[snorky]

subscribed for future reading enjoyment

[Inn-Tune]

I'm glad you guys enjoyed this. I've written a few quick tech threads over the years on various board so I'll put a few more up if anyone wants to read further.


CenCali07STI good work sorting berdugo's confusion out.

Originally Posted by berdugo

Inn-Tune,

Does humidity affect the power too? Lets say 80-90% humidity, if it affects the power at all. Thanks

As some others members pointed out, as humidity increases power will decrease, but temperature has a much larger affect on power.

Originally Posted by r12rex

This is definitely some good info. Numbers. Nice. Looks like you did the math correctly to me. Not bad for Sunday morning. It only makes sense though that a FMIC equipped car would produce more power than a TMIC equipped car. How much a gain could one get from a stock turbo STi and a FMIC set-up? I can't really see it being too much, but I'm sure the tempatures will be quite a bit lower.

I'd love a FMIC set-up, BUT...to keep it cop-friendly, I think I'll stick to my TMIC. Of course this could change in the future...


Kind Regards,
Ryan

Ryan you got the point of the thread and that's nice to see. In the top mount thread people acted like I was saying you can't make any power on a top mount. I know you can. I took my Suby out a couple months ago and ran a low 11 with NO intercooler just to prove a point. What I'm talking about here is making MORE power and consistant power.

Onto your question, since we're talking about % gains, keeping the percentage equal, the lower the HP you start with, the lower the gain in HP with be from intercooling. For instance a 50% gain on 200 hp (non intercooled) is 100 hp while a 50% gain on 400 hp (non intercooled) is a 200 hp gain.

Then you figure in your usage. Here are a few examples:
If it's a street car that never gets raced, power probably isn't much of a concern at all so it's hard to argue for changing anything on a stock turbo setup.

If you autocross on a stock turbo, the front mount will make power delivery a more consistant and you'll have more overall power, but you may not be able to make use of any extra power on some courses. Some people also complain about lag with a FMIC, but honestly on a 6 speed if you're out of the powerband on a stock turbo, you're in the wrong gear.

If you rally, you have to consider the benefit of the consistancy and power vs. the vulnerability of having an intercooler up front. Personally I feel if your IC is going to get smashed, your radiator would have been smashed and you'd be done anyways, but some people feel otherwise. I feel that when you're running restricted you have to maximize the power potential of the limited amount of air you can ingest so good intercooling is vital.

If you drag race, slow shifting can negate the advantage of extra power from the front mount on a stock turbo, but those that shift very quickly do see a benefit.


To be clear, this is how I feel about the stock turbo only. As the power level goes up, the advantages of a GOOD front mount become overwhelming.

[ride5000]

mike, the only issue i have with your otherwise good breakdown is your number for compressor outlet temp... it's way, way too high.

seriously, that's the absolute worst compressor efficiency EVER.

where did 415f come from? was it aps? if so, i can see why, because the higher the delta between ambient temp and compressor outlet temp, the better the intercooler "works."

[Inn-Tune]

That is the actual reading on a real STi. Also remember the outlet pressure was just over 27 psi so it's going to be quite a lot hotter than your average 1 bar setup.

You are correct that it's pretty high because the efficiency of the compressor is being pushed. From what I've seen most people do this so it's not out of the ordinary.

[LSE]

interesting. so subaru would get a much better performing car if they just moved it to the front...So why is it that they keep insisting on the top mounted ic?

is it cost? Is it really that much more expensive to run those pipes in an already expensive car?

It seems like a no brainer, the 08 should have gotten it.

[ride5000]

Originally Posted by Inn-Tune

That is the actual reading on a real STi. Also remember the outlet pressure was just over 27 psi so it's going to be quite a lot hotter than your average 1 bar setup.

is that with the vf39?

You are correct that it's pretty high because the efficiency of the compressor is being pushed. From what I've seen most people do this so it's not out of the ordinary.

do you really see "most people" running more boost than the oem map sensor can even register?

i don't know what kind of people go into your shop but the list of folks i know running 27+ psi on vf39s is very, very, very short.

they do this on pump gas? with what, ~10 degrees of timing? if so, i'd hate to see the egts at the end of 4th gear..

who tunes these cars this way? would YOU tune the car this way?

a long time ago (>4 years) a friend of mine did some tests with a td04 at 18psi, and was netting compressor outlet temps in the 200s. your numbers are 200 degrees higher than that, so you can understand my incredulity.

[fourseasonsandles]

How does the math work for this with DEI?!



On that note.. Great write up Mike!

[ride5000]

Originally Posted by ride5000

a long time ago (>4 years) a friend of mine did some tests with a td04 at 18psi, and was netting compressor outlet temps in the 200s. your numbers are 200 degrees higher than that, so you can understand my incredulity.

fwiw, according to the calculator here:
Stealth 316 - Turbo Outlet Temperature

comp efficiency would have to be 53.5% to cause a rise from 70 to 413 degrees at 27psig.

[RONIN]

Originally Posted by fourseasonsandles

How does the math work for this with DEI?!



On that note.. Great write up Mike!

WTF...

[RONIN]

Originally Posted by ride5000

fwiw, according to the calculator here:
Stealth 316 - Turbo Outlet Temperature

comp efficiency would have to be 53.5% to cause a rise from 70 to 413 degrees at 27psig.

Vote for the calculator as a sticky

[Inn-Tune]

Originally Posted by LSE

interesting. so subaru would get a much better performing car if they just moved it to the front...So why is it that they keep insisting on the top mounted ic?

is it cost? Is it really that much more expensive to run those pipes in an already expensive car?

It seems like a no brainer, the 08 should have gotten it.

Cost is always a big factor, but the engine layout of an STi lends itself very well to a top mount. Because the exhaust ports face the ground and are very low in the engine bay, and to avoid requiring an oil pump for the turbo, the turbo gets mounted up higher in the engine bay. If they put the turbo in the front and wrapped the header up there, how would they get the exhaust to the rear of the car while retaining normal ground clearance? That's not happening with the current layout, so they mount it up in the rear where the exhaust can get out cleanly. Then once the turbo is there right next to the throttle body you might as well have the compressor outlet flow neatly into a top mount and into the engine.

Another key element is packaging. A top mount setup can much more easily be transplanted into various other chassis, while a front mount often requires different piping, core mounting, etc. for proper fitment.

Then there's the trademark Subaru hood scoop. It's one of the big things that has set Subaru apart for a long time and no doubt they plan on keeping it. They even put them on the GC8 when it was totally non-functional simply because of branding.

I'm sure there's a lot more to it, but those are a few key reasons.

Originally Posted by ride5000

is that with the vf39?



do you really see "most people" running more boost than the oem map sensor can even register?

i don't know what kind of people go into your shop but the list of folks i know running 27+ psi on vf39s is very, very, very short.

they do this on pump gas? with what, ~10 degrees of timing? if so, i'd hate to see the egts at the end of 4th gear..

who tunes these cars this way? would YOU tune the car this way?

a long time ago (>4 years) a friend of mine did some tests with a td04 at 18psi, and was netting compressor outlet temps in the 200s. your numbers are 200 degrees higher than that, so you can understand my incredulity.

No...a VF39 wouldn't make 525 hp on a basic bolt on STi on gas. Th numbers used were with the APS TR70 rotated turbo kit iirc.

I never said anything about the boost level I see people running. I said I see tons of people coming in that are pushing the compressor efficiency of their turbo. At 17 psi on a VF39 at 7000 rpm on a 2.5L STi engine you are pushing the compressor map hard and tons of people do that. You can only use pressure as a reference for compressor efficiency when you state an amount of airflow and the compressor in question. When I say 7000 RPM on a 2.5L STi engine with a VF39 that implies an amount of airflow, so that's fine for estimations as well.

That calculator is a great find. I used to refer to that site for their fuel pump flow data.

I just ran the calculator for two examples:
16G at 21 psi, 100 F underhood temps
This is off the compressor map from about 5800 rpm or so on when run on a 2.5L STi, but people do this anyways. At 7000 rpm you're under 50% efficiency, but even if it was as high as 50% efficient, outlet temp from that calculator says 423 F

When I tune a small 16G I taper the boost to about 17 psi so efficiency is about 60% at 7000 rpm. That calculator still says the outlet would be 329 F under those conditions and I don't doubt it.

[ride5000]

Originally Posted by Inn-Tune

No...a VF39 wouldn't make 525 hp on a basic bolt on STi on gas. Th numbers used were with the APS TR70 rotated turbo kit iirc.

i'm glad i didn't buy that hairdryer.

as i suspected it looks to me like aps was painting their example in the most favorable light.

I just ran the calculator for two examples:
16G at 21 psi, 100 F underhood temps
This is off the compressor map from about 5800 rpm or so on when run on a 2.5L STi, but people do this anyways. At 7000 rpm you're under 50% efficiency, but even if it was as high as 50% efficient, outlet temp from that calculator says 423 F

without being on the compressor map, i'm curious as to how you determined that you're running <50% efficient?

When I tune a small 16G I taper the boost to about 17 psi so efficiency is about 60% at 7000 rpm. That calculator still says the outlet would be 329 F under those conditions and I don't doubt it.

with the larger cores there is a substantial amount of thermal inertia that can even out charge air temps quite a bit, allowing brief forays into the hot zone without corresponding rises in post-ic charge temps. typical blasts through the lower gears can go by quickly, and the heatsink effect of the IC core's mass allows you to go into a bit of "thermal debt."

you can't get away with that on a road course though!

[modaddict]

Originally Posted by LSE

interesting. so subaru would get a much better performing car if they just moved it to the front...So why is it that they keep insisting on the top mounted ic?

is it cost? Is it really that much more expensive to run those pipes in an already expensive car?

It seems like a no brainer, the 08 should have gotten it.

IMO, the main reason is crash test safety and scores with the NTSA (?)

You put a fmic on the car....you get rid of the bumper beam. This is why Evo's weren't allowed in canada, I believe.

Couple that with the reasons already mentioned and you have your reason. I do believe the safety factor is the largest weight in their decision, though.

[Inn-Tune]

Originally Posted by ride5000

without being on the compressor map, i'm curious as to how you determined that you're running <50% efficient?

I have the compressor maps for a lot of turbos including the 16g's and many GT and T series Garretts.

[ride5000]

i have never seen a compressor map for a 16g series turbo with a 50% island on it.

you want to post it up and help the community out?



i know you're talking out your ass, but i'll play along anyway; i do enjoy watching people hang themselves, bit by bit.