Turbo Guru Required...

[Omi]

Just copying the same text I used on a few other forums, that's why it looks like I'm talking to non-E30 nuts!

I need to work out the best turbo for a specific application - I've already checked the Ray Hall calculator, but that only shows turbos he sells and I'm hoping to avoid Ԛ£400+ for a ball-bearing custom GT if there's a Ԛ£150 solution in the local scrapyard.

I'm converting my NA BMW to FI, with the cunning use of mirrors and magic... Before you call me nuts, it's perfectly reasonable and a good way to essentially double power while keeping the same great car and handling and without dropping another unsuited engine in there.

Engine is a BMW M42. 1796cc originally, slight overbore for pistons.
Going 8:1 compression with custom JE forged pistons.
Forged crank as standard.
Forged rods as standard.
Sodium-filled valves as standard.
Solid lifters off M3 S52 engine.
Cosworth/Mercedes intercooler.
Custom tubular manifold.
Megasquirt n Spark Extra ECU, with MAP, TPS, Knock and Wideband O2 sensors.
Custom Blue Flame exhaust.
Uprated fuel pump and 50lb injectors.

According to my calculations I'm looking at reliable boost of 14-17psi, which translates to 260+bhp.

Looking for the best turbo to handle that boost all the way to the ~7000rpm limit, with lowest boost threshold possible.

Might need my head examined too.

Thoughts please gentlefolks?

Omi

[Jon_Bmw]

What do they think over at e30 tech, its not there usual cup of tea, they're a bit obsessed by the m20. No doubt Ixer is trying to get you to buy a holset hx40 or something along those lines.

Can you not ask from that ray hall calculator place what all the relevent specs are, A/R ratio etc etc then try and match something up from there.

Are you going for a custom manifold or are you limited to t3/t4/t28/t04e etc etc by the manifold?

[Omi]

Strange, but true, iXer was trying to get me on an HX35!

The recommendation over at Ray Hall was a GT25 with their 290bhp kit (.63AR), but they don't have 28's mentioned anywhere on the site, and that's a standard 2 litre charger, so I'm wondering whether that might be better.

Have also heard that the GT25 has a wastegate that can't be adjusted beyond a few PSI... All very confusing.

Not too fussed about turbine flange, as it's going to be a handbuilt manifold anyway... just means the difference between buying a T3 flange or a split pulse T25 jobbie.

[Ant]

Omi, secure a Turbo for a 200SX S13/14/14a

the capacity and valve count is the same afterall, so no worries with AR etc

Dont know what it is with e30tech, anything less the the HX35/40 and "its too small"

I beg to differ, and so does Fozz.

GT25 or 28 is fine, a T3 will work well too but you'll be compromised by the outlet design, the GT series you can run the Whoosh(w/gate) pipe seperate for better flow after the turbo

you'll not need injectors that big either M8 42/44 lbs will be plenty

Were running 42s on the M20s and even over 1bar only seeing PW in the 70% region, plently more yet then

[RowdyBurns]

If not a 200sx turbo as suggested by ant, a stock cossie T3 with a .48 exhaust housing would probably work quite well and they are fairly plentiful on ebay - expect topay about a ton. Failing that most specialist cossie breakers will sell you a good condition second hand unit for Ԛ£125 - 130.

It should see you right with the power figures you have suggested and makes a good budget option.

[RowdyBurns]

Just remembered, I think i actually have a T25 from a Nissan CA18DET engine sat around in the garage, if any one is interested?

[Turbo-Brown]

Think you'd be better off with turbos from the later 200SX cars.

Was under the impression that the T25 from the S13 car wasn't good for big boost, but the T28 from the later ones was, and is more efficient to boot

[e30_Turbo]

I beg to differ, and so does Fozz.

I do

My Gt hybrid, based on a turbo from a skyline is more than enough for me, tons of power from as little as 2.5k and all the way to the redline

I'd start small and work to needing a bigger one, boost is far to addictive to not want more!

Mark.

[Omi]

Managed to confuse myself even more...

Someone give me a model number or a specific donor car with a low boost threshold from a 1.8 running 8:1 compression which will deliver full boost low, and all the way to the redline.

The more I look into this, the more confused I get. Probably not a good sign for the project, but there are only a few points I'm totally stuck on, and this is one of them. I'll post back with the others when I get that far! lol

Meanwhile, an internal wastegate would be easier to manifold and downpipe, but I understand that will restrict boost on many stock turbos?

And what's this about MSnSE being able to drive each coil individually, rather than running wasted spark?

[Ant]

Omi, take rowdy up on that spare he has M8, its perfection for the M42 !!

As for the MSns-E, for you I'd go for an EDIS 4 setup and ignore the HEI for cam position, downside of full wasted spark is you'll have to add 3 extra coil drivers to your MS setup, easy enough but its more work that way

[Jon_Bmw]

Omi, take rowdy up on that spare he has M8, its perfection for the M42 !!

As for the MSns-E, for you I'd go for an EDIS 4 setup and ignore the HEI for cam position, downside of full wasted spark is you'll have to add 3 extra coil drivers to your MS setup, easy enough but its more work that way

Yeah i think Ant's suggestion of the t25 off a 200sx is definatly a good starting point, and if you find it can't keep up then i'm pretty sure a t28 is a bolt on job. I'll be able to tell you more in a few days about whether a t28 will bolt onto a t25 flange as i'm going to see a s13 turbo with a t28 on it soon.

Do you notice how many turbos blow headgaskets over on e30tech, perhaps this is because of the "bigger is better" craze that Americans have. I remember reading a holset hx50 would be a good starting point for a m20, ffs a hx50 is about twice the size of my head!

[Ant]

Must be the cheap fuel Jon, cant see any other reason

my T3 is "way too small" according to our mates over the pond, but I have a massive IC large bore charge pipes and run up to 10 psi all day long, only see 4 degrees IAT increase on WOT boosted too,

They must get boost only from 4K onwards, what about some awesome midrange though both mine and Fozzys setup produce a healthy 8ish PSI on large throttle openings around the 2.5K rpms mark, I'm sure yours is similar

Bigger is better .................... Sometimes

bottom line for OMi, if the T25 is good on a 16V 1800cc Nissan engine, sure ticks all the right boxes for the M42