blow thru vs draw thru???

[Full_Tilt]

This thread has me thinking.

When you dont move the IAT on a draw through setup, you are pretty much having to compensate for the compressor efficiency based on flow, without taking into account the pressure.
If you did move the IAT sensor, you would be able to compensate directly for the compressor efficiency with the IAT tables.

The more I think about it, the more I like the idea of Blow-through, at least from a theoretical perspective. You are accounting for Flow, Pressure, and Temperature and basically putting it all on one map. I can see how Blow through would be the way of choice with a turbo setup.
With a supercharger you have a direct relationship between RPM and pressure, so I can see how draw through would be just as effective. I can also see how with a supercharger not relocating the IAT would be fine as well, since the compressor efficiency will be based on pressure (predicted by rpm) and flow (read by MAF).


P.S.
This is what I call a tech thread.

 

[beefcake]

This thread has me thinking.

When you dont move the IAT on a draw through setup, you are pretty much having to compensate for the compressor efficiency based on flow, without taking into account the pressure.
If you did move the IAT sensor, you would be able to compensate directly for the compressor efficiency with the IAT tables.

The more I think about it, the more I like the idea of Blow-through, at least from a theoretical perspective. You are accounting for Flow, Pressure, and Temperature and basically putting it all on one map. I can see how Blow through would be the way of choice with a turbo setup.
With a supercharger you have a direct relationship between RPM and pressure, so I can see how draw through would be just as effective. I can also see how with a supercharger not relocating the IAT would be fine as well, since the compressor efficiency will be based on pressure (predicted by rpm) and flow (read by MAF).


P.S.
This is what I call a tech thread.

i did move my iat right to before the intake to get a more accurate reading.


with the iat being right at the draw point, i like to know the temp right before it hits the intake

 

[lito]

Properly designed both will work great, poor DT design will suffer of backwash, poor BT design will suffer from turbulance. The real big difference is that in a BT you can vent to atm.

This thread has me thinking.

When you dont move the IAT on a draw through setup, you are pretty much having to compensate for the compressor efficiency based on flow, without taking into account the pressure.
If you did move the IAT sensor, you would be able to compensate directly for the compressor efficiency with the IAT tables.

The more I think about it, the more I like the idea of Blow-through, at least from a theoretical perspective. You are accounting for Flow, Pressure, and Temperature and basically putting it all on one map. I can see how Blow through would be the way of choice with a turbo setup.
With a supercharger you have a direct relationship between RPM and pressure, so I can see how draw through would be just as effective. I can also see how with a supercharger not relocating the IAT would be fine as well, since the compressor efficiency will be based on pressure (predicted by rpm) and flow (read by MAF).


P.S.
This is what I call a tech thread.

MAFs do not measure flow.

 

[Full_Tilt]

Well its measuring the mass of air to go across the sensor, which would directly correspond to its pressure, temperature, and flow, right?

I guess what I was trying to say is that measuring air mass per second means different things as far as pressure and flow, which is what effects the compressor efficiency. Like say with a draw through turbo setup, you wouldnt be able to compensate for changes in the compressor efficiency because you wouldnt know the pressure or temperature of the charged air. X g/s at the compressor inlet wouldnt always correspond to being at the same place in the compressor map. Or am I just over thinking this?

 

[lito]

Well its measuring the mass of air to go across the sensor, which would directly correspond to its pressure, temperature, and flow, right?

I guess what I was trying to say is that measuring air mass per second means different things as far as pressure and flow, which is what effects the compressor efficiency. Like say with a draw through turbo setup, you wouldnt be able to compensate for changes in the compressor efficiency because you wouldnt know the pressure or temperature of the charged air. X g/s at the compressor inlet wouldnt always correspond to being at the same place in the compressor map. Or am I just over thinking this?

Yes, you are overthinking it, I guess you are trying to make another kind of modelling fit into a MAF system and it does not work that way. Putting it in a VERY basic way, MAF sensor will give you amount of air in weight, hence mass, per time and you know how much fuel mass per time your injectors can deliver plus the volume of the cylinder you are filling, a commanded relation is fixed and the PCM knows how much to inject to achieve it. This simplified system does not need to know temperature or pressure of the air used, it would not even know if air is being pressurized or not.

In this simplified system IAT plays no role (in the real thing it does but in two different was) on the fueling. There are no MAP sensor.

 

[Full_Tilt]

I think see what youre saying.
I guess I was picturing in my head that the maps would be scaled in g/sec, so I couldnt see how you would tune ignition timing in boost, when in reality they must be VE tables...

My mind is still caught in speed density thinking. Mass air is such a different way to picture engine load.

 

[lito]

I think see what youre saying.
I guess I was picturing in my head that the maps would be scaled in g/sec, so I couldnt see how you would tune ignition timing in boost, when in reality they must be VE tables...

My mind is still caught in speed density thinking. Mass air is such a different way to picture engine load.

In this simplified model there are no VE tables for fueling, depending on the airmass and knowing what is the cylinder capacity you know how much VE is dealing with, timing tables are referenced to this indeed.

 

[Wnt2gofst]

Paxton kit ordered. With Draw through cold air.


Thanks every one for the help.

 

[TexasBlownV8]

..may have missed it...but has anyone mentioned the fact of the differences in intercooling recirculated air vs. once-compressed air?
With a draw through, air compressed through the blower is fed back into the blower inlet. Compressed air is hotter than non-compressed air, and this recirculating effect causes the air to be used to be hotter, going into the intercooler, reducing the effectiveness of intercooling and also adding to heat-soak on the intercooler.

With a blow-through, there's a blow-off valve that vents to atmosphere, so un-used compressed (and heated) air is blown out of the system. Air that goes through the intercooler is therefore heated at a minimum, since it's compressed only once in the blower. This results in lower intercooler output air temps and less heat soak on the intercooler system. With the maf and IAT after the intercooler, any 'leak' or discharge to the atmosphere before the blower is not important to the PCM, so you can blow-off the un-needed hot air. Then when you go into boost, the system closes and cooler air ends up coming into the engine.

That's the big advantage of blow-though vs draw-through: lower air temps are possible, and thus, more net boost and more power. With lower IATs, detonation is also less likely.

 

[assasinator]

^^^^^ other reasons i use blow though. takes care of a lot of little things.


IE, i had a torn coupler running 16psi. i could hear the turbo spool, but very little power. i stayed out of it, and the car drove fine till i got to work and fixed the tear. the tear was outside of the maf circuit. blow off valves are just after the turbo. i can place them where it packages best and no recirculating.

 

[chuck@evoperform]

..may have missed it...but has anyone mentioned the fact of the differences in intercooling recirculated air vs. once-compressed air?
With a draw through, air compressed through the blower is fed back into the blower inlet. Compressed air is hotter than non-compressed air, and this recirculating effect causes the air to be used to be hotter, going into the intercooler, reducing the effectiveness of intercooling and also adding to heat-soak on the intercooler.

With a blow-through, there's a blow-off valve that vents to atmosphere, so un-used compressed (and heated) air is blown out of the system. Air that goes through the intercooler is therefore heated at a minimum, since it's compressed only once in the blower. This results in lower intercooler output air temps and less heat soak on the intercooler system. With the maf and IAT after the intercooler, any 'leak' or discharge to the atmosphere before the blower is not important to the PCM, so you can blow-off the un-needed hot air. Then when you go into boost, the system closes and cooler air ends up coming into the engine.

That's the big advantage of blow-though vs draw-through: lower air temps are possible, and thus, more net boost and more power. With lower IATs, detonation is also less likely.

Essentially this would be correct if you were recirculating all the time. But, this is not the case.

You are only recirculating air when off throttle, where as when you are on throttle, the recirc valve closes and all the air is forced into the engine.

Also, there is Boyles law to consider, that yes, says when a gas is compressed it heats up, but also when it expands cools down. I am not saying that all of the heat that is built up on pressure side of the system will be dissapated when it is recirculated, but the overall heating effect should be minimal.

I am not saying that a recirc system is better at all though. I personally prefer a blow through setup on turbo and centri charged systems, and even turbulence affecting MAF readings can be greatly reduced in just about any plumbing by taking advantage of something called laminar flow.

 

[Wnt2gofst]

Also what are the 47lb injectors good for whp wise?

 

[beefcake]

Paxton kit ordered. With Draw through cold air.


Thanks every one for the help.

thanks for the order!!!

 

[Wnt2gofst]

thanks for the order!!!

Now I need bigger injectors...LOL

 

[atistang]

my 89 always suffered from turbulence on a blow through setup. used to drive me crazy

as you can see the maf was in a bad spot

if i were to do it again i'm almost certain i'd go with a draw through

 

[Wnt2gofst]

Ok so maybe some one can answer this. The cold air 4fq112-060is it draw through or blow though? From looks is designed to be a blow threw.

http://www.vortechsuperchargers.com/product.php?p=181

http://www.paxtonauto.com/product.php?id=279

 

[Coyotetivct]

Yes it is blow through.

Did beefcake tell you where he got his 135mm MAF housing? You would not need to worry about an upgraded sensor if you went that route.

Or you could put it in the intercooler like the Procharger. I think JPC has it that way.

Save you about $500 dollars.

 

[Wnt2gofst]

Yes it is blow through.

Did beefcake tell you where he got his 135mm MAF housing? You would not need to worry about an upgraded sensor if you went that route.

Or you could put it in the intercooler like the Procharger. I think JPC has it that way.

Save you about $500 dollars.

NO he didn't. But I talked to tuner and he can get me a new MAF. He is already ordering it. SO not worried about it. He already has some new 80lb injectors he was going to use for his wife's turbo car. But he letting me get them. LOL

I am learning a lot from different people. Specially you and HLYWD. Seen that the kit comes for blow threw already which why mess with it, I just upgrade the MAF and be done. I got it figured out now.

 

[beefcake]

the standard kits are blow through kits.

my kit is a preproduction kit / non carb kit.

i don't think this is a question that ever came up. i know we talked about the air upgrade, but that was due to the stock being gone,

a good tuner, can tune either. John suggested I switch to blow through, but i love my fat MAF lol

 

[Wnt2gofst]

the standard kits are blow through kits.

my kit is a preproduction kit / non carb kit.

i don't think this is a question that ever came up. i know we talked about the air upgrade, but that was due to the stock being gone,

a good tuner, can tune either. John suggested I switch to blow through, but i love my fat MAF lol

You are correct we never talked about it.

I started doing research and got my self confused..LOL

Now with some help and what now I am on the right path. haha

I am just ready to get it. Get it in and return from Iraq and let it rip...