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PostPosted: 15 Aug 2016 15:38 
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While researching for some new cams I came to the conclusion that I think the internet cams specs for the mivec lift is incorrect. We believe that the lift are as follows:
Inlet low speed: 7.58mm
Inlet high speed: 10.41mm
Exhaust low speed: 8.24mm
Exhaust high speed: 9.38mm

I am unsure how these measurements got calculated?
Looking at the 4G9x manual it lists nominal cam hight as follows:
Inlet low speed: 33.58mm
Inlet high speed: 36.41mm
Exhaust low speed: 34.24mm
Exhaust high speed: 35.83mm
I don't know what the base circle or the rocker ratio is. But no matter what values I use I cannot get them to equal the internet specified lift. Unless the base circle is different for all 4 lobes? I doubt this is the case but does anyone have any cams out of the car (or cam cover is currently off) that they can measure the cams base circle?
And does anyone know the rocker ratio? I read a long time ago 1.544 from Kelfords but I'm not 100% sure on this? Or does anyone have a rocker out of the head and can measure this?

I find it interesting that the measurements in the manual show a 0.5mm limit on the cams. This by the approx rocker ratio of 1.544 would give a lift loss of almost 0.8mm before they become "out of spec"
NA or turbo that's potentially a bit of hp lost.

I'll end up pulling my car apart to get these values as I like to know things but if someone can measure them for me it would be greatly appreciated.

Regards
Jason

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PostPosted: 15 Aug 2016 19:54 
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The only way to get the correct numbers is to do your own measuring.

If it's only the lift you're concerned about, it's really easy.
If the cams are out it's the difference between the narrowest and widest points on the cam, times the rocker ratio.The actual rocker ratio varies throughout it's lift, nominally about 1.6.
The other way, you just need a dial gauge on the valve. Measure it directly.


I've done all this with the Diamante 30M cams.
They won't be the same as the 4G92 cams but should be close.

viewtopic.php?f=29&t=6760&hilit=degreeing+cams

Cut and paste.
...................................................................................
The intake cam lift is, 3.6mm, valve lift 6.8mm small cam.
big int cam lift 5.8mm, valve lift 9.5mm.
Small ex cam lift 4.2mm, valve lift 7.5mm.
Big ex cam lift 5.6mm, valve lift 9.5mm.
...............................................................................


The rocker arm moves in an arc so as you can see, it's not a fixed ratio, they never are, so as per normal, hardly anyone ever figures it out. It's even too hard for the cam manufacturers.

I could well have made some measuring mistakes but nobody will point them out because nobody else will bother measuring, they just like to buy sub standard aftermarket parts which are shiny.


I can't realistically see anyone's aftermarket cams being better than stock. Not without having more lift or more duration or both, then they've got to be dyno tested to prove it.


So the short of it is that all specs are wrong until proven otherwise.

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6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 15 Aug 2016 22:49 
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That's the issue I'm having. I've been quoted 272 deg cams at 7.6mm lift. This appears to be not enough lift and 272 deg doesn't really tell me much without telling me it's x at 1mm lift.
I've degreed the mivec cams. 240 deg at 1mm inlet and 228 deg at 1mm exhaust. But I didn't check the lift of the cams when I did it and it was only recently I thought about the valve lift being possibly incorrect.

Why is the rocker ratio dynamic? Isn't it the measurement from the top of the valve to the rocker pivot point and then the measurement from where the cam rubs on the rocker to the rocker pivot point. Then the difference is that calculation?
I haven't really looked into this much. I just have been recently due to thinking a slightly smaller duration with more lift might be better suited to the rpm range I want to use. (Under 7500rpm)

Thank you

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ADR 37/01 Legal.


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PostPosted: 15 Aug 2016 23:05 
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A quick google and I know understand why it's variable. Looking up honda stuff is helpful. Similar to the mivec but obviously a lot more information on them.

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PostPosted: 16 Aug 2016 10:43 
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A 272 degree cam is an upgrade on something like an Evo but it's totally rubbish compared to what you get on a mivec out of the factory.

When you degree a factory solid lash adjuster cam, it's good to do it at actual lash too.
272 is the advertised duration that you would get at working lash.
Measuring a cam at 1 mm or at .050 tells you nothing about actual duration, it's just for comparing one cam against another cam at the same lift.
Typically the mivec cams will be 260 ish and 300 ish deg at working lash.

Yes Honda stuff is useful for info.

Nissan have a version too for the SR20 it's quite similar....the VE head.

Maybe there's info on that?


You can never spend too much time measuring things.
The more you know the better.
The more you know, the more you realise everyone else just makes it up.
The more you know, the more you know that people who work on cars for a living tell lots and lots of lies.
Salesmen are the worst.


It's like those adjustable cam gears. They need measuring too because the zero marks are never at zero.You NEED to know where zero is before you can make adjustments to them.
Or better still, don't bother wasting your time with them, mod the stock ones instead.

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6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 17 Aug 2016 16:16 
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I agree the mivec cams are better then most cams for their intended purpose. But for me with a turbo on it and not wanting to rev it to 8500 rpm i think there migh be some advantage with smaller cams.
Measurements at 1mm are important to compare against each other as well as hp potentail as not all "272" cams will be the same.

I'll hopefully measure stuff this weekend and have some solid data to go by. I'm actually hoping to get more measurements and actually work out the lobe centreline rather then calculating it like I did last time.
And your right about the cam gears. I will even measure the cams and then adjust the gears by 10 degrees and check if my measurements change by 10 degrees. (Maybe all the markings are slightly wrong on the gears)

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GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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PostPosted: 17 Aug 2016 17:55 
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There's only really 2 ways to make power.
One is with boost (torque), the other is with revs. Torque x revs = power.
If you don't want to rev it out hard then you've got to give it more boost and if you're going to do it that way there's no advantage to using the mivec.


Once you measure a few more things you'll also figure out that pretty much every commonly accepted mod is a fail in some way or another.
Like fitting bigger fuel pumps and hotwiring them and using aftermarket FPRs.
The end result is always higher uncontrolled fuel pressure...........but the owners don't know because they don't understand the reading that they should be getting on a gauge.

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6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 17 Aug 2016 18:40 
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I still think there is a benifit to mivec even without the rev's. Even if the mivec is there for idle and cruise (ecconomy) and then change over the cams at a certain boost & revs to cams that will suit the desired power.
I'm fussy with idle and fuel economy but want to make big power. So this works for me.

I agree most mods are a waste of time. In your example I have used the stock reg and an intake walbro 460 lt pump. Unlike most I've adapted the later model EVO resister pack (2 actually) to drop the voltage low enough not to overrun the reg (upgraded lines both to and from the tank also) then the motec switches the relay at a certain RPM and boost to maintain fuel pressure.
Although this isn't ideal as its more things that can possibly go wrong it's still better then 60psi fuel pressure at idle or a cheap aftermarket fpr (even if it's expencive it's still probably cheaply made)

Anyway doesn't look like anyone else has the info I need so I'll just try and squeeze it in this weekend.

Regards
Jason

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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PostPosted: 17 Aug 2016 19:31 
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The way around the fuel pressure problem is to use multiple stock regulators in parallel.
Stock fuel pressure depending on the car is usually 3 bar or 43 ish PSI.
Most people don't understand that with the vac line connected, the usual spec for the fuel pressure at idle is 33 PSI. That's what you have before mods. Usually after doing it all wrong you end up with 38 or more PSI at idle which totally cocks everything up.
In my own case I'm using 2 walbro pumps in 3 stages, also using 3 stock FPRs in parallel and the fuel pressure is "perfect".
Perfect in that it's 100% stable at idle at 33 PSI even with one pump running at part speed (resistor) AND the second pump (manually activated because it won't normally run at idle) running at full speed.

But anyway, seems like you know what you're doing.


Back to the mivec........the longer cams you get with the mivec go well with bigger turbos.
If you've got shorter cams, they'll work best with a slightly smaller turbo.

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6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 17 Aug 2016 21:40 
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Your fuel system sounds interesting. Why 3 regulators though? I would have thought 2 could have done it. Do they all have there own return to the tank?
Mine is better then most but still isn't perfect. But I haven't seen any I'll effect from it. Although as I type this I do find the mixtures are a little leaner at idle and cruise when the car is hot (30 mins plus driving) I might take a look at fuel pressure as maybe this is varying slightly due to slightly overrunning the reg (No other sensor varies but I never really paid attention to the oil pressure)


I agree with the big turbo suits big cams. If the mivec cams suit a NA with a pressure ratio of approx 1:1 across the head then that'd what you need to achieve with a turbo which generally means a big hot side.
To small of a hot side and you end up with a pressure ratio that doesn't suit the cams.
I actually have significantly higher inlet pressure the exhaust pressure. Which is leading me towards an engine that is overscavanging (only a theory) and hence why I'm looking at cam details and perhaps main them smaller.

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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PostPosted: 17 Aug 2016 23:17 
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Jayz-1 wrote:
Your fuel system sounds interesting. Why 3 regulators though? I would have thought 2 could have done it. Do they all have there own return to the tank?
.


A single stock regulator gets outflowed by a walbro pump even at low voltage (resistor fed)
Adding a second stock reg in parallel cures that problem.
In the case of 2 pumps running together, the 2 regulators are outflowed.
The 3rd regulator cures that.
The second pump sits inside a 2 to 3 litre tank near the radiator.
The returns from all 3 regulators fill that tank which then overflows back to the main tank.
That means that the auxiliary tank is always full and I've theoretically got a 1200HP fuel system with perfect regulation. I've also still got stock fuel lines from the main tank to the engine compartment which I've never had any intention of changing.
The second tank on it's own has enough capacity for over 1 min at full load so it's sufficient but there's no reason I can't make it a bit bigger. It's made from a piece of 5 inch exhaust pipe so nearly bullet proof.
Everything has been pressure tested and flow tested. The second pump kicks in with the mivec at 3500 or 4500 (half way to the rev limiter) depending on which ECU I'm running, I can also switch it on manually as an over ride. I've got 2 different stock ECUs with slight differences / modifications.

I'm not interested in aftermarket FPRs.........they're all junk.They leak down when you shut it off and don't flow enough. Also low quality and don't last any length of time. All factory parts are superior.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 22 Aug 2016 11:26 
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So about 8 or so hours of my lift gone measureing these cams at ever 0.001" but I'll only list the common measurments people use.

All Base circles measure up at 30.00mm

Inlet small
Cam 33.40mm
Lift 5.44mm
Duration at 0.10mm - 221.5
Duration at 1.00mm - 175.5
Duration at 0.05" - 168.5

Exhaust small
Cam 34.3mm
Lift 6.73mm
Duration at 0.10mm - 230.0
Duration at 1.00mm - 183.5
Duration at 0.05" - 175.0

Inlet big
Cam 36.4mm
Lift 9.53mm
Duration at 0.10mm - 278.0
Duration at 1.00mm - 240.0
Duration at 0.50" - 234

Exhaust big
Cam 35.7mm
Lift 8.76mm
Duration at 0.10mm - 278.0
Duration at 1.00mm - 227.0
Duration at 0.50" - 220.0

Things to note 0.10mm was difficuilt and anything smaller to measure was inconsistent. (Any measurement above this was consistent within +/- 0.5deg)
Lift is about 0.8mm smaller then the internet suggests on the big cams and about 2mm on the small cams
Measurements were with the 0.1mm inlet and 0.2mm exhaust valve lash. With no lash the duration was about 3 deg more at 1.00mm. But got progressively more at lower valve lifts.

Little dissapointed in the lift. But the duration at 0.10mm and 1.00mm matches the Kelford 280 specs (other then the kelfords 11mm lift) for the Evo.

Anyway that's the info I have for anyone interested.

Regards
Jason

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4G93 Mivec Turbo.
GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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PostPosted: 22 Aug 2016 15:25 
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Also for my engine both the inlet and exhaust centerline was retarded by 3.5 deg cam (7 deg crank). Probably due to the taller 1.8lt block.
So for those with a 1.8 block it is definatelly worth checking and not just having the cams at "0".

Also my cam gear markings were spot on as after I adjusted them I rechecked the valve timings.

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GT3076, Motec, Forged etc.
ADR 37/01 Legal.


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PostPosted: 23 Aug 2016 13:05 
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Jayz-1 wrote:
So about 8 or so hours of my lift gone measureing these cams at ever 0.001" but I'll only list the common measurments people use.

All Base circles measure up at 30.00mm

Inlet small
Cam 33.40mm
Lift 5.44mm
Duration at 0.10mm - 221.5
Duration at 1.00mm - 175.5
Duration at 0.05" - 168.5


Jason



You've got me a bit confused here, so I'll just quote the top bit.


If all the base circles are 30 mm, that's the cam diameter at it's narrowest point.
If it's 33.40 at the widest, that's 3.40 mm cam lift.
The 5.44 mm is then valve lift?
Duration at 0.1 mm (close to working lash), I'd expect to be at least 250 deg?


Did you get any numbers for intake opens, intake closes, exhaust opens, exhaust closes?
Then you've got overlap too?


Jayz-1 wrote:

Inlet big
Cam 36.4mm
Lift 9.53mm
Duration at 0.10mm - 278.0
Duration at 1.00mm - 240.0
Duration at 0.50" - 234




So same goes here, 6.40 mm of cam lift, 9.53 mm of valve lift and 278 deg of duration, which I would have expected to be a bit longer, but maybe not?
Maybe that's where the RS cams come in?


Good work, it's good to see some real measured numbers.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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PostPosted: 23 Aug 2016 13:14 
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Cutting from your top post.
Book numbers.

Inlet low speed: 7.58mm
Inlet high speed: 10.41mm
Exhaust low speed: 8.24mm
Exhaust high speed: 9.38mm

Then your measurements.
Inlet small Lift 5.44mm
Inlet big Lift 9.53mm
Exhaust small Lift 6.73mm
Exhaust big Lift 8.76mm

It doesn't quite fit with the spec, but it's to be expected.
Maybe there's been a few revisions over the years?
If you never measured, you'd be relying on nothing other than guesswork, like everyone else does.

_________________
6G72 mivec Twin TDO5 20Gs up and running.
6G72 mivec bored and stroked to 3.4 litres...Frankenmitsi build
6G74 mivec bored and stroked to 3.9 litres....Frankenmitsi build.
6G75 under construction....4.2 litres bored and stroked.Another Frankenmitsi.


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