Whats the highest boost with apex and stock compression?

[ken_climb]

....with premium pump fuel. It would be so nice to have stock compression in the mountains, for the quick blurps a guy needs to do every so often. I know 7 is safe, but anyone run higher? Do you think you could run 10? Then with striaght 100ll av gas maybe 12-14?

 

[ripntear]

Ken i know Mike was running stock compression with c-16 and 19lbs of boost, heavier valve spring though.

 

[Darko]

Haha, if you think thats all thats done to his motor i got some ocean front property in Saskatchewan to sell you.

 

[summitking]

sled

Ken i was talking to Myles and he said the apex with the low comp pistons and one extra stock gasket made the mcx sled way snappier off the line. Im going to be doing that this summer and next week im going to have all the exaust ceramic coated to make it a bit faster.

 

[KnappAttack]

summitking, less compression will not make a engine snappier. It would be less snappy. ken climb, make sure you re-torque the stock head gasket at a minimum. 7.5 lbs is fine at sea level and obviously you can add boost as you go up in altitude, however it seems the mountain guys stay in the throttle for longer periods of time, I would stay at that boost level. 10 and the motor would be toast in about 4 miles with pump fuel. 12 lbs is right there with 100ll. They run soo sweet with a stock engine setup. You just can't beat the stock Yamaha pistons and rings for ring seal. Mike Knapp#17

 

[ken_climb]

So Mike, you think about 12lbs with 100ll av at sea level or up at elevaton?

 

[ken_climb]

summitking, less compression will not make a engine snappier. It would be less snappy.

I think Summit king was comparing a thick head shim to low comp 10:1 pistons.

 

[summitking]

sled

Yes that is what i was comparing it to. Hey ken If you want to get out riding with the synergy turbo let me know.

 

[KnappAttack]

Ken, boost calc. says 13 lbs. 100 octane. Stock comp. That is at 1000 ft. Mike

 

[ken_climb]

So at elevation say 5,000' where the barametric pressure is a couple pounds less then at sea level, a guy should be safe to run 14lbs of boost with 100ll?......That would be fun with stock compression!

 

[ken_climb]

So say that mcx hp claims are correct ( 12lbs boost = 260hp@ sea level) This is with they're head shim that drops the compression down to, what is it, 9:1 or something? How much more H/P would you have with stock compression and 12lb's boost and good fuel at sea level? A guy must lose alot of (stock) power dropping is compression like that.

 

[KnappAttack]

Yep, 5000 ft says 14 lbs with 100ll. 270 HP. with that combo. Boost Calc. is very neat at top in the sticky in case you haven't seen that. They respond much more with stock motor. Your HP may vary in regards to exhaust and tuning also. I think you'll like it. Make sure though you torque head gasket down. 38 lbs is what they talk with stock studs and nuts. Mike

 

[ken_climb]

Thanks, Yah I can't get that boost calculator on my computer. Do I have to download microsft excell? Mike how much hp does the calculator say with 9:1 compression (like with a head shim) and 14lbs of boost?

 

[KnappAttack]

Ken, yes you need excel. It says. 90.7 octane at 5000 ft and 261 HP with .060 head shim @ 9.41 comp. ratio and 14 lbs. boost. The mid range and off boost power is not there as you start taking away comp. Don't let the peak on boost #'s fool you. They feel better with more compression! Its all about give and take. Mike

 

[BigDog05]

Mike: Can you tell me what number I have wrong in the boost calculator?

I'm using 138 base HP
10.3 Base Dynamic comp ratio
88 base octane
1000 ft altitude
13 lbs boost
10.3 new compression ratio
but I come out with 101.9 octane needed.
Stock 05 RX1 Thanks John