Does anyone make a kit that isn't over turbo'd for 91 octane?
 

I've been looking at various turbo kits; I want something that will fit well for a daily driver running 91 octane. My power goals, compared to many, are pretty modest. 250-300whp would be my goal. Under 250 I'm questioning if the cost is worth it. Over 300 I don't want to deal with the risks and extras required to run this engine and driveline at that power level. Every kit I look at advertises that the turbo is good for 400 hp, or 440 hp, or even over 500hp. This isn't a feature. It's just a waste of money and it provides a slower reacting turbo that doesn't build power until later in the rpm band than I'd prefer for what I'm doing with it.

I'm honestly considering having a kit built based on an IS20 GTI turbo - though I'm not sure if that's possible - as it seems to be a much better fit for a daily driver with realistic power goals for 91 octane, tuned to run at about 275whp which it should be fine with.

Of course I've looked at superchargers as well. The Jackson racing kit seems to develop its power a little too late in the rpm range. The Edelbrock kit has some serious issues with the map sensor. The harrop kit is close, very close. It just needs a smaller pulley. But in the end, with any SC kit, I'd be giving up precious power to driving the supercharger and I'd rather put that into the tires.

The AVO turbo kit seems to be closest, but dear God, can we get a kit designed around a turbo from this century? Even then it's still more turbo than this engine needs or will ever reliably use on 91 octane.

So, back to the original question. Are there any kits that come with a turbo that isn't selected for the MORE POWER crowd?

A turbo has a range. Your tuner can adjust and adapt for that range.
With that said, if you want a turbo car that uses 91 octane that doesn't make good power, many automakers are ready for your trade in

Such a generalized statement that’s blatantly untrue in light of tuning ranges, turbo choices, and overall build. Agree with @ contact a tuner first and go from there before you rule anything out, even the sc kits. Or just trade it in.


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Torque is what breaks things and having power later on and not having a ton of torque hit down low will actually be beneficial for longevity. A larger turbo is not necessarily an issue and may be a blessing as spooling slower will generate less torque down low. A good tuner can use a ton of tricks with timing etc. to get faster spool.

Anyway I'm fairly certain a gtx28XX will spool up fine on this engine. When I had a speed 6 on a gt3071 I was hitting 20+ lbs at like 3200rpm.

What is untrue about using a turbo at the very bottom of its useful range being a waste? I'd much rather size the turbo to be in the middle of its range at the power potential for this engine and fuel that's available to me.

Which kit and what kind of fuel?

What’s untrue is that the kits in question can be tuned to bring boost on earlier or later. You generalized turbo kits, without citing a specific example and lump all kits into a category of high boost high hp high spool time, when time and times again people on this forum have documented different results. See comments from @ as testament to my statements. A gtx28xx spools just fine for both 400+hp applications and <300hp applications. Your statement over generalized without taking into consideration how turbos on this platform behave.


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I don’t know of a kit that is designed with a turbo that has no overhead, but if you call the manufacturer then they could probably source a smaller turbo. You may see torque drop off at higher rpms and run higher IATs, but for a daily driver with modest goals, you probably will be fine. Like others said, torque down low leads to preignition and/or rod snapping more than up high, so you will be limited, even if you want more torque fill down low.

Maybe brush up on how turbos are rated and tuned a bit?

I didn't mean no overhead, I meant a turbo that is in the middle of its usable range at the power potential of this engine and the fuel I have available. Turbos that are good for 275-440 hp, or what ever, being used for 275 hp seems like a waste.

You could ask JDL to give you something like a Garrett 2560r with their kit. It's tiny and is typically run on Miatas.

I still don't understand why you're so obsessed with running a turbo outside of its efficiency range; you're not going to benefit by running a tiny turbo at 20psi vs a slightly larger one at 10. You're only to get crazy IATs. Almost every available turbo kit uses an appropriately sized turbo that makes between 240 and 300whp depending on your tune and goals.

JDL offers their kit with the GTX2860R Gen II turbo. Full-Race offers the EFR 6258 with theirs. I think those are the smallest turbos available in a kit for these cars.


Edit: I just scanned the Garret site, and it looks like that is the smallest GTX turbo they make. What turbo do you have in mind that is even smaller?

The mazdaspeed 6 was an atp gt3071 and e85.

I tried looking in the FI dyno thread to see spool characteristics of diff turbos, it's unfortunate most dynos in there do not show it.

If you get a small turbo like that on a WRX then you will be able to get more low end horsepower/torque at the expense of top end horsepower/torque, but adding more torque down low may not be possible with high compression. I get that you want to broaden the torque curve, but 91 limits more of your low end than top end.