Running MR Pro6 in a Vortex mapped for U4.4

RussellSimpson

Had twisted map my vortex ECU for VP U4.4 but gonna try MR Pro-6. Anyone have any suggestions on fuel trim adjustments for the Pro-6 race fuel?

2023 KX450.. Pro-circuit ported and polished head.. with a full pro circuit exhaust system.. a No Toil power flow air filter kit and of course the Vortex ECU mapped for VP U4.4!

I read where the fuel trims should be leaned out slightly cuz the Pro-6 has a lesser oxygen content..and I've also read where they should be richened slightly cuz of the fuel density or (specific gravity) of the 4.4 being more dense than the Pro-6..Really don't wanna damage my awesome race engine..and can't afford $400 for twisted to remap my ECU again..Any suggestions?

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Moto520
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Moto520 7/31/2026 7:57pm
7/31/2026 7:57pm Edited Date/Time 7/31/2026 7:59pm

You know the answer…..run it!  A little lean this way….a little rich the other way….sounds like you are right in the middle.  Run it and report back

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captmoto
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captmoto 8/9/2026 9:10am
8/9/2026 9:10am

How about calling Twisted? My buddy called them with a question about race gas and got a straight answer in about a 5 minute conversation. 

FahQ
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FahQ 8/15/2026 6:42pm
8/15/2026 6:42pm

My concern would be the Mon ratings of those two fuels, and possibly the flame speed. 
The U4.4 tune might have a bit more timing advance than what might be safe for the pro 6

mshea397
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mshea397 8/24/2026 9:22am
8/24/2026 9:22am

Not an exact answer to your question, but my 2 cents.  I have a 2024 KX that is similar to yours.  I have the full Race Tech top end.  The same package as reviewed by Swap and Keefer (piston, full porting with epoxy, seats with 5-angle valve job, vortex, full-FMF exhaust, vortex, etc.).  The mapping is for VP T4+ or Pro6.  I was running T4+ earlier in the season and just got a can of Pro.  It made a huge difference.  Very smooth and linear with a ton of over-rev compared to the T4+. 

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RussellSimpson 8/24/2026 10:28am
8/24/2026 10:28am Edited Date/Time 8/24/2026 10:28am
mshea397 wrote:
Not an exact answer to your question, but my 2 cents.  I have a 2024 KX that is similar to yours.  I have the full Race...

Not an exact answer to your question, but my 2 cents.  I have a 2024 KX that is similar to yours.  I have the full Race Tech top end.  The same package as reviewed by Swap and Keefer (piston, full porting with epoxy, seats with 5-angle valve job, vortex, full-FMF exhaust, vortex, etc.).  The mapping is for VP T4+ or Pro6.  I was running T4+ earlier in the season and just got a can of Pro.  It made a huge difference.  Very smooth and linear with a ton of over-rev compared to the T4+. 

Thanks that's good to know I've heard a lot of people say the pro 6 gives it a nice mid-range top end kick and I went ahead and bit the bullet andjust sent my ECU back to twisted to have them map it straight up for Mr Pro 6 HT so no more guesswork I guess.. thanks for the input

RussellSimpson 8/24/2026 10:29am
8/24/2026 10:29am

Guess I don't like guesswork too much so I went ahead and sent my ECU back to twisted development and had them map it specifically for Mr Pro 6.. Thanks for the replies fellas!

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