds extrude honed while the engine was apart, that being the only modification. None bothered to dyno the engine but all reported a positive butt dyno. You might search extrude hone or intake manifold, the word porting would probably crash the server.

[DSPTurtle]

Are you sure the butt dyno increase wasn't from the reduction of dollars in their wallet insulating their butt from the seat?
Sorry, I couldn't help myself Brian!!!

[pkabush]

Originally Posted by DSPTurtle

Are you sure the butt dyno increase wasn't from the reduction of dollars in their wallet insulating their butt from the seat?
Sorry, I couldn't help myself Brian!!!

Thats silly. Clearly it was the the weight savings from lightning the wallet