Bc Stroker (2.75l) Turbo Choices

[HarrisRacing]

I am nearing completion of my build and need to decide on a turbo. I have narrowed it to a few choices and would like some feedback on my selection and math (because garrett boost advisor and BW match-bot programs slightly differ in recommendations).

Engine is the following:

BC stroker on stock N1 bores = 2.75L

9:1 CR

SS BC valves oversized +0.5mm intake and exhaust

Ported cylinder head (nice smooth setup...nothing crazy)

Tomei Poncam A's

Divided T4 tubular manifold

Haltech Platinum PnP ECU

850cc injectors

Tomei oil pump

Greddy Sump

Side drains for pan (2x -10 lines to breather, etc).

Car is R32 GTR and is street car with plans to track on occasion. Pump gas most likely all I will run which is "93 octane" here (98 RON?)

BW 8374 EFR 1.05 AR

Match bot shows Boost comes on strong at 3200, and 532 HP at 7500 rpms

BW 8374 S300SX .91AR

Again extremely similar numbers to the 8374 EFR with exception of the ability of the compressor to come on earlier?! With the .91 AR housing and the shallower compressor map, this should make 16 psi boost at 3000 rpms. Technically this should be a better combo for 532 BHP?

Am I missing something between these plots because I was assuming the EFR would have made more HP on top end?

BW EFR 9180 1.05 AR

15 psi boost at 3800 rpms. At 20 psi now a 50 HP gain making 580 BHP.

(Next post will be Garrett Turbos).

Edited April 7, 2015 by HarrisRacing

[Kinkstaah]

I have this kit (essentially, but its on a Neo)

I use a GTX3076R (.82ar)

It's very responsive. It makes about 407kw for a manual on E85. (but at 21psi, may be reachable on 98)

I would say a better fit is probably a GTX3582, but of course it depends on the application of the car, supporting mods, and all that jazz.

If I had the balls and didn't live in Victoria, I'd probably use a Precision 6466 if I didn't have to consider the local arm of the law.

[GTRNUR]

If your never planning on running E85 then you should consider lowering the compression closer to 8-8.5:1. This will allow you to run those larger turbo's at least a bit closer to 1.5kg/cm without hitting the knock limit.

There is little point in running a huge turbo when you can't boost it more than 1kg/cm boost with it, that is unless you want that big turbo for visual appearance, and don't care about the combined lag and lower power level.

[GTR_JOEY]

Dude sorry to burst your bubble, but you are not going to make 16psi by 3000rpm with an 83/74.. Especially with that size engine on that fuel. 3500rpm would be a good result for 16 pound in my opinion

Though I do agree the 83/74 with the smaller turbo is your best option for power and response

[PranK]

Hi All, I have removed the posts about legalities of cars in the States. Please stay on topic in here.

If you want to chat about legalities and importing, you could always start a thread in the new US forum.

[HarrisRacing]

Dude sorry to burst your bubble, but you are not going to make 16psi by 3000rpm with an 83/74.. Especially with that size engine on that fuel. 3500rpm would be a good result for 16 pound in my opinion

Though I do agree the 83/74 with the smaller turbo is your best option for power and response

Thanks and I totally agree. I must be using some bad VE numbers. More than likely I am too high on the VE at the low rpms and too low on the high rpms. I'm trying to reverse engineer other people's graphs to see what to expect for VE. The calcs in match-bot display HP in flywheel HP, and NONE of my calcs come close to some of the numbers that others have hit on pumpgas. Very curious to see what Geoff or others would use for VE on an RB26DETT that's stroked and ported.

[HarrisRacing]

Here is the latest model that I have for an 8374 EFR in the match-bot software.

I'm using RPM, VE, Boost, calc'd HP as follows:

3200 rpm, 90%, 15 psi, 254HP

3500 rpm, 90%, 21 psi, 313HP

4500 rpm, 110%, 21 psi, 444HP

6000 rpm, 110%, 21 psi, 561 HP

7500 rpm, 105%, 21 psi, 623 HP

8500 rpm, 100%, 21 psi, 613 HP

I guess the question is, if you plot this in excel, does it look like a good graph. Match-bot shows that the turbine and the compressor on this engine (90% VE at 3200 rpm) should make the 15 psi boost no problem BUT Theory and practice are only the same in theory...not in practice.

[HarrisRacing]

I reverse engineered some 2.6L VE numbers and came up with the following:

RPM - VE

3000 - 72

3500 - 72

4000 - 80

4500 - 100

5000 - 111

5500 - 117

6000 - 120

6500 - 121

7000 - 121

7500 - 118

8000 - 115

These numbers support some dynos that prove that the 8375 turbo is maxxed out at ~68 lbs/min airflow. It also supports the boost threshold of such setups. I am assuming this setup had CAMS.

If I use these VE numbers, my estimated 2.75L HP dyno comes up as attached on pump gas and 21 psi boost by 4k rpms and dropping to 18-17 range above 7500 on the 8375 and .91 housing.

Feel free to play with my Match-bots:

low rpms

high rpms

Edited April 12, 2015 by HarrisRacing

[HarrisRacing]

And here is the 8375 .91 AR twin scroll at 21psi (dropping to 17) VS. the 8374 EFR IWG .92 AR twin scroll turbo which can hold 21 psi to my redline. As you can see they are almost IDENTICAL in spool and power with exception of the EFR being able to support the extra flow (74 lbs / min) on the top end and carrying 21 psi all the way to redline of 8500 rpms. Pretty much projected to make 50 whp more from 7500-8500 from the little extra push from the compressor.

Again these are pumpgas projections on low boost (21 psi max). On my stroker motor I DEFINITELY give the nod to the 8374 EFR on .92. On a 2.6L, however, it didn't make this much difference!

Shame of it all is that if the 8375 was offered with the same turbine as the 8374EFR, I think the 8375 (cast) would matche the 8374 EFR almost identically at 18 psi (or lower) on 2.6L.

8375 results from match-bot are in post above.

2.75L 8374 EFR .92 IWG T4 divided matchbot results:

low rpm

high rpm

I know I'm replying to myself, but I still think I'm trying to offer solutions for some of the stroker guys out there.

[bigmikespec]

Did you get my PM?

[HarrisRacing]

Added a comparison of the following:

2.75L engine

8375 cast compressor w/ .91 AR T4 housing (76mm turbine, 60mm compressor)

8374 EFR w/ .92 IWG (74mm turbine, 61.4 billet compressor)

7670 EFR w/ .92 IWG (70mm turbine, 57mm billet compressor)

One graph at 19 psi the other at 21. Both the 8375 and the 7670 EFR are out of breath on this motor at high rpms and cannot sustain the boost. Still for a $600 turbo, the 8375 is really showing how nice it is, but the 8374 EFR is still the king of the powerband on this setup.

One thing to note...I also compared the new FMW (billet) compressors in the Airwerks turbo with these and found exterme similarities between them. I'm SURE the EFR's are better and spool better and transient response is better, but the compressor and turbine maps plot extermely similar to the following:

7670 EFR .92 IWG = S200SX 57mm FMW w/ 1.00 (or maybe .88) housing

8374 EFR .92 IWG = S300SX 62mm FMW w/ .91 AR

Basically there are your journal bearing comparisons. But after you add the Wastegate and recirc valve, you are getting back up in the ballpark of EFR's and might as well get the technology.

So the comparison is starting to show for me:

8374 EFR .92 IWG ~ $2300

S300SX FMW 62 w/ .91 EWG ~ $1150 + $400 wg + $150 BOV = 1700

S300SX cast 60mm w/ .91 EWG ~$600 + $400 wg + $150 BOV = 1150

Edited April 15, 2015 by HarrisRacing

[HarrisRacing]

Decided to go with Geoff's advice from Full-Race. Even though I'm on relatively small cams, Match bot and real results agree that the EFR 8374 with IWG .92 housing should be an incredible street turbo.

the deciding factor was an Ebay auction that popped up and I snatched the turbo in seconds. I will not tell what I bought it for, but it is $600 less than I have ever seen advertised which seems insane to me...and it was a 100% ebayer with the correct BW part number: 179357.

We will see if it shows up next Tuesday.

now to find a header that fits R32 accessories.

Patrick

[Piggaz]

That should be quite a stonker of a setup!!

[GTR_JOEY]

I wonder how close the 83/74 and 83/75 are in frame size dimensions.

If it was a direct bolt in it would be my upgrade option for sure when the time came.

Maybe Geoff could answer this if he's hanging around

[HarrisRacing]

I wonder how close the 83/74 and 83/75 are in frame size dimensions.

If it was a direct bolt in it would be my upgrade option for sure when the time came.

Maybe Geoff could answer this if he's hanging around

Doesn't look anywhere close to direct bolt in from the dimensions from their catalog. Looks like the EFR is significantly larger, plus that strange offset housing with no dimension? And the fact that there is no clearance dimension from the wastegate canister.

That being said, I do see that the journal FMW is the same dimensions and is a worthy swap if just trying to get more top end. I'd bet the front housing and wheel are all you'd need and I do recall reading a post where Geoff says that all BW setups are individual component balanced so you can just swap the front wheel and cover without need for complete balancing (I could be mistaken there...I have been reading a ton of turbo stuff lately).

Sure would be a cool back to back dyno comparison just showing what swapping a compressor wheel would do! (hint).

Hope this helps.

Edited April 21, 2015 by HarrisRacing

[GTR_JOEY]

Yes I do remember him saying the same thing about balancing components. It would be a great comparison but I'm sick of not being able to drive my car so what I have will do for now. Cheers for the info mate!