Restriction In The Exhaust

[zebra]

Tyres diff all same, stock ecu and nistune I was doing 100km/h in 5th at 3000rpms, PFC now I'm doing 2600rpms -normal motorway cruising. And no gay 22" rims, running 18" RAYs wheels

so how do I know what tyres you have............

[rondofj]

From my sig, sir

[GTSBoy]

If it's 2600 vs 3000, then at 7000 indicated it should be really revving to 8000, if the error remains linear.

The tacho (whether in the ECU or at the tacho itself) is a pulse counter. There is no "voltage" to get wrong. If it's counting pulse wrongly at the ECU, then that doesn't bode well for all sorts of things. After all....the whole point of the ECU is to know exactly how fast the engine is turning over, no?

I would be looking into this problem as a matter of some concern. Do not sweep under the carpet.

[XKLABA]

Hey just a quick one, where does the ECU get its revs from ( rhetorical question ), could it be the CAS playing up maybe

[rondofj]

Maybe you guys are onto something...it looks like its pointing to the CAS again. Scotty had pointed that out earlier when it was running inconsistently with the Nistune, its not now.

[Manuel Kasko]

Maybe GTScot is right,

Not maybe, His right unless they decided to change your diff or you are wrong.

[Badgaz]

most dyno's will have an inductive loop to measure rpm off cylinder 1....i wouldn't trust the gauge to be dead accurate.

[Ben C34]

most dyno's will have an inductive loop to measure rpm off cylinder 1....i wouldn't trust the gauge to be dead accurate.

Nothing to do with dynos currently being discussed....

[Badgaz]

i guess i offered that as a way he could check his speedo/rpm gauge calibration...what are you the f**kin forum police?

[zebra]

Just worked it out

with a 245/40/18 tyre

100km/h should be 2500rpm in a R34 GTT manual

[Ben C34]

i guess i offered that as a way he could check his speedo/rpm gauge calibration...what are you the f**kin forum police?

Settle down Bro! Are you having a bad day?

I guess I didn't guess that by your post.

Going on to the dyno to check it would be an option,, as would using an automotive multimeter with tacho function to compare stock gauge (you could buy a multimeter instead of paying for the dyno hire)

But that's not really the issue. The fact that it changed by only changing ecu implies to me that there might be a problem.

[Badgaz]

my speedo is currently having problems...i fix it by bashing it(not recommended..breaks windscreen).....mine doesn't like going above 60km/h until its warmed up...but i'm curious as to wether its his RPM or speedo that is incorrect....the speedo drive/sender is off the gearbox right? and the rpm is signal. It could be just a coincidence that it happened when ecu's changed?

[hy_rpm]

I'm not guessing wildly

Are you a mechanic superben ?

Do you even work on cars your self or just pay people to do the work

Is has been proven time and time again larger cams than std always shift the powerband higher on any car

Yes you will gain power up top but is it worth the loss down low which is up to owner and driving style choice and purpose

Yes you can get the manifold runners tapped and check the egt and engine backpressure under load on the dyno to confirm but the price to get that all done you could have gone to a new rear housing but do as you like it's your money and time

[hy_rpm]

The rpm signal is usually sent to the ecu first and then cluster

So to confirm if the cluster is out is as easy as comparing the rpm on the ecu to the cluster

[Badgaz]

i take it that thats the same for speedo too?

[Ben C34]

I'm not guessing wildly

Are you a mechanic superben ?

Do you even work on cars your self or just pay people to do the work

Is has been proven time and time again larger cams than std always shift the powerband higher on any car

Yes you will gain power up top but is it worth the loss down low which is up to owner and driving style choice and purpose

Yes you can get the manifold runners tapped and check the egt and engine backpressure under load on the dyno to confirm but the price to get that all done you could have gone to a new rear housing but do as you like it's your money and time

Yes I do ALL of the work on my car . Amongst other things I wired up the ls coils, put the rb30 bottom end in, do all tuning and recently put some type b cams in. Not that that is particularly relevant.

You are guessing as to how much the power band will shift. Typically better cams will have more lift which will create more flow all over and therfore increase power in all parts of the Rev range, making the shift to the right not as bad as you would imagine.

Have you put in cams? Not that I care.

[Ben C34]

i take it that thats the same for speedo too?

Nope. It goes to the speedo direct then to the ecu.

Certainly odd that it's the opposite of the rpm signal.

[hy_rpm]

Yes I've replaced plenty of cams and a mechanic by trade so work on cars day in day out

I ve driven a few cars before and after performance cams are fitted and yes you won't notice the power loss if you have a heavy foot and drive in the powerband of the new cams everyday but most people just give it a squirt here and there and ain't alway revving above 4000rpm

dailying it and cruising will be where you feel and notice the power loss downlow between std cams and performace cams

[hy_rpm]

That's why vtec or vvl was produced so as to not sacrafice power downlow there is 2 cam profiles used and switched at certain rpms

[Ben C34]

Ok. As per any mod it comes down to personal situation and preference.

Just to clarify it is the duration that shifts the power band.

The extra lift increases flow all over.

I was saying you were guessing at the 50kw loss at 4000rpm. I wasn't arguing the potential of a loss somewhere.

I also changed turbo, and put on water injection, at the same time as the cams so can't make a direct comparison on the loss, but for reference from an older thread

my car has a different turbo setup but thought i would gilve ,my 2 cents,

found with stock cams my car was making 321awkw and then with poncams 260 9.15's went up to 344awkw, boost was came on sooner with more midrange and topend torque/power, was quite happy with the results,

will be good to see the setups you guys have and see the differences in power with/without cams,