really dumb turbo question

[phatmanace]

folks,


I know this is really dumb - but gonna ask anyway!

do turbo's pull boost when the engine isn't loaded (i.e in gear and you're driving!)?


if I put my mx5 in neutral. and give it some beanz - I don't see the boost gauge move at all. same thing happened when I test drive a MR2?


is the turbo spinning up, but the wastegate held open?, or something else?


-ace

[r5gttgaz]

The engine needs to be under load to produce the exhaust gas quantity to drive the turbo.

[MrFlibbles]

phatmanace said:

folks,


I know this is really dumb - but gonna ask anyway!

do turbo's pull boost when the engine isn't loaded (i.e in gear and you're driving!)?


if I put my mx5 in neutral. and give it some beanz - I don't see the boost gauge move at all. same thing happened when I test drive a MR2?


is the turbo spinning up, but the wastegate held open?, or something else?


-ace

They dont boost when not under load, but I dont know why.

[phatmanace]

r5gttgaz said:

The engine needs to be under load to produce the exhaust gas quantity to drive the turbo.

hmm - ok, I didn't realize that - I assumed that an engine spinning at a certain speed would produce a certain amount of exhaust gas, regardless of load... although I guess if it's pulling you up a hill, it would have to burn more fuel to keep the revs up.

thanks for pinging me back anyhow!

-ace

[Red Devil]

MrFlibbles said:

They dont boost when not under load, but I dont know why.

Here's why. It's all to do with pressure - no load = no boost.

When an engine is put under a load, there is greater resistance to the expansion of combustion gases in the cylinder. This increases combustion pressure and temperature, and this increases the pressure and temperature of the exhaust gases. An engine under a heavy load will thus drive its turbocharger at a greater speed than if the same engine is run at the same RPM under little or no load.

This has the effect that a turbocharger delivers boost, thus increasing power (and fuel consumption) only when such a power increase is demanded by putting the engine under a heavy load. For example a vehicle accelerating from rest will put its engine under a heavy load, thus causing high boost pressures to be delivered by the turbocharger. This is detected by the fuel injection system, which delivers more fuel to provide more power. Once the vehicle reaches a constant speed and constant engine RPM, load decreases significantly, the pressure of the exhaust gases through the turbo drop, boost decreases and so does fuel delivery.

The engine is not loaded at all when in neutral........

[MilnerR]

Is this why turbos feel as though they're pulling really hard up hill?

Interesting post, you learn something new everyday

[phatmanace]

hmm - thanks for all the replies, does that mean then, that a SuperCharger would push boost even on an unloaded engine as it's being driven directly from the crank?

[cptsideways]

phatmanace said:

hmm - thanks for all the replies, does that mean then, that a SuperCharger would push boost even on an unloaded engine as it's being driven directly from the crank?

Yes but no, its throttled so running in a vacuum or with a bypass valve. Running in a vacuum is more efficient & is what you'll find on production cars

[Mr E]

Mine will move from -60psi to -30psi if I blip the throttle hard. Never into positive boost.

It's also why I will hold the car on the handbrake if I want to launch hard. Loads the transmission up (always a good plan) and starts to load the engine.

[MrFlibbles]

I wish I had a turbo again

[_Al_]

MrFlibbles said:

I wish I had a turbo again

I'll swap you my MR2!

I'm not normally this generous but a friend in need and all that...

[_Batty_]

MrFlibbles said:

I wish I had a turbo again

rover or MR2?

[sparkyhx]

sort of related question - I know turbo cars produce a lot more torque, but the other day I saw some dyno day figures and they included TypeR, TegR, S2000 and their torque was a pitiful 140lb but 200+ish bhp whereas the turbo ones were well over 200lb of torque - does that mean if you show one of these high reving vtec cars a hill they will pack their bags and have a hissy fit?, cos quite frankley 140lb of torque wouldn't pull the skin off a rice pudding.

I love my car on a hill it pulls like a train.

[MrFlibbles]

sparkyhx said:

sort of related question - I know turbo cars produce a lot more torque, but the other day I saw some dyno day figures and they included TypeR, TegR, S2000 and their torque was a pitiful 140lb but 200+ish bhp whereas the turbo ones were well over 200lb of torque - does that mean if you show one of these high reving vtec cars a hill they will pack their bags and have a hissy fit?, cos quite frankley 140lb of torque wouldn't pull the skin off a rice pudding.

I love my car on a hill it pulls like a train.

I've had a few turbo cars in the past and now have VTEC power.

The car I had before the S2000 (240bhp ish) was an old Rover 620 Ti (2.0 Turbo - 197 stanndard, mine was decatted and the boost upped slightly).

Driving teh two back to back - the 620 actually felt faster by a considerable margin - it wasnt quicker by any means, but thats what torque does for you.

[Holst]

sparkyhx said:

sort of related question - I know turbo cars produce a lot more torque, but the other day I saw some dyno day figures and they included TypeR, TegR, S2000 and their torque was a pitiful 140lb but 200+ish bhp whereas the turbo ones were well over 200lb of torque - does that mean if you show one of these high reving vtec cars a hill they will pack their bags and have a hissy fit?, cos quite frankley 140lb of torque wouldn't pull the skin off a rice pudding.

I love my car on a hill it pulls like a train.

If the Honda is not reving much then it wont pull very well uphill.

But if you are in the right gear then its no problem at all.

On my way to work there is a steepish hill and if I want to overtake up it then I will just drop down a gear (or two) and then you have all your power avalable. Although ive never driven a high performance turbo car I imagine you will have the same problem if you dont have enough revs and drop off boost.

[sparkyhx]

Holst said:

sparkyhx said:

sort of related question - I know turbo cars produce a lot more torque, but the other day I saw some dyno day figures and they included TypeR, TegR, S2000 and their torque was a pitiful 140lb but 200+ish bhp whereas the turbo ones were well over 200lb of torque - does that mean if you show one of these high reving vtec cars a hill they will pack their bags and have a hissy fit?, cos quite frankley 140lb of torque wouldn't pull the skin off a rice pudding.

I love my car on a hill it pulls like a train.

If the Honda is not reving much then it wont pull very well uphill.

But if you are in the right gear then its no problem at all.

On my way to work there is a steepish hill and if I want to overtake up it then I will just drop down a gear (or two) and then you have all your power avalable. Although ive never driven a high performance turbo car I imagine you will have the same problem if you dont have enough revs and drop off boost.

I'm not saying it will be completely gutless cos you've still got 240hp, but torque is also very important in how fast cars are in real life situations. I' have yet to find a hill (and believe me there are lotsin Halifax) that slows me down between gear changes, mine it just pulls and pulls

[anonymous-user]

When you start comparing torque, you ideally want to do it at the wheels. If an engine revs high, but with comparatively low torque output, it can run shorter gearing giving the same torque at the wheels as a torquier engine that doesn't rev as high and has consequently lower gearing. Awful explanation, sorry!

[RobCrezz]

LexSport said:

When you start comparing torque, you ideally want to do it at the wheels. If an engine revs high, but with comparatively low torque output, it can run shorter gearing giving the same torque at the wheels as a torquier engine that doesn't rev as high and has consequently lower gearing. Awful explanation, sorry!

exactly.

[Mr E]

LexSport said:

When you start comparing torque, you ideally want to do it at the wheels. If an engine revs high, but with comparatively low torque output, it can run shorter gearing giving the same torque at the wheels as a torquier engine that doesn't rev as high and has consequently lower gearing. Awful explanation, sorry!

But quite correct. Torque at the wheels matters. Everything else is dick measuring.

[sparkyhx]

Surely torque on a dyno is measured at the wheels?