While all these dyno predictions are fun, one less exiting element of making sure tuning Monty to the next stage doesn’t end in disappointment, is the part of my brief that dictates…
”I must retain Monty’s sweet idle quality I’ve worked so hard to achieve” .
The truth is over the last 30 years we've all become very used to flawless OEM levels of idle quality with our daily driver cars, so this ends up being the minimum standard we're prepared to accept, back in the day we all put up with a lot of poor engine behaviour we just wouldn't accept today. At this point in the tuning process, I'm relatively confident we’re on the right track to give Monty roughly 200hp and a nice broad spread of torque, but I do anticipate some challenges ahead if I don’t want to compromise on idle quality. As with all challenges in life, I always feel it’s best to anticipate and create a plan to overcome them in advance.
Below are the four key challenges we will face in getting Monty to idle nicely in his next state of tune, I have also listed how I'm planning to overcome each one.
1. An Unstable MaP Signal - Largely the function of the Newman Phase 3 cams. The ECU relies heavily on the MaP signal for my fuel and ignition tables to deliver good results, but also for the effective opperation of the PID closed loop and ignition timing based idle management strategies, an unstable MaP signal is therefore always a bad thing for idle quality!
The Solution - Replace the current MaP referenced Speed Density engine load calculating strategy twith a TPS referenced Alpha-N strategy, but only at idle and during low speed driving (0-5% TPS) and this purely to provide the ECU with a more stable reference to work with. After 5% TPS we will blend back smoothly to the MaP referenced engine load calculating VE (fuel) and ignition tables.
2. Reduced Exhaust Gas Velocity - This is not good for idle quality and low speed driving and again is largely the function of the Newman Phase 3 Cams. However, our decision to take the head further than the A.L Developments recommended the 38mm on the exhaust ports certainly won't help. Being honest, in terms of idle quality we've actually made it harder for ourselves by bringing the exhaust ports out to 40mm, but the bigger ports will give more torque and horsepower over 3,500rpm, and especially from 5,000rpm all the way to the new self-imposed 7,500rpm engine speed ceiling, so we're definitely going with 40mm.
The Solution - Our cam/valve timing strategy detailed below in point 4 will have the biggest positive impact here, but by going no larger than 40mm we have still retained a 1.6mm anti-reversion lip on the primaries, this lip will help to mitigate the negative impact overlap has on idle quality and slow speed drivability by acting as a barier to limit revertion pulse driven exhaust gases coming back into the combustion chamber where they'll promote a less stable burn cycle.
3. Port Size Imbalance - Enlarging the exhaust ports to 40mm and the subsequent loss in gas speed has already been covered above, however number 4 exhaust port is massive compared to the other three as it includes the exhaust gas recirculation void. While I have long since deleted the EGR system by blanking it off, the giant void remains and effectively doubles the size of number 4 exhaust port, this port size imbalance is not going to help idle quality.
The Solution - TiG weld up the void, this will be completed prior to the head going to the mill for all four 38mm exhaust ports to be enlarged to 40mm. In reality the EGR void probably only has a small impact on idle quality, but every little helps and by port matching the head on the exhaust side to match what A.L Developments achieved on the inlet side of the head will certainly give further gains in torque and horsepower over 3,500rpm, and especially from 5,000rpm all the way to 7,500rpm.
4. The Newman Phase 3 Cams - These cams are really the biggest enemy of a refined idle, unlike my current mild Phase 2s I've been running for the last three years, the new Phase 3s are now far more your traditional 'Fast Road' camshaft specification, they deliver quite a step up in valve overlap which is never good for idle quality.
The Solution - Advance the inlet cam by 1 degree to move the overlap away from the target idle for less exhaust contamination within the combustion chambers especially with the lower gas velocity we've introduced by bringing the exhaust ports out to 40mm. The effect of advancing the inlet cam by just 1 degree from Newnan’s base settings should ultimately deliver a more stable burn cycle that will promote significantly improved idle quality.
The rest is all really down to the way we calibrate the excellent closed loop idle management features within my EMU Black ECU, I used these features to great effect to deliver a beautiful 'drum roll' 970rpm idle on my Phase 2 cams. However, I strongly suspect even if we full optimise the potential of the PID IDACV management and ignition based idle management strategies, and even after implementing the above four solutions, I think it's highly unlikely I will be able to keep my 970rpm target.
Maybe I'm wrong and we'll be able to get Monty's fully warmed Duratec to
'purr like a kitten' at 970rpm on the Phase 3 cams after all? However, to be honest if we end up having to settle on 1,100rpm or anything a little below I really don't have any issues with that, what I 100% will not accept is any lope, hunting or choppiness.
Wish me luck with this one chaps
