So I think Im seeing the end of the useful power with this cast 78/75 On3 turbo I have on my setup. I know Im over the intended HP rating of it but its close to winter so its staying for now.....maybe.

I have space constraints on this engine setup so Id like to stay with a T4 flange if at all possible for my next turbo. Its not a dedicated race truck (although it could be how its setup) so I kinda would like both worlds next time. Im looking at the S480 lineup of turbos in a T4 flange. Im about 850 rwhp now and limited by the turbo I do believe. Its fighting the turbine wheel above 5500 rpms and boost falls off a few psi after hitting peak. At 27 psi its slower than at 20 psi ET wise. At least thats my opinion on it. Maybe Im wrong as this is all relativity new to me within last few years.

The other question is my friend has a new 7675 BMF On3 that I could get to use the rest of this year. Would that be of any help to me to change or just a waste of time? Meaning would that pick up power over mine now even though the exhaust side is the same? I figured the wheels would possibly help being different and all. If so how much you rekon? I need 3-3.5 tenths to reach my goals this year of 9's in this heavy ass truck ( almost 4k lbs with weight and driver in it).

I have the fuel and the Holley ECU to do more cause I know thats gonna get asked...lol.

 

A 480 at that power level should really have a T6 flange, and large downpipe. If a T4 is all that'll fit, a 480 T4 will still be better than the 7875 though. I don't see the On3 being much if any better, it's still turbine limited.

 

Yep you were right. The BMF On3 that I tried this weekend sucked just as much on my setup. Im sure it could be badass on a twin setup for which it was on on my buddys car but not mine. Boost still falls off top of first gear.

So onto a T4 S48x series turbo. I need more exhaust side obviously. Now with a T4 flange and say a bigger exhaust such as a 1.25 a/r 96 wheel will that still spool relatively decent? I know everyones opinion on that is different but say for a street truck would it be ok? Im not in boost much driving on the street anyhow but I figured with the smaller T4 flange it would spool quicker than a T6 flange would. Is that thinking correct? Also would you think it would have the same issues Im having now of being turbine limited? I wouldnt think so but Im no expert either.

Thanks for the help thus far anyhow. Also Im running a 4" exhaust thats maybe 18" long and have been this way since I built it. Its 3" or 3.5" (cant remember exactly what they are) off turbo and immediately goes to 4".

 

The spool is really not much different, that is largely controlled by the turbine dimensions and geometry. Why not just step up to t6, if you are going to a different turbo anyway it isn't that much work to change the flange, you are very likely going to want a larger downpipe. IE you are into a re-fabrication of that section of the hot side, now is the time to go big.

 

I know Ive been thinking more about it lately. Im just worried about slow spool more than anything. And the fact that Im not sure if I can manage a divied flange for the T6. I get I can spool quicker on the tbrake and with the software but worries are on the street. I dont expect a t6 to spool like this 7875 but if I could get it decent Id be game. Converter is flashing over 5k so should be enough Id guess. Gettin a new one this winter anyways.

 

I think if you can get it set up for twin scroll you will be in good gravy. The s475/s480 has a better drive ratio.

 

There's very little difference in spool with the T6. Get the 1.10 T6 with the 96mm turbine if you're worried about it.