dodgetrucker75

on my 98, i really dont want to run fire/o-rings on it...yet, but i cant get the pressures down on my twins, im running the s300 wastegate at about 30psi, and an external gate set around 20-25psi, and i can still bury a 60psi gauge real easy, the external gate is about 1 1/4in. can i go with a bigger ext. gate? like a 38 or 44mm? will that even lower the pressure? also at around 50psi. intake pressure, the cold pipe pressure is around 25-30psi. i did do the retorque on the stock bolts but still makes me nervous @ 50psi. my only other thought was to run a second ext. gate from the manifold to the exhaust to bypass both turbos @ about 45-50 psi. what do you think?

BigErksG2

even though your top charger may have an open wastegate, it will still pressurize the charge air, hence the difference in intake pressure and cold pipe pressure. the most efficient way to bring your boost down is to defuel it a little... the plate works great for this and it is way cheaper than another wastegate. once you o-ring or fire ring your head, all you have to do is move the plate and youre back to 60-70 lbs of boost. a wastegate should be utilized in moving volumes of air when the exhaust turbine is insufficient in size to prevent over spinning the turbine and/or creating too much drive pressure. the turbine on the s400 is plenty big to move a large amount of air and still remain efficient without a wastegate.

dodgetrucker75

defuel thats the other thing i dont really want to do but im goinig to have to do something... i havent even come close to trying the water/meth yet as it used to be about a 10psi increase also, thats another reason i was thinking about a second gate, but does that sound like a bad idea just to limit pressure for the time being?

BigErksG2

i would refrain from water/meth and high pressures... they both put a strain on your head gasket. choose one or the other but both could get you into alot of trouble. I pegged my 60lb boost gauge a few times with my twins setup and didnt have a problem with the stock head gasket. 50lbs should be ok without the water/meth. I understand you dont want to defuel and stuff like that but choosing not to could make your head upgrade come a little sooner than expected. The money you put into a second gate could be money towards an o ringed head and studs and once you get that done, the wastegate will be pretty useless and a waste of money. my advice, de tune it a smidge until you can get the head strapped down and sealed up.

dodgetrucker75

i really want to avoid pulling the head at all costs, just not a very fun job, and at the moment, i cant really aford the downtime of getting the orings done, but i can get the other gate done fairly quick without very much cost, and with that setup i should be able to control over all boost pressure, be able to run water meth, and use all of my fuel capabilities, and have minimal drive pressures, other than time and cost of the extra gate, would there be any down falls to that set up, untill i get the ambition to pull the head?

BigErksG2

i see what youre trying to do but my view is to get as much air in the combustion chamber with as little fuel as possible to hopefully eliminate smoke (inefficiency) and maximize economy. youre going to reduce the amount of air with the additional wastegate and increase fuel then offset the temperature by adding water/meth which is really hard on the headgasket because of the premature detonation. i would leave water/meth out of the equation and just use the air you have to keep the egt's cool. you can never run a diesel engine too lean. maybe someone else can chime in with their thoughts....

dodgetrucker75

do you think that i will have an egt issue doing that with the injectors i have? i was hoping the ddp3's wouldnt give me an egt issue with the amount of air these twins can push @45psi, i dont have an issue the way it is but cant use all the pedal at initial take off. also i have been toying with an idea for the last few months... seems how i dont run a fuel plate of afc, i wanted to modify an afc to run on a pull cable for a max fuel limiter, heard of anything like that before? any ideas? worth trying that option?

BigErksG2

two simple choices are control fueling with the plate or your foot. I havn't gone past 1/2 pedal for the past 3 weeks because im trying to get my orings to seat. its not bad for a temporary thing but you might want to use the plate to defuel just a little so you can mash it and get 50lbs of boost at wot then use the starwheel to adjust the pre boost fueling.