[Half-Inch Stud]

[QUOTE=Milepost;4613327]

Originally Posted by ponjohn

?..Runner taper is like voodoo magic, no one wants to discuss the formula if there is one.
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This might help!! Has some very good info.
http://www.swartzracingmanifolds.com/tech/index.htm

Shoot for a 9 degree cone, until learning from reading has occurred. Technical keywords "Nozzles and Diffusers" will get you there on "basics", which we are looking for the rules of thumb, rather than the advanced math. All about keeping mass flow ((momentum))while changing CSAs, direction, inlet/outet pressures.

[Tom Vaught]

[QUOTE=Half-Inch Stud;4652539]

Originally Posted by Milepost

Shoot for a 9 degree cone, until learning from reading has occurred. Technical keywords "Nozzles and Diffusers" will get you there on "basics", which we are looking for the rules of thumb, rather than the advanced math. All about keeping mass flow ((momentum))while changing CSAs, direction, inlet/outet pressures.

Would that be a full angle of 9 degrees, HIS, with a 1/2 angle of 4.5 degrees?
or a 1/2 angle of 9 degrees. Assume 9 degrees full angle.

Tom Vaught

[Milepost]

[QUOTE=Tom Vaught;4653157]

Originally Posted by Half-Inch Stud

Would that be a full angle of 9 degrees, HIS, with a 1/2 angle of 4.5 degrees?
or a 1/2 angle of 9 degrees. Assume 9 degrees full angle.

Tom Vaught

Calculating the amount of taper for the runner isn't really so hard. On our big stroke Pontiacs shoot for the opening at the plenum to have about 25-30% more CSA than the CSA at the intake port opening. If using a manual transmission and/or a shorter stroke combo add another 3%-8% of area. Also the standard deck Pontiac will need an intake manifold runner length of about 5"-6" for HIGH RPM builds (total avg intake track length of about 11"-11.5"). Use 6"-7 1/2" long intake runners (total avg intake runner length of about 12"-13") for most bracket race builds. Use longer runner length for lower RPM builds. Hope this helps.

[cgeise]

My Dynomation software shows that an opening 30% larger at the plenum - 10.5 in up from valve is 1.7degree taper ?? if I play with the software and get anywhere close to a 9 degree set up - power suffers ??? Is it just the way we here are calculating this -- or ???

[Milepost]

Originally Posted by cgeise

My Dynomation software shows that an opening 30% larger at the plenum - 10.5 in up from valve is 1.7degree taper ?? if I play with the software and get anywhere close to a 9 degree set up - power suffers ??? Is it just the way we here are calculating this -- or ???

I believe the amount of taper in degrees is calculated from the face of the intake port at the cyl head and up to the opening in the plenum. Been told the taper is usually close to about 4 degrees. BTW-Curt Do you happen to know the average port length on your Tiger heads?

[cgeise]

I have messued it - and the pot along with the intake is aprox 10.5 - If i remember right

[cgeise]

measured and port - got in a hurry

[Milepost]

Originally Posted by cgeise

measured and port - got in a hurry

I can understand that! ....Ya just got to take advantage of those sunny days in Seattle! LOL Thanks Curt

[Tom Vaught]

[QUOTE=Milepost;4653612]Been told the taper is usually close to about 4 degrees.

Agree, that is why I was asking HIS about his number. I like the CSA percentage change deal much better.

Tom Vaught

[john marcella]

Taper is not a cut and dry thing by any means. Every motor will tolerate taper levels differently, depending on many factors.
There are some motors that have an 80%+ increase in area in less than 3 inches in the runner.

Programs that suggest runner lengths, wile good are only so good. Most all of them are factored at a standard temp or atmosphere, and we dont race at those temps that they are using as standard. The speed of sound is relative to the local atmosphere and temp , and we are tuning sound waves.

I wish all this could be simplified or generalized like some of you are trying to make it, but it just cant

And even the best manifold guys cant nail it first shot, if you want it right you have to test , test , test.

[RA462]

Guess I would say I have learned alot by making one. Bottom of the runner intersects the head at 90°. Top of runner is at 5°. 6.8° on the side with between the ports at 0°. Well I have 25% tapper to my ports. Think it will make more power than a Victor? To bad it's just a "green" E85 bracket car. Zoom that unit!

[twinturrbo406]

Originally Posted by john marcella

Taper is not a cut and dry thing by any means. Every motor will tolerate taper levels differently, depending on many factors.
There are some motors that have an 80%+ increase in area in less than 3 inches in the runner.

Programs that suggest runner lengths, wile good are only so good. Most all of them are factored at a standard temp or atmosphere, and we dont race at those temps that they are using as standard. The speed of sound is relative to the local atmosphere and temp , and we are tuning sound waves.

I wish all this could be simplified or generalized like some of you are trying to make it, but it just cant

And even the best manifold guys cant nail it first shot, if you want it right you have to test , test , test.

... i agree, testing is an absolute must, i've been to a ProStock teams shop, and they literally had an entire room, stacked to the ceiling, with bunches of racks full of sheet manifolds, you could barely walk in there with out fear of one falling and knockin' you out !!! ...
... and the best part, they sell them off for scrap to local guys that dont have a clue what they are for, except weight ...
... there many factors to take into consideration, some of which are intake port centerline to manifold centerline convergence angle, and convergence of plenum entries, in reference to pulse sharing, distance between inlet radius at the plenum entry, distance between inlet radius and surrounding walls, you could spend a bunch of time on one, and find out what the engine doesnt want, lol ...
... another area often over looked is surface texture ... i just love manifolds ...

[twinturrbo406]

Originally Posted by Milepost

I believe the amount of taper in degrees is calculated from the face of the intake port at the cyl head and up to the opening in the plenum. Been told the taper is usually close to about 4 degrees. BTW-Curt Do you happen to know the average port length on your Tiger heads?

... 5.3 inches ...

[RA462]

Almost done. Went with 1095 sleeves I had to have someone make for me since I can't buy them anymore. I also copied what was done to my E85 carb. Anyone have a tune for the carbs they would like to help me with?

[Half-Inch Stud]

Sorry to leave you all hanging. 4.5 deg & 4.5 deg. It's just a starting point, not the be-all, end-all.

Ya know since the port height is 2x the width, there can be great debate on flaring the width faster to yield a round inlet vs keeping the "squareness" for focused plenum.

Runner taper helps feed the most mass-volume through the head (short-turn) and CYL expanse. Let's conside how to feed those RUNNERS;
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Me thinks the small open plenum is a frustration. Basic goal is to have a steady stream through the venturis, yet momentum preservation pre-venturi, and post venturi seems and typicall wholly ruined on most vehicles.

Does anybody have performance data (dyno or track) on "torque tubes" on the carb airhorn? Once that difference is seen, then the plenum design will have a similar design importance.

Seems it would be fun and profitable to debate small single-plane plenums vs long& large plenums(Wenzler, DNE, bathtub, OFFYL Dual Quad), when run with a single carb having the largest throttle plate CSA(CFM rating?).

[RA462]

It's alive! I need to rig up something better for the linkage. The pedal is rock hard and I think the cable is going to break even without return springs hooked up yet.

[ponjohn]

Originally Posted by RA462

It's alive! I need to rig up something better for the linkage. The pedal is rock hard and I think the cable is going to break even without return springs hooked up yet.

Interesting you have the carbs slightly skewed.

Like the Tarantula ( I think) bbc intake from back in the day.

[Tom Vaught]

Originally Posted by ponjohn

Interesting you have the carbs slightly skewed.

Like the Tarantula ( I think) bbc intake from back in the day.

The (passenger side) #2 Cylinder Intake Port/Head is about 1 inch forward of the (driver's side) #1 Cylinder Intake Port/Head on a Pontiac. You need a slight "skew" to get the throttle blades centered over the actual intake runners in some cases. You can win bets in a bar with a "Engine Expert" who has always been trained that the #1 cylinder will always be the "front most cylinder" in the block. Pontiac did not follow that "rule"

#2 is the most forward cylinder on a Pontiac. It also screws up machine shop guys trying to install rods on pistons.

Tom Vaught

[grandville455]

Man that looks AWESOME! Can't wait to hear how it runs!

[goatracer]

Originally Posted by RA462

It's alive! I need to rig up something better for the linkage. The pedal is rock hard and I think the cable is going to break even without return springs hooked up yet.

We ran into the same problem. We bent up a some 1/4" round stock and threaded the ends for heim joints. Worked perfect.