maximum boost on stock motor/91 pump gas?

[kuvasz]

There has been many threads about running boost with head shims, head gaskets and lc pistons.
What I wanted to know is what is the maximum boost you can run on 91 octane can you run a stock apex engine at sea level?

Has anyone tried mixing diesel/gas at higher boost levels? If so what % did you mix them?

 

[Riceburner]

MPI told me 7.5 on a 2011 and newer. 1/1 pulley ratio.
We have run 6.5 on an 06 Apex with MPI SC & no issues.
I'm pretty sure Mr. Sled tried 8 psi and blew up a pre 2011 . His post would be on here somewhere.

 

[kuvasz]

thx riceburner,

i'll keep it safe and go with 6lbs.

 

[kinger]

Yes no more than 6psi on stock engine. A $70 shim is a great way to pump up to 10-11 psi and more margin for error on the fuel.

 

[sledheadgeorge]

Yes no more than 6psi on stock engine. A $70 shim is a great way to pump up to 10-11 psi and more margin for error on the fuel.

X2. I have 27,000 km on stock motor with head shim at 10 lbs boost. No issues with motor. Current leak down test shows 2.5 psi leak at worst cylinder.

 

[kingtut]

This makes me wonder if there is a head shim or not on my apex. I run 93 octane at 10 or 11 psi. Was told stock engine, not stock pumps.

 

[sledheadgeorge]

This makes me wonder if there is a head shim or not on my apex. I run 93 octane at 10 or 11 psi. Was told stock engine, not stock pumps.

Check your compression ratio. That will tell you if there is head shim.

 

[kinger]

Stock would never survive at 10-11 unless your way up in altitude on a stock motor or running gas that is higher than 93 like say 95-98 octane.

 

[sledheadgeorge]

Stock would never survive at 10-11 unless your way up in altitude on a stock motor or running gas that is higher than 93 like say 95-98 octane.

Well then I really don't know what to say. I have stock motor with head shim and have had no engine problems what so ever running 91 octane at about 1400 m elevation for the past 14 years on that Warrior.

 

[Riceburner]

Well then I really don't know what to say. I have stock motor with head shim and have had no engine problems what so ever running 91 octane at about 1400 m elevation for the past 14 years on that Warrior.

He meant totally stock, no shim.

 

[sledheadgeorge]

He meant totally stock, no shim.

LOL. I guess then it all boils down to the age old question. What do you consider stock?

 

[kinger]

Stock is stock headgasket to! LOL Shock motor with shim is just that. So a stock motor 6psi. Stock with a shim 10-11 forever. They are robust engines for sure!

 

[ghost rider]

I run 7 psi 94octane....no ethanol added -pump high test. In Canada our 91 (med grade) has up to 10% ethanol and I'm not a fan of that fuel due to water issues.
It has been this way since 2009 with no issues.
114 octane when dialled to 14 psi (running 660ft drags only) stock no shim. Cold air intake helps.

 

[nate007]

You can get away with a little more than 6-7 psi on a stock motor and 91oct if you have a control box with timing retard. If you have a really efficient intercooler to lower intake air temps that helps too.

Sent from my LG-US996 using Tapatalk

 

[kuvasz]

that's to everyone for their input. i'm currently running 7lbs of boost on 94 octane with no problems so far. thx again.