Air Intake

[Berw]

Ok my first posting here. I run a Phoenix with a Lotus Esprit 2.2 Block breathing through twin 45’s and KN Filters.

This is a big bit of metal and it gets hot under the engine, cooling is well sorted via, 4 core rad and electric pump, but obviously under bonnet temp is high, and I’m wondering what sort of power increase I could get from feeding cooler air into the carb intake.

Car is a pure racecar and runs in Malaysia with shade temp of 33 degree C, so even ambient air temp is high. I’m thinking of taking off the KN’s and building an air box with an air in take tube feeding air from in front of the Radiator, via a conical performance filter.

This will not be an easy job, as space is at a premium under the bonnet, and because of the capacity of the engine, and the revs it will pull I need to fabricate a big box, so I’d like to get some idea of what sort of power increase this may be worth.

Does any one know if this would be worth the effort what sort of power gain could I get.

Thanks Kelvin

[stylussprinter]

Ok my first posting here. I run a Phoenix with a Lotus Esprit 2.2 Block breathing through twin 45’s and KN Filters.

This is a big bit of metal and it gets hot under the engine, cooling is well sorted via, 4 core rad and electric pump, but obviously under bonnet temp is high, and I’m wondering what sort of power increase I could get from feeding cooler air into the carb intake.

Car is a pure racecar and runs in Malaysia with shade temp of 33 degree C, so even ambient air temp is high. I’m thinking of taking off the KN’s and building an air box with an air in take tube feeding air from in front of the Radiator, via a conical performance filter.

This will not be an easy job, as space is at a premium under the bonnet, and because of the capacity of the engine, and the revs it will pull I need to fabricate a big box, so I’d like to get some idea of what sort of power increase this may be worth.

Does any one know if this would be worth the effort what sort of power gain could I get.

Thanks Kelvin

I can only go by my own experience doing exactly what you're planning. Dunnell told me that I wouldn't get the power that my engine showed on his dyno if it didn't get cool air and plenty of it Hence cutting/shutting an airbox without any intake holes pre-cut which I bought from a motorsport company who had developed the box for a 2.3lt Duratec fitted to their Lotus 23 Replica. The box is 215mm deep so it can be cut shorter but I kept all it's depth to aid airflow. I put a 100mm diam' pipe into it with Sikaflex then to the BMC F1 filter at the grill facing forwards. 150mm diam' would have been even better but I couldn't get it in
Dunnell said that I'd probably lose 8 to 10 bhp at the top end if air was drawn via the engine bay Obviously the greater the bhp the more the loss . Even with your ambient temp's there's still going to be a differential from engine bay to at the grill temp's Yours chukking out 270bhp ---- there just HAS to be an advantage

[alecmartin19]

a cold air feed for your engine will definately increase your output. the scientific reason for this is the stoichiometric ratio. which is for petrol around 15:1 thats 1 part fuel to 15 parts air by density. warm air is less dense than cool air. if cold air is more dense, it means that you add more fuel to meet the stoichiometric ratio. more fuel in means higher calorific value of the charge entering cylinder. this means a greater release of energy and thus, more power. how much more you will get would only be a guess. a rolling road session would need to be undertaken under controlled conditions but if you think that under bonnet temperatures probably reach into 3 figures, getting 30 degree ambient air will be a big bonus.

hope that gives you a slight understanding into why cold air helps.

[alecmartin19]

previous post slightly wrong. its by mass not density but i guess the mass of air increases with an increase in density so partly right. the correct stoichiometric ratio for petrol is around 14.7 to 1 and not 15 to 1 which would in fact give a slightly lean mixture.

[Berw]

.Hi Thanks for the info, I understand the physics, fuel air ratio, just wondered if in practice it was worthwhile, looks like it is if Rob reckons on 10 bhp.
I assume that there must be some constant (like the coefficient of expansion for metal) whereby you can calculate the mass/density of a gas for a given temperature). I work for an oil and gas company, so I’ll ask one of our process engineers out of interest.
I think your temp figures are right, (I’m getting 70 degree C in the tyres, and the engine runs at 98 C), so the under bonnet must be way up, even at ambient 35 I’ve got to be at least halving it,
Rob, can you remember where you bought the air box?

Thanks for the input Kelvin

[Berw]

Just got the following from our engineering dept (I always knew they had a purpose).

The formula to calculate gas density
Pressure x Mol Weight = Density x R (Gas constant) x Temperature
Assuming pressure is the same, equation can be simplified as
Density 1 x Temperature 1 = Density 2 x temperature 2

1 and 2 indicate the air initial and final conditions
Temperature is in Kelvin i.e. deg C + 273.15

Example:

Air density at 0 deg C and 1 atm is 1.29 kg/m3
Therefore air density at 35 deg C and 1 atm is
1.29 x (0 +273.15) = Density 2 x (35+273.15)
Density 2 = 1.14 kg/m3

OK if I run these calc then the Density of the Air at 35 C is 11 % higher than at 70 C (my under bonnet tem is at least that) and If I assume 90 it is 20%.

So keeping it simple I should be looking to ‘burn” 10 to 20% more fuel after I fit the air intake.

Thanks for the input

Kelvin
(Of course using degree Kelvin is a coincident so Rob do try the calculation id degree’s Robert)

[stylussprinter]

H'mmm , degrees Robert This may provoke a '' Matt Downes '' comment along the lines of how much of a ' nutter ' you are . I seem to recall a photo of Stylus & driver he sent me with the caption '' who's this nutter then ''

Kelvin , I'll dig out the website , email etc , if not the invoice , for the guy who sold me the blank airbox and report back ok.

[stylussprinter]

Got it Kelvin His name is John Bridge and the company is still in existance although not manufacturing the 23B replica right now , due to the slowing trade.
The website is http://www.mambamotorsport.co.uk -- look under components and the airbox is shown cut/shut for the Duratec . Mine was supplied in plain f/glass without any holes nor clip fittings . It was late coming because the poor guy had 2 feet of flood water all through his offices and workshop BUT he appologised and charged me £120 only as a goodwill gesture . A really nice guy. Please mention me as your contact if you do try him.

phone 01793 784720 email john@bridge-eng.co.uk

[MattD]

[quote="stylussprinter"]H'mmm , degrees Robert This may provoke a '' Matt Downes '' comment along the lines of how much of a ' nutter ' you are . quote]

We're all Nutters on here...

Must be for spending 2 yrs or so in a garage, building a car out of some bent tubes, sticky back plastic & oily old donor parts. Then after all the Ministry red tape, we embark on a programme of "must have" upgrades, just so it goes/stops/turns/scares the crap out of us/etc a bit better.

"Normal" people pop down the road & buy a nice Lotus......

[stylussprinter]

Well with global finances as they are , the price for a LOTUS second hand has plumeted Difficult to justify building for some people when the alternative Elise can be had for £6000 now BUT we just like being individual don't we

[alecmartin19]

but there are loads of lotus on the road. don't very often see another stylus going past you do you! a very exclusive club.

cheers for the extra input on the fuel air ratio. i know some people may not understand it but hopefully it has helped explain to others how it all works. i like all the scientific stuff that goes in to making an engine work and getting its best performance. i work on the rolls royce RB211 for a living so engines are a big part of my life. i like noise! its an addiction i'm sure.

[stylussprinter]

but there are loads of lotus on the road. don't very often see another stylus going past you do you! a very exclusive club.

cheers for the extra input on the fuel air ratio. i know some people may not understand it but hopefully it has helped explain to others how it all works. i like all the scientific stuff that goes in to making an engine work and getting its best performance. i work on the rolls royce RB211 for a living so engines are a big part of my life. i like noise! its an addiction i'm sure.

Noise is great -- love it but noise plus acceleration AND speed , is bloody fantastic which is why I like continually fettling

Text me when you can get to Aston Clinton again Alec

[alecmartin19]

will do rob! hopefully not too far into the future! i'm working this week. finish on monday morning. are you about during the week next week?

[stylussprinter]

will do rob! hopefully not too far into the future! i'm working this week. finish on monday morning. are you about during the week next week?

Any day next week -- just let me know

[Berw]

Hi Rob
Never heared back from your supplier on the air box, but I just bought the box off a Lotus Sunbeam on ebay, at my frinds plae in Wales, will get it carried out to me in Malaysia with my next visitor, and start the installation.
Kelvin