Engine 850: B5234T/2.3/20v/T5: much difference between a 15g and a 16g ?

[PNuT]

18 jod 18.....

[irf]

Originally Posted by jod t5

Now im not so sure i agree with all you "big is best" boys...., it is possable for instance to get well over 20psi out of a 15g, so why would you want to spend 100's on a new turbo, backpipe, manifold and remap when with a little "knowledge" you can get your, quicker spooling 15g to earn its money...
Sure you are likely to get more range out of a 19 but with a well set up 15, im sure you will not see yourself embarrassed...lol......Pushing 25psi i think not...!!
cheers
jod

from what i've read jod pushing past 16-17psi on a 15G isn't really worth it as you generate more heat then anything else.

i agree in some respects that people are maybe too quick to rubbish the 15G. remap with a decat etc has got my car going quite nicely.

i have just bought an 18T though. god, i feel so smug!!

[Jod T5]

Originally Posted by PNuT

18 jod 18.....

Ok Mark so how much is a 18 going to cost...., plus remap and exhaust....
The point i was trying to make is that the 15g is a very versitile little baby, caperble of producing all the air input a T5 could ask for, provided the fueling is catered for....
cheers
jod

[Jod T5]

Originally Posted by irf

from what i've read jod pushing past 16-17psi on a 15G isn't really worth it as you generate more heat then anything else.

Bearing in mind the size differences between the turbos, including hybrid in traditional guise, my limited knowledge would expect the difference in heat disappation to be minimal, heat sink however effects all our cars, irrespective of turbo styleee...
What i do know tho is that with the removal of the "overboost"/Maf air cool limiter, with the correct fueling the 15g is awesome bit of kit, playable to the limit with stock set up then as far as you like with 3" pipework and some jiggery-pokery...

Originally Posted by irf

i have just bought an 18T though. god, i feel so smug!!

Enjoy Smirf bro, maybe roll it at uxbridge so the graphs can be compared with the current set up....
cheers
jod

[st5ve]

The 15g is a very nice turbo as is the 16t, there should be plenty of second hand examples around, someone flagged up the 16t has 2 types of flange I beleive the 15g has as well it may have a third but I know there is 2 for def. I have a 15g with a full 3 inch downpipe and remap, it holds boost very well and my standard boost gauge goes straight off the scale. What ever you choose if you want more performance I don't think there is any diffrence if it is a straight swap.

Do all 850 R's have the 16t or just the manual, not sure if the auto R has a 15g or 16t?

[foggyjames]

Turbo sizing is always a tricky one (whole books have been devoted to it), but here's the long and the short of it, as I see it.

A given turbo at a given shaft speed (overspeeding the turbo = bad) can only deliver a certain charge pressure into a certain engine configuration. That side of it is mainly to do with compressor sizing. That's fairly straightforward, really. You want the smallest possible compressor (to minimise load on the exhaust side, and hence speed up spool-time) which will deliver your desired boost pressure at your desired RPM limit. Note that many factory turbo setups now cannot efficiently deliver full boost at the RPM limit - they figure that people would rather have better spool-up at the expense of high RPM power.

On the other hand, the hot/exhaust side (and its relationship to the compressor sizing) is more complex. Essentially, a smaller exhaust side will promote faster spool, as gas pressure is increased (because you're putting a bung in the exhaust), but it will also seriously hold the car back at high RPM.

What does this mean in practical terms? You need to buy a turbo to suit your application, basically. For the T5s, the TD04 series turbos are actually all quite similar, and specifically have very similar exhaust sides. They're designed to aid spool-up, but are a limitation to high RPM power. Having said that, they're fine to over 300bhp, so how far do you want to take it? Pick whichever TD04 suits, and run with it. They're all very similar.

Admittedly, an 18T/19T, matching downpipe, custom remap, etc...although a very nice setup (and more or less the ultimate low-risk 'factory' style setup), doesn't give you that much bang-for-buck over a standard 15G with a chip. It would cost very little more to fit a much larger turbo than an 18T/19T...BUT...the con-rods rapidly become a headache.

Taking it beyond the remit of this thread, for a moment...here are four 'stages' I suggest...

1) 15G/16T + MBC or standard remap. 280bhp or so.
2) 18T/19T + downpipe + custom map. 300bhp or so. Fairly expensive.
3) Bigger turbo (Garrett GT28xxR?) + downpipe + custom map. 350+bhp. Fairly expensive. Power limited by strength of con-rods. Unknown territory. Risk of engine implosion.
4) Bigger turbo (Garrett GT3071R, typically) + *built bottom end* + DP + custom map. 4-600bhp. Very expensive, but safe.

Most people skip stage 3, so we don't know what the limits are. I suspect 350-400bhp with a later T5 engine with the larger factory rods. 330 is probably about the limit on an early (pre-850R) engine.

cheers

James

[dooby]

Originally Posted by ttacornwall

Do all 850 R's have the 16t or just the manual, not sure if the auto R has a 15g or 16t?

Hiya,

my 1997 model year 850R auto has a 15G (straight flange), which I believe is standard.

Cheers, Pete

[Kerry_T-5R]

Originally Posted by ttacornwall

The 15g is a very nice turbo as is the 16t, there should be plenty of second hand examples around, someone flagged up the 16t has 2 types of flange I beleive the 15g has as well it may have a third but I know there is 2 for def. I have a 15g with a full 3 inch downpipe and remap, it holds boost very well and my standard boost gauge goes straight off the scale. What ever you choose if you want more performance I don't think there is any diffrence if it is a straight swap.

Do all 850 R's have the 16t or just the manual, not sure if the auto R has a 15g or 16t?

Hi, only the manual 850R's have a 16T turbo (the S/V & C70 T-5's also have 16T's). The 850R estate has a 15G with overboost which is the same as a 15G apart from it has 30 seconds of extra boost.

Cheers

Kerry

[st5ve]

Originally Posted by T4kerry

Hi, only the manual 850R's have a 16T turbo (the S/V & C70 T-5's also have 16T's). The 850R estate has a 15G with overboost which is the same as a 15G apart from it has 30 seconds of extra boost.

Cheers

Kerry

Thanks, that confirms what I thought.

[bb54]

thanks everyone, basically i found a supplier in japan from a skyline mad mate that could supply a 16g cheaper than i could get a 15g over here and was wondering if any oomph benifits could persuade me to go the (not liked by me) ebay route.
many good points have been made by all, some of which im aware of some which im not.

i run without a cat and and use an mbc so by the sound of most replies i recon i should stay with the 15g for spool up benifits, get the ecu limits removed to run more than 14psi and finnally get round to grafting my old saabs 55mm abbott racing intercooler in to deal with any extra heat thats generated.
the AR I/C can also be mounted upside down with the in and out at the top which will shorten the pipework and hopefully aid spoolup time.

jod... he he,i know the 15g's can produce plenty of psi cos when i first bought a doner t5 it wouldnt hit cut till 21 psi for a while (why,i have no idea),then settled down to the normal 14-15 psi cut.

a couple of people mentioned the flange issues... not a prob as i have a phase 1 connical cat and a phase 2 straight flange.

t4 kerry... i could be wrong but i thought the only 850 to be equipped with the 30 sec overboost function was the T5-R .
appologies if im wrong.

so... anyone got a smoking free 15g for sale ?

cheers all,wayne.

edit. anyone seen my missing thanks,i was on 206 a few days ago he he