I've been reading the book Turbocharging by Hugh MacInnes and although dated, the formulas remain the same. There is not any information there about remote mount turbos, but I did see some racing applications where the turbo was a ways from the engine. On pages 70-73 there is a lot of info about exhaust systems. The book states that "...temperature, pressure, and velocity should be maintained as much as possible.", and "any velocity or pressure lost in the exhaust system must be regained in the turbine housing." The book does not recommend wrapping the exhaust pipe to retain heat. There is no formula to determine exhaust velocity loss over a certain distance, but based on this information, I would say the next smallest A/R housing would be the place to start on a rear mount.

The book does address turbine housing selection & matching on page 39. It suggests you start off with a larger A/R so as not to overboost the motor.

The book gives a formula on pages 37-38 for matching as follows:
Data needed (my data in parens):
Engine size (383 CID)
Engine type (4 stroke)
Maximum speed (6000 rpm)
Maximum boost pressure (15 psi)
Ambient temperature (90 degrees- worst case)
Barometer (29.0 Hg average)

I'll throw in the non-intercooled math here if anyone wants to copy it
Steps:
1. Convert displacement to cubic feet: 383/1728 cu.in/cuft.=227 cubic feet
2. Calculate ideal volume flow through the engine: (.227/1 revolution) X (6000 rpm/2)=681 cubic feet
3. Allow for restrictions, etc. (80% efficiency): 681 X .8=545 cubic feet
4. Calculate air density: Pressure ratio=(Manifold pressure absolute/inlet pressure absolute), or (2.03 X 15 psi+29.0 barometer)/29.0 barometer (to convert the boost to inches Hg, you multiply X 2.03). 15 psi is 30.45, so my final calc here is 30.45+29/29=2.05. The book then refers to a reference table for r and y values. In my case, r=2.05 and y is .22.
5. The ideal temperature rise is calculated as y X (ambient temp +460 degrees, which converts ambient to absolute), so my math is .22 X 550=121 degrees F.
6. The actual temperature rise is the ideal temp / compressor efficiency (get this off a compressor map). I'm using .65 for mine, so 121 / .65=186.
7. The intake manifold temperature is calculated as ambient + actual, so I get 90 + 186=276 degrees F.
8. The density ratio is (inlet temperature/outlet temperature) X (outlet presure/inlet pressure), or in my case (90+460/276+460) X (2.03X 15+29.0/29.0) or .75 X 2.05=1.54.
9. The compressor inlet flow is the engine flow X density ratio, or in my case 545 CFM X 1.54=839.3 CFM.

You can use this figure to select the proper compressor based on the maps the manufacturers distribute, such as this page (these charts use LB/MIN figures instead of CFM as calculated above. To convert CFM to LB/MIN, multiply CFM by .069, I got 58 LB/MIN for my motor, and using these charts a T76 would be the right size, they also have maps for the GT turbos linked off their home page, and a GT42 looks good for my application). Intercooling adds more math here.

There is an online turbo sizing site here that lets you plug in your numbers. It requires Java, and "engine capacity" is in CCs, so 350 rounds to 5800 and 383 rounds to 6200. I tried it w/ a 383 @ 14 psi & it showed using two GT25 turbos.

I would think the cost of custom machining housings and/or impellers/turbines for just one company would really escalate the price of the turbo in the STS application, even if they do it themselves.

 

as you say

off their site btw

If you were to take a conventional turbo and place it at the rear, you would have lots of lag and consequently, our turbo wouldn't work properly if mounted up front.

 

The only difference is the a/r on the turbine housing. They use a smaller then conventional size.

 

FWIW, that book is being totally rewritten/reworked by a guy named Mark Warner. It will be out later this year. I just happen to know because I'm getting some photo credits.

 

Great news, I've had my copy for close to 20 years. It would be cool if they add in the remote mount turbo or at least a decent formula to size one.

JL Turbo is making over 520 HP & 630 TQ with a T04E60-1 @ 14 PSI. According to all the info I've read, this unit is way too small for that application, but it obviously works.

Saw your car was in Car Craft. Excellent ride & engineering. I dropped my subscription after Jeff Smith was replaced.

EDIT
I bought a turbo calc program that allows plug in numbers and plots an entire RPM range on the turbo map. It also factors in pressure drops for the IC and inlet side. According to this, for my 383, the Master Power 62-1 is the best unit. The GT40 was close, but ran out of range on the top end.

For the thread starter, the big hangup I saw for DIY was fabricating the turbo mount pipe. From what I've seen, this is a cut down 90 degree 3" pipe with a swaged end to slip over the existing exhaust pipe, and the turbo & wastegate mounting flanges are then welded on. I priced some parts at JC Whitney, Ebay, & Summit and it looks like about $60 worth of parts plus labor to cut & weld as needed.

 

I found a reman GT42 today for $615 shipped. The numbers on it look pretty good, and this is the key part of the system. I'm going to chronicle my work on page 9 of my website. I'll try & make a parts list with costs involved for those that care to follow.

 

I often refer to: http://www.turbomustangs.com/forums/...?s=&forumid=15

I know it's about mustangs but there is a gm section and same principles apply. Besides the DIY section can keep me reading for days.

There is a sts in the for sale section that list some specs on the turbo:

the sts kit is a ls1 kit with a gt-40-67

Jason Robb

 

Thanks for the link, I've picked up some good info from the F**d guys in the past when I built a spring loaded tensioner for the ATI P600B. I couldn't find the STS kit FS there (searched "STS" and also "Rear" in the marketplace forums).

EDIT
I just found it in our FS forum.

 

subscribing...

 

Are you planning to run the GT42 as a rear mount? That's a big, heavy turbo to be mounting in that location. Also, I'm not sure if they make an exhaust housing small enough for this application.

 

Yes.

I realize there may be some issues with this, but as with most of the mods I have done to this car, that is half the fun and all the frustration .

I sized it based on the motor size, expected boost level, & engine/turbo/intercooler efficiency.

If this one is too big (not sure if there is such a thing when it comes to power adders ), I can always sell it & buy a GT40.

EDIT
The turbo I received is a Garrett TP3801 off a F**d Powerstroke ! I've contacted the seller for an exchange or a refund.