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Author: Todd Marcucci
How hot does the manifold get? My own temperature testing showed that the intake air temp went as high as 125 degrees in mixed driving after 20 minutes (with a 70 degree ambient) once the engine was warmed up. I also found that the head is essentially the water temp, at least, while I was checking exterior head temps the fans kicked on when the head hit about 190 degrees. The fan switch is set to engage at about that point, maybe a few degrees higher. That means the outside surface of the head is probably no more than 5 degrees cooler than the coolant. I also checked the temperature of the manifold (near where I checked on the head) and found it to be no more than 5 degrees cooler than the head. That means that once your car is warmed up, your head and manifold are both very hot!
If the heating the manifold reduces power, why would Honda heat the manifold in the first place? Heating the intake manifold is beneficial in extremely cold climates where ambient temperatures are below freezing frequently. As temperatures go below freezing, any moisture present in the throttle body or IACV valve may freeze and cause them to stick or freeze up. This could have potentially annoying or dangerous consequences. Heating the throttle body and IACV (and manifold) can help prevent this. This is rare, though, and downright unnecessary in warmer climates. Unless you park your car under snow drifts overnight, you should not need coolant passed through these two items. If you do live in cold climates, you should open up the hole that provides coolant to the IACV and throttle body to be safe (see below). You will still recieve the benefits of having the insulator in place of the stock gasket which provides no insulation at all.
Where can you get the manifold insulator? The good people at Hondata manufacture these, which is who I obtained the one in this article from. See Hondata's web site for more information as well as pricing and availability. You can also download a PDF file here. I was very impressed with their knowledge, pricing, and professionalism.
What You Need
Removing the Manifold
Using the "show car" position for the hood prop will greatly simplify things:
By twisting/turning the prop you can liberate it from the stock mounting point, then insert it into the slot by the under-hood fuse box. Then just use the prop point on that side of the hood like the other, and you've got twice the space to work!
Since we will have to remove the fuel rail, you want to relive the pressure in the fuel system. In the in-cabin fuse box, by the driver's left knee, remove the 15A fuel pump fuse...
...and then start the car. You'll notice it doesn't "catch" and start running- you've interrupted the fuel supply. Just a second or two, the time it would normally take to start the car, is enough to bleed off all the fuel pressure. This insures you won't leak gas all over the place when you remove the supply line to the fuel rail (and that the rail will be empty).
We'll start with removing the intake tube and airbox lid. In the case of an aftermarket intake you will need to remove the pipe at the throttle body, perhaps more:
There are a few vacuum lines that are attached to the intake tube and airbox lid that you will need to remove. The large hose near the throttle body is for the air (smog) pump. The smaller one is for the PCV to the valve cover. Use pliers to remove the two clamps and tubes. There are a few lines "snapped" to the back of the airbox lid you can see here:
These do not need to be removed here, but at the fuel rail. To get to them, remove the PCV valve from the valve cover (it just pops out) and the beauty trim from the top of the fuel rail with a 10mm socket:
Underneath it, you can see the two lines that you need to disconnect so you can remove the intake hose:
In this instance, we marked the upper and lower hoses so they would go back in the proper place. Once you remove these, you should have everything free:
Next, remove the following vacuum and coolant lines with a pair of pliers:
The lines might be a little stubborn, give them a gentle tug and try prying them carefully with a flathead screwdriver. Be careful not to tear them. Now, disconnect the intake air temperature sensor (IAT) connector, and Idle Air Control Valve (IACV) connector:
The connectors should just take a gentle pinch and pull to release them. The IACV connector is covered with a boot, just press on the flat portion that faces down and it should release. Now we need to remove the fuel rail, so we will be able to get at the bolts that hold the manifold on. There are similar connectors on the injectors- remove them like you did the others, then use a 10mm wrench to remove the cable stay on the back of the manifold (near the IACV):
Pay close attention to the coolant supply line going to the IACV in the third picture above. It is close to a same-sized vacuum connector to the left of it, and if mixed up, you will suck coolant into the intake (very bad!). Marking these hoses and their locations is a good idea.
Now, using the 22mm wrench, remove the fuel rail "damper." It's the hat shaped piece shown below. Be careful not to lose the two crush washers on either side of the banjo fitting. You will not reuse these (they will have to be replaced) but you don't need them loose in the engine bay, either.
Now we can remove the last of the myriad of hoses- the airbox vacuum lines, the air pump hose, the brake booster hose, and the IACV coolant lines:
We sure hope you don't mind the smell of antifreeze, since you probably just got some of it on you. Instead of draining the coolant and wasting all of it, we recommned losing a little and just topping off afterwards.
Finally, the fuel rail. Disconnect the vacuum lines shown, then remove the bolts/nuts shown:
And then one last coolant line:
And you can simply pull the fuel rail away from the head/manifold:
Now we can start on the manifold itself. Using a 12mm socket, extenstions, and a U-joint, start removing the top nuts/bolts:
Note that you have to remove a cable clip to get to the last nut on the top. I also found that I could only get to it with a wrench, not with a socket.
Now you can get to the lower bolts. It's hard to see, but in order from front to back, this is how I got to them:
The process for the #4 port bolt is similar to the #3 one (sorry, no picture). To get the manifold free, You must remove the support brackets:
This uses two 14mm bolts up top and one below on the block. There is also a front bracket (sorry I don't have pictures) that "lifts" the manifold up from the block. Unfortunately the block bolts are inaccessible due to the alternator mount- you can, however, remove the manifold bolts with the 14mm wrench. These screw up into the bottom of the manifold. You will have to do it by feel, but these two can be removed without too much trouble.
Once you do this the manifold will be mostly free. If you are just replace the factory gasket with the insulator, you can pull the manifold away from the head enough to remove the old one and insert the Hondata. If you want to actually remove the manifold, you still need to disconnect the water outlet housing and hoses, though. The simplest way to do this is to just remove the housing and leave the hoses connected to it. Using a 10mm wrench, loosen these bolts. There are two- one on top (in the picture) and one directly below it, underneath the hoses. This one you will unfortunately have to do by feel:
Now we have a few miscellaneous clips that you can remove or disconnect the hoses from, and the coolant temperature sensor. The sensor is like the others, press in on the flat section (towards you) and pull gently.
Last, we have the throttle cable. The throttle cable is on the driver's side and is secured by a 12mm locknut:
You should now be able to pull the manifold up and out. Be careful, there might be a few lines that hang up on the manifold- check to make sure everything is clear. When you get it out, set it aside.
The Hondata Spacer/Insulator
The Hondata spacer is an exact copy of the of the factory gasket, excepting that the
Hondata spacer is thicker, blocks a coolant hole, and is made of a vinyl-"ish" material
(as opposed to the thin steel factory one):
The Hondata spacer is an exact copy of the of the factory gasket, excepting that the Hondata spacer is thicker, blocks a coolant hole, and is made of a vinyl-"ish" material (as opposed to the thin steel factory one):
Simply slide it in place where the stock one was, between the manifold and the head. A
few random facts for you regarding the installation:
In case you are curious about the cooling path, here is a primer:
Coolant flows from the small hole in the head, through the gasket and into the manifold, to the stub near the #1 runner. This is the hole you will need to create in the insulator if you wish to allow coolant to flow from the head into the throttle body and IACV. A soft hose joins this stub to a hard line (on a "tree" with others), then to another soft line that connects this to the throttle body (at the base). Coolant flows through a small piece of the TB at the base of it. It flows out of the TB through a small stub which connects to a soft line going to another hard line, then another soft line, to the IACV. This valve controls the cold-start fast-idle bypass of the TB. In short, it kicks the throttle when the engine is cold. It does NOT use the coolant for this purpose, though, it is controlled via an electrical connection by the ECU. The coolant runs into the IACV, then into a "pocket" machined into the side of the manifold under the IACV housing, then back out the IACV through a stub and another assortment of hard and soft lines. It exits this pointing down and heads to the thermostat housing where it rejoins the rest of the engine coolant.
For those of you who would like to see the ports. First, the head (starting with #1):
And the manifold, again, starting with the #1 cylinder runner/port:
No, this isn't a mysterious 5th cylinder port. It's the port for the water outlet, the one that's coupled to runner #4. Note the proximity. There is about 1" square of aluminum webbing between them on the runner side.
Using the dremel and grinding bit, slot the forward bracket holes further towards the edge on the driver's side. The idea is to allow for the bolts/manifold to move further away from the head, since the Hondata insulator is thicker:
You do not need to slot it much, about .1" (1/16" to 1/8") is plenty.
Rather than re-explain the disassembly process in reverse order, here's a short list of the
reassembly steps (basically reverse what you have just done):
You will likely have a fuel leak if you reuse the crush washers that go on either side of the fuel line, under the "damper" (even if you overtorque them). You will need to replace these washers to prevent a leak at the fitting and a fire hazard. You can order them from Majestic Honda using the following info:
Enter in the part numbers using their parts lookup, and you can buy them online. If you want to browse their catalog for them, they are number 2 and 39 respectively on the "FUEL PIPE" parts page. Your local dealer should also be able to get them, but will likely NOT have the first one in stock. Some large dealers will stock these since they are used on a few other Hondas.
It is recommended to allow the Loctite to cure at least 12 hours before running the car. In instances where the car was driven immediately following installation, the Loctite may not have had enough time to set and the bolts lost torque. You will need to reapply the Loctite for it to work properly if you re-torque which is not an easy task. It is recommended you allow the Loctite to set the first time so you do not have to worry about it later.
Before driving off, you will need to top off the coolant. Honda Genuine Coolant is now all pre-mixed (50/50) so you will not need to add any water. Fill the system to the top and close the radiator cap tightly. Before taking the car anywhere, let it warm up (until the fans come on), then run the heat a minute or two and turn everything off. Let the car cool and check the overflow tank and radiator levels. Add any coolant if necessary. It may be necessary to do this once or twice to be sure you have all the air purged out of the system. I have not had good luck with using the bleed valves that Honda provides so I do not recommend even trying them.
The data is in the table below. Measurements were taken with an ambient of 68°F to
70°F, for both data sets, throughout the testing. The same path was driven, with the
same speeds and even same gears used. The driving was kept as consistent as possible.
The times for events were also approximately the same. Essentially, the testing
"variables" were kept as consistent as possible.
The numbers point to an obvious trend: reduced temperature in the manifold. The only numbers that don't make sense at this point is the 0-70mph run. I'm not sure why there was an 18°F rise with the insulator compared to the stock numbers. Honestly, I'm not sure why the temperature rises at all, I would think that the airflow through the manifold would reduce the temperature quickly. It might be that the slowing down and idling I did (less than 10 seconds) before the 0-70mph run was enough to heat soak the manifold such that the air temps rise, but that still doesn't explain the higher differential with the insulator.
The most startling number is the head/manifold "delta" temperature, the difference in temperature between the head/manifold junction. While this does not entirely determine the IAT or even the temperature of the manifold, it is a large factor- it tells you how much insulation or resistance the manifold has from the heating effects of the head itself. Since the surface area where the head contacts the manifold (the flange) is the largest area for heat exchange, this is an important bit of information. For this test, it was measured here:
There is a "dimple" in the head and a crease in the manifold that are no more than 1" apart. Since they are the closest areas to the gasket while still having some "meat" between them (and were easy to get to!), I decided to measure there. The results as you can see are astonishing. The "start" condition was after a 20 minute test drive (seperate from the others) with mixed 70mph freeway and 30-40 start/stop driving. The route was the same and the ambient temp was within the range for the other tests (i.e. the variables were as similar as possible). The "stop" condition was when the fans kicked on. In both cases, this was exactly 185°F, and start-to-stop took between 1 and 2 minutes. I considered this a good test as it mimicked "average" driving and insured that the fans did kick on, which would happen in moderate traffic or at a stoplight. The highest differential is obviously preferred, since it means the greatest resistance to heating through the head.
Stock, there was an 8°F temperature differential at the start, and a 5°F one when the fans kicked on. There was a 50°F difference with the insulator, and it was consistent for almost 2 minutes. The difference in temperature did not rise, meaning that while it did get warmer, the insulator kept the differential- something that you simply cannot do when stock.
For the remainder of the "tests," and for both average driving and average overall temperature, the numbers are clear: at least a 10°F drop, closer to 25°F in "hot" conditions such as idling. With the spacer the intake took noticeably longer to heat when both warming up and idling, and seemed to have a higher resistance to "heat soak." At the end of the testing, when stock, the IAT didn't seem to want to go above 130°F (that was the most I saw after 20 minutes of testing and mixed driving). With the spacer, it seemed to still want to creep, though I never saw above 110°F. On top of that, the manifold cooled more quickly with the spacer, and came back down to the high 80's with part throttle driving. Stock, the temperatures never went below 115°F after seeing 130°F. In all, I would say that a 25°F+ drop in IAT, or a potential 12+ HP gain, is well worth the effort!
As always, feel free to email the author with comments, critiques, etc.
This page last updated 6/9/03.
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