As per telecon... VF34 IHI within boundries is a nice package IMHO. Ask too much of it and it may have issues on bearings/exhaust housings. Its transient responce is faster than the equivalent GT28, but the GT28 is a "beefier" unit, bigger shafts, bearings etc, but with the bigger some added inertia above that of a VF34.
If planning steps for upgrade, then from VF34 you are into hybrids to mount onto your existing "other" equipment (mani, DP etc) and IHI hybrids are not as widely available or understood compared to garretts.
low 300's VF34 fine. reliable high 300's, then not from VF34 IMHO without running into its "reliability margin", and available space in the installation, under the exhaust mani is very limited for bigger housings etc.
Once done however, you would have a solid 300+bhp, sustained power delivery to over 7K starting from 3.5K, and acceleration terms, using my original
ibiza's times, were 5s to 60, and 10.5s to 100mph and 160mph+ (from ~320bhp/280lbft)
If you are considering this as part of an upgrade path, then beyond this, rods/pistons (perhaps), and bigger turbo again, BUT this is where the decision for a JS based VF34 conversion may limit other available upgrades. I went thru the same thing myself and opted to go no compromise, and start over, new equal length mani etc, and have'nt looked back since. ( equal length mani for IHI based fitment turbo's so would also work on VF34 no
problem.)-price being higher tho.
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