: Engine question: OHC vs. OHV



Night Wolf
02-28-08, 07:36 PM
Alright, I've been wondering about this for awhile... it's not for any specifc engine or even brand.. just a general question, hence it here in the lounge :)

But, *not* counting DOHC, just SOHC, 2 valves/cylinder.... what does an engine benefit from OHC vs. OHV.

Not counting things like ease of working on, or replacing various items etc.... it goes both ways. But just in terms of the engine, way it runs, power etc....

I guess a second part would be, why are so many... actully the large majority of engines today that are still 2 valves/cyl, OHC design and not pushrod?

Personally, it seems like unless the engine is DOHC, 4valves/cyl... then there is no benefit with an OHC engine vs OHV. Other then less internal drag from engine components, but even that is marginal at best.

I~LUV~Caddys8792
02-28-08, 07:43 PM
I'd heard somewhere that SOHC engines have the least amount of moving parts, so maybe that's the main advantage?

From the SOHC engines I've driven, it seems like they make their most power at midrange RPM's.

What have I driven for SOHC engines???... Ford 4.6L V8, Ford 5.4L V8....that's actually all I can remember for now. The majority of cars I've driven are OHV, but I see a good amount of DOHC engines at work and stuff.

Night Wolf
02-28-08, 07:53 PM
Well, the SOHC design is the most simple of the common valvetrain systems.

Thats the only benefit I am easily able to come up with, less internal drag. Cheaper to make? maybe slightly.... and that alone is a reason to use one design over another.... but when talking just the engine, what the driver feels from within the car and when driving the car.

As for where the engine makes power.... eh, it's all about the cam profile, there are DOHC engines with high low-end torque and pushrod engines that make most power at high RPM.... for factory cars, the engine is tuned to produce most power in the RPM range it'll be used most... mostly midrange RPM, especially when talking cars, though it's just a general statement... always exceptions :)

Destroyer
02-28-08, 08:59 PM
Well you know I own two DOHC V8's (Ford 4.6) and I still prefer OHV V8's. Dont get me wrong, the power is there (especially in the Cobra) but it doesn't come on till 4,000 rpm's or so and even though it sounds great at rpm's up to 7k or so, I hate winding the motor that high. I much prefer an LSx motor that still has the top end power but more power in the bottom end as well. The SOHC 2 v motors are good too but I'll always like OHV motors best.

Stoneage_Caddy
02-28-08, 09:25 PM
OHC makes for a very light valvetrain , which is a big reason you can spin them so high ...

wasnt untill recently with the ls pushrod engines starting with the z06 that you see similar redlines , becuse GM uses very exotic metals in the valvetrain to get the weight back down ...

but for some reason the ohc design just doesnt make good down low torque. ive looked at cylander heads for years of boath design types , flow wise there really isnt a change ...one head can be made to flow just like the other. So it isnt a matter of air delivery that does it. I wouldnt expect valvetrain weight to have an effect on where the torque comes on. rather i expect the weight to have an overall effect on output. and it isnt like a rotataing assembly where more weight brings huge torque down low but wont allow the engine to spin worth a damn.

yet toss a set of DOHC heads on a small block and its torque band marches right up the tach ....so for some odd reason where the cam lives dictates how the engine naturally acts ...


As far as my personal favorite , its hard to say , my all time fav engine dates back in its earliest form to a WW1 french bi plane engine , a 4 cylander DOHC engine .....with its cylanderhead cast into the engine block , no headgaskets to worry about .... 50 some odd years after it first flew in a plane it was building 1400 hp from less then 3 liters on a dyno....this came with some revisions by drake and later offenhouser.... and a stuck wastegate on the turbo ...one of the winningest engines ever at indy.....so i guess im a DOHC guy , but im always charmed by a american pushrod V8 ...

I~LUV~Caddys8792
02-28-08, 09:39 PM
So do the LS generation Chevy small blocks have a top end that matches their stout bottom end?

IIRC, my LT-1 Roadmaster had a pretty decent top end...it seemed like that engine made good power until right before the 5200 rpm redline. With the 4.9, it seemed like after about 4200 rpm, power dropped off until it shifted at about 4800-4900 rpm point. That's one of the things I disliked about the 4.9 most. The L05 350 is the same way too, and I guess the TPI is similar also.

I love how OHV engines have lots of scoot off the line, but I wish they didn't run out of steam at higher RPM's and speeds. If I could find either an OHV engine with good top end power, or a DOHC engine with a good bottom end, then I'd be in heaven. :cloud9:

My engine doesn't really start to make any torque until 2000 rpm, then it builds from there. Same with that '95 S500 I drove last summer. Audi's 4.2L 40 valve V8 makes good low end torque for a DOHC engine...I drove a '99 A8 a while back and was very impressed with the powerband on those.

Destroyer
02-28-08, 10:24 PM
Well Chad, the LSx motors have the bottom end power and great top end power which is what makes ranks them high with me. In all honesty though the LSx is a 5.7 vs 4.6 litre in the Fords. It would be a much better comparison if Ford used a motor of the same displacement to get a better idea of the OHV vs OHC or DOHC comparison. My Cobra is modified with the '04 Mach motor, not so much the motor itself but its got the 4:10 gearing plus exhaust/pulleys and all. Its fast off the line but once it hits 4,000 rpm is when the power really comes on. It just pulls hard all the way 7000+rpms. Its fun but I would prefer the power to come on in the 2000 rpm range. Its what I'm used to and what I prefer. I raced a ram air T/A a couple of weeks ago from a 60mph roll and pulled more than 3 car lengths on it. That was fun but I was in 3rd gear and over 4500rpms when the race began. I loved the Olds 455 I installed in my 67 Cutlass. You could back it up with a 2.73 gear and it would still fly off the line but it didn't have the pull in the upper rpms. In fact it was only good for 4500 rpms or so. The Mark VIII isn't quite as much fun cause its all stock and the automatic transmission doesn't help thing either but I will be putting 3.73 gears in it plus a true dual exhaust and induction to spruce things up a bit.

Stoneage_Caddy
02-28-08, 10:36 PM
So do the LS generation Chevy small blocks have a top end that matches their stout bottom end?

IIRC, my LT-1 Roadmaster had a pretty decent top end...it seemed like that engine made good power until right before the 5200 rpm redline. With the 4.9, it seemed like after about 4200 rpm, power dropped off until it shifted at about 4800-4900 rpm point. That's one of the things I disliked about the 4.9 most. The L05 350 is the same way too, and I guess the TPI is similar also.

I love how OHV engines have lots of scoot off the line, but I wish they didn't run out of steam at higher RPM's and speeds. If I could find either an OHV engine with good top end power, or a DOHC engine with a good bottom end, then I'd be in heaven. :cloud9:

My engine doesn't really start to make any torque until 2000 rpm, then it builds from there. Same with that '95 S500 I drove last summer. Audi's 4.2L 40 valve V8 makes good low end torque for a DOHC engine...I drove a '99 A8 a while back and was very impressed with the powerband on those.

on paper i think the LS is very strong in the top end .....the strongest most OHC like small blocks were the 68-69 chevy 302s , which would live great lives turning over 7 grand and making 500-600 hp doing it ...

sadly tho . its the 3rd alternative that i had the most enthusiasim for ....the camless engines , which had computer controlled solenoid valves ....when i first learned of them 7 years ago it had real promise ...for some reason tho its never taken off , and now that hybrids are the rage i dont think they will ever arrive before fuel cells come online fully ....
computer controlled solenoid valves would have changed the auto world even more then fuel injection did ....lift , timing, duration,compression ( mean effective compression ratio)ALL infinatly variable , down to each cylander ....

Lets just start with this
A 4 cylander 2.2 liter engine , turbocharged @ 21 psi, 13:1 compression
Already this engine has a death sentace , 21 psi on a 13:1 engine (10 psi on 8.5:1 is normal)
With camless , on the street in action the engine's turbo bypassed and the engine running along at 12:1 , a nice torquey profile for the valves and youd have a peppy little engine for city traffic
But should you need to pass , at an instant the turbos spooled to 21 psi , the compression hung to 13:1 and your sitting on 400 hp , perfect for a short burst
Open highway you can run 7 or 8 to one light boost and the valves all set up for the best fuel mileage possible ....

then there the other possiblitys , running 2 cylanders on the high compression , the other two on high boost low compression

or even running the engine on a single cylander smoothly ....

Night Wolf
02-28-08, 11:26 PM
I've often thought about the camless engine too....

All the research I;ve done says technology isn't there for it...

I call BS. It would be a really neat combo.

As for power delievery..... seems like my 4.6 Town Car has smooth and seemless power delivery thru the whole RPM band, and thus pretty much at any speed.

Where as the 4.9 DeVille was a beast off the line, the 4.6 TC dosn't offer the neck-jarring effect, yet it'll still spin the tires if too aggressive on the gas. But at the same time, while the 4.9 died off in the upper RPM range, the 4.6 seems to just pull the same.... not like smaller 4cyls that actually pull harder as they are gaining in RPM.... there is no gain or drop off, it just seems to stay the same. I'm sure the 3.27 gears help a bit, along with the wide ratio transmission... but it makes for a very enjoyable car to drive.... if going under 60 or so, go to pass (not floored) and it'll downshift to 2nd nice and pull smooth, or if on the highway, and do the same, it'll go down to 3rd and hit 90 like nothing... floor it and it downshifts to 2nd is then theres the nice quick boost in speed :)

But when talking about OHC vs. OHV.... the 5.0 used in 80's and '90 Town Car was 150hp with dual exhaust.... the 4.6 used in '91+ Town Car was 210hp with dual exhaust.... I know the 5.0 HO was 225hp, I'm not sure what the Mustang GT 4.6 is, I think 265hp? Although there a bunch of other variables envolved with that power difference.

But, back to the original question.... the main benefit of SOHC over pushrod is simply the more simple and lighter valvetrain?

Stoneage_Caddy
03-01-08, 12:47 AM
Camless was feasable navistar did it , and renalut was supposed to use it in the laguna generation that came out recently ...the main issues was the voltage ....really a 42 volt system is neeeded , something that has been proven possible in the GMC and Chevcy hybrid trucks

hope that made sense i drank more tonight than i have since 2001 , im so drunk right now i dont kno what im doing

LS1Mike
03-01-08, 03:15 PM
A LSx is stout all the way through. All 3 of my LS1 cars were over 320 flt/lbs of torque from right around 1300 RPM to 5800. A lot of it has to do with their head design.
It only take me one cam to out run a Mustang, Honda, Toyota and so on and so forth...:)

Destroyer
03-01-08, 08:35 PM
.
It only take me one cam to out run a Mustang I already beat an LS1 Z28 and a ram air T/A. I also got my arse handed to me buy a really loud cammed Ram air T/A and I ran neck and neck with an '05 GTO w/exhaust and probably bolt ons. Its fun but the car is going to get me in trouble so I'm gonna sell it and maybe get a stockish Mustang GT vert or Z28 vert (LS1 or LT1). Damn, I love street racing but I'm too old to be doing it IMO and it definately isn't worth the risk. :cookoo:

CTSV_Rob
03-01-08, 10:37 PM
Funny, with that logic I should get rid of the CTS-V... Naaaaaah

Destroyer
03-01-08, 11:32 PM
Funny, with that logic I should get rid of the CTS-V... NaaaaaahShhh!, I'm trying to convince myself I'm past all this stuff and I can drive it like a sane normal person should but almost everytime someone wants to run............I run. Its like EVERYONE wants to race it as soon as they realize its a Cobra. I dunno what the hell it is with this car. I'm guessing most just want to say they beat a Cobra and figure a non S/C version would be an easy kill.

I~LUV~Caddys8792
03-02-08, 02:03 AM
My next car should be fast.

Cadillacboy
03-02-08, 02:25 PM
My next car should be fast.

but no furious ,lol

LS1Mike
03-02-08, 03:37 PM
My next car should be fast.

You'll shoot your eye out kid.:bouncy:

I~LUV~Caddys8792
03-02-08, 08:06 PM
Yeah probably.

LS1Mike
03-02-08, 09:26 PM
Yeah probably.

Eh, you will be alright, it is the insurance that would kill you!

I~LUV~Caddys8792
03-02-08, 09:33 PM
Can't be much worse than it is now.

LS1Mike
03-02-08, 09:40 PM
What do you pay now?

I~LUV~Caddys8792
03-02-08, 09:42 PM
Under my parent's plan, $1764 a year for comprehensive.

LS1Mike
03-02-08, 10:15 PM
Holy Poop!

I~LUV~Caddys8792
03-02-08, 10:22 PM
But it's about $400 a year less if we pay both or bills on time.

Night Wolf
03-03-08, 12:56 AM
Thats $150/month....

Eh, I guess not *too* bad.... then again on parents plan, 1 car and no collision.

I've got the Town Car and Amigo, both with $250 ded. on comp, no collision, covered for 100/300/100, on my own plan and it's like $125/month or so.

I was going to drop the Isuzu since it needs an engine and I can't drive it... but it would save me about $10 or $15/month, and then i have to turn my plates back in, then pay to have them back, like $50.... so its like fine then I'll just keep it insured. Hopefully I'll find a replacement engine soon, but I guess if a tree falls on it, it manages to catch on fire with no battery and an empty gas tank, or someone wants to roll it down the hill and take it, then I'd be covered :)

The lowest rates for car insurance (Allstate, who I have now) was the highest for home owners insurance, and the lowest for homeowners insurance was almost the highest for car insurance, the happy middle was still higher then both. I would have preferred to use just one company and get a multi-policy discount, but alas none worked out... so I have seperate.

nickc50310
03-03-08, 03:57 PM
Holy Poop!


If my CTS was not registered as a company car the rate would be 275 per month.

Hence why I probably wont be buying anything REALLY fast within the next 3 years.