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 APBA Engine Rules for 1.5 Liter Stock Class Hydroplanes

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Car : AE86
Posts : 1116
Join date : 2009-04-12
Location : Nor Cal

PostSubject: APBA Engine Rules for 1.5 Liter Stock Class Hydroplanes   Fri Jul 15, 2011 3:18 pm

These rules have some interesting info in them.

42.1 The purpose of these rules is to promote an entry level class of Inboard hydroplane racing for drivers 14 years of age or older, who will be attracted
by relatively low initial cost and economy of operation. It shall be the responsibility of the 1.5 Litre Stock Technical Committee to make technical rule
recommendations pertaining to the class to the Inboard Racing Commission.
42.1.1 Competing boats will be powered by a SOHC, 4AC (1587cc) Toyota with a maximum bore including overbore of 3.235 inches and stroke of
3.03 inches.
42.2 Toyota SOHC-4A (1587cc)
42.2.1 Any external brackets used to support or drive accessories may be added or removed. Pulleys or belt drives may be removed. Pollution control
devices may be removed and applicable holes in the motor may be plugged. Any modification to the block or head for the sole purpose of water
inlet or outlet (cooling of motor) is permitted.
42.2.2 Carburetors: Autolite, Holley, Motorcraft model 5200, Weber 32/36 DFAV or DFEV. Throttle bore sizes: Primary = 1.260”, secondary =
1.417”. Venturi size = Primary – 1.030”, Secondary – 1.070”. Any jets may be used. A carburetor wedge (maximum thickness - 1 inch) may be
used to level the carburetor. Choke plates may be removed and plugged. Air scoops and velocity stacks are permissible. The intake manifold
must be stock as supplied by OEM. If a crack develops on the intake manifold it may be welded on the outside provided that the intake runner
surfaces remain untouched in an “as welded” condition. Electric fuel pumps are permitted.
42.2.3 Fuel. (See General Technical 40.18.12)
42.2.4 Head: Combustion chamber volume shall be not less than 30cc.
42.2.5 The block may be decked. Top of piston may rise above the block surface a maximum of .005”.
42.2.6 Camshaft - Any after market cam can be used providing it meets OEM profile under these class rules. No modification to the rockers or
rocker related equipment will be permitted. The camshaft may be advanced or retarded by use of an adjustable cam gear.
42.2.7 Valve head sizes intake 1.417”, exhaust 1.221”. A valve job must be Stock (3 angle) configuration. The last (innermost) angle does not
extend more than .250” below the valve seat angle. Any valve guide may be used for replacement. Valve seats may be replaced, only with OEM
size seats. Any valve spring that fits the OEM retainer and does not require machining to the head may be used. No modifications to the intake
or exhaust ports (grinding and/or polishing) will be permitted. Milling of the “block face” of the head is allowed.
42.2.8 Distributor and ignition systems must be stock OEM. Any spark plug wires may be used.
42.2.9 The oil pan may be modified to fit the boat and/or to increase oil capacity. The oil pick up to the oil pump may be modified to match the
configuration of the pan. Baffles in oil pan are permitted. The valve cover may be modified to help motor venting.
42.2.10 Any aluminum flywheel or Toyota Flex Plate is permitted. Ring gear must remain stock.
42.2.11 Any cast stock replacement piston available on the open market for 4AC, 2 barrel, single overhead cam, 1587cc Toyota engine may be used.
42.2.12 The balancing of reciprocating and rotating parts is permitted.
42.2.13 The cylinder head, crankshaft, piston rods, block, oil pump, cam followers shall be OEM.
42.2.14 Grinding and/or polishing of carburetors, intake manifold passages, intake and exhaust ports, combustion chambers, connecting rods, valve
parts or configuration changes in any way is STRICTLY PROHIBITED.
42.2.15 Rings must be stock replacement.
42.2.16 Head Gasket: .043 Minimum compressed reading
42.2.17 Piston and piston rings may be stock or replacement available on the open market, must meet OEM specification. Milling of pistons is
not permitted. The distance between the top of the piston and the top of the first ring must be no less than 0.235”.
42.3 Minimum inspection procedure for 1.5 Litre Stock Toyota.
• Engine specifications and inspection procedure shall be the responsibility of the 1.5 Litre Technical Committee and the Inboard Chairman.
• Check combustion chamber: Pistons must not extend above the block surface more than .005. Cylinder head chamber volume 30cc minimum.
• Check valve train: Camshaft may not be reground. Check valve sizes and face angle. Camshaft may be advanced or retarded by use of an adjustable
cam gear.
42.3.1 Procedure to check stock cam profile and rocker arms in Toyota 4AC.
42.3.2 Install an 8 inch degree wheel on distributor. Install a pointer on block. It is recommended that the degree wheel have one degree markings.
42.3.3 Rotate engine in normal direction until the lifter is on the heel of the camshaft lobe. Set dial indicator on valve spring retainer. Adjust valve
lash until dial indicator reads .001. Set dial indicator back to zero. Rotate engine in normal direction until dial indicator reads .050 stop. Set degree
wheel to zero degrees or TDC mark on degree wheel. Rotate engine in normal direction and check every .050 thousandths lift. Read degrees on
degree wheel. There is a 4 degree + or - factor for rocker arm wear.
42.3.4 Camshaft Profile (per Al Grabinski Jr. 10/04/00)
Intake Exhaust
0.001 Preload

42.3.4 Camshaft Profile (per Al Grabinski Jr. 10/04/00)
Intake Exhaust
0.001 Preload Degree 0.001 Preload Degree
.050 Lift 0.0% .050 Lift 0.00%
.100 7.5 .100 6
.150 12.5 .150 12
.200 18 .200 17.5
.250 23.5 .250 23
.300 30.5 .300 30
.350 43 .350 42
.364 51 Max .364 51.5 Max
.350 56 .350 60
.300 69 .300 71
.250 76 .250 78.5
.200 82 .200 84
.150 87 .150 89
.100 92.5 .100 95
.050 99 .050 101
Lobe Separation: Go max lift on intake; Set wheel to 0; Go max lift on exhaust – should read 107.
42.3.5 Check lobe spacing: Set dial indicator on intake valve spring retainer. Rotate the cam until the heel is clear of the rocker arm. Adjust to zero
lash and stop at .005 inches valve lift. Set the degree wheel to zero degrees. Rotate the cam in normal direction of rotation to 0.050 inches valve lift.
Record the degree wheel reading. Repeat the above procedure on the exhaust valve except that the degree wheel is not reset to zero. The two angle
recordings are subtracted to obtain lobe spacing; 107 degrees.
Check carburetor: Throttle bore size: primary = 1.260”; secondary = 1.417”. Venturi size = primary - 1.030”; secondary - 1.070”, carburetor wedge
may be no more than 1” in thickness.
Check all parts for any grinding, polishing and any other alterations from the furnished stock configuration.
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