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The turbo on the CTR, K20C1 engine, is a MHI TD04, optimized for higher RPMs, so better at redline performance, whereas the smaller turbo on the K20C4/C6s (RDX, Accord, TLX), IHI RHF5, provides better performance on the low to mid range. This is more optimum for fuel economy, more useable boost, as most folks aren't redlining their engines.

K20C1 Turbo (18900-5BF-A01)


K20C4/C6 Turbo (18905-6B2-A00)


However, if your going the tuning route, bolt on mods, and moderate-high map, turbo upgrade is a good idea, as you'll end up in diminishing returns at redline, as the IHI RHF5 turbo will spin faster with mods, pushing more superheated compressed air that negatives the boost pressure and also diminish bearing durability. Note though, known life timed stock parts when tuning are CVT and connecting rods, going over 400 HP results greater potential for bent connecting rods.
 

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2021 Acura TLX A-Spec SH-AWD
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Discussion Starter · #8 ·
The turbo on the CTR, K20C1 engine, is a MHI TD04, optimized for higher RPMs, so better at redline performance, whereas the smaller turbo on the K20C4/C6s (RDX, Accord, TLX), IHI RHF5, provides better performance on the low to mid range. This is more optimum for fuel economy, more useable boost, as most folks aren't redlining their engines.

K20C1 Turbo (18900-5BF-A01)

View attachment 27021
K20C4/C6 Turbo (18905-6B2-A00)


However, if your going the tuning route, bolt on mods, and moderate-high map, turbo upgrade is a good idea, as you'll end up in diminishing returns at redline, as the IHI RHF5 turbo will spin faster with mods, pushing more superheated compressed air that negatives the boost pressure and also diminish bearing durability. Note though, known life timed stock parts when tuning are CVT and connecting rods, going over 400 HP results greater potential for bent connecting rods.
Thank you for the info! I was wanting to do it with a cold air intake once one comes out and a downpipe.
 

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However, if your going the tuning route, bolt on mods, and moderate-high map, turbo upgrade is a good idea, as you'll end up in diminishing returns at redline, as the IHI RHF5 turbo will spin faster with mods, pushing more superheated compressed air that negatives the boost pressure and also diminish bearing durability. Note though, known life timed stock parts when tuning are CVT and connecting rods, going over 400 HP results greater potential for bent connecting rods.
What Acura let alone TLX has a CVT??
 

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What Acura let alone TLX has a CVT??
Apologize for the confusion, was referring to known stock Honda life limited parts in general with respect to tuner community on 4 cylinder engines, flash back coming from good old days between the 1.5L and 2.0Ls engines. Honda has had a number of cars with CVTs but on their smaller engines. I imagine some ILXs had them too, many there were simply rebadged Civics. Yup, just confirmed with a quick search, and sure enough back in 2013 ILX:



Comparing it to a more recent Civic CVT, 2021 for comparison.


Slight discursus, not to go too far off topic, hope moderators don't mind. But reminds me that when they debuted the new Integra, which BTW should have been a 2023 ILX in my opinion, rumors where the automatic version would feature a CVT as well. So imagine the Integra AT would be similar in design.

Also, here's also a good teardown video of the Honda's in house 10 speed used in the RDX/TLX, interesting they're moving away from ZFs:
Wheel Tire Automotive tire Motor vehicle Vehicle


And then get back on topic, on 4 cylinder turbos. Someone correct me if I'm mistaken, as I haven't stayed current on the latest and greatest, but to my knowledge the highest output 4 cylinder from factory, to use as a bench mark would be the M139.


Forgot to mention, with Honda corporate deciding to offer Type R crate engines direct this year. So I'm surprised Honda/Acura simply doesn't offer higher output out of the gate. Especially as third parties have demonstrated the engine capable of much more with mods. And other competitors making higher output 4 cylinders from factory like on the M139.


Range of 50-100 HP boost can be achieved with just an ECU remap, using higher octane, and/or fuel injector upgrade on Type R. And on the opposite end of the spectrum the highest output K20C1s I've heard of 800-1000+ HP range. stage 4 level modifications. That touch all the three C's, compression, combustion, conversion upgrades. Compression - intake/filter, intercooler, turbo; Combustion - octane and fuel injectors, valves; and Conversion - in addition to the forged connecting rods mentioned above, upgraded pistons, even custom re-bore and re-cylinder sleeve, install custom bearings, camshafts, ported cylinder heads, and exhaust side - high temp values.

Though the TLX K20C6 is pretty much a C4, guessing due to different engine mounts. I imagine still would be possible to take C4/C6 series to the same level, but comes down to cost.
 
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