I am the process of researching and running calculations for a custom turbo for my jeep. Any thoughts? I already looked at 505 performance and by the turbo application, they didn't do the math. I think they just bolted up the largest turbo on the market(thats why its so expensive) and pushed it out the door.

So my calculations are based on a system that will spool up at 1800 rpm and go till 5300 rpm redline.  Im trying to look for a turbo manifold. I was thinking of modifiying a manifold from an older CJ-5/7 4.2 liter application. I already punched enough numbers and I just have to go find a turbo now and design the system to work. Has anyone done something similar?

Again, Don't point me to distributers of forced induction. The fun part of jeeping is making your own stuff.  

I got done doing my research and im just going to build a 4.6 liter stroker. Its cheaper, more reliable, and easier. The turbo set up is a nightmare to get done. Like I said, I don't really like to go with other peoples set ups.  

i put a turbo on my 97 jeep wrangler it is on 6psi spools at 1800rpm and is very efficient if you want to do it. it is very easy my set up was about 300 dollars including a front mount intercooler and i used a small turbo off of a 06 suburu wrx and it took me about a day to do my own exhaust oil lines and cooling lines it was simple  

ok, im interested. Can you PM how you did it exactly. what about injectors? reprogramming the ecu? Exhaust manifold set up? what other mods to do to make this work? any engine upgrades you suggest? It sounds promising. You got pics?  

Thats definatly interesting... why not post up what you did so we can all learn from it! Oh, and add some photos too!  

I own a company in Oregon www.badimpression.com and also looked into adding a Turbo kit to our product offerings. After extensive research, I went to a company that designs and builds turbos for the exact specification per your motor and your expectations. Dont go to somebody that will not offer you the same!! I used GP Moto in Oregon 503-317-2959. The owner is Sean Logan and has been building custom turbo kits for the racing comunity as well as a few OE manufactures that were looking to do a factory offered design. Sean has all of the correct equipment and know how to do it correctly as well as correct many of the other engineering design problems that I had wrong with my Rubicon. Either way, do it right or dont do it. Using the all wheel drive dyno at his shop he can re-program your ecu and do your tuning right.

Good luck!!!  

I just tried calling him and no answere. My motivation is back up on this ideal project. I still kept all my notes and calculations. I just need help in contacting him.  

YES, tell us all what you did! Especially for $300, I am interested in an extra 6 psi.  I live in Denver, and regularly go up to 10,000 ft. when I wheel.  6 psi would return my 4.0L to sea level, or thereabouts, and net me a 20% gain in HP!  I suspect the stock computer and injectors could handle that adjustment.  Plus, it is additive, which I like.  I looked at 505 Performance too, and for $3000 I can get a nice V8 instead of a turbo...  I can buy a whole junker Suburban with a running 454 V8 in it for $1500 on Craigslist... Why would I spend $3 grand?  -But- $300 I can sneak into the household budget.  Gotta get past the wife...  

By the way, I googled GP Moto and they have moved to a new address.  Their new address and phone number is:
GPMoto
2525 25th Place
Portland, Or 97210
503-274-0070 office
503-243-5566 Fax  

well birddogdave, I can always look into the specs of the subaru turbo and see if it fits into the range of our engines. My designe is for a turbo to help in the output of the engine without sacrificing reliability. I found one place that sells the exhaust manifold or 650. thats when I started to hang up the hat on the turbo idea. I started getting into the price range that equates to building a stroker and still getting the same power. The hardest part of the turbo I see is making a manifold that will work, and working with the ECU to get the power I want. Everything else is almost a bolt in custom set up. I can EASILY make one for less then 505 performance and probably get better output and power delivery. Like I said, I don't think they did any homework, they just found the largest turbo on the market(thats what they used, Because I do REASERCH), and hope for the best. The Turbo they used is for engine size bigger then 6.2 liter and power outputs above 1500 Horspower!?  Unless Thats what you would want to build your inline 6 for. If I wanted that much power, I agree with you, just throw in a big block drivetrain and go to town. My calculations come out at 331 hp at the crank stock 4.0 and 384 hp at the crank using a 4.6 liter strocker motor. Keep in mind, this is taking account for 10 psi of boost,proper injector size, Mass Flow Rate, Air Fuel Ratio, Air density, and about 3 pages of calculations. Of course these numbers are NOT Concrete numbers. But If one person was to stick as close as possible to the numbers when assembling the turbo, the outcome is highly close and possible.

Possible turbos to use:
Garrett ;GT3071R w/intern W.G./46lb/min/71mm/56trimm/.50AR(stock and stroker)
and     ;T3/T04 50 trim w/.48 AR(maybe, still punchin numbers)
       ;GT37, 52 trim/.54 AR
       ;GT35R 68mm/58 trimm/.70 A/R
       ;GT32 71mm/52 trimm/.52 A/R (stock 4.0 only)

These are numbers on the COMPRESSOR only. Its important to match the compressor first to the application. I got these by looking at the compressor maps of each one and finding wich one best fits the application. I got my numbers using Pressure Ratio, Density Ratio, Temperature of air going into the engine, the mass flow rate of the engine at different RPMS.

Basically, you don't want a turbo that spools up fast and dies out faster before you hit the peak rpm range of your engine. Basically you will "choke out". On the other side, You don't want a turbo that takes forever to spool up to boost, and when it finally gets there, you are hitting redline of your engine(Thats what 505performance did )Not to bash on this company, but they are from the same home town im from and I wouldn't trust these guys with my Remote Control Nitro engine. .

Any ways: The stock 4.0 can safely go up to 5300 RPM before failure. I did my ideal turbo choices based at 1800 rpm spool up and hitting the best efficiancy at 3000 RPM. I kept in mind that by the time 5300 rpm is hit. you just start to fall off the graph of the turbo. BASICALLY, the ideal turbo.

I did calculations for the stock 4.0 and a 4.6 liter stroker. There is ALOT more to this. My reference was "Street Turbocharging" by Mark Warner, P.E. It is put out by "HPBooks". the website is www.penguin.com

This book explains it ALL!! from the math, design, fabrication, wonderfull examples, and it is geared to ALL cumbustion engines. Just plug your engine specs into the formulas. Even goes into the inner differences between turbos.  

Ok, you obviously know your way around a calculator.  Too much math for me, besides it's hard to do those equations with my crayons...    

I disagree with your RPM points, however.  When I am wheeling (rockcrawling), the engine works between 1200 and 2200 rpms (approximate, I didn't take notes last time ).  I don't want a sudden burst of power at 1800 rpm, I might launch myself somewhere I don't want to go.

Here's why I like a turbo added to the engine;  the 4.0L has one of the most primitive and goofy setups for intake and exhaust still driving around on US roads.  The intake and exhaust are on the SAME side, with the intake TOUCHING THE EXHAUST MANIFOLD!  So if you are in the Artic, you have a nifty intake-air heater.  However, most of us south of Anchorage kinda want to keep the intake air COOL, so it will be more dense.  Well, a turbo would overcome some of the inefficiency of the intake system of the Jeep, because it would mechanically stuff more air in there...

A stroker is a great low RPM solution, except that we live in the thinness of altitude here in Denver.  We lose about 20% of our engine power up here, (except on turbo-charged vehicles.)  A buddy used to tow with a 454 3/4 ton Suburban, and he said when he went down to sea level, he had way more power.  He bought a turbo Diesel, and on that same trip to sea-level he felt like he had the same power as here at altitude.  That's the turbo overcoming the lack of ambient PSI.

A turbo has a wastegate - it bleeds excess pressure above the wastegate's setting.  A small turbo, one that would spin up quickly, could reach it's limit of compression without exceeding the airpressure of sealevel.  That would mean I could leave everything else stock (since this engine works fine at sea level), and get back that 20% inefficiency without having the engine make enough power to blow up my dana 44's with their 36" tires.  I don't want to make a giant-killer here, that$ more money$$$ in broken part$.  Plus, I like the reliability of stock parts.

The same friend with the Suburban built a supercharged Mustang once.  He took me for rides, and basically the supercharger would never STOP adding boost - he had to be careful he didn't blow up the engine at higher speeds.  It just kept pulling stronger and stronger the higher his RPMs, and the power built exponentially.  That is NOT the effect I am looking for.  I want to have the turbo spin up quickly, and make predictable power.

Now - all this makes sense to me, but I could be wrong.  It's not like I actually did any research or anything...  I also was hoping to find a turbo that made boost at lower RPMs, maybe off of a small diesel or something.  I want it to be on an existing vehicle that may be found languishing in a junkyard somewhere;  I want to liberate the pieces without bleeding money.  Some boring, non-sexy vehicle that no-one is paying any attention to.  Most of those delivery trucks have smallish turbos on their diesels...

That's why a $300 system salvaged from a Subaru WRX sounds so attractive...  

first of all, I like your set up on your wrangler. Im running 4:1 in the t-case to help with gearing and running the same size tires you got.

I have no problem in the rocks or off road. I just hate getting on the highway and trying just to keep up with the slow cars. And I do like a little speed once in awhile.

I agree that a small turbo is the best fix for these engines. If you do find a turbo, try to find one from a engine as close to the same size of the 4.0.
Maybe from a grand national, or from a small turbo diesal.

I suggest a Garrett GT35 range used if you can find one. So far this is the one that best fits both worlds of reliability and power without any choke out or serious lag.

Go to ebay. These guys are getting rid of turbos for penneys because they upgrade thier cars for faster stuff. The only thing that concerns me is building the Exhaust Manifold. That is the true hurdle in this project. You can always detune a turbo to desired PSI until more money comes in to support Higher boost. Im telling you NOW, we WILL have to swap out injectors to avoid detonation. Im thinking of some factory replacements from ford motorsports around 24 lb/hr. We might beable to get these from any checker for not much money.

If you are serious about this, Go get the book I referenced. It WILL answere all your questions. It only costs 20 bucks. Cheaper then taking a semester in collage

My math is also based on running a intercooler. And its not the calculator: just basic knowledge of algrabra to get the numbers.  

another way to prevent detonation is to run richer or a DIY alky injection kit. I am in the process of turboing my 89 jeep comanch 4.0L ( building it to a stroker 4.6L with forged pistons 4.2l crank, turbo camshaft, will deep dish the pistons and use a thicker heag gskt to lower cr) supposedly the stock injectors from 96 and up should be able to handle a low psi flow rate. Now this is all hersay at the moment until I test and tune its up in the air and I am new to this so if Im off here please feel free to correct. As well any ideas if the stock intake will take up to 15 psi of boost...? (not gonna run that high yet but I'm thinking of building a street comanche and I want to try to run upwards of 15-20 psi of boost for on track and around 12-15 psi on street. Any Ideas or cautions are always appreciated.

Cheers, Jesse  

Go buy the book that I referenced:

This book explains it ALL!! from the math, design, fabrication, wonderfull examples, and it is geared to ALL cumbustion engines. Just plug your engine specs into the formulas. Even goes into the inner differences between turbos.

My reference was "Street Turbocharging" by Mark Warner, P.E. It is put out by "HPBooks". the website is www.penguin.com

Just make sure you build a bullit proof bottom end to handle any pressure above 10 psi.

Like I said: just go buy this book and run calculations on what you want.

the biggest hurdle like I said before is the exhaust manifold. You can alway run a remote system but you will lose effeciancy in your system.

GO Buy the Book. trust me  

Oh I am in the process of looking for the book and i Know that a remote mount setup is now where near optimal but i wont hard mount it till my engines built to handle a higher psi. Why do you say the exhaust manifold is the biggest hurdle...? just the fab of it or we talking making it hold up to the exhaust pressures and heat temps...?