E85 / Flex Fuel on the Subaru WRX: One Year of Daily Driving Experience
John shares a year-plus of E85 on his WRX with a Cobb flex-fuel kit, DW300, and a Ron Watson E50 tune: big power vs 91, cheaper fill-ups despite worse MPG, stock clutch holding, and one long-trip hiccup when ethanol ran low.
Full video (11 min): E85 Changed my Car | 1+ Years of Experience · John's YouTube channel
Get the parts
- Android head unit shown / related (Amazon, link from the description)Buy ↗
- Universal 10-inch head unit (Amazon, link from the description)Buy ↗
- Boomba BPV (Amazon, link from the description)Buy ↗
- Invidia Q300 cat-back (Amazon, link from the description)Buy ↗
- Perrin shift stop (Amazon, link from the description)Buy ↗
- ISC coilovers (Amazon, link from the description)Buy ↗
- Find Cobb Flex Fuel WRX kits on eBaySearch on Amazon ↗
- Dasaita head units on eBay (link from the description)Search on Amazon ↗
- Phatbotti Tuning (mention "John Nguyen" for $50 off)Buy ↗
As an Amazon Associate I earn from qualifying purchases. Some links are affiliate links.
John shares a year-plus of E85 on his WRX with a Cobb flex-fuel kit, DW300, and a Ron Watson E50 tune: big power vs 91, cheaper fill-ups despite worse MPG, stock clutch holding, and one long-trip hiccup when ethanol ran low. This 11 min guide covers the Cobb Flex Fuel kit + DW300 fuel pump with tools, parts links and.
Overview
After more than a year on ethanol, John says E85 changed how his WRX feels. With a Cobb flex-fuel kit, DW300 pump and a Ron Watson (Phatbotti) E50 tune, the jump from stage 1 on 91 to stage 2 on ethanol was the first time power felt dramatically better — more addictive than stage 1 alone. He fills with about seven gallons of E85 and watches the Accessport climb from the mid-teens ethanol to around E48–E50 as it mixes. Daily commuting (~20 miles) has been trouble-free on a stock clutch; the one hiccup was a long Sacramento-to-LA trip when ethanol ran low and the car stuttered. MPG is worse, but E85 is often about a dollar cheaper per gallon in California so fill-ups can even out. He likes Ron Watson's approach of keeping low-RPM torque safe and stacking power higher up. Links and the Phatbotti discount from the description are below.
Vehicle & fitment
- Product
- Cobb Flex Fuel kit, DW300 pump, and Phatbotti Ron Watson E50 tune for the WRX
- Shown on
- Subaru WRX (John's daily, third year of ownership from new around 2018 in the description)
- Cobb Flex Fuel kit + DW300 fuel pump (per John's mod list)
- Phatbotti / Ron Watson E50 tune — mention "John Nguyen" for $50 off per the description
- John runs roughly E48–E50 day to day; Accessport reads ethanol content live
- Stock clutch and internals holding under this power level per John
Always confirm fitment for your exact year and trim with the seller before buying.
Tools & parts
Tools
- Accessport (for live ethanol readout)
- Basic hand tools if installing the flex-fuel kit / pump (not shown in detail here)
Parts
- Cobb Flex Fuel kit
- DW300 fuel pump
- Phatbotti Ron Watson E50 tune
- E85 fuel
Step by step
- 1
Mixing a partial E85 fill▶ 0:45
About seven gallons of E85 into a partial tank; the flex sensor and tune handle the blend on the fly.
- 2
Watch ethanol climb▶ 1:20
Accessport starts around E16 after the fill and climbs as it mixes.
- 3
A year-plus later▶ 1:53
Daily use has been great aside from one long trip where ethanol ran low and the car stuttered.
- 4
Stage 2 on ethanol is the jump▶ 3:17
Stage 1 on 91 was nicer; stage 2 on E85 was the first real addicting power bump.
- 5
Stock clutch holding▶ 4:44
Turbo-back, ethanol, Ron Watson tune — still on stock clutch and internals with no drama for John.
- 6
Why Ron Watson▶ 5:00
Keeps low-RPM power safe and stacks torque higher so the setup stays reliable.
- 7
Targeting E50▶ 5:35
Blend climbs toward E48–E50 in a few minutes; he's tuned for E50 and sits around E49.
- 8
Pull comparison feel▶ 7:10
A roll-on from ~3k shows how much stronger ethanol feels in the chest vs 91 stage 2.
- 9
MPG vs price▶ 7:44
Worse MPG, but E85 often ~$1/gal cheaper in CA, so fill-ups can even out despite more stops.
Wiring notes
- Flex-fuel sensor and pump wiring are part of the Cobb kit install (not walked through in this experience video). Follow your tuner's guidance.
Get the parts
- Android head unit shown / related (Amazon, link from the description)Buy ↗
- Universal 10-inch head unit (Amazon, link from the description)Buy ↗
- Boomba BPV (Amazon, link from the description)Buy ↗
- Invidia Q300 cat-back (Amazon, link from the description)Buy ↗
- Perrin shift stop (Amazon, link from the description)Buy ↗
- ISC coilovers (Amazon, link from the description)Buy ↗
- Find Cobb Flex Fuel WRX kits on eBaySearch on Amazon ↗
- Dasaita head units on eBay (link from the description)Search on Amazon ↗
- Phatbotti Tuning (mention "John Nguyen" for $50 off)Buy ↗
As an Amazon Associate I earn from qualifying purchases. Some links are affiliate links.
FAQ
What vehicle does this install fit?
It is shown for the Cobb Flex Fuel kit + DW300 fuel pump. Phatbotti / Ron Watson E50 tune — mention "John Nguyen" for $50 off per the description Always confirm your exact year, trim and factory audio with the seller.
How long does the install take?
John's full video is 11 min. Plan on that much time for a careful DIY install, plus extra if you are new to dash work.
What tools do I need?
Tools called out in the guide: Accessport (for live ethanol readout); Basic hand tools if installing the flex-fuel kit / pump (not shown in detail here).
Where do I get the parts?
Use the buy links on this page for the unit and any harnesses John used. Some links are affiliate links.
Is this beginner-friendly?
The guide breaks the job into 9 steps with timestamps into the video. If you can remove trim panels carefully, you can follow along.
John's Subaru WRX
More photos →Photos from @ngooyen on Instagram. Follow for more.
Full transcript
Show the full transcript (70 lines) +
0:00second here oh, oh
0:45I, now I was like around a 20, and I was like half way, because it filled up the
0:50Car all the way, about seven gallons of
0:54so and
0:56Definitely what I like to do that I do have a flex
0:59sensor so
1:01there just is oll that stuff on the fly your your tuner will definitely take care of that too, but um
1:20juice so right now it says, I'm at e16
1:53And my experience with a five has been great
1:57for the most. There was one time where the
2:00the
2:01Car when the car when I was driving to LA. I was about a 400 something 400 whatever Sacramento LA
2:10My, 85 was kind ofmit a low and, and there was very little a little gas.
2:13And it started to stutter a little bit I
2:45Kind of addicting to have it, because if I don't have 85
2:49Let's just say
3:1785 and maybe not do the whole stage two thing because it was like
3:22The first time I really, notice a bump in power performance
3:26Like the performance was like so much better. So like going stage zero or stock to the stage one
3:32Yeah, I noticed it the shifting was a little bit cleaner and like the power is a little bit better-
3:36I go on a stage two and then
3:47And it was like, what I wanted. So definitely if you guys were looking for more power
3:56You have to get the ethanol, it's the go-to
4:00So right now like my WRX my aXS port is still saying that I'm still running at e16, so I'm still keeping it kind of chill right now.
4:10So yeah, ethanol
4:26Besides that one time I had to hold like a year and a half I had this for in about a year and four-months
4:30There was only one hick up up and it's because I had a really long
4:33Road trip and I was a little bit low the daily commute and stuff like that which I drive about 20 miles every day no issues. It's great
4:44Stock clutch
4:45Has been great, it's been holding up
4:47For for those who are curious about what my my mods are I'm basically turbo backed
4:55With ethanol
4:57andi tuned with
5:00What's his name, name Ron Watson so the link is description below Ron Watson is
5:04Probably the one
5:06The best tuners and the thing is when you're running E85 you definitely want to have a really good
5:10In order because you get a lot of power but you put too much power
5:14Down low
5:15I'm low
5:16Rpms you might better run
5:19He definitely pushes. He pushes the power up to close to the top and keeps the, and keeps it a very reliable and safe because like I said
5:25I've running stock internals and everything
5:28The clutch and stuff like that and the power it's still, it's still there. My ethanol has it has rise to
5:35From E17 E 16 to now it's climbing to what E46 so now I'm actually
5:43Having about it took about like see it took about five minutes for it to have that mixture
5:59so my E48 right now I'm tuned for E50 you can go E60 E there's like that but from what my tuner there said the the performance is like not that much much and it's you run into that friction issue
6:12for the 4
6:17E48 which is probably you know is my estimate I was trying to get that kind of like E
6:2349 E50 and it might climb up a little bit in my but it's stabilizing around if you
6:28basically E50 and right now it's 40 e 49.2 which is great
6:35But yeah, yeah, um I could do a poll I havees I have a Q 300 and and it sounds great I
6:45Have the boom but bypass with the Cobb SF intake, so nice makes a nice wishing sound. I
6:53Just the Senate just like six set up so very very nice setup here going on
7:03See what these
7:10So we'll do a Pult or a second your pull real quick
7:13About 3,000 rpm on my role into a throttle and accelerate and up to
7:26Can you like can you feel the difference
7:34Feeling your chest regular stage 2
7:3791 if you go ethanol
7:41There's a like you're just gonna you're gonna like just want it
7:44and you just always want to fill up with a hole and for my experience you do get less mpg
7:49but it kind of makes up for it because
7:5385 it 85. E85 is a lot cheaper so
7:56gas around California second month this time it was about three dollars and fifty cents
8:00I just filled it up cost two $2 and fifty cents so so
8:04So it's usually a dollar cheaper so yeah, you're be going to the fuel station
8:09more
8:42So I hope you guys enjoy that video about what ethanol is and a
9:21We're here to learn
Machine-transcribed from the full-length video and lightly cleaned (product names fixed). Watch the video for exact wording.
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