afm , throttle body

[daz the plumber]

before i get my car re chipped , would any one advice me to change the throttle body and afm to the larger size .once the car is chipped that is it, no more mods or i will be back to the same position .ive had a new cam , induction kit , carbon trumpets , nothing drastic .the thing is the trumpets are 38mm so am i defeating the object .

[Cider Andy]

If you're having a bespoke map written you certainly need the induction mods in place first.

[clive f]

I`d go for a 72mm plenum, and the insulator spacer between the inlet manifold and the trumpet base, as already said, do it all before the mapping or you`ll be back to have it done again afterwards.

[blitzracing]

The AFM is fine on the 3.9, and one of the tuners I spoke to said power actually dropped with a bigger AFM ! You will need bespoke chipping for the larger AFM, as the airflow / voltage charateristics are different and I hope you have a very deep wallet !! If you just do the throttle body etc, and off the shelf chip might well be OK with a bit of time spent on the Rollers to select the best one. (TVR power have boxes of chips for a reasonable price.) These ECU's are pretty adaptable however, and on the whole dont need rechipping each time you add a minor mod'.

Mark

[The AJP Griff]

blitzracing said:

The AFM is fine on the 3.9, and one of the tuners I spoke to said power actually dropped with a bigger AFM !

Thats interesting stuff.I'm not saying it's wrong either,but we did loads of induction work and experiments on the dyno,and found that the smaller AFM thats fitted to TVR Griff/Chims as std is restrictive to the airflow from 150bhp upwards,and the larger Bosch type of AFM is restrictive from 200bhp upwards.Therefore,the conclusion was that if your engine produces north of these figures,then you neeed something larger to stop restricting the airflow and so allow the engine to make more bhp.As every 4.0 tiv makes circa 200bhp from std,they all need something larger than what is currently available,in order to realise their full potential.
I'm really surprised that nobody has come up with a larger AFM than the Bosch one,to be honest.

[GreenV8S]

The AJP Griff said:

I'm really surprised that nobody has come up with a larger AFM than the Bosch one,to be honest.

I'm skeptical that there's much gain to be had here, but all you would need to do is shove the sensing element in the side of any size tube you fancy. You would need to recalibrate it, of course, but with it being a linear predictable change you might even be able to get away with winding up the fuel pressure or increasing the injector size.

[blitzracing]

Ive gone down this route somewhat. I took the standard 5AM and bored it out as far as it would go (+6mm ). Obviously this changes the airflow- voltage ratio, so I tweeked the internal resistors to get an identical voltage output as a stock unit and modified units on the same air flow source. On the bench I managed to get the two outputs identical from .7 -4 volts (90 % of the AFM's range), but when fitted to the car the fueling was very poor. I think the pulsed airflow from the engine is somewhat different from the smooth airflow I was using, so it needs recalibrating on my car. Next stage would be to fit the 2 AFMs to the car, compare the voltages and tweek them to match. Ill give it a go at some point.

On the restriction side, I did some expermenting on the bench. With the bored out unit flowing 4 volts worth of air (A 4.5 ltr under full load / revs = about 4.5volts), I then put the standard AFM into the air stream. Now if this was a major restriction the voltage on the bored out unit would have dropped, but there was no perceptable change. Admittedly it was not quite maximum airflow, but it was getting there. Id be interested to know how the limiting power factor is measured, as if you take the AFM out, the engine wont run anyway. A bigger or different AFM needs a remap, so more than one thing has changed, so it nullify's the results anyway. A simple pipe inserted to represent the AFM wont have the same flow charateristics as its not a venturi shape.

Mark

Edited by blitzracing on Thursday 10th July 13:10

[daz the plumber]

may be its best to leave the afm and throttle body alone.do you think the mods ive done require a new chip .the cam is nothing drastic , act induction kit and carbon trumpets .the only problem i do get is theres a glitch between 1100 up to 1600 where the engine seems to be lumpy .ive had experts look at this and they said a re chip would help.the biggest thing that attracts me to the new chip is the mpg ,been told that its improved .

[blitzracing]

Grrrrrr I hate some "experts". All they want to do is sell you a new chip at great expense. I suggest you ask them exactly how a re chip will fix it, as your low speed options on a catalyst car are VERY limited fueling wise. A lot of the hype you read about rechipping is refering to the stock Range Rover mapping, which was poor. The TVR mapping is much more fit for purpose, so the gains are pretty small if at all.

Mark

[GreenV8S]

daz the plumber said:

the biggest thing that attracts me to the new chip is the mpg ,been told that its improved.

[blitzracing]

Same old, same old. The catalyst mapping controls the fueling very closely around Lambda 1 (14.6:1). You cant deviate from this point as the ECU simply pulls it back whatever you do, as the lambda switching point is set in stone (wide band units excepted). The ECU also cuts the fueling on the over run, so how can you gain significant MPG?. Admittedly you can reduce the cold start fueling, which is pretty excessive, but what the gains are I dont know. If you make it leaner in the open loop region, you will loose power, and could damage the engine as well. Im sure any significant fuel saving refers back to Range Rover mapping.

Mark

[The AJP Griff]

blitzracing said:

On the restriction side, I did some expermenting on the bench. With the bored out unit flowing 4 volts worth of air (A 4.5 ltr under full load / revs = about 4.5volts), I then put the standard AFM into the air stream. Now if this was a major restriction the voltage on the bored out unit would have dropped, but there was no perceptable change. Admittedly it was not quite maximum airflow, but it was getting there. Id be interested to know how the limiting power factor is measured, as if you take the AFM out, the engine wont run anyway. A bigger or different AFM needs a remap, so more than one thing has changed, so it nullify's the results anyway. A simple pipe inserted to represent the AFM wont have the same flow charateristics as its not a venturi shape.

Mark

[/footnote]

The physical restriction wasn't measured on a bench,we wanted it to be measured on an engine in use,so thats why we did it on the dyno-real world if you like.All the bench theory in the world is no use without the proof of dyno figures to back it up
To measure the effects of the physical restriction that the AFM's cause,we inserted them ito the induction pipe of my Griff whilst it was running on the Omex system.Then we saw the BHP drop with each different type,and overlaid the graphs compared to the completely unrestricted pipe i was running
Joo at TCS has the results in graph form,and posted them up on here at one time.

[daz the plumber]

so why do rpi say the chip was mapped for a 2 ton range rover so the car is running rich untill hig revs .don`t think there chip would be any good as its made for a totaly standard car , they say the car runs lean thus saving fuel . allso the chip stops that wiff of fuel on start up and lifts the rev limiter 500 revs . i was told tvr did not spend enough time and money on fueling these cars .i would try one but £400 is little more than a joke .

[blitzracing]

I totally agree about the real world, and certainly cant argue with the test method, assuming the throttle body and trumpets are still stock. I remember the tuner I spoke to was very specific that the reduced preformance was with the stock inlet system, and by far the biggest improvement in air flow was to get rid of the coiled inlet tubing. But I guess we (and ACT) knew that....

Mark

[blitzracing]

daz the plumber said:

so why do rpi say the chip was mapped for a 2 ton range rover so the car is running rich untill hig revs .don`t think there chip would be any good as its made for a totaly standard car , they say the car runs lean thus saving fuel . allso the chip stops that wiff of fuel on start up and lifts the rev limiter 500 revs . i was told tvr did not spend enough time and money on fueling these cars .i would try one but £400 is little more than a joke .

You've hit the nail on the head. RPI sell Mark Adams chips, and if you look at his ebay chip sales, he quite clearly says what you get for your money, but 90% refers to the RANGE ROVER MAPPING. Its also very non specific about the catalyst maps, that as Ive said simply cant run rich or lean (in closed loop)as such. TVR power had access to the relevent "development" hardware to do the mapping needed for their cars, so the improvements are much smaller. Easy for people to say TVR did not spend enough time when there is £400 for a 10p chip in the balance!

Mark

Edited by blitzracing on Thursday 10th July 16:35

[GreenV8S]

daz the plumber said:

so why do rpi say the chip was mapped for a 2 ton range rover so the car is running rich untill hig revs

That's something you would have to ask RPI, but people who are intimately familiar with the TVR 14CUX installations have said that no TVR ever left the factory with the stock 'RR' chip and I'm inclined to believe them.

While you weigh up the various views being offered, you might like to consider that RPI are basically resellers and not technical specialists. They're good folks and very helpful but I would be extremely cautious about taking anything they say as gospel.

Mark Adams has worked on my V8S several times over the years with various engine specs. With the standard (Chim 4.0 cat) engine it was noticeable that the car drove much better afterwards (as expected, the power and fuel economy gains were very small and certainly not worth the cost of the work in their own right). After modifying the engine, Mark's work enabled me to realise the full potential of the mods while retaining the same driveability. You'll get benefits with a standard engine but it's far easier to justify the cost of this work if you haver modified the engine.