heel2toe

iTrader: (41)

Let me start off by saying that I'm afraid of the direction that this thread may go down. With that being said I am looking for feedback backed with data and/ or some sort of explanation as to why one would be better than the other.

Now onto my question. I auto-x my car and while every course is different I find that given the gearing of my car and the current power it is making, I am pinging off the rev limiter more than I would like. There have been times where I've probably held it there for a second as well on the rev limiter. Now I know this is bad and I cringe at the thought of said act. However, I want to go fast and letting up or shifting into 3rd typically isnt the fastest way around the course.

So it got me thinking about upping my rev limiter. Currently it is set to ~7800 but it usually doesnt step in until around 7900.

My car is stock block and the head has GSC Beehive valve springs, HKS 272's Kiggly HLA and MAP H11 Headstuds. Im not too concerned with my head but rather my bottom end specifically the rod bolts or even the rods.

Now im not sure there is a right or wrong answer here but would my engine be better off with me continuing to bang the rev limiter or alternatively raise the rev limiter a coupe hundred RPM? While a couple hundred RPM may only yield an extra .1 second before Im on the rev limiter again it may offer an additional couple MPH which would necessitate me to let off.

Given my lousy cams and smallish turbo (BBK Full) I know power is falling off up top. I will not change when I shift from 1 to 2. Im just wondering if it will give me that extra cushion where I won't constantly be on the rev limiter or if Im asking for trouble revving it out a little higher?

I will be happy to host a GoPro video on youtube of said scenario if need be it to further explain where I am coming from.

Any feedback that you'll have on this topic would be much appreciated. I tried to be clear and concise with my explanation but if you have any questions feel free to ask and I would be more than happy to try and further explain myself. Thanks in advance.

griceiv

iTrader: (2)

you should be fine up to 8300 on the stock rods with upgraded valve springs.

we have run an 8k limiter on a stock long block for years and hit it all the time with no apparent effects.

okevolutionVIII

iTrader: (71)

I personally would bump it up 200-300 RPM and only hit the rev limiter when it's needed.

heel2toe

iTrader: (41)

Marshall- Thank you for chiming in. Just curious where you came up with the figure of 8300? With your rev limiter set at 8grand what was the highest you've seen the car actually rev? I just checked my what I have mine set to and at 7796 I've seen it rev as high as 8049 and this was not a misshift or anything just what it got to from smacking the rev limiter...

okevolutionVIII- Thank you for your feedback; sorry I dont know your name! Can you expand on why you said only bump it a couple hundred RPM? If I'm understanding you correctly if I were to bump mine 300 rpm it would now be set to around 8100 and assuming what I saw before in terms of what I set it to and what I experience is linear it will end up cutting me off around 8300. Is this what you meant?

griceiv

iTrader: (2)

there are LOTS of threads that talk about max rpm. the drag racers are doing 8300 (or more) on stock long blocks. with GSC beehives and hks cams your valve train should be good for 9k or so. we really just need someone smart to come in here and set us straight (paging English Racing) vs my parroting of forums search results. I'd like to know what rpm stock rods/rod bolts/pistons are good for also. I'm sure someone somewhere has a story of 9k rpm on a stock bottom end.

I've turned the limiter up to 8300 before for nationals and survived, and have survived 4 years of 8k redline (TONS of time riding the limiter at that level).

Faisalm

There's an old thread somewhere with input from STM and English Racing.

English Racing stated that 8k RPM is very safe on stock internals, 8500 RPM is still also safe but they would recommend cams and springs and all that.

STM have gone 9,000 RPM on a stock block but they do not recommend it at all, though (IIRC), their motor went after 50k miles. Now obviously the 50k miles weren't all on 9k RPM but it gives you an idea of how long a stock block can take abuse.

heel2toe

iTrader: (41)

May I clarify a couple things to make sure we are all on the same page.

1- I dont know if our rev limiter cuts fuel or timing but whatever the case there is some sort of "delay" which translates into the theoretical rev limit i.e the one set in Ecuflash and the actual rev limit seen if you would to ping off of it.

In my case Ive seen a variance of ~200 rpm. Is that 8300 the one set in Ecuflash or actually experienced?

2- Im not exactly looking for what is the max safe RPM. What I am trying to determine is if hitting the rev limiter bad for the motor?

Also, I should edit my original post as cams and turbo used are irrelevant, given that this isnt about power.

AreSTG

iTrader: (4)

sounds like you agree raising it will only give you a theoretical 0.1sec more time before hitting the limiter. So, assuming you are still going to hit it either way, I feel it has to be safer to bounce it at the lower number. Now if you could raise it 1,000rpm and still be safer than your current limiter, that'd be interesting.

My only experience riding the limiter is on a built block and holds no water

kyoo

iTrader: (29)

i agree with this. unless it's totally crucial, i don't think it's gonna be "worth" the extra wear/tear/risk. if you're fighting guys down to the tenths though, sounds like it will be safe enough.

heel2toe

iTrader: (41)

Yeah the .1 or so seconds was just an educated guess but it's probably around there. I can take a look back at some logs but IIRC going through 2nd gear only takes a couple seconds so a couple hundred RPM's can only yield so much additional time.

I agree with your train of thought that if I am still going to hit the rev limiter the lower it's set the safer it'll be. However the more I raise it the less times I should be hitting the rev limiter...My other thought is that while it may only give me an extra .1 seconds before Im back on the limiter, it will also give me a couple extra MPH. Im at work so I don't have any logs in front of me but I believe 2nd gear tops out around ~67mph at my current rev limiter. Say the max speed I can hold at a given corner is 68mph. If I were to raise it and say the new rev limiter yields a new top speed of 70mph those extra 3 mph would give me the cushion I need so I wouldn’t have to bang off the rev limiter.

If that is the case and I can safely rev it out a little higher I would be killing two birds with one stone as I will limit my time on the rev limiter as well as give myself a couple extra mph in the top of 2nd to play with.

slowsrt4:(

iTrader: (13)

I wouldn't risk it, but with your springs u should be good to rev to at least 8200

heel2toe

iTrader: (41)

Im not concerned about my head as with those springs are good to 8500 on S2's so I'd imagine they'd have even more room with my whimpy HKS cams.

Im more concerned about what my stock block can support in terms of revs.

And to add to that, what Im trying to determine and have yet to get an answer is to whether banging off the rev limiter is detrimental to the health of my motor.

GotWheelHop

iTrader: (39)

With the extra MPH you will gain, you will reach the corners quicker in autoX and won't be on the limiter as often. It sounds trivial to most, but on a tight autoX track that couple MPH makes a difference.

heel2toe

iTrader: (41)

Well that's what gets me. There is only so much speed you can carry into a corner. While I may only gain a couple MPH it could be the difference from pinging off the rev limiter and needing to lift or hold that speed.

The benefits to raising the rev limiter are pretty self explanatory. If my motor could support it I would rev it to the moon.

This still doesnt answer my question though. Well, maybe it does...if I can SAFELY rev to say 8300 or 8500 then I will gladly raise my rev limiter. And in that situation I'd imagine that I wouldnt be on the rev limiter nearly as much.

However what I am trying to figure out is what is actually happening while hitting the rev limiter. Whether it's pulling fuel or timing EGTs must be rising which certainly isnt a good thing. However would this be negligible or an actual measurable change?

Travis@GSC

iTrader: (2)

Typically it will cut ignition, then a few hundred RPM after cut fuel. Rev limiters are pretty violent on the valvetrain. We have seen(on other platforms) shims spit out, even on shim under bucket set ups, and valve float due to rev limiters. Its possible to throw a rocker, but that seems to be pretty rare on a 4G63.
OP, your springs and valvetrain will be just fine, but yes, your limiting factor is the bottom end for max RPM. I wouldnt suggest holding on the rev limiter(for reasons above), soft pedal at the top end or short shift to stay out of the limiter. Since you are already loosing power up top I would say short shifting and keeping the revs lower will be much better in the long run.