having weird engine problems please help

[Jdizzle659]

so i put 100 octane gas in for one tank just for fun since i've done it before on other cars running at the track so i didn't see the harm. I was doing a 40-100 pull to compare times and was unable to reach 100mph in 4th gear... I am very confused because around 97mph in 4th gear i was hitting the rev limiter and boost of course dropped completely off. Now i've done 40-100 pulls before and i can hit at least 105 in 4th. If anyone has any clue as to why this could happen please fill me in. I have a 2007 mazdaspeed 3 with intake, downpipe, racepipe, and cat-back.

[Speed3Rookie]

You have a dashhawk? If so log your run. If it's below 50 in Texas you are probably experiencing boost or fuel cut.

[AutoEuphoria]

Change your tires/wheels lately? Could throw off your speedometer.

Were you doing the entire run in 4th?

[Jdizzle659]

I started in 2nd. Thank you for the response. My tires are pretty old.

[Jdizzle659]

I don't have a dashhawk, and last night did drop down to low 30's for the first time since last winter. If it is one of those two do you think it would do this all winter long? and thank you for responding.

[Speed3Rookie]

I don't have a dashhawk, and last night did drop down to low 30's for the first time since last winter. If it is one of those two do you think it would do this all winter long? and thank you for responding.

Very possible...

[AutoEuphoria]

Are your tires properly inflated? Rolling resistance could rob you a few MPH, as could wind resistance if it's windy.

[Jdizzle659]

You have a dashhawk? If so log your run. If it's below 50 in Texas you are probably experiencing boost or fuel cut.

would the boost or fuel cut feel the same as throttle cut when it overboost?

[AutoEuphoria]

Boost cut feels like you slammed on the brakes for a half second.

Honestly, though...I hope you have at least a boost gauge if you're tinkering with the car. You need to know how much boost you're actually running...it will help you avoid boost cut and help save your motor.

[Jdizzle659]

Boost cut feels like you slammed on the brakes for a half second.

Honestly, though...I hope you have at least a boost gauge if you're tinkering with the car. You need to know how much boost you're actually running...it will help you avoid boost cut and help save your motor.

I have a boost gauge... I'm running stock boost at 15.6 also. Like 2 months ago I had a manual boost controller on it for less then 10minutes and it was overboosting in 4th, 5th, and 6th gears, so i took it off. I was asking because i know what overboosting feels like and that is not what i was experiencing last night.

[chrisp]

your wasting your time putting in higher octane fuel. Unless your car is tuned for it your making your engine work harder to burn it

[F430TECH]

so i put 100 octane gas in for one tank just for fun since i've done it before on other cars running at the track so i didn't see the harm. I was doing a 40-100 pull to compare times and was unable to reach 100mph in 4th gear... I am very confused because around 97mph in 4th gear i was hitting the rev limiter and boost of course dropped completely off. Now i've done 40-100 pulls before and i can hit at least 105 in 4th. If anyone has any clue as to why this could happen please fill me in. I have a 2007 mazdaspeed 3 with intake, downpipe, racepipe, and cat-back.

Did you happen to fill it up at MSR in Cresson? I am always tempted after a weekend of work to fill up with it, but it would be wasted on the Drive home to Houston...

[Jdizzle659]

Did you happen to fill it up at MSR in Cresson? I am always tempted after a weekend of work to fill up with it, but it would be wasted on the Drive home to Houston...

No i didn't fill up at MSR in Cresson. I have no idea what or where that is lol. The car ran like shit with that octane level. I wouldn't do it if i were you. I would never do it again unless i was tuned for it

[F430TECH]

No i didn't fill up at MSR in Cresson. I have no idea what or where that is lol. The car ran like shit with that octane level. I wouldn't do it if i were you. I would never do it again unless i was tuned for it

Thas wierd because our cars hav an automatic knock sensor like most modern cars and with 100 octane they should automatically advance timing until they hear knok then back it off a bit. 100 octan should of resulted in knock comin in abit later therefore ore timing therefore more power...

[F430TECH]

No i didn't fill up at MSR in Cresson. I have no idea what or where that is lol. The car ran like shit with that octane level. I wouldn't do it if i were you. I would never do it again unless i was tuned for it

Thas wierd because our cars have an automatic knock sensor like most modern cars and with 100 octane they should automatically advance timing until they hear knocking then back it off a bit. 100 octane should of resulted in knock coming in a bit later therefore more timing therefore more power...

[spdjnke]

The car is not meant or tuned to run 100 octane, remember the higher the octane the more it resists detonation, and therefore you are experiencing limp mode from the ecu to prevent you from blowing the bottom end out of the motor.

[PCspeed3]

This damn car is impossible to mod haha.