Whats Your MaP (kPa)?
Discussion
A quick question as per the title and probably only for those with aftermarket ECUs who have access to this information easily, well two questions actually 
. I recently noticed a Griff 5.0 litre that belongs to a mate produces noticeably different Map figures to my 4.0 Chimaera, I should also say at this point he runs a Kent 885 cam.
My mate's Griff 500 is like this:
These figures in contrast to my 4.0HC that runs a Stealth cam and a lightened 18lbs flywheel:
Question One: I appreciate a cam will play a big part here but is there really such a big difference between the V8 Development Stealth cam I have and the 885 in my mates Griffith?
Obviously the other big difference is my mate has a 5.0 litre and I have the baby 4.0, but even so I'm still quite surprised at the differences, overall my mates Griff MaP figures are significantly lower than mine except as you would expect under hard acceleration where the two engines produce the same figures, but his idle kPa's do also seem more stable than mine too
.
Question Two: Are these differences more a result of the different camshaft profiles used or does the capacity difference play a bigger role in all this than I'd assumed?
Discuss
. I recently noticed a Griff 5.0 litre that belongs to a mate produces noticeably different Map figures to my 4.0 Chimaera, I should also say at this point he runs a Kent 885 cam.My mate's Griff 500 is like this:
- Idles at just 35 kPa
- When pulling away and his engine initially loads up his kPa momentarily peaks at only 55 kPa
These figures in contrast to my 4.0HC that runs a Stealth cam and a lightened 18lbs flywheel:
- Idles quite a bit higher at 50 kPa
- When pulling away my engine initially loads up a lot higher peaking momentarily at 80 kPa
Question One: I appreciate a cam will play a big part here but is there really such a big difference between the V8 Development Stealth cam I have and the 885 in my mates Griffith?
Obviously the other big difference is my mate has a 5.0 litre and I have the baby 4.0, but even so I'm still quite surprised at the differences, overall my mates Griff MaP figures are significantly lower than mine except as you would expect under hard acceleration where the two engines produce the same figures, but his idle kPa's do also seem more stable than mine too
.Question Two: Are these differences more a result of the different camshaft profiles used or does the capacity difference play a bigger role in all this than I'd assumed?
Discuss
Edited by ChimpOnGas on Monday 17th September 12:02
Steve_D said:
Not sure we should respond to this as the shortness of the post leads me to believe you are not who you say you are.
Steve
Steve
very funny Steve, should I make it longer?Now how about your thoughts on my questions mate
I value you opinion, and I'd be especially keen to see the MaP figures from others running a V8 Developments Stealth cam
Perhaps the Kent 885 is just a more streetable profile than the Stealth cam I run?
I'm not complaining about my Stealth by the way, I actually love it, I'm just interested in better understanding if the lower MaP figures I saw on my mate's 500 are more down to cam differences, the extra engine capacity... or maybe something else I hadn't considered
My SC 5.0 Griff running the original 5.0 Cam had a Kpa of around 50 at idle this would increase to around 135ish with 6psi of boost.
To be honest the Kpa reading is irrelevant it’s really just a graph to allow the ecu to work out load on the engine. If the graph was not set up to read correct KPa in the first place (roughly 95kpa engine off, give or take a little depending on altitude) and was just set to give a figure for the Ecu to show load then you could have completely different readings with the same result.
35kpa on your mates 5.0 seems wrong to me that is very high vacuum for a 5.0 engine but camshaft overlap compression ratio etc etc can affect it.
As said it’s really an irrelevant figure unless it’s been properly calibrated to read true it’s just a point on a graph to help tune the engine.
Chris
To be honest the Kpa reading is irrelevant it’s really just a graph to allow the ecu to work out load on the engine. If the graph was not set up to read correct KPa in the first place (roughly 95kpa engine off, give or take a little depending on altitude) and was just set to give a figure for the Ecu to show load then you could have completely different readings with the same result.
35kpa on your mates 5.0 seems wrong to me that is very high vacuum for a 5.0 engine but camshaft overlap compression ratio etc etc can affect it.
As said it’s really an irrelevant figure unless it’s been properly calibrated to read true it’s just a point on a graph to help tune the engine.
Chris
I'm not so sure, both cars in this case are using the exact same MaP sensor and both are on the same engine management system, so I'd say the comparison is fair.
I'm interested in naturally aspirated cars really, what I'm looking to establish is what vacuum different RV8 TVRs idle at on different cams.
There was definitely a big difference between my mates 5.0 litre Griffith running an 885 and my 4.0 Chimaera on a Stealth cam, and it's not just numbers on a screen, its noticeable to the ear and in the minimum idle speed each engine will tolerate to remain smooth.
Its a shame I can't now compare the detailed specifications of each camshaft as I expect this would be quite revealing, I suspect my Stealth has quite a bit more overlap than the 885.
Anyone else want to share their figures, idle and peak load MaP in kPa as you pull away would be great as this is where the Griff 500 fitted with an 885 differed most from my 4.0 Chimaera running a V8 Developments Stealth cam.
I too was amazed my mate's Griff managed 35 kPa at idle, it was however remarkably smooth so I feel confident we can trust the number.
I'm interested in naturally aspirated cars really, what I'm looking to establish is what vacuum different RV8 TVRs idle at on different cams.
There was definitely a big difference between my mates 5.0 litre Griffith running an 885 and my 4.0 Chimaera on a Stealth cam, and it's not just numbers on a screen, its noticeable to the ear and in the minimum idle speed each engine will tolerate to remain smooth.
Its a shame I can't now compare the detailed specifications of each camshaft as I expect this would be quite revealing, I suspect my Stealth has quite a bit more overlap than the 885.
Anyone else want to share their figures, idle and peak load MaP in kPa as you pull away would be great as this is where the Griff 500 fitted with an 885 differed most from my 4.0 Chimaera running a V8 Developments Stealth cam.
I too was amazed my mate's Griff managed 35 kPa at idle, it was however remarkably smooth so I feel confident we can trust the number.
All I am saying is that it all depends on how the graph was set up. If they set the graph for a 1.5 bar map sensor it would read about 35kpa when in actual fact it is in reality roughly 50 Kpa. If the car was tuned to that scale it would still run perfectly. The only reason I say this is that when I was looking at the readings on mine they were a mile out as the engine tuner (very well respected Tvr Guru but not Joolz) had set my graph as a 1 bar sensor when I was using a 2 bar Sensor as it was forced induction. Easy way to test is do they both read the same Kpa when the engine is not running?
Chris
Chris
SuperApeInGoodShape said:
SILICONEKID 357HP said:
Throttle response is much slower ,well that's what I've been told .
MAP with TPS for Acceleration Enrichment is a good combo.Alpha-N /TPS on its own is a bad predictor of load at anything but full throttle.
True engine load is what you need to know, and what you and your ECU really should be working with.
So what's this Alpha-N thingy anyway
Well, Alpha is just throttle angle and N is just RPM (engine speed)
So with Alpha-N injector duration (opening times) and ignition timing can only be a calculation based on those two parameters.... neither of which are a true refection of engine load. Even with the two it doesn't matter how clever the calculation is you could never say what you end up with is true engine load
Vacuum on the other hand is a far a more accurate representation of true engine load because an engine is just a big vacuum pump pulling against a restriction valve (the throttle butterfly), as you open the throttle the vacuum (or depression to use the correct term) falls in the inlet manifold/plenum chamber, conversely if engine speed is high and the engine is pulling hard against an almost closed throttle butterfly the depression will increase considerably.
So if you know your depression you actually don't need your throttle position because depression is a reflection of the throttle position and to some degree engine speed, it's important to remember at this point that the principle of using depression to measure engine load was used to great effect long before throttle position sensors, electronic fuel injection and distributorless ignition systems, it's also completely proven.
A manifild absolute pressure sensor is really nothing more than an electronic vacuum advance unit, rather than physically translating manifold depression into mechanical movement acting on the base plate of the distributor to advance the ignition timing, the MaP sensor translates manifold depression into tiny variations in voltage which of course is something a ECU can work with.
Clearly an engine management system using a MaP sensor to determine engine load will be measuring true engine speed and throttle position too, this is critical additional information. But to do away with the MaP sensor and just rely on engine speed and throttle position (Alpha-N) is missing a massive trick as far as I'm concerned, doing so on a race car may be fine but for a car used on the road that must be as smooth as possible under a myriad of driving conditions and so true engine loads you really would be mad not to use MaP.
It may be what you've heard Daz is that throttle response is better using Alpha-N but this really shouldn't be the case, a good system using MaP should still have a TPS and use it along with the ECU software and the ECU itself to implement transient enrichment (snap acceleration) strategies and other clever tricks too.
Don't worry , you're not losing out on anything.
The trouble is with these threads that crop up occasionally is that people don't actually know what they want to say when they talk of load on an engine. Without some kind of rotational load cell on the end of the crankshaft how would anyone know what the load was anyway?
People seem to think that somehow an engine with x throttle position at y revs going uphill sees more load than an engine at x throttle position and y revs going downhill. Here's the thing, they're the same load, and therefore the same airflow and therefore the same fuel and ignition requirements. If they weren't you'd have to have an uphill map, and a downhill map, and every incline in between map. Admittedly going uphill the load is held for longer time, and going downhill that same load is over in an instant, but for x throttle at y revs it's the same load each time every time.
Because of this you can quite confidently predict that the fuelling and ignition requirements are the same each time for that x throttle and y revs .. hence the reason alpha-n is actually a very valid mapping option. I would argue that after tuning ecus for nigh on 15 years,for tuning an aftermarket system it's probably also the best and what it's worth here's my own reason why.
With throttle angle v revs you can replicate every acceleration run every time at different throttle positions and hence different loads. With vacuum and air flow meter you always seem to get a slightly different run, so you end up spending much more of your time in steady state mapping strategies. This causes high engine bay temps, and in my experience certainly air flow meter outputs seem to vary more than i would consider acceptable on a run after run basis meaning that the oft-quoted afms are best mantra is sadly not true uness you take great care to keep their temps stable. In the tight confines of the TVR bay this is a very important point to remember.
Because of all this, and for time-limited aftermarket mapping (who wants to pay for months of mapping time, other than a major manufacturer?) you can get a very very very good alpha-n map in a comparatively short time. Indeed I would go so far as to say that most of the maps i've seen mapped on MAP sensors fall way below that of the alpha-n maps I've seen, and I think this is down to the fact that alpha-n is so easy to get accurate comparative runs in a short time frame.
The reason alpha-n gives a more urgent feel when you quickly open the throttle is that it not only skips through the fuel map as soon as you open the throttle, it also skips through the ignition table quickly too. For sure you can have throttle angle based fuel enrichment on afm and MAP based systems, but i've yet to see an aftermarket ecu with transient ignition adjustment in the same fashion. By default therefore any MAP or afm based sensing must be laggy by nature.
The pro alpha-n argument becomes even more valid once you start throwing wilder cams etc into the mix. By their nature, MAP sensors and to some extent AFMs are affected by the reversal effects imparted by wild cams, large bore intakes with low gas speeds etc etc.
There's arguments to say AFM is best as it takes into account engine wear ..to which I say if your high performance sports car has engine wear to that extent you need to rebuild it!
I'm very much pro alpha-n for oh so many reasons.
There's a caveat to all this though, and that's the quality of aftermarket throttle position sensors. The only reason I can see that I would ever move away from alpha-n mapping is when the consistency of the quality of the position sensors becomes an issue,as it's the primary load axis for alpha-n mapping of course. But then you still have the issue of that same sensor being used for accel enrichment and idle threshold parameters on MAP and AFM based systems, so everyone will be in the same boat to a lesser or greater extent anyway by then ...
The trouble is with these threads that crop up occasionally is that people don't actually know what they want to say when they talk of load on an engine. Without some kind of rotational load cell on the end of the crankshaft how would anyone know what the load was anyway?
People seem to think that somehow an engine with x throttle position at y revs going uphill sees more load than an engine at x throttle position and y revs going downhill. Here's the thing, they're the same load, and therefore the same airflow and therefore the same fuel and ignition requirements. If they weren't you'd have to have an uphill map, and a downhill map, and every incline in between map. Admittedly going uphill the load is held for longer time, and going downhill that same load is over in an instant, but for x throttle at y revs it's the same load each time every time.
Because of this you can quite confidently predict that the fuelling and ignition requirements are the same each time for that x throttle and y revs .. hence the reason alpha-n is actually a very valid mapping option. I would argue that after tuning ecus for nigh on 15 years,for tuning an aftermarket system it's probably also the best and what it's worth here's my own reason why.
With throttle angle v revs you can replicate every acceleration run every time at different throttle positions and hence different loads. With vacuum and air flow meter you always seem to get a slightly different run, so you end up spending much more of your time in steady state mapping strategies. This causes high engine bay temps, and in my experience certainly air flow meter outputs seem to vary more than i would consider acceptable on a run after run basis meaning that the oft-quoted afms are best mantra is sadly not true uness you take great care to keep their temps stable. In the tight confines of the TVR bay this is a very important point to remember.
Because of all this, and for time-limited aftermarket mapping (who wants to pay for months of mapping time, other than a major manufacturer?) you can get a very very very good alpha-n map in a comparatively short time. Indeed I would go so far as to say that most of the maps i've seen mapped on MAP sensors fall way below that of the alpha-n maps I've seen, and I think this is down to the fact that alpha-n is so easy to get accurate comparative runs in a short time frame.
The reason alpha-n gives a more urgent feel when you quickly open the throttle is that it not only skips through the fuel map as soon as you open the throttle, it also skips through the ignition table quickly too. For sure you can have throttle angle based fuel enrichment on afm and MAP based systems, but i've yet to see an aftermarket ecu with transient ignition adjustment in the same fashion. By default therefore any MAP or afm based sensing must be laggy by nature.
The pro alpha-n argument becomes even more valid once you start throwing wilder cams etc into the mix. By their nature, MAP sensors and to some extent AFMs are affected by the reversal effects imparted by wild cams, large bore intakes with low gas speeds etc etc.
There's arguments to say AFM is best as it takes into account engine wear ..to which I say if your high performance sports car has engine wear to that extent you need to rebuild it!
I'm very much pro alpha-n for oh so many reasons.
There's a caveat to all this though, and that's the quality of aftermarket throttle position sensors. The only reason I can see that I would ever move away from alpha-n mapping is when the consistency of the quality of the position sensors becomes an issue,as it's the primary load axis for alpha-n mapping of course. But then you still have the issue of that same sensor being used for accel enrichment and idle threshold parameters on MAP and AFM based systems, so everyone will be in the same boat to a lesser or greater extent anyway by then ...
Edited by spitfire4v8 on Friday 28th September 19:45
spitfire4v8 said:
Don't worry , you're not losing out on anything.
The trouble is with these threads that crop up occasionally is that people don't actually know what they want to say when they talk of load on an engine. Without some kind of rotational load cell on the end of the crankshaft how would anyone know what the load was anyway?
People seem to think that somehow an engine with x throttle position at y revs going uphill sees more load than an engine at x throttle position and y revs going downhill. Here's the thing, they're the same load, and therefore the same airflow and therefore the same fuel and ignition requirements. If they weren't you'd have to have an uphill map, and a downhill map, and every incline in between map. Admittedly going uphill the load is held for longer time, and going downhill that same load is over in an instant, but for x throttle at y revs it's the same load each time every time.
This is just wrong, unless we mean different things by 'load'. By this logic an engine with the throttle held at 50% would have the same load when the car were jacked up and the wheels spinning freely as it would when it were towing a 3 tonne trailer. The trouble is with these threads that crop up occasionally is that people don't actually know what they want to say when they talk of load on an engine. Without some kind of rotational load cell on the end of the crankshaft how would anyone know what the load was anyway?
People seem to think that somehow an engine with x throttle position at y revs going uphill sees more load than an engine at x throttle position and y revs going downhill. Here's the thing, they're the same load, and therefore the same airflow and therefore the same fuel and ignition requirements. If they weren't you'd have to have an uphill map, and a downhill map, and every incline in between map. Admittedly going uphill the load is held for longer time, and going downhill that same load is over in an instant, but for x throttle at y revs it's the same load each time every time.
Edited by spitfire4v8 on Friday 28th September 19:45
SILICONEKID 357HP said:
Maybe I ask too many questions 
Not really Daz, in this case your question helped me learn some new stuff from spitfire4v8
The post from spitfire4v8 was really interesting and informative, there were a number of points that (when I really thought about it) made a lot of sense to me
The way I see it we should thank him for taking the time to share his knowledge, and you for asking the question that stimulated his response.
SuperApeInGoodShape said:
This is just wrong, unless we mean different things by 'load'. By this logic an engine with the throttle held at 50% would have the same load when the car were jacked up and the wheels spinning freely as it would when it were towing a 3 tonne trailer.
This is just the issue. People have different ideas of what load is.Load to me is the force exerted at the puston crown at a certain rpm and a certain throttle opening.
In your scenario that load might exists for a long time towing a trailer ie you could be at 50percent throttle and 3000rpm for a minute on an incline.
But if you took it out of gear and were initially at say tickover and snapped the throttle to 50percent exactly then just as the rpm passed through 3000rpm the load on the piston crown would instantaneously be the same as towing the trailer. If it wasnt then youve undermined all mapping whether throttle or map or afm based.
At 50percent throttle and 3000rpm the airflows are the same.
If youre saying its not the same please explain why. Also explain what you mean by load.
Edited by spitfire4v8 on Saturday 29th September 08:29
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