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The FC build vid today was probably one of the best yet. Really enjoyed it.
The G40 is efficient at low boost, but gotta believe the big compressor and Mar-M turbine wheels are going to hurt response even in the smallest 0.84 housing with that 35 lb/min peak flow rating. Not the best choice for autox, but then neither are staggered wheels/tires, nothing that can’t be adjusted/changed later though.
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Rob’s channel is one of the very few I have the notifications set to let me know when new ones are uploaded. Fun watching the work on the various cars in the garage now since the 4 rotor are behind the everyday man’s ability to build but the 2 and 3 rotors cars are things people can glean plenty of info and apply it to their build if they want to try thing. Thanks Rob!
I missed that the 1.06 housing is on it, which peaks at 39 lb/min turbine flow
Even for the max power level of the compressor this is way big imo. Kind of not seeing it, along the same line as the turbine housing selection on the Vette project. The twin scroll housing and efficiency can only do so much to offset this.
Even the 0.84 T4 @ 35 lb/min peak is on the high side imo, but would be a better match for sure. Maybe had no choice but to take what was offered, but anticipating that spool is going to suffer compared to the smaller frame sizes.
Isn't anything below .9 usually considered small for a rotary in general? I don't think I've ever seen a recommendation for .8x before. Or am I misunderstanding what you are saying?
an A/R number is only a dimensional relationship of the turbine housing for a given turbo frame size. The number that actually matters is how much flow it can pass before flatlining, at which point emap will increase dramatically
A/R = area / radius around the turbine centerline
two different areas with two different radiuses can have the same A/R value, but their respective peak flow values are going to be entirely different, which is where the turbine map comes into play
so if there is some awareness of what exhaust flow value will be generated for a particular power level of a particular engine, it allows a more optimum approach to an initial turbine housing selection
there are other factors though; efficiency being one example fuel type, desired response level, sustained wot use and so on that may need to be refined for, but again imo 39 lb/min peak turbine flow is pretty high for a 13B, perhaps 750 whp ime and this compressor is maybe just above 3/4 of that before overspeeding occurs.
The G40 Turbine map
Lower 30ish range is likely more appropriate (indicated above to show how far back that is in the G40 turbine flow range) —> G35-900 1.06 div-T4 for top end or G30-770/900 for autox type low end response. The 770 makes more sense for autox because no real need for more than low-mid 60ish lb/min compressor flow for traction purposes (slicks/DOT-R tires, less for harder rubber).
Looking at it from the other direction, I’d estimate the 20B with G42-1450 he made 1000 whp with is around low-mid 50ish lb/min turbine flow. Just under 2/3 of that is low-mid 30ish lb/min for a 600 whp 13B. Garrett did a stupendously awful job of documenting the G42 turbine map (three housings, but only one undefined flow curve, pretty sure it’s the smallest housing though), but in general they tend to overlap going from one frame size to the other. So looking at the G45 turbine maps the lowish 50 lb/min range seems appropriate for the largest 1.28 G42 housing he was using.
Which one notable person here referenced the turbo was way too small for that power level. Apparently it wasn’t, possibly because some of what is explained in this post is not being accounted for. IMO that pretty much sums up the entire Garrett G-series line wrt how people on this forum are maybe not fully appreciating the actual numbers the technology is capable of producing, but are possibly still rooted in the past methodology of sizing references instead.
Latest FC build development is not any surprise, but as you can see in the turbine map below, the 1.06 on this particular turbo is still way oversized for a 13B at the projected max power level potential and not going to offer much improvement over the 1.19. Stepping down to the G35-900 1.06 would be much more appropriate at a minimum per the projected optimum turbine flow line at 32 lb/min though. The G30 1.06 is going to offer the best response, but likely limited to E85 fuel to achieve that safely.
That said, 350 whp is well below what a G30-660 is capable of. Without posting the critical descriptive words though, a lot of other things going on beside the turbo selection.
sad cat needs another beer …
Originally Posted by TeamRX8
an A/R number is only a dimensional relationship of the turbine housing for a given turbo frame size. The number that actually matters is how much flow it can pass before flatlining, at which point emap will increase dramatically
A/R = area / radius around the turbine centerline
two different areas with two different radiuses can have the same A/R value, but their respective peak flow values are going to be entirely different, which is where the turbine map comes into play
so if there is some awareness of what exhaust flow value will be generated for a particular power level of a particular engine, it allows a more optimum approach to an initial turbine housing selection
there are other factors though; efficiency being one example fuel type, desired response level, sustained wot use and so on that may need to be refined for, but again imo 39 lb/min peak turbine flow is pretty high for a 13B, perhaps 750 whp ime and this compressor is maybe just above 3/4 of that before overspeeding occurs.
The G40 Turbine map
Lower 30ish range is likely more appropriate (indicated above to show how far back that is in the G40 turbine flow range) —> G35-900 1.06 div-T4 for top end or G30-770/900 for autox type low end response. The 770 makes more sense for autox because no real need for more than low-mid 60ish lb/min compressor flow for traction purposes (slicks/DOT-R tires, less for harder rubber).
Looking at it from the other direction, I’d estimate the 20B with G42-1450 he made 1000 whp with is around low-mid 50ish lb/min turbine flow. Just under 2/3 of that is low-mid 30ish lb/min for a 600 whp 13B. Garrett did a stupendously awful job of documenting the G42 turbine map (three housings, but only one undefined flow curve, pretty sure it’s the smallest housing though), but in general they tend to overlap going from one frame size to the other. So looking at the G45 turbine maps the lowish 50 lb/min range seems appropriate for the largest 1.28 G42 housing he was using.
Which one notable person here referenced the turbo was way too small for that power level. Apparently it wasn’t, possibly because some of what is explained in this post is not being accounted for. IMO that pretty much sums up the entire Garrett G-series line wrt how people on this forum are maybe not fully appreciating the actual numbers the technology is capable of producing, but are possibly still rooted in the past methodology of sizing references instead.
Although I like the 3 and 4 rotor builds, rotary vette, I enjoy the FC vids the most just cause it reminds me of working on the Tll in the garage back in the day and seeing what works/doesn’t work as well.
Latest FC build development is not any surprise, but as you can see in the turbine map below, the 1.06 on this particular turbo is still way oversized for a 13B at the projected max power level potential and not going to offer much improvement over the 1.19. Stepping down to the G35-900 1.06 would be much more appropriate at a minimum per the projected optimum turbine flow line at 32 lb/min though. The G30 1.06 is going to offer the best response, but likely limited to E85 fuel to achieve that safely.
That said, 350 whp is well below what a G30-660 is capable of. Without posting the critical descriptive words though, a lot of other things going on beside the turbo selection.
sad cat needs another beer …
In the video, Rob calls out all the issues that limit it from making more power that the turbo is capable of and is fine with it because that's how he wants the car for now. He has shown he could easily swap out more parts to reduce intake temps and improve flow and make a lot more power. For example, he specifically talks about his choice to keep stock intercooler with tiny piping restricting flow and also not cooling down the air.
So what is the reason for your post? Did you miss the part in the video where Rob talked about it?
but that it wasn’t recognized from the get go says plenty for those with the discernment to know and as was stated …
but don’t misunderstand my words again, my only intention is to share truth rather than sit in the seat of scorn regarding untruth. Doing my best to convey that, but have my own faults and weaknesses as well, humbly so ... 🙇♂️
I don't think the renesis rebuild was meant to do anything special. That's why it was a budget rebuild.
It's pretty cool to go from not knowing much at all to now see decent machine work, fuel rails, wiring, extreme tolerance dowel pins, jigs for repeatable work, etc.
I wouldn't necessarily trust Rob to work on my car, but I appreciate that he seems to own most of his mistakes and treat them as learning experiences. Even if he's not always the best example of how to do something, I can learn from whatever mistakes or problems he might make with his cars. Most other automotive channels on Youtube have too much pride to admit when things go wrong, and/or weird relationships with their suppliers preventing them from being honest about how well the parts actually work. As an example, the red RX-7 built by the Throtl channel a few years ago blew up an engine on the dyno and tried to sweep it under the rug. I don't think those clowns are bright enough to understand what went wrong in the first place, and they certainly didn't share enough details to help anyone who might encounter the same problem. Conversely Rob's videos show enough details that the people watching have helped notice problems and point them out so he can solve them or at least understand what he did wrong for next time.
I suspect they let that RX8 engine get too hot. They should have done a better job flushing out the cooling system (especially the heater core) after trying the stop-leak goop on the original engine. Hopefully there will be a video discussing the engine teardown in detail. As an aside, I'm not sure I'm ready to accept that RX-8s have 'old car' problems like cracked dashboard plastics. I suppose time flies when you're having fun.
Last edited by scotty305; Apr 24, 2022 at 01:14 PM.
it would be more accurate to say that people with older school rotary engine experience still don’t fully comprehend what makes the Renesis truly unique and different than the prior 13B engines. The intake and exhaust essentially works on a different design principle; i.e. zero port timing overlap. It can’t be treated the same wrt either rebuilding it or modifying it for that very reason.
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So any way, in one of the latest vids they now claim that the FC issue is the stock ports are max’d out despite only making 350 whp and they’re going to port it with the addition of semi-PP housings. This will make more power with a proper flowing intercooler, but still fails to acknowledge they have the wrong turbo for the application. That turbo would be more appropriate for a full-on PP engine, but even then it still needs a tighter A/R turbine housing imo.
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yeah, the previous vid building the new turbo manifold was a pleasant change to watch. I felt like they’re pushing it using T321 16 Ga. tubing considering how large and heavy the turbo is, but we’ll see. Initially it should be fine, but even T321 is going to eventually suffer at anything above 1700°F and the long term stress is potentially an issue. My 18 Ga. Renesis NA manifold had to be retired after a long seasoned life and it didn’t have a turbo hanging on the end of it.
I almost spit out my drink all over myself when it was stated they understand turbine AR sizing well though, maybe a bit too forgetful of other recent Vette and FC vids …
the AWD 4R isn’t really my cup of tea over the 2R/3R cars though, but wish them well with it.
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again admitting to not being a fan on the AWD project, but watching the latest 4-rotor engine/turbo build hit 1350 whp in only 3 dyno runs was both impressive and amazing. Still had to skip through a lot of the played up blah-blah reality tv fluff , but going to give credit where it’s due; great job Rob.
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Not sure why he hit it out of the park on the latest 3 and 4 rotor engines, but dives head first into the rocks far below on the 13B choices though.
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fuel type, desired response level, sustained wot use and so on that may need to be refined for, but again imo 39 lb/min peak turbine flow is pretty high for a 13B, perhaps 750 whp ime and this compressor is maybe just above 3/4 of that before overspeeding occurs.
