Hello,

I have a 2005 MDX which is rated at 265 hp (based on old hp rating) with it's SOHC engine. I was wondering why they went with SOHC vs using DOHC. The engine is very smooth, quiet and powerful as it is but wouldn't it have had the potential for more horsepower if it was DOHC.

If someone wouldn't mind taking the time to answer the above and to also explain some of the benefits and differences between the two technologies.

Thank you,

 

Cost and simplicity. Maybe all Honda wanted was 265 HP out of that thing. If it can be achieved more cheaply, why not?

 

Sohc you have the high and low lift of the cam built into one cam. Dohc you have your low lift cam and high lift cam separate thats why you feel the kick when vtec kicks in. Thats why the kick is less pronounced on sohc.

 

Uh no. Not at all.

DOHC controls intake and exhaust valves separately. SOHC controls them from the same camshaft with another set of lobes.

I assume the decision to use a SOHC head was because they could achieve their power goals with a simpler and cheaper design (SOHC compared to DOHC). SOHC is not fundamentally bad, it just gives less adjustability compared to DOHC, since you can't adjust the intake and exhaust cams separately without machining a new camshaft. The valvetrain differences may come into play in very high RPM circumstances, but for most engines, the same thing can be accomplished with SOHC as can be with DOHC.

 

Wow. Just ... wow.

My guess has to do with the application of the motor. Generally speaking a SOHC setup gives you better low end torque. Truck -- low end torque = good.

Here is a relevant and somewhat interesting bookmark I have:

http://paultan.org/archives/2005/06/22/soh...hc-valvetrains/

 

DOHC=top end power
SOHC=low end power

or in combination with large displacement(think DOHC v8) you can have the best of both. read the link steveo posted, its a better answer than any of us can give.

 

Thanks everyone for the replies and input and thank you to Steve for the link, that basically explained it all

 

There's a few problems with that link 'explaining' the merits of the two valvetrain configurations. Like the graphs he shows doesn't support his conclusion that a SOHC has better "low end power". The torque curve for the DOHC engine is higher at throughout the rev range!

The choice for any engineering task comes down to accomplishing the goals for the lowest cost. Why use a more complex DOHC system when a simpler (cheaper) SOHC (or even pushrod) engine suffices?

DOHC engines *tend* to be able to rev higher and have higher torque at the upper range, which makes them good for racing, not needed as much for an SUV. You'd need an automotive engineer (not some dude on the internet) explain all the benefits and tradeoffs involved, but I believe this is mostly due to the fact that DOHC engines tend to have more valves per cylinder so they breathe in and out more efficiently as well as better valve control at higher rpms.

Now all we need is a good "torque vs horsepower" debate!

 

There is more to the measurement than absolute numbers and I do not see how this guys graphs disprove (or for that matter prove) his point that SOHC configurations produce more sustainable torque down low. That piece of information is by no means revolutionary or particular to him.

So I guess I am sitting here wondering ... you want to discredit this person for laying out a solid foundation to his claims while at the same time making your own claims with no factual evidence to support them just an "I believe."

 

I'm not trying to discredit that guy, but when someone presents data that is contradictory to their claims, you gotta raise the flag.

My main point: using those graphs as an example, a SOHC valve train on the same engine does not have more power, low end or otherwise, then a DOHC configuration.

Now you can make data and statistics say anything you want, but he could have at least used data that backuped his point.