Chrysler 2.0L SOHC & DOHC power difference

[92saturnsl2]

In the 90's Chrysler began installing their new 2.0L I4 into their small cars. The first engine was a SOHC 16 valve design. Later on, they developed a DOHC version, also with 16 valves.

The SOHC engine had 132hp vs 150hp from the DOHC (from Wikipedia.) Given that these are both 16 valve designs, what explains the DOHC version's higher power output? Is there some inherent advantage to having two cams as opposed to one, if the number of valves are the same? It would seem to me that you can set cam parameters (duration, lift, overlap, etc.) just the same whether there's one cam or two... But there must be some reason Chrysler adapted the engine to DOHC and was able to gain a few ponies from it. Otherwise if there was no difference, they would have just tuned the SOHC more aggressively and saved themselves the cost of a second cam!

I realize that having DOHC can mean that the intake and exhaust cam can be timed independently, but these engines did not feature VVT of any sort.

 

[joekingcorvette]

I believe with a twin cam the engine can take in a lot more air and let more air out more efficiently.

 

[chrome]

The engine designer can extract the same amount of power from a single cam vs twin cams when using similar valve lift and timing specs. The difference is when a more aggressive cam profile is specified for more power (more lift, duration), the cam(s) need to work against high spring rates as well as higher rpms.

A single cam may be limited in rigidity, or cam lobe width to do the job reliably at this power level, so a twin cam setup is used.

 

[Jarlaxle]

I recall the DOHC Neons had a slight compression bump, hotter cams, and a better exhaust system.

 

[pezzy669]

I had a '99 Neon with the DOHC 150HP and did a lot of research back when I had that car - there was an awesome Neon forum because this car was such a hoot to drive (albeit being severely unreliable).

Rumor was that the DOHC intake (runners and maybe ports and intake valves) was tuned by Lotus, the DOHC also IIRC had a higher redline than the SOHC. The Mitsubishi version installed in the Eclipse was functionally the same engine but it was flipped around with the intake in front and exhaust facing the rear - Mitsubishi version made 10 less HP.

Honestly on paper it looked like a great engine, but it had a lot of design faults and reliability concerns. Mainly the major headgasket issue that affected all cars 1995-1998 and part of the 1999 model year run, I did not luck out and my '99 was before the updated gasket. This also affected the Eclipse 2.0 for pretty much same time period. DOHC had hydraulic lash adjuster design faults that were never corrected during the 1st gen Neon model run, updated parts were released but required all new lash adjusters and rockers arms. This mainly affected the Neon with the manual trans because the issue would arise during high RPM operation - the cloud cars and vans were all automatic so had a lower redline that would not allow the issue to occur. I had a lot of cold start issues with that car even when it was only 3 years old - it was undriveable for at least 2-3 minutes after any cold start (even at 70 degree ambient outdoor) and 2 Chrysler dealerships could not figure out what the issue was even after reproducing it so I just lived with having to idle for a bit before I tried to drive off.

My '99 was traded in 2003 with ~85k miles on the clock needing a head gasket, some various seals replaced (tail lights would fill with water) and passenger door frameless window never sealed right. I got $400 for the trade on a 5 year old car with under 100k miles - pretty certain they probably sent it to the scrapyard. That soured me on Chrysler until I went through the same rodeo on a 2012 Fiat 500 that was just as terrible.......but incredibly fun to drive.

 

[kkreit01]

Yep -- I had the SOHC 2.0 in a Neon. 18 less HP, and less problems.

 

[ms21043]

I have 2004 neon R/T that was bought new. It has 315k on it now and it has been a super reliable car. The suspension was upgraded years ago with Hotchkis and Koni parts and a set of quality light weight (non Chinese) wheels and summer performance tires. It's still a lot of fun to drive which is probably why I still have it.

It has the 150 horsepower SOHC engine.