[I~LUV~Caddys8792]

Do you fellow Cadillac lovers prefer pushrod type engines or the DOHC/SOHC setup? and why? For me, I prefer the pushrod design in anything with 8 cylinders or more. I say this because pushrod engines offer more low end torque, which IMO is what you want when you are lugging around big heavy cars and trucks. Now for the smaller 4 & 6 cylinder motors, I think having a DOHC or SOHC setup is best because you dont really need a lot of low end torque in a small Honda. and because an OHC setup works well with a manual tranny. It revs fast, you shift a lot, it seems to work well. For some reason, almost all of the 4 cylinders and a lot of the 6, 8 and 12 cylinders seem to be SOHC or DOHC, why is everyone abandoning the pushrod setup?

 

[ben72227]

oh you know, pushrod is old technology, only Pontiac uses those things anymore:lildevil:

But really, pushrod may be "torquier" and more simple and smaller, but they also have lower RPMS, you have difficulty when using crossflow cylinder heads in straight engine configurations, limited valve flexibility, also, some countries tax based on engine displacement, so OHC's usually have the advantage there too.

 

[I~LUV~Caddys8792]

ahh very interesting, I kind of got to drive my buddies '91 Talon TSI AWD turbo today, and the first thing I noticed is how fast that motor revs up. If you just touch the throttle, it begins to gain RPM's fast! It's got a DOHC 2.0 Turbo I-4.

 

[90Brougham350]

Keep in mind the LS7 is a pushrod motor that redlines at 7 grand. They both have their advantages and disadvantages. Personally, I'll stick with rods.

 

[90Brougham350]

A pushrod motor can wind up just as fast as an overhead cammed engine. It takes lightweight components and a loose convertor, but it's just as possible!

 

[EcSTSatic]

Pushrod engines = More parts to wear out. More mass to overcome.

Pushrod vs OHC

 

[terrible one]

Cool link.

I would like to learn more about OHC engines, I only have service experience in the pushrod category, so I don't feel that I can really cast a vote on the subject.

 

[Nocturn]

more parts to wear out? Vs 4 camshafts, and timming gears etc...thats debatable.

Rev speed depends on the flywheel and engine components..not just cam type.

 

[EcSTSatic]

more parts to wear out? Vs 4 camshafts, and timming gears etc...thats debatable.

Rev speed depends on the flywheel and engine components..not just cam type.

I hear what you are saying Nocturn. Mainly I'm referring to hydraulic lifters in a pushrod engine. They seem to be the first thing to wear out and difficult to replace. Not like the parts of an OHC engine.

I don't even think there is a pushrod engine made with four valves/cylinder is there? It's a more efficient design IMHO.

 

[Jesda]

Pushrods are simpler and require fewer expensive parts, which is why theyre so easy to maintain and so cheap to build.

 

[90Brougham350]

The natural progression of production engines simply led to the pushrod V8 being the most popular and efficient to build (at least in the United States). There's a reason pushrods are still around. We know the technology inside and out, and there's been so much done with them over the past 100 years. This Canadian article is short but it does a good job. http://www.canadiandriver.com/articles/jk/040421.htm

 

[davesdeville]

I have arguably one of the best pushrod engines out there, the 500, and one of the best DOHC engines out there, the northstar. They're both kick-ass. OHC is an older technology than pushrods believe it or not, and most engine makers went pushrod because it's usually more compact than OHC, since you stick the cam in the valley rather than having to have it above the head.

The generalizations about both (low vs high rev capability, torque vs hp, etc) are true for the mostpart. But OHC can do torque, and pushrod motors can rev. Bring aftermarket modification into the equation and there's really no telling which is better, just two different ways of getting somewhere fast.

I don't even think there is a pushrod engine made with four valves/cylinder is there? It's a more efficient design IMHO.

"Chevrolet recently introduced a 3-valve version of its Generation IV V8 which uses pushrods to actuate forked rockers, and Cummins makes a 4-valve pushrod straight-6 Diesel, the Cummins 600."

Pushrods are also getting variable valve timing technology, a la the new Pontiac 3.9 V6.

 

[terrible one]

I have a box of old pushrods and they are fun to play with.

 

[EcSTSatic]

I have a box of old pushrods and they are fun to play with.

Sort of like an industrial pickup sticks game.

BTW, the new 'vette has a 7 liter, 500HP pushrod V8!

 

[terrible one]

Sort of like an industrial pickup sticks game.

BTW, the new 'vette has a 7 liter, 500HP pushrod V8!

Haha, never thought of that before. Good idea!

I usually just throw them into a box or foam or something, since I don't have any throwing knives.

They would probably make good straws if you weren't very thirsty.

I've got 32 of 'em.

 

[Stoneage_Caddy]

Sort of like an industrial pickup sticks game.

BTW, the new 'vette has a 7 liter, 500HP pushrod V8!

and in testing ran all the way to 7500 RPM ....and never launched a single pushrod ....

The Buick Indy was a Pushrod V6 , i think it turned a tad over 10 grand and in the end was fed by around 38 psi of boost ....but they did have issues with pushrods every now and then (these were LOOSELY based on the 3.8 GNX stuff)

 

[Stoneage_Caddy]

Now for my soapbox ....

Ive seen and worked on alot of valvetrains in my life , detroits with 5 exaust valves and no intake valves , roatrys ,2 strokes(reed and case indutction),DOHC ....even got a chance to look at a scroll valve 351 Clevland , which would rev as high as the con rods would allow.....

OHC as one of you pointed out is pretty darn old , trace the roots back far enough and your looking at a frenchman or a italian as the first , either way it was in a biplane , not a car , in WW1..Pushrod is just as old ....Varible valve has been around since the early 30s if memory serves ....tho back then it wasnt computer controlled , clutches and centrifugal weights did the work...

One of the greatest engine of our time isnt made and hasnt been made since the early 70s. The Offy,Drake,Miller 4cyl , they ranged from 91 to 270 inches and by the late 70s with a turbo made over 1,000 hp ....For a long time holding records for most HP per cube....Quite possibly they were the perfect engine ..... There desgin lent itself well to massive ammounts of boost ...as there was NO cylander head , the head was cast right with the block as one peice....the bottom end was bulletproof , it was so well built that the crankshaft couldnt be installed how you would think it should be installed ....you basicly thread it into the block like you would a camshaft ....These were DOHC (HEMI before Chrycor got the idea), and trace ther roots back to the 20s (actually WW1 france if you take some liberty with it).....Only a few made it into street cars , the vast majoirty went into Indycars and Midgets .....probably one fo the few engines in motorsports that were used compeditively for over 40 years continueosly (the small block chev might be nippin at this record too).....I could talk all day about these...

Now , the perfect Valvetrain nowdays is the Camless design , useing electric or air operated solenoids to run the valves......Were talking infenatly varible valve timing , you can give each cylander exactly what it needs at whatever event , whatever RPM , Load .....Even with varible cam engine right now you can only go so far with the timing , your still stuck with a solid stick and a few mesaly degrees of variation .....Hondas gone about as far as it goes , and that was at aloss of torque , if honda got rid of the cams on the S2000 they could make that 250hp and most liekly make every bit of 250lb ft down low in the rev band , and pry 60+ mpg out of it on the highway ....then if you think about it you remove a great deal of the fricition and weight the engine has to rotate thru freeing up even more power ...

So why dont we have it ? We need more power , Renalt says it needs to use a 48 volt system to make camless work .....Siemens/Navistar thinks they can do it on 24...at any rate 12 wont cut it .....power and technology costs money ....

But if someone wanted to push the hybrid evelope as far as it can go use a 1.0 liter camless alumin turbo diesel on the miller cycle with the hybrid system behind it ....toss it in something the size of a Malibu and youll have something pretty darn neat

 

[terrible one]

Stoney, that made for a good read. I'm interested in these Offy, Drake, Miller 4 cylinders you speak of.

 

[[email protected]]

Interesting engine that Drake Miller thingy.

I'ev always wondered why they haven't used solonoid type valves, I always assumed it was due to component life, but the 48V reason is interesting as I had heard they planned on switching to 48V in the next few years.

 

[lawfive]

Pushrods, **DROOL, DROOL**

-- CTS-V troll, out!