Engine Sizes

[CaptainRAVE]

I prefer turbos over na. There's something childishly exciting about the whoomph you get when a turbo (or two) kicks in and even with spooling issues and VODs I'd still rather have it.

+1 I love the whine of my supercharger

 

[Shimmyhill]

You seemed to overlook my comparision to an infinitely more advanced engine with quad cams, that made less power, less torque, and was unable to rev as highly as the 'outdated' pushrod engine.

That's what I was actually talking about.

My post was nothing to do with reliability? The whole point of it was that you can engineer pushrods to deliver accurate, high-RPM, operation if required.

Hardly a fair comparison is it those two engines... but lets not distract the resident loony as its fascinating

 

[Lashout_UK]

Hardly a fair comparison is it those two engines... but lets not distract the resident loony as its fascinating

It was nothing to do with being fair Shimmy, I was just demonstrating the fact that you can engineer and build high-RPM (i.e. accurate) pushrod systems if you need to - as well as that, in essence, a very simple engine can outperform a much more technologically advanced, and complicated, one that costs considerably more

You do realise that the old pushrod V8 walked all over the McLaren engine, though, right, and not the other way around? Just checking

 

[Shimmyhill]

It was nothing to do with being fair Shimmy, I was just demonstrating the fact that you can engineer and build high-RPM (i.e. accurate) pushrod systems if you need to - as well as that, in essence, a very simple engine can outperform a much more technologically advanced, and complicated, one that costs considerably more

You do realise that the old pushrod V8 walked all over the McLaren engine, though, right, and not the other way around? Just checking

Hehehe im not doubting or arguing anything, just using a race engine vs a road engine was my my 'issue'

I imagine that if one were to tune said Bimmer engine from the McLaren to the edges of its reliability for short use then it would put out more power power than the V8 and being a cam engine would have far better MPG cos of the timing of the valves init

 

[daveydave]

3.0 V6....I heart N/A

 

[Lashout_UK]

Hehehe im not doubting or arguing anything, just using a race engine vs a road engine was my my 'issue'

I imagine that if one were to tune said Bimmer engine from the McLaren to the edges of its reliability for short use then it would put out more power power than the V8 and being a cam engine would have far better MPG cos of the timing of the valves init

Haha

Yea, I know what you mean about the race vs. road thing. I guess the F1 was pushing the envelope back in the day for a 'road' engine. though.

Don't forget that the Nascar engines are heavily restricted too - just allowed a single carb, no fuel injection, limited combustion chamber dimensions and displacement, and so on.

They last for about 800-900 miles flat out though, which isn't too bad for the output. In stock form, though, I'd expect the McLaren to keep going flat out for longer - at least, I'd hope it would!

 

[Rich1988]

No, but the opportunity to do so is there.

thats a stupid thing to say surely? you can have a knife so the opportunity is there to stab someone, doesnt mean everyone does and they have to ban knives.

 

[DAIR]

thats a stupid thing to say surely? you can have a knife so the opportunity is there to stab someone, doesnt mean everyone does and they have to ban knives.

Whats stupid about it..... The opportunity is there. Simples!

 

[Xez]

I prefer turbos over na. There's something childishly exciting about the whoomph you get when a turbo (or two) kicks in and even with spooling issues and VODs I'd still rather have it.

I can see where your coming from, going from my 2.0 NA Clio to a 1.8T. I much prefer N/A purely for the noise and engine urging you to push it. The turbo on the other hand is great for just cruising around. But I cringe whenever I take it to the red line as it sounds like it's about to break

 

[crinkleshoes]

I've driven Yank V8 (LS series, the best of their V8s), and have driven the BMW V8

I also driven smaller 6pot, 4 pot both NA and turbo.

I know what you mean, but for me when I'm on it then I'm at higher RPMs in a turbo anyway and the delay is less
When I'm just cruising, I don't care about the delay personally as I'm taking it easy anyway.

But I guess that is just me, I have a cruise around and a drive spiritedly mode ...

I like the sound and power of the V8s, but I would still always pick the more refined BMW V8

Fair enough...

 

[rypt]

you can engineer and build high-RPM (i.e. accurate) pushrod systems if you need to

You really can't.

There amount of actual valve open/close time control you have is stupidly low with a pushrod setup. As I said, some "race" pushrod engines may be up to +-90degrees

 

[Lashout_UK]

You really can't.

As has been pointed out several times, I've already demonstrated that you can, so make of that what you will

If you want more control over opening and closing time then you just give it variable valve timing, if you're that desparate for it.

Did you also know that the shorter camshaft drive of a pushrod engine, due to the location of the cam in the block, can result in a much more accurate initial action (especially during changes in engine speed) than the long chain system that OHC systems have to endure? That's even more important once the engine's got a few miles on it and the chain's stretched and the tensioner's worn.

More inertia in a pushrod based system though, which can cause floating at higher RPMs - but again, just something you can engineer out if you know what your aims are and what you're doing.

It's certainly not superior, by any stretch, but both approaches can work well

OT but the additional length and height of overhead cams causes a lot of packaging issues too, along with complication, so there are all sorts of pros, cons and considerations to be made - like the additional benefits of a lower centre of mavity, lower total engine weight, etc....but then an OHC design allows you greater freedom for designing a better port and valve layout, better plug location, and so on...

 

[rypt]

No, all you demonstrated is that you can make some decent power (mainly due to the huge volume) ... and for racing engines you don't care about emissions (or fuel consumption since everyone has to run pushrod).

OHC also do not have to be chain, in fact many race engines use gears.

The problem with pushrod setup, as I have highlighted, is that there can be upto 90degrees delay between you giving the command "open the valve" and the valve actually starting to open due to the huge amounts of play you have in the all the rods, connection points, etc.

With OHC once the cam strikes you have far less delay and can be sure that the valve will actually do as told within a few degrees.

 

[Lashout_UK]

No, all you demonstrated is that you can make some decent power (mainly due to the huge volume) ... and for racing engines you don't care about emissions (or fuel consumption since everyone has to run pushrod).

OHC also do not have to be chain, in fact many race engines use gears.

The problem with pushrod setup, as I have highlighted, is that there can be upto 90degrees delay between you giving the command "open the valve" and the valve actually starting to open due to the huge amounts of play you have in the all the rods, connection points, etc.

With OHC once the cam strikes you have far less delay and can be sure that the valve will actually do as told within a few degrees.

Except that the instance I demonstrated had a smaller displacement, 4 less pistons, an infinitely less complicated valvetrain and yet more power, torque and high RPM capability?

Nascar engines aren't that bad on fuel flat out either, they tend to do about 5mpg which isn't unreasonable given what they're doing. I think discussing emissions on race engines is a little irrelevant anyway - but what's that got to do with anything?

I know many engines use gear-drive systems. Lots of road engines use them too.

Where are you getting this 90 degree figure from, by the way? As far as I was aware the usual kind of error induced by a pushrod system was in the 10 degree range, maybe 20 at a stretch, and of course there's a minor variation in valve lift when comparing designed to actual motion. If you had valves that weren't doing, to that extent, what they were supposed to for over a third of the duration of the cam then you'd end up with an engine that would run very poorly....

Anyway, all I'm driving at is that it won't stop you from building a valvetrain that's capable of sustained high RPM operation. One of those instances where despite it being undesirable, you can work around (or with) it. Hence why you can build a pushrod engine that'll do 10,000RPM, reliably, and out-statistic a larger engine with twice the number of valves, three more camshafts, four more cylinders, fuel injection and more expensive materials.

 

[rypt]

Less complicated valve train?

OHC is less complicated than pushrod fyi

And you demonstrated a race engine and a road engine, totally different beasts.

90 degrees is the sort of error you would see at high RPM in (a poor I'll admit) pushrod setup (11k+ ... why do you think F1 does not use pushrod in their 18-20k rpm engines?)
You have to start using more and more exotic materials to help cure it.

Anyway, I really cba with this discussion anymore, too tired from lack of sleep due to having "fun" plus I need to fix my car after half the electrics died