Which is more important: taper & tuned length or gasket matching?

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Which is more important: taper & tuned length or gasket matching?

Post by NewbVetteGuy » Tue Sep 26, 2017 1:27 pm

Folks, I need help with a decision on my build.

Background: SBC 350 with a long-runner "FIRST Fuel Injection" intake, 195cc Profiler Heads, Mike Jones roller cam, multi port fuel injection handled by Holley EFI.

Goals: Loads of torque, at least 400 FWHP @ 5,500 RPM or higher, and as much fuel economy as possible.


Here's my issue/the decision I need to make: My beauty of a long-runner TPI-style (but WAY bigger in every way) intake's ports, at the connection to the head, are smaller than my head's intake ports (very close to a Felpro 1206 at 2.150" high x 1.300" wide). Ken who owns First Fuel Injection, can do a very basic CNC gasket match of my intake and would do so included in the price of the intake, but I'm not sure whether it's the "right" thing to do. In a torque-focused build, with a long-runner intake where wave tuning and air velocity are critically important, should I leave the intake as-cast or have it opened up to match my heads' intake ports?

From what I've read so far and THINK I know: the intake wave tuning, including the strength of the wave, and definitely the velocity of the air going into the cylinder would like to see a nice smooth transition but also would benefit from a slow taper. I'm mildly afraid that opening up the last section of the intake runner will result in the air slowing down and could reduce in a less intense wave tuning effect. (To me the idea of having the air traveling through the intake and slowly tapering down and increasing in speed only to reach a larger, more open void is similar to the idea of an exhaust wave termination box and could really screw stuff up. I'm not looking for max air speed through the first 3/4s of the intake tract only to have it slow down immediately prior to the valve, I want it to be at max velocity INTO THE CYLINDER.


What should I do? (Is it better to just have the smaller diameter intake ports dump directly into the larger head intake port (my thought is to keep air velocity up or is it better to have the intake "gasket matched" to the heads' intake port dimensions?)

I keep hearing that power goes up exponentially as air speed goes up (until the port goes turbulent) and CFM increases are only linear so I'm very nervous to make any trade off that gives up airspeed, ESPECIALLY given my torque-focused goals.






Adam

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Re: Which is more important: taper & tuned length or gasket matching?

Post by NewbVetteGuy » Tue Sep 26, 2017 3:13 pm

Please see the image here for what the intake's port exit looks like with a simple CNC gasket match to a Felpro 1206 -is this beneficial?

What if I smoothed the large "step" more- would there be benefit there?


Reminder: I'm a newb at this whole engine building thing. My last major purchase decision is for my build is hung up with this intake (and I have to decide whether to leave it untouched or get it CNC "gasket matched" or not prior to purchasing).

https://www.facebook.com/photo.php?fbid ... 9b64cbace2

https://www.facebook.com/photo.php?fbid ... 9b64cbace2
Image


Adam

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Re: Which is more important: taper & tuned length or gasket matching?

Post by MadBill » Fri Sep 29, 2017 8:55 pm

I'd suggest you calculate the runner and port areas at the gasket surface and also 0.5" and 1.0" up into the runner and down through the port. Converting the areas to circles, you can draw an idealized straight round runner/port for visualization purposes and determine how best to make it a smooth taper or constant area. For example, if the port was clearly 'bell-mouthed' larger than what would give such a taper, you might chose to just ignore the step, but if opening up the last inch of the runner brought the assembly closer to ideal, then you could go that route.

The one common approach that doesn't work is blindly matching both to an arbitrary gasket size. Doing so usually results in a port with a fat 'aneurysm' right at the joint, which disrupts the flow more than any minor mismatch.

As I read the picture, the gasket match work shown has negative value; better to hand-match as above.
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Re: Which is more important: taper & tuned length or gasket matching?

Post by joe 90 » Fri Sep 29, 2017 9:33 pm

The step is there to reduce reversion which reduces low down torque.

When you match the ports you'll get a loss of low down torque and maybe an increase in torque higher up the rev range.


Why not leave it as it is, then dyno it.
Then do whatever to the ports and dyno it again.


Then you'll know when you got it wrong.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by digger » Fri Sep 29, 2017 11:24 pm

if the intake manifold is the correct size (in terms of CSA) for the application then you dont need to match the head. the step may indeed add some anti-reversion but IMO a small step does nothing either way as the step/missmatch size as a proportion of diameter is a low % the flow wont really see much in the way of losses compared to what is happening down near the valve and throat. Sometimes have the manifold smaller of offset puts the air entering the head on a better trajectory for going past the valve if it changes the bias

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Re: Which is more important: taper & tuned length or gasket matching?

Post by CharlieB53 » Sun Oct 01, 2017 9:56 am

Do you have flow numbers for the manifold?

Do you have flow numbers for your heads?

How different are they?

You may consider looking for heads that more closely match the manifold.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by Newold1 » Sun Oct 01, 2017 9:50 pm

Your TPI intake has a round port inlet in the plenum transitioning to a rectangular port at the head so it is really not practical to calculate taper over the runners length and the only real sizing would be from a calculation for area at the inlet versus at the head. that CNC cut seems to be a pretty short cut and as such the column of air will not really change much over that short distance and the runner exit is going to pretty much function at its size and shape at the beginning of that machine cut. I think you would be better off to hand port the runners with a 6" burr tool and put an longer transition from farther up the runner that smoothly opens to come closer to your actual cylinder head port size. Don't match to the gasket as they are usually a bit larger than the port size if they are correctly sized to the head port. I would also avoid creating that abrupt transition area over and around the injector inlet opening. Keep the bump area just before and up to the injector opening as it works to stop a disruption to the injector cone spray pattern. For your goals of smooth power and torque with optimized economy I would keep things gentle and even and keep air/fuel mixtures well blended and unseparated or scattered.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by jsgarage » Tue Oct 03, 2017 4:29 pm

Depends on what you're using the engine for. As Digger said, in some (most?) engines, small intake ports dumping into big head ports tends to increase drive-ability and mileage, and fall flat on its face at higher rpms. Such setups used to be created with 'anti-reversion plates' or intake port-plates. Good for calming down an aggressive race setup used on the street. If you don't currently spend much time above maybe 5500 rpms, it should work just fine with zero port matching. If you do commonly rev higher, port-match maybe 1" in for less fall-off. If all you do is race, swap the intake for a larger unit & save yourself some work.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by NewbVetteGuy » Thu Oct 05, 2017 11:05 am

Thanks guys!

This helps a lot! It sounds like, given my mpg and torque goals, I'm far better off just leaving the intake as-is and then if I decide I'm going to be super brave and try to hand port it- gently open up the end of the intake ports to match the head ports.


Appreciate everyone helping me not make a mistake like this.



Adam

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Re: Which is more important: taper & tuned length or gasket matching?

Post by David Redszus » Thu Oct 05, 2017 11:17 am

A change in tube area, either due to expansion or contraction, will always result in a flow reduction.
The amount of flow reduction will depend on the area ratios. For most every application, the area ratio (and flow loss) is small enough to be ignored.

Inlet taper and tuned length should never be ignored; they are far more important with respect to power optimization.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by cjperformance » Fri Oct 06, 2017 5:35 pm

NewbVetteGuy wrote:
Thu Oct 05, 2017 11:05 am
Thanks guys!

This helps a lot! It sounds like, given my mpg and torque goals, I'm far better off just leaving the intake as-is and then if I decide I'm going to be super brave and try to hand port it- gently open up the end of the intake ports to match the head ports.


Appreciate everyone helping me not make a mistake like this.



Adam


Yep good advice has been given. For your useage leave it alone if csa is ok for your goals. If csa is ok the step will not hurt one bit (actually help low down) on a mild hp big tq streeter and the realistic in use rpm range it will see. And keep in mind that if you port match it you need to map csa of the runner 'before' you start grinding so that you know you wont be ending up with a runner that starts small and ends big, it may 'look' great at the runner/gasket/port face but may dissapoint the right foot!
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Re: Which is more important: taper & tuned length or gasket matching?

Post by tresi » Sat Oct 07, 2017 11:33 am

To port match like that only moves the location of the mismatch. Either the mismatch is at the head or an inch up the manifold.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by David Vizard » Sat Oct 07, 2017 8:35 pm

Which is more important: taper & tuned length or gasket matching?


Let me answer this question with another just to get you thinking here.

Do you suppose for one moment that the guy that designed the gasket qualified it on a flow bench?

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Re: Which is more important: taper & tuned length or gasket matching?

Post by groberts101 » Sat Oct 07, 2017 11:40 pm

Not only that ^^^.. but do you suppose all the gasket openings are identically sized?

Cookie cutter gaskets are hardly precision sized parts and I've seen plenty of porters mistakenly grind port openings to gaskets only to find the next set of fresh same part # gaskets don't quite line up like the previous set did.

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Re: Which is more important: taper & tuned length or gasket matching?

Post by NewbVetteGuy » Mon Oct 09, 2017 12:16 am

Ok guys this gets a bit more complicated fairly quickly. I'm honestly getting pretty depressed at this point; just no idea what to do.


My intake is cast as a 1204 port, but it's always been designed to be CNCed to open up to a 1205 when required; the previous picture I posted as a 1206 cnc profile.

Here's a picture of the intake's gasket matched up to my Jegs Profiler 195cc heads' intake ports centered on the bolt holes: Image -The dimensions of the gasket are actually a decent match for the heads' intake ports, IF I could actually center the ports on each other, but with the gasket centered on the bolt holes the bottom of the gasket blocks the bottom of the intake ports a bit and obviously there's this dead-end wall of metal on the heads' intake ports on the top.

Here's a picture of the intake's gasket pushed down as low as it can go on the bolt holes: https://www.facebook.com/photo.php?fbid ... 0f6d7ec0e6 Better, but still hitting on the top. (I can take a picture of the gasket centered on the intake holes, too and it's honestly almost a perfect fit.

Again, the gasket is way over-sized vs the as-cast intake port size.


Here's the supposed measurements for gasket and the heads' intake ports:
Gasket dimensions: 2.150" x 1.250";
Head intake port dimensions according to Jegs: 2.150" high x 1.300" wide
Felpro 1206 gasket (I think): 2.12" high x 1.31" wide
Gasket that Jegs recommends for this head (555-120000): 2.12" high x 1.34" wide


I don't understand why the gasket, with nearly identical dimensions to my heads' intake ports match up so poorly; it's like the gasket just sits too low....

If I have the intake opened up from it's as-cast Felpro 1204 dimensions and beyond its' "very typical" dimensions of the 1205 gaskets to a 1206 gasket (you've seen the picture earlier in the thread) and then need to have the heads' further opened up to avoid the wall of air smacking into the top of the intake port, I just get scared that the increase in volume and csa there is going to slow the air way down. I'd really rather not have the heads have to get ported at all.

What should I do? The intake MFGR has a CNC and will pretty much do any dimensions I tell them but obviously only BEFORE they ship it to me... The 1.300" port width is PERFECT and the gasket and the heads are both very happy there; I'm going to throw out the idea of just having the intake opened to a height of the Felpro 1205 height of 2.09" -and error on the side of the intake being smaller. Anyone have any good ideas?


-What would it cost to just buy the intake as-cast and have it and my heads taken somewhere local (Seattle area) and properly matched? -Any ideas?




Adam

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