Pushrods vs Overhead Cams

[GLD-086]

Hopefully this will create a interesting topic.

Anyway I've never understood why people compare these two together. Does it really matter what configuration the cams are in?

I LMAO at the wankers that bag on Pushrods for being old, even though Overhead Cams have been around for almost 100 years.

Also do you think Holden should keep with the recipe they know, and continue working with Pushrod V8s, or jump to a OHC? Personally I think they should stay with OHVs. It's worked for them for well over 40 odd years.

Discuss people.

[VSO.38]

OHC and DOHC engines are good for higher revving engines but for a V8 I would rather a low revving engine with plenty of torque which is what you get from OHV engines... but thats just my opinion

[VT-565]

Personally I think they should stay with OHVs.

I will add my bit on this, but just to clear it up, OHC and pushrod engines use OverHead Valves man.
I am a firm believer in if you want to crystal ball holdens future powerplants, look to the states. And to throw some sand in the eyes of the pushrod-baggers, the LS7 PUSHROD engine won powerplant of the year at a convention in europe. The judging board was made up of engine experts from all major countries including japan, so i say "get that up ya!"
OHC might be easier to work on or breath better or whatever, but if it aint broke, dont fix it. pushrods for a long time to come.

[SICK SS]

OHC and DOHC engines are good for higher revving engines but for a V8 I would rather a low revving engine with plenty of torque which is what you get from OHV engines... but thats just my opinion

thats not totaly true y dose a stock 6 lt out rev a och 5.4lt ford motor?

[LowVp]

OHC is the best way to go simply because there is less parts to move and less drag as there are no lifters, pushrods and rockers to lift, cam sits straight on top and does the work directly

[VT-565]

thats not totaly true y dose a stock 6 lt out rev a och 5.4lt ford motor?

How true that is.
The ford engine is quite weird as the top end is suited to a shorter stroke engine. The ford bottom end is a truck engine.

As for less moving parts with OHC, look at the lengths of the timing chains or belts versus that on a pushrod engine. Also, on direct acting overhead cams, valve lift is 1:1 with lobe lift on the cam, so you have to physically have a much bigger cam to get more valve lift, whereas on a pushrod engine, you can simply change the rocker ratio to get more effective valve lift. If you really want to get picky, OHC engines have more weight above the centre of gravity of the vehicle, too.

[grigor]

The main reason pushrod engines are doomed is VVT.
You can't separate inlet and exhaust valve timing easily, when both lobes are on the same bump stick.
Fit twin cams and away you go. You don't see too many twin cam pushrod engines do you, just makes so much more sense to go twin OHC with variable cam timing on both cams.
Simplicity wins.

[VT-565]

The main reason pushrod engines are doomed is VVT.
You can't separate inlet and exhaust valve timing easily, when both lobes are on the same bump stick.
Fit twin cams and away you go. You don't see too many twin cam pushrod engines do you, just makes so much more sense to go twin OHC with variable cam timing on both cams.
Simplicity wins.

Simplicity? Ha ha ha ha
VVTi...VTEC....**** me dead....how much **** can these guys come up with?
I dont know where the simplicity bit comes in.....four cams (twin OHC V8), 4 advance-retard motors, two timing belts/chains and not to mention, the management of the cams.
Versus 1 cam, one chain, lifters and pushrods. I was going to put rockers in there too, but some OHC engines use them still.
I think this will be as endless as the "turbo vs. supercharger" debate, but I've made my statement.......for now

[MasterOfReality]

Umm, isnt the current most powerful naturally aspirated V8 in the world the new AMG 6.3 litre V8 (they are actually 6.2l, but badged 6.3l due to German classifications)?

375kW @6800rpm and 630Nm @5200rpm, redline 7200rpm.

There is also a turbo charged version on its way as well, with a specified power output of 525kW and over 1000Nm of torque.

So there goes the argument about pushrod donks being better for torque, turbo charged or not.

[1991_Vn2nV]

Umm, isnt the current most powerful naturally aspirated V8 in the world the new AMG 6.3 litre V8 (they are actually 6.2l, but badged 6.3l due to German classifications)?

375kW @6800rpm and 630Nm @5200rpm, redline 7200rpm.

There is also a turbo charged version on its way as well, with a specified power output of 525kW and over 1000Nm of torque.

So there goes the argument about pushrod donks being better for torque, turbo charged or not.

Ummm not if those stats you gave are correct, because...

LS7 is 377kw @ 6300rpm and 637NM of torque @ 4700rpm with a 7000rpm redline. Whack a charger on that and use the LSX block and you're laughing

[MasterOfReality]

Ummm not if those stats you gave are correct, because...

LS7 is 377kw @ 6300rpm and 637NM of torque @ 4700rpm with a 7000rpm redline. Whack a charger on that and use the LSX block and you're laughing

ahah, ok, what if it was based on engine size?

I believe the LS7 is a 7 litre and only produces 2kW and 7Nm more?

Therefore the AMG produces more hp per cubic inch.

[SweetWagon]

ahah, ok, what if it was based on engine size?

I believe the LS7 is a 7 litre and only produces 2kW and 7Nm more?

Therefore the AMG produces more hp per cubic inch.

well if were talking hp per ci, then bmw takes that one... new v8 4.0L, 309kw 400nm.

[HaMmErD]

well if were talking hp per ci, then bmw takes that one... new v8 4.0L, 309kw 400nm.

those torque figures are a bit lame for a v8 .... although considering its only a 4.0l .... id be dissapointed IMO

[SweetWagon]

dont really need torque when it revs out to 8000

[grigor]

[QUOTE=EcotecManiac;587599]Simplicity? Ha ha ha ha
VVTi...VTEC....**** me dead....how much **** can these guys come up with
I dont know where the simplicity bit comes in...

OK you've had your rant. I'll explain the simplicity bit for you.
The thread was pushrods V's OHC.
No one's argueing that enormous power can made in a pushrod engine.
But this is a Commodore forum and GM is told to get it's engines to pullute less, get better economy and at the same time make more power or nobody will buy the car.
So why has the latest V6 got OHC? To get the VVT to work.
Why did Ford toss the old SOHC and go twin cam? To get the inlet/exhaust VVT separation.
That's what I'm talking about simplicity. If GM could have made a cheap twin cam pushrod engine, don't you think they would have gone that way?
My engine experience goes way back to Lanz Bulldogs and 2-stroke Commers; I love simple engine designs, but they've all gone as they could never comply to today's tough pullution standards.

[klaw81]

do you think Holden should keep with the recipe they know, and continue working with Pushrod V8s, or jump to a OHC?

Well it's not really up to Holden, is it? When did Holden last design an engine from scratch? All of the current engines in the current Holden line-up are based on designs done overseas as far as I know. My guess is that GM in the US will keep going down the Gen 3/4/5 "more cubes, more power" route for a few years yet, and that Holden will keep importing them because it's far cheaper and easier than designing their own...unless the US car industry has to make some big changes to combat global warming.

There is nothing fundamentally wrong with pushrod engines but they WILL die eventually, because variable cam timing will become unavoidable (along with lots of other efficiency-boosting measures) to keep up with ever-tightening emissions laws. Also, sophisticated OHC configurations can be used to eliminate other inefficiencies...BMW has done away with throttle bodies entirely in some of their new engines and are using the valves as separate throttle bodies for each cylinder!

[50LTRv8]

This question really has 2 parts

Does it matter what config you have to make power?

The answer is no not really, you can create huge amounts of power from reach engine config.

Engine power and power derlivery depend more on stroke length and piston diameter than if it uses an ohc or pushrods.

Should Holden continue with pushrods?
The answer is no it can't, emission laws with force companys to cut the fat and overhead cams seems to be a good way of doing this.

For example the bf ford gets a 10% saving in fuel because they fiddled with the twin cam phasing which is pretty good if you ask me

50LTRv8

[J_D]

I noticed in last months Wheels mag that the 6ltr Clubsport got about 12.6L/100km on their road test, not bad fuel economy for an "old" pushrod engine.

[vlv8vic]

Not completely what you are talking about but...

badly tuned V8, over revved engine =
(they were nasty to get out.. no valve damage!)

[1991_Vn2nV]

I noticed in last months Wheels mag that the 6ltr Clubsport got about 12.6L/100km on their road test, not bad fuel economy for an "old" pushrod engine.

Exactly. When a 6.0L V8 HSV that weighs 2 tonne gets better fuel economy than a 2.0L 4 cylinder Evo Lancer which weighs several hundred kilo's less....

[klaw81]

Exactly. When a 6.0L V8 HSV that weighs 2 tonne gets better fuel economy than a 2.0L 4 cylinder Evo Lancer which weighs several hundred kilo's less....

Fuel economy isn't really in the EVO's design brief, I'm guessing, while it is (indirectly) in the HSV's. The EVO has much shorter gearing and would probably be doing about 2400-2700rpm in top gear at 100km/h, whereas the HSV has a very long overdrive and low-end torque that means it can lope along at 1500rpm in top gear on the highway and get quite good fuel consumption.

If you're thrashing both of them, I bet they both use fuel like it's going out of fashion. Making that amount of power takes a certain amount of fuel.

[VE427]

maybe you should just sell it and buy a ford, there better anyway

[1991_Vn2nV]

Fuel economy isn't really in the EVO's design brief, I'm guessing, while it is (indirectly) in the HSV's. The EVO has much shorter gearing and would probably be doing about 2400-2700rpm in top gear at 100km/h, whereas the HSV has a very long overdrive and low-end torque that means it can lope along at 1500rpm in top gear on the highway and get quite good fuel consumption.

If you're thrashing both of them, I bet they both use fuel like it's going out of fashion. Making that amount of power takes a certain amount of fuel.

The HSV came back with a fuel economy of something like 13.4L or 12.6L per 100km. Thats better fuel economy than I get in my buick V6 OR my Ecotec V6 and its not that far behind the alloytec.

[klaw81]

The HSV came back with a fuel economy of something like 13.4L or 12.6L per 100km. Thats better fuel economy than I get in my buick V6 OR my Ecotec V6 and its not that far behind the alloytec.

What's your point? Fuel economy on the highway is mainly about gearing, aerodynamics and the torque/weight ratio at cruise speed - the maximum engine power has very little to do with it.

I get an average of 11L/100km or less on a city/highway cycle from my SV8 which makes about 270kW, so the Clubsport ain't that special. I imagine the difference is mainly in gearing and about 200kg less...and the fact that Holden's factory tuning on their V8's (and 6's too actually) is traditionally pretty poor.

[1991_Vn2nV]

What's your point? Fuel economy on the highway is mainly about gearing, aerodynamics and the torque/weight ratio at cruise speed - the maximum engine power has very little to do with it.

I get an average of 11L/100km or less on a city/highway cycle from my SV8 which makes about 270kW, so the Clubsport ain't that special. I imagine the difference is mainly in gearing and about 200kg less...and the fact that Holden's factory tuning on their V8's (and 6's too actually) is traditionally pretty poor.

I wasnt saying it was special... I was using it as an example of pushrod engines returning decent fuel economy, which yours obviously does too.. The point is when pushrod engines are making that much power, that much torque, then why is OHC so special? The Ford 5.4L engine uses more fuel while being a lower capacity engine, making less power, less torque.