Designing a cold air intake for a Daimler Dart?
Discussion
I am looking into designing a 'cold air intake' system for my Daimler SP250/Dart. Below is a link to my ideas to date. Don't laugh too much, the stuff used is very 'Blue Peter' just to get the concept together. I am looking to use two K&N oval air filters in custom designed housings. Two potential problems could arise, one not getting enough air through or two, maybe getting too much air pressure through and the 1-3/4" SU carbs not working properly. Any experts out there with any worthwhile tips on air flow and pressure in such a setup? The ducting pipes will be 2" (50mm ID). if there is a risk of over pressure into the carbs, then I am thinking of some sort of basic one way pressure relief in the filter housing.
Why do this some of you might ask? Well I live in South Carolina, USA and for about 4 months of the year the weather is very hot (30 deg C plus / 90-100 deg F) with humidity around 80-90 percent. the underbonnet temps get very high and the stock air filters are nestled nicely on top of the V of the engine with only steel wool screens sucking in all that super hot air.
Or am I just wasting my time????
http://s293.photobucket.com/albums/mm42/geeman237/...
Why do this some of you might ask? Well I live in South Carolina, USA and for about 4 months of the year the weather is very hot (30 deg C plus / 90-100 deg F) with humidity around 80-90 percent. the underbonnet temps get very high and the stock air filters are nestled nicely on top of the V of the engine with only steel wool screens sucking in all that super hot air.
Or am I just wasting my time????
http://s293.photobucket.com/albums/mm42/geeman237/...
What you are proposing is worthwhile.
I would look to running 3" pipes if you can as the 2" may be a little restrictive because of their length.
Don't bother with a scoop on the front of the pipe it's making things more complicated than they need be.
Keep the front of the pipes as high as possible to keep them clear of dirt from the road although I doubt it rains to much where you are.
Over pressure would only happen with a big scoop and high speed so don't worry about that. All that would happen is you would get the very mild effect of a turbo or super charger. The carb adds the right amount of fuel to the air passing through...if you pass more air it adds more fuel.
Steve
I would look to running 3" pipes if you can as the 2" may be a little restrictive because of their length.
Don't bother with a scoop on the front of the pipe it's making things more complicated than they need be.
Keep the front of the pipes as high as possible to keep them clear of dirt from the road although I doubt it rains to much where you are.
Over pressure would only happen with a big scoop and high speed so don't worry about that. All that would happen is you would get the very mild effect of a turbo or super charger. The carb adds the right amount of fuel to the air passing through...if you pass more air it adds more fuel.
Steve
geeman237 said:
Two potential problems could arise, one not getting enough air through or two, maybe getting too much air pressure through and the 1-3/4" SU carbs not working properly.
Ah the old faithful "how much faster will I go with a big air scoop on the bonnet?" question which seems to crop up fairly regularly in the racing fraternity despite having been solved by Mr Pitot and Bernoulli a couple of hundred years ago. Well I guess it depends how fast you reckon your Daimler Dart will go. If it'll crack 150 mph you might almost be into something measureable 
The stagnation pressure (ram air effect if you like) rises with the square of velocity and assuming it was even possible to make something 100% efficient that didn't suffer flow losses internally the percentage gains over standard atmospheric pressure you'd expect would be as follows.
50 mph - a monstrous 0.3%
100 mph - 1.2%
150 mph - 2.7%. Something you could actually spot on a dyno.
If however you got half of the above you'd be doing well and in any case the SU carbs would carry on working just fine because they don't care what the incoming air pressure is.
So cold air is always a good thing but ram air effect is unlikely to be one of your main concerns with a Daimler Dart.
Thank you for the comments. At least I might be heading in the right direction. I will take the advice on board. With the radiator in the car there isn't much room to route the ducting anywhere else. The car is fitted with twin 10" electric fans (mechanical fan ditched due to rack and pinion steering conversion) mounted on a shroud over the radiator. I may also look back at seeing if a single filter and box could be mounted and then ducting split to each carb. Overall I am aiming for something with more of a nod to a period look rather than the Too Fast Too Furious blue silicone tubing look. (No offence to those that lean towards that look). I am have been onto K&N and they say the engine would need a 263CFM requirement, based on the 2.5 litre engine and 6,000 rpm limit (not that I go there, close sometimes). If I end up with a design I'll be sure to follow up.
Thank you
Thank you
If you have a shuftie in here http://www.pumaracing.co.uk/diagnose.htm
you'll see that about 25 sq inches of filter area per 100 bhp is ample which with your 140 bhp makes it 35 sq inches total. Not as big as you might think. A panel filter 7" x 5" or a round filter just 4" diameter x 3" high (or vice versa) is all that's needed.
I'd be more tempted to have the filter(s) up the front and just ducting going to the carbs rather than trying to make custom airboxes for each bank. Seems like a shed load of work.
you'll see that about 25 sq inches of filter area per 100 bhp is ample which with your 140 bhp makes it 35 sq inches total. Not as big as you might think. A panel filter 7" x 5" or a round filter just 4" diameter x 3" high (or vice versa) is all that's needed.
I'd be more tempted to have the filter(s) up the front and just ducting going to the carbs rather than trying to make custom airboxes for each bank. Seems like a shed load of work.
BTW, the single equation that K&N use to estimate airflow requirement is a complete nonsense which takes no account of the engine design, 2 valve or 4 valve, ancient or modern, standard or tuned or the most important thing, actual bhp output, and is based on highly efficient race engines. Your old Daimler only has a requirement for about 180 CFM, not the 263 they are trying to sell you.
I'm not going to go into the maths unless people actually want me to but I'll probably add it to the website as a technical article one day.
I'm not going to go into the maths unless people actually want me to but I'll probably add it to the website as a technical article one day.
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