Topic: Honda SOHC iVTEC vs Honda/other DOHC engines

[honda41]

Question for you all:

Not getting too much into the "inner workings" of Honda's SOHC iVTEC vs DOHC engines, what benefit(s), advantage(s), and/or disadvantage(s) are there driving a vehicle with either engine type??

Thanks!

[The Mighty Duck]

You mean between an SOHC i-VTEC and a traditional (for want of a better term) DOHC?  Because Honda does manufacture an DOHC i-VTEC as well (it's used in their SiR models and I think various others).

I don't have an answer - I admit I barely know the difference been SOHC and DOHC, period. 

[JD]

SOHC is geting a little dated and Honda is moving, with their new 1.8L 4 cylinders in the 2006 civics, to using DOHC.  VTEC is simply a change in the cam timing and lift, allowing you to get some more power in the upper rev range.

It allows for something like this:

0-5,500RPM:  Cam has a more retarded timing and lower lift.  This allows higher fuel economy and less emissions, but with less power.

~5,500RPM-Redline:  Cam changes over to a more aggrssive timing and lift, allowing for freer engine breathing and more power, at the expense of fuel economy and emissions.

Basically, VTEC/VVTI, etc... Is an attempt to meld the fuel efficiencies of a economy-tuned engine at low RPMs, but once you get into the throttle and pass a certain RPM, you see the advantages of a more performance-oriented engine.

If you're comparing a SOHC VTEC engine a regualr SOHC/DOHC engine, then it depends on the engine build... An engine that is built with just a performance cam and aggressive timing will be faster.  A VTEC engine doesn't 'get on the cam' until high in the rev range...  It would make a faster engine, obviosuly, if it was on teh performance cam all the time...

If you're serious about performance, you can always buy a VTEC controller for ~$500 and lower the vtec activation point to like 3,500 rpm... But that's not a huge gain. 

If you like a fast engine, you want an eingine built that way.  VTEC simply allows great fuel eocnomy and a bit of power on teh top end when it's needed.

[The Mighty Duck]

I thought VTEC was also intended to allow for the greatest ammount of torque at every RPM level as well?  i.e. whereas other four bangers produce their greatest torque levels at higher RPMs, the VTEC will produce more torque than a similarly built traditional engine at lower RPMs.

[articsteve]

Question for you all:

Not getting too much into the "inner workings" of Honda's SOHC iVTEC vs DOHC engines, what benefit(s), advantage(s), and/or disadvantage(s) are there driving a vehicle with either engine type??

Thanks!

DOHC engines can be made to produce more power than a SOHC motor of same size and configeration but have more moving parts.  The Honda SOHC VTEC motor still uses a single cam but acts like a normal DOHC to some extent without the extra cam and all its drive mechanisms.  ivtec balances performance with efficiency and by manipulating the torque thru its multistage single cam and computer inputs.

 http://www.leecao.com/honda/vtec/dohcvtec.html

[si]

I'd just like to clarify the myth that all DOHC engines are generally better than all SOHC engines.

[articsteve]

I thought VTEC was also intended to allow for the greatest ammount of torque at every RPM level as well?  i.e. whereas other four bangers produce their greatest torque levels at higher RPMs, the VTEC will produce more torque than a similarly built traditional engine at lower RPMs.

That's what it does; closes the valves in two stages instead of the traditional one.

[articsteve]

Ok, here is a really good diagram of iVTEC in DOHC


http://asia.vtec.net/article/k20a/

[hondasalesguy]

Honda's engine philosophy has changed greatly in the past 8-10 years. I once read some internal Honda literature where they described torque as an UNDESIRABLE side effect of engine power, due to its twisting force. And this was back when Honda only made 1 V6 engine, in the 97 Accord, which was something like 170 HP, not exactly a torque monster. In the years since, with them making the 3.0L V6 in the Accord and the 3.5L in the Odyssey/Pilot/Ridgeline as well as all the Acura V6s, they have started to come around to the North American way of thinking, that torque is GOOD, that people like a decent amount of power down low without having to rev the engine to within an inch of its life... (Of course in the case of an S2000, Civic SiR (1999-2000) or Prelude, this is a very satisfying way to go as well...)

Point is, they now agree that DOHC, despite its extra complexity and cost, is going to give them better power while maintaining their prime objective, which is economy and clean emissions. And iVTEC is the latest greatest method of giving their vehicles a balance of both power and economy.

[lee_8]

JD I believe the new 1.8L motor is still SOHC. 

[The Mighty Duck]

IIRC, the Civic is getting a 1.8L SOHC i-VTEC.  The Si coupe is getting a 2.0L DOHC i-VTEC.

[mark]

I thought that not long ago, Honda replaced their DOHC V6 in the Accord with a SOHC.  I don't know what the current one is, but this happened a few years ago.

Some of the newer MB engines are also SOHC if I remember correctly, and using only 3 ( gasp) valves instead of 4 (or 5) per cylinder.

[The Mighty Duck]

Yes - the Accord V6 uses a SOHC VTEC.  The four banger version has got a DOHC i-VTEC.  That was the case in 2005, anyway - I imagine it will be the same for 2006.