20B Garrett G55-1850, any experience?
 

For a time attack circuit only semi-pp 20B track car wanting ~1000rwhp and alright/good response, would a Garrett G55-1850 turbo with a 1.12 A/R turbine be good? Running maybe ~30psi at peak power. Wanting to know if anyone out there has tried out this combination or a similar combination and how it is. Very curious and open to any suggestions more fit for this application 😄

https://cimg7.ibsrv.net/gimg/www.rx7...127dba5540.png
Idea of where ~30psi at 9000 rpm lands me on the Compressor Map using one of the forum’s turbo selection guides

I'd be tempted to target a couple of psi less (or ideally more in the midrange and control wastegate with turbine speed target) and use a G45-1500. Should have heaps better response and a much broader power band even if you land 25hp short of target (might still get there under turbo speed limit). Seems to be a pretty big gap in the G series line-up, I'd be tempted to look at gen2 GTX if you really want something in between. G55 frame seems better suited to 3+ bar boost target 2 stepping drag cars.

I see, I was wondering that as well. After some minor digging around I’ve found that the GTX4720R Gen II 76/80mm will probably fit my goal better but Garrett only has the compressor map for the 88mm which is too big :banghead: Would be perfect if a G47-1600 existed but eh it’ll likely be a fat while till that releases


https://cimg2.ibsrv.net/gimg/www.rx7...b7d07a62b.jpeg
As seen, only the 88mm map can be found

I looked at this not too long ago and imo there really isn’t anything that great past the G42-1450 1.28 A/R, or at least not in the same league as that one imo. As mentioned, you might consider 950 whp using it instead with the efficiency benefits.
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Actually I’ve also seen somewhere on this forum that Race Ported motors get 15% more power with the same boost than stock port motors so a semi-pp motor could possible get >20% more with the same boost so the G42-1450 could very well be enough to get to 1000 wheel after all! :lol: Big thanks to both Slides and TeamRX8!

Assuming that ported motors do get more up with the same boost, I can run it lower in the graph while still making tons. ((((4 displacement*9000rpm*90ve*2.7pr)/5660)*0.076 convert to lb/min)*7.69 convert to rotary rwhp)*1.2 ported gives more power = 1,084 rwhp :bigthumb: Assuming I only get 15% more power from the port I still have 1030 rwhp.


https://cimg3.ibsrv.net/gimg/www.rx7...333ccf0c24.png
Redone compressor map for G42-1450

you’re a bit off-base there; you only get more power with more effective airflow and the appropriate fuel to balance it out

you’ll need approx. 135 lbs/min compressor flow to hit 1,000 whp.

so you can see that your compressor map projection is a bit off …

What do you mean by more effective airflow? Currently have a Pro-Jay Typhoon Intake Manifold set up with a 102mm DBW Throttle Body. Fuel is no worry, I can crank up the pump and injectors. Pump is a Fuelab 600lph twin screw brushless pump, 3 x Injector Dynamics ID1700x and 9 x Injector Dynamics ID2600x

The larger porting doesn't have a significant influence on thermodynamic efficiency, only air flow at higher rpm, you need to reflect that in the maths by changing the VE not effectively skewing the power from air factor as you seem to have done. Generally speaking most of the equations people use are only valid at the lowest rpm the engine achieves peak power, which is more likely 8000rpm even if they carry that power to higher rpm(or you taper the VE figure back down).

your line above is peaking at approx. 115 lbs/min, which would only be ~865 whp.

the only way to achieve 135 lbs/min on the *indicated* G42-1450 map is to be at approx. 2.5 Bar and is right on the zoom-zoom-boom rpm limit edge of doom.

what porting can do is possibly allow you to achieve that same flow at a lower boost level when the other components also support it, but you’re probably looking at a full bridgeport or semi-PP at a minimum to get it down to only 2.5 Bar (that’s a bit beyond my knowledge base on a 20B and somebody else would need to confirm it).

In addition to the impact of those changes in other areas then you also have to be more concerned about Emap/turbine flow capability to avoid exhaust manifold/system back-pressure, which the engine is generally more impacted by as you get into the BP, semi-PP, and PP porting configurations.

That said, Rob Dahm already proofed the G42-1450 on a 3-rotor and he recommended a 950 whp limit. You can possibly get a bit more out of it by using a turbo speed sensor and an ecu control strategy to not exceed the max. turbo rpm speed, but the closer you operate to that limit the sharper the razor becomes and the more possible it is to slit your engines throat with it.

Because Rob did initially exceed 1000 whp with the turbo, but it was operating on the right side of the maximum rpm limit. While the map flow isn’t *indicated* past that limit, it should easy to recognize that given the indicated compressor efficiencies there the compressor can generate higher flow beyond what is shown.

The flow capability isn’t the issue, the issue is that the compressor wheel material can’t handle the rotational forces acting upon it past that limit. So you can easily make 1000 whp and it will if you allow it, and the rest of the configuration supports it, but the compressor bomb is ticking away out there and at some point will go off.
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Ah okay I see. I guess I was too focused on the 1000 rwhp mark. 950 will have to do and honestly it’s already plenty plenty much. >900 is my new goal although >910 would be nice. What Bar and lb/min would you guys recommend? I’m thinking now about 2.6 Bar at 120 lb/min (~920 rwhp) - how do you guys think that’ll do? Although of course there will be things I have missed or got wrong and please do point them out since I’d rather be wrong and then corrected rather than left to my own stupidity. :o:

Assuming decent intercooler and exhaust my maths is saying about 2.6 bar absolute for around 900whp on ethanol. Might have to go a touch higher on water/regular fuel. Obviously give or take a bit on porting/peak power rpm.

Intercooler is a 22” x 14” x 4.5” Garrett Charge Air Cooler Core with full 3” Tubing. Exhaust is a 4” Into a dual 2.5” side exit. By Ethanol do you mean the racing stuff like at One Ethanol or E85? I assume the racing stuff.

to be honest I don’t think there would be any perceptible difference between race ethanol and any nominal pump e85 over about 60% ethanol content, the larger the injector to port length the more noticeable with higher eth content due to charge cooling. Maybe the guys running up around 60psi boost can see differences in fuel behaviour in terms of combustion stability but I think it is irrelevant for most people as they are so far inside the stable combustion bounds of the fuel. If I was running a flex sensor or knew the content of the pump fuel I wouldn’t bother with racing fuel myself, if you are going to that effort may as well use methanol.

New Map!
 

Hopefully better than the G55 and previous turbo plots, feedback welcomed ;)

https://cimg4.ibsrv.net/gimg/www.rx7...85c69d3eec.png

Probably pretty close, noting when you adjust for true inlet density and some intercooler/piping/throttle loss you probably push up .1 of a bar or more on the map near peak power and shift a touch to the right. Hopefully you would be hitting full boost a fair bit earlier too.

Alright big big thank you to both Slides and TeamRX8! :worship:

semi pp with projay

you will make 1000rwhp at less than 23-24psi of boost on e85

just need a compressor and turbine to keep up with it

G45-1500 with a 1.44 will get you there

With the formula I usually use, with 24 psi (2.6 bar) of boost it gets me only to 121 ish lb/min which is only ~930 rwhp. Not only that it’ll be right at the very edge of the right hand limit of the compressor map so if anything the G42 ‘keeps up’ better at this boost level. I feel the G42-1450 will be the better choice for my boost and hp level. Thanks for the help though!
https://cimg5.ibsrv.net/gimg/www.rx7...b8fd77ed7.jpeg

Unfortunately, ignoring that ~133 lb/min compressor flow is required to reach 1000 whp with a Wankel engine means the end result is highly unlikely to match up with the earnest expectation of what was anticipated.

Which as was pointed out previously; the G45-1500 compressor is clearly biased towards high Pr operation and I personally wouldn't recommend chasing 1000 whp on a rotary engine way out in the 60% and less compressor efficiency zone with it, even with low emap that would result from an excessively oversized turbine housing. Just can't stress enough that people focus too much on the A/R value, when in fact it's the Pr vs. lb/min flow rate that matters the most. That's what determines which A/R is the proper selection, assuming there's a turbine map (kind of important that there is imo). Further, when the turbine flow curve flat-lines, it indicates that turbine flow has peaked and from there on EMAP is going to be coming on strong ... those are the tools you need to be arming yourself with before starting your build.

Glad to see that you've picked up on this from the earlier discussions, as indicated below:

https://cimg9.ibsrv.net/gimg/www.rx7...92d8c47b72.png

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For your setup, I'd look into a Gen 1 GTX5008R if you can get your hands on one. Or GTX5518R if you need more power.

https://limitengineering.com/GTX5008R.html

The G42 series is so-so. The G45 is just bad.... completely mismatched wheels. G55 series is okay if you pick the right one. They really need a G50, probably in development.

As I said earlier in discussion a G47/G50 would’ve been a good choice but neither will come out anytime soon (I think)

Your formula is wrong

The G45-1500 easily makes 1000RWHP on a 20B

we also made 800RWHP on less than 2 bar of boost on a G45 on a 13B and that was through a torque convertor.

I have real world results, you guys giving advice based of what you might "think" should really go back to the drawing board. Some horrible advice in here.

Mismatched wheels?

G45 spools faster than a G42 and has 1:1 emap at 2.5 bar boost compared to 2:1 emap on a G42
all on a 13B

All the testing I did was BACK TO BACK on the same car with in the same week.

What set up did you use to get 1000 rwhp? eg: boost, lb/min, intake manifold, porting etc etc.