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Mcx 270 boost pressures

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seano700

Active member
Dec 10, 2007
234
31
28
Peace River, Ab
I've been doing some testing and tuning the past few days. This is my first mcx kit and I'm a little Leary on boost pressures expected.. The recommended pressures seem pretty high for pump gas, so I want to be sure before adjusting

Sled is a viper with 270 kit
Instructions indicate 15psi @ sea level for 91pump
I live at 1800 ~ 2000 ft, where I'm testing..
Out of the hole it spikes to 17, and quickly bleeds back to 15 or sometimes 16 (digital AEM guage, whole numbers only, no decimals)
I'm guessing the spike is created by the automatic altitude pressure compensating valve.

I did a quick google search and 2000ft is about 95kpaa or 13.7 psia.. Doing the math one would expect 1 psi additional pressure to compensate for my elevation (13.7 ~ 14.7)? Correct?

Does this make sense? Is this safe?

I would have never ran 16psi on pump gas with my PL nytro @ 2000ft.. I ran more like 12 psi, and 15-16 at 5000ft and up. That being said I realize the kits use totally different gear.

Thanks in advance
 

turbo800

Well-known member
Lifetime Membership
Nov 27, 2007
846
205
43
Northern,UT
I have no idea how thick the head shim is included with the kit or how much it lowers the CR, but, I would have to agree that 17 psi boost seems wild for pump fuel. I guess I always assumed the 240 & 270 kits were for race fuel, but NO, right on their webpage "The Arctic Cat 7000/ Yamaha Viper turbos, like all MCXpress kits, are built for use at any elevation, and run on 91 octane pump gas."

I would have to think they are ALSO doing timing adjustments for that kind of power on pump fuel!
 
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MRFUSION

Active member
Aug 8, 2008
162
27
28
50
Peace River AB
Seano we run all the Nytro 270 kits we built at that boost level with no issues to date. MCX really does their homework on these kits. Issues won't be with the turbo but truly getting the true 91 octane that's required. Drop to 14 if you are worried for a bit of a safety margin if you like. 14 PSI will still get your panties all wet Im thinking. Just my opinion. Cheers
 
A

am bush

Member
Jan 15, 2008
134
9
18
mcx

I would never trust if you are getting 91 every time , 100 LL , is regulated a lot closer, and you never have to worry about you octane. Piece of mind!
 
P
Feb 6, 2012
13
5
3
37
What mcx says for boost and octane rating is spot on. The mcx kit has consistently been the best running kits on the market for years. Of course now with boos-it in the picture we now have two major players. But as stated the quality of fuel from your local pump is what u would worry about. Both my apex and nytro have been fuelled by 100 ll just to be save. I know with gas prices these days it might seem like a lot of money for the av gas. But at 330 barrel first time with barrel purchase and then $275 to re fill it after it's very cheap insurance.
 

Tuesday

Well-known member
Premium Member
Nov 26, 2007
1,708
191
63
Lacombe, Alberta
What mcx says for boost and octane rating is spot on. The mcx kit has consistently been the best running kits on the market for years. Of course now with boos-it in the picture we now have two major players. But as stated the quality of fuel from your local pump is what u would worry about. Both my apex and nytro have been fuelled by 100 ll just to be save. I know with gas prices these days it might seem like a lot of money for the av gas. But at 330 barrel first time with barrel purchase and then $275 to re fill it after it's very cheap insurance.

Agree...

14-15lbs in alberta 17-18lb at elevation. 9000km and still pulling strong.
 
C
Mar 2, 2011
19
0
1
Is the Mcx 270 just set at what it is and unable to turn it up or is there a way to increase the boost? Just feel like my viper is on the sluggish side
 

TBird

Well-known member
Premium Member
Jan 16, 2008
673
149
43
North of Sweden
Is the Mcx 270 just set at what it is and unable to turn it up or is there a way to increase the boost? Just feel like my viper is on the sluggish side

It's easy to rise boost by tighten the wg, but do NOT rise it because "it feels sluggish", you have to know how much boost it have.
 
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