I've recently come to a crossroads with my build: Magnum 76/68 is maxxed out and I want to do something different to keep expanding my knowledge and to keep my interest in the project truck. After talking with KB about his experience with Vicalma's compound 4.8l he did a few years ago, I think I'm going to give it a try.

Truck is a 4000lb 03 rcsb street truck 4.8l (additional specs in signature). I dove into the math and have come to a similar conclusion on turbos that KB used on Vicalma's truck, and the turbos Forced Inductions just spec'd me.

Truck Goals: 800+hp at 20-24psi boost
Forced Inductions Recommendation: Borg Warner 62/68 .88 A/R and Borg Warner S480/96 1.32 A/R.

Generally speaking from what I've come up with, keeping the turbos at the same PR for a total of 24psi WOT will mean the S480 is providing 9psi boost, and the 62mm is compounding/adding an additional 15psi boost for a combined 24psi. Spool on the street from 62mm will be quick and will be wastegated at around 9psi referenced to intake manifold. The top end spool from the S480 should also be awesome with it wastegated at 9psi referenced to the intermediate intake pipe between the two turbos.

I guess, if anyone wants to rack their brain, I'm hoping to get some input. I'm not shooting for any records and big single or twin turbos is common place - I'd like to try something different. Any and all comments are appreciated, especially the technical turbo talk! Thanks for looking!

 

I wish I had something to add... but I have literally no experience with compound turbos.

 

What are you goals, just a hp number? If thats the case you would be better off with just the S480. Depending how you size the turbos you might actually bring in boost too fast with the small one (and bend rods in the process). It can be made to work, just will be tricky to tune via wastegates and springs, and will ultimately add a lot of complication to the system. Different though, especially on a gas engine. Diesels tolerate a bit more abuse with something like this.

 

If you are thinking compound.
Give Kyle a call. He has built one and worked on one.

 

HAHA me either!

Atomic, goals really don't include a HP figure - I want to go faster than 10.86...low 10s high 9s, I understand I may very well break the motor in the process. I understand a single S480 would be better suited to a high HP goal, however what are you thoughts for a compound set up at the track? I'm just curious as I go to the track pretty frequently.

I agree with boost coming on too fast could be a potential issue and the turbo recommended by Forced Inductions is actually a larger exhaust wheel than KB used so that may help. It definitely adds complication to the system but that and the tuning considerations intrigues me. I'm planning on having each wastegate set up on a MBC to dial it in after initial data collection. I'll probably monitor boost and outlet temperature for each turbo just to get a better idea of whats going on in addition to EGTs and backpressure. Additionally, I'll be spraying meth in the intermediate charge pipe between the two turbos to recover some air density, in addition to the dual nozzle kit before the throttle body.

Thanks Trick. I contacted Kyle and he gave me some good info on the compound set up he worked on. Based off of his recounting of how that truck drove (in past posts, and just the other day when I talked to him) it sounds like a hell of a lot of fun and is certainly different.

Turbo sizing (compressor and turbine, A/R, etc) is really where I have the questions/wanted a sanity check from some of the more experienced guys on here.

 

If this is a track only truck then compound will offer no advantage over a properly sized single since spool time is generally not a concern at the track. All of your gains will be in the fast spool department.

 

Its not a track only truck, I'm looking forward to being able to drive it again on the street once this is all finished.

 

It will certainly drive with any combination of turbos, your foot controls them after all. The magic will be in tuning the system to have the responsiveness you need with the control you also need to keep everything in check. Screw up a wastegate and you can easily hit 50psi of boost.

 

Atomic, It's really very easy to tune and setup. No harder than any other setup I've played with. It responds just like a single turbo, just has more potential and defiantly spools faster than a single 80 on a little 4.8.

Vics truck was a ton of fun on the street and make great power for a 4.8, that's for sure. We made 642 on a mustang dyno with just 12psi and eventually turned it up to 18 at the track. Ran mid to upper 10's with a very poorly tuned chassis, lol. Vic said it reminded him of his old street bike, crack the throttle open and it would just go! No issues with boost coming on too soon either.

I think the turbo sizing from FI is spot on and you should be very happy with it, but I would set the primary boost control off the manifold rather than the tube between the turbos. I think that will do a much better job of controlling it.

 

Well, time to get to partying!