What's the advantage of OHV(pushrod) to OHC engine?

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quote:

Originally posted by Spitty:
I think we nned to decide if we are talking about In line engins or V engines, a V engine can be smaller and lighter due to it useing a single cam in the middle of the V.
In an in line engine there is not much advantage in having the cam in the block.
snip...


That was the point I was making about the engine in my truck, a simple, little inline 4. Its valve cover can't be much higher than a similar pushrod one. Same with the Tech 4 that was in my daughter's 90 Beretta. Both engines had good enough low end torque for easy launches with a manual.
 
quote:

crypto,
just what do you need a belt driven OHC in a garden mower for anyway ?

I'll choose rugged simplicity any day over gimmicky technology.

The Honda GC OHC lawn and garden motors are terrific, though they do seem to be an exercise in engineering. Nonetheless, and contrary to what many people thought would happen with Honda’s use of an internal timing belt to drive the plastic camshaft, these engines have proven to be durable, run flawlessly, use little gas, always seem to start on one pull, and sound very refined (I know that’s only aesthetics). So, based on my experience of currently owning both types (a flat head and a SOHC) I’ll take the pleasing, if not gimmicky, OHC over the crude, raspy, pollution belching, hard starting flathead any day. Besides, I can buy a sticker to put on my mower that says “Powered by Honda.” Now, if I could only get a NOS kit, K&N, and coffee can muffler for it…
 
I think we nned to decide if we are talking about In line engins or V engines, a V engine can be smaller and lighter due to it useing a single cam in the middle of the V.
In an in line engine there is not much advantage in having the cam in the block.
I see the difference in OHC v OHV this way, traditonally in the US, Gas has been cheap, and the roads have not favoured High Speed travel, people have bought Large cars with big lazy 'V' engines, and Bags of Torque. In Europe gas is expensive, yet for 50 or more years there has been a network of High Speed roads, cars purchased tend to be small (ease of parking) and of small displacement, 4 cyl is typical (good gas consumption) yet they must be able to scream down the Autoroute when required, torque was secondary. (Drag raceing is an American passtime, Road raceing European)
 
quote:

Originally posted by HEV:
Nonetheless, and contrary to what many people thought would happen with Honda’s use of an internal timing belt to drive the plastic camshaft, these engines have proven to be durable, run flawlessly, use little gas, always seem to start on one pull, and sound very refined (I know that’s only aesthetics).
I don't doubt that any honda product is reliable; however, Briggs flatheads are pretty **** reliable too. I've got one from 1960 that has at least 1000 hours on it, still starts on the second pull. (like it's designed to) I really don't see any good reason for OHC in a small engine - performance isn't an issue and it will never be MORE reliable than a flathead or OHV. Flatheads do drink the gas, but OHVs are quire efficient. I doubt there's enough difference to worry about in fuel use between briggs OHV, honda OHV, and honda OHC. I'm sure the OHC is reliable, but how much does it cost to fix/rebuild? Probably alot more than any OHV from the same manufacturer.
 
One thing many people get wrong is thinking an OHC is vastly more "high-tech" then an OHV engine. The only real difference is the valvetrain arrangement. Most modern OHV engines have just as many high-tech features as OHC engines. It's simply a different schoool of thought.

OHV engines have less parts, and are cheaper to make. This can mean a cost savings to a customer or more money to spend on other areas. In the early 90s GM tested a DOHC 4.0L engine against a supercharger OHV 3.8L. The OHV was cheaper to make even with the supercharger and provided better acceperation and gas mileage.

OHC engines tend to have better valve control, but only if their are DOHC engines. A 2-valve OHC engine has little benefit over a 2-valve OHV engine. However they can more easily adapt a 4-valve head.

-T
 
Hi Oz. If you are talking about something like a bent cranks (like from hitting an object), then according to my Honda Dealer, they are actually cheaper to repair than the Honda OHV motors since they use bushings, not main bearings (like the OHVs do, for commercial durability). It’s actually not a very complicated motor. I do wonder why Honda even designed a OHC motor for their premium residential line verses a revised OHV model with bushings instead of bearings. Must be marketing. They are a very good motor though. They certainly have less noxious emissions than my Briggs.

My experience with the Briggs flat head motors have been hit and miss. My older (circa 1967) Briggs was very durable, still running fine when I got rid of it three years ago. However, I recently junked a 5 year old 3.5 HP model. What a piece of excreta. They don’t makeum like they used to.

BTW, did you ever get a hold of those cheap Chinese Honda knockoffs?
 
quote:

Originally posted by labman:
... I once saw an engine from the 20's where the pushrods were external to the block.

Aircooled engines have the pushrods external to the block. All small aircraft engines are still made that way. Aircooled VW's with external pushrods were still common in the 1970's. There are tremendous packaging and simplicity advantages to OHV in horizontally opposed designs. A single cam lobe can actuate valves on two oppsed cylinders, something a "V" engine cannot do.

Porsche in the 1960's and much more recently, Subaru, decided to build high-revving opposed engines that use overhead cams, despite the complexity and bulk.
 
quote:

Originally posted by T-Keith:

OHC engines tend to have better valve control, but only if their are DOHC engines. A 2-valve OHC engine has little benefit over a 2-valve OHV engine. However they can more easily adapt a 4-valve head.

-T


SOHC still has the advantage of being able to move the valves quicker with much less spring force since the spring doesn't have to handle the pushrod too. Quicker valve actuation, lower wear on high speed engines.

I agree that in lower speed engines it doesn't make much difference.
 
A little off topic, but I think Detroit sticks to existing designs due to cost savings and resistance to change, Japanese mfrs are quicker to adopt variable valve timing and other advances. Go back to when disc brakes were common on Euro cars and Detroit said there was no advantage to disc brakes, etc. Very slow to adopt advances. Look how long Chevy used the PowerGlide 2 spd tranny!!! $$$
On the DOHC issue, still don't know why Subaru on the the 2.5L was able to go from DOHC to SOHC and still get the same HP a couple of years ago...99?
 
quote:

Originally posted by Spitty:

I see the difference in OHC v OHV this way, traditonally in the US, Gas has been cheap, and the roads have not favoured High Speed travel, people have bought Large cars with big lazy 'V' engines, and Bags of Torque. In Europe gas is expensive, yet for 50 or more years there has been a network of High Speed roads, cars purchased tend to be small (ease of parking) and of small displacement, 4 cyl is typical (good gas consumption)


Pushrod engines usually get better fuel economy than a DOHC engine of the same displacement.
 
quote:

Originally posted by John K:
A little off topic, but I think Detroit sticks to existing designs due to cost savings and resistance to change, Japanese mfrs are quicker to adopt variable valve timing and other advances.

From three-speed automatics, to distributor caps (as opposed to distributorless ignition), to vacuum-servo (as opposed to electronic-servo) cruise controls, Japanese manufacturers stick to existing designs as much as (if not more than) American manufacturers do.

Variable-valve timing is neat, but mainly useful as a way to avoid the displacement tax.
 
quote:

Originally posted by sbc350gearhead
Pushrod engines usually get better fuel economy than a DOHC engine of the same displacement. [/QB]

That's an interesting idea, can you give an example, you must also consider power out-put.
 
The better way to say it would be, a typical OHV engine that has about the same or more horsepower than a smaller OHC engine will typically get better mpg. Of course the OHV engine will almost for certain have way more torque too.

Kind of hard not to like that; same or more horse power, better on fuel and gobs more torque.
 
Those of you bashing OHV do you realize the LS1 was ALL NEW the only thing it shared with older smallblocks is the bore spacing. GM sunk a lot of R&D into it and it has paid off well as others noted 400hp and 28mpg. Not saying it is better than OHC just saying it is not dinosaur technology, as others have said just a different train of thought to arive at a similar goal(move a car). Personally I like the raw torque my LT1(pushrod) provides, then again I have a RWD chassis capable of planting that torque. I think that is another detail you guys are missing most of the Japanese imports are FWD try hooking 320hp/350+ft.lbs at 5400/4100rpms respectively with FWD on the street isn't going to happen so to make those cars fast instead of torque they turn to HP and make the power after the car starts rolling and traction is not a problem. Still end up with a quick car just went about it a little differently and wouldn't things be boring if everything were the same.
 
quote:

Originally posted by Spitty:

quote:

Originally posted by sbc350gearhead
Pushrod engines usually get better fuel economy than a DOHC engine of the same displacement.
That's an interesting idea, can you give an example, you must also consider power out-put. [/QB]

The new Malibu's 3.5 has more power and better gas mileage then Toyota's 3.0.

-T
 
I always consider the Toyota 3.0 V6 to be a bit of a 'Dog' in terms of power and fuel consumption.
I was thinking, back in the 60's, in England you had the Austin OHV engine as used in the Mini that was 848cc and the Hillman Imp, all Aluminium, SOHC slant 4 of 875cc both these engines were available in various states of tune, but it seems the SOHC always had the edge in terms of HP and economy, perhaps because of the RPM available.
I think that you will find more variation within engines of any given type, than to draw conclusions based on the Cam location.
 
quote:

Originally posted by T-Keith:

quote:

Originally posted by Spitty:

quote:

Originally posted by sbc350gearhead
Pushrod engines usually get better fuel economy than a DOHC engine of the same displacement.
That's an interesting idea, can you give an example, you must also consider power out-put.
The new Malibu's 3.5 has more power and better gas mileage then Toyota's 3.0.

-T [/QB]

problem is, the Toyota 3.0L v6 is 10+ years old. The comparable GM v6 in 1993 was the (bark, bark) 3.1..... ?

OK, that was tacky... let's move up to the GM 3.8L...~20% larger displacement (than the TMC 3.0) and and STILL less HP.....

how many ways can you spell dog???

fast forward to something not 10 years old...

The Toyota 3.0L has been replaced by a 3.3L v6. Which STILL puts out more power (225hp/240#) than the Malibu's "new" 3.5L (200/220#).

and... is still smaller....
 
Toyota had a 3.0 back in 93? I'm pretty sure it was a 2.5 back then. The 3.5 isn't exactly cutting edge either. Simply a freshened and enlargened 3.1. Sounds a lot like the Toyota V6 to me.

-T
 
quote:

Originally posted by T-Keith:
Toyota had a 3.0 back in 93? I'm pretty sure it was a 2.5 back then. The 3.5 isn't exactly cutting edge either. Simply a freshened and enlargened 3.1. Sounds a lot like the Toyota V6 to me.

-T


no.....the 2.5L v6 (156 hp, btw) was last used in the Camry and Lexus 250 in 1991. I had one. A different 2.5L was used in TMC trucks for a awhile longer, I'm not sure what was different about it but it wouldn't swap when my 1st 2.5L spun a rod bearing...

(also: my bad, the 3.0 came in 1992)

Haven't driven the TMC 3.3 yet, probably won't as they have gone to interference valves and wired/cable-less throttle. and the new Camry is way too stuffy for my tastes.

[ December 14, 2004, 05:15 PM: Message edited by: kenw ]
 
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