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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 09-26-2007, 09:53 PM   #1
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Default New turbo pickens outs time

So I broke down and bought a BEGi 1.8 T25 flange turbo mani. So now I need a T25 flanged turbo. Goal is 300-325 whp, with good mid range, and nice spool. Motor will be a mildly built 1.8 (a little crank work, overbore, fancy pistons, forged rods) with probably a stock 99-00 head.

These damn GT turbos are friggin expensive. Please help me pick out the right one. Can't afford a mistake. I'm thinking GT2871R. 2 questions, which would be the better turbine housing for my goals, .86 a/r or .64 a/r? Also, it's an internally gated turbo. Will an internal gate work at 300 whp or should I go for an external gate? Will there be any flow issues with a BEGi directed pulse mani if I add an external gate to it? I'd assume it's not ideal due to the directed pulse divider.

Should I also consider a GT2876r? It looks like the 6 has a 4" inlet, with a smooth entry, that can be machined for anti surge which I like.

Anyway, I'm a helpless little bitch when it comes to picking out MY turbo. Please help. Thx
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Old 09-26-2007, 10:00 PM   #2
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I don't have a turbo recommendation, i just know the GT2871R is an awesome turbo and it should work good for you goals. I am interested in how you plan to add an external gate to your Begi mani? Are you going to weld a flange to the mani itself like the HE-X project? If there was problems using the directed pulse mani with an external gate i don't think they would make it an option on the T3 manifolds.
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Old 09-26-2007, 10:02 PM   #3
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I'm getting a gt2871r for my 1.6 build. I'm currently in the process of trading/selling my borg warner s256 monster turbo.
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Old 09-26-2007, 10:09 PM   #4
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Ditching the Greddy, eh? I probably will someday too. In the meantime, my benchmark is your 255 RWHP figure

Forgive my recurring n00bness, but what's anti-surge?
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Old 09-26-2007, 10:10 PM   #5
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Gt3071r!
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Old 09-26-2007, 10:12 PM   #6
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more lag than i want with that personally. You can get over 300whp with the 2871 pretty easily with forged internals.
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Old 09-26-2007, 10:13 PM   #7
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call stephanie, I'm fairly sure that the external gate on the T3s is just welded on similar to the HE-X photos. They could probably modify the manifold for that if you want to go that route.
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Old 09-26-2007, 10:22 PM   #8
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I have a GT2871R with the .86A/R because that's the default turbine. If I were gonna use just one turbo I'd go with the .64 and I think it would rock, that's what I'd do if I were you. Also, there's like 3 different compressor trims. I got the larger one.

Physically it's pretty small, similar in physical size as my GT2554R.

I'm gonna send you a PM about it.
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Old 09-26-2007, 10:30 PM   #9
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255.4 hp, thanks. new goal is 269+ whp before I pull off the kit to beat the Greddy/Link car on FM's site. might be tough with the cat. And yes, I'm sure their graph is corrected 15-20%.

anti surge is an option where they'll machine the compressor inlet in a manner which I believe creates a venturi that helps suck air in and helps prevent air from being blown back out when you lift up.

Al, why 3071, and which version?

Ark, that's a good idea. I just looked at the HEX pics again and see where they welded up a neat little fitting with the flange on it. I was thinking of just adding the flange w/o the runners because I don't have mad skillz like BEGi does. This mani has an EGR pipe welded on, so I was also thinking about using that as a point to attatch the external wg. The real problem with an external wg of course is the downpipe. I was planning on buying a standard BEGi T25 pipe. Again, I'm kind of skill set limited when it comes to making a custom wg tube. I suppose though I could rock an old style BEGi or FM downpipe and try to weld up my own wg tube and blend it in. I don't want to have to build a complete dp though.

Tim, you're going to run TWO 2871s? You are a MADMAN my friend.
I didn't see any compressor options listed for the T25 style 2871.... so that's going to just make me more confused. ugh


thx

Last edited by Ben; 09-26-2007 at 10:47 PM.
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Old 09-26-2007, 10:33 PM   #10
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When on the dyno, disconnect your cat man, it might be worth it.
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Old 09-26-2007, 10:44 PM   #11
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i did some figuring way back when and I was trying to figure out what would be the best turbo for about 350whp on a 1.8. and it came out to the 3071... from what I figured the 2871 probably couldnt make it that far or it would probably be working really hard to do it. i came up with a 2.6 press ratio and 42lb needed to make that power if anyone wants to check my math.

oh yeah and how big is your exhaust/dp and what kind of muffler do you have?
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Old 09-26-2007, 10:47 PM   #12
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I may try one gt2871/.86a/r turbine and one GT2554. If I cant get it to work I'll swap the turbines to the smaller .64 (?) and get that single set up nicely. Then I'll sell it to someone here and put two larger TTs (GT1548 or gt20's) in parallel cause I know that works.

If I was smart I'd just put WI on my current setup to get 275rwhpish and save for the 135i. I no smart tho.
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Old 09-26-2007, 10:51 PM   #13
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2.5" tony pipe, 2.5" hi flow magnaflow cat, 2.25" cat back, xcelerator brand 1 in, 2 out muffler w 2" duals

The entire exhaust will be replaced this winter as part of the engine swap.
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Old 09-26-2007, 11:04 PM   #14
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damn. dyno that thing with just the downpipe on.
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Old 09-27-2007, 12:00 AM   #15
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Ben,

The .64 will be fine for 300 rwhp I think. I have the 2876R .64 and you've seen my numbers (257rwhp) at a whopping 9 psi. For comparison, I was running just shy of 200 rwhp at 4.5 psi (estimated).

Spool is reasonable for a 300 hp car.

http://y8spec.com/dyno/20070714_tuningdyno.gif

I run it externally gated. Just welded the flapper door shut. I'd really suggest going external for that power level because I'm not sure the internal gate can flow enough to keep boost down. You see the problems the 2560 guys have with boost spikes....

Matt
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Old 09-27-2007, 12:00 AM   #16
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..or maybe this guy I know will let you borrow his 3" and test pipe to chase FM's record...
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Old 09-27-2007, 09:12 AM   #17
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I'm very familiar with your charts [email protected], and they were a major influence in me thinking I want a 2871 vs your 2876. Don't get me wrong, I love your power (your graph looks a lot like mine actually), but I just want it to come on a little earlier.

If I knew that I could afford headwork and cams this winter, then I'd probably rock the 2876 and rev to 8500. Which would be cool, but I don't see it happening. My original plan was to use a cheap sleeve bearing T3 or T3/T4, and having a little flow left over to play with, but this GT stuff is expensive.

koto, don't think I won't take you up on that.
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Old 09-27-2007, 09:23 AM   #18
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If I had to choose a turbo for myself, with the same goals as Ben. I'd go with a 2871 52 trim with a .64 A/R. (specially 472560-15)

it can support 45 lb/min (400BHP). sharing the same turbine as the 2876 it should spool very similarly (however they note better boost response.

while the 2876 can support over 450BHP, that's about the only difference. a lighty larger compressor wheel and different stlye compressor housing. How much difference does that intake inlet make
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Old 09-27-2007, 11:42 AM   #19
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I have pondered the possibility of swapping cold sides. I'm not entirely sure what or how I would bolt to the shaft, but isn't it possible to pull the compressor housing and wheel and put something else on there instead?

what compressor/housing does the 2871 use?
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Old 09-27-2007, 11:54 AM   #20
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the 2876 48 trim has a 52.7mm inducer and 76.0mm exducer and supports 50 lb/min (450hp or so)

the 2871 52 trim has a 51.2mm inducer and 71.0mm exducer and supports 45 lb/min (400hp or so)
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