Bosch Motronic Alpha-N question
Discussion
Hi all, a question which may be very silly - I don't know enough to know, so please forgive me if this is the case.
Context: I'm having my 1998 Porsche 911 engine rebuilt, it's going from 3.4 litres to 3.7 and will be having some cams ground for the new capacity.
Lacking any sense of proportion I'm considering the Jenvey ITB kit for these engines - but that would mean working out how to manage air-metering.
I'll likely shelve this aspect if the only answer is Emerald/DTA/similar, as the time spent working out how to run the dashboard etc is probably extensive.
Hence my question - can the stock DME be modified/mapped to run happily with TPS/IAT instead of a MAF?
Context: I'm having my 1998 Porsche 911 engine rebuilt, it's going from 3.4 litres to 3.7 and will be having some cams ground for the new capacity.
Lacking any sense of proportion I'm considering the Jenvey ITB kit for these engines - but that would mean working out how to manage air-metering.
I'll likely shelve this aspect if the only answer is Emerald/DTA/similar, as the time spent working out how to run the dashboard etc is probably extensive.
Hence my question - can the stock DME be modified/mapped to run happily with TPS/IAT instead of a MAF?
Dammit said:
Hence my question - can the stock DME be modified/mapped to run happily with TPS/IAT instead of a MAF?
Obviously the engine management system will need to be updated or replaced to suit the capacity increase. Do you intend to have somebody deal with this for you? If so, that is who you need to ask about required hardware changes and the potential for using a different type of load sensor.I know that the DME can be mapped, and of course it will be mapped to suit the capacity increase, cams etc.
What I don't know is if the way in which it manages the engine can be changed - I suspect the answer is no, but I have found some reference to people successfully modifying Motronic ECU's to run Alpha-N in the BMW world, so thought I'd ask.
Being able to map the ECU ≠ being able to change from MAF to Alpha-N
What I don't know is if the way in which it manages the engine can be changed - I suspect the answer is no, but I have found some reference to people successfully modifying Motronic ECU's to run Alpha-N in the BMW world, so thought I'd ask.
Being able to map the ECU ≠ being able to change from MAF to Alpha-N
Maxx Automotive do a piggyback kit for early Motronic fitted to BMW E30 M3s.
http://maxx-automotive.com/pp.html
http://maxx-automotive.com/pp.html
Dammit said:
Could you give a bit of detail on why that's the case?
This may be obvious to you, but it's not obvious to me.
For e.g. I am uncertain why the physical properties of a device would change depending on who is using it.
I'm not familiar with that ECU but I know enough about the ECUs I've used to be reasonably confident that what you're trying to do is possible. If all else fails, it would be possible to make/buy a signal conditioner to make the new load sensor look like the old one. Somebody familiar with that ECU might be able to suggest an easier/cheaper approach. But I'm not offering to do it for you, so my answer doesn't move you forward. What you need is a quote from somebody willing to actually do the job.This may be obvious to you, but it's not obvious to me.
For e.g. I am uncertain why the physical properties of a device would change depending on who is using it.
The mapping will be done on top of whatever mods you need to make to support the new sensor type. The skills and tools that would be needed to make these mods are closely related to the skills and tools that would be required to map it. The person making the mods certainly ought to be capable of mapping it afterwards and if they are not going to map it then you can't know the mods are going to work unless/until the person who will map it afterwards approves them. This is why I keep coming back to the comment that you should start from the person who is going to map it, and if they don't know the answer you need to look elsewhere. Unsubstantiated opinions from the internet are no use - you need to talk to somebody willing and able to do the work, and theirs is the only answer that really matters.
McVities said:
Instead of trying to change the management, why not enclose the ITB's within a plenum and then run the intakes to the original MAF?
^^ THIS(You get the added benefit of more torque as well at lower engine speeds because you can leverage the secondary tuning of the plenum volume and clean air duct work)
On a different note: vacuum.
This is required to run the brake booster, air-oil-separator, fuel pressure regulator and a bunch of smaller stuff.
If, for the sake of argument, one were to move from a single throttle body at the entrance to the plenum, and moved to individual throttle bodies at the end of each plenum runner this would (I am guessing) significantly reduce the level of vacuum in the intake/plenum upon which the various systems rely- potentially to a point that is too low.
?
This is required to run the brake booster, air-oil-separator, fuel pressure regulator and a bunch of smaller stuff.
If, for the sake of argument, one were to move from a single throttle body at the entrance to the plenum, and moved to individual throttle bodies at the end of each plenum runner this would (I am guessing) significantly reduce the level of vacuum in the intake/plenum upon which the various systems rely- potentially to a point that is too low.
?
This is all bench racing at this point.
Background:
- I have a 1998 Porsche 996
- this is the cable throttle model year (more on this shortly)
- It's on 64,000 miles and in rude health
- I have no sense of proportion
- I'd originally planned on having it rebuilt at around 80,000 miles in order to fix the issues that Porsche didn't - bearing shells, IMS bearing, bore-ovality etc
- But then succumbed to a massive bought of "whilst we're in there" planning
Actual plan:
- I bought a couple of 3.4 litre heads from a breaker, they're both with a race-engine builder and head-porting specialist
- He's also got a complete intake, FVD-homage equal length exhaust manifolds, and all the gaskets that are needed to put everything together
- Once my spot in his queue rolls round he's going to put the heads on the flow bench and work out a) how they can be optimised and b) what the cam should look like bearing in mind what he has found, the new capacity of 3.7 litres, how many angels can fit on the head of a pin etc
Thing that caused me to start this thread:
- The engine designer mentioned that the current throttle may be too small
- This is usually resolved by simply banging a GT3 throttle body on
- But this won't work with mine - the cable version won't fit, the eGas versions won't work
- So I had a look on the Jenvey site and found their ITB setup for the 996 whilst looking for a larger single throttle body
- They do sound good
All of that said, the goal for the engine is to be a tractable, reliable, torquey unit that also gets nicely angry at higher revs - rather than a diesel style lump of torque then chokes, or a race engine that has nothing low down then it's armageddon from 5,000rpm upwards.
Background:
- I have a 1998 Porsche 996
- this is the cable throttle model year (more on this shortly)
- It's on 64,000 miles and in rude health
- I have no sense of proportion
- I'd originally planned on having it rebuilt at around 80,000 miles in order to fix the issues that Porsche didn't - bearing shells, IMS bearing, bore-ovality etc
- But then succumbed to a massive bought of "whilst we're in there" planning
Actual plan:
- I bought a couple of 3.4 litre heads from a breaker, they're both with a race-engine builder and head-porting specialist
- He's also got a complete intake, FVD-homage equal length exhaust manifolds, and all the gaskets that are needed to put everything together
- Once my spot in his queue rolls round he's going to put the heads on the flow bench and work out a) how they can be optimised and b) what the cam should look like bearing in mind what he has found, the new capacity of 3.7 litres, how many angels can fit on the head of a pin etc
Thing that caused me to start this thread:
- The engine designer mentioned that the current throttle may be too small
- This is usually resolved by simply banging a GT3 throttle body on
- But this won't work with mine - the cable version won't fit, the eGas versions won't work
- So I had a look on the Jenvey site and found their ITB setup for the 996 whilst looking for a larger single throttle body
- They do sound good
All of that said, the goal for the engine is to be a tractable, reliable, torquey unit that also gets nicely angry at higher revs - rather than a diesel style lump of torque then chokes, or a race engine that has nothing low down then it's armageddon from 5,000rpm upwards.
Dammit said:
the cable version won't fit
That should be a relatively minor problem to solve compared to the other changes you're contemplating.If you do decide to go to a throttle body per cylinder it seems common to take a vacuum line from each runner to a common 'vacuum plenum' which serves to smooth out the pulsing and average out the variation between cylinders to give a signal suitable for MAP sensors, vac ignition advance and so on. If you also need a vacuum supply for a brake servo, I think that would need to be handled separately.
If you stick with a single throttle and need to enlarge it, and if that means you're sticking with an AFM for load, you might find you need to enlarge the AFM too. This would kill two birds with one stone by reducing the restriction (so you gain the full potential from the other mods), and increasing the measuring range of the AFM (so you can maintain accurate fueling at the top end).
Edited by GreenV8S on Saturday 19th August 23:15
I've been fighting jenvey ITBs on an LS1 v8, and the main sticking point has been thermal stability (balance hot and they're unacceptable cold). I think this is largely because the TBs are a bit on the big side for my engine, and I've made arrangements to retain the IAC, which means the TBs are too close to closed on idle really. I've not completely given up yet, but it has dampened my enthusiasm. I somewhat blame the design of jenvey's castings, and I'll probably try stiffening them further (I think they distort as they warm, which tweaks the linkage). Do you have a link to the TBs you're considering?
FWIW (different application and all), I'm making half as much vacuum as I was on idle (something like 75kPa).
FWIW (different application and all), I'm making half as much vacuum as I was on idle (something like 75kPa).
These are the ones: http://www.jenvey.co.uk/products2/throttle-body-ki...
Interesting to hear of your experience with them.
A bit more context - I have a Volvo 850R that has a (much) larger MAF housing in order to give more resolution and therefore better control at higher revs. It's putting out around 360 bhp, and if fun - in a wait for it, wait for it, boom! type way.
But throttle response is not it's strongest suite - the 911 is a totally different story.
I in no way want to lose that crisp throttle response - if it could be improved then that would be awesome, but it can't lose the edge it already has.
I'm worried that a single large throttle body will take that edge off slightly - genuine concern, or not an issue?
Interesting to hear of your experience with them.
A bit more context - I have a Volvo 850R that has a (much) larger MAF housing in order to give more resolution and therefore better control at higher revs. It's putting out around 360 bhp, and if fun - in a wait for it, wait for it, boom! type way.
But throttle response is not it's strongest suite - the 911 is a totally different story.
I in no way want to lose that crisp throttle response - if it could be improved then that would be awesome, but it can't lose the edge it already has.
I'm worried that a single large throttle body will take that edge off slightly - genuine concern, or not an issue?
Despite what you read on the 'net, it's generally actually very difficult to have a throttle body that is really "too small"!
Ok, if you fit a 20mm throttle body to a 7.0 litre engine, it's going to be too small, but in most practical cases, the pressure loss across a fully open throttle is tiny, and makes little or no different to plenum density at WOT. (Remember, the plenum acts to recover the dynamic pressure of the higher velocity flow through the bodies orifice)
in 2017, there is really only 1 reason you need individual port throttles, and that is because you are running a cam profile with a lot of overlap, so charge reversal and charge robing is an issue at low speeds (idle to say 1500rpm ish). With a Plenum and single throttle, the plenum at low load / speed is at a negative pressure (high loss across the choked throttle plate). With a high overlap cam, at low speeds where the velocity, and hence dynamic pressure in each inlet runner is low, you tend to get "puffs" of combustion products and fresh charge getting pulled back into the plenum, where they are then promptly swallowed by one of the other cylinders. This leads to rough, and variable combustion at light loads. Old race cars were the prime case in point, often simply unable to idle below 2krpm without stalling! (today, thanks to dual VCT this is much less of an issue, unless you have an engine without VCT, as the OP does in this case!)
When you fit individual throttles to each runner, what you are doing is massively reducing the volume between each throttle plate and each cylinder, and hence hugely reducing any low speed flow reversals. And because each throttle plate is necessarily choked (supersonic flow) none of that reversal pulse can get back into the plenum and get ingested by a next door cylinder. So, swap to ITBs and you can run a much "hotter" camshaft and still have stable combustion events at low engine speeds and loads (you often loose some smooth driveability at low throttle openings however due to the much larger effective throttle curtain area, resulting in increased gain on the engine load vs throttle angle characteristic)
For throttles a good rule of thumb is to stay below 1% losses at WOT. ie 1kPa loss out of 100 kPa. As dynamic pressue is 0.5 x density x (velocity x velocity), on a standard atmospheric day (and ignoring upstream filtration, dirty and clean air duct losses) 1kPa loss occurs at an airspeed of 40m/s. In reality, because something like 60 to 70% of that dynamic pressure will be recovered by the plenum, the effective plenum pressure loss at 40m/s will be just 0.3 to 0.4 kPa.
So, how much air is 40m/s in say a 70mm throttle? Its' the throttle area (negating the small restriction of the throttle shaft) x average velocity over that area, in this case 0.154 m3/sec. ie, 154 litres of air per second can flow through that hole with a maximum loss of just 1kPa !!
So what size engine can that support. To make the Maths easier, lets round the amount of air available to 150l/sec and lets take a 3.0l engine and assume it has 100% volumetric efficiency (ie completely and perfectly fills it's swept volume on every induction stroke).
For every 2 revolutions of that 4 stroke engine it ingests 3litres of air. So, each crank revolution needs 1.5litres of air.
Finally, 150 litres/sec divided by 1.5 litres/rev is 100 revs per second, or 6000 revs per minute.
So, a 70mm throttle can support a 3.0 litre engine at 6000rpm without any appreciable pressure loss!
And as the area of a circle increases with the SQUARE of it's diameter, as the throttle gets a bit bigger, the losses decrease by the square of the increase.
Ok, if you fit a 20mm throttle body to a 7.0 litre engine, it's going to be too small, but in most practical cases, the pressure loss across a fully open throttle is tiny, and makes little or no different to plenum density at WOT. (Remember, the plenum acts to recover the dynamic pressure of the higher velocity flow through the bodies orifice)
in 2017, there is really only 1 reason you need individual port throttles, and that is because you are running a cam profile with a lot of overlap, so charge reversal and charge robing is an issue at low speeds (idle to say 1500rpm ish). With a Plenum and single throttle, the plenum at low load / speed is at a negative pressure (high loss across the choked throttle plate). With a high overlap cam, at low speeds where the velocity, and hence dynamic pressure in each inlet runner is low, you tend to get "puffs" of combustion products and fresh charge getting pulled back into the plenum, where they are then promptly swallowed by one of the other cylinders. This leads to rough, and variable combustion at light loads. Old race cars were the prime case in point, often simply unable to idle below 2krpm without stalling! (today, thanks to dual VCT this is much less of an issue, unless you have an engine without VCT, as the OP does in this case!)
When you fit individual throttles to each runner, what you are doing is massively reducing the volume between each throttle plate and each cylinder, and hence hugely reducing any low speed flow reversals. And because each throttle plate is necessarily choked (supersonic flow) none of that reversal pulse can get back into the plenum and get ingested by a next door cylinder. So, swap to ITBs and you can run a much "hotter" camshaft and still have stable combustion events at low engine speeds and loads (you often loose some smooth driveability at low throttle openings however due to the much larger effective throttle curtain area, resulting in increased gain on the engine load vs throttle angle characteristic)
For throttles a good rule of thumb is to stay below 1% losses at WOT. ie 1kPa loss out of 100 kPa. As dynamic pressue is 0.5 x density x (velocity x velocity), on a standard atmospheric day (and ignoring upstream filtration, dirty and clean air duct losses) 1kPa loss occurs at an airspeed of 40m/s. In reality, because something like 60 to 70% of that dynamic pressure will be recovered by the plenum, the effective plenum pressure loss at 40m/s will be just 0.3 to 0.4 kPa.
So, how much air is 40m/s in say a 70mm throttle? Its' the throttle area (negating the small restriction of the throttle shaft) x average velocity over that area, in this case 0.154 m3/sec. ie, 154 litres of air per second can flow through that hole with a maximum loss of just 1kPa !!
So what size engine can that support. To make the Maths easier, lets round the amount of air available to 150l/sec and lets take a 3.0l engine and assume it has 100% volumetric efficiency (ie completely and perfectly fills it's swept volume on every induction stroke).
For every 2 revolutions of that 4 stroke engine it ingests 3litres of air. So, each crank revolution needs 1.5litres of air.
Finally, 150 litres/sec divided by 1.5 litres/rev is 100 revs per second, or 6000 revs per minute.
So, a 70mm throttle can support a 3.0 litre engine at 6000rpm without any appreciable pressure loss!
And as the area of a circle increases with the SQUARE of it's diameter, as the throttle gets a bit bigger, the losses decrease by the square of the increase.
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