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However, when you look at the combined turbine flow of two 0.49AR G25 turbos, it starts 19 lb/min @ 1.3 PR, which is well below where the G35 0.83 and 1.01 AR turbine flow curves start, and from there it jumps up to just above the 0.83 AR flow curve until 2.0 Pr, where it then moves up to the 1.01 AR flow curve until 3.0 PR (32 lb/min) and then flat lines. So on paper it looks peppier than a G35 0.83 low-mid, but then extends out to the G35 1.01 on the top end. Except those housings only come in an open V-band inlet configuration and this is like a divided configuration. The divided T4 housing is only in a 1.06 AR. Looks tasty
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While there isn't a ton of information Garret really gives out on these turbos, they make drop in turbo upgrades for F150 Ecoboost engines that kinda sound like what you're wanting to do. Packaging may be a concern with their odd housings, but they are pretty small all things considered. I don't think they'd be good for a huge power goal though or would be the best match for a rotary.
they’re pretty small and only about 1/2 the flow; 27 lb/min peak. Looks more like a derivative of the smaller GBC turbos they recently released. They’re not very efficient.
It’s an interesting idea, but not really pursuing it. I only need maybe mid-60 lb/min max, but more importantly strong lowend response. Looking pretty hard at a G30-770 T4.
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old timers may remember (2003-2007) my twin TO4E 44 Trim setup that i ran for over 10,000 miles. when i ditched the stock turbos i wanted 80 pounds per minute but didn't want to do the GT42 as it was so large. a TO4E 44 Trim can do 40/42 so just bolt on two of them. i went through 5 iterations as to hotsides. made 500 at 20 psi but it was somewhat laggy. ATP came out w a really nice flowing backside. i used 2 3 inch downpipes merged with a Burns Stainless collector. two compressor outputs into the IC. there is a thread on it somewhere.
Last edited by Howard Coleman; Jan 2, 2022 at 06:44 AM.
but given the technology then and an eventual 0.60 A/R per turbo that would be expected.
the technology today with improved flow range, spool, and efficiency is what intrigued me to revisit it again.
doubling up the G25-550 compressor map and highlight the 70%+ efficiency range, at least for now it's likely not possible to get the same low response and efficiency on a single turbo system. Especially in the 2.25 - 3.0 Pr range.
Conversely, I think turbine efficiency will be significantly better on a mid/large frame turbo in the top end. You might still win on response but probably find even with slightly higher compressor efficiency for the same MAP the single wins out in the top end? For the cost and plumbing complexity vs boost threshold benefit I still find a ~900cc twin screw supercharger at a nominal 25-30% above engine displacement flow compounded more appealing for torque band. I accept it will be slightly more expensive but the bottom end torque will be miles ahead on any single (regardless of parallel twins or not) compression/turbine stage system than can do 90 pounds flow.
no, not on a rotary (edit: wrt a supercharger, the worst possible choice for 13B forced induction imo), but feel free to show an example to back up such a claim
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I would love to see someone do a two turbo setup. Maybe something similar than what was oem but with a bigger first turbo and a bit larger second turbo. I would personally also like to see someone adding a small electrical turbo to help boost a medium size turbo. I have a 6262 PTE divided and get full boost at about 3600rpm but would love to start full boost at 2000 rpm.
I’m not seeing any results on that anywhere, but I was speaking of SC in general because it’s generally lacking enough flow range to be useful through a wide rpm range on a rotary. Which in the case putting one in series with an older style turbo, suiting the SC to work down low and the turbo to kick in at higher rpm was potentially a suitable product of an earlier time. Now having that dragging down the power output doesn’t make it a suitable compared to other choices.
Even you were going twin EFR at one point (?, not sure if still ongoing). Which my hats off to you because that’s an even tighter fit than two G25s. The point being, twin modern turbos that can perform down low and up high are now a potential choice of the current time. Such that staging them sequentially is not even going to be necessary imo.
I did just order one of the Mac’s Pivot engine lifts after seeing it in your thread; greatly appreciate you sharing that. With the engine being set further back in the RX8 chassis, that should be the perfect solution I was looking for.
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Yeah. I love the pivot so far. You might have to play with where you mount it on the engine. Once I got the DCT attached, it didn't pivot as much as I had wanted due to the balance.
I still have the twin EFRs, in a box haha. I have no idea if it will work, but something fun to play around with once I get some time. Trying to get the 3 rotor driving first.
I know this is mostly irrelevant to the topic, but It is an RX7 and twin turbos. It's on a stock alum. 5.3LS with a BMW DCT gearbox and twin EFR 6758s that I got from an Indycars team after IRL switched to 7163s. If I tip-in at say 5000rpm, it'll go from high vacuum to 180kpa in .25s. It also makes 600wtq by 3500rpm and carries over 550wtq past 7000. I know not everyone's cup of tea, but EFRs are the ****.
but compare the 6758 comp map to the Garrett G25-550 comp map and you may want to consider swapping them out; note the efficiency differences (~6% peak)
the smallest 6758 turbine housing is 0.68, so net effective is 1.36 for the twins, biasing them heavily for top end, at least on a 13B
so the 0.49 V-band housing that Pulsar makes for the G25 (0.98 A/R net on twins) and the combined turbine flow output makes them much more viable on a 13B imo per the modified turbine map I posted up earlier in the thread
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but compare the 6758 comp map to the Garrett G25-550 comp map and you may want to consider swapping them out; note the efficiency differences (~6% peak)
the smallest 6758 turbine housing is 0.68, so net effective is 1.36 for the twins, biasing them heavily for top end, at least on a 13B
so the 0.49 V-band housing that Pulsar makes for the G25 (0.98 A/R net on twins) and the combined turbine flow output makes them much more viable on a 13B imo per the modified turbine map I posted up earlier in the thread
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I agree, the new G Series compressor and turbines way outflow the EFRs size-for-size. EFRs are now 10 year old tech, but they're also genuine motorsports quality with nicer castings, plus optional aluminum CHRAs. My Indy 6758s weigh 11lbs each! It's also hard for people to quantify the benefits of the TiAl turbines. The transient is really a seat of the pants thing that you have to see to believe. I'll take a couple more psi of EMAP to drive the compressors if that means I have better transient and boost threshold.
Those Pulsar clones do look cool, but I haven't seen anyone do a real side-by-side with genuine Garretts. I really wonder how closely they were able to copy the wheel aero? I'd definitely consider some Pulsar G30-770s if I had an itch for more power, but not much need at the moment.
The Pulsar housing is interchangeable with Garrett and Garrett only offers the 0.49 in a T25 inlet vs the Pulsar V-band option allows an easy 2” pipe connection between each 13B exhaust port and turbo. In general I’d only consider the Pulsar turbos for proof of concept due to the low entry cost. I know the quality isn’t the same level, but buying two Garretts without being sure if it will pan out well is a bit of financial risk. In either case I guess you can sell them off on ebay to get some of your money back though.
not sure I’d be too concerned about a pair of iron CHRAs with 600 lb-ft in an RX7 😂 must really be a blast with the DCT trans though 🤯
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The Pulsar housing is interchangeable with Garrett and Garrett only offers the 0.49 in a T25 inlet vs the Pulsar V-band option allows an easy 2” pipe connection between each 13B exhaust port and turbo. In general I’d only consider the Pulsar turbos for proof of concept due to the low entry cost. I know the quality isn’t the same level, but buying two Garretts without being sure if it will pan out well is a bit of financial risk. In either case I guess you can sell them off on ebay to get some of your money back though.
not sure I’d be too concerned about a pair of iron CHRAs with 600 lb-ft in a FD 😂 must really be a blast with the DCT trans though 🤯
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I didn't realize that Pulsar had so many options for housings. It'd be fun to have both in hand and do some measuring.
BTW, I'm still an FC peasant. I couldn't afford an FD roller when I started building my car lol. The DCT is super fun, though. https://imgur.com/lklpdSF
There are plenty of shops with solid reputations who use otherwise expensive components in builds using Pulsar as default, offer clients the option of Garrett but happily posting up the Pulsars on example builds. I wouldn't be surprised if Pulsar is making some of the Garrett product?
That v8 would be awesome to drive. Pretty tight package.
yeah, possibly more direct/shorter still in an RX8 chassis.
still say two G25-550 turbos with 0.49 V-band housings has real potential, more than is being recognized perhaps per the combined turbine flow curve projected onto a Garrett G35-1050 turbine map I posted earlier in the thread (post# 26). Essentially starts off equivalent to a 0.70 A/R G35 turbine housing initially but then transitions to the equivalent 1.02 A/R G35 turbine housing at peak flow. In other words, it functions exactly like a single turbo with divided housing, doesn’t need to be sequential for low end response, and with a combined peak flow of 32 lb/min ought to sustain low-mid 600 whp on a 13B.
unfortunately it doesn’t fit into my current plans or I would look further into it for actual fitment and such.
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doubling up the G25-550 compressor map and highlight the 70%+ efficiency range, at least for now it's likely not possible to get the same low response and efficiency on a single turbo system. Especially in the 2.25 - 3.0 Pr range.
I couldn’t find where they specifically stated the turbo sizing, but referenced a -1450 G model as the single turbo alternative they were considering. So am thinking it must be a pair of G30s?
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