Hearing conflicting things about boost at low RPM...

[kehbleh]

Experts of MSF, I am confused regarding boosting at low (I guess that's a relative term) RPM in our cars. I've seen it on here, and I've heard it from my friend who's owned a pretty heavily modded Speed 6 for quite some time (GT3071 turbo): DON'T boost in the low RPMs unless you want to throw a rod.

Well, I've been doing my searching like a good noob. I've been looking at SRIs and TIPs because I plan on doing a nice bundle purchase of the two aforementioned mods and a COBB AP. And possibly a fuel pump if the numbers from the AP show that I need it. But in a lot of TIP reviews, everyone says "Oh the boost comes in at least 500 RPM sooner, it's so nice."

From what I've heard, boosting below 3k RPM is a no-no. But, I know with the torque curve on our car, we've already hit pique torque at 3k. There's still plenty of torque to be had at 2.5k, maybe even 2k, but everyone says to keep it out of boost until 3k. Well, what's the benefit of having a small turbo with such an early spool up if we can't use it?! In 1st, 2nd, 3rd, and to a lesser extent 4th, as I build to the 3k before I put my foot down, I can feel the torque already building..if I put my foot down at 2.5k, I know it's gonna go.

I think you guys see where I'm going with this. Is it safe in the lower gears to get on it at 2.5k or 2k? I could see if you upgraded to a bigger turbo that you'd need to avoid flooring it at 2.5k, because there'd probably be no boost at all and you'd be putting a tremendous load on the engine. But in the car as it is now, stock, seems like it would be more than happy to frolick around at 2.5k, even 2k in 2nd.

Are people over-exagerrating the 3k mark? I feel like I can feel when the engine is willing to run and where it'd struggle. I'm not gonna floor it at 2.5k in 6th...but 3rd? Doesn't seem like the car would mind...

[rghispanic88]

Test it out and see how it goes

[G26]

no reason to be going wot below 3000rpm anyway.

[Zdraveca]

Originally Posted by rghispanic88 Test it out and see how it goes

Ahahahahaha THIS^!!!!!!

Sent from my T-Mobile G2

[Mizzle]

Don't go WOT below 3k.
Problem solved.
Close this thread.

[stupidslow_ms3]

I usually race people in the 3500-3800 rpm range in 2nd or 3rd gear. 2500 seems way to low to be flooring it from unless u from a dead stop.

[kehbleh]

Originally Posted by stupidslow_ms3 I usually race people in the 3500-3800 rpm range in 2nd or 3rd gear. 2500 seems way to low to be flooring it from unless u from a dead stop.

Well it's not racing..it's just driving around the city. Just truckin along at 2500 when a lane opens up..why not let 'er gallop! I was trying to foster discussion with this thread to learn more about how my car works but apparently some people are content with JUST DON'T DO IT LULZ. Thanks guys.

Also worth noting that nowhere in the owner's manual does it warn about accelerating fully below a certain RPM.

[TRex]

my answer to this time and time again is WHY WOULD YOU WANT TO DO THIS

regardless if it is bad or not more power will be had if you simply downshift...stop being lazy...should have bought an automatic

[kehbleh]

Originally Posted by TRex my answer to this time and time again is WHY WOULD YOU WANT TO DO THIS regardless if it is bad or not more power will be had if you simply downshift...stop being lazy...should have bought an automatic

If the power's there, why not? Of course the answer to that is because it will damage your car. But why even have a small turbo at all if you can't put your foot down till 3k? Just seems counter-intuitive to me.

[silvapain]

I go WOT at 2000 RPM all the time. I'm at 21 PSI by 3000.

[rtabagaboy]

Well a BT should not spool at those low RPMs so you are putting less load on the engine at low rpm with a BT. This is why some people see BT as a safer option to the stock turbo, because the don't build boost until later in the RPM band.

Edit: In stock form the flow path is restrictive so it doesn't build boost at low rpm. Once you add breather mods that physical limitation goes away and you can boost 20+ Psi @ 2500 RPM.

[kehbleh]

Originally Posted by rtabagaboy Well a BT should not spool at those low RPMs so you are putting less load on the engine at low rpm with a BT. This is why some people see BT as a safer option to the stock turbo, because the don't build boost until later in the RPM band. Edit: In stock form the flow path is restrictive so it doesn't build boost at low rpm. Once you add breather mods that physical limitation goes away and you can boost 20+ Psi @ 2500 RPM.

Hm, that makes sense. If stock it were impossible for it to boost that low due to air restrictions then there'd be no need to warn the consumer about it. It feels like it's got enough umph in it that it's got at least some boost though (specifically 2.5k in 2nd gear). Also...what's a BT?

[rfinkle2]

Check the thread below out when you have a moment.

Some evidence shows that the Mazda factory tune (pretty lean in high boost situations, with aggressive timing), combined with catless downpipes (i.e. boost spikes) in early days of modding the ms3 led to the bent rods.

http://www.mazdaspeedforum.org/forum/foru...st-zoom-82908/

[kehbleh]

Originally Posted by rfinkle2 Check the thread below out when you have a moment. Some evidence shows that the Mazda factory tune (pretty lean in high boost situations, with aggressive timing), combined with catless downpipes (i.e. boost spikes) in early days of modding the ms3 led to the bent rods. http://www.mazdaspeedforum.org/forum/foru...st-zoom-82908/

Thanks! THIS is the kind of stuff I was hoping would turn up! Very interesting.

[rfinkle2]

Originally Posted by kehbleh Thanks! THIS is the kind of stuff I was hoping would turn up! Very interesting.

One thing to note is cld12pk2go (the linked thread's creator) has some pretty extensive knowledge of tuning the mazdaspeed3 (and other platforms {blown mustangs on spraying meth I believe}) for that matter.

He also runs an e85 mix with 100% meth injection.

Point being, his car is tuned properly.

Another thread concerning low rpm boost (not bothering to down shift) lol.

pwnin' some WS6

[kehbleh]

Originally Posted by rfinkle2 One thing to note is cld12pk2go (the linked thread's creator) has some pretty extensive knowledge of tuning the mazdaspeed3 (and other platforms {blown mustangs on spraying meth I believe}) for that matter. He also runs an e85 mix with 100% meth injection. Point being, his car is tuned properly. Another thread concerning low rpm boost (not bothering to down shift) lol. pwnin' some WS6

To be fair, I'd say not downshifting on a highway is straight-up lazy. You're not gonna have passing power lugging around in 6th. However, if you're going 30 mph in 3rd gear, you don't need to downshift to 2nd to get the power you need. And there you have the origin of my question.

[Bucker]

I do all of my logs from 2500-redline...

I personally have no issue going WOT under 3k RPM in 2nd or 3rd, but thats me.

[kehbleh]

Nevermind, big turbo ha.

Originally Posted by Bucker I do all of my logs from 2500-redline... I personally have no issue going WOT under 3k RPM in 2nd or 3rd, but thats me.

Well that's the thing, it feels plenty strong and fine doing it, but everyone says DON'T SMASH GAS BELOW 3K OR HAVE FUN PICKING YOUR MOTOR UP OFF THE ROAD. Which is why I started this thread in the first place...I wasn't sure if those guys were talking about bigger turbos, or if it didn't matter how the car FELT, that damage was still being done when gassing it below 3k.

[laxplayermjd]

i just drive my damn car however i feel like it,whichever rpm its at. Have you heard the one about not taking these on long trips too?

Ive got full boot between 2500-3k rpm. Only truth i see behind this is why go it in 6th gear on the highway, racecars downshift

[AtTheDriveIn]

Originally Posted by laxplayermjd Have you heard the one about not taking these on long trips to?

I want to know this too. I've driven from Virginia Beach to San Diego twice and no issues so far. I've also driven many times between Texas and Cali. Most of my miles are highway at 72k.

[Spoofmastafly]

The whole don't go WOT under 3K RPM's doesn't come into play when your in 1st and 2nd gear, shit or 3rd gear. I start my logs in 3rd gear at 2500rpm. People are mainly speaking of in 4th, 5th, and 6th gear you dont want to go WOT under 3k rpm. Downshift.. or baby the throttle till your above 3k rpms and go at it.

You can't really go WOT in 1st gear, well u can but your not going to hit 20psi.. might hit 20 psi for a second or two in 2nd gear, depending on when you shift.

[Jake5713]

My only thing here is, I have always been advised to start when I datalog to start the log at 2.5 k
Is this wrong
@rfinkle2


---
I am here: http://maps.google.com/maps?ll=44.739728,-93.107847
-Jake

[drag0nfire]

Hi all,

Sorry in advance for the dumb question, but I just read the whole thread, and I still don't understand what happens when you boost at low rpms.

If I have a CAI with a stock tune, it boosts easier, right? Does that mean I am at increased danger for problems associated with boost at low rpms?

Thanks!

[jv92red]

This has been talked about many times in the blown engine threads. In a nutshell - a bolted K04 motor is capable of torque of 300ftlb+ at these low RPM's. Check out the dyno threads for K04 setups an you'll see 300ftlb+ levels at the wheels which means higher actual torque at the flywheel given drive line losses. This amount of energy down low in the RPM range is what overworks the stock rods. The engine is not spinning fast enough yet to be able to cope with the energy exerted on them - this leads to fail. BT's don't reach full boost till 3000+ so this is not so much an issue when going BT.

I'm no engineer so I'm sure someone can explain the reciprocating/rotational mass better than me but when it comes down to it, we only have 4 rods to distribute the generous amount of torque that built K04 motors put out at low RPMs. I would suspect the rods on a V12 Lamborghini Aventador with 510lbft @5500RPM would have less energy exerted on any given rod at it's 5500 RPM peak as it has 8 more rods and 3000 more RPM's to deal with that energy. Again I am no engineer so if someone can jump in and explain better than this or correct the above please do.

[icto0389]

Originally Posted by jv92red This has been talked about many times in the blown engine threads. In a nutshell - a bolted K04 motor is capable of torque of 300ftlb+ at these low RPM's. Check out the dyno threads for K04 setups an you'll see 300ftlb+ levels at the wheels which means higher actual torque at the flywheel given drive line losses. This amount of energy down low in the RPM range is what overworks the stock rods. The engine is not spinning fast enough yet to be able to cope with the energy exerted on them - this leads to fail. BT's don't reach full boost till 3000+ so this is not so much an issue when going BT. I'm no engineer so I'm sure someone can explain the reciprocating/rotational mass better than me but when it comes down to it, we only have 4 rods to distribute the generous amount of torque that built K04 motors put out at low RPMs. I would suspect the rods on a V12 Lamborghini Aventador with 510lbft @5500RPM would have less energy exerted on any given rod at it's 5500 RPM peak as it has 8 more rods and 3000 more RPM's to deal with that energy. Again I am no engineer so if someone can jump in and explain better than this or correct the above please do.

I've always had an engineers mind, and when explained like this it makes a lot of sense.

This is MO on why its not a good idea...

If i can laugh at a SOHC ITT Civic as i pass him @60 in 6th (which is like 2200rpm) and hes got it matted in third as i slowly pull away faster and faster and....then BOOM. im not laughing anymore....

well, It makes sense because.... 300ftlbs of TQ @ 2200 means that with each revolution of the crank the rod is pushing very hard for a longer time to get the rotational mass converted into HP. all this tq force is applied for a much longer duration to each rod, possibly stressing the components about 50% more than when @ 3k (since at this higher RPM the rod received the same TQ but for a shorter time. IMO this means 50% less stress and TQ displaced to the engine when at higher RPM.) Now im sure if you ask an engineer; he could probably prove this with math. and im sure he will tell you that there are additional lateral forces on internal components as the RPM's increase, AKA redline BOOM...

After reading through the tread i am 100% sure that at these low RPMs and such a large amount of Air and fuel being thrown in for such a low combustion cycle it changes the chemical process (only slightly) when the fuel is ignited, which from what i understand could have or probably did cause the early years of BOOM!


You know what, the general message of this thread, and i would agree...


JUST DON'T DO IT....

[kmac]

I don't understand why this is so hard to grasp. Eventually u will bend a rod or wear your rod bearings due to the tremendous amount of load and cyl pressure. So considering you didn't get the answer u wanted u just keep asking till u get the one u want. So here u go , It's great for the car , you should do it anytime given the chance . The more the better.

[Jake5713]

For logging is it or is it not safe to start at 2500 rpm
This is something I believe is in @Abilor guide
This is something I need to confirm


-Jake

[rfinkle2]

Originally Posted by Jake5713 For logging is it or is it not safe to start at 2500 rpm This is something I believe is in @Abilor guide This is something I need to confirm -Jake

It is safe to log from 2500 rpms. Yes.
(I believe that Cobb, the Perm team, Phate, atvfreek would ask you to log from that rpm in addition to your tuner. I think cld12pk2go would ask you to start @ 2000 rpms)

If you are logging, and see kr>2 @ any rpm, I might let off the go pedal.

To the best of my knowledge, 95% of the logs on this forum are started @ 2500 rpms.

[kmac]

Creating torque that low is not good for any engine that's not built.

[8.5MS3]

theyre all wrong op

i go wot in 4th at 2k and the car eats it up, i gotz datalogs to prove it

bunch of paranoid bitches on their rag up in this joint

[Atlanta]

Originally Posted by 8.5MS3 i go wot in 4th at 4k and the car eats it up, i gotz datalogs to prove it

I don't think anyone said that WOT at 4k is bad. They are talking about 2k and 2.5k WOT.

[kehbleh]

Originally Posted by 8.5MS3 theyre all wrong op i go wot in 4th at 2k and the car eats it up, i gotz datalogs to prove it bunch of paranoid bitches on their rag up in this joint

Your avatar is fitting haha.

[8.5MS3]

oo my bad i meant 2k

[rfinkle2]

I guess it all comes down to risk. The rods in our cars are documented as being the weak link.

Is there more chance of breaking / bending something @ high load low rpm?... it certainly seems like a sound idea, both from a mechanical standpoint and opinions of other members.

Are some of the guys willing to take the risk? Yes. With a bit more success now than in the past.

In 1st, 2nd and 3rd, I think it is unavoidable tbh.

While datalogging, it is going to be asked of you to be sure the car is timed properly.
The remainder of the time, I guess it is entirely up to you if you decide to downshift or not.

[Mizzle]

The rods are not a weak link if they handle 500whp (which they do.)

Flooring your car in 5th or 6th at 2,800 rpm because you're too lazy to downshift = blown motor. Not because they're weak, but because they're spending a lifetime in that crank rotation making maximum torque... when suddenly shitty gas detonates from the raised temperatures and *poof* blown engine.

Until you fully tune your car, downshift at 3k when accelerating from 4th on up.

[silvapain]

It's all detonation. Cylinder pressures spiking drastically BTDC bend conrods, not boost.


Tapadatass

[8.5MS3]

i have peak tq pushed out to 4k

so i dont care when i floor it haha

[rfinkle2]

And the debate continues. LOL.

[wankular]

The long trip controversy had to do with cruising too long at one RPM and then trying to accelerate and boom. PTP John had a long thread about it, something about oil pooling somewhere.

Also I think a guy blew up while in cruise control.

[kmac]

Cyl pressures r way higher at lower rpms and detonation also plays a huge roll in bending rods, but if we look at this in terms of this was a real engine in displacement terms instead of a weed wacker. If u had a 4.6 twin cam cobra and it made peak torque at pre 3k or 3200 and if your making 350 in a 2.3 now your 4.6 technically makes 700wtq at those rpms eventually there is definitely going to be a problem . Instead of looking at it as the wtq not being that much at that rpm compare the wtq to rpm and displacement and It's a little scary.