At the level you are bigger injectors gives your map headroom safety so the ecu can ensure you never run lean. Swapping injectors is a simpler job than the downpipes and imho is a necessary step for engine safety and future proofing.
Downpipes help to reduce exhaust back pressure to get an earlier spoil as well as reducing engine bay temps. Disadvantage is a much louder exhaust and a smell of petrol as the primary cats help remove unburnt fuel.
At this level of tune your tuner should recommend pulling some timing in order to keep torque to a safer 600lbsft. This isn't to nanny the transmission but to protect the stock rods.
That said there isn't a magic line below which you are safe. Increase torque and power and you increase the risk of failure both in the trans and the engine. There are plenty of cars running stage 4.25 with no issues as well as a fair few that have had trans failures and engine failures. There are plenty of cars that have had a variety of trans failures even at stock levels too.
It's a simple equation of increasing power increases risk.
Arrived 29/5/09 Reborn 12/1/17
Engine built @ RiversideRacing
Litcho rods/pistons/RaceIC/BOVs/oil cooler/susp+handling kit/front diff
Race Developments ported manifold/AT Power TBs
RF street zorst+DPs
Xtreme18 Clutch/Dodson 1st gear+shaft/trans brace
2015 alloys/nav upgrade/Nismo cluster
DSC susp controller
DBA front/Varis CF bonnet/2016 Lights
TTE7XX turbos = >900bhp 700lbsft 30-130mph in 8.19s
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