Ram airbox, Programable ECU mapping..

[Zico]

Hoping some tech savy guys on here might be able to offer some advice..

We finally chose the new powerplant for the new Grp4 Escort rally car, its a JRE (John Reid Engineering) long stroke, 2.3 Vaux XE 16V, all steel internals, Big valve touring car head running on Jenvey TB's through a fully programable DTA ECU and produces 293bhp with aprox 230lb/ft torque.

The ECU has been mapped but Im gonna build a custom carbon fibre airbox which will remove hot air scavenging and add a degree of Ram effect at higher speeds. They say EFI engines are unaffected by the Ram-air effect, but this Imo should work differently due to the Jenvey TB's and because the ECU is fully programmable.

Q- Will this Ram effect be significant enough to create a dangerous lean burn situation at higher speeds of 100-120mph ?

Significant enough to warrant adding an air flow meter (as per turbo'd engines) to the intake, and adding this to the 3D mapping?

Found these links informative but unconclusive

http://www.sportrider.com/tech/146_9508_ram/index.html

http://www.karlsnet.com/mopar/ramair.shtml


I doubt it will be required but I'd just like to be sure.. Any advice/help, greatly recieved.

Thanks.

[AU N EGL]

RAM air does not work below MACH 1. But bringing in cold( colder) air from the out side of the car vs hot air from the engine compartment does make a big difference.

[Zico]

Please excuse my stupid questions..

Im aware that the effect is minimal, my calculations give me a Ram effect of 1.3 - 1.6 percent at these speeds. Although offset by the increased drag factor, its still worth doing imo, due to the cooler air intake temps which offer a greater increase ..

I'm sure I read somewhere that this Ram effect can be enough to mess with carbs fuel/air mixture. Would it affect throttle bodies in the same way to require the need for a MAP sensor input, or will this be read and catered for live by the O2 sensor?

[Locost47]

Originally Posted by AU N EGL

RAM air does not work below MACH 1. But bringing in cold( colder) air from the out side of the car vs hot air from the engine compartment does make a big difference.

I strongly disagree with the first part of this but then totally agree with the second. Ram effect is vastly overestimated a lot of the time but it certainly makes a difference well below sonic speeds.

As a very loose rule of thumb, just compare the dynamic pressure at the speed you're travelling against atmospheric ambient.

Dynamic pressure = 0.5 * density * speed^2
120mph ~ 54m/sec
density ~1.225 kg/m^3

therefore dynamic pressure at 120mph is about 1800Pa.

Atmospheric ambient will be somewhere around 101300Pa, so about 1.8% 'more air' (similar to Zico's figures). So not a lot, but some.

At 170mph it's about 3.5%, which is (very) roughly equivalent to a 10 degree Celsius drop in intake air temperature - so it's becoming more worthwhile, but cooler air is always better, especially since only the quickest cars (& probably a bigger proportion of bikes) will see that sort of speed for any meaningful portion of a lap.

[Nero]

So in effect you want to introduce another variable i.e. pressure from airspeed into your airbox design on an expensive race tuned engine. Cold air is straight forward enough: air density is proportional to temperature, so at around 30 degrees Celsius every degree is worth 0.3 % in density.
Forget ram effects....look at the efforts manufacturers go to to get rid of such variables. Spend more time getting the airbox design correct...or close to avoid maldistribution of pressure within the airbox.

[phoenix]

Originally Posted by Zico

Hoping some tech savy guys on here might be able to offer some advice..

We finally chose the new powerplant for the new Grp4 Escort rally car, its a JRE (John Reid Engineering) long stroke, 2.3 Vaux XE 16V, all steel internals, Big valve touring car head running on Jenvey TB's through a fully programable DTA ECU and produces 293bhp with aprox 230lb/ft torque.

The ECU has been mapped but Im gonna build a custom carbon fibre airbox which will remove hot air scavenging and add a degree of Ram effect at higher speeds. They say EFI engines are unaffected by the Ram-air effect, but this Imo should work differently due to the Jenvey TB's and because the ECU is fully programmable.

Q- Will this Ram effect be significant enough to create a dangerous lean burn situation at higher speeds of 100-120mph ?

Significant enough to warrant adding an air flow meter (as per turbo'd engines) to the intake, and adding this to the 3D mapping?

Found these links informative but unconclusive

http://www.sportrider.com/tech/146_9508_ram/index.html

http://www.karlsnet.com/mopar/ramair.shtml


I doubt it will be required but I'd just like to be sure.. Any advice/help, greatly recieved.

Thanks.

I would avoid adding any air flow meter if I were you.

I am not sure if DTA has an input and fuel correction maps for barometric pressure, but if it does simply put your borometric pressure sensor inside your ram air box.

You can then use the mapping to give a 1:1 ratio between air pressure increase and the increase in fuel. i.e. if you get 1.3% higher air pressure add 1.3% more fuel to keep the air/fuel ratio correct. Also stick your inlet air temperature sensor in the ram air box for temperature correction.

If the DTA does not offer the above options, then why not use a wide band lambda sensor and run in closed loop lambda mode, which will correct any mis-fueling?

However, if you do nothing, the leaning off effect will be very minimal; if you are running at 12.5:1 air/fuel ratio on the dyno, for example, 1.3% more air would change the air/fuel ratio to 12.66:1 - you are not going the melt any pistons or burn out any valves with such a small change.

Phoenix

[Nero]

I've been researching this for the past 4 weeks for an article in Race Magazine and for my own car. Added pressure into a well designed airbox is less of an issue for Carbs as even something like a very well setup pair of weber DCOE's are a relatively crude device when compared to a good ECU and injection.
The bear in the woods is not the added pressure as a whole but the effect that the variable levels of pressure can have within an airbox, particularly one not designed for such things. You can have a variable maldistribution accross cyls which is dependant on airspeed of the vehicle and a localised pressure sensor will not address these issues.
You can contact me at www.racemagazine.com.au if you want a copy of a paper that details airbox design...beware that it is 6.5mb though. There are also some very good SAE papers and Prof Blairs work is also worth a good read.

[Zico]

Originally Posted by phoenix

I would avoid adding any air flow meter if I were you.

I am not sure if DTA has an input and fuel correction maps for barometric pressure, but if it does simply put your borometric pressure sensor inside your ram air box.

You can then use the mapping to give a 1:1 ratio between air pressure increase and the increase in fuel. i.e. if you get 1.3% higher air pressure add 1.3% more fuel to keep the air/fuel ratio correct. Also stick your inlet air temperature sensor in the ram air box for temperature correction.

If the DTA does not offer the above options, then why not use a wide band lambda sensor and run in closed loop lambda mode, which will correct any mis-fueling?

However, if you do nothing, the leaning off effect will be very minimal; if you are running at 12.5:1 air/fuel ratio on the dyno, for example, 1.3% more air would change the air/fuel ratio to 12.66:1 - you are not going the melt any pistons or burn out any valves with such a small change.

Phoenix

Excellant, that explains it perfectly.. This is a 1st for us.. using throttle bodies, having used carbs since we started, so its all a bit high tech for me . We're hoping to take delivery of the engine on monday so Im not yet 100% what DTA model it is but they are generally well specced and Im pretty sure both inputs are a standard feature.

Thanks for sharing your knowledge.

[AU N EGL]

Originally Posted by Locost47

Atmospheric ambient will be somewhere around 101300Pa, so about 1.8% 'more air' (similar to Zico's figures). So not a lot, but some.

At 170mph it's about 3.5%, which is (very) roughly equivalent to a 10 degree Celsius drop in intake air temperature - so it's becoming more worthwhile, but cooler air is always better, especially since only the quickest cars (& probably a bigger proportion of bikes) will see that sort of speed for any meaningful portion of a lap.

Yes Mathmaticly one can caculate the difference. However, ON TRACK will there be a real and MEASUREABLE DIFFERNCEat 1.3 or 5%? Dont think so as there are too many other factors involved.

Now if you want some fun, put a small radaitor in your intake and circulate Liquied CO2 though that radiator too cool the incoming air even more. Plus wrap your fuel lines to lower fuel temp as well.

We do quite a bit of experimentation with throttle bodies to get more air into the manifold. Larger tbs Smaller, ported and Polished tbs. different air intakes and all kinds sizes and other changes.

[Nero]

IF you look at the top end ECU's you will find that thy have closed loop tuning for each cyl, partly to counter pressure maldistribution and other factors.
DTA are a fine system much the same as Moted, but they are a fair way behind leading spec....still far far better than webers.

[Notso Swift]

Originally Posted by phoenix

I would avoid adding any air flow meter if I were you.

I am not sure if DTA has an input and fuel correction maps for barometric pressure, but if it does simply put your borometric pressure sensor inside your ram air box.

He did say "like a turbo car uses", so for the last 15 years that would be a MAP sensor which is exactly what he should do if the computer takes it as well as a TPS.
But if you can only have one use the TPS on a NA car, drivability is what you need and tuning on MAP is too slow to respond. (IMO)

Nero
Did you mean to write MoTeC instead of moted, if so they DO have closed loop on each cylinder available, you just need to tick the right boxes and open your wallet!

[Nero]

yep meant motec...last I asked there was a substantial difference between the bosch motorsport closed loop and the motec. I'll have another look.

[phoenix]

Originally Posted by Notso Swift

He did say "like a turbo car uses", so for the last 15 years that would be a MAP sensor which is exactly what he should do if the computer takes it as well as a TPS.
But if you can only have one use the TPS on a NA car, drivability is what you need and tuning on MAP is too slow to respond. (IMO)

In that case I probably took 'air flow meter' too literally.

As I understand it (we have Pectel on a turbo engine) the ECU uses the MAP sensor in conjunction with the charge temperature sensor to allow computation of charge density, by integration of the two readings via two maps.

But in addition to MAP, we can also map against ambient barometric pressure. We don't, because we compete in the UK and are not competing in the Alps or up Pikes Peak, but we use fast (next cylinder firing) Lambda correction instead.

I'm not sure how fast the Pectel reacts to the ambient barometric input and map, but the ECU is generally capable of reacting to all other inputs - including TPS and MAP - to tune each cylinder correctly for the next cycle - upto 10,000 rpm at least, so I suspect Motec and DTA are as capable.

But as I was saying previously, unless you are running very lean anyway for some reason, going leaner by 1.3% because of increased air pressure will probably go un-noticed on the dyno, certainly on the track and it would be highly unlikely to cause any engine failure.

I think, as others have pointed out, that with carbs the fuel metering is dependent on the pressure differences in the venturis, and I can see that increasing the pressure on the inlet side would change the pressure variations seen inside the carb and could therefore mess up the air/fuel ratio.

And of course carbs are not able to cope very well with altitude changes because barometric pressure variations affect the air/fuel ratio. I remember on a trip to Austrian GP years ago, struggling up an Alp with engine power dropping off, apparently with every 100 metres we went up!

[Zico]

Thanks for all your replies guys, very helpful.
Would have been better waiting until I'd taken delivery and knew the exact Ecu spec and current set-up before asking, but at least I have a far clearer idea of the set-up possibilities.

Thanks again..

[Zico]

This thread is mainly about the ECU's capabilities but for anyone using the search function.. I thought Id link a PDF Thesis that also covers the RAM effect, intake accoustics and tuning formulae. (page 45 onwards)

https://dspace.lib.cranfield.ac.uk/b...is_Yechury.pdf

[Chucky]

Originally Posted by AU N EGL

Yes Mathmaticly one can caculate the difference. However, ON TRACK will there be a real and MEASUREABLE DIFFERNCEat 1.3 or 5%? Dont think so as there are too many other factors involved.

Yes, there is.

A decent V8 Supercar ram air intake will give 2-2.5kpa at 240kmh or thereabouts.

[Locost47]

I'd second that, but also add that people in racing often put in a lot of effort to make gains smaller than 5% or which would be equally or more difficult to identify a laptime benefit from. In this case it's free and every little helps, surely?