Does a V engine provide more torque than a Straight engine?

[bigfatnick]

I thought this seemed odd, i was flicking through the paper at work last night it was "the globe an mail" a canadian paper that wipes the floor with the uk papers. Its got a Q&A page, someone wrote in asking why modern cars use inline4's rather than v4's, as V4's would provide more torque. The guy answering the question babbled on about how I4's fit in fwd's just fine, are cheaper to make, lighter etc. But it seemed to me, unless im mistaken, that a V engine shouldnt provide more torque than a straight engine, it still has the same number of cylinders, it still has conrods pushing on the same crank (albeit from a different angle). If anything, a v engine should output less torque than a inline engine, as it has to spin too lots of cams/pulleys/extra belts etc.

I was always under the impression torque was down to how an engine was tuned, its displacement and maybe the number of cylinders, but thats probably down to displacement, rather than anything else.

Am i wrong? I suppose the only examples we would have would be straight 6's against V6's, and as far as i know, one isn't torquier than the other. Did the guy who replied to this letter miss the point?

[kambites]

I can't think of a good reason that cylinder layout should make any difference to the power curve of an engine at all.

[odyssey2200]

NO

I longer stroke engine will usually have more torque.

The angle of the V and the number of cylinders will effect the "smoothness" of the delivery.

A 90degree V8 should have a smooth delivery with a power stroke every 90 degrees

[bigfatnick]

i'm actually trying to think of examples of low torque v engined cars (with the exception of bike engine v8's) and i cant really think of one. Honda nsx maybe?

If a long stroke provides more torque, is there any reason a V engined car would require a longer stroke. i cant think of one.

[Glosphil]

Going baxk to the 1970s

Ford 2-litre V4 97hp & 120 ftlb

Ford 2-litre inline 98hp & 111 ftlb

So V4 did actually have more torque. but I don't know at what revs. the respective torque figures were produced.

[bigfatnick]

Glosphil said:

Going baxk to the 1970s

Ford 2-litre V4 97hp & 120 ftlb

Ford 2-litre inline 98hp & 111 ftlb

So V4 did actually have more torque. but I don't know at what revs. the respective torque figures were produced.

but couldnt that be down to how the engine was tuned/setup/designed rather than just being a V4?

If i remember, the ford v4's were van engines, so probably tuned for torque, rather than economy?

[thunderbelmont]

Inherently, inline engines, particulary 6's, produce their torque at lower revs than a Vee engine of the same number of cylinders with the same capacity. While the Vee *might* produce more, the straight will produce it lower down the band and be more useful.

Key example: Mercedes V6 truck engines - 12 litre, vs Cummins 11L straight-6. For the same horsepower output, the torque figures are pretty well the same, but the Vee produces it's torque in a more peaky band higher up the revs. To get the best out of the Merc, you have to rev the fk out of it, and keep the revs up. The Cummins on the other hand will pull and pull and pull down to silly low revs - to the point where the Merc would have given up and stalled! The Cummins is far more economical too!

[kambites]

thunderbelmont said:

Inherently, inline engines, particulary 6's, produce their torque at lower revs than a Vee engine of the same number of cylinders with the same capacity. While the Vee *might* produce more, the straight will produce it lower down the band and be more useful.

Why?

[thunderbelmont]

The engines that I've come across (to compare) often show the Vee engine with a shorter stroke than the inline.

Since horsepower is a function of torque mulitplied by revs, and generally speaking Vee engines produce their power at higher revs (for the same capacity), that means that the torque peak must be at higher revs.

That torque peak could be higher than the inline engine, but it may have less torque on average over a band compared to he inline engine.

In many ways it's apples and oranges.

Another comparison - 12v straight six Opel vs 24v straight six Opel (as used in the Omega/Carlton/Senator) They had the same bore & stroke. The 24v had more horsepower, and had more torque (195lb-ft vs 177lb-ft), but it was produced at higher revs, and thus required more "driving" because the grunt wasn't there at low revs like the 12v variant. Then compare against the 24v V6 engine in the later Omega. it's got F-all torque at low revs compared to the inline 6 (either 12v or 24v). It has more torque ultimately (199lb-ft vs 195lb-ft), and revs the best part of 600rpm more than the old 12v inline six.

If you're dragging a trailer, the old 12v is the best one of the lot.

[kambites]

I can't think of a good reason that V engines should have a shorter stroke though? Or that you shouldn't produce a long-stroke inline engine.

[aeropilot]

bigfatnick said:

If i remember, the ford v4's were van engines, so probably tuned for torque, rather than economy?

The Essex V4's were indeed used in Transits, but were also fitted in Corsair's, Capri's and Zephyr's.

[wheeljack]

The whole argument about long stroke for the same cylinder swept volume providing more torque is incredibly specious. Torque is a function of lever length but it is also a function of force as well, for the same cylinder pressure a smaller bore will have smaller force cancelling out the "mechanical advantage" of the longer lever. There is a widely used term in the industry called BMEP, which is a normalisation of torque output with respect to capacity of an engine regardless of configuration, and the BMEP figures for I6's and V6's with hugely varying bores and strokes have comparable BMEPs.

Anyway a vee engine should not provide more torque than an inline engine (or vice versa) with all other things being equal. However making everything else equal for a V6 and an I6 is where the problems begin. Torque is a function of the ability of the engine to breath and the package requirements between a I6 and a V6 when fitting into a chassis (especially transverse vs longitudinal installations) can and will effect the engine's breathing capability. BMW by having their I6 installed longitudinally for RWD make life easier for themselves when it comes to engine breathing, a large reason they get such good power & torque figures.

I had to help design a concept motorcycle racing engine (I3, I4, V4, V5 and V6), calculating the out of balance forces and moments for an array of engine and crankshaft configurations, and to aid breathing with good inlet tracts the vee angle could be no less than 75 degrees. However this had negative effects on the out of balance moments on a V6, which is potentially less of a problem for a racing engine than a road engine.

Edited by wheeljack on Monday 11th January 00:54

[Nigel Worc's]

aeropilot said:

bigfatnick said:

If i remember, the ford v4's were van engines, so probably tuned for torque, rather than economy?

The Essex V4's were indeed used in Transits, but were also fitted in Corsair's, Capri's and Zephyr's.

and SAAB's ?

[pwd95]

I don't think the layout makes a difference, it's down to cam profile surely. Do the engines compared in previous posts have the same cam profile, induction size, fueling etc. Very difficult to proove this one.

[B'stard Child]

thunderbelmont said:

Another comparison - 12v straight six Opel vs 24v straight six Opel (as used in the Omega/Carlton/Senator) They had the same bore & stroke. The 24v had more horsepower, and had more torque (195lb-ft vs 177lb-ft), but it was produced at higher revs, and thus required more "driving" because the grunt wasn't there at low revs like the 12v variant. Then compare against the 24v V6 engine in the later Omega. it's got F-all torque at low revs compared to the inline 6 (either 12v or 24v). It has more torque ultimately (199lb-ft vs 195lb-ft), and revs the best part of 600rpm more than the old 12v inline six.

If you're dragging a trailer, the old 12v is the best one of the lot.

^ that last statement I agree 100% best towcars I've ever ownered were fitted with 3.0 12V's - you hardly knew you had a trailer behind you

[Squabbler]

Interesting how those are compard to a boxer engine? I guess it has less torque than both.

[vz-r_dave]

bigfatnick said:

i'm actually trying to think of examples of low torque v engined cars (with the exception of bike engine v8's) and i cant really think of one. Honda nsx maybe?

If a long stroke provides more torque, is there any reason a V engined car would require a longer stroke. i cant think of one.

What make's you suggest the NSX?

NSX 3.2 - (304 N·m)

Wouldnt say that was low for the output imo

[snotrag]

A Boxer engine is effectively a Vee engine, just a 180degree Vee, no?

To throw another one into the mix...

Wather than the cylinder layout being different.

What about th crank/firing order layout? IE the difference between a cross plane crank and a flat plane crank?

This has a bearing on what part of the cycle a cylidner is at at any one time, in relation to the other cylinder? And governs how many and at what point the pistons each do their 'work' stroke on the crankshaft?

[aeropilot]

Nigel Worc's said:

aeropilot said:

bigfatnick said:

If i remember, the ford v4's were van engines, so probably tuned for torque, rather than economy?

The Essex V4's were indeed used in Transits, but were also fitted in Corsair's, Capri's and Zephyr's.

and SAAB's ?

Yes, but technically these were the different Cologne V4, which is why I didn't include them in the list of Essex V4 equipped vehicles.

[havoc]

I'd suggest that there are a lot of factors affecting torque more than the cylinder layout (as posted above).

I'd also suggest that packaging and cost are more relevant for 4-cylinder motors, which typically inhabit only mass-market cars, or derivatives thereof. An I-4 only needs one head (which on a DOHC engine is quite large in comparison to the block, unlike the old SOHC (or even pushrod) stuff), one cambelt, and one of each manifold.

V-engine advantages are:-
- more compact
- lower c-o-g
- (potentially) better balanced
...so suit a performance car more.