Noticed whilst reading the piece on the new Focus ST in Test Drive mag that the ST & its main rivals (Golf Gti, Astra Vxr) all deliver max torque low down - ST - 1600rpm, Golf Gti - 1800rpm, Astra Vxr - 2400rpm (Diesels in disguise ).

Is this a nod to the success of performance diesels (Golf GT PD 130 / 150, Seat Leon Cupra/FR PD 150 etc) with their low down grunt?

Most of the petrol turbos that have this characteristic will have a 'constant' torque curve from low down to the upper mid range. However these cars will lose out (in relative terms) at the top end as the exhaust back pressure through the small(er) turbos builds up and limits the available boost at high rpm.

e.g. the Mk1 Octavia vRS holds peak torque of 235Nm from 2000rpm to 5000rpm - makes for linear power delivey but the power peaks at a fairly low 5500rpm.

Yep peak torque on the Scooby (bigger turbo) arrived at around 3k and was held pretty much to the red line

Chris

OOh, but if they aren't too revvy at the top end, then why not just get the diesel?

(Those who take that comment seriously need to hold their breath and count to 5000)

Personally, I quite like one diesel characteristic, the instant acceleration when you put your foot down... power when you need it. Certainly beats waiting for an NA car coming on cam. If a petrol turbo can give you a compromise between diesel flexibility and revviness, then it makes it a very useful and fast car in the real world.

OOh' date=' but if they aren't too revvy at the top end, then why not just get the diesel?

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In relative terms the Octavia vRS suffers a little at the top end but it will still rev to 6500+ rpm (unlike your Fabia :P ) its just that the power is tailing off past 5500rpm due to the small turbo.

In relative terms the Octavia vRS suffers a little at the top end but it will still rev to 6500+ rpm (unlike your Fabia :P ) its just that the power is tailing off past 5500rpm due to the small turbo.

:eek: I thought it was the lower rev range NOT the small turbo :confused:

Have you got large feet then?

Personally, I quite like one diesel characteristic, the instant acceleration when you put your foot down... power when you need it. Certainly beats waiting for an NA car coming on cam. If a petrol turbo can give you a compromise between diesel flexibility and revviness, then it makes it a very useful and fast car in the real world.

genuine question:

do turbo diesel engines generally not suffer from lag like a petrol turbo? or is this minimized by the Fabia/PD engines having a funky variable geometry turbo?

genuine question:

do turbo diesel engines generally not suffer from lag like a petrol turbo? or is this minimized by the Fabia/PD engines having a funky variable geometry turbo?

If anything, the diesel engine suffers with lag worse because the engine has no power without a turbo. The way they get round this is by fitting a smaller turbo which spins up around 1500-1800rpm to reduce the off boost time

Chris

If anything' date=' the diesel engine suffers with lag worse because the engine has no power without a turbo.

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I can vouch for the "no power without" statement......as can anyone who'se had the, by now imfamous, "vacuum tube incident"

do turbo diesel engines generally not suffer from lag like a petrol turbo?

Drive a Focus TDCi and you'll see :thumbdwn:

The 1.8 100ps one we've got at work is dangerous IMHO coming onto roundabouts etc.