Moderator: martauto
Jesus325iTouring wrote:You'll not regret it,you've helped out a friend in need,can't get better than that Geoff.
Thanks for reading through Ezagood. Hope it was worth itezagood wrote:ffewjust read 17 pages
Me too, which was one of the reasons I did it. Fitting the engine, gearbox, prop-shaft, diff, suspension, wheels etc to an open frame is so much easier than phaffing around under a monocoque. It meant that I could do the whole job on my garage floor using minimal specialist alignment tools, rather than having to lift a monocoque up in the air with a lift (which I do not have at home). Building the frame was also a huge amount of fun that showed progress fairly quickly, which was thus a fairly rewarding experience. Unlike my gearbox upon which I have only ever been able to make slow progress.ezagood wrote:yes well worth the read. ive always fancied doing a full chassis car.
. Good news (hopefully) about the gears too, how has your communication went with ARMA? Have you been able to be as strict with the mid-process quality control as you were hoping to be?
Ta, will do Theo. SFAIK, GT2860RS is the popular upgrade on the SR20 with identical profile turbine flanges. The GT2871R has the identical turbine to the GT2860 (as the name would suggest) but with a bigger (71mm exducer) compressor wheel. The GT28 turbine housing is available from Garrett in two A/R values (0.64 and 0.86) and unless you are planning on building a drag car I would suggest choosing the smaller of the two. Self evidently the GT2871 holds the promise of the pumping the most air in order to deliver the most hp (provided your engine can handle the rigours). However, keep in mind that the both the GT2860 and GT2871 have the same turbine wheel, same turbine housing and (most importantly) the same internal wastegate (given that they differ only in their compressor).Theo wrote:That's a nice leaf blower there, I'm slowly talking myself into a GT2871r
Looking forward to reading about the gearbox rebuild, keep up the good work!
billgatese30 wrote:Wow, the hairdryer looks nice Geoff, even if they are the gay option compared to a supercharger
You must be confused Chris, what could be more gay than wearing a rubber belt? I’ve been on their case at least once a week. I also keep reminding them that if they bugger up the job they replace the material at their cost and start again. TBH though, if they bugger up again I’m pulling the plug. I’ve reached the point where I’d rather find an overseas supplier than take any further chances on the local bumpkins.billgatese30 wrote:Good news (hopefully) about the gears too, how has your communication went with ARMA? Have you been able to be as strict with the mid-process quality control as you were hoping to be?
Hi Chris,CHR1S1990 wrote:Hi Geoff,
don't think I've posted on here before but I've been watching from the beginning, brilliant car. Sorry to be a little OT with current affairs (nice turbo!!) but could you possibly give me some information on how you designed your intake manifold? Feel free to pm me, 'don't want to spam your thread.
Keep up the good work.
Nice info Geoff, thanks for posting it up. I wish I could go for a an external wastegate setup but the large number of modifications required to run one really puts me off (management, MAF, manifold, water and oil lines for turbo, exhaust, intake pipework etc)GeoffBob wrote:Ta, will do Theo. SFAIK, GT2860RS is the popular upgrade on the SR20 with identical profile turbine flanges. The GT2871R has the identical turbine to the GT2860 (as the name would suggest) but with a bigger (71mm exducer) compressor wheel. The GT28 turbine housing is available from Garrett in two A/R values (0.64 and 0.86) and unless you are planning on building a drag car I would suggest choosing the smaller of the two. Self evidently the GT2871 holds the promise of the pumping the most air in order to deliver the most hp (provided your engine can handle the rigours). However, keep in mind that the both the GT2860 and GT2871 have the same turbine wheel, same turbine housing and (most importantly) the same internal wastegate (given that they differ only in their compressor).Theo wrote:That's a nice leaf blower there, I'm slowly talking myself into a GT2871r
Looking forward to reading about the gearbox rebuild, keep up the good work!
Theo, you would do well to take note of the fact that the 0.64 A/R GT28 turbine chokes at roughly 0.18lbs/min airflow, and the 0.86 A/R GT28 turbine at roughly 0.21lbs/min. You can thus conclude that, each and every hp over and above roughly 170hp through the 0.64A/R GT28 turbine is due to airflow via the wastegate. Likewise, for each and every hp over roughly 200hp via the 0.86A/R GT28 turbine. What this means is that, while the bigger compressor holds the promise of more power, the GT28 internally wastegate turbine holds the promise of boost creep. This all depends on what sort of hp you are aiming for of course, but if its more than 300hp I’d suggest opting for the larger 0.86A/R housing (albeit at the cost of delayed boost) since without the larger A/R housing the GT28 internal wastegate will not be able to cope with the 13lbs/min of air required to get you from 17lbs/min up to 30lbs/min total. This is (sadly) exactly the problem I ran into with my GT3267 whose 0.69A/R turbine chokes at 20lbs/min, and whose internal wastegate was only good enough to flow 10lbs/min before the internal wastegate began to choke. From that point on the turbine pressure began to build and from 300 to 350hp I was running on pure boost creep. This is why we couldn’t take my engine over 5500rpm in my earliest posted dyno plot (after which detonation kicked in due to the ever climbing boost, despite the fact that the wastegate was wide open). After that I fitted the external wastegate and bolted the internal wastegate closed ”“ problem solved.
If its power that you are pursuing, with minimal turbo lag as a requirement, I would honestly suggest you look at something with an external wastegate as an option (such as a GT3071, for which you’ll need a new manifold). With that said, Garrett’s product here is clearly exactly what you are looking for with minimal (if any) modifications required to fit. The point I am making, however, is to just be aware of the fact that in order to stop the GT28 internal wastegate from chocking you’ll need a turbine housing that flows the most air possible before you even need to think about cracking the wastegate open. And that by definition means one thing: Expect your engine to come on boost at higher RPM than you are used to, or choose the 0.64A/R housing and don’t reach the hp you might be aiming for. Personally, I’ll happily sacrifice peak hp for low rpm torque coming out of a corner.
Just my thoughts
I have heard of modifying an internal wastegate, but I have never attempted it myself or seen it done. It really depends on how much space is available. If there is room enough to bore a bigger hole and you can fit a bigger flap to the arm then I don’t see why not. You won’t know unless you try and it’s not worth attempting (for risk of damaging the turbine housing irreparably) unless you know for sure that you have a problem that needs to be overcome. With my GT3267 the problem was blatantly obvious, for which there was two possible solutions 1) swap the turbine housing for one with a larger A/R (there was a 0.86 ex stock as I recall) but same internal wastegate, at the expense of increased lag or 2) fit an external wastegate and bolt the internal closed until the new turbo arrived. I opted for the latter and I’ll never go back.Theo wrote:Nice info Geoff, thanks for posting it up. I wish I could go for a an external wastegate setup but the large number of modifications required to run one really puts me off (management, MAF, manifold, water and oil lines for turbo, exhaust, intake pipework etc)
The version of the GT2871r you posted a link to is the one I'm likely to get. It's a direct fit with no modifications necessary other than a revised ECU chip and a MAF from a 300zx. I don't have a power target as such, I just want as much power as I the car can handle without becoming too lairy (At a guess 340/350bhp?) The present turbo is working at it's limit which is a further motivation for upgrading.
With regard to boost creep, is it not possible to modify the internal wastegate to improve flow? Or would it be hard to improve the flow significantly?
By the way, over in the UK the GT2871r is much more popular than the GT2860rs, not sure why though - possibly because the most popular supplier of off-the-shelf ECU chips supplies a chip to run the 2871 but not the 2860.
Ah yes, very goodMillRat wrote:Geoff, I have the answer to your lag problem.....
Anti-lag
I'd research as many power and torque curves as possible for both turbine housings (A/R=0.64 and A/R=0.86). If you are satisfied with the sort of hp made by the smaller of the two then I would pick that one, for its torque curve will surely indicate more torque at lower rpm than that of the larger turbine housing. If, however, you require the greater hp of the two then be sure that you are satisfied with the later delivery of torque. Many of those that say that they are happy with the later arrival of torque may be budding "street racers" and unfamiliar with the demands of the race track.Theo wrote:Cheers Geoff, I'll be sure to go for the .86 version when I do loosen the purse strings. According to other SR/2871 owners the increased lag from the large turbine isn't too bad, I suppose I'll just have to suck it and see I suppose.
I'm not sure what the current power output is Geoff, I do have a dyno graph on paper from the previous owner of the engine when it ran 1 bar boost (rather than the 1.25 bar I now run), smaller injectors with a different ECU chip and a rather crude exhaust - it made 263bhp & 255ft-lbs at the flywheel or if you prefer to deal with wheel figures it was 221bhp & 213 ft-lbs.GeoffBob wrote:I'd research as many power and torque curves as possible for both turbine housings (A/R=0.64 and A/R=0.86). If you are satisfied with the sort of hp made by the smaller of the two then I would pick that one, for its torque curve will surely indicate more torque at lower rpm than that of the larger turbine housing. If, however, you require the greater hp of the two then be sure that you are satisfied with the later delivery of torque. Many of those that say that they are happy with the later arrival of torque may be budding "street racers" and unfamiliar with the demands of the race track.Theo wrote:Cheers Geoff, I'll be sure to go for the .86 version when I do loosen the purse strings. According to other SR/2871 owners the increased lag from the large turbine isn't too bad, I suppose I'll just have to suck it and see I suppose.
Oh, and should you be unhappy with your choice, all that is required is a change of turbine housing (since it is only the A/R of the housing that differs between the two), which Garrett conveniently sell separately. I am in the same position with my new GT30 turbine, with a range of A/R housings at my disposal should I choose to try them. For obvious reasons I have opted to start with the smallest (A/R=0.63) since I require my turbo to spool up as fast as possible powering out of corners.
Theo, where you will see a big difference is in that your existing GT25 turbine chokes at only 15lbs/min air flow. If your wastegate on that turbo can handle 10lbs/min then you'll be lucky to make it to 250hp (how far off am I on this figure?). With a 0.86 A/R GT28 turbine you'll make it to 210hp through the turbine alone. If the GT28 internal wastegate can handle another 12lbs/min and that should see you good for 330hp, provided the engine can reliably deliver.
I'd be very interested to hear from you what other SR20DET owners have achieved with a similar setup to your own with the addition of either A/R turbine GT2871R.
I'll see what I can do for you Theo. The article comes from the book Turbo, Real World High-Performance Turbocharger Systems by Jay K. Miller, published by Cartech books. I wouldn't describe the book as a definitive work on turbochargers, but its still worth having on the bookshelf and a thoroughly interesting read. The first two chapters are ideally suited to those who are entirely new to the inner workings of the turbocharger. This is also the only book I have sen thus far that deals with turbines maps as wells as compressor maps. Most only deal with compressor maps.Theo wrote:If you get a chance to scan that document on the Disco Potato that would certainly be of interest, turbos (like many things in life) are a bit of an unknown to me, so I'm keen to get a better understanding on the ins and outs of them.
Thanks Eta, Much appreciated!eta wrote:I have just read this. I am simply in awe of your work Geoff.
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But the thing that hurts the most is you know that the design WORKS!!! Its just a shame that you have to rely on the shambles of a shower of dickheads to do the work.GeoffBob wrote:If not them I’m out. Lesson learned
