Since our stock SC is losing efficiency at 20psi has any one thought of or tried reducing the SC rpms and supplimenting boost with a rear mount turbo to bring back 20 psi but with less parasitic drag to the crank??? Google "compound boost". Looks like it's working for lots o folks!

 

Perhaps 35 PSI ?

 

I'm liking the sound of that... Proper fueling & tuning might be tricky, but not imposible...

 

LOL! 35psi KABOOM!
No, I've been reading about the lean issues at boost over 21. Lack of tuning options would nix that for now. But, look at the turbo Eurocharged car. They picked up 60 HP by eliminating parasitic drag from the SC. Their car had the same boost and flow as our SC but no drag on the crank. No low end power either. My thinking is underdrive the SC to bring it down to say 12psi thus increasing efficiency then using the STS style turbo to bring boost back up to 20psi. HP would be gained by less drag on the crank not more boost. The turbo output is plumbed right to the throttle body.

 

Good luck. You might solve the turbo lag issue the Eurocharged car experienced - but how would you plum the charge air from the rear mount turbo into the stock system using the factory SC and still run it thru the intercooler?

 

The low boost rear mount turbo does not generate a lot of heat and has some time to cool before the SC. The SC does not heat the air as much because its not working as hard. Existing IC cooler is used. Supercooler HE that we already have is enough (take this with a grain of salt I'm brainstorming here).

 

I've had this exact same thought, though I'm not in a position to follow through with it.
Here are a couple of articles on twin-charged setups. Neither use a rear mount, but the articles should give some ideas as to how you can do the setup.

The first is a twin-charged C32, though it is not a compound boost setup. The supercharger is turned off at high RPMs:

Autospeed - Insane!

Here's the article on the Ford Mustang Hellraiser. It uses compound boost:

Ford Mustang Turbo Kits - Hellion 1,000 HP Bolt-On Turbo Systems - Hot Rod Magazine

One thing to remember about compound boost is that the pressure ratios are multiplied rather than added.

If you decide to go this route, please keep us all informed.

 

I hear what your saying. I've spend some time tearing into my SRT6 - so I often look at things a little differently.

Our SC'er bolts (and ports) directly to the intercooler. There is no way you'll be able to induct added the turbo charge air into it.



If you try to tap in after the IC (say right before the manifolds) you'll then have SC lag as it tries to compress air in the pipe back to the turbo - until the turbo catches up. Unless you devise some big one-way check valve.

If you run the charge air from the rear mounted turbo under the car, (perhaps where the resonator was) you'll either drag the added pipe or perhaps run it next to the exhaust pipes (sounds hot to me) - unless you plan to run it through the interior.



I'm not saying it can't be done - just seems like way to much $$, added weight and added points of failure that our ECU won't handle to reduce a little parisitic drag.

 

Brian, I didn't think about the charge pipe problem (dragging or no room), but you are not understanding where the turbo connects.

The charge pipe from the turbo simply connects to the throttle body where your air intake (SL55 y-pipe) is now. In place of your CAI. See what I mean? Your air intake would be at the back of the car at the turbo inlet. The pressurized charge pipe connects to the stock throttle body. No changes to the SC, IC, manifolds, all stock.

 

ive been thinking of this idea since we got out srt. i have a 66mm over 94mm on my cummins, the small spools the large turbo. alot of Dmax guys have been putting vortecs on thier trucks with a turbo feeding in. in turn the blower creates extra drive pressure for the turbo therefore the turbo spools faster then if it was alone, ie the eurocharged turbo car.

its a great concept and alot of guys have proven it works. the only problem i see is the lack of fuel. and dont forget the turbo srt6 was pushing less boost psi wise, but more cfm. some people dont realise that there is more then just pounds of boost, cfm plays a major role. food for thought i used to have a srt-4 with a ported td04 and 22# boost i made 327hp, i went to .50 trim and at 16psi i made 324hp at 23psi i made 416hp.

heres a pic of my compund turbos on my truck.
230bf108.jpg




as for room under the car, isnt there a sts powered limited?

 

I see - I don't know what the final cost would be - My truck already had a aftermarket turbo installed and I think the entire kit was around $4K.

There is plenty of room to mount the turbo in place of the resonator - and perhaps enough room for the intake filter as well...

Are you planning to do this?

 

I think in place of the rear muffler with a snorkle intake up inside the rear fenderwell would be the easiest location. I found a Garrett GT42r locally for SUPER CHEAP I'm grabbing after work today. If it's too big I'll resell it later. Even if your boosting into the SC the bottleneck should keep CFMs the same going into the motor. My goal is increasing efficiency of the SC.

 

a 42r is wayyy too big, especially if its a 4202
the smallest turbine side you can get is a t4 flanged .86ar iirc. given the enthalpy loss through the exhaust piping (even with ceramic coating and heat wrap) itd be way to laggy



thats roughly what a stock motor looks like mapped out on a gt4294r

you need to be down in the gt35-gt37 range to make efficient and streetable power

 

Thank you sir! Please help me choose. Remember we want LOW boost pressure with high air volume.

 

I believe the technical term is "twincharging", and no-I do not believe anyone has done it.

Twincharging is a bulky, heavy, and generally overly complicated method. A larger turbo alone can usually exceed the performance of any twincharging setup.

 

Wrong, twin charging is what the new VW motor has, also that sheik on Autospeed. An unloader valve is switching between SC and turbo. This would be a turbo compressing air then the SC compressing it further.

 

Remember the supercharger is limited to 30psi. it has no ability to produce that much on this engine by itself but you start compounding boost and PSI inside the blower is going to get pretty high. If you can compound it and keep it under 30 psi we should be safe though. Ditching the overdrive pullies and using the turbo to produce the desired psi might be required. Should be fun would love to see someone try this.

 

Same boost as a 181 pulley=19.5 pounds or whatever.
Same airflow or CFM as a 181 pulley, BUT using a LARGER pulley on the supercharger to REDUCE boost, crank drag, temps.
Same power as using a crank pulley + added power from less crank drag (substantial).

 

gt42r is quite large for our setup and ball bearing. the blower will help spool the turbo but the lowest i would go is the GT32 . the gt3271 is a 51/64 .78ar. any r style garrett turbo is a ball bearing which requires oil and water, i would stick with journal bearing turbos.

it will be hard to tell what size you need to go with for least amount of lag, but i would stick with the oem pullies for stock blower boost levels and aim for 25# total boost with around 35-50 lb/min from the turbo.

 

Been working on this for years now finally got the big parts together and on the car had to send the turbo back to get fixed but other then that it ran just fine.. will let you know how it goes when complete witch might not be to to long just got to get the turbo back. then tune