Intake Air Pipe Length
Discussion
Bit long winded this but hopefully there is an expert amongst us who can offer advice.
Having wrapped the AFM and intake pipe in insulation I found the pinking under full throttle the car used to do had dissapeared and that power seemed to be up a bit.
This proved lowering the intake temp seemed worthwhile (we have very high temps here so it's more of an issue than in the UK) so I fabricated a sealed box round the AFM and filter, insulated it from engine bay heat and ran a 80mm pipe down to the front of the car.
The intention was to then fabricate a scoop to try and create a positive pressure in this box when moving. However I thought I would give it a try just to make sure all wiring was ok and in the meantime the cars characteristics seemed to have changed dramatically.
It is even louder (exhaust), has an even thump when idling rather than an offbeat rumble, runs smoother at low revs but definitely has less grunt.
I then tried it without the box lid on and with no pipe so in effect it was pretty much how it was before but it was still different, the power band seemingly narrowed to about 3-5000 whereas before it would pull from 2000 all the way up to a gearchange.
The only real change was the length of the pipe between the plenum and AFM, previously shortened anyway to around 300mm to allow the AFM to sit in a direct line (where the coolant tank normally is), it was cut to 200mm to allow room for the box (otherwise the bonnet strut would hit the box when lowered).
In a roundabout way then what I am asking is -
What effect does plenum to AFM pipe length have and is there an ideal length to suit all applications ?
Having wrapped the AFM and intake pipe in insulation I found the pinking under full throttle the car used to do had dissapeared and that power seemed to be up a bit.
This proved lowering the intake temp seemed worthwhile (we have very high temps here so it's more of an issue than in the UK) so I fabricated a sealed box round the AFM and filter, insulated it from engine bay heat and ran a 80mm pipe down to the front of the car.
The intention was to then fabricate a scoop to try and create a positive pressure in this box when moving. However I thought I would give it a try just to make sure all wiring was ok and in the meantime the cars characteristics seemed to have changed dramatically.
It is even louder (exhaust), has an even thump when idling rather than an offbeat rumble, runs smoother at low revs but definitely has less grunt.
I then tried it without the box lid on and with no pipe so in effect it was pretty much how it was before but it was still different, the power band seemingly narrowed to about 3-5000 whereas before it would pull from 2000 all the way up to a gearchange.
The only real change was the length of the pipe between the plenum and AFM, previously shortened anyway to around 300mm to allow the AFM to sit in a direct line (where the coolant tank normally is), it was cut to 200mm to allow room for the box (otherwise the bonnet strut would hit the box when lowered).
In a roundabout way then what I am asking is -
What effect does plenum to AFM pipe length have and is there an ideal length to suit all applications ?
Dunno!
BUT my induction pipe and elbow has been shortened and i have an invoice from Tower view in me book of receipts to move and re-position the AFM - for some reason.
Also my poke comes in one big huge burst at 3,000 rpm then just does not stop. At around 2k its like a ford fiesta only worse.
It has a re-profiled cam fitted and the guy who had the work done used to live in London?. Perhaps he got fed up of lighting up the tyres at the lights on Bond Street all of the time!
MikeB
BUT my induction pipe and elbow has been shortened and i have an invoice from Tower view in me book of receipts to move and re-position the AFM - for some reason.
Also my poke comes in one big huge burst at 3,000 rpm then just does not stop. At around 2k its like a ford fiesta only worse.
It has a re-profiled cam fitted and the guy who had the work done used to live in London?. Perhaps he got fed up of lighting up the tyres at the lights on Bond Street all of the time!
MikeB
Hi Chunder,
It might be worth emailing Richard at RT Racing, pistonheads nickname RolexBlue2000. He modified his 450SE with a cool air intake. I am sure he wrote an article on it in Sprint magazine a good few years ago. I will try and find it for you and email it. It may take some time to find though !!
Regards
Nige'
It might be worth emailing Richard at RT Racing, pistonheads nickname RolexBlue2000. He modified his 450SE with a cool air intake. I am sure he wrote an article on it in Sprint magazine a good few years ago. I will try and find it for you and email it. It may take some time to find though !!
Regards
Nige'
Thanks chaps - RT used to sell a cold air ram kit for V8 wedges through Wedge Auto's so may email him to see if he can shed any light.
I think this involved a box fitted round the filter in the normal position that was then piped down to a small scoop hung off the front chassis just behind the radiator.
Nige, if you have a copy of the article that would be very useful.
I may post on the general engine stuff because it's really what effect the plenum to AFM pipe length has that I am after.
I remember my Sunbeam Lotus ran very rich after fitting a direct bolt on filter box and not putting the trumpets back - something to do with the trumpet shape and length affecting air intake velocity. I imagine the length of the air intake pipe on a V8 wedge may affect things the same way - I reckon Tim at ACT would know a fair bit about this ?
I think this involved a box fitted round the filter in the normal position that was then piped down to a small scoop hung off the front chassis just behind the radiator.
Nige, if you have a copy of the article that would be very useful.
I may post on the general engine stuff because it's really what effect the plenum to AFM pipe length has that I am after.
I remember my Sunbeam Lotus ran very rich after fitting a direct bolt on filter box and not putting the trumpets back - something to do with the trumpet shape and length affecting air intake velocity. I imagine the length of the air intake pipe on a V8 wedge may affect things the same way - I reckon Tim at ACT would know a fair bit about this ?
Richard's solution was to make a box for the fliter and connect it to a scoop that was at the bottom of the car. Worked well but and there is always a but, the scoop was ideally positioned to take in water and potentially hydraulic the engine if the car encountered big big puddles or floods.
The best place to take cold air in is from the bottom of the windscreen. It is a high presure zone and unlikley to get puddles anywhere near it.
The best place to take cold air in is from the bottom of the windscreen. It is a high presure zone and unlikley to get puddles anywhere near it.
shpub said:
Richard's solution was to make a box for the fliter and connect it to a scoop that was at the bottom of the car. Worked well but and there is always a but, the scoop was ideally positioned to take in water and potentially hydraulic the engine if the car encountered big big puddles or floods.
The best place to take cold air in is from the bottom of the windscreen. It is a high presure zone and unlikley to get puddles anywhere near it.
What's a puddle
I think I've cured the possibility of water being drawn up by also re-routing the ducting from the two front spoiler entries, originally designed for brake cooling I assume, but that was actually used to feed fresh air to the dash vents.
The passenger side one now also feeds air into the same box - increases the amount of cooler air available and should either of them become immersed air will be drawn up the other one as it is easier to pull air up a pipe than water. They both produce equal amounts of positive pressure at the air box when moving as well so air does not flow in one and out the other. Any moisture drawn into the box will collect in a semi-circular chamber at the bottom and then evaporate off.
The chances of the front spoiler entry and the scoop, which is set slightly higher and quite a way back (more or less directly under the drive belts), both becoming waterlogged is non-existent here unless I drive into the sea !
I am yet to actually fit the scoop and it will be pretty big and with a 75mm pipe and a 40mm pipe feeding a near airtight box it should be interesting to hook up a meter and see if it actually produces positive pressure at speed. If it does it should only be 1 psi or so above atmospheric and the AFM should see the increased air volume and increase fuelling to suit hopefully increasing initial throttle response once on the move (maybe substantially at higher speeds).
Then again it may do nothing but I had some old zinc sheet that needed to be used or thrown out anyway !
I fitted the scoop and insulated intake pipe and took the car out for a drive.
Upon starting there was plumes of smoke from the exhaust. I realised it was over fuelling big time and took the lid off the cold air box thinking something must be blocking air flow - still the same. To cut a long story short I had to increase the spring tension on the AFM just to get the car to idle ok. Have no idea why this happened - nothing had been touched that should have affected this. Anyway, the car is due to be set up again properly shortly by someone who knows what they're doing so I wasn't overly concerned.
On the road the car sounded great with a much harder exhaust note. After a thorough warm up I gave it a full throttle run and the difference was amazing. No sign at all of pinking and the first two gears dissapeared in a couple of seconds each. At higher speeds the pick up is also dramatically improved with instant power available. Induction noise has dissapeared and the note on acceleration is a real howl, I will have to time the car to 100 once it has been set up because it really pulls strongly. Another plus is engine temp as it was 35 deg C and it took much longer to reach 90 at standstill and for the fans to cut in than it did before, virtue of the fact the intake air is practically the same as ambient.
It is also now cracking on the overun with a vengenance - not sure whether it's the fact the AFM and mixture need a good set up or the force of air at speed pushing past the AFM flap. To test what pressure was being developed I connected a differential pressure meter with one lead in the cold air box and the other open under the bonnet. Results were interesting showing 4 mbar postive pressure in the box whilst cruising at 60. Half throttle at any speed produced a 0 reading with anything above that a small vacuum. This would be why throttle response has improved because there is a charge of air sitting there ready to be sucked up when the throttles opened.
After an hours fun I pulled into the garage and immediately opened up the lid on the air box. Previously the AFM was too hot to touch - now it was actually cool and no warmer than the door handles !
Therefore can thoroughly recommend this mod, probably not as worthwhile in cooler climates but it seems to have helped my car considerably. Once I have some cash I will use the very poorly built sheet metal air box and scoop as a pattern and get them made either in some kind of alloy or GRP but for now, after expenditure of about 15 quid on rivets and 1m of 75mm duct together with some old sheet steel and air con ductwork insulation, well pleased.
Upon starting there was plumes of smoke from the exhaust. I realised it was over fuelling big time and took the lid off the cold air box thinking something must be blocking air flow - still the same. To cut a long story short I had to increase the spring tension on the AFM just to get the car to idle ok. Have no idea why this happened - nothing had been touched that should have affected this. Anyway, the car is due to be set up again properly shortly by someone who knows what they're doing so I wasn't overly concerned.
On the road the car sounded great with a much harder exhaust note. After a thorough warm up I gave it a full throttle run and the difference was amazing. No sign at all of pinking and the first two gears dissapeared in a couple of seconds each. At higher speeds the pick up is also dramatically improved with instant power available. Induction noise has dissapeared and the note on acceleration is a real howl, I will have to time the car to 100 once it has been set up because it really pulls strongly. Another plus is engine temp as it was 35 deg C and it took much longer to reach 90 at standstill and for the fans to cut in than it did before, virtue of the fact the intake air is practically the same as ambient.
It is also now cracking on the overun with a vengenance - not sure whether it's the fact the AFM and mixture need a good set up or the force of air at speed pushing past the AFM flap. To test what pressure was being developed I connected a differential pressure meter with one lead in the cold air box and the other open under the bonnet. Results were interesting showing 4 mbar postive pressure in the box whilst cruising at 60. Half throttle at any speed produced a 0 reading with anything above that a small vacuum. This would be why throttle response has improved because there is a charge of air sitting there ready to be sucked up when the throttles opened.
After an hours fun I pulled into the garage and immediately opened up the lid on the air box. Previously the AFM was too hot to touch - now it was actually cool and no warmer than the door handles !
Therefore can thoroughly recommend this mod, probably not as worthwhile in cooler climates but it seems to have helped my car considerably. Once I have some cash I will use the very poorly built sheet metal air box and scoop as a pattern and get them made either in some kind of alloy or GRP but for now, after expenditure of about 15 quid on rivets and 1m of 75mm duct together with some old sheet steel and air con ductwork insulation, well pleased.
It's difficult to say whether the plenum to AFM length will have any effect at all. Inlet tuning is based on trying to get the positive pressure from the shock wave, produced by the inlet valve opening, to bounce back from an open end just as the valve is closing. This has the effect of pushing a little extra mixture into the cylinder. The problem is that the reflection may take place at the plenum chamber, in which case the tuned length will be from the valve to the plenum. If not, you can calculate the tuned length from
2940 x sqrt(degF+460) / engine rpm
So if your inlet air temperature is 100F, and you want extra power at 3000 rpm, the tuned length is 23.5 ins. As you can see from the equation, if you lower the intake air temperature and keep the same tuned length, you will move the engine speed at which you get the extra boost higher.
The drawback (as there always is) is that in creating a positive wave at one point in the inlet tract you also create a negative wave half way along the pipe. This means that at a different speed to the one you get the boost, you will get less power. Hope this helps.
2940 x sqrt(degF+460) / engine rpm
So if your inlet air temperature is 100F, and you want extra power at 3000 rpm, the tuned length is 23.5 ins. As you can see from the equation, if you lower the intake air temperature and keep the same tuned length, you will move the engine speed at which you get the extra boost higher.
The drawback (as there always is) is that in creating a positive wave at one point in the inlet tract you also create a negative wave half way along the pipe. This means that at a different speed to the one you get the boost, you will get less power. Hope this helps.
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