It was a long time ago for me on these charts.
I think that your VE is too high for this engine, better 75%.
So CFM should be about 475-500.


You have too many lines for me.
So draw two vertical lines at 475 and 500 CFM.
Then draw L->R at your 3 desired PR.


Where these lines intersect on the map is the turbo efficiency.
Want closer to center island and away from left edge/surge line.
Want to see 3 intersection points to cross thru efficiency island.


GT35 looks pretty good, 20G maybe a little small.

 

I think this motor is fine at the 85% VE estimate. That is already on the low end of expectation.

The diagonal line is the surge line. It is inside the left hand side of the map which shows both turbos will not surge.
The cfm will change with the PR. The lines are color coded for the PR being used. Key is at the bottom. At 20psig (RED) the far right vertical line is at 5k rpm and the left vertical is 2500rpm. Both of these lines are within the compressors range. The use of an intercooler will reclaim some of the lost effieciency at the far right of the map.

The 20g map at a PR of 2.36 or 20psig boost being created before 1600rpm with full boost at 2500rpm and gains efficiency as the engine increases through the rpm range until appx 4200rpm where it starts to drift into the lower effiecncy islands and spinning the turbine shaft at somewhere around 130000rpm. Again, an intercooler will restore some of the efficiency list to hear.

Both of these maps work well for this displacement and rpm range. Just for fun if you look at a 15g map and plot the 2.4l at 5500rpm 95% at 17psig you will see that the right most vertical line is WAY outside the compressors efficiency. But this is what my SRT4 runs all day. It was equiped with a very nice intercooler from the factory.

These maps give a rough estimate at best. In the real world VE changes through the rpm range and changes with different AFRS, temperature, humidity, altitude and a few more variables that escape me at the moment.

 

Let's throw an hx35 up there which work just fine at 10psig and would still perform well at 20psig. An intercooler should be used in both situations.

The random t3 50 trim map isn't a good fit for the 4.0 at any PR.

On the other end of the spectrum and also not a good choice is the Borg Warner S476. I have one in my shop currently and it's just a stupid big turbo. This turbo will surge on the 4.0 as the surge line is to the left of any map point. Turning up the boost does not solve the surge issue as can be seen with the pink surge line at 45psig.

 

I like the 20g best for a daily driver. Ya sure its going to fall off up top but how many times do you push it to redline? I mostly see 1500-3000 rpms and that is where that turbo would shine.

 

Even at 20psig the 20g will keep pulling to redline. 5000rpm puts the Compressor at the 68% efficiency island which is why a good intercooler is used. That 50 trim would not be able to do much even with an intercooler.

 

Whenever I do a turbo build, it gets an intercooler. I dont care if your turbo ends up in the middle of the efficiency island, its still getting one. Colder the air, the better all the way around.

Going back to the 20g, be realistic on this one, how many people would run it at 20 psi on their Jeep? I can see 10 psi on a low compression mild build.

 

Realistically I would. I see no reason not to? I'm already running 10psig with a supercharger why not double it up while increasing efficiency?

 

Because a lot of reasons! Cylinder psi up the butt on an engine not designed for it! What type of fuel would you use? Meth? 20 psi is past using a piggyback system. A stand alone ecu with very well working knock sensors would be a must. Not many engines can handle 20 psi boost when not designed for it. Possible? Yes it is. But how long will it last and how much are you willing to spend? Personally, I would love to see you do it (it would make a ton of power!) but I would call you crazy at the same time.

 

Cylinder pressure doesn't increase in a linear fashion with boost. Just because you double your HP output does not mean cyl. Pressure doubles. I would be running what I do now 93 pump with -30 windshield wiper fluid. The aem fic is equipped to handle 25psig. I have a very well working knock monitor that shows knock well before I can hear it. I've boosted engines in the past that where never factory equipped with FI. I am willing to spend almost nothing on this Jeep. It's a $50 m90 sitting on my jeep. I have 2 spare engines just sitting around. Has anyone found the limit of these engines with a good tune? What is your set up?

 

On a 160k engine, 12.5psi popped a head gasket. Now this was at the front corner that has that head bolt tightened 10 less than the other bolts and the gasket was already rusted about half way through.

Replaced with MLS and new head bolts and so far all has been good for another 15k.

I've heard and read many times that the stock head gasket is only good to 12psi.

With ARP head bolts or studs and forged pistons and forged Scat rods or stock rods with ARP bolts should be good to 16-20psi as long as the tune and cool intake air temps are good.

 

That's what I'm looking at. Forged pistons 8.5:1. The rods are pretty solid on these engines so is the crank. I bet even at 20psig that still puts the motor under 400hp@ crank.

 

93 with washer fluid is honestly not going to cut it at 20 psi. Too much cylinder psi for that octane level. And like I said, that is only cause the Jeep engine was not designed for boost. My Juke with a 10:1 compression ratio sees 24 psi on 91 octane only. It is designed for boost. Again, I would love to see you test it out. I have never done it so I cant say its not possible until I see it happen...

That is very similar to what LS engines do. They are good up until about 15 psi then start popping head gaskets. The way we fix that is going to an aftermarket "6 bolt block". That meaning the block has 6 more bolts per head then a standard block (have to run matching heads). We run those up to 30 psi without head gasket issues.

 

What changes would you make so the engine can handle positive pressure?

 

Like Marty already said, forged low CR pistons and rods would be a must. Head studs too. A low quench would help some. Past that I would do an aluminum head. They dissipate heat better (in the actual combustion chamber, not talking about water temps). Less heat = less pressure. After all that, the fun part starts, choosing the right cam. The goal would be to design one that has low dynamic compression. This can be done with large durations (overlap) or by messing with the valve timing events. Both ways have pros and cons. And if you are serious about 20 psi, that block needs to be o-ringed and use a copper head gasket.

 

SO much depends on the whole combination.
Remember boost is just a measure of 'boost build up' in the manifold. With a poor flowing manifold, stock poor flowing head and stock valves and stock low lift low duration cam, you would be able to 'see 20 psi' but not have the corresponding high cylinder pressure. But what you will see with the higher boost is higher charge air temps and then need meth and intercooler.

Which makes more power- stock head and 12psi or big valve ported head and 10 psi?