BHP - big car vs small car

changes

Hi

I am not very knowledgable about engines.

I have a question on BHP of cars. I had a passat 130 BHP and liked the power it gave. I am now looking at getting a smaller car like a corolla or an astra type size.

In order to have similar power relative to the size of the cars would 100 BHP give me the same power considering its a smaller car or would i need 130 BHP. Is BHP solely based on the engine or is the cars weight factored into it?

Thanks

Zonda999

It is factored on weight to a certain extent indeed but in your case again, you would need 130 bhp again to have the same kind of power IMO, to put it vaguely. I'd say that because in this case the weight difference wont be that big at all

But in reality, every engine delivers its power differently so even if you had 140bhp in a car the size of an astra, it still may not feel as fast as your passat. While i'm talkin about it, your passat 130 bhp would have delivered its power in a kind of a lump, as in there'd have been a very sudden delivery of power, all VW PD TDi engines were simliar. In a different engine with similiar power, you would probably get a smoother delivery power over a bigger rev range, which you may or may not prefer

Abelloid

Power to weight ratio is important, yes.

changes

changes wrote: »

Is BHP solely based on the engine or is the cars weight factored into it?

Based on engine only, weight of car not factored in. A test drive would be your friend

Atomic Pineapple

a 90 bhp Corolla with a N/A engine is going to deliver power very differently to a 130bhp TDi Passat also.

daveharnett

changes wrote: »

In order to have similar power relative to the size of the cars would 100 BHP give me the same power considering its a smaller car or would i need 130 BHP. Is BHP solely based on the engine or is the cars weight factored into it?

A car's BHP depends on a number of things (mostly engine and drivetrain), but not on the car's weight. So, you are correct, the power-to-weight ratio is a better predictor of how quickly a car will accelerate. It's worth noting that for high-speed cruising (ie. motorways), lots of power is still preferable to a high power-to-weight ratio.

Mc Love

Henry Ford on here has a festy with 130bhp i think!

changes

Thanks for replies

I'm begining to regret selling my passat. I'm running about in a 10 yr old peugeot 1ltr at the min. A big change in power, noise and comfort.

Yeah a test drive is a must, i don't think i'd like to go lower than 100 BHP again full time. 130 would be nice but it = more road tax also as i couldn't afford a 2008 or newer

EPM

You're forgetting about torque too. You Passat was diesel and that will have more pull lower in the rev range whereas a petrol will need to be revved much higher for comparable performance.

Having a figure you wont go below doesnt really make sense. All cars are different and you need to try them out

changes

EPM wrote: »

Having a figure you wont go below doesnt really make sense. All cars are different and you need to try them out

Thats prob a good point, i don't really know enough about it really. I had this notion that it was an exact thing where an 88BHP would be less powerful than a 90BHP etc.

I'll do a bit of test driving.

EPM

changes wrote: »

Thats prob a good point, i don't really know enough about it really. I had this notion that it was an exact thing where an 88BHP would be less powerful than a 90BHP etc.

I'll do a bit of test driving.

Well it is more powerful but there are other factors such as gearing to take into account. A car can be hampered by poor gear ratios taking away and power advantage

pajo1981

changes wrote: »

Thats prob a good point, i don't really know enough about it really. I had this notion that it was an exact thing where an 88BHP would be less powerful than a 90BHP etc.

It is an exact thing, but your 90HP engine will not be able to put out its peak 90HP all of the time.

Some engines (e.g. diesels) put out more of their peak power more of the time and so can feel faster.

alias no.9

pajo1981 wrote: »

Some engines (e.g. diesels) put out more of their peak power more of the time and so can feel faster.

The opposite is in fact true, the more linear the power delivery, the less noticable it is. The VAG TDi PD delivers it all in a lump and you really notice when the power kicks in so it feels faster, but they certainly don't put out more of their peak power more of the time.

Mr.David

EPM wrote: »

You're forgetting about torque too. You Passat was diesel and that will have more pull lower in the rev range whereas a petrol will need to be revved much higher for comparable performance.

Having a figure you wont go below doesnt really make sense. All cars are different and you need to try them out

+1

I reckon its more the torque than power you appreciated.

A decent check without actually driving the cars would be in gear times that represent overtaking e.g. 50mph-70pmph etc

SV

If it's a petrol you're buying, make sure you remember the power isn't going to be as apparent as the diesel.
Diesels are usually a lot higher in torque than petrols and this leads to people thinking it's all down to bhp.


edit: didn't read the thread :P

changes

SV wrote: »

If it's a petrol you're buying, make sure you remember the power isn't going to be as apparent as the diesel.
Diesels are usually a lot higher in torque than petrols and this leads to people thinking it's all down to bhp.

I was thinking on either the 1.6 petrol corolla or the 1.7 diesel astra, or the 1.4 astra (if it wasn't too sluggish), also the 1.6 focus - 2004 - 2006 years.

I like the VW Golf also but they are too dear.

pajo1981

alias no.9 wrote: »

The opposite is in fact true, the more linear the power delivery, the less noticable it is. The VAG TDi PD delivers it all in a lump and you really notice when the power kicks in so it feels faster, but they certainly don't put out more of their peak power more of the time.

Power for power, a diesel will put out a higher average HP than a petrol.

C0N0R

changes wrote: »

I was thinking on either the 1.6 petrol corolla or the 1.7 diesel astra, or the 1.4 astra (if it wasn't too sluggish), also the 1.6 focus - 2004 - 2006 years.

I like the VW Golf also but they are too dear.

I would be of the opinion that you won't find these cars as quick as your 130 passat. But you will have to test drive to find out.

EPM

pajo1981 wrote: »

Power for power, a diesel will put out a higher average HP than a petrol.

No it wont. If you compare like with like. 2 litre turbo diesel against a 2 litre turbo petrol I know which one my money'd be on. Try a normally aspirated diesel against an equivalent petrol and it's the same thing.

pajo1981

EPM wrote: »

No it wont. If you compare like with like. 2 litre turbo diesel against a 2 litre turbo petrol I know which one my money'd be on. Try a normally aspirated diesel against an equivalent petrol and it's the same thing.

OK, i didn't consider the turbo factor - i was comparing the output graphs of the similarly powerful 110HP 1.6 FSI and the 1.9TDI.

I didn't bring in displacement as it's not really relevant.

SV

pajo1981 wrote: »

OK, i didn't consider the turbo factor - i was comparing the output graphs of the similarly powerful 110HP 1.6 FSI and the 1.9TDI.

I didn't bring in displacement as it's not really relevant.

that doesn't make any sense.

power for power the diesel will be higher, erm..what?
Of course displacement is relevant as it's the only thing that can be compared.

and like for like in that regard, the petrol will always put out more power.

pajo1981

SV wrote: »

that doesn't make any sense.

power for power the diesel will be higher, erm..what?
Of course displacement is relevant as it's the only thing that can be compared.

and like for like in that regard, the petrol will always put out more power.

peak vs average. simple.

SV

pajo1981 wrote: »

peak vs average. simple.

Still doesn't make any sense.

pajo1981

SV wrote: »

Still doesn't make any sense.

two hyp cars. both have the same peak output but different av. outputs. Which is faster?

It's an invalid measure tbh as (even negating drag) more power is required to accelerate at a higher speed... i.e. a lot of extra power required to give a little more acceleration at higher speeds and so on...

average torque adjusted to take into acount rev range was probably the one I was looking for :rolleyes:

Matt Simis

SV wrote: »

Still doesn't make any sense.

I think he means measuring a cars HP at any given moment when not accelerating.. I guess a diesel has such a narrow power band that its like driving a petrol at 3k rpm everywhere (more HP, but you generally wont drive like that). So the diesel would be "sitting on" more HP till you accelerate then the RPM scales up the power on the petrol and diesel, with the diesel hitting its torque ceiling a lot faster.

He is probably correct, but Im not sure of the benefits..