Help working out how much boost I can run...
Turbo Mini Forums

I've got TM disease and I've got it bad.

Been thinking about my SC12 suck through setup (I know, but I'm committed now) and doing some research on the compressor. No Map available for it, but I've tracked down the original manufacturer and found some spec's on it.

They say it's good for 11,000 RPM, but my pulleys are 1:1 so I'm only going to get say 7,000. They where spec'd like this for 12psi, but I reckon it's capable of more. So If I talked nicely to Fast Carl, I'm sure he'll make me another pulley. If, for example, I had an 80mm pulley, I would have 1.375:1 and a max compressor speed of 9625 rpm at 7000rpm (Nice and safe, but 70mm would put be bang on 11,000 at 7k rev's).

Data I found:

Theoretical Discharge Volume per Revolution - 1160 cc/rev
Max RPM - 11,000
Max Pressure Ratio - 1.8
Max Discharge Volume at Max RPM (Press Ratio 1.8) - 605 M3/h

It will be EFi so fuel shouldn't be a problem, just wondering how well this would work on a 1275 (8:1 CR) if I ran it closer to it's limit. How would putting fuel in with the air effect it, obviously a liquid won't compress like oxygen will.

Data is from here:

http://www.ogura-clutch.com/products.html?...105&category=3#

70mm.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

By my calcs using an MG metro cam, at 1:1 it'll be running 12 psi (not accounting for losses owing to bends and heat etc.)

With the 1.375:1 I calculate around 21 psi.

But with the 70mm (1.57:1) You'll get a whaping 28pis boost!.

You state a max PR of 1.8, which is 12psi. So whatever mad Robert says, 1:1 looks good to me. Maybe a bit higher to account for losses!

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Air flow and pressure ratio go hand in hand. the pressure ratio will depend on how much air flow the charger produces compared to how much the engine consumes.

So at 11,000rpm with a pressure ratio of 1.8 the air flow rate iis 605m3/h. If your engine will not consume 605m3/h at 7000rpm, the 'excess' air flow causes the pressure ratio to rise.

The max pressure ratio the charger is capeble of will of course ultimately determine the max boost pressure. In real terms, you need to decide how much boost you wish to run within the limits of the charger, calculate and estimated air flow that the engine will consume at 7000rpm with the desired boost, and then run the charger speed that gives you the air flow at that boost.

Interesting...

Talking to Luke, he's running 15psi on his 1100 and it's been fine.

The cam is a 274 with 1.5 rockers if it makes a difference.

28psi does sound fun, but I doubt it would stay drivable (or running). I reckon about 18psi would be a good compromise. What ratio would I need to get that?

EDIT: Thanks Sprocket.

"The max pressure ratio the charger is capeble of will of course ultimately determine the max boost pressure. In real terms, you need to decide how much boost you wish to run within the limits of the charger, calculate and estimated air flow that the engine will consume at 7000rpm with the desired boost, and then run the charger speed that gives you the air flow at that boost."

Unfortunately that bit is beyond me, hence the question...

Edited by apbellamy on 23rd Jun, 2011.

The MAX pressure ratio determins the max boost. Pressure ratio is an absolute value. Taking the example of the 1.8 max pressure ratio, an absolute charger inlet pressure of 14.5psi (atmospheric pressure) will discharge at 26.1psi absolute, which is a max permissable 12.1psi 'boost' (disccharge minus inlet pressure) the charger is capeble of achieving. It will most certainly not achieve 28psi boost if you go by the manufacturers specs

Peak torque rpm of the 274 cam will is published by Kent. Use this with one of those turbo calculator thingamybobs with the boost set at 12psi, then calculate the air flow with 100%VE and 75%VE giving you an idea how much air the engine will consume.

Once you have an air flow figure for the engine, you can then try and work out what speed to run the charger at at peak engine torque RPM.

You could always just stick it on with the 1:1 ratio, see what it does, and then work out where to go with it, since we don't have the charger map we don't know what the air flow is less than 11000rpm and 1.8 pressure ratio. Simply trying to calculate from the volume discharge per revolution doesnt work, since taking the max 605m3/h and working back, does not give 1160cc/rev at 11000rpm, there are obviously pumping losses.

Hang about and I'll work out a calc. 1293cc?

1293 - yes

Calc - thanks.

I'll have a dig round and find a turbo calc later and try and learn something

http://www.superchargerperformance.com/sup...r-modifications

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Estimate of peak power at 5500rpm

Air consumption of 231 m3/h at PR of 1.8, 75%VE at 5500rpm. Peak power gives 98hp and torque of 94lbft

Air consumption of 309 m3/h at PR of 1.8, 100%VE at 5500rpm. Peak power gives 131hp and torque of 125lbft

Or peak power at 6000rpm

Air consumption of 253 m3/h at PR of 1.8, 75%VE at 6000rpm. Peak power gives 107hp and torque of 94lbft.

Air consumption of 338 m3/h at PR of 1.8, 100%VE at 6000rpm. Peak power gives 143hp and torque of 125lbft

all the above calculated with an AFR of 12.5:1 and SFC of 0.5. Bear in mind that these are estimates to give you an idea what you may or may not end up with. I have used the peak power rpm for the 274 cam from my dyno charts with the 1400 and same cam with 1.5 rockers. Power peaks around 5500rpm and then is pretty flat up to 6000rpm before it starts to tail off.

So realisticaly you shold expect to be somewhere between 98hp worst case, and 143hp in an ideal world with an airflow somewhere between 231 and 338 m3/h at 5500 to 6000 engine rpm.

Basically without the charger map, its going to be dificult decide on the charger speed to give this air flow at 1.8 PR. Certainly running the charger at 11000rpm at 7000 engine rpm will push the pressure ratio through the roof since the engine will never be able to consume 605m3/h at 1.8PR

605m3/h roughy equates to 250hp

You should also account for the fact that you are not using an intercooler and the adiabatic efficiency of the blower.

If, for example, the air temperature after the blower is 100 Deg C rather than 25 Deg C, then the boost pressure will be higher as the air is trying to take up approx. 25% more space.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

oh and the charge temps will be around 90 to 100 degrees C

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Interesting...

So 12psi is a good road spec (based on 6k revs). So if I go do some calculations and find that more boost is possible, I could have two fuel/ignition maps and just swap the pulleys over for more power...

Andy, i have read a post from Ben which stated that the coating on the rotors comes off when you start running 14 psi...

I have ordered a new pulley for mine now it's running water injection.
IMO you will need to run some sort of cooling aid if you are heading away from bens 10psi pulley.....

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Ah right, I misunderstood/misread your post. Stick with what I've got ad add N2o for more power

Realistically, if I can get 140 bananas out of it I will be happy. Should make a fairly fast road mini, especially if my my diet ideas work...

Aluminum, fiberglass and lots of holes

Ben reckons 14 psi max, the coasting inside was stripping, this was after 1 year of racing. When he pulled it down to check.

Manufacturer still says 12psi max