How much boost pressure?????

[cmd951]

I have a 3 cylinder yamaha engine that has a MCxpress rear mount turbo on it and have a few questions on set up of the machine. I have measured the head spacer and it is a good 1/16 of an inch thick. It is tuff to get in beside the engine with a tap measure..... From what I have read this should equate to around 9.5 compression ratio. Is this correct thinking? So at that compression ratio how much boost am I able to run with 91 octane fuel in the sled? The sled is set up with a air/fuel gauge and it reads just into the rich side when pulling 10.5 pounds boost. Does adding boost lean the engine down with the same 91 octane fuel or will it stay on the rich side of the gauge and detonation will be my concern? The sled does not have a boost controller on it that I can see. The hose from the turbine goes directly to the wastegate plunger. I plan on installing a manual boost controller so I can turn it up and down by simply twisting a controller rather then adjusting the connecting rod between the waste gate and plunger.
If somebody could answer me these question it would be greatly appreciated as I am still learnigng the trips to this sled. Also, I ride 95% of the time at around 1600 feet. Can I turn the boost up if I ride 8000 feet and still use the same 91 octane fuel? I believe the cam timing is stock as well. My goal is to run around 13-14lbs boost at 1600 feet on 91 octane fuel and then turn the boost controller down to 10lbs if I can only access 87 octane fuel out in the country.

Thanks for any input;

 

[cmd951]

ttt

 

[Boyko]

So ya got boost, welcome aboard, I have a vector with a different kit on it, a few dudes are running the same kit as you and thay can probbaly be more help than me thay have been at it longer and are pretty sharp and pumped a lot of fuel througt them. I am asumming your head spacer is 2mm, now depending if the installer split the stock gasket or used 2 of them your looking at 9 to 1 or 8.5 to 1 cr with 2 gaskets. I run around 14 to 16# of boost at 3200, feet, 8.5cr on 100LL fuel, if I go to the hills at 8000 feet I will have to adjust my boost controller to get the boost back up, somewere on the hiway going there I loose a few pounds of boost, no need to mess with clutching or jets just a twist of the knob. At 13# on 92 pump you should be safe running 11.5 on the air fuel meter at WOT. Oh ya I'm not a big fan of 92 premium you should look into getting soom good gas.

 

[Ted Jannetty]

I have a 3 cylinder yamaha engine that has a MCxpress rear mount turbo on it and have a few questions on set up of the machine. I have measured the head spacer and it is a good 1/16 of an inch thick. It is tuff to get in beside the engine with a tap measure..... From what I have read this should equate to around 9.5 compression ratio. Is this correct thinking? So at that compression ratio how much boost am I able to run with 91 octane fuel in the sled? The sled is set up with a air/fuel gauge and it reads just into the rich side when pulling 10.5 pounds boost. Does adding boost lean the engine down with the same 91 octane fuel or will it stay on the rich side of the gauge and detonation will be my concern? The sled does not have a boost controller on it that I can see. The hose from the turbine goes directly to the wastegate plunger. I plan on installing a manual boost controller so I can turn it up and down by simply twisting a controller rather then adjusting the connecting rod between the waste gate and plunger.
If somebody could answer me these question it would be greatly appreciated as I am still learnigng the trips to this sled. Also, I ride 95% of the time at around 1600 feet. Can I turn the boost up if I ride 8000 feet and still use the same 91 octane fuel? I believe the cam timing is stock as well. My goal is to run around 13-14lbs boost at 1600 feet on 91 octane fuel and then turn the boost controller down to 10lbs if I can only access 87 octane fuel out in the country.

Thanks for any input;

The way the kit comes from MCXpress it the max amount of boost you could or should run on 91 octane fuel, if you turn up the boost you MUST switch to higher octane fuel, a rule of thumb is 1 octane for 1 lb. boost.

A manual boost controller is a piece of crap at best if you have an accurate gauge you will see what I am talking about, they are inconsistant and cause boost spikes.

Also you should know that you will not be able to turn the boost lower than the wastgate is set to with any boost controller.

The Wastgate determines minimum boost pressure at WOT.

Your Dancing on the land mines with pump fuel.

 

[cmd951]

I understand that the minimum boost is what you have the wastegate set at. But with the head spacer I should be plenty safe at 9 to 1, 13lbs boost and 91 octane fuel. By the a/f gauge it is plenty rich at 10.5 boost. Can I not keep turning up the boost until the a/f gauge starts backing off into the middle of Stoich?
Also, no I do not know how these MC kits come set from new as it is a used sled.

 

[Anonymous]

Head spacer = Not a good idea.... I know that!

 

[BigDog05]

cmd951: Detonation is independent of A/F ratio.

You will lower your A/F ratio by increasing boost, however it has nothing to do with your octane.

 

[BigDog05]

cmd951: check out this page

http://www.ty4stroke.com/viewtopic.php? ... ht=#315467