Boosting In 5th

[Maxx Mazda]

From what I gather, boosting in 5th at high rpm is no diofferent than any other gear, it's the low rpm, high load and high boost that kills it.

 

[mazdaspeedwerx]

my car was set at 15 psi for a very long time and there is a nice hill on a local highway tht I drive every day usually at wot and I have had no problems at all. I have hardly any supporting mods either just a 3" exhaust cai and a boost controller

 

[JOMO]

I blew mine from a bad tune (lean) in 5th at about 5krpms. Good tune, you should be fine. Just to clear it up. If I was cruizing in 5th and had to pass, i would get on it, I would hit full boost and it was fine.

But when I blew, I was running sombody, redlined 4th, shifted into 5th BAM. Not casual driving in 5th. That was no problem. But running lean was the reason.

 

[Maxx Mazda]

THanks for the input JOMO. I remembered that this was why you blew. What were you tuned with? I gave my car a hard pull in 5th here, after redlining 4th, and no problem. 210KPH before I let off

 

[JOMO]

I had the mpi with extra injectors. Bad tune, and running lean in the upper rpms.

 

[Maxx Mazda]

Ah... I'm going with Microtech.

 

[JOMO]

Im running the haltech E6X right now with 650cc injectors. But I dont have the car right now, its in the shop getting 3rd gear fixed.

I hear nothing but good news about microtech. Are you running a fmu right now?

 

[avarela86]

Im running the haltech E6X right now with 650cc injectors.

Haltech for the WIN!! Manuel owns....I'm tuned pretty rich cause i wanted to be on the safe side and today was the first time I actually boosted in 5th because a buddy told me about this thread and how its all talk about the myth. Car didn't really go far during the pull so ill stick to downshifting. It's the safer road and there's A LOT more response. Specially on only 5.5 PSI with all supporting mods except internals. FMIC,HKS BOV,HAltech F10x,Tial wg,GT28rs, exhaust and intake.

 

[JOMO]

Haltech for the WIN!! Manuel owns....I'm tuned pretty rich cause i wanted to be on the safe side and today was the first time I actually boosted in 5th because a buddy told me about this thread and how its all talk about the myth. Car didn't really go far during the pull so ill stick to downshifting. It's the safer road and there's A LOT more response. Specially on only 5.5 PSI with all supporting mods except internals. FMIC,HKS BOV,HAltech F10x,Tial wg,GT28rs, exhaust and intake.

Man, 5.5psi. I dont know how you do it alfredo. Thats like getting blue balls.

 

[ghettobubba2001]

Y'know, this thread just made me think of something.

Early this spring, I was on my way back to college at Penn State (in central PA) after visiting my family in Philly. After about 3 hours of steady highway driving (I'd say a consistent 75-80mph), I was going up into the mountains when my MSP started having .. seizures, I guess I'd call them.

I was going up the largest incline of the trip -- 18 wheelers are restricted to the right-hand lane and can barely manage 20mph, to give perspective -- and pushing on the gas to maintain the speed I was at before the incline. I was boosting, but NOT much -- I'd guess around 4psi, MAYBE 5psi. About halfway up the mountain, my car started bucking like mad. I had to ease on and off the gas to make it to the top. Once there, I pulled over to check things -- all hoses fine, everything looked fine, WTF. Got back in the MSP and continued driving.

I got back to my college about a half hour later, let the car rest for about an hour, and then went to drive to Wal-Mart. On the way to Wal-Mart, the bucking started again, I got a CEL, and I once again pulled over to check under the hood. STILL nothing. I drove the rest of the way to Wal-Mart very carefully, with the CEL still on, listening carefully to try to figure out what was going on. Got to Wal-Mart -- still completely puzzled.

Came out of Wal-Mart @ 20 minutes later. Started my MSP. CEL was gone, and the car drove perfectly normal. Or at least as normal as we ever get, haha.

I have the MAM SRI, MAM FMIC, Greddy Type-RS BOV, relocated MAF to boosted pipes, and a custom cat-back exhaust. That was THE only incident I've ever had like that with my MSP, though I've mildly boosted in 5th gear plenty of times before.

Maybe it was the additional stress that the mountain incline produced? s*** if I know.

mebbe its fuel cut was it like 70 degrees outside?

 

[igdrasil]

I have boosted in 5th for long, (variable cause it would speed up too fast), Uphill for more than 5 mins. After a few minutes you could smell something was running hot....the manifold.

I have also done WOT in 5th up to speed governor, let go, then hit again, and so on.

Just monitor your A/F, Water Temp and ping/knock. Oil pressure and temp could be a good idea too.

 

[igdrasil]

From what I gather, boosting in 5th at high rpm is no diofferent than any other gear, it's the low rpm, high load and high boost that kills it.

I think is the high load/high boost in high rpms what kills the engine.

If you are boosting in 5th and see lower acceleration than usual, let off, you will kill the engine in the next few seconds.

Couple of days ago I disassembled the last engine I blew...pistons were perfect. 2 good rods, 1 bent rod, 1 broken rod in pieces.

Killed @ high rpm, high boost.

 

[JOMO]

I think is the high load/high boost in high rpms what kills the engine.

If you are boosting in 5th and see lower acceleration than usual, let off, you will kill the engine in the next few seconds.

Couple of days ago I disassembled the last engine I blew...pistons were perfect. 2 good rods, 1 bent rod, 1 broken rod in pieces.

Killed @ high rpm, high boost.

Well said. Thats another reason for me to believe why my motor went. High rpms in 5th means high load. I have my blown block in the garage. I should post some better pics now since I dont have to crawl under my car to snap them. I could tell you though, that in cylinder #4, their is about one inch of my rod still connected to the piston. And about 6 humongous gargantuan holes.

 

[Maxx Mazda]

Hey JOMO for your Haltech did it come with a harness or did you need to splice?

 

[Dpwhitehead1]

i think that is more of what I was leaning towards with my post about boost jomo. thanks for explaining better.

 

[Rainman]

Y'know, this thread just made me think of something.

Early this spring, I was on my way back to college at Penn State (in central PA) after visiting my family in Philly. After about 3 hours of steady highway driving (I'd say a consistent 75-80mph), I was going up into the mountains when my MSP started having .. seizures, I guess I'd call them.

I was going up the largest incline of the trip -- 18 wheelers are restricted to the right-hand lane and can barely manage 20mph, to give perspective -- and pushing on the gas to maintain the speed I was at before the incline. I was boosting, but NOT much -- I'd guess around 4psi, MAYBE 5psi. About halfway up the mountain, my car started bucking like mad. I had to ease on and off the gas to make it to the top. Once there, I pulled over to check things -- all hoses fine, everything looked fine, WTF. Got back in the MSP and continued driving.

I got back to my college about a half hour later, let the car rest for about an hour, and then went to drive to Wal-Mart. On the way to Wal-Mart, the bucking started again, I got a CEL, and I once again pulled over to check under the hood. STILL nothing. I drove the rest of the way to Wal-Mart very carefully, with the CEL still on, listening carefully to try to figure out what was going on. Got to Wal-Mart -- still completely puzzled.

Came out of Wal-Mart @ 20 minutes later. Started my MSP. CEL was gone, and the car drove perfectly normal. Or at least as normal as we ever get, haha.

I have the MAM SRI, MAM FMIC, Greddy Type-RS BOV, relocated MAF to boosted pipes, and a custom cat-back exhaust. That was THE only incident I've ever had like that with my MSP, though I've mildly boosted in 5th gear plenty of times before.

Maybe it was the additional stress that the mountain incline produced? s*** if I know.

Sounds ALOT like fuel cut caused by a boost leak. Very surprised to hear that there was no loose hoses. I would also look for any cracked couplings or cracked pipes.

I too have had these symptoms many times when getting my plumbing sorted out. Boosting the car on the highway under load (e.g passing while travelling up a long grade) was one of the worst situations to aggravate the symptoms.

R

 

[Turtle of Time]

I wanna blow my engine

 

[MrDiggler]

I have noticed a part throttle lean condition in mine that can show up between 3.5-4.5k rpms. The car has to be under moderate load (like going uphill), with boost less than 6 psi (my max is close to 8), and it can happen in 2nd through 5th. The engine can stumble pretty bad, but it takes just the right combo of load/rpm/boost to make it happen. My trick is now to sense when it's likely and actually feed it enough throttle to make the ECU go open loop. You can instantly sense the change in the engine when it gets the extra fuel. Power actually drops off a hair, but it won't stumble after that. I obviously am not running any aftermarket EMS.

As for boosting in 5th, I do it all the time. It's my favorite way to pass in traffic between 65-80 mph...on level ground. No need to downshift, just a tiny stab of the gas and the little GT25 zips you right up to speed. If I'm going up a long incline (and we have tons, like PA), I actually turn off my A/C and try to keep the motor from boosting much at all. It's all about the load you place on it. Some motors might do it for very long stretches, some might not even make a full top speed pass before letting go. I'd say A/F management is a big part of it.

 

[PlatinumMSP]

if you actually know how to drive, you wont be boosting in 5th until your well over 100mph period

 

[BOOSTR]

I have never not boosted in 5th. As long as you don't subject the engine to extreme situations it will be fine. That's been my experience with two mazda built turbo equipped cars. I've logged over 214,400 miles on the Probe and 59,000 on the MSP.