should io upgrade sc from 45 to 62

[NitroDann]

Theres a long winded post of mine here somewhere that explains how boost is ONLY a measure of restriction.

Nothing else.

Yes head flow is restriction.

Wozzah!!!???

Dann

[NitroDann]

Blow through a regular fizzy drink straw, large restriction large pressure, feel it in your cheeks.

Now try a Macca's straw, less restriction less pressure.

Open your mouth and try, no flow restriction, no pressure.

You there warren?

Dann

[gslender]

But Dan you are comparing sizes that are double in diameter in the straw example, and your mouth is order of magnitude in differences.

The head flows between the 1.6 and 1.8 isn't twice as large and certainly not 10x more.

There is no logical reason other than cylinder capacity for the difference. You'd notice a more pronounced difference adjusting the cam overlap then just replacing the head.

I'm struggling to believe a doubling of boost is primarily due to head flow.

I'll need more fact base evidence to be convinced it makes that much difference.

G

[gslender]

Would it be possible for his timing to be aways out and boost is just going straight out the exhaust??

Cam timing for sure. I remember a mate who installed cams and lost heaps of power due to less boost! Turned out he had too much overlap and for FI installations you need less, which is opposite of what you do for a NA engine.

G

[NitroDann]

Its the volumetric efficiency of the engine which IS affected by capacity, cams, and head flow. A 240hp turbo setup for an NC may do it at 8psi, however bolt that onto a car with similar capacity like like an S2000 and dial the turbo -FLOW- to 240hp and guess how many psi that is? Zero. No boost to get 240hp out of an S2k. They make it stock. Same capacity though right? Difference is...

Drum roll...

Head flow.

Another example.

BP4W engine
Stock internals including head
GT2560
10psi

200rwhp

Remember that the boost NOT flow is set by the boost controller and wastegate.

Now we add mild cams, no other change, and we make 220hp. The car still is at 10psi, because the wastegate and controller hasnt been touched.

Anyone building a n/a motor will tell you cams increase flow.

Now we reduce boost to 8psi and make 200rwhp again. We make less boost because the head flows more and is less of a restriction.

Adding the cams has improved flow, and so at the same boost levels, with less restriction we get more airflow, and more power. However at the same horsepower (and hence airflow) with less restriction (due to mild cams) the car 'makes less boost'.

Follow me now?

Dann

[mhj]

facinating
so would the 62 be better than the 45
and assuming yes...by how much?
enjoy

[gslender]

Well, to stay on topic, plenty of 1.8 with the M45 easily get to 12psi with reduction pulleys. Stock engine with an M45 setup to work with no IC is normally set to around 6psi to keep intake temps down. Go with a larger crank or smaller nose pulley and you push 9psi and require an IC. Go smaller/larger with pulleys and folks get more boost with either a 1.6 or 1.8 and I've just not seen folks mention any real difference due to which engine they have.

If the difference between 1.6 and 1.8 heads was that significant then none of the above would make sense .... There would be special 1.8 vs 1.6 pulleys and all sorts of differences .... There just isn't, at least amongst those using chargers.

Dan, maybe what you know of how turbos behave doesnt translate to charger setups. For example, changing the cams can have a positive or negative effect on the spooling, of which has no effect on a chargers ability to produce boost when needed.... I guess that might vary flow characteristics for turbos but not so much on chargers??

G

[gslender]

Actually, your VE point is worth exploring...

The 1.6 is 86kw in stock form, the 1.8 is 98kw, or a 14% improvement.

Adding a M45 with flows 45cu per rev isn't going to double (or halve) its flow pressure just changing between the above engines.

Yeah?

:p

[wozzah1975]

Hi All,

looking at the displacement of both those Superchargers the mp45 should be more than enough for the power you're making.

Your boost does seem low, what ratio are the pulleys?

As Dann stated, there are a number of things that effect boost. Boost is a restriction, the more efficient the engine is, the lower the boost will be as a general rule.

A few things.
in relation to the 1.6/1.8 engine statement.
If you fit the same size blower, with the same drive ratio the 1.6 will have more boost than the 1.8, one reason being the displacement of the engine, the other reason because of cylinder head flow. The engine simply needs less air.

Cam overlap and timing also effects boost, if the inlet valve is open for longer there is less boost, but more air being passed into the cylinder generally speaking (or should be!)

What are the specs on the rest of your engine?

Cheers
Woz

[mhj]

got the smallest nose pulley. standard crank pulley
beyond the breathing and injectors the engine is standard

[gslender]

got the smallest nose pulley

measure the diameter as this is ultimately the real determinate.

I think mine is 55mm and produces nearly 12psi (on a 1.6) but I still maintain you won't seem more than 15% less than that with the same pulley on a 1.8 - which would be > 10psi (so not 5-6psi). And that also aligns with the large population of MX5 Nutters in the UK who mainly seem to run with SC instead of turbos.... must be the colder weather or the fact that you find used Mini chargers over there for around $300 each !!

G

[NitroDann]

Cold weather will give decreased boost. Its all the same air mass though.

Dann

[wozzah1975]

got the smallest nose pulley

measure the diameter as this is ultimately the real determinate.

I think mine is 55mm and produces nearly 12psi (on a 1.6) but I still maintain you won't seem more than 15% less than that with the same pulley on a 1.8 - which would be > 10psi (so not 5-6psi). And that also aligns with the large population of MX5 Nutters in the UK who mainly seem to run with SC instead of turbos.... must be the colder weather or the fact that you find used Mini chargers over there for around $300 each !!

G

how did you arrive at the 15% less figure?

Woz

[NitroDann]

He posted earlier.

Hes assuming that the stock manufacturer quoted horsepower figure differences directly relate to VE, and hence boost pressure at a given flowrate, and nothing else at all affects it.

Dann

[wozzah1975]

Actually, how does head flow make any difference. The charger should be filling the intake when exhaust is closed, so the only reason you see positive boost is due to the minimal overlap between intake and exhaust valves (cams). The head just can't account for any real measurable boost difference as that's like saying too many bends in an IC will account for 3-4 psi boost.... And it doesn't.

Cylinder size yes, as that is volumetric capacity that does impact the boost pressure at 4000x per minute. So taken to extremes, on a 5.0L V8 you'd only see a small psi due to the massive volumetric difference.

But head flow? Really?

G

Head flow has everything to do with boost (amongst alot of other things). See what happens to the boost when you reach the limit of your cylinder head flow......Boost goes up, power stays the same......

Woz