THIS outlines every difference between DOHC and SOHC neon engines, and information you need to do the swap
This is not a how to swap. Read this. Buy a haynes manual and go for it... actually... do a 2.4
Co-written by 95to96transplantneon and fsu182
If you want to swap your SOHC (single over head cam) engine out for a DOHC (dual over head cam) engine, this is the information that you need. (However this information will helpwith the person wanting to swap DOHC to SOHC as well.) I am writing this with the idea that the person reading it knows enough about internal combustion engines and has enough mechanical inclination to attempt the project.
1. What are the Differences between the SOHC and the DOHC?
The differences between these two enginesare primarily in their cylinder heads. They share the exact same block.
The DOHC (Engine Code = ECC) has two camshafts inside the head. One camshaft opens and closes the intake valves, allowing air and fuel into the combustion chamber. The other set operates the exhaust valves, allowing exhaust gasses to flow out of the combustion chamber after the air and fuel mixture is burned.
The SOHC (Engine Code = ECB) engine has only one cam, which opens and closes both the intake and exhaust valves.
Both heads have the same numberof valves (16.)
The compression ratio is also different between DOHC and SOHC engines, because the cylinder head combustion chambers are different. The DOHC has a larger combustion chamber. To compensate for that, the DOHC has a raised piston dome with 4 valve reliefs. The valve reliefs are machined indents in the piston top that allow the valves room to open during normal engine operation.The SOHC has flat top pistons.
The bore for both the DOHC and the SOHC is 3.445 in
The stroke for both the DOHC and the SOHC is 3.267 in
The intake and exhaust manifolds are different for each head design. The DOHC has larger exhaust ports that are more eliptical in shape, while the SOHC has smaller, round exhaust ports. The intake port is also larger on the DOHC head. The DOHC manifolds have larger ports to match.
The DOHC engine has a rev limiter of 7200 RPM.
The SOHC engine has a rev limiter of 6750 RPM.
The 2.0 DOHC engine is rated from the factory with 150 hp @ 6500 RPM with 133 ft/lbs. @ 5600 RPM of torque
The 2.0 SOHC engine is rated from the factory with 132 hp @ 6000 RPM with 129 ft/lbs. @ 5000 RPM of torque [/align][align=left](NOTE: This SOHC rating is for engines produced from 1996 to 1999. SOHC engines produced in 1995 have a hotter cam and prouduce more power)
The compression ratios are as follows
9.6:1 for DOHC
9.8:1 for SOHC
9.3:1 for California controlled SOHC also know as the TLVE(NOTE: this version of the SOHC engine was created to produce lower emissions)
You can get creative and swap a SOHC head on a block that has DOHC pistons and it will yield a compression ratio of 10.3:1 (more compression = more power)
You can swap a DOHC head on a block that has SOHC pistons and it will yield a compression ratio of 9.3:1. This setup is an ideal setup for turbo applications. The lower compression will allow you to run a higher PSI of boost, while the individual cams will allow you to custom tune your timing much easier.
(NOTE: when swapping only heads, you also need the appropriate timing belt and components, along with intake and exhaust manifolds, pcm, wiring harness, etc.)
Other differences between the complete DOHC and SOHC motor assemblies are
Both the intake and the exhaust manifolds are different. They will not swap over.
(SOHC motors have two versions of the intake manifold, Plastic and Aluminum)
The fuel rails are different between the SOHC and DOHC.
The SOHC cars are equipped with a single-outlet muffler
The DOHC cars are equipped with a better performing dual-outlet muffler
While both the SOHC and DOHC motors have 19lb injectors, they are different. The DOHC injectors are longer and will not fit a SOHC.
DOHC cars equipped with manual transmission have a final drive of 3.94
SOHC cars equpped with manual transmissions have a final drive of 3.55
2. What parts do I need to complete the SOHC to DOHC swap?
Read the details on each item, to ensure that you need it.
You will need:
I. DOHC engine (complete)
Proper injectors and fuel rail (read above)
On a side note:
1995 m/y Neons have separate IAT and MAP sensors and the intake manifold has provisions for both sensors.
1996-1999 m/y Neons have an intergraded IAT/MAP sensor requiring only one hole in the intake manifold.
On 1996-1999 m/y Neons it is possible to use the 95 manifold however it will take some modification.
On 1995 m/y Neons you will not be able to use a 96-99 intake manifold.
II. DOHC PCM of the same year as yourcar
Read the information under DOHC Wiring Harness
III. DOHC Wiring Harness
[/font]Make sure the wiring harness will work with your car. If you have a 96+ engine, you need a 96+ harness. If you don't want to buy a wiring harness, you can convert your stock SOHC harness to work the DOHC engine. It requires more work and custom wiring.
To convert a SOHC harness to DOHC, you need to change the cam positioning sensor plug, and extend the coolant temp sensor plug, it needs to be long enough to reach passenger front side of the head.Sensors may not be plug and play. You may need to buy new sensors for certain applications.
If swapping DOHC to SOHC the harness will be long enough to reach.
There are some differences to some of the harnesses depending on the year:
(early 97 wiring harnesses are odd, they may have differences such as VSS, alternator, brown wire that goes to the starter, TPS, and the IAC motor all have different plugs. From what I can gather it is a Frankenstein harness between the 96 harnesses and late 97-99 harnesses)
1995 PCM has a single plug that connects to the frame, motor, and cabin wiring harness.
1996-1999 PCM has two plugs that connect to the frame, motor, and cabin wiring harness.
1995 model year has unique plugs for almost all the sensors in the engine bay.
1996 model year is a hybrid between 95 sensors and 97-99
1997 - 1999 No changes were made to the wiring harness between these years... use all the same sensors.
1995 has a separate MAP and IAT sensor.
1996-1999 have an integrated MAP / IAT sensor.
1995-1996 use the PDC for the fan relay.
1997-1999 use a separate fan relay located just below the driver side headlight.
1995-1997 use Bosch plugs for the injectors.
1997-1999 use the USCAR square plug
The plug change happened mid year so some 97's have Bosch style some have the USCAR style.
1995-1997 use the same alternator and starter.
1998-1999 use the same alternator and starter.
They only fit the correct years harness.
IV.DOHC Motor Mounts
There are two different types of motor mounts. There are steel mounts and aluminum mounts. The steel mounts are interchangeable; the aluminum mounts will only work on the type of engine they came off of. If you have the aluminum mounts, you will need to buy new motor mounts.
3. Is it worth it to swap from a SOHC toa DOHC?
If you happen to have an extra DOHC engine, or got one really cheap, then you may find this swap worthwhile. If you plan on continuing to modify your car with a turbo or other performance parts then you may find this swap worthwhile. If you simply want to change your engine out to gain this horsepower and do no more, then you are better off to spend your money or some performance parts for your SOHC engine and enjoy them. Different people have different opinions of these engines and this process. What is undeniably true is that you gain a better flowing engine, individually adjustable timing between the intake and exhaust valves, a higher rev limiter, a higher powerband, and a slight ego boost. You also gain a little extra weight, and an additional cam to purchase if you plan on upgrading them in the future.
4. Is the 420a engine from an eclipse the same as the neon DOHC?
No, the Neon 2.0 DOHC (Engine code: ECC) and Avenger/Sebring/Eclipse/Talon2.0 DOHC (Engine code: 420a) are different. Similar, but different. In other words your neon does not have a 420a engine. This is a common misconception among new 1st gen DOHC owners. The 420a head is unique and has reversed flow; The exhaust manifold sits in front of the car and wraps down in front of, then under the engineblock.The air intake is routed behind the engine towards the rear of the compartment to enter the head. Many bottom end parts for a 420a will work for the ECC such as pistons, rods, timing components, bearings, head gasket, etc. Another common swap is for neon owners to use the valve cover from the 420a (which is has raised lettering that reads: "DOHC 2.0L 16 VALVE."
Also note that the neon DOHC (ECC) shares onlyits cylinder head in common with one other engine: the Chrysler 2.4 DOHC engine found in the 1st gen stratus, caravan, etc. They are the exact same casting number. If you look at the back of the cam gears on the ECC's head, they read "2.4 front." This is because the gears are flippedwhen used on the 2.4 DOHC. The camshafts, however, are different. The bottom endon the 2.4 is also different. It has a longer stroke and produces more torque. It is also popular to swap the 2.4 DOHC into 1st gen neons. In most cases you will find a 2.4 swap to be more worthwhile, but requiring more work and parts.
Information courtesy of 95to96transplantneon, spudsterier, das2123, Jr. Mechanic, Ghost Neon 2, allpar.com, and myself.
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RE: if you want to do an engine swap SOHC to DOHC (2.0)
A couple of things I would like to add:
1. When I put my DOHC harness on my SOHC neon, I did not need to extend the cam sensor plug, and the CTS wire is actually longer on the DOHC than it is on the SOHC, meaning you do not have to modify it.
2. There were a few changes to the wiring harness from 97-99. Off the top of my head, I can think of the VSS, alternator, brown wire that goes to the starter, TPS, injectors (which is listed), and the IAC motor all have different plugs. This is between an early 97 and a 98. There may be a couple others, but I think that is it.
RE: Information for a 2.0 engine swap - SOHC to DOHC
i have a wrecked 97 sohc atw/ haun turbo kit i just bought a 95 sport w/ mtx and bad motor so i want to put the motor out of the 97 into the 95 what kind of wiring mods will i have to make?will the 97 motor 95 mtx combo even work?