Ive recently been thinking about single turbo spool up times and how much the quoted values differ from the actual setups. Id have thought it would be all different due to the induction volume. I.e a 2.5" pipe system with small FMIC is going to spool faster than 3.5" with massive FMIC??
Are there any rough calculations to figure out changing spool times as i have very long piping on my FMIC and also a big intercooler. My GT40 (american version) spools to 1bar by around 4.5-5K which seems high compared to some and the only thing i can think it the excessive piping? Whats say an extra 1.5metres of piping at 3" going to do to spool times apart from increase them?
There a loads of variables that alter spool up point here\'s a few. Porting, exhaust manifold design, turbo hotside footprint, A/R ratio of hotside, bearing type, exhaust / silencer design and size, cat or decat, inlet tract design etc etc
The example you give with the 2.5 inch pipe and small cooler would spool slower than the larger set up because there is more back pressure in the inlet tract. But with the exhaust manifold the opposite is true a smaller pipe increases gas speeds which aids spool up, though limits ultimate HP.
Kevin