GT28RSR .64 vs GT28RS .86 vs GT2871R .86

GT28RSR .64 vs GT28RS .86 vs GT2871R .86

OK guy needs some votes and what you would do if you were in my position. My current setup is:

GT28RSR 0.64,
Forged Rods,
Forged Pistons,
Fully Balanced,
Very Light Headwork,
Standard Cams,
H&S Downpipe,
3" System,
380cc @ 3.8Bar,
255 Fuel Pump,
FMIC,
Paddle Clutch,
320mm Brembos,

Whilst mapping the car PT noticed that my brand new turbo was smoking so I called up TD and I will be sending it back under warranty for a replacement however it puts me in a predicament as I have clearly maxxed out the RSR and know how the car behaves with it, should I go bigger? Don’t get me wrong I’m quite happy with the current setup but I’m unsure as to exactly how the car will be if I change it.

Here is my current map:
http://www.online-presence.co.uk/_coupe/rollingroads/148.jpg

My engine if fully capable of running the power until the injectors’ max out which I would estimate to be about 400BHP MAX. Should I change the turbo and if so why?

garrett only seem to rate the GT28RS to 360 BHP, you want more than that dont you??

If I was in your position with the forged engine I'd probably want nearer 400 bhp, so I wouldnt stick with the RSR.

only the 2871r will get you close to 400bhp, the others simply won't flow enough air

Jamie

Is running a bigger turbo going to change much if you're still running a 9.4:1 compression ratio?

Not necessarily I want about the same BHP as torque I would be very happy with 350BHP & 350FT/LB with good spool up. I'm not just interested in 'pub figures' as I don’t wanna sacrifice too much ft/lb for BHP hence the high CR.




Very good point. I would assume that I will have higher torque lower down so less lag but what will happen further up the rev range?

only the 2871 will get you past 400bhp, but at the expense of lag and torque.

You'll still get 340-350lb-ft though

Spoolup will be at about 3,500rpm, with max boost well before 4k rpm

I dont think u have maxed out the RSR tho dude. There is a few other people pushing 340-350bhp from that turbo.

Ross

Yes, I think I have maxxed it out the reasons are:

Reason 1 - You can see that as the back pressure increases the turbo chokes up the higher end of the rev range because of the 0.64 housing.

Reason 2 – The fuel return was blocked at the time of mapping so my duty cycle is currently at 85% Rob pulled out from 15 degrees ignition to 7 degrees to be safe until I get the fuelling sorted. That alone could give it an extra 10BHP.

Reason 3 - 327BHP @ 1.2Bar I don't think the turbo can go much further as the RS is rated to 360BHP and the R is rated to 310BHP so all things being equal the RSR should be somewhat in the middle about 335BHP. Also have the 'other people' that made 340-350 been on PT’s dyno at 18 degrees ambient?

Reason 4 – Look at the torque produced 335ft/lb is very high in fact it beats all RS powered cars in the hall of fame and is nearly knocking on the door of Nigel who has 6ft/lb more with at GT2871R. As BHP is a measurement of torque against speed I would say this figure also shows that the turbo is pushed to its limits.

I think the RSR is now a mismatch for my setup as when I brought it I originally I had standard rods and the GTA combo clutch so my power was limited by these items alone. Now that I have forged rods and a paddle clutch I am safely able to run more power up to my next weakest link with is of course the 380cc injectors. Since I have the opportunity to change the turbo I am very much considering it therefore asking for some comments as to what choice to make.

@ H2ypr when are you due in for mapping on your RSR?

the high torque and relatively low power also indicate you may have some sort of restriction in your setup be it intercooler, inlet or exhaust

@ JohnS
Could it not be my 9.4:1 CR?
What do you think on the turbo choice?

I'm going for the 2871R but with the 0.64, option! how come you aren't looking at the smaller housings?

I am. I looked at the 0.64 @ GT2871R and to be honest IF I do change turbo's it will probably be out of the RS with 0.86 and 2871 with 0.64.

@ Eldinho which one is yours as Garrett list 5 GT2871R's
http://www.turbobygarrett.com/turbobygarrett/products/turbochargers.html


Today I plan to plot my engine on various compressor maps and upload them (if I get time). Also gathering data to plat an excel graph for RSR vs RS vs 2871

I've not actually ordered it yet, plan to do so in the coming days!

TurboJ - remember that my 2871 is a 0.64, not the 0.86

If you want some charts for the 0.86, contact Flea

Just spoke with Rob @ PT today. He remembers my caravan very well (Personal joke).

According to him the problem I have is that my RSR 0.64AR with 62Trim simply cannot hold the power higher up the rev range and the high CR will not let him run any more advance lower down.

If I jumped to the RS 0.64 or 0.86 he said that I probably wouldn’t notice much of a change as he still wouldn’t be able to run any more advance. So it was recommended that a GT2871R will be able to flow more air at lower boost pressure meaning cooler intake charge and more advance.

Because I still want my power band relative lower down the 0.64 AR with 76 Trim would be the one to go for.

As I mentioned earlier Garrett do 5 different version of the 2871R in 0.64 so Rob said he would look over the compressor maps and choose one for me sometime this week

@ Nigel I have found fleas graph and an RS with 0.86 so I just need somebody to donate an RS & R 0.64 graph with similar spec to our cars then I can plot an Excel graph comparing all the different turbos and AR. This would be very useful for everyone on the forum.

Any one wanna comment on this?

Thought about some WI to help with the charge temps?

I thought it would have. I have it fitted but Rob said i shouldn't use it.

Right plotted my engine on some compressor maps using all the data I have about my car including the last dyno map to be as accurate as possible.

Running 1.2Bar with rpm points 1000, 2500, 3250, 5000, 7063 & 7250

GT28R:
http://img249.imageshack.us/my.php?image=gt2860rlz6.jpg

GT28RS:
http://img206.imageshack.us/my.php?image=gt2860rsch5.jpg

GT2871 48 Trim:
http://img206.imageshack.us/my.php?image=gg2871r48trimft6.jpg

GT2871 52 Trim:
http://img249.imageshack.us/my.php?image=gg2871r52trimxp6.jpg

GT2871 56 Trim:
http://img129.imageshack.us/my.php?image=gg2871r56trimmb8.jpg

Looking at these maps the GT2871 with 48 Trim looks best for my setup what do you lot think?

i think turn the boost up

Why did you look at the 55 trim GT28R rather than the 62?

Don't know it dosen't matter as either R is too small for my setup.

Why?

As you know I've got the same rods and pistons as you. I'm going to be sticking to the GT28RS 0.64 and get a thicker head gasket to drop the CR to somewhere between 8.8 to 8.5.

I'll also have a stage 2 TI head, ported manifold, raise the rev limit to 7300 and run about 1.5Bar.

With the WI on I'm hoping to get the 360bhp quoted by Garrett.

Basically WI don't mean more power in all cases as good intercooling and high octane fuel is more important as there are other ways to cool the cylinder e.g running richer fuel etc.

I would like to discuss this however it's a whole new topic that would require a new thread

Your CR is 9:1 I would consider it as waste of time and money to drop it to 8.8:1 as 0.2 of a CR you won't notice jack. Most of the modern turbo engines including the high power Subaru etc run 9:1. Also with the headwork Barbz has done the ports are open quite big so you suffer air speed lower down so a higher CR can only be a good thing in your case. It all depends on where you want your power Ken. Some people may disagree in what I have done however I am building it very specific for what I want. Once you’re built and dynoed then I guess you’ll know more as each build is always different.

turbo j i have 340bhp and 330lt of torque on the rsr setup with standard rods and pistons at 1.35bar

What waste of time and money? I've only got to order a thicker gasket.

Anyhow, I thought you were happy with your setup, what's this talk of a new turbo for?

you'll get bored too Ken

@ alessandro can I have a peak at your dyno graph then so I can compare?

@ Kenno Please don’t take offence but if you’ve ordered your pistons in 9:1 then why are you bothering with changing the CR why didn’t you just get them in 8.5:1 in the first place? I specially choose mine in 9:1 for my own personal decision I didn’t plan on running 9.4:1 as I didn’t know my block and head had been skimmed by so much, but what’s done is done. I may change it at a later date but for now I’m sticking with it.

The standard Fiat gasket is only £30 from the main dealer so what gasket, from where and how much is your thicker one?

I am happy with my setup however since the turbo had to come off and I have the ability to go further why not? As I said earlier when I brought my turbo I had standard internals and GTA clutch but now I have forged internals and paddle clutch so I can go more if I change the turbo.

@ eldinho very true I get bored when my car is working I like fixing/changing things

Anyone able to comment on the compressor maps I uploaded?

[quote=TurboJ]@ alessandro can I have a peak at your dyno graph then so I can compare?

I think kenno might have a graph of mine as i aint got a scanner at the mo.

No offense taken.

I don't pretent to know that much about tuning, I'm learning things as I go along, as I suspect are you despite your motorsport course.

Also lets be honest here. You didn't 'order' your pistons. A GB was going and we all tagged on. At the time, we were advised to run a slightly higher CR (8.8:1) however as it turned out the pistons came out as 9:1 (or do we have you to thank for that??)

Anyhow having now seen your results and reading the comments of some highly respected tuners I've decided to go back to nearer the 8.5:1 CR.

Now I could try to sell the pistons and have some more made up, but then again I could buy a thicker gasket. Given the headache you had with selling your CP pistons i'll go for the thicker head gasket. Where from and how much it will cost i'm not sure but i'm confident that I can get one.

Yes - I do have alessandro's graph and yes i've compared it with yours. IMO it makes it obvious that you've made a costly mistake by not taking Ricky's advice and dropping the CR.

good post Ken

I guess it all depends on what we want from our setups. Barbz did recommend to me a CR of 8.8 to make the most out of the engine build, and I guess nobody knows better than him on building a 20VT. J has gone a bit higher, but seems happy with this. I think I'm going to stick with 9:1 and see how it goes. Hopefully not boom

In terms of CR, the general trend whether it be factory or modified is to increase. That said, a factory product is built from the ground up with the latest technology therefore they are designed to run this CR out of the box. In many instances a higher CR is due to the prevelance of increased octane fuel, an adaptive ecu and light pressure turbos. Most VAG modders will drop their CR from 9+ to middle-high 8s, old school but nothing like as bad as the low 8s and 7s that Cossies and older Porsches run.

I think there are to many people focusing on the static C/R

would some one be able to give me the details on the C&B cams that everyone is using??

there are many other factors at play that will effect your decision on C/R

the turbo that is being used will make more of a difference

High C/R seems to suit larger turbo's running relitively low boost, remember that whats more important than boost is flow

a smaller turbo will have to run a higher boost level than a larger turbo to produce the same flow, the problem with higher boost pressures is that you will have a hotter charge entering the cylinder and as a result you will have to retard the ignition

there is a lot more at play than i have explained above but it may make some points clearer for some people

all of this is theory and some times does not playout exactly as you expect.

But what ever you do make sure you pay attention to the turbo you plan to use before you finalise your decision on your C/R

Just for the record i have driven cosworth with C/R's of 6.8-1 and 8.9-1 plus the standard setup, most people would say that 6.8-1 is really low and off boost drivability would be horrible when in fact it was hard to tell the differnce as he speced turbo that suited the low C/R

Jay, Running the GT2871 will be quite a good compramise for your setup, you wont have to run such a high Boost pressure to make the BHP you want

Also looking at the flow maps you have uploaded the GT2871 seems to cover most of the bases

I don't pretent either i am learning too that is why i choose a motorsport course. I'm still only a first year




Well in all honestly I planned to run 8.8-9:1 CR as Flea/Barbz etc runs 8.8:1 and JohnS runs slightly higher than 9:1 (he won’t say exactly what that is) so I am not the only one who has increased the static CR and I still feel there is nothing wrong with running 9:1.

The only possible mistake I have is that I skimmed my head and block too much and ended up with 9.4:1 (long story). I had the option to use a decomp plate to bring it back down to 8.8:1 whilst the engine was apart but I thought lets experiment, however it’s not the end of the world as changing the turbo to a bigger compressor could benefit to this factor. I am studying motorsports and it is all about testing your ideas and tweaking the results and I feel I have been very open in what I have been doing unlike some people who keep data away from the forum.

After another set of results if I wanna change the CR then off pops the head and on goes a decom plate. It’s no big deal for me as I am able to do this at no real extra cost (just my time and parts). I choose to experiment with my own ideas rather than follow the flock as if I don’t then I haven’t really learnt anything. My car is my toy, project and experiment and I have learnt so much from it.

So can we please now drop this and have some ideas on a turbo choice thank you

Also I’m am still compiling a graph to compare all the turbos but using this excel 2007 is a bit of a pain

You know what TurboJ, I have absolutlely no idea what you are talking about here (well I do see the larger scheme of things) but, I tell you what, I would love to know more. Is there any decent books that you recommend to get your head around this aspect of engineering?

WOW talk about rasing the dead

So what was your choice in the end j?

GT2871 48 Trim

This would be a good book to start off with

Thanks Begbie and thanks TurboJ for the info! Already ordered