The idea of bypassing coolant passages through the intake system is an old trick used by many old skool racers. It involves bypassing the coolant lines that normally course coolant through the throttle body to keep it from freezing up in the winter time. In the summer and in areas with year-round warm climates, this coolant adds unneeded heat to the intake charge into the engine. So bypassing these coolant lines could feasibly free up a few horsepower (everything counts in a N/A application). Under EXTREME weather conditions, there have been cases of sticking throttle plates as the result of this modification (you have been warned!). Look closely at the Type R intake manifold and you will notice the majority of water heating sources have been eliminated.

With the B16a setup, you have 2 options. (1) Leave your fast idle thermo valve on the intake manifold or (2) simply eliminate it. If you choose to eliminate it, you have to vacuum seal the holes it left behind. On the R intake manifold there are no provisions for the fast idle thermo valve. Option (1) is the easiest method as it doesn't involve removing the fast idle thermo valve and it requires 1 coolant hose routed from the spigot on the IACV to the spigot on the engine head. Vaccum seal the 2 coolant nipples on the throttle body. (Refer to Fig 1.2)

Option 1

Option (2) is slightly more complicated but totally eliminates coolant passing through the throttle body and intake manifold.

Note: You will notice strange idle behavior on cold starts. The idle will cycle oddly until the motor is fully warmed up. Here are the steps:

Parts needed:
- rags and a container for spilling coolant
- 1 meter long fuel hoses (just to be on the safe side)
- Hondata heat-shield gasket (optional) - completes the whole package! Test prove intake temperatures dropped dramatically with the gasket. Hondata boasts approximately 3% power increase. Replaces stock intake manifold gasket.
- patience

1. To access the required coolant spigots, it's best to remove the intake manifold.
2. Remove the throttle body, fast idle thermo valve, IACV and coolant hoses attached (get some rags and a container ready as coolant will pour out from these spigots).
2. Cut the required length of fuel hose and connect it from the thermostat housing to the spigot on head. (Refer to Fig 1.1)
3. Remove the clips and coolant hose attached from the spigot on the steel pipe to the IACV.
4. Cut the required length of fuel hose and connect it to the spigot on steel pipe. The other end attaches to the small nipple on the intake manifold. Make sure you cut the correct length hose. (Refer to Fig 1.1)
5. Use vacuum caps to seal off nipples on throttle body and IACV. (Refer to Fig 1.2)
6. Bolt the intake manifold back on and connect the hose from the spigot on steel pipe to the small nipple on the intake manifold. (Refer to Fig 1.3)
7. You are done! This is what it should look like. (Refer to Fig 1.4)
8. Remember to fill up on coolant/water before you start the engine.

If you choose to retain the IACV with Option (2), route the spigot on the steel pipe to one end of the IACV. The other goes to the spigot on the head. Now route the nipple on the IM to the thermostat housing.

This method of bypassing coolant to the throttle body/intake manifold can be adapted for all B-Series motors.

Fig 1.1

Fig 1.2

Fig 1.3

Fig 1.4