S&S Manifold Length Calculator

Sine, Cosine, Hike!

We know you were day dreaming about sex when the triangles were floating about the blackboard, or for those of you who were already warped, you were doodling motorcycles while the teacher droned on about sines, cosines, tangents. Now all these years later when you finally got the money to build your dream bike by ripping off some other poor fool in the stock market, all you can do is thumb through catalogs hoping to find the right manifold for your V-Twin.

Points in Two Dimensional Space

Well, you can use trig for all sorts of useful pursuits...In this case trying to figure out what TC88 or EVO S&S manifold to order for your bored, stroked and milled big twin. For our RSR Closed Loop Fuel Injection system (discontinued in 2018) we used modify S&S inlet manifolds for either two or four injector systems and heliarced on a new billet o-ring flange for our 56mm (2 3/16") throttle body.

Above picture is an efi  Sportster manifold we did 25 years ago.

We would order S&S Super D large throat manifolds using this calculator and then set them up for turbo or normally aspirated engines. All 113/120/135 ORCA Motors started out with SA inlet castings that we machine and reconfigure. S&S subsequently sort of left the Special Application business.

Special Application Heads

Big valve S&S Special Application heads like we used in our 113/126/132/139 ORCA Motors have raised ports which effectively raises the inlet casting. If you are using regular S&S Super Stock cylinder heads the port is not raised. We use special order S&S 16-3619 manifolds that we custom ordered for bore size and specify the length with this calculator.

S&S SA/B1 and S&S SA/B2 / B3(T143) heads are different and require different manifolds. Besides changes in valve size they have different bolt patterns and the ports are different. You can order B2 heads for EVO style single cam engines. We used B2 heads on the 139 ORCA and our 126 SA B2 Road Road.. Above is a manifold design for our Turbo Orca FXR.

Roll the Dice

Like the man always says...check it twice and check it once again. S&S has had a lot of trouble with people ordering the wrong manifold so they've changed their policies and the part numbers now reflect a specific inch dimension. S&S sells fixtures that you use dial calipers to determine the manifold number to order. You assemble the engine, you buy the fixture, you measure and you order. It's yours to keep.

A stock TC88 manifold is a 410 which equates to 4.100" between some point in space between your inlet ports. All this is supposed to end up with you having a manifold with .015" clearance on each head or a total of .030" to allow for expansion.

S&S makes literally hundreds of combinations as they have different heads, carburetors etc to deal with. 50 years of history to keep track of.

We use this calculator ourselves but use it at your own risk. They make nice paperweights. The S&S SA/B1 manifold pictured below was for a 113" Fuel Injected Turbo. S&S List price before we started our machining is $259.85 OUCH! We're on the wrong side of the counter!

Points of Confusion

When you order a manifold S&S will ask you to call out a center to center dimension of the cylinder heads inlet ports which is their designated size. At one time you could call out the short distance between the edges of the inlet port. There is a chance they will machine the manifold and use this number...not the center of the inlet ports.

The actual final machined manifold will install .015" off of each inlet port surface so the actual center to cener of the manifold will be .021" larger than tghe inlet port center line

Here we are measuring the short side of a Super D manifold we modified for our RSR EFI System. This particular motor had B1 inlet ports modified to 1.875".


    You need Two entries:

    1. Cylinder Head (not manifold): Short side port width (inches)

    2. Cylinder Head: Inlet Port Diameter (inches)

    Picture above: The final machined inlet manifold will have a center to center distance (lower red arrow) .021" wider that the actual inlet port centerline. These ports are at 90 degrees to each other with an upward angle of 40 degrees blending into the manifold entry.

Inlet Manifold Length/Number Calculator: S&S Big Twin TC/EVO

Cylinder Head Short Side Port Width
inches See upper redline in photo above. You need the short side width on your motor's cylinder head inlet ports.
Inlet Port Diameter

S&S Manifold Number An expression i.e. 410 equals 4.100 inches (TC88 Stock). Center to center inlet ports.

Note: This result has added .021" to the actual inlet centerline to give you the desired .015" clearance to allow for expansion of the engine.

S&S EVO and Twin Cam Manifold Numbers

Engine Application
Old Manifold Size Number
New Manifold Size Number
Stock Height V2 XL 883, 1100, 1200, 79"
91" Sportster

79" Retro Big Twin
100" Sportster
100" Retro Big Twin
89" Sportster
100" V2 Big Twin
88" & 100" V2 Big Twin
111" Super Sidewinder Plus

100" Twin Cam

93" & 113" V2 Big Twin
117" Super Sidewinder Plus

Stock Height V2 Big Twin & Twin Cam
107" Twin Cam

98" Big Twin
124" SSW+ & Twin Cam

103" BT & Sportster V2
116" Twin Cam

139" ORCA V2 (2C heads on V2 SA case)