Generally speaking a pair of smaller turbos will spool faster than one larger turbo, however it all depends on the sizing of the turbos. What one calls "small" versus another might not be the same yanno
Here is a useful "monkey math" formula I came up with years ago to help with acquiring junkyard turbos for other projects:
"Donor" is the vehicle you're leeching turbos from.
"Project" is your vehicle you're putting turbos on.
- (donor displacement) x (donor redline) x (project QTY) = (project displacement) x (project redline) x (donor QTY)
- 2.2l x 6200 x (project quantity) = 5.4L x 6500 x 1
- 13640 x (project quantity) = 35100
- (project quantity) = 35100 / 13640 = 2.573
As you can see you need approximately 2.573 Dodge Daytona turbos for your mightly 5.4L.
If you are "dead set" on using Dodge Daytona turbos you can use the same formula and evaluate "redline" on your 5.4L. Just because Ford lists this figure at 6500 doesn't obligated you to spin your crank that fast.
So, same thing...
- (donor displacement) x (donor redline) x (project QTY) = (project displacement) x (project redline) x (donor QTY)
- 2.2l x 6200 x 2 = 5.4L x (project redline) x 1
- 27280 = 5.4L x (project redline)
- (project redline) = 27280/5.4 = 5051.85 rpm
So to use a pair of seemingly undersized Dodge Daytona turbos on your 5.4L V8, you'd have to decide that your redline is now 5051.85 rpm - otherwise you'll overspeed the turbo's compressor and impeller wheels and risk frying the bearings.
Some notes about my "monkey math".
- It doesn't take into consideration compression ratio and assumes both vehicles are the same.
- It assumes the OEM (donor) turbo was sized appropriately for the car they put it on.
Considering the "factory" curves using a Lincoln Navigator Intake Manifold in place of the F-series truck manifold, I don't think a 5000 redline would be awful. HP and Torque are both very high according to this graph I stole from the web (Muscle Mustangs & Fast Fords Magazine):
While horsepower continues to increase past the 5000 rpm redline, torque goes down, and ultimately that is the important thing to pay attention to.
Considering your truck's exhaust manifolds look like this...
... you have much room for improvement. A four-into-one tubular header that points directly up for the turbo to sit on is probably the best solution - and you may have to make this either by your own hands or pay a shop to make them.
I'm assuming you can cut and drill metal, but if you can weld you can make your own headers if you take your time and plan it out a bit. You can purchase "weld els" from a variety of sources in mild steel or stainless and make your header tubes that way, OR you can be like me and continue the "monkey theme" and use ordinary black pipe and hack that up into crude sections, welding that to steel plates for a turbo flange and the header plate. Plate can be purchased at most home centers as is black pipe - very common materials.
The first step is to create the turbo flange and collector - which is just a piece of 1/2" steel cut out to fit the flange of the turbo (use a turbo gasket as a template) then miter four short sections of black pipe to form the collector, then weld the snot out of it
Then, mount your cylinder head on a stand or rest it on the workbench, and make a simple "jig" to "float" the turbo flange/collector where you ultimately want it to be in relationship to the cylinder head - mine's made out of scrap I had laying on the garage floor - as long as it holds the flang/collector still it doesn't matter what you make it out of - flats, angle iron, metal rods, etc. My jig bolts to one of the head bolt holes on the cylinder head so I can move to two bolt #2 for the driver's side and bolt #3 for the passenger side, thus placing the turbos ahead of the throttle body. This was for an EFI 460 which has a big "gooseneck" type thing with a throttle body mounted on the front of it, directly in the center of the engine. Your 5.4L if I'm not mistaken, has the throttle body further back towards the firewall if I'm not mistaken. You can figure that out on your own though. Basically you want to place the turbos forward of the throttle body so you can minimize the tubing bends on the intake side. Some guys put their twin-turbos next to the accessories and/or in front of the engine, but that makes the exhaust and intake sides longer
Once the turbo flange/collector is "floating" in place, bolt your header place to your cylinder head:
Now that you have both ends of the turbo manifold in place, it's time to join them together. Again, you can use pre-made weld-els or if you don't mind crude hack up some black pipe, like I did:
Once complete, make another one for the other side, moving the jig so the headers end up being a mirrored image of each other.
Yes, they are ugly. But they will flow better than the stock log manifolds and put the turbos above the wheel wells just ahead of the throttle body which is where I want them. Weld-els or hydraulically bending pipes would have been cleaner, but for $100 and one trip to home depot, well, was just too easy
Here's the whole article I wrote about this:
DIY Turbo Manifolds
So there you go, some "monkey math" and some "monkey turbo headers".
