dohc vs sohc

[Migra]

I heard that '98 is the last year they were putting a dohc in the RS's, and that 99 on was all sohc. Does anyone know why this is, and as to the advantages of each? Turbo and n/a.

[SabreKhan]

SOHC gets better gas mileage and is easier to repair, in most cases. I'm not sure what Subaru's reasoning was, but mpg and warranty costs would be a guess.

[freakray]

The dohc was prone to head gaskets blowing, I have driven cars with both and the dohc had a much torquier feel to it (but that could also have been that the dohc'ed Impreza I had was a coupe while the sohc'ed is a sedan.).

[danny8630]

DOHC, all the way.

[Migra]

After googling for a bit, I found that the sohc 2000 RS had 166lb/ft of torque, and the 98 had 162. No real difference there, it very well could have been the coupe platform. What are the general advantages of a dohc vs sohc?

[kichigaijap]

The general difference betweent the 2 is that the DOHC had the stronger block and the SOHC had the better head. The advantages of the DOHC was that it would have been a better engine to turbo if it was running a MAP system... The advantage of the SOHC motor was that it was a better candidate for an all motor application... Though both handle boost well and both were decent all motor engines... Those were I think the major differences between the 2...

[Jay!]

I've heard many stories of head gasket issues in the DOHC motors, as Ray mentioned... Just what I've heard. (Well, read, really.)

[Migra]

Assuming I go dohc for the sake of turboing later (I'm cheap, and can't afford to go NA) and am worried about a head gasket blow, is there anythign I can do to upgrade so that I don't run into head gasket issues? Or, something I can do to change my driving so that I don't have head gasket issues?

[jmrev]

why would they even think of single overhead camshafts?

[kichigaijap]

Dude dont add a post if you dont know what you are talking about... All I have to say is dont rice so much you have a toyota celica and you have a nismo img under you SN... I bet I know more about toyota than you ever could know... In this situation the 2.5 SOHC motor is the better engine... So knock it off and go back to your Toyota board...

[Migra]

No flame war please
What is a MAP engine?

[kichigaijap]

sorry man just was a bit grouchy at the time... anyways a MAP or a MAF is basically the type of air sensor you are using... MAF came out during the DOHC engine runs while the MAP came out with the SOHC engines...

[Jay!]

It refers to the type of sensor the engine uses to measure the amount of air coming into the intake manifold. Subaru switched from MAF to MAP in 2000, IIRC, because I've heard '99 SOHC guyss complain that they can't use the same intake parts are the rest...

MAF - Mass Air Flow
MAP - Mass Air Pressure

[Migra]

Thanks, I'd not heard of Mass Air Pressure before, Mass Air Flow is what I'm more familiar with. So in conclusion, the census is that the dohc is a more powerful setup (potentially) with turbo than the sohc, and the sohc is the more fuel economic and safe version to go with. I assume this is why the WRX still uses the DOHC setup.

[kichigaijap]

Yes but keep in mind that engine is totally different from the RS engines... Even the new 2.5 Turbos in the STi and Legacy and Forester... Just keep that in mind...