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Discussion Starter #1
Does anyone perhaps know this figure for the 3.2 busso engine? I am trying to calculate effective compression and maximum torque values, CFM and an ideal plenum and intake runner size. Trying to figure if a longer duration or slightly higher lift cam will be good for power up to 7300rpm but without losing the power low down.

Also, what is the flowrate of Busso injectors at their maximum cycle?

Can one improve airflow through the maf by removing the gauze in it, or is the gauze there for a purpose?
 

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Thanks Gertie. Is it safe to assume a maximum of 75% duty cycle on the injectors or is 70% a safer bet?
 

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The literature I can find on BMEP : it is a linear relation towards peak torque:

https://en.wikipedia.org/wiki/Mean_effective_pressure#BMEP_typical_values
For example, a four-stroke motor producing 160 N·m from 2 litres of displacement has a bmep of (4π)(160 N·m)/(0.002 m³) = 1,005,000 N/m2 =1,005 kPa (10.05 bar). If the same engine produces 76 kW at 5400 rpm (90 Hz), its torque is 134 N·m and its bmep is 8.42 bar (842 kPa).

Plug in 289 Nm for a 3.2 liter gives 1135 kPa or 11.35 bar
 

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Thanks Gertie. Is it safe to assume a maximum of 75% duty cycle on the injectors or is 70% a safer bet?
Much more, Injectors run close to 90% - 95% at WOT and peak revs.

If you choose an injector for a boosted application, you want to play safe, but OEM choose it on the money for N/A, very little "fat" in it when boosting

EDIT - Just remembered that while testing standard injectors - we hit 100% duty cycle at 1.1 bar MAP and starting to go lean. So in normal environment 90% duty cycle at atmosphere MAP
 

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Jip, don't exceed 90%.
 

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Much more, Injectors run close to 90% - 95% at WOT and peak revs.

If you choose an injector for a boosted application, you want to play safe, but OEM choose it on the money for N/A, very little "fat" in it when boosting

EDIT - Just remembered that while testing standard injectors - we hit 100% duty cycle at 1.1 bar MAP and starting to go lean. So in normal environment 90% duty cycle at atmosphere MAP
Jip, don't exceed 90%.
Ok thanks, that helps a lot :yes:
 

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Discussion Starter #8
I just found the values for Brake Mean Effective Pressure on the Busso 3.2 V6: It is 11.5 bar. After power calculations, my engine would have been around 1 bar higher at 12.3 bar which is an 7% improvement in performance. The clean-up job that was just done would probably be worth around 0.2 bar bmep so I'm looking forward to results after the remap :smoker:

Essentially this will improve with a new S/S exhaust, induction and Unichip-Q so I'm happy.:biglaugh:
 

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For a production engine, does this bmep compares well with the other. I might go dig into my books again.:biglaugh:
 

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If I remembered correctly, BMEP is the performance indicator to measure how powerful an engine is. It is always measured in bar. My IC engine books are all still in Cape Town, so cannot look for the reference figures.
 

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My guess is BMEP is around 11.5 bar. This goes to 13 bar for some direct injection engines and many boosted engines. Ring bypass then become a factor. BMEP does not relate to effective compression ratio, which have to do with cam duration. Meaning the valves are still open on the compression stroke and is not compressing. Then you can use a higher comp. ratio.

I believe the gauze is there to break water up and it does make a difference in performance. I measured 3.5whp more by removing it from a 2ltr. Don't remove the square blocks because the flowmeter will not measure correctly anymore.

My tuner do not like more than 80% working cycle on the injectors. On 1000cc injectors 70% is barely effective on 550cc 80% is max and on the Alfa's standard 190/220cc may be ok with 90% if the fuelpump and filters is VERY GOOD. The problem in this, lies in the recovery of the fuel pressure before the next injection. If the pressure do not get back to 3bar, the injector will p!ss out and not spray properly meaning you will have cr*p combustion and little power.

A 267deg cam is around the limit with std valves and seats on the Busso but on idle I lost the booster due to overlap. With 267deg(GTA2) I still had full lowdown torque but with 259deg(GTA1) and round seats and flat angled valves the overlap increased more and caused a torque drop low down. The valve job increased the flow, and power, close to the longer duration cam. This is not a problem as a 3.2 have more torque than needed on a front wheel drive at 2000/2500 rpm and didn't effect my towing a caravan as I stay above 3000 rpm.
 

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Discussion Starter #13
Thanks Corrie for that usefull info. Just to put things into perspective:

BMP is a function of how effectively your engine converts fuel into pressure, which is what we are specifically looking for as pressure can be converted t torque which can be converted to power. In other words, how much pressure is being put down on the piston crown. It virtually equalizes all engines as it comes down to a single unit that equates how well an engine is performing regardless of RPM. So it can be directly calculated by taking maximum torque and multiplying it by a specific constant.

In the case of 4 stroke petrol engines the formula is:

Brake Mean Effective Pressure = (2pi*n * t ) / (d/10)

n = No of Revolutions per Power Stroke. For a 4 stroke engine, 2 every 2 revs is a power stroke.
t = Torque in Nm.
d = Displacement in CC

So for a 3.2 Busso:
n = 2
t = 300
d = 3179

Therefore: (2pi x 2 x 300)/(3179/10) = (3770)/(317.9) = 11.86kPa

This is a good figure. Lets consider the BMEP of a 1750 tbi engine:

(2pi x 2 x 340)/(1747/10) = 24.46kPa. That is because a turbo compresses much more air into a cylinder than NA can suck into it.
 

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Ok, this is interesting. It's not a commonly used measure though; first time I've heard of it.
In Internal Combustion Engine Theory it is a very common term. True the IC students is a rather select group.

It is the only way to determine Horse Power from an engine without a dynometer. It is also usefull to determine what will happen with a known engine in different configurations and cams.
 
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