Why is the battery box vented via the "ram air" system?

[Smokehouse]

This one confuses me...The first time I really got under the hood of this thing I noticed there's a duct running over to the battery box...does this seem like a waste of ram air or am I missing something?

[Haltech]

i guess they figured it would help longevity due to being placed so close to the turbo.

[Smokehouse]

Originally Posted by Haltech i guess they figured it would help longevity due to being placed so close to the turbo.

Hmmm...never thought of that one, I've just never seen that done before.

[bykeryder4life]

a cool(not cold) battery will perform better than a battery thats hot as fuck. It will give more consistent performance and will start the motor faster/better. This car is pretty high compression so the battery needs to be good to get it cranking.

[fbpem1]

Originally Posted by bykeryder4life This car is pretty high compression

i would consider this car a low compression motor, its not high by any standard.

[Smokehouse]

Originally Posted by fbpem1 i would consider this car a low compression motor, its not high by any standard.

sub 10 is low to me when considering a stock motor..doesn't the MS3 run some 9.5?...my GTO was 10.1...then again a Terminator Cobra is 8.5...

[mexicant]

Originally Posted by fbpem1 i would consider this car a low compression motor, its not high by any standard.

9.5:1 compression is high for a factory turbo car. My dsm is 7.8:1 compression.

My ford truck was only 9.1:1 compression from the factory naturally aspirated

[Tomas]

Originally Posted by 08ms3bm 9.5:1 compression is high for a factory turbo car. My dsm is 7.8:1 compression. My ford truck was only 9.1:1 compression from the factory naturally aspirated

yes, you are right, it is high for a turbo.
9.5:1 does not require a 1200 amp battery or something like that to crank the engine though. 400 amps and even less is probably enough.
Where you really need massive cranking amps is on diesels. Even the tiny turbo ones. Not jsut due to pressure in the comb chamber but also centrifugal mass.
You can probably hand crank the ms3.

[Tomas]

Originally Posted by bykeryder4life a cool(not cold) battery will perform better than a battery thats hot as fuck. It will give more consistent performance and will start the motor faster/better. This car is pretty high compression so the battery needs to be good to get it cranking.

Incorrect 1.
Cold batteries output lower amps than hot ones.
Keeping a maintenance free battery ( closed cell ) cool is for safety issues. Too hot = expand = crack / or even boom

Incorrect 2.
on the compression theory.
The high compression ratio is only under boost.
When the car is at still stand and the turbo isn't spooling the compression is less than a NA engine. Not sure on ms3 but probably about 8:1 or so???

[Smokehouse]

Either way it seems a bit silly to me (other than the heat in the engine bay part due to the turbo).

If it didn't draw in so much water driving in the rain I'd find a way to pump it into my SRi instead of the battery box...

[Tomas]

Originally Posted by Smokehouse Either way it seems a bit silly to me (other than the heat in the engine bay part due to the turbo). If it didn't draw in so much water driving in the rain I'd find a way to pump it into my SRi instead of the battery box...

I've muled that idea too. One could even connect the chute to the stock air box. There are ways to circumvent water getting in the intake like cutting a ridge 1/2" wide along the engine facing side of the plastic elbow just after it starts going upward for drainage. Not sure if this would work.
You'd lose some of the positive pressure but there should still be plenty left. At nay rate more than the stock choker set up.

[Hectik1]

Originally Posted by Smokehouse Either way it seems a bit silly to me (other than the heat in the engine bay part due to the turbo). If it didn't draw in so much water driving in the rain I'd find a way to pump it into my SRi instead of the battery box...

Thought about the ram air for SRI idea too.

[smakdown61]

Originally Posted by Tomas Incorrect 1. Cold batteries output lower amps than hot ones. Keeping a maintenance free battery ( closed cell ) cool is for safety issues. Too hot = expand = crack / or even boom Incorrect 2. on the compression theory. The high compression ratio is only under boost. When the car is at still stand and the turbo isn't spooling the compression is less than a NA engine. Not sure on ms3 but probably about 8:1 or so???

Compression ratio has nothing to do with the turbo. The ratio of volume at BDC to TDC. You use bore, stroke, and clearance volume to calculate it. None of which change at any rpm.

[igve2shtz]

Originally Posted by smakdown61 Compression ratio has nothing to do with the turbo. The ratio of volume at BDC to TDC. You use bore, stroke, and clearance volume to calculate it. None of which change at any rpm.

Right on. Thank you.

[FCmaniac]

Batteries need a form of ventilation. All cars that have the battery enclosed should have some form of ducting going to it to keep it cool. My RX-7 had a duct tube going to it too from the grill area.

[Smokehouse]

Originally Posted by FCmaniac Batteries need a form of ventilation. All cars that have the battery enclosed should have some form of ducting going to it to keep it cool. My RX-7 had a duct tube going to it too from the grill area.

I know my Mustangs and GTO didn't...might be a Mazda thing.

[FCmaniac]

Here's some info I found:

What is the purpose of the battery exhaust vent tube ?
Answer: When a battery is charged and discharged, water contained in the electrolyte is decomposed, generating hydrogen and oxygen gases. These gases are vented out of the battery through the exhaust vent tube to prevent potentially damaging high pressure gas accumulation.

[Lex]

It's to vent harmful and potentially explosive gases. This is why you can't use the stock battery in the trunk - you need a sealed battery for that.

[FantasmoNegro]

Both sides of the Compression arguement are correct. The Mazda is high compression for a factory force induction motor. Most NA cars that run this CR required premium fuel before the advent of knock sensors. Most factory FI engines ran about 1 to a full 2 points below what our car comes with. But because Mazda is running direct injection in this car they got a little bit braver with the CR, but not totally confident, thus the reason why we have such a cocksucking knock sensor. (Mazda making up for the benefits of direct injection with higher CR is why I say yall are stupid for running a higher AF ratio than 12-12.5:1 and thinking it will be fine.)

Now what Thomas was saying is correct to a degree as well. Different things can effect the static compression ratio and I think that is what he was hinting at. When your motor is in motion more things than just the mechanical aspects effect how much compression happens within the cylinder. Cams play a major role and so does any added atmospheric pressure, timing, as well as variable valve events. Which makes me even more iffy about being brave with my engine as far as so called "New tuning methods and theory for DI" are concerned.

Just trying to prevent a future shit fest.

[Tomas]

Originally Posted by Sleeper 362 Both sides of the Compression arguement are correct. The Mazda is high compression for a factory force induction motor. Most NA cars that run this CR required premium fuel before the advent of knock sensors. Most factory FI engines ran about 1 to a full 2 points below what our car comes with. But because Mazda is running direct injection in this car they got a little bit braver with the CR, but not totally confident, thus the reason why we have such a cocksucking knock sensor. (Mazda making up for the benefits of direct injection with higher CR is why I say yall are stupid for running a higher AF ratio than 12-12.5:1 and thinking it will be fine.) Now what Thomas was saying is correct to a degree as well. Different things can effect the static compression ratio and I think that is what he was hinting at. When your motor is in motion more things than just the mechanical aspects effect how much compression happens within the cylinder. Cams play a major role and so does any added atmospheric pressure, timing, as well as variable valve events. Which makes me even more iffy about being brave with my engine as far as so called "New tuning methods and theory for DI" are concerned. Just trying to prevent a future shit fest.

Exactly, thanks.
I just didn't want to get into bmep ( break mean effective pressure ) and other stuff. Just wanted to make a simple argument that the ms3 does not really have to overcome a lot of resistance to get cranked up. If you are really interested in this stuff, though, please read on!

The mean effective pressure is an abstraction of the pressure exerted into the combustion chamber of an internal combustion engine. Mean Effective Pressure is defined as the average pressure that the gas exerts on the piston(s) through one complete operating cycle of the engine. This definition can be expressed in terms of the work per operating cycle as

Work Per Operating Cycle = (Mean Effective Pressure) x (Swept Volume per Operating Cycle)

Since the work per cycle can also be expressed in terms of torque, the work equation becomes

(Torque) x (2 π Revolutions per Cycle) = (Mean Effective Pressure) x (Swept Volume per Operating Cycle)

The Swept Volume per Operating Cycle is its Displacement. For a two-stroke engine, the operating cycle is one revolution; for a four-stroke, two revolutions. Hence, Mean Effective Pressure in terms of Torque and engine parameters is

Mean Effective Pressure = 2 π (Torque) x (Revolutions per Cycle) / Displacement (May be incorrect! 4th Feb 09 RicardoUK)

Mean effective pressure is abbreviated MEP. BMEP or "Brake" MEP is for denoting dynamometer testing. IMEP is the MEP produced in the combustion chamber (acting on the piston crown) while BMEP is what remains at the flywheel after friction losses in the moving parts of the engine. FMEP (friction mean effective pressure) is a measure of how much MEP is lost to friction so:

BMEP = IMEP - FMEP

BMEP is calculated by taking the torque exerted by the engine over a revolution for a two-stroke engine and two revolutions for a four-stroke, and dividing it by its displacement. In SI units, for MEP in pascals

MEP = 2 π T / V for a two-stroke,
MEP = 4 π T / V for a four-stroke.

where

T is torque (in newton metres)
V is volume (displacement) (in cubic metres)

if you want to calculate directly in Bar then use formula below,

MEP = 4 π T / (V*10^5) for a four-stroke.

For example, a four-stroke motor producing 160 N·m (the rotating speed is irrelevant, but the torque is the power divided by it) from 2 litres of displacement is going to have (4π)(160 N·m) / (0.002 m³) = 1005000 N/m² = 1005000 Pa = 1.005 MPa of BMEP (or 10.05 bar).

If the same engine produces 76 kW at 5400 rpm (90Hz), its torque is 76000 W (or N·m·s-1) / 2π / 90 s-1 = 134 N·m; its BMEP will be (4π)(134 N·m) / (0.002 m³) = 0.842 MPa (8.42 bar). As piston engines always have their maximum torque at a lower rotating speed than the maximum output, the BMEP is lower at full power, it's because the efficiency is lowered by more friction losses, air viscosity, below optimum combustion, etc.

Another way to look at this. Because power is proportional to torque x speed, the power will continue to increase until the point where torque is decreasing more rapidly than speed is increasing. Peak power will occur at the RPM where torque is falling at exactly the same rate as speed is increasing. Obviously peak torque (torque neither rising nor falling with change in speed) must have occurred earlier in the RPM range.

To gain a step, the formulas for coming directly from power are, because P / (2πf ) = T

MEP = P / (f·V) for a two-stroke,
MEP = 2P / (f·V) for a four-stroke

where

P is power (in Watts)
V is volume (in cubic metres)
f is rotating speed (in Hertz)

MEP is a useful comparison tool between different engines, and is a good indicator of the level of performance achieved by the designer and manufacturer. As suggested by the formula for BMEP, it can be considered as an indication of specific torque - ie torque per unit displacement. This makes BMEP useful for comparing the torque produced by engines of differing displacements. It is important to remember that the values produced by the formula are for theoretical analysis only, and do not reflect the actual pressures inside an individual combustion chamber.

[Tomas]

oh, yeah.
that was a wikipedia quote. Not the people start thinking I am plagiarizing or unworthily taking credit here.

[FantasmoNegro]

Originally Posted by Tomas oh, yeah. that was a wikipedia quote. Not the people start thinking I am plagiarizing or unworthily taking credit here.

That is what I thought the point you were making was. I beleive I was wrong in my post. I beleive that the normal CR people talk about is Static Compression and the pressure you were talking about was MEP, but to cam grinders its also called compression ratio as well. My other cars cams are so good at making power because it doesn't focus on clearing air as quickly as possible like most cams do but instead it increased the cylinder pressures within the cylinder.