Blow through v such through turbo conversion?

[911st]

As to the location of the Air Flow Meter, Porsche used a suck through approach on there 944Turbo.

Most doing conversions to 3.2 Carrera's are doing blow through.

Dose anyone have any info on the differences or advantages of the different approaches?

Also, was there a larger AFM on any of the 80's big V8's that might be adapted.

Thx.

[midlife]

Here are my thoughts:

If you use an off the shelf chip, you will need to use what it was designed for. I believe Protomotive uses blow through. Because the AFM is not mass flow you will get a different reading blow vs suck.

A 3.2 AFM goes out of range at high RPM even with natural aspiration. The added flow do to the turbo could make it go out of range sooner for suck configuration. For blow, the door opens less for the same mass flow.

The temperature reading at the AFM will be closer to what the engine will actual see with a blow through.

I am planning on blow through for my conversion.

Keep us posted on your progress.

Mike

[spence88mph]

Hasn't this been covered in length!!??

[911st]

I read through a former post several times some time ago.

From my memory there were a couple of points made and a rant that made things confusing. However, I did not feel like I could make any conclusions from it.

I was leaning toward a suck through thinking if I was going to do it, I would do it in as much of a factory way as I could, using the 944T as the model w 944T injectors, Turbo S fuel pressure reg, and hopefully a custom SW chip.

However, a blow through can be such a clean install and it am thinking that having a restriction on both the suck and the blow side of the turbo would not be the best. Even if Porsche did do so.

But, not sure.

Thx

[spence88mph]

Suck through is the way to IMO:
a. no chance of oil going through the afm
b. the casting of the afm is very weak so getting a good seal on the intake side is challenging as you can thread the afm VERY easily (I eventually had mine certed)
c. I think it would easier on the flapper no getting hit by boost (this might not be the case though)
d. you will get an un restricted flow from the turbo, but this might cancell out with the restricted flow on the cold side??

But no AFM is ultimately the goal. If you plan to go beyond 10psi I'm told the AFM starts becoming a consumable. You can make a very clean, easy, install with blow-though but the AFM is doing very little once boost kicks in apart from restricting flow...

here is my very simple install...

http://www.youtube.com/user/spence88mph#play/all/uploads-all/2/WOIdTnFQYD4

As I've said earlier I'm switching to MAP once I have time, trialling a piggy back computer that will transform the motronic to be MAP and completely tunable...hopefully.

I really think if you plan on doing mod just stick with a protomotive chip, they have so much experience with turbo 3.2s, well turbo porsches full stop, why mess with such proven chip/s?

[911st]

Yours is blow through?

Are your headers the OBX, they look great.

Did Brian make your muffler to fit on the GT turbo?

Dose Protomotove make a chip that works with suck through?

You know they can mod your Motronics system to a MAP conversion that includes a TPS?
I know it is a $2k price but he might give you credit for the chip you already bought.

[spence88mph]

Mine is blow through, I advise against it, I never thought about it prior to doing the conversion.

Yep OBX, they cop some flack on here in terms of build quality but I can't fault them, they still look as good as the day I mounted them too, 321 is a great material. I haven't heard of any OBX systems failing, unlike some other aftermarket headers, mine are nearly 2 years old too.

Brian is the man, yes he made the exhaust up a v band, first he'd ever made, the fit and finish is PERFECT! I showed it around to a few turbo shops over here before I mounted it as I was hunting a vband clamp, everyone couldn't believe how light it was and they all said it would be way too loud, it's really no louder than the stock 3.2 until you gas it... then it's armageddon!! For normal driving it's very civilized. Brian is an awesome guy to deal with too.

Ask Todd at Protomotive, he's a cool guy, I would imagine it wouldn't change things.

Yes I do know you can do that motronics MAP mod through proto, a friend over here did it. It's a great simple plug and play solution but ultimately I want a system that can be tuned on the dyno to my engine on the fly, if I change something I can easily tune it to match, not possible with the proto system.

[gsmith660]

Nice install! I agree the goal should be get rid of the AFM all I read was that the barndoor style worked fine in the application it was designed for but was not ideal for a turbo application when air fuel ratios are paramount and that is why I dumped CIS and dismissed motronic for the fact that the only way to tune it was to have someone program a chip for you (more expense) and had lots of dodads that were really expensive also and went with the EFI system I went with I researched most of the systems out there and kept coming back to the fact that most system manufactures don't want you to mess with the tuning and design the system as such IMHO so that is why I went with a megasquirt open source system from Bitzracing, it was ready to go right out of the box and has some impressive tuning programs that most are free.

Originally Posted by spence88mph

Suck through is the way to IMO:
a. no chance of oil going through the afm
b. the casting of the afm is very weak so getting a good seal on the intake side is challenging as you can thread the afm VERY easily (I eventually had mine certed)
c. I think it would easier on the flapper no getting hit by boost (this might not be the case though)
d. you will get an un restricted flow from the turbo, but this might cancell out with the restricted flow on the cold side??

But no AFM is ultimately the goal. If you plan to go beyond 10psi I'm told the AFM starts becoming a consumable. You can make a very clean, easy, install with blow-though but the AFM is doing very little once boost kicks in apart from restricting flow...

here is my very simple install...

http://www.youtube.com/user/spence88mph#play/all/uploads-all/2/WOIdTnFQYD4

As I've said earlier I'm switching to MAP once I have time, trialling a piggy back computer that will transform the motronic to be MAP and completely tunable...hopefully.

I really think if you plan on doing mod just stick with a protomotive chip, they have so much experience with turbo 3.2s, well turbo porsches full stop, why mess with such proven chip/s?

[911st]

Originally Posted by spence88mph

Yes I do know you can do that motronics MAP mod through proto, a friend over here did it. It's a great simple plug and play solution but ultimately I want a system that can be tuned on the dyno to my engine on the fly, if I change something I can easily tune it to match, not possible with the proto system.

With the MAP conversion he gives you the program to acces the chip and fine tune it. Or, he will redo chips as needed for a small fee.

Thanks for the help.

[beepbeep]

Blow trough is possible but not recommended. Flapper-type AFM will work better than hot-wire as it doesn't get hot. Hot-wire MAF will get messed up from the oil seeping past the turbo seals as it heats up the wire after shutdown.

If possible, suck-trough is always a better option.