low rpm turbo = better fuel economy ??

lsvag

Wrench Pro
Points
16
Location
england
Car
Toyota Starlet 1.3
Golf gti 1.8t 20v (180) averages 35mpg
honda integra type R 1.8 vtec averages 31mpg

the golf is a turbo, if a low rpm turbo was fitted onto the integra, would the fuel consumption increase ?? or would you need to make the gears longer ??

but then again, it is also said that fuel economy is reduced while on boost, which you would be with a low rpm turbo driving around the street. would the fuel economy decrease if the turbo in the GTI was swapped with a bigger one that doesn't produce boost around normal driving rpm??

and another question, which method consumes less fuel, feathering at lower gear, or going full throttle at a higher gear ??
 
Last edited:
Re: RTC

If cruising at a steady speed then use as high a gear as possible and keep the throttle pressed slightly but constantly, rather than pressing and letting off repeatedly. (in many cases anyway) "full throttle" will obviously use more fuel. High engine rpm increases drag and wear on the engine so fuel consumption is increased. However, if accelerating it is better to rev slightly higher than cruising revs just enough to get you to accelerate nicely without having to mash your throttle through the floor. In my own opinion anyway.
 
Last edited:
Usiong your logic

the f 40 is red and faster than most cars

If I paint my car red then it will be faster than most cars


BTW perhaps you could explain how a low rpm turbo works
 
I think you mean a low pressure or low boost turbo.

The VTEC engine would not like having a turbo fitted, you'd have a big problem with detonation. By lowering the compression you'll have a chance to get a turbo working on it though but that undoes the parameters for this comparison.

Generally the more air you put into an engine the more fuel it will use as it needs to maintain the air to fuel ratio. The key is finding the optimum point and making an efficient engine.

The throttle/accelerator position directly affects the amount of fuel going into the engine. Find the peak point of efficiency in the rpm band and sit at that in the correct gear. For hills you'll need to drop down a gear but keeping the RPM in the sweet spot is perfect.
 
Ah and for reference in the Golf GTi the peak power to efficiency point is just a shade over 3000 rpm (so 72mph in 5th gear) this is just as the turbo is producing boost.
 
?? Low RPM turbo? If its a low pressure one (below .6 bar) then what is the point in fitting it to a petrol? I know they are added to deisal's, but why to a petrol? The gain in speed will be so little, the cost of it would give you a heart attack. Plus, I have never heard of someone adding a trubo to get BETTER fuel eco.

MPG has a lot more than what sort of engine and spec you have. A lot of it comes down to weight, airodinamics and the biggest component ''THE DRIVER''.

I have had just over 30mpg in mine on a motorway run. As to, have I had 7mpg. Its all about how you drive. :blink1:
 
youve also to look at the difference in the engines.
gti lowish reving - 6500 redline and 9.5:1 compession
ITR doesnt even waken up till 6500 rpm and has 11:1 iirc

and as you said gears, im sure the ITR being more a sports/ track day car will have shorter gearing than the golf so more likely to be using higher rpm for the same speed in the highest gear.

and how slow are you driving your golf to get 35mpg average ? i live out in the country with the same engine and only get average 32 only time i see above 35 is on motorways at a shade over 70.


welcome to the site anyway
 
I regularly got 35-37 mpg out of our A3 on a mainly urban cycle! Good oil, highish tyre pressures and careful gear selection help. (Any sort of fun or real driving and this dropped to around 31 though!) I can't get my A4 near the 41mpg claim for extra urban though 37 is tops so far.
 
Don't forget that it's not just the engine that affects economy, so "putting engine X in car Y" won't magically reproduce the same economy.

Other factors include gearing (the Integra Type R has VERY short gearing), aerodynamics, weight, drag, tyre selection.

To answer your second question, I find that more throttle in a higher gear gives better economy than feathering a lower gear (assuming you're not laboring the engine in the higher gear).
 
this is all true, but even though the integra weighs soo much less than the gti, smaller frontal area (which = less drag/aerodynamics) still drinks more. the tyres are grippier on the ITR so that means worse mpg.

but then again, do gear ratios and/or tyres make that much of a difference ?

btw the average mpg's were from manufacture claims so it may be different from real life.
 
but then again, do gear ratios and/or tyres make that much of a difference ?

all of this makes a difference. Tyres can make a huge difference. As per BBJ's comment, have to agree, this is surely a pointless exercies any possible beneift, if their really is any which doubt, would be more than absorded by the mamouth cost incurred by modifying the engine to suit.
 
?? Low RPM turbo? If its a low pressure one (below .6 bar) then what is the point in fitting it to a petrol? I know they are added to deisal's, but why to a petrol? The gain in speed will be so little, the cost of it would give you a heart attack. Plus, I have never heard of someone adding a trubo to get BETTER fuel eco.

MPG has a lot more than what sort of engine and spec you have. A lot of it comes down to weight, airodinamics and the biggest component ''THE DRIVER''.

I have had just over 30mpg in mine on a motorway run. As to, have I had 7mpg. Its all about how you drive. :blink1:


Manufacturers have started doing it.
F1 is thinking of doing it. Not obviously for fuel reasons but emissions.
Turbo'd cars will do better MPG than the same car without the turbo.;)
 
but then again, do gear ratios and/or tyres make that much of a difference ?

rather than look at differnt cars stick with the gear ratios here

your car sits at 3000rpm in 5th
say you change your ratios and end up sitting at 4000 in 5th for the same speed.

your car is going to be using more fuel
 
rather than look at differnt cars stick with the gear ratios here

your car sits at 3000rpm in 5th
say you change your ratios and end up sitting at 4000 in 5th for the same speed.

your car is going to be using more fuel

It will use more, but in all probability not that much more.
 
do gear ratios and/or tyres make that much of a difference ?

They can make a huge difference.

That's why hybrids and other economy cars run skinny, low resistance tyres.

It's also why manuals tend to be more economical than your conventional auto.

The manual usually has anywhere between 5 to 6 gears, compared to an old school auto's 4 gears.

This allows gears 5 and 6 in the manual to be taller, overdrive gears that help economy.
 
It's not so much the ratios (or lack of 'em) which causes a problem, it's the torque converter which absorbs energy.

Mine is a 6 spd steptronic auto, still of conventional design but the torque converter locks up in higher gears at steady speed to almost eliminate hydraulic pumping losses. Fuel usage is very modest for a large car but I don't do much urban driving which would probably have a serious negative effect upon the economy.
 

Similar threads


Please watch this on my YouTube channel & Subscribe.


Back
Top