while adjusting the valves on the wifes 325ic this past weekend it occured to me...what is the benifit of a DOHC vs aSOHC engine? Seems to me that DOHCdemands more weight what with 2 cams andgears and the overhead (no pun intended) would sap any benefit from such an arrangement...is it valve angle positioning or something? Plus,
I just changed the oil on my 1990 300TE the other day..the oil pressure indicator was not right...after putting 7 quarts of Castrol GTX 20-50 in the gauge is right up to where it should be...I think the previous owner put synthetic in, I really do. Is this possible? Plus the engine runs much better..smoother idle, better restart as well....I never liked synthetic oil myself...cliff

 

Cliff,
I've been 'in love with the DOHC design since Jaguar adopted it from their race engines back in the late 50's. I think that the benefits in response and hp potential outweigh the additional weight & mechanicals. It's like comparing solid lifters to hydraulic lifters back in the day-you could alway eek more horsepower from solid lifters, (except in the 426 Hemi, which I never fully understood). Now with variable valve timing, engine sensors and ECU's, I think DOHC setups are even more power conducive. More more flexibilty in camming exhaust valves separate from intake and 'overhead' makes things happen fast. Other than Carrol Shelby's initial input, I was never really sure why Lamborghini designed the Viper motor for Dodge with pushrods, instead of OHC's. Sometimes I think massive cubes and torque overcome all else.

Not that I'm gonna ditch my 103 for a 104 DOHC (however envious I am of the 104 DOHC, although their head gaskets leak as well)....but I do want to supercharge.[sm=badbadbad.gif]

Kevin

 

Cliff,
BTW, good choice on your oil weight for that 300TE. That's exactly what I wound up using after trying Mobil 1 (I actually bought the wrong product for the trip-thought I was buying Mobil High Mileage dino). Synthetics should NOT be used in high mileage engines, especially older designs that were not designed around synthetics in the first place. The lubricity and vicious nature of synthetic oil tends to make the stuff leave you engine, rather than stay in it.

What you observed using the dino 20-50W is exactly in line with what I observed. My E Type Jag would only run on Castrol GTX 20-50W without burning oil-everything else left the engine. My head gasket in the 103 is leaking far less with the 20-50W and I'm actually not seeing the oil level drop weekly as before.

Kevin

 

SOHC yields a better low end torque, but DOHC would give you better peak torque and horsepower. DOHC is a lot easier to work with as well especially when it comes to valve timing and such.

I'm an OHV guy though.

 

thanks gang...appreciate the outstanding input on this...not too may sites that provide such valuable responses...cliff

 

One of the problems with OHV design is that unless you use roller rocker arms, they (valves) have a tendency to flutter/float at high rpm. This is much less of a problem with SOHC and DOHC designs-my '92 103 engine will easily achieve 6,200rpm and the 104 DOHC will easily achieve 7,000rpm. That's factory too....numbers that we used to dream about obtaining in stock muscle car engines with OHV's. The V-10 in my Dodge work truck has a fuel computer shut off at 4,500rpm. Surely that is conservative, but it ain't gonna push 7,000rpm with factory OHV's either-if it was deprogramed.[sm=badidea.gif]

Kevin