The EC Carburetors Designed Tillotson JT-207 Cylinder Head for the 196 Box Stock Classes.
If you have been in the racing or performance engine game for any time, you know the cylinder head is considered where all the engine power potential resides.
The Tillotson JT-207, or TIL-1 as it's internally known, was designed to address many issues in the box stock classes. First, to be the first consistent factory spec cylinder head to prevent the head of the month competition. Next, to directly compete and exceed the performance of the stealth ported factory heads like the JT-151. EC Carburetors, with our decades of experience, were tasked with these goals. We create the first and only fully CAD-designed cylinder head specifically for the 196 box stock classes. We were able to maximize areas and improve the architecture within the rule restraints to make a superior cast clone head. Not only did we improve the flow and performance, but we also made the casting much thicker to prevent warping and distortion. The Tillotson JT-207 is the best cylinder head on the market for 196 racing.
Our success in making the Tillotson cylinder head and engines perform so well caught the attention of NKA for them to request a sealed version of the 196R, which includes the JT-207 Cylinder Head. This makes it legal for both the 196R and 196RS Classes. This head is also legal with ARKA.
Flow testing by Young Engines. TIllotson vs JT-158
.050" - 15.9
.100" - 30
.150" - 43.5
.200" - 46
.250" - 47
.300" - 48.5
.350" - 50.5
.050" - 15.9
.100" - 30
.150" - 42.6
.200" - 44.1
.250" - 46
.300" - 48
.350" - 48.5
AKRA 2020 Rules for Cylinder Heads
It must be OEM casting only. All cylinder heads used must be the "JT" or "TG-1" 4-bolt valve cover 6.5hp GX200 Clone series heads with 22cc style combustion chamber design. Valve seats may have up to three angles, 45 degrees valve face and 30 degrees top relief, and 60 degrees bottom relief. Cutting of valve seats allowed to ensure a proper seal. Intake seat maximum ID.899", Exhaust seat maximum ID.862". The outside face of the valve may not be below the floor of the combustion chamber(i.e., don't sink the valves). No Go's for the intake opening vertical(flat to oval sides) .962" - No Go: Horizontal(flat to flat sides) .950" and the exhaust exit vertical(flat to oval sides) .974 - No Go: Horizontal(Flat to Flat Sides) .967". Both ports must also retain their original D shape design. No visual tech on surface finish, no adding material, cannot touch the seat or valve guide in the porting process, and no rifling or dimpling of the port area. Valve guide length 1.055" minimum (new gauge will check the proper length as well as guide location or depth .890" into the port area) also checks spring pocket flatness, stock guides only. Head gasket/s maybe aftermarket, must be of stock configuration, gasket thickness is a non-tech item, sealer allowed to ensure a proper seal. Depth check between the valves, front to back, and side to side may not vary by more than .005" max. No copper or aluminum gaskets are allowed. Any stock configuration exhaust gasket allowed, sealer permitted, the header may also be run without gasket, sealer only. Allen head bolts permitted on the header to head. Aftermarket flanged bolts of similar OEM design(head size, diameter, length, and thread length/pitch) allowed as a replacement for stock head bolts. No studs allowed, No additional washers allowed. Breather hole on valve cover may be tapped with 1/4" pipe tap to accommodate breather fittings; no oversize drilling allowed. A tube attached at the valve cover breather hole and run to a catch can is mandatory. Must be functional.
NKA 2020 Rules for Cylinder Heads
40.4.19: Cylinder Head
220.127.116.11: Approved Heads
Only "JT" 4-bolt heads and "TG-1" heads will be allowed. Any other heads need to be approved with NKA before the competition.
18.104.22.168: Sanding and Machining: No sanding or machining of carburetor or exhaust mounting surface.
22.214.171.124: Valve Seats
126.96.36.199.1: Valve seats can have up to three angles as cut by the manufacturer:
Ð”Ñ’Ð›â€ºÐ”Ñ’Ð²€Ñ™Ð•Ñ“Ð•Ñ• 60-degrees bottom relief
Ð”Ñ’Ð›â€ºÐ”Ñ’Ð²€Ñ™Ð•Ñ“Ð•Ñ• 45-degrees top relief
Ð”Ñ’Ð›â€ºÐ”Ñ’Ð²€Ñ™Ð•Ñ“Ð•Ñ• 30-degrees top angle relief
188.8.131.52.2: Porting, grinding, or matching to the ports or combustion chamber is prohibited.
184.108.40.206.3: No angle milling of the head. The measurement is taken from gasket surface: depth check to combustion chamber floor cannot vary more than .005" in any direction.
220.127.116.11: Minimum Combustion Chamber Volume when mounted on engine @ TDC is 26.5cc's. This is to be done after the event and when the engine has cooled down to a reasonable temperature. The Head gasket is required, but the thickness is non-tech and can be either steel or aluminum. Multiple head gaskets are allowed.
18.104.22.168: Head Dimensions
22.214.171.124.1: Maximum Head Thickness: 2.640" as measured from the valve breather mounting surface to in-between the valve seats and the combustion chamber.
126.96.36.199.2: Head thickness from the valve breather mating surface to in-between the valve guides is 1.150" Max.
188.8.131.52.3: Intake Port: DELETED
184.108.40.206.4: Exhaust Port: DELETED
220.127.116.11.5: Port Depth: Measured from the top of the valve seat to the port floor; Intake: .880" Max Exhaust: .830" Max. Valve bowl height gauge is the preferred measurement tool.
18.104.22.168: Intake/Exhaust Seat
22.214.171.124.1: Intake Seat: .899" Max
126.96.36.199.2: Exhaust Seat: .862" Max