Been Thinking About It...

[StrangeRanger]

Start with the compressor map. They're not at all difficult to read and you should be able to find one where the curve for your your intended boost and airflow runs through the middle of the efficiency "island" and avoids the surge line. You know you're looking for a small trimmed T04 or something equivalent so you really won't have a lot of curves to plot out.

Then comes sizing the turbine which is at least as much Black Art as it is science.

 

[crash-harris]

Anyone know what model turbo came stock on the 7.3L? I may have a chance to get a good one for cheap but I can't really findout much about them without knowing what model they are.

 

[Emerald 74 4X4]

Which 7.3? The originally N/A, then Turbo in 1994 IDI engine, or the 7.3L Powerstroke DI engine that was offered in 1995? They were both Garrets.

The one that Ford used on the IDI engine was smaller and probably more of what you are looking for. I can't remember how the exhaust inlet flange is designed on it though. These are probably harder to come by because they only turboed this engine for 2 years I think.

Ford put a couple different turbos on the DI engine. The fist ones were mounted at the bottom of the turbine housing with some VERY hard to get to bolts. The second ones were much easier to remove (two long bolts through the top). The problem with using these turbos as a DIY turbo is that they spin the opposite direction than that of most other turbos which makes the housings kind of odd to bolt up to some applications. Also the oil feed and drain are on the bottom as they were mounted to a pedestal that relayed oil to the turbo from the rear of the engine using an o-ring face seal (kinda like the oil pressure port in the rear on a small block chevy motor, but not pipe thread). I know they came with .60 and 1.00 A/R compressors and two or three different turbine housings as well. The ones off the T444E International Trucks had bigger turbines I believe. Some of them (i think 1998 and up) also had a provision for a hydraulic actuator to a warm-up valve located at the turbine outlet (some people think its an exhaust brake. It's not unless forced to otherwise). The turbine inlets are also a v-band clamp with a special divided flange and locator pin. I don't know if they are available as fabricated pieces for DIY or not. Also the Compressor outlet is a v-band clamp o-ring face seal that you would also have to adapt (not too difficult I suppose)

They are kind of their own beast.

 

[crash-harris]

It's a '94 F250 444E. Any idea about Garret's model number(s) for it?

 

[Emerald 74 4X4]

Here ya go...
http://www.ford-trucks.com/forums/898054-obs-7-3-and-sd-7-3-what-is-the-difference.html
http://www.ford-trucks.com/forums/826342-turbo-model.html

It should be a 1994.5 if its DI engine. It should be the TP38 Garrett. Of course you always take everything thats on the internet with a grain of salt.

 

[wallaka]

Should be a GTP38 if the PS or a GT38 if the IDI. Haven't found a map for it, but here's one for the ball-bearing version of the GTP38, the GTP38R: http://www.turbobygarrett.com/turbobyga ... mp_map.pdf .

Should be pretty similar, but the non-R will spool slower. They all have about a 1.0 A/R.

 

[crash-harris]

Gah! Looks like it's suppose to have a 1.10 A/R. Maybe I'll get lucky this summer and come across either a T04 or a HX35 on a trip north to Columbus' Pick N' Pull.

I am so ready for this truck to get turbo'd, everytime I start it I think, *whistle* :mrgreen:

 

[crash-harris]

I just realized that I'm not sure where the best place is to get oil pumped to the spool. Planning on puting a fitting in the oil pan for the return line.

 

[Emerald 74 4X4]

I ran mine off the front cam galley port. Its easy to access and tap into.

I am so ready for this truck to get turbo'd, everytime I start it I think, *whistle*

I just took my truck out of the shop and down the road this last weekend for a little "test run" mainly to see if the brakes worked alright. It whistled the entire time...it was weird...

 

[crash-harris]

I almost forgot, if I run 30 lb/hr. injectors, any idea what mileage drop I could expect over the stock 12 lb/hr injectors? Or would installing the 30 lb/hr. injectors just allow more fuel flow when needed instead of feeding a ton of gas into the chamber verus the 12 lb/hr. injectors?

Also wondering if MegaSquirt has sequential firing for the injectors now or if they still have bank fire (bank fire = mileage drop?).

 

[StrangeRanger]

The stock injectors aren't 12#, they're 14# but that rating is at 39 PSI. Installed on a 300 witha 58 PSI regulator they flow 17#. The 30# units you are considering would provide enough fuel for almost 400 HP. Do you really expect to make that sort of power? You always want to run the smallest injectors which satisfy your engines fuel/air requirements; larger than necessary only leads to drivability issues

 

[crash-harris]

Oops, I forgot that they were 14 lbs Thanks for clearing that up. It actually looks like (from my calculations) that I can get away with less. The calculations that I posted estimate about 375 BHP if I just slap any spool and intercooler on. Could I get away with 19 lb or 24 lb inctors and a new regulator (allowing 55-60 psi)?

 

[StrangeRanger]

I screwed the numbers up. Supercharged engines typically are less efficient than normally aspirated ones. I should have used a BSFC of .55, not the .50 that I used which is typical for N/A engines

To be really efficient, you need a boost referenced regulator because flow is based on the pressure drop across the injector. If the downstream side is higher than atmospheric then the flow is reduced accordingly.

In round numbers at a BSFC of .55, a 90% duty cycle and a 55 PSI drop across the injectors:

14# = 163 HP
19# = 222 HP
24# = 280 HP
30# = 350 HP
36# = 420 HP

I really question whether you can get 375 HP out of a 300 at that boost level. I used the same numbers you did (although 42°C is pretty unrealistic for ambient) and ran them through this calculator http://www.turbofast.com.au/tfcalc.html. It gave 275 HP which seems a far more realistic number.

FWIW If you ignore all the thermo and simply ballpark the expected HP:

150 HP * ((14.7+8)/14.7) * (4500/3500) = 297 HP.

It pretty much has to be a number lower than that since that number ignores all the thermal losses and inefficiencies and assumes that the engine can be made to breathe as well at 4500 as it does at 3500.

 

[crash-harris]

Looks like I did my calculation for *C incorrectly, I ment for it to be relativly 80*F, so it should have been 26.67*C instead of 42*. I did it on the calc again and it came out just shy of your HP number. So it looks like 24 lb/hr would be just shy of creating maximum power (in theory), though like you said, numbers should probably be a little lower (and I don't doubt that). But still, would that just allow that much more fuel when needed to make that power? Or will it deliver around that amount even while cruising without opening up the turbo?

 

[StrangeRanger]

EFI systems when properly tuned maintain a warm engine at 14.7 air-to-fuel ratio at all throttle openings and conditions except WOT where they run intentionally rich. Whether you run 24 or 30 lb injectors this will be true. The 30 lb units will provide a little more protection against leaning the engine out at peak.

The drivability issue is due to the fact that at throttle tip-in, the larger units can meter too much fuel until the EFI system catches up. This can cause some surging, stumbling and general drivability headaches.