35 over 3b twins... More Fuel=less boost? Can anyone explain?

[94cummins4x4]

OK guys heres the deal. I have my 96 twin turbo with stick and dual disc, i had some pensicola 90 horse injectors( marine 300's) in it and had the twins system set to purge off at 50psi( as low as the purge valves would set) and saw 51-53 psi all the time at wot, now i changed to some ddp4's and the truck is an animal compared to before (dropped half a second in the 8th mile) but i barely see over 40psi... i dont understand i figured i would be seeing more boost... The ONLY thing i changed was the injectors... i cant figure it out.. maybe someone else has a thought... thanks for any help, i will be doing studs a o rings in a week or so and really want to let the twins push some air but at the moment there is no need haha

[96coalroller]

I think you may have just answered your question... 50 psi on stock HG and bolts you maybe popped it? its always gonna run better when you switch from those crappy pensacolas.

[mopar or no car]

But he says it runs better, and with less boost. Don't see how a blown head gasket would give these symptoms-mine sure didn't.

Jordan

[bjorkmae]

Out of curiosity was the nozzle size on a ddp4 vs a 90 hp pensacola? On a side note after I rebuilt my turbo stock charger I had to re-tune the truck as it ran completely different. Seems strange since I didn't touch fueling or even change the turbo just changed its bearings and seals. But I did port the turbo housing, but still that shouldn't affect it that much right?

[Dual K20s]

Get rid of the purge valves. They are for safety, not regulating pressure.

Have you tried testing for leaks?

[94cummins4x4]

On stock gasket and bolts in the head I need the purge valves or the gasket is sure to fail I believe the 90s were 4x13 and the ddps are 5x16 and no it has not pushed the headgasket yet have looked for leaks and haven't found any yet I guess I will plug the purge valves and see what happens

[bh10]

FYI, DDP 4's are 5x14's.

[Dual K20s]

Use a wastegate or limit the fuel to your twins size. The valves are not designed to operate repeatedly. They have a tendency to break when used often.

Try building a simple tool to pressurize the intake and check for leaks. And checking for oil in the coolant or vice-versa and bubbles in the radiator while running are good checks to see how the headgasket is.

[JeepinOverU]

Get a second wastegate for the big turbo if you need to limit pressures to 50psi.

[94cummins4x4]

Well I adressed the purge valves and it builds boost faster but still stonewalls at 42 psi goona wire the wastegate shut and see if that allows for more boost thanks for the ideas guys