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Making the K hold torque to 8krpm...

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tuning vtc vtc tuning
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22K views 53 replies 20 participants last post by  BSIVOLJR  
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#1 ·
Alright guys, I've done some searching around and have yet to see an all motor setup that really makes me want to follow it. Specifically speaking, because of a lack of holding power out to redline. Which I really don't understand because K-heads are supposed to be the best flowing honda heads yet.

I've looked at many setups and dynographs and they all seem to have the same story after about 6krpm torque starts dropping off rapidly. This is quite disappointing as, coming from the b-series realm, where your average lsvtec setup on ctr cams will pull trq out to ~7800rpm.

Its my understanding that camshafts have the biggest affect on this, and even the dyno's of a certain high dollar manufacturer share the same story with all other k cam's, the torque just doesn't hold; which in my opinion is totally unacceptable. Holding torque is essential to making big all motor power.

I know this post isn't really a question, more of a rant. So anybody else feel free to throw your opinion in here. :up::down:?
 
#2 ·
It is an interesting concern.

Stroke has the biggest affect since it is the primary reason for the powerband curve to shift left or right.

So when combined with the right gearing and tires it works out in the end.

In my opinion you are looking for the wrong signs on the dynographs. It is all relative.

Take the extreme example of the 400whp IPS motor

Image


Look where tq is peaking and where power flats out. There are many factors that contribute to this. Stroke first, but you need the right cams, exhaust header and intake along with tuning, ignition etc...
 
#3 ·
LOL, where are you trying to make power? 15,000 RPM?
Why does a cam need to continue making torque past 7k if the bottom end can't spin that high? It is cheaper to change gearing for most applications, and for those that can't they can only make as much power as the circumstances allow.
 
#4 ·
I do not want to be quoted out of context though. It all maters and other factors play an important role. What I mean by primarelly stroke.. is in the even that you have a setup with xyz components peaking tq at XXX rpm, stroke would be be easiest way to move the powerband but without the right header and intake.. it will not happen..

Check this out...

99mm K24a with ported head 88m pistons

Image




99mm k24a with 89mm pistons and stock head, stock RBC and 2 liter header

Image


See how the tq dies early?
 
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#5 ·
Honda motors have always had the reputation of being high revving, peaky motors, I guess I just assumed the new generation motors would retain that charectaristic since it seems to be a great design as proven by previous generation motors. I dont think what I'm asking is unreasonable.

Nikos, that is a very valid point. I will think on this more.

EDIT: wow that 1st graph looks good, only 220trq and over 300whp. Thats nice.
 
#11 ·
You are misreading the situation. B-series appear to "pull trq out to ~7800rpm" because they have no midrange. The improvement on the k-series has always been recognized as the midrange power. That is what VTC does for you. So it's not that the top end power is falling so much as the midrange power was dramatically increased.

There really is no such thing as a motor with an infinite torque band. All motors are going to reach peak volumetric efficiency within a certain rpm RANGE. Typically peak torque happens in that area.

Anyhow, if you've tuned b-series motors, you know that depending on how you set your cam gears, you can accentuate the midrange or the top end, but not both. Most people opt to accentuate the top end, which results in a flat looking torque band. But really, it's only optimized at the top end. With k-series, VTC allows you to optimize torque everywhere. That's why you've got the big bump in the midrange.

:up:
 
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#14 ·
chunky` said:
You are misreading the situation. B-series appear to "pull trq out to ~7800rpm" because they have no midrange. The improvement on the k-series has always been recognized as the midrange power. That is what VTC does for you. So it's not that the top end power is falling so much as the midrange power was dramatically increased.
Click to expand...
I really don't think it has as much to do with VTC as it does displacement. Disregard midrange power alltogether and your see what I'm talking about; Look at the losses in trq after 6k on a k-series vs a b-series dynograph. There is anywhere between 20 to 30wtrq lost over the next 2krpm on a k-series whereas its around 10-15wtrq on most b-series dyno's. I'm beginning to think this is a flow issue with the head rather than a camshaft issue as thought before.

chunky` said:
There really is no such thing as a motor with an infinite torque band. All motors are going to reach peak volumetric efficiency within a certain rpm RANGE. Typically peak torque happens in that area.
Click to expand...
I have no delusions in that area. I'm not asking for an infinite power band, I just like the idea of a motor that likes to rev is all. I'd be willing to sacrifice some midrange power to have more flat powerband up top.
 
#15 ·
Does anyone have a full dyno pull with VTC locked at 0-10 degrees vs the full and final tune they can post? I'll try to get one together tonight if no-one does. That should help greatly illustrate the difference.

The stroke will determine the VE ceiling(Like chunky and Nikos were saying). However, if you look at some 86mm builds, torque has no issues keeping up given the correct cams.

I challenge you to find any N/A B-series making 210lbs of torque at 10,000 rpm and over 230 lbs at 9,000rpm :p :slapsyouinthefacewithaglove: :D
 
#21 ·
Video 9 has an overlay of dyno pulls from each cam angle 0-50. It shows you that even at 6000rpm, VTC is at work, optimizing torque. At 6000rpm, the graphs show 50deg VTC is 5lb-ft higher than 30deg. When you start higher, you appear to fall further.

Overlay some B-series and K-series dyno plots that are from 2.0L builds and you'll get an even clearer picture of how VTC raising up the midrange is affecting your perceptions of top end power falloff. A 2.0L K-series will have no trouble keeping up with a 2.0L B-series on top end, but will destroy it in midrange so long as VTC is being utilized.
 
#23 ·
nikos said:
Here's HIGH CAM COMPOSITE

Image
Click to expand...
this is what chunky is talking about... the 40 deg curve loses about 26 ft/lbs from 6k to 7.5k, while the 10 degree curve only loses about 12 ft/lb over that same range.. but thats because at 40degrees it was making 16 ft/lbs more than at 10 degrees.. now imagine that 10 deg. curve as a B series curve, since it cant benefit from the midrange gains that VTC give
 
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#25 ·
I don't understand what you are saying? These motors make as much tq at 3-3500 as they do at 8-8500, and like you said there is not B series going to be making these kinds of torque numbers? I haven't seen a perfectly flat torque band on any NA motor... It has to peak somewhere, and I thin the middle of the powerband is the optimal place for it to peak...
 
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#27 ·
jon v said:
I haven't seen a perfectly flat torque band on any NA motor... It has to peak somewhere, and I thin the middle of the powerband is the optimal place for it to peak...
Click to expand...
Optimal for daily driving maybe, not for racing. You stay in the upper 2500rpms when your racing with a nicely geared transmission; so you want torque in that area to be as flat as possible. This just isn't the case with the K-series unfortunately; (unless you have a stupid low redline like 6500 or 6k). I'm just one who likes to rev. You have to think of it like this, for every 10wtrq more you can hold till 8k, its 20 more whp.
 
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#30 ·
I'm just talking optimum performance in general. I mean, the way I look at it, its 2.4l, its gone make some good midrange torque anyways due to displacement.

Yeah the more I look at it, the more I just think its a result of more stroke. I would think it there would be a way to compansate for it however, with cams and/or head porting.
 
#32 ·
If you looked at one of the graphs that Nikos posted, there is a built k24 that revs to 10k while holding torque. It's all in the combination. It's not something you can just slap together, but it is possible. Think about it, almost 400hp at 9000rpm. It's ridiculous. I never dreamed that would be possible when I started tuning n/a hondas over a decade ago.
 
#34 ·
In absolute terms, I have yet to see a B-series that is making 200+ lb-ft of torque at 10k rpm.

nikos said:
Image
Click to expand...
Forget about the midrange, look at absolute numbers. It doesn't matter if the torque is rising or falling; if the ACTUAL torque is greater, you will be going faster. Period.

I don't think you quite realize how difficult it is to sustain torque production on a big displacement motor into high revs.
 
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#35 ·
You may be right, I dont think its rocket science either though.

A 2nd look at that dynograph though, and that would be a totally accpetable powerband for me (considering I'm only wanting to rev to 8500 or so). If I could have that on a street car but at a lower power level I would be perfectly happy.
 
#39 ·
As far as delaying a sharp torque falloff in a high displacement 4 banger? It's not rocket science, but there is a science to it.

Anyhow, just compare the raw numbers on torque for a 2.0L b-series and a 2.0L k-series at 8000rpm. The K-series is no high RPM slouch. You can build a k-series that loves to rev, that is reliable, and that isn't ridiculously expensive.

It won't have the same power delivery as the b-series, but you'll be going faster regardless of how the power delivery feels.

Anyhow, if you're looking to rev to 8500, check out my latest dyno. It's pretty linear in the RPM range you specified, but I'm hoping that a better header will bring up my midrange even more to 160+ lb-ft of torque.

Image
 
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#45 ·
hahaha, this thread was awsome. I don't understand how the TS couldn't see how a motor makes a Tq curve. And How having a motor making peak Tq or hold close to peak Tq will mean that it makes Peak HP way way above that. You can not have a powerband that is holding flat for 6k Rpm. (without boost). Peak Tq is made when the motor is able to bring in the prefect amount of air, the valve is open just long enough to fill the combustion chamber. not to long, not to short. This only happens once in an RPM range, When you add Vtec this happens twice, when you add VTC this happens 100 times. Giving you a large Bump in the Tq curve.

If you want to hold Tq to 8k then you need a motor with Giant ports and a giant cam, that allows the motor to pull in a ton of air, any RPM under 8k the motor will have no trouble filling the combustion chamber with air. Really low RPMs with have a very low port velocity. causing a lot of undesirable air movement in and out of the ports and intake manifold. Your motor will have awful low - mid-range power. and Will make peak HP well into the 11-12k rpm range.

He made a comment earlier that every 10Wtq you add at 8k gives you 20whp. Not true. 10 x 8000 /5252 = 15whp. I don't except 25% off to be an exceptable error.
 
#47 ·
i can agree with everyone for the most part but i think what hurts the k-series torque at high rpm is VTC. my understanding of the system is, its supposed to help with low to mid range torque on a stock configuration...but if you build it (motor) the problem is keeping the VTC to also keep top end torque going. Niko can you get some graphs comparing hp/tq on motors with VTC and k's without it? I'd like to know where my knowledge stands.
 
#48 ·
This isnt correct.
On a motor with no variable cam phasing such as a B series, you setup the cams and then leave them, you cannot advance/retard them on the fly. Since most people want high end power they dial in the cams so they make most power in the upper rpm range. Unfortunately the midrange is going to "suffer".
With VTC you have the ability to adjust the intake camshaft on the fly. You have X advancement for midrange and Y for top-end ie you get the best of both worlds. The issue isnt VTC or the K-series cant keep top-end torque going, you only assume this since torque looks like it drops of fast compared to other motors. This is untrue as its been pointed out before that the "other motors" are simply lacking midrange torque.
To keep torque from falling on the big stroke motors you need the correct induction/exhaust/camshaft/compression and headport.
I think the only real disadvantage of VTC at high revs is that the gear is quite heavy and would sap some power.....
 
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