Correct Tahoe, Mine was around 9.5-9.7:1 looking through the actual data (even though chart can't read below around 10.5:1). Although I do agree that the OEM cats are restrictive thereby creating a lot of heat, I do not believe it is nearly enough heat to burn a valve. Our cars do not come with shorty log manifolds with primary cats immediately after them (these style setups create tremendous heat & pressures pre-cat). Instead, they have long tubular primaries with the catalytic converter much further back in the system so the pre-cat air volume is significantly larger than on most modern applications. In addition, there are many Ford owners with significantly more HP running much higher EGTs on OEM catalytics without having any issues whatsoever. In theory I agree those statements can be true (as are any extreme examples), but in this specific application in stock form it seems a bit overly cautious.

I will be taking my OEM cats off sometime in the next few months and I will post pictures to show if there is any damage of any kind and post the pictures for reference. Either way ... I will be upgrading cats to a high flow cat for more optimum air flow in conjunction with the RPI exhaust. I am curious to see if it will pick up more low end to mid-range torque, or if it will again be more high end HP. Both are great outcomes, but I would prefer more torque.

With that said, I think I have figured out the cure to the torque / throttle response problem on the 4.3Ls ... but that is for a later date.
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[QUOTE=jaymoney;3203888]Very informed comments, i think you have summed up the issues perfectly.

For 4.3L I managed 100BHP per liter for the GT4 series race cars- this performance level did feel quite magical at that time (2005) and was adequate enough - but we expect more now.
How was that performance achieved? - simple, its not rocket science nor brain surgery - low flow catalysts and cylinder head porting not cost effective for volume production. The important point here is the catalyst, many of you have mentioned how restrictive is.. and it is... but it is absolutely necessary to pass worldwide emissions legislation. The inlet cams are 256 duration with 10.9mm lift (from memory, could be the odd .mm out)- which is pretty aggressive for a road cars. But try and pass cold start emissions and drive up the first hill on the cycle with those cams, its a real struggle. Back off from these cam settings though, and lose performance. The correct answer would have been variable valve lift technology to decrease inlet valve lift at start, to say, 7mm lift. This way you get the emissions pass at 7mm and get the performance at 11.0mm - not rocket science as there are manufacturers using this tech in production today, but a cost in tooling and development the factory could not meet. Way around this catch 22 situation - make the catalyst as big as possible and load it with as much exotic metal as possible, creating a half-way house. A loss in performance due to exhaust gas flow restriction yes, but not as much as trading camshaft dimensions to get an emissions pass to sell the car. I paint this picture to show the desperate struggle to get any car into production with some form of performance increase over previous model and not part of a more sinister grand master plan.

Now the car is out of warranty and owners complain of poor performance in 2011- in steps aftermarket tuner and fits a 200 cell density catalyst without any hope, or care, of passing the stringent emissions legislation the factory had to contend with, and achieves massive performance gains that makes people question if the people at the factory knew what they were doing. Arhh, people will say, there are auto makers out there with big power output who pass the same emissions standards - Yes, but those guys pull off the bigger parent / group companies for parts, shared development, tooling and relationship with suppliers who give new products at the best prices. Little old Aston Martin is on its own and has little money spare for development.

I hope this paints a different picture, as the small changes to V8 performance output across time was ALL they ever had in their back pocket. So although it looks a dubious walk (4.3L > N400 > 4.7L > Vantage 'S'), it is as Stuart suggests, reactionary and compliant with constraints. Unlike BMW lets say. The BMW mini one Vs cooper is a classic example of 'staged' paid for performance. The only difference except for the price between these two cars is a throttle map - at least Aston have never done that - yet....

 

Are you saying the standard ECU is 9:1?? or after ECU reflash the fuelling is 9:1???

 

Mike, so in the long run do you think one can expect to experience any sort of engine damage using less restrictive cats? Or what is your take on that?

 

I'm a fan of the truth, even when I'm not a fan of the truth. Thank you for responding here.

 

Thanks for addressing those questions, Mike.

Just so you understand, I didn't mean to suggest that you or your team was intentionally hamstringing the motor...I think the limitation came from higher up.

It seems odd to want to be an "engine company" and then prioritize the engine funding as last on the list, doesn't it? And Dr. Bez did come from Porsche, who is the master of exactly this kind of thing...a new model with a few more hp every year, keeping people coming back for more. It's very good from a business perspective, and while they may not have expressly stated it to you, they were indicating where they wanted the performance to be based on the amount of development dollars they were doling out to you.

Not to be argumentative, as I really appreciate your perspective, but it's just that I have a feeling there is more to it than any of us know.

 

[QUOTE=007 Vantage;3204593]I do not believe it is nearly enough heat to burn a valve. Our cars do not come with shorty log manifolds with primary cats immediately after them (these style setups create tremendous heat & pressures pre-cat). Instead, they have long tubular primaries with the catalytic converter much further back in the system so the pre-cat air volume is significantly larger than on most modern applications.

It's all about what happens inside the combustion chamber and what the gas temperatures and pressures are when exiting the cylinder head. You are suggesting that the 'outside' design of exhaust and after-treatment systems influences gas temperature - they dont - they have to contend with it...

Valve burn-out - Believe it - this is the reason why GT4 service intervals are short compared with other race cars. The fuelling at the top end delivers 850 deg C gas port temp - exhaust valve heads drop off at 870 C, but you will only find that out at your peril - I hope you dont. But I have seen this time and time again, where those not experienced nor qualified dabble with something as serious as re-flashing ECU's. 20 hours to drop the engine and replace it, and 30 hours or so to recover a failure in rebuild is an expensive way to find this out...

 

As long as the cats were made correctly there would be no adverse 'health' problems whatsoever associated with this type of modification (Save OBD lamp for rear sensor if this aspect has not been looked at).
My concern throughout this thread is with ECU re-flash and long term health. And even if the V8 cats did fail, all that is needed to correct the condition would be a cat replacement. Unlike the V12, when its cats fail they are ingested by the motor and fail the motor....!

A problem I have seen on a particular brand of replacement cats is that when they removed the middle pipes they did not re-fit thee heat shielding. This caused less than a fingers gap between the driveshaft boot and would have dried up the grease leading to failure...

 

Tracking.. thanks Mike for the response.. I'm looking to have a set of cats installed somepoint next yr before heading to Europe (Germany).

 

Mike, why would combustion temps and EGT be higher in this engine in particular leading to concerns about exaust valve burnout? I never hear about this being a problem with other engines, many making much higher hp/liter and not requiring such extremely rich conditions. Is there a design issue with the cylinder head?

 

850C = 1562F ... there is no way these motors are running anywhere NEAR those EGTs on a small displacement NA V8 running only 12.5 AFRs ... that is borderline fear mongering.

I have two close friends running 1000hp+ in their Ford GTs on essentially stock motors and even they are not having any such issues on the 5.4L versions of our engines. One of them is BOTH supercharged and turbocharged ... not a sinle one of them has burnt a vavlw or blown the motor .... these ford motors are capable of withstanding extreme levels of stress.

Now if my AFRs were 15.0:1 or higher ... I would start being concerned ... but at a perfect 12.5:1 I'd be shocked if EGTs were 1250+ @ WOT .

Furthermore ... stock primary catalytics fail all the time and motors never blow up. In 95%+ cases the cat is just blown through and there is a gaping hole, which would be less harmful to the engine (albeit emissions would be worse.

I am with Tahoe on this one ... its an internal combustion engine .... all the same rules apply.

Besides ... you should want my motor to blow up, that way you can sell me a new one (which is the main intention anyways)
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Thanks for joining the conversation Mike. Great info.

 

Little bit of a long answer but we should get there...

EGT's are not hotter in this engine than any other I have developed / calibrated. The maximum permissible exhaust valve head temperature limit is 850 deg C and the catalyst matrix temperature limit is 950 Deg C. The catalyst would take temperatures of up to 1000 deg C but conversion efficiency is risked when running for prolonged periods at such a high temperatures.
Combustion gas outlet temp is effected by spark angle the most. A retarded spark causes a hotter burn, more advanced would return a cooler burn. To achieve the same gas outlet temp for each spark angle condition, the retarded spark would need more fuel, whereas the more advanced spark would require less fuel to achieve the same gas outlet temperature.
The spark angle would need to change for variables such as inlet air temperature, barometric pressure, fuel grade, coolant temperature and compression ratio - what dictates spark angle is the level of detonation (knock) allowed.

So, to commence the mapping sequence an inlet air temperature, coolant temperature and oil temperature is controlled on the reference fuel grade and the spark is advanced to the point where detonation occurs. At low speeds, at wide open throttle, the fuelling is set to 13:1 AFR as this is best for power. At these conditions the gas temp is, say, 600 deg C at 1000 rpm and rises up to 850 deg C at 13:1 up to, say, 5000 rpm. From 5000 rpm onwards, at the ignition angle where detonation occurs, the fuelling value needs to be increased to keep the 850 Deg C gas temp maximum control point - this is quite normal. This process gives the spark and fuelling curves at reference conditions, and offset mapping is conducted at different fuel grades, barometric pressure conditions, air inlet, coolant and oil temperatures to program spark and fuel curves for all these conditions.
This means that whatever the variable, the engine produces the same gas outlet temperature profile, and when compared to other engines this temperature profile is the same. But, to achieve this temperature profile the fuelling value required, is a little excessive (rich) - granted.
This is mainly due to the compression ratio being reasonably high - 11.33:1, up to 12.0:1 maximum which requires quite a retarded spark curve (when compared with other engines) to control detonation, which means a hotter burn which requires a richer AFR.

So as I have mentioned in previous posts, some ECU 'tuners' have noticed this rich profile and no-doubt cash-in on the fact the fuel can be leaned out (back closer to 13:1) to return more power. But as they do not monitor gas temperatures or test the engine at the extremes which affect spark / knock (inlet air temperature, fuel grade, barometric pressure, coolant temperature), how do they know across all of these conditions, when the car is away from the dyno, the EGT's will be safe? - they dont...

When these cars are used on the racing circuit, because they are continually operated at high speeds where the gas temp is on the limit (850 deg C), explains why the seats degrade faster than when the car is used in normal road driving conditions. Normally this would not happen in the race world as the engines are modified with exotic parts. Aston Martin fitted a standard road car engine to all race cars - testament to how strong the motor actually is i think.

hope this makes the situation clearer for you?

Mike.

 

What do you mean, Mike, that the V12 would ingest a failing cat into the engine? I thought they were downstream of the engine. Please explain.

 

Hi 007....
It's not about the specific BHP output or how an engine outputs a gas temperature based on this measure, its all about internal combustion chamber design and the variables that effect spark advance angle, fuelling and jointly how these parameters output a gas temperature.

You can take my comments or you can leave them, it is yours as is any other forum members choice. What you or anybody else says is just as relevant as what I say -this is just a chat between folk who like talking about Astons- there is no right and no wrong, just opinions... and btw im not here marketing a product im here as an enthusiast.

However, one thing I am 'all about' coming from factory to aftermarket world, is to dispel the myths and Bull that some, not all, aftermarket folk trade on. Excessive BHP claims for exhausts is one area I will not tolerate neither is excessive and untrue claims from ECU 'tuners'.
My opinion is that the very important point of this discussion and getting it right, is for the very many people who own Astons and read this forum but never post. The data we produce here needs to stand as a reference for those people to benefit from making choices for whatever they decide to do with their car, and in that respect what we say needs to be right.

The only point I will budge on is where you say the engine gets nowhere near the temps I suggest. It is possible with the extremes of sensor and engine mechanical parts in production that some engines run cooler whilst some run hotter, and the calibration does have an element of safety programed into it which could be eroded if these conditions did not apply to your application. But now we get to the other bone of contention I have with ECU flashing - what about product liability?? Somebody other than OEM has programmed the brain - what if electronic throttle snaps wide open without driver pedal demand, due to an error in the program - who picks up the liability / litigation bill when the car does some damage??

Sorry to bore people but I could talk all day about the pitfalls of ECU re-flashing, it is something I strongly recommend against as is TCU re-flashing.