20 replies to this topic

[malc_west]

I'm sure it's been done too death but can I have people's pros and cons on a turbo compared to a supercharger. The car in question is to be turned in to a light weight road legal track weapon that will see some week end road use trips to Wales and the like. Cheers

[mini13]

Wellll....

 

with a turbo, utimatly you can make significantly more power, and also dial the power up and down with a boost valve, efficiency is higher giving better fuel economy,

 

with a charger, you get a more linear power delivvery ( although this varys depending on the charger type) exhaust is louder ( turbo's act as a silencer pretty well)

 

rough figures, with a eaton charger, your looking at 150-160 hp tops, and general driving down around 30mpg,

with a rotrex charger, as they are more efficient, and you can get an intercooler in much easier, you are looking at about 200hp tops, fuel economy is likly to be a bit better as they take a bit less to drive them, say 5 hp better?

With a turbo 200+ is pretty often done, and 250+ is possible, economy wise Ive known people to get 40-45mpg on a run, ive also achived that too.

[malc_west]

Wellll....

with a turbo, utimatly you can make significantly more power, and also dial the power up and down with a boost valve, efficiency is higher giving better fuel economy,

with a charger, you get a more linear power delivvery ( although this varys depending on the charger type) exhaust is louder ( turbo's act as a silencer pretty well)

rough figures, with a eaton charger, your looking at 150-160 hp tops, and general driving down around 30mpg,
with a rotrex charger, as they are more efficient, and you can get an intercooler in much easier, you are looking at about 200hp tops, fuel economy is likly to be a bit better as they take a bit less to drive them, say 5 hp better?
With a turbo 200+ is pretty often done, and 250+ is possible, economy wise Ive known people to get 40-45mpg on a run, ive also achived that too.

Thanks, so when driven hard is it possible for the turbo to always sit in the correct range for boost or is lag a real issue? Also another question I've stumbled across while scouring the depths of the net is that turbos due too low revs and a milder cam involve caining your engine less when you drive it compared to a tuned na. How does the super charger fair in this manner? Thanks

[mini13]

"lag" is not really an issue with modern turbo's also most people confuse lag and boost threshold, with modern turbo's such as the gt 17 you can be seeing boost down at around 2k rpm, where as you were looking at more like 3.3.5k for the old t3 on the metro turbos.

 

Yep, turbo's dont like a racy cam, even on an all out 200+ hp motor you'll be looking at cams of around 270 degrees, so off boost you get a nice docile engine, the MG metro cam is vey good in a turbo motor, as is the kent 274i.

supercharged engines are a lot more tolerant of hotter cams, as you dont have a turbine in there messing with the pulses/pressures, but id say 290 degrees is absolutly as far as you want to go, as the trade off of low in probably isnt worth it.

 

really the best thing to do is decide what sort of power you want and look at a spec to suit, as an example the basic stuff for around 180 hp...

 

rebuilt 1293 bottom end with cast omegas ( 10cc dish?)

36x31 head with enlarged cambers ( probably about 28cc yur aiming for a compression ratio of about 8.5:1)

1.25:1 rockers with either an MG metro,  Kent 274i, or avonbar phase 2 turbo cam.

Gt17 turbo form a saab 9-5

decent intercooler, and 18-20 psi boost

[mini13]

that of course ignores the clutch and gearbox...

[malc_west]

So current I have a metro turbo clutch fitted with lightened flywheel and a standard gear box. What would I do to get it 200bhp capable?

[Steve220]

RTS and straight cut gears if you're going to be driving spritely.

[mini13]

as above, the standard gearkit starts fgiving out around 140-150 hpish, metro turbo clutch is good fro about 120-130hp ish.

 

the RTS (roberts twin spring)  is essentially a pair of vertos clutch pulled apart and two springs stuck into one unit, doubleing its powerhandiling ( approx)

[haz]

I have no personal experience with a-series and forced induction but my only input would be this:

 

Shared gearbox and engine oil + turbo is not a great combo. Turbos like clean oil... and I would presume they also prefer semi or fully synthetic oil but that is very much an assumption.

 

Charger would be a safer and more reliable option IMO.

[REDICE]

A charger looks way cooler... 

[Steve220]

I have no personal experience with a-series and forced induction but my only input would be this:

Shared gearbox and engine oil + turbo is not a great combo. Turbos like clean oil... and I would presume they also prefer semi or fully synthetic oil but that is very much an assumption.

Charger would be a safer and more reliable option IMO.

Why can you not get clean oil from a Mini's set up?

[jaysmini1983]

 

I have no personal experience with a-series and forced induction but my only input would be this:

Shared gearbox and engine oil + turbo is not a great combo. Turbos like clean oil... and I would presume they also prefer semi or fully synthetic oil but that is very much an assumption.

Charger would be a safer and more reliable option IMO.

Why can you not get clean oil from a Mini's set up?

 

You could in therory run the turbo on a seperate pumped oil system if you wanted to go all out. 

the oil would be clean but not really upto modern technology is what Haz is saying.

[haz]

That’s a very good point Jay. You wouldn’t need a huge volume of oil either. A small oil cooler’s worth would be plenty.

[Steve220]

I'm still not understanding your logic, gents. Oil goes to the turbo almost immediately after the oil filter, so I'd say its the quality of the filter that is the governing factor. I'm as least worried about the oil being dirty on my mini as I have been on my previous turbo cars.

Edited by Steve220, 14 October 2019 - 02:06 PM.

[haz]

Oil filters only remove the larger contaminants (I say large, generally around 1 thou or 25 microns)

Plus the fact it’s mineral oil. No bueno compadre.

It’ll work, don’t get me wrong, but turbo life will be reduced.