Inline vs V

[Dakkon]

This may have been asked before, so appologies if so, however:

Just curious, assuming the same capacity and No. of cylinders will there be any difference in bhp and or torque between and inline engine and a 'V' engine?

Thanks,

[Mr2Mike]

Dakkon said:

This may have been asked before, so appologies if so, however: Just curious, assuming the same capacity and No. of cylinders will there be any difference in bhp and or torque between and inline engine and a 'V' engine? Thanks,

It depends! For engines in a relatievly low state of tune the difference will be minimal.

However, a cross plane V8 has a firing order that makes it difficult to utilise tuned length exhausts as effectievly (hence why flat plane cranks are used in some high performance V8's), so an inline engine may give better power in highly tuned applications. The V8 has the advantage of a shorter crank and better balance though.

[Dakkon]

The only reason im asking is that I currently own an E30 325, I was driving a 2.5 V6 Probe yesterday and the Probe was absolutely gutless and rubbish, yet on paper they are the same capacity and similar bhp, I was just a little supprised, which in turn got me thinking about the actual engine configuration itself.

[anonymous-user]

More likely to be weight making the greater difference there I'd have thought, no?

[350matt]

All things being equal then no, engine configuration shoudn't make much difference, however a vee engine will be shorter leading to better torsional behaviour for crank and cams so better valve control and more power. However the intake and exhaust systems are more difficult to package and achieve the correct tuned lengths, (but not impossible). Also different manufacturers will have different preferences for their engines, Ford = cheap as possible and BMW = best performance but heavy. So unless you're comparing different configurations from the same manufacturer then you're on a hiding to nothing really.

Matt

[Marquis_Rex]

Mr2Mike said:

Dakkon said: This may have been asked before, so appologies if so, however: Just curious, assuming the same capacity and No. of cylinders will there be any difference in bhp and or torque between and inline engine and a 'V' engine? Thanks, It depends! For engines in a relatievly low state of tune the difference will be minimal. However, a cross plane V8 has a firing order that makes it difficult to utilise tuned length exhausts as effectievly (hence why flat plane cranks are used in some high performance V8's), so an inline engine may give better power in highly tuned applications. The V8 has the advantage of a shorter crank and better balance though.

Actually this argument doesn't carry over to V6s/I6s.
The reason why a cruciform-crank V8 has lower power compared to a single plane crank V8 is due to the uneven firing of the former. It is unavoidable in having two cylinders fire consequitively 90 degrees apart. This can lead to "charge robbing" unles special attention is put into packaging the design of the manifolding and it can also lead to uneven cylinder to cylinder air flow distribution due to uneven residuals levels in cylinders. None of these problems is insurmountable. The imbalance and vibratary nature of a flat plane crank is another issue however as is their blatantly aweful NVH sound quality characteristics. Ferrari get round it by throwing money at it...and having incredibly low reciprocating masses.

Optimising both configs with effective manifolding (Not trumpets straight to atmosphere) you'll find only about a 2 percent difference in power- with benefits to the single plane layoutat high speeds-hardly seems worth it to my mind.
It makes even less sense on a boosted engine.

The only uneven firing 6 cylinder layout I know of is a 90 degree V6 such as used on the Masserati/Citroen SM, with 150/90 firing impulses. This gives an interesting burbly characteristic. No modern V6 uses this uneven firing at all, as cars like Audi and Merc 90 deg V6s use offset crank pins to get even intervals instead.

The only benefit I can see of the Inline Six config vs a 60 degree V6 in terms of breathing (not balance), is packaging. The inline six can effectively package a well optimised intake manifold, with more freedom for port/runner angle of attack into the cylinder and if it uses some sort of varaible resonance intake manifold more freedom to package appropriately sized resonance connection tubes. Packaging benefits should NOT be underestimated when it comes to peformance- it can make the difference between a class leading engine and a poor one in terms of performance.

[Marquis_Rex]

350matt the BMW M50 alloy engine is 160-170 kgs all in, one of the lightest engines in its class. Given, itscrankshaft is heavy at about 25 kilos, but it doesn't need to double up things like sprockets and VCT units.

[NST]

'Ford = cheap as possible and BMW = best performance but heavy'

The Probe V6 isn't the Duratec V6 that is used in the Cougar/mondeo. Probe V6 is a mazda unit. the difference performance is probably entirely down to the weight of the two cars. i would imagine the Probe the is a heavy car.

[Dakkon]

I think you may well be right about the weght of the cars, yet I was still suprised as to how gutless the Probe was.

Thanks for all the info.

[Mr2Mike]

Marquis_Rex said:

Optimising both configs with effective manifolding (Not trumpets straight to atmosphere) you'll find only about a 2 percent difference in power- with benefits to the single plane layoutat high speeds-hardly seems worth it to my mind. It makes even less sense on a boosted engine.

Just a shame Lotus didn't cotton on to this before designing the V8 in the Esprit!

[Marquis_Rex]

Mr2Mike, quite, alot of people who were involved with the design of the Lotus engine would agree with you too!