Most of those cars mentioned with sequential setups cost more than the houses we live in and add a few zeros for the companies R&D budget. The only sequential turbocharged cars available (off the top of my head, correct me if i'm wrong) in the sub 100k catergory in austrailia are the subaru liberty B4 and the Mazda RX7, the later i have had alot of experience with through my workings with Mazda Motorsports race program from a couple of years ago.
To go a sequential setup it needs to be very accurately setup and tuned. Issues with turbulence and overspeeding the primary turbo (a common problem with both the RX7 and the B4) come into play and it's too hard (in my opinon) for we street tuners and backyard boys to play with.
As ddgonzal said it would be possible to set it up as a turbo per 2 cylinders and run it like that and then its just an issue of changing the back housings and wheels to reduce lag (on the T25) to make it more drivable.
Like L18 and Timo said 2xT25's is alot of air to push for only a 1.8.
I still think S15BB is the go, and that is my rant for friday

You can never say that one type of setup is better than the other because they are designed for different purposes.

Twin turbos give excellent low-end response, but the turbos need to be small, therefore not as good top end.

You need a larger turbo than you can use with a twin setup (unless its a V8) to make really big top end power.

Twin sequential turbos give the best of both worlds with one little turbo for low-end and a big turbo for top-end. But like YRL0SS explained they are impracticle for the backyard builder.

And, yes, turbos ARE designed to work at specific engine RPM. For example, the RX7 we are building at the moment will have a TO4S BB turbo that will give a power band from 3000 - 8000 rpm. This is the deciding factor when designing the port shape for the 13B.

But lets not stray from the original question. I reckon you should get an S15 T28.

you definitely aren't going to get excellent low end response from two T25's on a CA18. with only 2 cylinders feeding each turbo they'll take an eternity to come on boost! Or are you guys thinking of mounting them in series? it all sounds pretty dodgy to me. just go with madtimo's advice and the proven T28bb upgrade

Ok then s15 t28 it is
Im really glad I asked this question,

I thought about these turbos mentioned and remembered there is a sight somewhere about comparisons.........I'll find it now http://members.iinet.net.au/~sayers/biscuits/turbos.htm
There is one more tubo they never mentioned its the T25G the only difference is the compressor housing its a .80 A/R compared to the .60 A/R apparently its have one on my car and I have a spare one.

Hope this comes in handy

Allan

Just for interest I rang the local nissan dealer today and found out that a S15 t28 bb new is $1700 which I recon is not a bad price, what do you recon?

Have you priced a second-hand one? I reckon it would be cheaper to buy a second hand one and get it rebuilt.

I heard SSS automotive have a few going cheap at the moment.

GCG at Condell Park do good pricing on Garrett GT25 Turbos.

I got a really big (As per my avatar) turbo for less than $2000.

I think the smallest replacement ballbearing turbo (Equal to any Nissan offering) goes for $1300 new. This was a few months ago now, they might be even cheaper thanks to a favourable Aussie Dollar.

Chris

we use a turbo off a WRC evoloution handeld up to 60 pound of boost

do gcg have an email adress? For $1300, is that a T2?