Maybe pushrods aren't so bad after all... :)
07-04-04, 03:33 AM
#1
Super Snuggles
Thread Starter
Maybe pushrods aren't so bad after all... :)
From an interview in Car and Driver magazine:
"A pushrod is basically a metal tube designed to transfer the reciprocating motion of a valve lifter, riding on the camshaft, to the valve.
I found the pushrod fascinating 20 years ago, back when I was a high-school car geek devouring car magazines. It was about the time the Japanese car invasion began and Detroit started to worry about loss of market share here. In the mid-'80s, Detroit stuck by the pushrod, and nearly every available engine used it. Domestic cars were for the most part, however, mediocre contraptions that allowed foreign automakers to make inroads into the U.S. market. Back then our 10Best Cars competition had five spots for domestics and five for imports. In 1983, the pickings were so slim that the Chevrolet Caprice Classic made the list.
When asked what made Japanese cars better, critics gave a variety of answers, but one stuck in my mind: While the Americans produced crude, underperforming pushrod engines, the Japanese were turning out sophisticated four-cylinder, single- and double-overhead-cam engines with twice the number of valves per cylinder.
The idea of locating the camshafts in the cylinder head was not new, but to a populace still unaware that a 1929 Duesenberg Model J, for example, had double overhead cams and four valves per cylinder, the overhead-cam engine sounded advanced, exotic.
The pushrod was the scapegoat for all that was wrong with Detroit. "No doubt about it. In the '80s, the pushrod was a hated component, a symbol of the uncompetitiveness of the domestic industry," says Sam Winegarden, GM's chief engineer for small-block V-8s.
I called Winegarden because I've always been fascinated by GM's decision to stick with the pushrod when it introduced a new small-block V-8 in 1996.
By the '90s, many domestic four- and six-cylinder pushrod engines had been scuttled in favor of overhead-cam designs. In 1995, Ford axed its venerable pushrod 16-valve V-8 for a V-8 that still had just 16 valves but now ran with a pair of overhead cams.
Keeping the pushrod seemed like yet another example of the General's hanging on to its glory years. But since then, I've come to see that, for a mass-produced V-8 engine, the pushrod layout has more advantages than disadvantages.
"Power is a function of airflow, pure and simple," says Winegarden. "If you're not going to fill the cylinder with valves, why have an overhead cam?"
Although you could design a V-8 engine that uses pushrods to operate four valves per cylinder, the layout lends itself to using just two. Four valves generally have greater total valve area than two, thus creating greater airflow and more power. In the case of the Chevrolet Corvette Z06 and its pushrod two-valves-per-cylinder 405-hp, 5.7-liter V-8, Winegarden says, "We've been able to meet the performance requirements by using more displacement. Two more valves per cylinder would get us another 10 percent in total valve area."
A modern engine is a dizzying array of compromises as designers strive to meet power, cost, reliability, and emissions demands. The Vette V-8 would ultimately have more power if it had four valves per cylinder, but it would lose ground in cost, complexity, and physical size.
"On the Vette, performance density is only beaten by some of the big Ferrari or heavily boosted engines," Winegarden continues. One of the huge advantages of the pushrod V-8 layout is its clever use of space. The camshaft and the pushrods lie in the unused area between the cylinder banks. A DOHC or SOHC V-8 is much wider and a little taller because the camshafts are on top of the cylinder heads.
Enthusiasts often talk about how much power an engine produces as a function of the combined volume of the cylinders (power per liter). But what's often overlooked is the power produced compared with the outside dimensions of a motor.
The small-block is a compact engine. I did some rough measurements of the Z06's V-8, the DOHC V-8 in the Porsche Cayenne S (335 hp, 4.5 liters), and the Northstar V-8 in the Cadillac SRX (320 hp, 4.6 liters). The small-block was about six inches narrower than the Porsche V-8, two inches shorter than the Caddy's V-8, and close in length.
That may not sound like much, but it gives designers more freedom to position the engine for good weight distribution and leaves ample room for suspension and steering components.
Don't forget about the weight advantages. The Vette's engine has one camshaft and a small drive chain that's connected to the crank. A DOHC V-8 has four camshafts and drive gears, beefy heads to hold the shafts, and two long chains. "Our V-8 is a simple and elegant design. It's pretty easy to put together, which helps the reliability, and costs," says Winegarden. He estimates a $400 saving over a DOHC motor. And, of course, with fewer parts comes less weight. (Winegarden says the aluminum small-block is 44 pounds lighter than the Northstar.)
GM also used this architecture for its truck engines. Spreading the tooling and design costs over a large number of vehicles reduced the per-unit engine cost. That's one reason the $52,385 Z06 can compete with sports cars costing twice as much.
So if the pushrod design makes such a good V-8, why does GM make a DOHC V-8 Northstar? "I'm not going to touch that one," laughs Winegarden. GM's party line is that some customers want what it calls "high-feature engines." Winegarden does admit there are some refinement benefits to the DOHC layout, but personally, I don't find the Vette's engine to be a bit unruly.
GM is no longer the pushrod's sole champion. Dodge has reintroduced the pushrod Hemi V-8. And this year, Toyota is running in the NASCAR Craftsman Truck Series with a newly developed pushrod V-8. Of course, that's a motor used only for racing, but is it so far-fetched to wonder if Toyota would make a production pushrod V-8?
Such an engine would be cheaper to build than the complex DOHC V-8 that's now in the Tundra pickup, and Toyota would also realize some marketing benefits from the huge racing investment. The irony is almost too sweet to imagine."
"A pushrod is basically a metal tube designed to transfer the reciprocating motion of a valve lifter, riding on the camshaft, to the valve.
I found the pushrod fascinating 20 years ago, back when I was a high-school car geek devouring car magazines. It was about the time the Japanese car invasion began and Detroit started to worry about loss of market share here. In the mid-'80s, Detroit stuck by the pushrod, and nearly every available engine used it. Domestic cars were for the most part, however, mediocre contraptions that allowed foreign automakers to make inroads into the U.S. market. Back then our 10Best Cars competition had five spots for domestics and five for imports. In 1983, the pickings were so slim that the Chevrolet Caprice Classic made the list.
When asked what made Japanese cars better, critics gave a variety of answers, but one stuck in my mind: While the Americans produced crude, underperforming pushrod engines, the Japanese were turning out sophisticated four-cylinder, single- and double-overhead-cam engines with twice the number of valves per cylinder.
The idea of locating the camshafts in the cylinder head was not new, but to a populace still unaware that a 1929 Duesenberg Model J, for example, had double overhead cams and four valves per cylinder, the overhead-cam engine sounded advanced, exotic.
The pushrod was the scapegoat for all that was wrong with Detroit. "No doubt about it. In the '80s, the pushrod was a hated component, a symbol of the uncompetitiveness of the domestic industry," says Sam Winegarden, GM's chief engineer for small-block V-8s.
I called Winegarden because I've always been fascinated by GM's decision to stick with the pushrod when it introduced a new small-block V-8 in 1996.
By the '90s, many domestic four- and six-cylinder pushrod engines had been scuttled in favor of overhead-cam designs. In 1995, Ford axed its venerable pushrod 16-valve V-8 for a V-8 that still had just 16 valves but now ran with a pair of overhead cams.
Keeping the pushrod seemed like yet another example of the General's hanging on to its glory years. But since then, I've come to see that, for a mass-produced V-8 engine, the pushrod layout has more advantages than disadvantages.
"Power is a function of airflow, pure and simple," says Winegarden. "If you're not going to fill the cylinder with valves, why have an overhead cam?"
Although you could design a V-8 engine that uses pushrods to operate four valves per cylinder, the layout lends itself to using just two. Four valves generally have greater total valve area than two, thus creating greater airflow and more power. In the case of the Chevrolet Corvette Z06 and its pushrod two-valves-per-cylinder 405-hp, 5.7-liter V-8, Winegarden says, "We've been able to meet the performance requirements by using more displacement. Two more valves per cylinder would get us another 10 percent in total valve area."
A modern engine is a dizzying array of compromises as designers strive to meet power, cost, reliability, and emissions demands. The Vette V-8 would ultimately have more power if it had four valves per cylinder, but it would lose ground in cost, complexity, and physical size.
"On the Vette, performance density is only beaten by some of the big Ferrari or heavily boosted engines," Winegarden continues. One of the huge advantages of the pushrod V-8 layout is its clever use of space. The camshaft and the pushrods lie in the unused area between the cylinder banks. A DOHC or SOHC V-8 is much wider and a little taller because the camshafts are on top of the cylinder heads.
Enthusiasts often talk about how much power an engine produces as a function of the combined volume of the cylinders (power per liter). But what's often overlooked is the power produced compared with the outside dimensions of a motor.
The small-block is a compact engine. I did some rough measurements of the Z06's V-8, the DOHC V-8 in the Porsche Cayenne S (335 hp, 4.5 liters), and the Northstar V-8 in the Cadillac SRX (320 hp, 4.6 liters). The small-block was about six inches narrower than the Porsche V-8, two inches shorter than the Caddy's V-8, and close in length.
That may not sound like much, but it gives designers more freedom to position the engine for good weight distribution and leaves ample room for suspension and steering components.
Don't forget about the weight advantages. The Vette's engine has one camshaft and a small drive chain that's connected to the crank. A DOHC V-8 has four camshafts and drive gears, beefy heads to hold the shafts, and two long chains. "Our V-8 is a simple and elegant design. It's pretty easy to put together, which helps the reliability, and costs," says Winegarden. He estimates a $400 saving over a DOHC motor. And, of course, with fewer parts comes less weight. (Winegarden says the aluminum small-block is 44 pounds lighter than the Northstar.)
GM also used this architecture for its truck engines. Spreading the tooling and design costs over a large number of vehicles reduced the per-unit engine cost. That's one reason the $52,385 Z06 can compete with sports cars costing twice as much.
So if the pushrod design makes such a good V-8, why does GM make a DOHC V-8 Northstar? "I'm not going to touch that one," laughs Winegarden. GM's party line is that some customers want what it calls "high-feature engines." Winegarden does admit there are some refinement benefits to the DOHC layout, but personally, I don't find the Vette's engine to be a bit unruly.
GM is no longer the pushrod's sole champion. Dodge has reintroduced the pushrod Hemi V-8. And this year, Toyota is running in the NASCAR Craftsman Truck Series with a newly developed pushrod V-8. Of course, that's a motor used only for racing, but is it so far-fetched to wonder if Toyota would make a production pushrod V-8?
Such an engine would be cheaper to build than the complex DOHC V-8 that's now in the Tundra pickup, and Toyota would also realize some marketing benefits from the huge racing investment. The irony is almost too sweet to imagine."
07-08-04, 11:56 AM
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I read that in the magazine and thought "what a pethetic attempt to try and make themselves feel better about a low tech engine" The only true advantage is space. Who here wan'ts to compromise performance for a little space. Not me.
I can stand the clanky sound of a push rod engine at high rpm.
Don't worry in a month or so I am sure they will write an artical explaining how the push rod engine must die. Car and driver flip flop all the time. I have been subscribing to that car magazine for more years than I can remember.
Oh they also praise the rotary even though they say "it has low torque and guzzles gas".
Brock yates drives a duelly pickup. Patrick Bedard is more interested in MPG than performance. Don't put too much faith in car mags.
I can stand the clanky sound of a push rod engine at high rpm.
Don't worry in a month or so I am sure they will write an artical explaining how the push rod engine must die. Car and driver flip flop all the time. I have been subscribing to that car magazine for more years than I can remember.
Oh they also praise the rotary even though they say "it has low torque and guzzles gas".
Brock yates drives a duelly pickup. Patrick Bedard is more interested in MPG than performance. Don't put too much faith in car mags.
07-08-04, 01:23 PM
#4
Super Snuggles
Thread Starter
Originally posted by Thaniel
I read that in the magazine and thought "what a pethetic attempt to try and make themselves feel better about a low tech engine" The only true advantage is space. Who here wan'ts to compromise performance for a little space. Not me.
I read that in the magazine and thought "what a pethetic attempt to try and make themselves feel better about a low tech engine" The only true advantage is space. Who here wan'ts to compromise performance for a little space. Not me.
You may have read the article, but it's obvious you didn't understand what you read. You simply have a bias against pushrod engines that you can't back up with anything more articulate than "low tech". Welcome to the club.
07-08-04, 01:45 PM
#5
Lives on the Forum
Originally posted by jimlab
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
See here
07-09-04, 11:53 AM
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Originally posted by jimlab
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
You may have read the article, but it's obvious you didn't understand what you read. You simply have a bias against pushrod engines that you can't back up with anything more articulate than "low tech". Welcome to the club.
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
You may have read the article, but it's obvious you didn't understand what you read. You simply have a bias against pushrod engines that you can't back up with anything more articulate than "low tech". Welcome to the club.
The reason the Author in Car and driver praises it now is for it's compactness. This is a valid point but not one I am really concerned about. The compactness does make the V-8's fit under rx-7's hoods and thats why they are popoular engines to swap in to rx-7's and other cars.
The argument for pushrod engines is so similar to that of people claiming the rotary engine is the best ever and nothing with pistons can be any good.
If you want an engine with a basic design that dates back to the dark ages that's your choice. I'm not saying it won't put out gobs of power etc... Nascar -> low tech, F1 -> high tech.
Personally I'll take the DOHC with variable valve control anyday
07-09-04, 01:49 PM
#7
Super Snuggles
Thread Starter
Originally posted by Thaniel
Well I could dig up all the articals about how the push rod engines are low tech but you obviously don't want to see them. There are MANY. Funny how ONE artical is written praising it and its paraded around.
Well I could dig up all the articals about how the push rod engines are low tech but you obviously don't want to see them. There are MANY. Funny how ONE artical is written praising it and its paraded around.
I'm well aware that it's old tech. That doesn't mean that it doesn't work perfectly well.
The argument for pushrod engines is so similar to that of people claiming the rotary engine is the best ever and nothing with pistons can be any good.
Personally I'll take the DOHC with variable valve control anyday
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07-10-04, 12:21 PM
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Originally posted by Thaniel
If you want an engine with a basic design that dates back to the dark ages that's your choice. I'm not saying it won't put out gobs of power etc... Nascar -> low tech, F1 -> high tech.
If you want an engine with a basic design that dates back to the dark ages that's your choice. I'm not saying it won't put out gobs of power etc... Nascar -> low tech, F1 -> high tech.
You are making some truly ignorant statements. Your *only* justification for bashing a pushrod motor is that it is 'low tech.' That term is meaningless. Would you care to give us your definition of 'low tech'? Why not look at the attributes of the motors such as hp:weight ratio, mpg, power delivery, reliability, maintainability, cost, size, etc, and do a meaningful comparison?
Last edited by paw140; 07-10-04 at 12:24 PM.
07-10-04, 06:55 PM
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i dont see how anyone can criticise the LSx series, it is one of the best, lightest, most effiecient v8's every made
that is uses low-tech isnt a copout, it just goes to show you that the most complex way isnt the best most of the time
LSx's philosophy is Keep It Simple Stupid, and damn it does it well
that is uses low-tech isnt a copout, it just goes to show you that the most complex way isnt the best most of the time
LSx's philosophy is Keep It Simple Stupid, and damn it does it well
07-10-04, 08:54 PM
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Originally posted by wwilliam54
i dont see how anyone can criticise the LSx series, it is one of the best, lightest, most effiecient v8's every made
that is uses low-tech isnt a copout, it just goes to show you that the most complex way isnt the best most of the time
LSx's philosophy is Keep It Simple Stupid, and damn it does it well
i dont see how anyone can criticise the LSx series, it is one of the best, lightest, most effiecient v8's every made
that is uses low-tech isnt a copout, it just goes to show you that the most complex way isnt the best most of the time
LSx's philosophy is Keep It Simple Stupid, and damn it does it well
07-10-04, 09:30 PM
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Originally posted by paw140
I totally agree. GM puts out some world class motors (at least their v8's). Too bad I can't say the same thing about their cars.
I totally agree. GM puts out some world class motors (at least their v8's). Too bad I can't say the same thing about their cars.
too bad the cars they put the engines in almost universally suck alot of ***
07-11-04, 05:11 PM
#12
Old [Sch|F]ool
What is interesting is that most of these "I want a high tech DOHC engine" people don't realize that OHC and OHC are older than pushrod designs.
07-12-04, 11:18 AM
#13
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Originally posted by paw140
Just because something is old technology doesn't necessarily make it ineffective and outdated.
Just because something is old technology doesn't necessarily make it ineffective and outdated.
07-12-04, 07:33 PM
#14
Old [Sch|F]ool
How many people who whine about "no tech" get all excited over sports. You know, running, throwing a ball, hitting a ball, catching a ball... about as low tech as you can get. 
(Yes I know there are some really high tech things they are doing with these no-techy sports... but that is my point. There is probably more high-tech goodness in a sliver of LT1 or LS1 than there is in 90% of the DOHC crap on the market... and they can DO that because pushrod engines are cheaper to produce)
(Yes I know there are some really high tech things they are doing with these no-techy sports... but that is my point. There is probably more high-tech goodness in a sliver of LT1 or LS1 than there is in 90% of the DOHC crap on the market... and they can DO that because pushrod engines are cheaper to produce)
07-12-04, 09:36 PM
#15
Originally posted by jimlab
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
You may have read the article, but it's obvious you didn't understand what you read. You simply have a bias against pushrod engines that you can't back up with anything more articulate than "low tech". Welcome to the club.
GM's pushrod LS1/LS6 performs at the same level as the competition's supercharged OHC engine and is far smaller and lighter. How is that a compromise in performance?
You may have read the article, but it's obvious you didn't understand what you read. You simply have a bias against pushrod engines that you can't back up with anything more articulate than "low tech". Welcome to the club.
The motor ran so well and ripped up the road even in a less aerodynaic heavier C4 chassis. And didnt even have the benefit of todays engine management. 10 years later the vette isnt making more power or going faster after reverting back to pushrods.
I loved the LT5. Motor made great power all through the RPM range. It destroyed everything in its Era.
Just think what the LT5 could do in a C5 chassis with todays electronics and some more innovations.
07-12-04, 10:25 PM
#16
Super Snuggles
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Originally posted by ZoomZoom
LT5.
LT5.
Just think what the LT5 could do in a C5 chassis with todays electronics and some more innovations.
07-13-04, 12:07 AM
#17
Old [Sch|F]ool
The LT5 was an amazing pile of junk. It was incredibly expensive, nearly doubling the cost of the car. The Z06's LS6 does not double the cost of the car. Fuel economy wasn't as good, it was very complex (see the $ above), it was bulky, it was heavy.
But it had DOHC so lots of weenies bought it. Well, they bought it the first year... production tapered way off after the first two years. Like from a few thousand to barely in the triple digits.
Engine management? GM's engine management hasn't changed much since the 80's. Modern ECUs have flash-programmable chips and the added complexity of OBD-II, but the main algorithms are still in use.
The LT1 and LS-engines have very high tech combustion chambers. How do you think they're running 11:1 on modern pisswater, with a factory warranty (bear in mind the OEM's have to think about things like morons driving WOT on bad gas up a long desert grade in August with the car fully loaded, stereo cranked up to ignore the detonation) How do you think people find they can get MPG in the high 20's and low 30's, even in the automatic-equipped cars that don't have a stupid tall overdrive? Hmm? Hell most "high tech" sport compacts with less weight and vastly smaller engines can't do that.
But it had DOHC so lots of weenies bought it. Well, they bought it the first year... production tapered way off after the first two years. Like from a few thousand to barely in the triple digits.
Engine management? GM's engine management hasn't changed much since the 80's. Modern ECUs have flash-programmable chips and the added complexity of OBD-II, but the main algorithms are still in use.
The LT1 and LS-engines have very high tech combustion chambers. How do you think they're running 11:1 on modern pisswater, with a factory warranty (bear in mind the OEM's have to think about things like morons driving WOT on bad gas up a long desert grade in August with the car fully loaded, stereo cranked up to ignore the detonation) How do you think people find they can get MPG in the high 20's and low 30's, even in the automatic-equipped cars that don't have a stupid tall overdrive? Hmm? Hell most "high tech" sport compacts with less weight and vastly smaller engines can't do that.
07-18-04, 05:41 PM
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lt5 does sound cool though. i personally don't like the sound of pushrod motors, but that's my only issue. and all this talk about airflow is hilarious.
yes a large bore will flow a crap load of air through small ports, but only for so long. that's why the redline is low. (one reason anyway) If they managed to make a decent sized dohc V8 with a 2/4 valve setup that would be nice. you can keep the velocity (and gain some swirl) by using 2 valves at lower rpm and then (much like vtec, sadly) kick the other two valves on past say 5K you could have a torquey high revving motor. wouldn't that just settle everyone hash?
yes a large bore will flow a crap load of air through small ports, but only for so long. that's why the redline is low. (one reason anyway) If they managed to make a decent sized dohc V8 with a 2/4 valve setup that would be nice. you can keep the velocity (and gain some swirl) by using 2 valves at lower rpm and then (much like vtec, sadly) kick the other two valves on past say 5K you could have a torquey high revving motor. wouldn't that just settle everyone hash?
07-18-04, 06:22 PM
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Pushrods are there to make raw horsepower and massive torque numbers, while an OHC engine will make good HP numbers I don't believe that it would make as much torque as a pushrod will. I don't look at a pushrod as a "low-tech" motor, I just see it as the manufacturer choosing not to change anything if its doing what they want and still making good numbers with no ill-effects. Yes a OHC will produce less pollution than a pushrod which I see it as why companies are choosing to go this route recently. For examlpe the new 2005 mustangs are now being made with 3 valves per cylinder and now produce less pollution than before. Whether it is .1 % less or 50% less its still producing less pollution than before. I believe that would be the companies "reason" for changing or adding valves or set-ups.
07-18-04, 07:01 PM
#20
Super Snuggles
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Originally Posted by RX7SpiritR
Pushrods are there to make raw horsepower and massive torque numbers, while an OHC engine will make good HP numbers I don't believe that it would make as much torque as a pushrod will.[/B]
I don't look at a pushrod as a "low-tech" motor, I just see it as the manufacturer choosing not to change anything if its doing what they want and still making good numbers with no ill-effects.
Yes a OHC will produce less pollution than a pushrod which I see it as why companies are choosing to go this route recently.
For examlpe the new 2005 mustangs are now being made with 3 valves per cylinder and now produce less pollution than before.
Whether it is .1 % less or 50% less its still producing less pollution than before. I believe that would be the companies "reason" for changing or adding valves or set-ups.
1) By actuating the valve directly with the lobes of the cam, you eliminate the need for lifters. Hydraulic lifters can collapse or pump-up at high rpm, causing damage to the valvetrain. The solution is to run solid lifters, but they typically require much more frequent maintenance. Overhead cam engines don't have either, so there's no maintenance and rpm is limited more by the airflow capacity of the head itself than by a mechanical limitation of the valvetrain.
2) The problem with running 2 large valves in a small bore engine is that the valves will be shrouded (too close to the edges of the cylinder to allow ideal airflow) and therefore there is a limit to the size of valves you can use. You can align the valves at different angles to get larger valves in the head, but the fact remains that you're limited by the diameter of the bore. A multi-valve head, on the other hand, can make better use of the available space with multiple smaller valves. This reduces shrouding of the valves, increases overall valve area (and therefore airflow potential), and reduces the weight of the individual valves, among other things. Lighter valves require less spring to control their movement, and the overhead cams eliminate the difficulty of reliably actuating multiple valves from a centrally located camshaft.
07-19-04, 05:17 AM
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BTW the ford 3-vavle-per setup is a SOHC system that is mainly desighned to get around the higher cost of DOHC setups
at least that what i got out of the ford pamplet i saw 2 years ago
at least that what i got out of the ford pamplet i saw 2 years ago
07-19-04, 06:43 PM
#22
Old [Sch|F]ool
Originally Posted by jimlab
There are two major reasons to go with overhead cams.
1) By actuating the valve directly with the lobes of the cam, you eliminate the need for lifters. Hydraulic lifters can collapse or pump-up at high rpm, causing damage to the valvetrain. The solution is to run solid lifters, but they typically require much more frequent maintenance. Overhead cam engines don't have either, so there's no maintenance and rpm is limited more by the airflow capacity of the head itself than by a mechanical limitation of the valvetrain.
1) By actuating the valve directly with the lobes of the cam, you eliminate the need for lifters. Hydraulic lifters can collapse or pump-up at high rpm, causing damage to the valvetrain. The solution is to run solid lifters, but they typically require much more frequent maintenance. Overhead cam engines don't have either, so there's no maintenance and rpm is limited more by the airflow capacity of the head itself than by a mechanical limitation of the valvetrain.
Weirdest HLA experience I've ever had was after I did an oil change on a Subaru powered by their new six. You know, the one that is only an inch or so longer than their four-popper. I thought it was weird sounding enough when I brought it in (what's this, a Subaru that doesn't sound like a pissed-off Chihuahua?) but when I started it up I heard a loud BZZZZZZZZZ. Oh ****! Shut down, make sure I put those belts back on properly and didn't leave a wrench down in there. Nope, everything looks fine.... start it up. BZZZZZZZZZ. Sounds exactly like something caught in a fan blade. Then... the oil filter finally fills up, we get oil pressure, and the noise goes away.
Normally they clatter like an old Honda. Never heard HLA's that sounded like someone left a wrench in the fan shround....
07-23-04, 06:25 PM
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Originally Posted by jimlab
Untrue. Again, this has nothing to do with the manner in which the valves are actuated. It's a matter of valve timing.
but good job for informing the Pushrods=evil crowd.
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