A rule of thumb, I find, is that the Compressor wheel and Turbine wheel should be closely matched in size, the compressor wheel being ever so slightly larger is optimum, something like a 1.1:1 ratio I've read. If the compressor wheel is much larger than the turbine wheel ie: GT2871R, GT2876R, GT3082R.. You get excess lag for the power level - you'd get less lag by moving up to the next frame sized turbo with a same sized compressor wheel and a larger turbine wheel.
Cool dyno read out there WazTTed, but why is Torque dropping off significantly like that at only 6300RPM, with these honking Turbo's? Seems like the Engine could do with some head work to support the extra air flow, either that or our manifolds are a significant choke point at that RPM. Pretty small powerband really.
Looks like I'm gonna go the RS's - with all the supporting upgrades mentioned and everyones input, it sounds like I might as well - I'll be happy if I can be fully spooled by 4 - 4,300 rpm - (guessing/ hoping) This will be my first big powered car (apart from my 1980 C3 Corvette which had a mediocre 220rwkw) So I don't wanna go the R's and be let down - might as well go big while I'm at it - worst case scenario, I spool 5-600 rpm later - BUT! Much harder. I've always been about power low down for daily driveability, but I'm willing to keep my foot on the accelarator for literally an extra second and a half for a more massive kick! - plus the leader gears or N/A diff will help.
Don't forget Blackbeast's advice You probably want to upgrade your fuel pump/system as well, don't want to miss out on the power due to not having enough fuel.
I'm using dual walbros they will give you more than enough fuel. Once you have it setup it looks/runs like an OEM setup, no noisy external pumps, no extra hosing....
Forum member Joe just put together a very similar motor might be worth having a chat. He's in Sydney too. Who is diong the build? Or have I missed that earlier in the thread...?
Will I need to change springs, seats, retainers & locks if I went with the Ferrea 1mm oversize valves - can anyone recommend a cheaper/as good option or a re they the only ones for the Z32?
Take it from someone who has had both of the turbos you are looking at. Since you are going to the trouble of rebuilding your engine with forged components don't waste your time with 2560R. Ultimately you will get used to the power and wish you had more. I originally started off with with 2560R on a stock internal engine and it went well but the 2860RS turbos are a lot nicer. Difference in lag you will not notice one iota!
There is way more gained by high lift cams than bigger valves. In fact I suspect on a dollar per kilowatt ratio you could leave the bigger valve job out and save a lot of money. While not losing very much power at all.
I did a lot of research about this years ago when i was planning a big build on my road car. I had the JWT R5's and a spare set of heads. Even had the bigger valves to put in. More I read the more I came to the conclusion the $2K for head machining seats and valves wasnt warranted unless you are reaching for really BIG power. Do a search on TT.net, for up to 350RWKW the valves are nice but not required to reach that power level. Over 400 RWKW is another story.
can you guys recommend me a good set of off the shelf cams & springs ie JWT milds - basically anything that's gonna assist with spool up OR - should I get them custom/ reground for what I need them for? Don't think it's worth bothering with the O/S valves by the sounds of it So it'll be - Forged & balanced rotating assembly 9.1 C/R Wiseco's Upgraded cams & springs mildly Ported heads ARP head stud kit AMS manifolds Selin twin intake kit twin 3A or suitable pods 3" dumps & test pipes & exhaust NISTUNE UDP GT28RS with .64 a/r housing
I always thought the JWT R4+ or R5 are a good way to go. I have R5's and JWT springs for the race car.
