Air Flow Meter
Discussion
From reading on here the standard 5AM meter fitted is restrictive over 150BHP, so I see some have changed to the bigger 20AM and a bosch unit. Are these bigger AFM's a direct fitment so I can keep the existing pipe work, or dose it have to be changed.
Will they work fine with the std ecu setup and what has to be changed.
Also what model/partno is the bosch unit.
Will they work fine with the std ecu setup and what has to be changed.
Also what model/partno is the bosch unit.
Ballistic Banana said:
They are a straight swap but there wiring needs changing IIRC.
I don't think they are restrictive over 150bhp either. I think I was told
around 300bhp. I am sure someone like joos or act will be along to confirm
BB
The 5AM is restrictive over 150bhp,as we(joo and i) found on my car in the earlier days of tuning my griffI don't think they are restrictive over 150bhp either. I think I was told
around 300bhp. I am sure someone like joos or act will be along to confirm
BB
Edited by Ballistic Banana on Friday 11th May 18:54
Even the larger Bosch/Semens or whichever brand,is still restrictive at the top end unfortunately.What i'd love to know is if there might be some way you could run two afms together
,or,put the 'element' from an afm in a much bigger pipe? 
)
"its restrictive" is not the same as "restricted". As I understand it the engine has to pull harder to get the air in... So its just like having little valves, craply ported heads, 30mm trumpets, skinny throttle body ~ ie all the things you try and upgrade to let the engine breathe easier.
After 150bhp an upgrade will release more power at all points onwards, is my interpretation of the infampous quote/misquote IIRC.
If your engine makes 350bhp with it ~ it might be making 400 without it / or a better flowing version.
Dave
After 150bhp an upgrade will release more power at all points onwards, is my interpretation of the infampous quote/misquote IIRC.
If your engine makes 350bhp with it ~ it might be making 400 without it / or a better flowing version.
Dave
I have found the following on ebay
http://cgi.ebay.co.uk/ws/eBayISAPI.dl
Is for use on the 4.6 range rover, looks like a copy of the lucas/sagem 20AM unit, what do you guys think.
http://cgi.ebay.co.uk/ws/eBayISAPI.dl
Is for use on the 4.6 range rover, looks like a copy of the lucas/sagem 20AM unit, what do you guys think.
It would be worth asking Oxflow if they can supply an upgraded version for RV8 TVRs.
I would like to see a selection of bhp/torque graphs that clearly demonstrate the restriction above 150bhp - there should be a marked change in the gradient of the bhp graph where it passes through the 150bhp level.
Anybody got graphs that show this phenomenon?
Jay
I would like to see a selection of bhp/torque graphs that clearly demonstrate the restriction above 150bhp - there should be a marked change in the gradient of the bhp graph where it passes through the 150bhp level.
Anybody got graphs that show this phenomenon?
Jay
Edited by Jay Ayegees on Saturday 12th May 09:59
chrispitman said:
...the standard 5AM meter fitted is restrictive over 150BHP, so I see some have changed to the bigger 20AM.....Will they work fine with the std ecu setup and what has to be changed?
RPi's website contains a great item on the upgrade from 5AM to 20AM airflow mass meter.
I think there are two separate issues with the AFM.
The obvious one is that it provides a restriction to the air flow. How significant that is compared to all the other restrictions is hard to say, but the better the rest of the engine is the more significant the AFM is likely to be. The figure of 150 bhp has been quoted as the point where the AFM restrictions starts to be significant, and that seems pretty credible to me.
The other issue is that the AFM becomes less and less sensitive to air speed as the air speed increases. You might have 300 bhp' worth of air going in, but it could be hard to tell whether it's really 300, or 310.
Putting the sensor element in a bigger pipe addresses both of these issues, but means that it will be harder to get an accurate figure at very low flow rates. Of course this would change the meter calibration meaning you have to remap the ECU. I suppose the ideal would be to find a perfect combination that enables you to upgrade the AFM, raise the fuel pressure by amount X and get exactly the same characteristics across a higher power range. Somehow I doubt the magic combination exists though.
The obvious one is that it provides a restriction to the air flow. How significant that is compared to all the other restrictions is hard to say, but the better the rest of the engine is the more significant the AFM is likely to be. The figure of 150 bhp has been quoted as the point where the AFM restrictions starts to be significant, and that seems pretty credible to me.
The other issue is that the AFM becomes less and less sensitive to air speed as the air speed increases. You might have 300 bhp' worth of air going in, but it could be hard to tell whether it's really 300, or 310.
Putting the sensor element in a bigger pipe addresses both of these issues, but means that it will be harder to get an accurate figure at very low flow rates. Of course this would change the meter calibration meaning you have to remap the ECU. I suppose the ideal would be to find a perfect combination that enables you to upgrade the AFM, raise the fuel pressure by amount X and get exactly the same characteristics across a higher power range. Somehow I doubt the magic combination exists though.
spend said:
If your engine makes 350bhp with it ~ it might be making 400 without it / or a better flowing version.
Picking up on what BB and Spend have said....
Does this mean that TVR's advertised bhp figures, which are widely regarded as over optimistic, are probably about right given that TVR and most other manufacturers (I guess) will get their figures from test bed engines rather that the final road going car ?? (ie. with out the standard AFM).
Those who have used a RR and attained figures of 260bhp+ are probably in line with TVR's own figures, assuming an improved AFM?
I may be wrong but I think BB has said he'd like to get rid of his AFM and have it all controlled by the ECU (think that's what I read!?!). If this can be done and the AFM is out of the equation, would this allow you to regain the lost bhp.??? I theory I mean... I know there are other factors as GreenV8s has pointed out..
G
Edited by GJR on Saturday 12th May 20:08
Hi
I have yet to see a power graph that indicates a restriction at 150bhp - on the contrary those I've seen seem to have a steeper curve after 150bhp. If there was a restriction around 150bhp one would expect to see a change in the gradient to a shallower slope around this point.
Jay
I have yet to see a power graph that indicates a restriction at 150bhp - on the contrary those I've seen seem to have a steeper curve after 150bhp. If there was a restriction around 150bhp one would expect to see a change in the gradient to a shallower slope around this point.
Jay
Thats about right I reckon. Peter normally does make the point that the AFM is fairly adaptable if you make other changes around the engine ~ other control systems would need more map fettling ~ any changes to breathing are directly measureable by the AFM.
I recently came across a thread in the archives where I proposed an alternate ECU forum - is it worth asking Ted for this again?
Dave
I recently came across a thread in the archives where I proposed an alternate ECU forum - is it worth asking Ted for this again?
Dave
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