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PR= pressure ratio. It is your boost level + atmospheric pressure divided by atmospheric pressure. If you are running one bar at sea level, it is (14.7+14.7)/14.7, or 2.

A very good rule of thumb is 1lb/minute equals 10 flywheel horsepower... 55lbs/hour would be good for 550fhp. This has proven very accurate in my automotive escapades.

A great book to read is "Maximum Boost" by Corky Bell. A nice easy to read basics book that clarifies a lot of what is being discussed in this thread.
Old 02-03-2010, 08:08 AM
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Originally Posted by djdawson2 View Post
The turbine section is more appropriately sized (vs. a 3076) with a 72.5mm wheel and a housing A/R of 1.12. All of this seems ideal for a 3.3 turbo running 1 bar or less of boost.
What would you think of a 4094 with maybe a 1.06 A/R turbine housing on an efi 930? I am in the process of trying to get one from a friend and plan on running no more than 16-17 psi (likely 16 psi) and using 1 3/4 primaries. My objective is to keep the heat out of the cylinders since I am only using pump gas.
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Old 02-03-2010, 09:24 AM
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Originally Posted by 930gt-40r View Post
What would you think of a 4094 with maybe a 1.06 A/R turbine housing on an efi 930? I am in the process of trying to get one from a friend and plan on running no more than 16-17 psi (likely 16 psi) and using 1 3/4 primaries. My objective is to keep the heat out of the cylinders since I am only using pump gas.
You've opened up more than one topic...

First, the 4094. Yes, you could use that turbo. What you would end up with is a fairly "high strung" build. Probably very little power below 4000 rpm. On top, you'd be able (efi) to expect 600+ whp properly tuned.

Second... Heat in the cylinders is related to total output, unless you are speaking specifically to heat problems associated with running too small of a turbine section. These are the sorts of issues you run into running an oversized compressor wheel... like your handle implies... a 30 hot side with a 40 compressor. This can be problematic when the ratio between exhaust manifold pressure and intake pressure is too high. The 4094 certainly wouldn't be at risk in this area.

Me... I wouldn't dream of using a 4094 on a 3.3 liter engine unless my goal was drag racing or all out top speed. I think you would find it quite annoying in everyday driving unless you raised your compression and dropped your boost.
Old 02-03-2010, 10:10 AM
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Quote:
Originally Posted by 930gt-40r View Post
What would you think of a 4094 with maybe a 1.06 A/R turbine housing on an efi 930? I am in the process of trying to get one from a friend and plan on running no more than 16-17 psi (likely 16 psi) and using 1 3/4 primaries. My objective is to keep the heat out of the cylinders since I am only using pump gas.
I think if you work with this you will talk yourself out of this large turbo.

Squirrel Performance
Old 02-03-2010, 11:44 AM
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unless you are speaking specifically to heat problems associated with running too small of a turbine section.
This was exactly what I meant before^^^ I felt like it was a direct possibility on my 67 with the .82 hotside.

Now as far as spool and all is concerned- it is not going to be the most fun down low, I accept that. But I do like to drag race and I LOVE highway pulls...(to 65 mph of course...). I did bump displacement with 98mm pistons and a 3.6 crank, so should make it slightly more tolerable down low, but never fun down there I agree. Also remember that I got a full twin valute system, so that should help a little.

CopBait- thank you for that calculator, that thing is pretty cool and I urge everyone to try it, just for the hell of it. . I put in that I want about 600 horse and it spit out 51 lb/m of airflow at about 5800 rpm. Then I looked at the 4094 and at 15-17 psi and 51lb/minute is right in the area I want to be in on the map. Also offers the possibilty of 700 horse at 1.5 bar on race gas even though I won't buy/or tune race gas.
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Last edited by 930gt-40r; 02-03-2010 at 01:15 PM..
Old 02-03-2010, 12:53 PM
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That is a great calculator... saves you the time spent on paper, which is where I've typically done my calcs. It also rings true when I put in some of my numbers... it comes up with expected results.

930gt... remember that you can only fine tune with the A/R on the hot side. Your choice of turbine wheel size needs to be correct, because you will only be able to adjust your boost threshold by 4 or 500 rpm by changing A/R... and you will not be able to correct a large imbalance between compressor size and turbine size... resulting in excess exhaust pressure and heat.
Old 02-03-2010, 03:45 PM
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and you will not be able to correct a large imbalance between compressor size and turbine size... resulting in excess exhaust pressure and heat.
Its like you said- the 4094r should not have that problem due to the size of the hotside wheel and housing.
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Old 02-03-2010, 03:51 PM
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Its like you said- the 4094r should not have that problem due to the size of the hotside wheel and housing.

Yeah... that will not be a concern with the 4094. However, I am going to predict that you will be disappointed with this turbo, unless you bump your compression and lower your boost to offset what will certainly be *really weak* bottom end performance.
Old 02-03-2010, 03:57 PM
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it will suck below 3500, but will be a rocket there on out. Think a .96 hotside may help?
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Old 02-03-2010, 04:04 PM
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If we are planning on living with the stock 930 wide gears, what is the best strategy or going to give us the highest average HP between gears and make us fast on the track.

A big mid range with a 6500 red line or mid to high range HP with a 7000-7200 red line?

Have not thought this one out. I know big HP is a ball but usually that means higher rpm red line and at some point close gears.
Old 02-03-2010, 04:40 PM
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I would seriously consider a 3788R. A more reasonably sized hot wheel, and a compressor that can still move close to 70lbs/hour.

If I wanted a top end car, that is what I would use.
Old 02-03-2010, 04:45 PM
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Originally Posted by 911st View Post
If we are planning on living with the stock 930 wide gears, what is the best strategy or going to give us the highest average HP between gears and make us fast on the track.

A big mid range with a 6500 red line or mid to high range HP with a 7000-7200 red line?

Have not thought this one out. I know big HP is a ball but usually that means higher rpm red line and at some point close gears.
To me, that is an easy choice. Except for anything other than a track with huge straights, having good low end punch and a strong midrange always works best... especially on cars with "long" gears.

I own an Audi that has incredible upper mid and top end power... and even with a close ratio 6 speed, I'm still waiting for boost to hit coming out of the tight stuff... and it is much harder to keep the car in the right gear.

Any day of the week (for track use), I would choose my Audi with 2 little turbos that hit at 2500rpm, but makes about 100 less peak hp.

In my opinion, you have to be one hell of a driver that is very good with left foot breaking while keeping your right foot in the throttle (to maintain boost) to make a high strung turbo car fast on the track. Look into Hans Stuck's history driving Audis. It took them a while to learn how to drive them fast. It can be done, but it isn't easy.

Last edited by djdawson2; 02-03-2010 at 05:14 PM..
Old 02-03-2010, 05:05 PM
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