b16ahybrid

I've heard so many different oppinions about what happens when you hit the factory(honda ecu) set fuel cut while under boost.
everything from lean condition and possible detonation to nothing, will happen....
The reason i ask is because i recently took my car out (been a while since i drove it last) and hit fuel cut while boosting (entering the freeway). I forgot how easly the tires cut loose and the rpm's shoot up to redline.... .....thanks guys and gals

rioninja

Smacking into it breifly isnt going to cause any damage.

Big Daddy Go Fast

I tapped the rev limiter today. I was boostin' like crazy in 2nd entering a highway. I didn't hear anything suspect. My ride felt fine afterward.

lazerus

redlining an engine wont usually hurt you...

b16ahybrid

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lazerus &raquo;</TD></TR><TR><TD CLASS="quote">redlining an engine wont usually hurt you...</TD></TR></TABLE>

it's not the redlining that i'm concerned with it's the fuel cut and boost i was more concerned with

iiilgsrlll

Did it a lot with my old integra. Either lost traction and hit the fuel cut or racing in 4th gear and not paying attention to the rev limiter. I have a lead foot so this was a frequent thing. Had the car for over a year and half with no incidents. This was also on FMU and missing link. I know everyone swears by Hondata or whatever but the truth is the ghetto setup worked out of the box.

vtec.dc2

from what i know it cuts one of injectors cycle.. it doesn't stop fuel delivery completely, just cuts one in every 4 or somewhere along that.. i've hit redline with boost couple times, i don't think its as bad as running lean at all times, redline isn't there to protect but to warn..

i raised my redline to 9k so i can shift at 8500rpm at all times and not hit it..

b16ahybrid

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtec.dc2 &raquo;</TD></TR><TR><TD CLASS="quote">from what i know it cuts one of injectors cycle.. it doesn't stop fuel delivery completely, just cuts one in every 4 or somewhere along that.. i've hit redline with boost couple times, i don't think its as bad as running lean at all times, redline isn't there to protect but to warn..

i raised my redline to 9k so i can shift at 8500rpm at all times and not hit it.. </TD></TR></TABLE>

So what about that one cylinder that now has less fuel but is still getting a spark? Or does it cut spark to that cylinder too?....
I know that i could get a lot more out of my engine if i raised my redline, as of rite now i have to shift by 8,200rpm otherwise it hit the rev limiter. Redline just begins at 8,250 for my engine (factory) And I know of a lot of cases were bone stock b16's have been reved to 8,500 daily and even some that see closer to 9k rpm with no problems..

sporkcrx

There's not much use raising the rev limit in turbo motors though. It's more for n/a where that's one of the areas that they need to make power. For turbo motors you can just raise the boost to produce more power.

ion_four

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sporkcrx &raquo;</TD></TR><TR><TD CLASS="quote">There's not much use raising the rev limit in turbo motors though. It's more for n/a where that's one of the areas that they need to make power. For turbo motors you can just raise the boost to produce more power.</TD></TR></TABLE>

This is completely false. The only reason you should raise the rev-limit on your car is if you have modified it to make power at higher rpm. Doing so on an NA car will gain you nothing, unless it has been modified. In addition, an FI car that has been modified to make more power at high rpm should also have the redline raised. It has to do with where you have designed the engine to make maximum power, irregardless of how it makes that power.

Anyway, this has nothing to do with anything, really. I used to worry about fuel-cut as a rev-limiter, but here are some examples that tend to show it isn't bad:
1) Honda uses it as the stock limiting method and they have smart engineers
2) Stock turbo cars such as DSMs use this same method (from what I have been told)
3) The same thing occurs when you leave the car in gear, but take your foot off the gas to deccelerate (injectors cut-out, leaning the engine to a 'functional' 20:1 or more A/F ratio.
4) This is how full-trottle shifting and full-throttle launch are enabled on hondata (and modified stock ecus) and cars aren't blowing up left and right.

It still seems to me that cutting spark would be safer, marginally, but in light of all this it seems unworthwhile to pursue to any lengths (though all MSD boxes can do it).

VaporTrail

Misconceptions abound....

Honda's ECU cuts fuel ENTIRELY. Injector duty reverts to zero in a condition where atmospheric pressure exceeds what is deemed acceptable. When used in conjunction with Hondata, the same thing happens, only you and your tuner can define what that acceptable atmospheric pressure is.

Now, you need 4 things for proper combustion:

Air
Spark
Fuel
Compression

Without fuel, there cannot be any combustion at all. Afterall, there is nothing to burn and thus, nothing to detonate.

sporkcrx

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ion_four &raquo;</TD></TR><TR><TD CLASS="quote">
This is completely false. The only reason you should raise the rev-limit on your car is if you have modified it to make power at higher rpm. Doing so on an NA car will gain you nothing, unless it has been modified. In addition, an FI car that has been modified to make more power at high rpm should also have the redline raised. It has to do with where you have designed the engine to make maximum power, irregardless of how it makes that power.</TD></TR></TABLE>

Completely false? I realize a n/a car needs to be modified to make power above the stock redline, I never said it was stock. I was saying why raise the rev limit to make power on a boosted car when you can just up the boost??? This way you're not putting a huge amount of stress on rods, since the stress on them is exponential (big word, I know) as the revs go up, ALONG with all of that boost! The only reason I can think of is if they have a huge turbo that doesn't spool for forever, and that's just a shitty choice by them. Here's a quote from the Honda builders hand book II reguarding nitrous engines (similar to boosted engines):

"As for the bottom end build for strength and reliability, choose rod ratios to make power at some efficient point, somewhere between 6000 and 7000 rpm for engines with two valves per cylinder; and up to 8000 or so for 4-valve per cylinder engines. Most engines breathe well at these engine speeds and with nitrous there is no reason to twist it real tight and tear it up. With nitrous you don't have to rely on high RPM to do more work in less time, just put more nitrous and fuel into the engine and it will make as much power as your bottom end and the seal between the block and head will take. Even the Pro Mod creatures don't spend much time past 7000 rpm. They've found they don't have to. Just put more nitrous and fuel and choose the right gear and put as many gears in the transmission as you can and go racing. Keep the engine in a very narrow power band and you can go very, very quick."

btw, long live pgmfi

Nextelbuddy

so with that in mind you can hit the rev limiter all day and night long in boost and that shouldnt hurt your motor? reason i ask is because when i pop the clutch in first gear and hold the e brake to do a burn out the motor bounces off the rev limiter in boost. i shouldnt be worried right?

SiRkid

i hit the rev limiter all the time.. lots do in 1st gear where if you shift to early youll bog or continue to light the tires up.
no worries. just dont do it all night long

but one thing I hate is dorks who bounce off the limiter in the burnout box at the track.... ickkkkkk.. sounds terrible. it sounds particularly bad on stock or slightly modded n/a honda's. raa raa raa raa raa raa raa raa raa raa raa raa while doing a peg legged burnout.

raene

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VaporTrail &raquo;</TD></TR><TR><TD CLASS="quote">Without fuel, there cannot be any combustion at all. Afterall, there is nothing to burn and thus, nothing to detonate. </TD></TR></TABLE>

Chalk me up for another one...

Detonation = preignition, correct? Detonation doesn't mean much to me, preignition implies the piston's moving up while the flame front's moving down... at least in my head.

Preignition is caused by, among many other things, too hot a combustion chamber. Heat in the combustion chamber can be caused by a prolonged lean condition. A fuel cut isn't a lean condition, it's a complete lack of fuel, therefore no heat is generated. So therefore hitting the rev limiter won't raise cylinder temps to a level where preignition may occur... in fact it shouldn't raise them at all. So smacking the rev limiter isn't bad for your car at all in terms of preignition happening.

Correct?

b16ahybrid

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ion_four &raquo;</TD></TR><TR><TD CLASS="quote">

This is completely false. The only reason you should raise the rev-limit on your car is if you have modified it to make power at higher rpm. </TD></TR></TABLE>

It would benifit me becaus my car makes power up to the fuel cut, (steady climb) so if i raised it to say 8,500rpm it would allow me to shift safely at 8,300 instead of shifting at 8,000 rpm to prevent from hitting the rev limiter...