Well, hypermax doesnt necessarily have a spring for my application, but they do have a double spring which they use on the race motors spinning 5K. I called my local dealer and I can get 6 stock springs for the 360 for $35, which I then could measure seat and lift pressures at the local machine shop. This would also let me get exact measurements and possibly compare them to other springs. I dont know why others have not tried this, i think the 360 is a good engine, when turned up of course. All i have to do now is still get rid of my preboost smoke issue.
There's a degree of difficulty to modifying DT's like you would a 7.3, a DMAX, a 5.9 Cummins in a pickup. Usually there's a "bottleneck" in every series of DTs. Mine is the pump. The plungers & barrels are just too small for anything more than minor streetable modification-maybe 30-50 more HP if you're lucky.
I would love to have 300 SAFE low-EGT, workable HP so I can still safely haul a 10 ton load. I don't want to race my truck or limit it to an empty truck running 1300* EGT on a drag strip.
Hypermax (Jeff or Ron) will tell you straight-up, when it comes to DTs, they are in the business of 1000-2500 HP DT's for tractor pulling. They offer nothing much more than their condolences to you when you want "streetable/useable" milder HP levels. They guys at Hypermax are the best, but they just don't have much other than some advice.
I wish it were different, but I've spoke with Jeff more than 10 times about this very subject.
If you have a pre-boost smoke issue, I would think turning the star (smoke) screw back a few turns might help, but I'm not sure which pump you have.
Let me know what you come up with on stiffer valve springs. I'd love some extra braking power from a PAC brake
. I bet a lot of older DT owners would love more, too. I'm close to needing a valve adjustment, so it would be a great time to do it.