I'm aware of how far turbo technology has come, and single turbos nowadays with a proper setup spool up fairly quick but which turbo setup would spool faster? (350-450hp) Twins have the benefit of spooling faster in general but with turbo technology nowadays, are twins any better at minimizing turbo lag than a modern single setup?

 

This has been covered to death here.

 

EFR 7670 comes close, but still spools ~500 RPM later than properly functioning sequential twins. You can especially feel it in daily driving, like when taking off from a stoplight. Granted, single has other advantages, and it is debatable whether that bit of extra low end really makes that big of a difference. But the dyno charts don't lie - sequential twins have a lower boost threshold.

 

My sequential twins FD with all the bolt ons spooled a little better from 750rpm to 1,500rpm than my EFR 7670 FC.

By 2,500rpm up the EFR 7670 has a huge advantage in torque response even if peak boost is a little lower as it has lower exhaust manifold pressure raising engine volumetric efficiency.

The EFR 7670 was spooling to 26psi faster than sequential twins hitting 14psi on initial 3,000rpm pull and the sequential twins lock into parallel mode after the 1st hit anyways with subsequent slower spool (but no transition)

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So, what would I do?
I'm trying something different again.
I ditched my sequential set-up on the FD and actually went up a size to EFR 8374, but kept the 9,000rpm rev limit and geared the rear down to 5.86:1 rear Big streetport and Turblown UIM for power over 8,000rpm. Will try low boost (10 creeping to 12 or 14psi) and 350-400rwhp.

Its going to be 4,000rpm down freeway though- so will likely have to play with exhaust a lot to kill drone/boom. Stock engine mounts and go to the rubber mounted banzai trans mount to tame drivetrain buzz into the chassis that creates the 2ndary harmonic with exhaust vibration/noise.

Remember, you can drive a stock FD on freeway at 70mph in 4th comfortably- so, should theoretically be able to achieve same dynamic...

 

Oh yeah, and I have a brand new EFR 7670 on stand by incase my weird ideas dont work out.

It was a REALLY good turbo.

 

I wouldn’t run diff gears like that unless I has an OSG gearset or a tremec box, even then unless you are tubbed for big drag radials it'svery short. 4.1 factory diff was fine with standard gearset, I have 4.77 with the OS, first is tall but the others are good. I don't think I would even run the 4.77 with factory gears and a big single, you could possibly argue that ratio with the tall 6th of a tremec and larger rolling diameter tyres.

 

Unless you run an actual variable geometry F1 style turbo, Sequential twins will always out spool a single capable of 500+ below 2500 RPM I would think just due to the size of them and the volume of exhaust. Sequential in my eyes is for people that aren't shooting for high power (above 400hp) and want to keep the heritage of the sequential setup. Its really simple, they've had over 30 years of Turbo advancements over the factory twins so the volume and spool characteristics better be way better. On my wife's car we are running an old Precision turbo from 2003 and the modern turbos of today can match the power output of that turbo and spool 1500 RPM faster, the FD turbos are more than 10 years older. My car will always be sequential just because I enjoy the car as it was designed plus a little extra. If you don't care about that, then single is the way to go for simplicity and power output, you just won't have the instant boost from 1000-2500 rpm. Pay attention while you are driving around and see how often you would be under that range and how important it is to you.

 

I will get it running and tuned on my 4.10 so I have a basis of camparison and whether or not I want to take the plunge to 4.30/4.77/5.86 rear.

But remember, Im not planning on using anything near the full potential of the EFR 8374.

I want ease of (race) driveability with some wheel torque still so I was planning 10psi base boost for ~250ftlbs torque and getting to it (10psi) early. Then boost creep to 12-14psi and 300ftlbs torque in the upper rpm to carry the power and with a natural progression.

On my ~340rwhp sequential twins at 14psi 4.10 I couldnt even spin the super light 305/30-18 rain tires (in the dry) in 1st gear. Pretty hooked up- never had a rotary like that. I was used to my 420ftlbs EFR 7670 FC. Like you say, 1st is just to get you rolling in that car.

 

ive found the muffler tip makes a huge difference in noise.

 

Yeah, I plan exhaust throttle (compression brake) for boost (creep) control- maybe I will use it for cruise as well.