Hello. I am in the middle of powering a 59 panel truck and deceided to not use a slobbering gas motor and am putting a diesel in it. Want also to get back to simple so may use a 6.9 or a 7.3 diesel. i would like to use a twin turbo for it over a single more for the looks. If i use the theory 1/2 the engine is 3.6 litres and use a turbo from a 3.5 mercedes diesel on each side into a common collector this shall work? Or is there some advanced math equations I am missing.

 

Here is how I've often done the "junkyard math":

new engine CID x new engine redline x "T" = donor engine CID x donor engine redline.

The above formula assumes the donor vehicle has a single turbo. Lets plug in some numbers.

445 CID x 4200 RPM x T = 212 CID x 4300 RPM

T = 1869000 / 911600 = 2.05024

For "near optimal" you'd need 2.05024 3.5L Mercedes turbos to feed your twin-turbo 7.3L powerstroke.

The reason why I made a point about taking redline/RPMs into consideration is in this example the two diesels have approximately the same redline. If you use turbos off a gas engine, you of course know that the redline of a gas engine is much higher. By taking rpm's into consideration, you can use this formula for any turbo off any junkyard vehicle to go onto any other engine of your choosing - because you're taking CFM into consideration, not just displacement.

CFM = ( cid x rpm x VE ) / 3456.

My junkyard formula makes some assumptions however... like the VE of both engines is the same. For a junkyard swap however, it's "close enough". But you can do pages of mathematics and calculate it all out to 0.0000001 accuracy if you really want to bother