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Old 01-22-2004, 09:02 PM   #31
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Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by calgary_redneck
I believe alot of companies are running with the concept at the moment I know for sure gm is working on it and plans to have some engines using it in the not to distant future how ever it will require going to a higher voltage electrical systems for sure to supply the soliniods that will be used to open the valves
assuming you use electric solenoids to open the valves... that's not the only option for a "camless" engine. You can also use lower-power solenoids if you pressure balance the valve, or use a force multiplier of some sort (hydraulic, pneumatic, etc).

I say "blame canada!"
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Old 01-23-2004, 10:20 AM   #32
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Re: Pushrod vs. SOHC vs. DOHC

f1 uses pneumatic valves with success.
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Old 01-23-2004, 11:14 AM   #33
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Re: Re: Pushrod vs. SOHC vs. DOHC

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Originally Posted by MustangRoadRacer
f1 uses pneumatic valves with success.
As has been pointed out to you, F1 engines still use cams to open valves and a pneumatic system to close them.
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Old 01-24-2004, 01:59 PM   #34
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Re: Pushrod vs. SOHC vs. DOHC

wow ivy mike that was inteligent
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Old 01-24-2004, 06:47 PM   #35
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Re: Re: Pushrod vs. SOHC vs. DOHC

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Originally Posted by calgary_redneck
wow ivy mike that was inteligent
Somehow, that doesn't sound like a compliment.
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Old 01-25-2004, 08:27 PM   #36
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Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by beef_bourito
What are the advantages and disadvantages, performance wise, of Pushrod engines vs SOHC and DOHC engines? Also what are easier to maintain?
valve actuation does not really have much bearing on power output as racing has shown.

however, if you need a small engine to make the hp of a large engine, you need to force feed it, OR increase the RPMs. when you increase rpms, xOHC designs allow more consistent valve actuation at higher rpms (chevy 350s run over 9000rpm in nascar so pushrods can move quickly)

the problem with xOHC designs is the increased size, noise and rotational moment of the moment.

For example, a SOHC 4.6 or 5.4 ford engine, is larger than the IH 444 block diesel. Kinda interferes with aerodynamic body designs.

Plus, take a cam for a V8, has 5 bearings to oil. The same v8, if only a SOHC has 10, if dOHC it has 20. This means increased demand on the oiling system to deliver high pressure oil to the very top of the motor - not an easy feat. (the most common failure of xOHC motors is in fact damage due to top end oil starvation)

Also, OHV motors are usually chain driven for the cam, nice and quiet and reliable - chains RARELY break. xOHC designs use external belts, which break often if not changed often and add a lot of noise.

Lastly, you now have cams and pulleys rotating at the outer extremes of the motor, making it a bear to hold still in the engine bay.

So, xOHC engines have advantages, but they have disadvantages.
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Old 01-25-2004, 11:18 PM   #37
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Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by quaddriver
Also, OHV motors are usually chain driven for the cam, nice and quiet and reliable - chains RARELY break. xOHC designs use external belts, which break often if not changed often and add a lot of noise.
Changed often? As in once every 5-7 years? And who ever told you that chains were quieter than belts?
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Old 01-26-2004, 10:07 AM   #38
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Re: Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by ivymike1031
Changed often? As in once every 5-7 years?
well the average american drives appx 15K miles a year, making each change on average every 4 years, and, the average american trades in his car at appx 58K miles so if the impending large labor bill was one of the reasons why he traded the car, the next buyer has a nice surprise to add to his total.

Quote:
And who ever told you that chains were quieter than belts?
My ears. An oiled chain buried inside the motor is far quieter than a kevlar reinforced rubber belt with cogs no less running on at least 2 pulleys behind a thin plastic cover.
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Old 01-26-2004, 11:02 AM   #39
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Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by quaddriver
well the average american drives appx 15K miles a year, making each change on average every 4 years, and, the average american trades in his car at appx 58K miles so if the impending large labor bill was one of the reasons why he traded the car, the next buyer has a nice surprise to add to his total.
Why change the belt at 60k, when the mfr likely recommends 90k-120k miles, or 7 years (whichever comes sooner)?

Quote:
Originally Posted by quaddriver
My ears. An oiled chain buried inside the motor is far quieter than a kevlar reinforced rubber belt with cogs no less running on at least 2 pulleys behind a thin plastic cover.
Well measurements don't support what your ears are telling you, except in very special circumstances (where someone went to a great deal of trouble to make a particularly quiet chain and a noise-attenuating cover to go over it).

some info on the subject:
http://www.hse.gov.uk/pubns/top10noise.pdf
"Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of timing belts available, there are also quiet designs that use different tooth profiles to minimise noise. There is also a very new design of belt for applications where noise is critical which
uses a chevron tooth pattern to provide very quiet running. Noise reductions in the range of 6 - 20 dB are often possible using this approach."

http://www.me.ic.ac.uk/dynamics/stru...cona2000_2.pdf
"Even if timing belts are generally considered as silent transmissions, when compared to mechanical chains, nevertheless a large interest is devoted to further enhancement of the vibrational behaviour under operating conditions."

http://www.babcox.com/editorial/us/us70343.htm
"Play in a gear or chain style cam drive can cause noise, retarded valve timing and/or ignition timing depending on the engine design and application. With rubber timing belts, noise is seldom a problem even at high mileages. Valve timing and ignition timing (if it reads off the camshaft) also remain steady because timing belts donít stretch."

http://www.powertransmission.com/fea...cdrivenews.htm
"The Browning HPT synchronous drive line from Emerson EPT combines the timing action of gears with the speed and noise level of belts. "
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Old 01-26-2004, 11:53 AM   #40
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Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by ivymike1031
Why change the belt at 60k, when the mfr likely recommends 90k-120k miles, or 7 years (whichever comes sooner)?



Well measurements don't support what your ears are telling you, except in very special circumstances (where someone went to a great deal of trouble to make a particularly quiet chain and a noise-attenuating cover to go over it).

some info on the subject:
http://www.hse.gov.uk/pubns/top10noise.pdf
"Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of timing belts available, there are also quiet designs that use different tooth profiles to minimise noise. There is also a very new design of belt for applications where noise is critical which
uses a chevron tooth pattern to provide very quiet running. Noise reductions in the range of 6 - 20 dB are often possible using this approach."

http://www.me.ic.ac.uk/dynamics/stru...cona2000_2.pdf
"Even if timing belts are generally considered as silent transmissions, when compared to mechanical chains, nevertheless a large interest is devoted to further enhancement of the vibrational behaviour under operating conditions."

http://www.babcox.com/editorial/us/us70343.htm
"Play in a gear or chain style cam drive can cause noise, retarded valve timing and/or ignition timing depending on the engine design and application. With rubber timing belts, noise is seldom a problem even at high mileages. Valve timing and ignition timing (if it reads off the camshaft) also remain steady because timing belts donít stretch."

http://www.powertransmission.com/fea...cdrivenews.htm
"The Browning HPT synchronous drive line from Emerson EPT combines the timing action of gears with the speed and noise level of belts. "
well if we beleive stats, honda and toyota are the most popular cars sold in the USA, and they recommend 60K...so....at any rate it does not matter. A belt needs changed. Period. A chain does not until end of engine life - period.

and I notice not one of the links was from an auto manu or testing magazine (like cd, rt, MT, aw, SC, ff, mm &c) who actually measure noise with a meter and report coincidently the same findings I do ;-)

PS - I defy you to stand outside a GM 3800 and find ANY xOHC engine that makes less noise. I stand on my position. You are free to argue the minority position as long as you desire.
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Old 01-26-2004, 01:08 PM   #41
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Re: Pushrod vs. SOHC vs. DOHC

yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time. On an interferance engine as many ohc's are this results in at least a few bent valves.
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Old 01-26-2004, 01:09 PM   #42
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Re: Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC

Chains are used in both push rod and OHC engines (BMW and Saab are examples on the latter). Chains tend to make more noise, especially when they become worn. (basic engineering)

Many high revving motorcycles use chains for the cams, but at high performance applications gears are common. This introduces however more noise.

The service interval on belts have become a lot better lately, 60k is very low. But the cost of a belt is low and many people can do it theirself if they want (not that much more complex than to change waterpump/generator/servopump/AC belt). A chain lasts longer, but not until the end of engine life (unless you have a low quality engine), and it's more expensive to change.

Both chains and belts are stretched somewhat during their life.

Both push rod and OHC engines need oil to the top of the motor, escecially with high performance engines when valve spring cooling is important.

The difference in size of a push rod and DOHC engine is very small, the increase in performance more than compensate for this.

The largest valvetrain problem is probably hydraulic lifters, which can cause wear of too high pressure against the cam or start to leak and the cam to lifter clearance till be off.
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Old 01-26-2004, 02:34 PM   #43
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Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by calgary_redneck
yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time. On an interferance engine as many ohc's are this results in at least a few bent valves.
What recommendations are you guys referring to? I have a Honda service manual in front of me right now, for 1996-2000 Civics, all models, recommending timing belt replacement at 105,000 miles for severe service, excluding where outdoor temps are frequently in excess of 110degF or colder than -20degF, in which case they say 60,000 miles.

Quote:
Originally Posted by quaddriver
I notice not one of the links was from an auto manu or testing magazine (like cd, rt, MT, aw, SC, ff, mm &c) who actually measure noise with a meter and report coincidently the same findings I do
I notice that you don't have any such findings to show us either. Not that I'd be impressed with NVH results measured by people working for a magazine - these people are english majors first, mechanics second, engineers "not at all," remember? NVH measurement is difficult to do right in a proper lab setting, let alone in some backyard dyno.

If the GM 3800 is your "gold standard" of engine refinement, then I know what sort of person I'm speaking to, and that it's pointless to continue this discussion of automotive technology...

I leave it to you to pursue an education in automotive design; it's not my job or desire to educate you (nor am I confident that it would be possible).
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Old 01-26-2004, 02:37 PM   #44
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Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by calgary_redneck
yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time. On an interferance engine as many ohc's are this results in at least a few bent valves.

90k miles is the recommended timing belt change for every Honda I've seen in the US. And I have never heard of one breaking before 90k unless someone went and screwed with it, the gears or the cover at an earlier point.


Quote:
Originally Posted by SaabJohan
The difference in size of a push rod and DOHC engine is very small, the increase in performance more than compensate for this.
While some manufacturers are getting better at making DOHC heads short, there is a very sizeable difference between your typical V configured engine in cam-in-block vs. OHC design. Though you are definitely correct that for basically any application the OHC has enough basic airflow advantage to compensate for this.
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Old 01-26-2004, 04:30 PM   #45
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Re: Re: Re: Pushrod vs. SOHC vs. DOHC

Quote:
Originally Posted by ivymike1031
What recommendations are you guys referring to? I have a Honda service manual in front of me right now, for 1996-2000 Civics, all models, recommending timing belt replacement at 105,000 miles for severe service, excluding where outdoor temps are frequently in excess of 110degF or colder than -20degF, in which case they say 60,000 miles.
In other words, as I said, Honda recommends a 60K interval. At least you now admit that. Sidebar: what interval does ANY manufacturer recommend for a chain driven cam? Whats that? We could not hear you say the word 'None' clearly.

Score: xOHC motors have cam driving mechanisms that require inspection, service and replacement on a frequent basis over the life of the car. OHV motors have cam driving mechanisms that require nothing and last the life of motor. Advantage OHV as originally stated.


Quote:
Originally Posted by ivymike1031
I notice that you don't have any such findings to show us either. Not that I'd be impressed with NVH results measured by people working for a magazine - these people are english majors first, mechanics second, engineers "not at all," remember? NVH measurement is difficult to do right in a proper lab setting, let alone in some backyard dyno.
Well, managing editor of C&D Csaba Csere has an engineering degree which is more than you do, and he himself has conducted such tests AND he has an online presence - feel free to contact him and inform him how useless his findings are. Its not all that hard to measure the noise output from the engine bay at any RPM. Why, I even hear the measuring devices are simple enough be used by high school students such as yourself! Aint modern progress grand?

Quote:
Originally Posted by ivymike1031
If the GM 3800 is your "gold standard" of engine refinement,
Actually, its the SAE who has named the 3800 from GM 'best', criteria being a number of factors not limited to power output, economy, emissions, reliability, noise, smoothness, service ease, and so forth. Please note, in the last few years it has supplanted even the SBC. An astute reader will notice a certain 'on topic commonality' between the two motors.

Quote:
Originally Posted by ivymike1031
then I know what sort of person I'm speaking to,
Hmm, forgive but Im not all that confident that you are all that intuitive, or even all that bright...

Quote:
Originally Posted by ivymike1031
and that it's pointless to continue this discussion of automotive technology...
Especially when you are not contributing any....

Quote:
Originally Posted by ivymike1031
I leave it to you to pursue an education in automotive design;
You are so funny mikey....you want me to do what you have not...but suffice to say, I am satisfied with my college education and degrees earned. I think I'll stand pat...however, when you do graduate high school, I highly recommend a college education if you can swing it. Very beneficial.

Quote:
Originally Posted by ivymike1031
it's not my job or desire to educate you (nor am I confident that it would be possible).
Perhaps the most accurate thing you have said to date in all of your posts...we (the reading public) agree, it would not be possible for you to educate myself, or anyone else reading here for that matter.

btw - that fact that you do have a chilton book for your car is admirable, many people fly blind. But please tell us you didnt 'rice it out', take if from someone much older and more experienced: it does NOT look cool that way.
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