A VVT question

[GordonD]

If the phaser advances the inlet camshaft 16 degrees at 1450 rpm and retards it again at 6800 under control from the ECU, why haven't I heard anyone mentioning:
(a) that upper limit being moved up by the same amount when ECUs are rechipped and the rev limit is increased?
(b) that upper limit being put above the rev limiter maximum so you can go all the way to the rev limit without losing power?

 

[skinner]

Do you know for sure that it retards at 6800? Iv'e heard 3 different figures on here.

I wondered if the original group n ecu advanced it all the time, this might explain the daft idle speed.

 

[edde]

If the phaser advances the inlet camshaft 16 degrees at 1450 rpm and retards it again at 6800 under control from the ECU, why haven't I heard anyone mentioning:
(a) that upper limit being moved up by the same amount when ECUs are rechipped and the rev limit is increased?
(b) that upper limit being put above the rev limiter maximum so you can go all the way to the rev limit without losing power?

Its also when oil temsp are high enough (or coolent i forget which) and when the MAP is showing 750m bar +

No need realy to fiddle with the cam timing for turning on and off it turns off at high rpm as it infact helps keep the power up high rpm levels.

I wondered if the original group n ecu advanced it all the time, this might explain the daft idle speed.

Nope advance it all the time and the engine sounds like a tractor at idle.

 

[stan*]

No need realy to fiddle with the cam timing for turning on and off it turns off at high rpm as it infact helps keep the power up high rpm levels.

so by reducing overlap you gain at higher rpms? how does this work lol



Gordon, its likely de-activated only when MAP figure is below xxxbar ASWELL as the rpm limit.

 

[edde]

No need realy to fiddle with the cam timing for turning on and off it turns off at high rpm as it infact helps keep the power up high rpm levels.

so by reducing overlap you gain at higher rpms? how does this work lol

No idea on that benR and the old captain slarty (thats a name going back a bit) had a few good arguments over it.

 

[bmh.01]

Controlled by coolant temp not oil temp edde. Would be better with oil temp though imo.

 

[BenR]

Quite simply, renault are cheap. They make cheap pistons that fail easily with excessive rpm, and thus the power dive at 6800 forces a gearchange.

Those who have 7800-8000rpm limits and live at them on track often, will be likely to see failure.


Cup racers are limited in rpm for this precise reason, and it is a renaultsport technical note that pistons will fail at above 7200rpm constant use.

In my opinion, i dont really bug renault about such a small issue, but there is no real reason to r****d the timing at peak power as normally the power should peak, hold then tail off.

 

[Fred@BTM]

blokey who looks after the r-sport engines has never had a problem with the pistons mate, he has had rod bolts let go though

not sure what the formula renaults rev to, think its only 7500

 

[BenR]

Neil wont have as the stock type engines were all limited.

I have never seen a problem related to rod bolts.

 

[GordonD]

The point I'm trying to make is that there's two possible scenarios.

The 1st is that the camshaft retarding 16 degrees at 6800 rpm makes no difference to power. If that's the case why did Renault bother doing it?

The 2nd is that the camshaft retarding 16 degrees at 6800 rpm does make a difference to power. If that's the case why don't engine tuners delay it for another 400 rpm until 7200 (or wherever) rpm when the rev limiter cuts in? Whether the pistons can survive prolonged use above 7200 and whether its them or the rod bolts that fail is a matter of where you put the rev limiter maximum. This isn't a question about where you set the rev limiter to, is a question a whether you can easily get more power above 6800 rpm just by tweaking a setting in the ECU. It doesn't take a lot of modifications to 172 or 182 engine to get it to the point where its power peak is above 6800 rpm.

 

[BRUN]

captain slarty !!!

thought he might have made a come back, never did though

 

[Fred@BTM]

last time i spoke to him he was in the med! that was years ago though

yoz's was a rod bolt failure, but it did rev to 8K for 60K miles!

i reckon someone needs to do a power run with and without the vvt connected, it does sound different with it disconnected

 

[BenR]

i cant remember yoz's being a rod bolt failure.

 

[Fred@BTM]

well we never did figure it out, but one of the rod bolts was missing its head and the cap was bent round

 

[BenR]

well that will happen on a full bore failure lol.

 

[Fred@BTM]

lol, it was a mess! ah memories

 

[BenR]

i blame yoz............renault were just the victims of his abuse.

 

[Fred@BTM]

yeah true LOL! it was using a bit of oil before hand

 

[ben_p]

Quite simply, renault are cheap. They make cheap pistons that fail easily with excessive rpm, and thus the power dive at 6800 forces a gearchange.

Those who have 7800-8000rpm limits and live at them on track often, will be likely to see failure.


Cup racers are limited in rpm for this precise reason, and it is a renaultsport technical note that pistons will fail at above 7200rpm constant use.

In my opinion, i dont really bug renault about such a small issue, but there is no real reason to r****d the timing at peak power as normally the power should peak, hold then tail off.

ive missed posts like this ...