High compression 408...t4 turbo?
High compression 408...t4 turbo? I have acquired a 408 from a buddy. It's 11.5 compression with Frankenstein m311 heads and I run e85. I have installed a custom spec cam already with the plans of running my 80/96 T4. My SBE 6.0 car currently traps 140+ with a goal to trap 150 running the 408. My concern is running the T4 turbo with high backpressure. I know a T6 is what it needs BUT I'm 100% setup for this t4 kit. I guess it will need between 800-900 to trap 150. Is the T4 worth trying?
I say run the T4 and see how far it can take you.
I feel like a 408 with high compression is gonna max out the 96mm turbine much sooner than say a 5.3/5.7 but it still should make plenty of steam.
A T6 with a big 110/114mm exhaust wheel would be the ticket but is gonna be $$$$, or there's twin 7875's if you decide to make a change.
There's a gent on here with a 370 and a 7875 running mid to low 9's in a heavy 4th gen Firebird making good power so you should be able to easily do better.
I feel like a 408 with high compression is gonna max out the 96mm turbine much sooner than say a 5.3/5.7 but it still should make plenty of steam.
A T6 with a big 110/114mm exhaust wheel would be the ticket but is gonna be $$$$, or there's twin 7875's if you decide to make a change.
There's a gent on here with a 370 and a 7875 running mid to low 9's in a heavy 4th gen Firebird making good power so you should be able to easily do better.
I went 9.8 @ 144 with a huron speed 7875. My 6.0 is a lq9 so I'm sure my backpressure is pretty high with the 7875. The T6 will require yet another radiator and battery will need relocated
That 96mm will certainly open that rpm window up though but you outta be able to hit 900whp maybe 1Kwhp.
There's a local guy here with a 408 80/96 T4 setup in a six speed car and he made 750whp on pump and 1Kwhp on race fuel.
Of course you may lose a little more through an auto and an auto will load the turbo differently than a manual but the reference is still sound.
Compare the effort of "trying" the T4 compared to just ditching it and completely redoing everything for a T6. Definitely worth a try. Worst case, you end up with valuable data.
He would need a pretty sizeable turbine to use that 408 efficiently though wouldn't he?
Trying to remember what size Garrett @randeez was using on his single 427 in his Escalade.
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To be worth the t6 swap I would want something with a 102mm turbine I think. They are big money turbos and probably more turbo than I'd ever need for a "street" car. I've seen threads about people running a t4 on bigger cube motors but I have no idea what compression they were
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Worse case scenario, too much backpressure and extreme EGT will burn up exhaust valves and the turbine. Keep a close eye on drive pressure and EGT.
Highly suggest seeing what it would take to convert your T4 setup to a T6 flange. Don't think its necessary to revamp your existing setup just for a flange difference unless the turbo placement won't fit a large frame turbo.
Highly suggest seeing what it would take to convert your T4 setup to a T6 flange. Don't think its necessary to revamp your existing setup just for a flange difference unless the turbo placement won't fit a large frame turbo.
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I don't disagree, T6 or twins are definitely the way to go.
He would need a pretty sizeable turbine to use that 408 efficiently though wouldn't he?
Trying to remember what size Garrett @randeez was using on his single 427 in his Escalade.
He would need a pretty sizeable turbine to use that 408 efficiently though wouldn't he?
Trying to remember what size Garrett @randeez was using on his single 427 in his Escalade.
Worse case scenario, too much backpressure and extreme EGT will burn up exhaust valves and the turbine. Keep a close eye on drive pressure and EGT.
Highly suggest seeing what it would take to convert your T4 setup to a T6 flange. Don't think its necessary to revamp your existing setup just for a flange difference unless the turbo placement won't fit a large frame turbo.
Highly suggest seeing what it would take to convert your T4 setup to a T6 flange. Don't think its necessary to revamp your existing setup just for a flange difference unless the turbo placement won't fit a large frame turbo.
i never tried a T4, smallest i had was a T6 BW80/96 1.32ar iirc - spooled up like a diesel but had about as much usable rpm. i probably have some logs showing it not able to keep 15psi past 5500rpm
as said above this is with a 427, 10.5ish compression is what they shot for i think, same m311 heads
Last edited by randeez; Nov 23, 2021 at 05:07 PM.
/\ this is what happened with mine, burnt up the seats and guides (knocked off what was exposed in the ports from CNC), blew out every exhaust gasket lol
i never tried a T4, smallest i had was a T6 BW80/96 1.32ar iirc - spooled up like a diesel but had about as much usable rpm. i probably have some logs showing it not able to keep 15psi past 5500rpm
as said about this is with a 427, 10.5ish compression is what they shot for i think, same m311 heads
i never tried a T4, smallest i had was a T6 BW80/96 1.32ar iirc - spooled up like a diesel but had about as much usable rpm. i probably have some logs showing it not able to keep 15psi past 5500rpm
as said about this is with a 427, 10.5ish compression is what they shot for i think, same m311 heads
Seems like from what you said its a much better turbo over the big VS unit you were using before.
Weird a 96/88mm turbine wheel is going to burn up a 408 or 427 but countless LS2s and LS3s run 83/75 or 82/75 turbines at full tilt and none of them burn all the exhaust bits up, its almost like bad luck magic on the bigger engines. T4 or T6 on a 96mm turbine doesn't make a huge difference because the insides of both turbine housings shrink down much much smaller than the inlets of the T4s. I know they open into the wheel opening pretty quickly but it is tiny in there.
If you have problems making 900hp on a 408 through a T4 96mm turbine or burn up exhaust guides valves whatever, you've got other issues. Maybe the people burning **** up are running 100% M1? Would be huge volume but the egts are relatively ice cold, so that doesn't make sense either.
If you have problems making 900hp on a 408 through a T4 96mm turbine or burn up exhaust guides valves whatever, you've got other issues. Maybe the people burning **** up are running 100% M1? Would be huge volume but the egts are relatively ice cold, so that doesn't make sense either.
The other evidence that T4 vs T6 in the same a/r on the same turbine wheel probably doesn't matter that much is lots of housings are listed in the turbine flow chart that come in both housings on BW Matchbot. The flange whether T3, T4 or T6 are not listed, so either Borg made a big *** mistake, are misleading people, or it doesn't matter.
Was thinking about the burnt valves and guides, etc, reread my comments, didnt mean to come across as a smart ***, just trying to be a joker.
But I wonder if the exhaust valves are floating on these deals when burning up valves and guides. I once ran a pretty small XER lobed cam (aggressive ramps and should be used in aspirated applications only) and with that cam, even with good dual valves, it floated the valves so easily, around 15psi like you saw, this was a PT7675 on a 6.0. I changed to a cam with gentler lobes LSL and the problem was gone, never had the problem or thought about it again.
Just wanted to throw that out there...lots of stuff could make exhaust valves float/bounce on a turbo deal, and b.p. is involved, but violent max effort lobes will exponentially amplify the problem!
But I wonder if the exhaust valves are floating on these deals when burning up valves and guides. I once ran a pretty small XER lobed cam (aggressive ramps and should be used in aspirated applications only) and with that cam, even with good dual valves, it floated the valves so easily, around 15psi like you saw, this was a PT7675 on a 6.0. I changed to a cam with gentler lobes LSL and the problem was gone, never had the problem or thought about it again.
Just wanted to throw that out there...lots of stuff could make exhaust valves float/bounce on a turbo deal, and b.p. is involved, but violent max effort lobes will exponentially amplify the problem!