A question for all the long-runner intake experts:

How does combining a tuned length intake with a large intake port head not completely screw up the intake tuning effect?



Exhaust Tuning discussion for context on why I ask: with exhaust length tuning you can choose your primary exhaust length to tune for max hp or max torque, using PipeMax and you can achieve that tuned length by either stopping the exhaust at that length (open headers) or by installing exhaust terminator boxes at that tuned length. -If you go the terminator box route, when the air hits the large open space that is the terminator box the tuned exhaust pulses treat the opening into the terminator box as open air, the air speed slows down dramatically and then traverses through the rest of the car just via pressure.



When you install a TPI intake or a FIRST intake onto a head with large intake ports (my FIRST intake is going on my 195cc Profiler heads that are insanely close to a Felpro 1206 gasket), the transition from the intake to the head dramatically opens up at the beginning of the head- this should both slow down the air speed AND negatively impact the tuning effect.


Is it just me, or would keeping the inside CSA roughly the same, or with a slow taper all the way to the pinch point, be a far better way to go?


-I've been looking at pictures of having a FIRST intake CNC opened up to a 1206 gasket and I've been matching my FIRST gasket up to my Profiler heads and I'm just realizing how much more volume there is at the heads' intake port opening and at the transition to the intake than there is in the runners and the parallel to exhaust terminator box seems to be a scary similarity...


We've seen some folks on here produce some big HP #s by combining a FIRST intake with largish port heads, and now I have to wonder, is this partly because it's making the runners effectively shorter and moving the effective tuned length higher in the RPM band? (But giving up torque to do so?)
-I can't help but think keeping that inside diameter/ volume / CSA relatively constant is a better way to go....

Adam

 

I'm not an expert, but I did stay at a Holiday Inn last night. Seriously, there are far smarter people here with more experience, but I have been reading and learning for years, in an attempt to really get a feel for what works and what doesn't.

Remember the "T" is for tuned. It's not just the air speed of the longer runner. There's actual RPM points for the pressure waves, and where and when they hit. ...and to your point, I think the large heads do exactly what you suggest. They slow down that pulse, and while ultimately making power, they sacrifice torque.

We're so often given numbers in a vacuum. "500" horsepower. Relative to what!? What was the goal? What kind of engine? ..and as most of us are amateurs, we often don't have the money to do true apples to apples, back to back tests on multiple set ups. I've often wondered the same thing about the FIRST. Is it really a TUNED port injection, that makes great torque? -Or is it basically just so big that it doesn't restrict flow, and when matched with good heads and cam (as it almost always is) the numbers (relative to nothing specific) just always look good. Remember how TPIS used to say their Miniram made 80 more horsepower than the stock TPI? ...but then that was at like 5800 RPMs (or something). Well of course it made 80 more, the stocker was WAY outta it's RPM band. But peak to peak, the MR only made like 18 more. Of course add heads and cam the it extended it's lead, but i'm simply illustrating how numbers are deceiving.

I have a 383 with stock RHS Pro Action 180 heads (1205), a port matched and heavily ported (by Darin Dochterman) GM base, and heavily modded (cut open and welded) SLP runners and plenum. Cam is a custom Voodoo cam spec'ing a little bigger than a GM Hotcam. My goal for the cubes, cam and heads were to provide a rock solid, fun street car. My goal for the intake was to remain relatively stock appearing and NOT hold back the rest of the engine. Much. LOL. ....but I think I've done that for the most part. Still, I know a HSR/MR/FIRST would certainly peak higher. I'd be curious though, how those intakes, including a stock intake, would perform with the proper tuning and the PROPER CAM. Even a TBI style intake. Can't just retune though, need to swap cams too. THEN...you can really look at the graph, RPMs, peaks, curves and really see if there was any TUNED effect, or simply a hunk of metal that allows the REST of your motor to run as intended, while not necessarily adding anything.

I'd like to think on my motor the long runners help. I hope they ADD by means of a harmonic tuned effect. My money is that they don't, at least in any butt dyno type of noticeable way.

On your engine, with that FIRST....and those big heads...I gotta think the same thing. Even WITH that harmonic wave coming through, the heads have to be sized properly to take advantage or it's exactly what you're describing. ...and as I asked earlier, is the FIRST really "tuned"? ...or is it just a bunch of air moving through a pretty intake? -Which is FINE by the way. Not knocking the intake at all. I've just always wondered, and since you kinda brought it up....

 

Yes ideally, taper to valve throat. On some heads like most large sbc heads the pushrod pinch is the min csa point

Intake runner length tunes for rpm range. Runner and port size in area sets flow to feed the engine. It sets the port velocity.

Exhaust header primary and collector lengths tune for rpm as well. Size of primary and collectors support the velocity profile needed for scavenging and have influence on power production

If motor needs a certain size head to make power and rpm range, intake has to match in order to not restrict the head

 

Thanks Orr89RocZ!

If I remember correctly, the inside diameter of the runners/ports also slightly alters the RPM tune length, but to a much lesser degree than length.


Adam

 

To expand on what Orr said, yes, you want to keep the volume at the opening of the heads as close to that of the pinch point as possible. This way, velocity is relatively constant throughout the entire length of head’s intake tract. Variances large enough to slow down the air flow too much can cost power throughout the RPM band. However, when you’re looking at a curved area, air needs to slow down a bit in order for it to make the turn without dropping flow (which determines HP potential). So, there is a little bit of a trade off to an extent.

That said, when you see a noticeably larger area at the head opening that makes you think of a funnel, the manufacturer does that so it will flow more on the bench and to make you think you’re getting a “bigger is better” head – as in they advertise a 1206 entrance compared to a 1205 entrance. If you look at the best of heads like the AFR Eliminator heads or some of the higher end Speier Racing Heads, you’ll notice that the cross-sectional area at the opening of the heads is about the same as the pinch point. They could increase their flow numbers by putting a funnel effect at the opening, but by them NOT doing that, their heads will (should) make better average power on the engine than those with comparable flow with the “over-sized” inlet.

They also keep that area as small as possible on these off the shelf heads so that you can make adjustments to that area (if needed) depending on the intake you’re going to run. The fully custom porters won’t start work on the heads until they know the intake their customer is going to run and port them as a single piece.

As far as your combo, it is what it is if you’re going to continue with those heads and frankly I wouldn’t worry too much about it. Considering the intake length and volume of air passing through there’s not much it’s going to do to the actual tuned effect – maybe cost you a couple HP in the midrange. I’d gasket match the intake and look straight ahead.