Potentially Stupid Question - Overhead Cam Engines
Discussion
AW111 said:
Our premier racing class in Aus is v8 "supercars". The organisers wanted more manufacturers involved, but have enforced a 7,500 rpm limit, 10:1 compression ratio, and I believe disallowed variable cam timing, to keep the pushrod dinosours competetive.
They brought in the 7500 rpm 10.1 CR in 1993 when they changed from group A to v8 rule as a cost benefit so the engines would last longer.mat205125 said:
Time belt and chain technology have also moved on greatly over time, as has lubrication systems, and lubricants.
With the thick old mineral oils that used to be used in engines, you'd never pump it up to the galleries in an OHC engine.
Oils have very little to do with the development of OHC engines, there's been thousands of OHC engines running on 20/50, since years ago. With the thick old mineral oils that used to be used in engines, you'd never pump it up to the galleries in an OHC engine.
See Lotus Twin Cam, Ford BDA, Fiat Twin Cam, Alfa Twin Cam.
Not forgetting that the Rolls Royce Merlins that powered many an aircraft back in the '40s have a four valve per cylinder overhead cam, I'm quite sure that they didn't run on fully synthetic 5/30.
Mr2Mike said:
And, by strange coincidence, I don't know of anyone that goes around challenging people to top speed contests. Leaving a 250bhp car in his dust is more likely to leave the 400bhp car owner crying into his wallet whilst he catches the bus for the next few months.
Only if you're poor in which case you cannot afford the 400hp car in the first place and the bus is the best place for you. Edited by Mr2Mike on Monday 3rd August 22:54
Of course you are right, nobody can go over 70mph in this country so we should all drive 320ds, this is PH after all.
Mr2Mike said:
And, by strange coincidence, I don't know of anyone that goes around challenging people to top speed contests. Leaving a 250bhp car in his dust is more likely to leave the 400bhp car owner crying into his wallet whilst he catches the bus for the next few months.
Why?Edited by Mr2Mike on Monday 3rd August 22:54
The 400hp V8 gets similar fuel economy to the 250hp turbo 4
Mr2Mike said:
And, by strange coincidence, I don't know of anyone that goes around challenging people to top speed contests. Leaving a 250bhp car in his dust is more likely to leave the 400bhp car owner crying into his wallet whilst he catches the bus for the next few months.
There will be a load of LS V8's going 150+mph this Saturday...Edited by Mr2Mike on Monday 3rd August 22:54
Coatesy351 said:
They brought in the 7500 rpm 10.1 CR in 1993 when they changed from group A to v8 rule as a cost benefit so the engines would last longer.
And it made sense in 1993, when ohc v8s were not that common here, but that's 22 years ago 
. Now that quad cam v8s are found in most landcruisers, the rules seem a tad silly.AW111 said:
Coatesy351 said:
They brought in the 7500 rpm 10.1 CR in 1993 when they changed from group A to v8 rule as a cost benefit so the engines would last longer.
And it made sense in 1993, when ohc v8s were not that common here, but that's 22 years ago . Now that quad cam v8s are found in most landcruisers, the rules seem a tad silly.Coatesy351 said:
But as v8 supercars have nothing to do with road cars anyway it still makes sense otherwise if there was no restrictions on rpm or cr there would be a horsepower war and the resulting higher costs. They Spin Nascar engines to 10000 rpm and they are only using a flat tappet cam, i would see v8 supercars going the same way.
There's the thing. It cost a lot more to spin a 2 valve pushrod v8 to a reliable racing rpm than it does a quad cam 4 valve. Personally, I would change quite a bit in the v8sc category, but that's getting too far off-topic.Regarding the packaging advantages of pushrod v8s, which means you can fit a larger displacement engine in the same physical space, I wonder why Toyota went dohc for the landcruiser v8s, both petrol and diesel? It it as simple as that's what they had?
AW111 said:
There's the thing. It cost a lot more to spin a 2 valve pushrod v8 to a reliable racing rpm than it does a quad cam 4 valve. Personally, I would change quite a bit in the v8sc category, but that's getting too far off-topic.
Regarding the packaging advantages of pushrod v8s, which means you can fit a larger displacement engine in the same physical space, I wonder why Toyota went dohc for the landcruiser v8s, both petrol and diesel? It it as simple as that's what they had?
Is a quad cam 4 valve cheaper as a high rpm race motor? I would have thought the extra complexity would make them cost more. I would say marketing is the reason for toyota as they cant be seen producing a "low tech" pushrod motor. Regarding the packaging advantages of pushrod v8s, which means you can fit a larger displacement engine in the same physical space, I wonder why Toyota went dohc for the landcruiser v8s, both petrol and diesel? It it as simple as that's what they had?
Edit they do make one though.
Edited by Coatesy351 on Tuesday 4th August 14:04
V8RX7 said:
You-said-"And 450bhp beats anything 200-250bhp."
And-I-was-pointing-out-that-it-doesn't.
Particularly-relevant-as-most-production-cars-with-LS-engines-in-are-heavy.
(spacebar-broken)
My apologies, I didn't make it clear enough. I was meaning in the same/similar car. 450bhp beats 250bhp. Who cares if the 450bhp is only 50-70bhp/litre and the 250bhp one 120bhp/litre. The only real decider is total output not state of tune.And-I-was-pointing-out-that-it-doesn't.
Particularly-relevant-as-most-production-cars-with-LS-engines-in-are-heavy.
(spacebar-broken)
For example, if you could have a Corvette as per current production with 460bhp from 6.2 litres 74bhp/litre or the same car with say a 2.5 DOHC n/a V6 tuned to say 120bhp/litre (the most pretty much any mass production n/a engine has managed). Any weight savings would be from the engine difference, which as established as the LS1 is compact and light, might be only a few kg, to none or even a slight weight penalty.
Which would you rather have and which would be the quicker? The 300bhp one, or the 460bhp one?
V8RX7 said:
skyrover said:
The 400hp V8 gets similar fuel economy to the 250hp turbo 4
Do-they-b
ks-!I've-ran-many-V8's-I-prefer-them-but-in-my-driving-they-average-8-14mpg.
At-the-same-time-I've-run-many-turbo-4-they-average-18-24mpg
(awaiting-new-keyboard)
But as posted earlier, a 2.0T Impreza is no better on fuel. I've also owned a S13 200SX which was only marginally better, but to be fair only produced 180bhp, so not really the same power ballpark. And all you have to do is look at the numerous threads about MK2 Focus ST's to see their mpg is appalling for only 225hp.
300bhp/ton said:
But as posted earlier, a 2.0T Impreza is no better on fuel. I've also owned a S13 200SX which was only marginally better, but to be fair only produced 180bhp, so not really the same power ballpark. And all you have to do is look at the numerous threads about MK2 Focus ST's to see their mpg is appalling for only 225hp.
The 1.8t engine in my Cupra R (remapped to 270bhp) regularly produces an average in mixed driving of 30mpg. 35mpg can be achieved on a steady motorway run. The latest BMW 2.0 turbo units, e.g. 330i, produce similar power but at *least* 5mpg greater on each of those figures.300bhp/ton said:
V8RX7 said:
skyrover said:
The 400hp V8 gets similar fuel economy to the 250hp turbo 4
Do-they-bks-!I've-ran-many-V8's-I-prefer-them-but-in-my-driving-they-average-8-14mpg.
At-the-same-time-I've-run-many-turbo-4-they-average-18-24mpg
(awaiting-new-keyboard)
But as posted earlier, a 2.0T Impreza is no better on fuel. I've also owned a S13 200SX which was only marginally better, but to be fair only produced 180bhp, so not really the same power ballpark. And all you have to do is look at the numerous threads about MK2 Focus ST's to see their mpg is appalling for only 225hp.
Soarer V8 (stripped out) 260bhp
Monaro V8 350bhp
RX7 V8 440bhp
Turbo 4
S14a 200SX 220bhp
MX5 270bhp
Sierra Cosworth 240bhp
Forester 2.5 275bhp
I tend to drive on fast A-B roads and twice a week I do the school run. it's very rare I sit on the motorway - which is where the V8's are more economical.
The Forester is terrible on fuel averaging 18mpg (as are imprezas) I assume this is because of the FWD although I believe they also run rich as std.
V8RX7 said:
300bhp/ton said:
V8RX7 said:
skyrover said:
The 400hp V8 gets similar fuel economy to the 250hp turbo 4
Do-they-bks-!I've-ran-many-V8's-I-prefer-them-but-in-my-driving-they-average-8-14mpg.
At-the-same-time-I've-run-many-turbo-4-they-average-18-24mpg
(awaiting-new-keyboard)
But as posted earlier, a 2.0T Impreza is no better on fuel. I've also owned a S13 200SX which was only marginally better, but to be fair only produced 180bhp, so not really the same power ballpark. And all you have to do is look at the numerous threads about MK2 Focus ST's to see their mpg is appalling for only 225hp.
Soarer V8 (stripped out) 260bhp
Monaro V8 350bhp
RX7 V8 440bhp
Turbo 4
S14a 200SX 220bhp
MX5 270bhp
Sierra Cosworth 240bhp
Forester 2.5 275bhp
I tend to drive on fast A-B roads and twice a week I do the school run. it's very rare I sit on the motorway - which is where the V8's are more economical.
The Forester is terrible on fuel averaging 18mpg (as are imprezas) I assume this is because of the FWD although I believe they also run rich as std.
Olivera said:
The 1.8t engine in my Cupra R (remapped to 270bhp) regularly produces an average in mixed driving of 30mpg. 35mpg can be achieved on a steady motorway run. The latest BMW 2.0 turbo units, e.g. 330i, produce similar power but at *least* 5mpg greater on each of those figures.
I have heard good things about the VAG 1.8. Not always 100% sure on the bhp claims on them though. A friend has an older Cupra, with the 180hp engine variant. On a run I'm sure it's pretty good mpg, although on his round town foot to the floor driving I think he was getting 22mpg.BMW 6 pots, can be economical. Why I've often considered something like a 328, 130 or Z3 as a DD. Although I think the max mpg of them is sometimes touted as the general average, which isn't really an accurate way to look at them.
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