alternative to replacing cam to gain greater lift duration?

[bldeagle10]

just a random thought i had, why must you buy a whole new camshaft to obtain a different lift duration. why can't you just buy custom length push rods that would offer the same lift changes? it's easy to get the custom pushrods and it seems like that would be a more economical option for a budget. say you want to go from .500" of lift to .600" of lift you just buy a rod thats .100" longer. obviously that was just a crude example...

is there some factor im not seeing as to why this would not work? please do be very specific with your responses, im pretty mechanically inclined

 

[5-90]

just a random thought i had, why must you buy a whole new camshaft to obtain a different lift duration. why can't you just buy custom length push rods that would offer the same lift changes? it's easy to get the custom pushrods and it seems like that would be a more economical option for a budget. say you want to go from .500" of lift to .600" of lift you just buy a rod thats .100" longer. obviously that was just a crude example...

is there some factor im not seeing as to why this would not work? please do be very specific with your responses, im pretty mechanically inclined

Because you then end up with the valve never closing - it ends up being ~0.100" off of the seat when it's supposed to be closed (or whatever you added to the pushrod, less a pinch for the hydraulic adjustment that doesn't work anymore.)

Pretty much the best way to give yourself more "duration" (as expressed in "valve open area," vice degrees of time the valve is off the seat) is by converting from a flat tappet cam to a roller-foot tappet cam.

Why? It's simple geometry - you're dealing with the tangent between the cam lobe and a circle of ~36" radius for the flat tappet, and the tangent between the cam lobe and a circle of about 0.450" radius for the roller tappet. This allows a more aggressive ramp on the cam lobe without mechanical interference (we're dealing with increasing the "area under the curve" instead of increasing the mere length of the curve. You end up with a bell curve that has much more pronounced slope for the opening and closing ramps and a less definite "peak" as opposed to the flat tappet cam.)

Work is apace (by Bosch, I believe) to go to a solenoid-operated valve. This would eliminate the camshaft entirely (making it easier to tun valve timing events for various RPM ranges,) and results in near-total elimination of the opening and closing ramps (making them effectively vertical, rather than merely sharply sloped.) I do not know how well this work has progressed.

The Coates Spherical Rotary Valve also has merit (q.v.) but it suffers from the difficult of having to change the entire valve assembly to effect a change in valve event timing (however, is sharply reduces the need for lubrication in the top end of the head, and effectively eliminates the "hot spotting" of the valve and seats - which has its own merits from the standpoints of engine efficiency and emissions control.)

 

[bldeagle10]

thank you for that explination, makes alot of sense now, the solenoid operated valves i thought were already in use on high reving motors like F1 cars? if they got that into a production car we could have alot of fun with our cars, i love push rods but with a quick tune you could have a lopey idle or something more sharp. the revs could be cleaner and faster. and you could program a variable valve timing set up where at different rpms you could set the durations for optimal performance. interesting...

 

[5-90]

Forgot to mention - there's also some effect to be had from changing the rocker arm ratio. Typical ratios (not available for all engines) are 1.5, 1.6, or 1.7 (I think you can also find 1.55 or 1.65 - anything else you'd have to have designed and purpose-built.)

This won't change the valve action profile (opening/closing ramp, valve timing,) but it does change the amount of valve opening. The cam lift is typically multiplied by the rocker arm ratio to get valve lift, for cam-in-block engines (some OHC engines don't have rocker ratios - they go straight 1:1. However, there are some OHC engines with rocker - "follower" - ratios in play. We'll leave those aside for the moment.

GIVEN: Camshaft lobe lift is .300" at the lobe nose (max lift.)

With a rocker ratio of 1.5:1 (1.5,) you have an effective valve lift of .300"x1.5, or .450" at the valve.

With a rocker ratio of 1.6:1 (1.6,) you have an effective valve lift of .300"x1.6, or .480" at the valve.

With a rocker ratio of 1.7:1 (1.7,) you have an effective valve liftof .300"x1.7, or .510" at the valve.

Note that the camshaft remained static the whole time - only the rocker arms were changed.

I should have said earlier - I only just thought of it myself.

I believe the OEM rocker ratio for the 6-242 is 1.6:1. Some aftermarket parts are available to get 1.7:1 (again, as I recall) - notably the rollerised rocker arms from Yella Terra. However - rollerised rocker arms typically require installation of a valve cover spacer (they need more room under the cover to operate,) and they aren't very cheap.

Upside? You've also eliminated some parasitic drag losses in putting the bearings in the rocker pivots (vice having two metal parts slipping against each other) - but the installation of rollerised rockers isn't so much a performance mod in and of itself, but is typically done in an effort to maximise the contributions of other mods.

But, if you increase the rocker arm ratio, that does become a performance mod in se, so it's still potentially useful.

I've tried to keep this pretty basic - I could spend literally days on camshaft and valve timing/opening theory - but that does require more theoretical background than you probably have (know anything about fluid dynamics, thermodynamics, or anything like that?) at the moment. I've just been doing this sort of thing long enough that I wasn't happy anymore knowing what would work - I wanted to know why it worked, and that involved a lot of reading over the last twenty years. And I still don't know anywhere near everything about the subject...

 

[bldeagle10]

thank you for that info, that really helped alot. i may not know anything about thermodynamics or fluid dynamics but i can follow all the info you have provided.

 

[5-90]

thank you for that info, that really helped alot. i may not know anything about thermodynamics or fluid dynamics but i can follow all the info you have provided.

Good. When getting into abstruse subjects like this (cam & valve timing theory...) it becomes difficult to know where to stop so I don't lose you entirely.

Believe me, it's very easy to leave someone totally at sea on something like this, and in very short order!

So, if you do have questions, feel free to ask - that's how we learn things, and it gives me an idea how far I can take explanations for you...

 

[O-Gauge Steamer]

Solenoid operating valves are in use on F1 engines. This gives several major advantages, not the least of which is variable valve timing. The teams run multiple engine tune strategies available to the Driver at the flick of a switch. Also... At 18,000rpm, a valve spring will shatter!

It is my belief that we will see this technology on the street once the costs and system longevity issues have been resolved. Racing technology has always made it to the street. Just a matter of time.

 

[5-90]

True.

Forgot to mention earlier - "lift" and "duration" on a camshaft are two different animals entirely.

"Lift" is the difference between the lobe base circle and lobe toe (typically listed at the valve, including rocker ratio, but more properly measured at the cam lobe.)

"Duration" is the time that the valve is off the seat (amount doesn't matter, but an "apples to apples" comparison is typically taken as "duration at 0.050" ") measured in camshaft degrees.

The reason that lift should be measured - and listed - at the camshaft lobe should become obvious after re-reading my second post in this thread (about rocker ratios.)

 

[CherBear]

I always wondered why camshafts havent been replaced with solenoids yet.
It would be like V-tech, but instead of a 2 mode cam, it would be near infinite.

 

[bldeagle10]

well vtec is just variable valve timing and lift electronic control, when you reach the rev you designate the solenoid to actuate (depending on which motor you have we will use a b16a2 as reference) so at about 5400rpm the ecu actuates the solenoid which allows oil pressure to basically lock the rocker arms together and they ride off the more agressive cam lobe which allows for more air intake. with solenoids you wouldnt need to cam at all and you could just program them to offer different amounts of air intake and exhaust release at any rpm you desire, it would take some tuning time to figure out the best set up but in the end you could have a high reving motor that has very consistent power gains with no drop offs. but for reliability of course you would want to limit the revs to 10-13k for performance oriented motors and even less for economy cars, the solenoids i would assume would create less resistance cause the crank isnt turning the cam and pushing valve springs and all that...its a good idea but who knows how long they can get the solenoids to last...and how expensive it would be to replace them...and of course you will get guys out there who will hack into the computer and try and get more revs from their motors and if the motor isnt balanced extremely well they will be blowing up...any ways, thats my little thought process on that situation.

 

[5-90]

I always wondered why camshafts havent been replaced with solenoids yet.
It would be like V-tech, but instead of a 2 mode cam, it would be near infinite.

Partly because the long-term reliability and consistency of operation isn't there yet (think about it - race engines get torn down for inspection & minor overhaul after pretty much every single race...) and partly because there's a lot of customer inertia - particularly here in the States, where there are plenty of people who still remember the fiasco that was the Olds 350ci Diesel (redesigned gasoline engine, instead of purpose-built Diesel. Adapted gasoline control system, instead of purpose-built Diesel. The essential construction details may be similar, but the actual construction and operation are worlds apart...)

After the Olds 350 Diesel blowup, there was the Caddy 4-6-8 mistake - how many of you remember that? (The Chrysler MDS works better than the old Caddy system did, but that's because we have better controls for that sort of thing now.)

Why are Diesels so common in Europe? Because they were done properly from the outset, and didn't have the "converted engine" mistake that we had foisted on us. All of the Diesels over there were designed as Diesels form the outset, so they could make workable small Diesel engines that lasted. Ditto the Japanese - same reasons (the small old Isuzu and Nissan Diesels were excellent! An old Komatsu three-cylinder Diesel would outlast most gasoline engines, and give useful power through the whole service life. The VolksWagen TDi has been swapped into - or at least the swap attempted - probably half of the compact pax & LT platforms out there.)

But, because we've been burned before, it's an awful lot of work to get us to accept anything new. Look how long it took OHC engines to catch on over here (some of us still don't care for them - I'd rather have the cam-in-block setup than OHC, but I'm funny that way...) but they've been commonplace in Europe and Asia for a good 12-15 years longer.

Even with racing proof of technology (recall the old manufacturer's mantra - "Win on Sunday, sell on Monday?") there's still some inertia involved in picking up new technologies in the consumer segment.

The consumer segment (at least the hobbyists and DIY-ers) are probably still reeling from the OBD-I mistake that California foisted on us - OBD-II makes more sense, has wider standards (because SAE took over,) and is somewhat more reliable. I've still run across cases where OBD-II was flat-out wrong, but they're much fewer and farther between (and no matter how much self-diagnosis the system does, a wrench who does his own thinking is rewarded with lower parts bills, fewer comebacks, and better job throughput.)

 

[bldeagle10]

heck ohc has been common in hondas for right around 20 years now. their first variable valve timing motor was in the 70s on a motorcycle. they seem to get things right, or at least on the right track from the get go. there are alot of things in the automotive industry that i would love to go in there and change, mostly weight issues...you dont need to produce big hp numbers if the car doesnt weight 4000lbs to begin with. gain some mpg with a lighter car, lower the hp minimally and you will still be quicker and more economical...

 

[5-90]

heck ohc has been common in hondas for right around 20 years now. their first variable valve timing motor was in the 70s on a motorcycle. they seem to get things right, or at least on the right track from the get go. there are alot of things in the automotive industry that i would love to go in there and change, mostly weight issues...you dont need to produce big hp numbers if the car doesnt weight 4000lbs to begin with. gain some mpg with a lighter car, lower the hp minimally and you will still be quicker and more economical...

Closer to thirty - I had a 1980 Accord with the 12v 1800c/c OHC I4 Not a bad engine, but it liked to spin main bearings (which was a pain. I ended up getting rid of it the third time the bottom end spun out on me.)

Reducing vehicle mass is why the unibody concept caught on - although it is somewhat more rigid than the box-and-frame typical construction (which is why we keep getting cracks in our XJ chassis in the corners of the rear opening and around the doors. No "give.")

Honda does do small engines right, and this has extended into their road vehicles. Toyota also does a good job. However, several of the things that were "innovations" when they came over here were commonplace for at least a decade before they got here - which is what I'm saying.

 

[Dr. Dyno]

Closer to thirty.

OHC engines have been around even longer than that. My first car when I was a student was a 1973 Mazda 818 with a 1272cc OHC, aluminium-headed I4 engine.

 

[5-90]

OHC engines have been around even longer than that. My first car when I was a student was a 1973 Mazda 818 with a 1272cc OHC, aluminium-headed I4 engine.

Here in the States, or elsewhere?

There's a certain amount of inertia with accepting new automotive technologies here, which has gotten worse since the Olds Diesel and Caddy 4-6-8 mistakes. I think we're recovering from that sort of thing finally, but I'm not sure...

 

[cruiser54]

1920s Alfa Romeos had DOHC with a supercharger, aluminum block and head. Block had wet sleeves.

 

[cemeyer]

1920s Alfa Romeos had DOHC with a supercharger, aluminum block and head. Block had wet sleeves.

That definately predates Ford, but Ford had a 427 SOHC in th 60's. The 650hp that it was rated at was just a tad conservative by 100-150 HP.

 

[5-90]

Alfas are Italian (I think,) and the Ford427ci "Cammer" was unusual and not a very common seller.

I'm not saying that the technology didn't exist - just that it wasn't very popular until recently. Look at the trouble Chevvy had getting the Corvair accepted - and that was after having the VolksWagen Beetle selling here for 15-20 years (the Covair was the same style of engine - just two extra cylinders - and the same layout. And the VolksWagen was built much more lightly.)

 

[O-Gauge Steamer]

My Brother and I built our 1925 Model T Indy car in 1970. We used a Rajo Model B OHC head from 1925...

Just sayin, nothing reall is all that new when it comes to cam placement. It has all been done.

And yes, the Europeans and Japanese are ahead of us fue tothe simple fact that for decades Detroit refused to retool the engines works figuring, "it works, why change it". With the cheapest gas on the planet, who cared if a 429Cuin engine produced 250hp...

Everywhere else on the planet, fuel was and is expensive. The manufacturers are driven to produce hp from limited displacements. Several Euro countries has extra taxes on vehicles based on displacement. Japan had a 1 litre limit on motorcycle engines for decades ehich is why so many of them are 997cc or 999cc displacement.

We have it easy compared to the rest of the world.

Corvairs... I remember when they came out. A friend of mine, his Dad bought one in 1969. 2 speed automatic in it. It actually ran very well. As I remember them, they started out at 140cuin and moved all the way up to 164cuin. Some of those were turbocharged and produced 180hp. Ralph Nader killed them off with really bad press that they did not deserve. A decent small car.

 

[cruiser54]

The Corvair was great. An early casualty of overreaction caused by an extremist lawyer-Ralph Nader.