Lets talk about cams

[RS2000]

The torque figures shown on the dyno printout are derived values and not the true torque value,

I'm confused. If were talking about the torque figures shown on the screen in Stan's video, shouldn't the above read:

"The torque figures shown on the dyno printout are NOT derived values and not the true torque value"

I thought derived torque was 'derived from the calcs' ?

[Magpie]

The video does not have RPM and you can't see if any correction has been made for final drive or gearbox ratios.

[hks_kansei]

Dyno torque measurements are after gearbox, final drive, and wheel/tyre sizes which all effect the measurement ny providing a reduction to the gearing (except in the case of overdrive gears)

It's the old leverage thing, longer handle gives more force/torque at the expense of more movement.
If you did a Dyno run in 1st you'd have a HUGE torque number.


There are sums to work it out, none of which I can remember.

But when I had my Mondeo it's dyno sheet showed torque at 400nm.
I did the sums, using the RPM it made max torque at, and the end result was somewhere in the region of 170nm, which was nearly spot on with what the factory spec said in the manual.



Basically, using Dyno torque as the figure is kind of like me lifting a 500kg weight with a block and tackle and then telling people "I can lift 500kg"

It's accurate in that it is legitmately what the car is putting to the road, but it's not what the engine makes. (Dyno a stock NB8B with a 3.6 diff then put in a 4.9 and you'll see torque jump)

[slug_dub]

looks like I had a massive 134 Nm of tourque

Wikipedia says that the B6-ZE in the MX5 made 136 Nm, so is wikipedia listing that as at the wheels or not at the wheels? (maybe wikipedia is full of crap )

[StanTheMan]

well
(142hp x5252)/7500=99.43 pnd-ft = 134nm at wheels
if the drive train has 25%loss
(177.5hpx5252)/7500=124 pnd-ft = 168nm at crank
that would net 32 Nm extra netted by CAI, Exsaust & 272 cams & stand alone ECU on an otherwise standard head & bottom end from OEM figures

bit different to 100% increase in torque. Which I thought it was.

It will be interesting to get patchy on a Dyno now. I'll wait until Ive installed adjustable cam gears for that. it will be nowhere near that just yet.

There I was thinking for a moment shite Ive had more torque than magpie with his agressive cams & throtle bodies. LOL

Thats why I asked. just seemed wrong.

[StanTheMan]

OK sorry Just worked out the correct RPM
NB8B wheels 538.687 rev for 1 km
4th gear 1:1 OEM 5 speed. max speed is 193 km/h
diff 4.1 torsen
(revolutions x speed)/60= rpm of wheel
rpm of wheels x Diff ratio = engine RPM
Right?

RPM=7104

Torque3 at wheels
105ft=pnd = 141nm
Torque at crank with 25%loss (assumed)
131 ft-pnd = 177 Nm

not that its really relevant.....sorry about that diversion.

cams....mmmm cam Gears. getting those in a little while when wifey is not looking

[madjak]

* when does the ports become a restriction for cams? For example are the ports to small for +10mm of lift?
The more lift the valve has the more air it can flow. But changing duration has a bigger impact than lift
* when should people start considering solid lifters? For example they want to rev their car to 8,000rpm at the track for multiple laps.
yes anything over 8000, or earlier if you install very high lift / high duration cams, or larger valves.
* when should the valvesprings be upgraded and when should doubles or upgraded singles be used?
Valve springs hold the valve against the cam. So as the max revs and/or the cam ramp angles increase due to lift then so must the springs. I was told by a builder that they now install the heaviest spring rate by default for any serious build. The higher spring rate of the Supertech Duals actually reduce cam wear over lighter springs because it stops any chattering of the valves at high revs. This chattering causes more wear than the increased friction due to the higher spring rate
* when does the standard valves become a restriction? i suspect that valves will offer more restriction than the ports but when does this happen if ever on a "hot" street cam.
They are a restriction as stock, but so is everything else. As you upgrade cams, ported heads etc the valve size becomes a bottle neck and has to be increased too. I actually think exhaust valve on a BP is the biggest restriction and just increasing the exhaust valve size, and adding good headers and an exhaust will work well even on a totally stock engine
* when does the throttle body become a restriction? this would not apply to a street car i believe, again correct if wrong. i think the skunk 2 or similar could be cheap insurance though on bigger cams due to harmonics and the throttle shaft but lets hear from people who know im mearly speculating.
The stock throttle body is never a restriction, however it is a liability. They get changed solely due to the throttle shaft failure rate on high reving engines. Maybe on the highest end builds stepping up to a larger throttle body will help a bit. I'm running a 70mm throttle body because it bolts up to my manifold and shouldn't break...I hope

Really you can think of upgrades like Intake flow, ported heads, bigger valves, bigger cams, larger exhaust headers, free-er exhaust as all being multipliers to power. Change any one and you'll only see a small net effect on power, but increase all of them together and you'll see a compounding multiplication effect to the power. But if any one is left as a bottle neck the gains in all the others are slashed. That's the trick to upgrading cams, it's all got to be done in balance with everything else to get optimal horsepower which is the hardest part. You need to set your goals and work to that target...

Really there are two builds that would be most common dríven around one upgrade due to cost. That is, is the head going to be ported or not. If not then you are targeting a lower end build with 272 degree cams and 10mm lift. Stock valve sizes are maybe ok, but upgrading them 1mm in size might be worthwhile and not that expensive. If you are porting the head, then you are really going the whole hog for max power.

[NitroDann]

looks like I had a massive 134 Nm of tourque

Wikipedia says that the B6-ZE in the MX5 made 136 Nm, so is wikipedia listing that as at the wheels or not at the wheels? (maybe wikipedia is full of crap )

Crank.

And kansei, the dyno can read in flywheel HP after driveline losses. Thats what I use.

[hks_kansei]

And kansei, the dyno can read in flywheel HP after driveline losses. Thats what I use

I've seen that, but don't some brands/settings use different methods for the calculation?

Some read drag as the car ramps down, and dont others just apply a rough estimate of 20% or whatever?

And I'd assume some rely on a more correct equation taking ratios etc into account.

[NitroDann]

Dyno knows rpm, dyno knows rwhp, dyno calculates torque, from hp, which is after losses.

[speed]

Casting faults aside, I understand that heads need to flow but also thought even flow was more important for generating power. True ?

[madjak]

Casting faults aside, I understand that heads need to flow but also thought even flow was more important for generating power. True ?

Yes every port needs to be balanced otherwise one cylinder will be seeing more air than another and will take more load. I'm not sure how you go about evening up ports when you don't have a flow bench. Even with a flow bench there must be a lot of trial and error to get it all balanced. I'm not sure if even flow is better than uneven higher flow though. If you are talking DIY porting then as long as each port is withing 5% you are probably ok. I suppose the concern is one cylinder running leaner than another which is getting more air... in that case 4 x EGT sensors might be useful to trim each cylinder.

Of course the best way is to use a CNC machine to make all the ports identical however that's not exactly a cheap option. I did check to see if a head will fit on my CNC bed and it will. However I can only machine from the top and side as it's basically only a 3-axis machine at that bench size... still it would make porting much faster and more accurate having 80% of the port already machined.

[StillIC]

Trying to balance flow through ports accurately is pretty much a waste of time IMHO. For these reasons:
-why would you limit a port than can flow more than another, say in a non-ITB arrangement, when you can happily just accept that one cylinder might make a bit more power? I do accept that with ITBs you would want to make up losses on a 'bad' port.
-the fuel mixture can be set so that discrepancies between the air intake of different cylinders still gives maximum or more than 99% of maximum power with same amount of fuel delivered, within a 12:1 to 13.2:1 air:fuel range.
-maximum flow of the port only matters when the valves are fully or almost fully open, for those few degrees of cam rotation.

CNCing is great, but I hand ported my heads taking two dimensions (height and width) every ~5mm port length, to the nearest 0.1mm, and porting to that tolerance. I did this to get the shape correct (taper in, constant section, then taper out to valve, all of reasonable proportion), rather than to make them all equal (although they are all pretty close as a result).

Getting the ports 'right' is more important than getting them the 'same' although I admit one leads to the other.

[speed]

My query came from a conversation with a race engine builder. He said that you can have a ported polished head that looks beautiful but doesn't perform. He then altered those very ports to flow evenly and gained a stack more power.

Maybe it makes more difference in a race engine but I would think the theory should still be the same.

[NitroDann]

If you cant dazzle them with brilliance..