Cold Air Intake, any measured differences?

[btoran]

csi2000s - nice looking car. what shocks are you running and did you cut the springs?

[csi2000s]

I'm running Koni Reds and the springs come from a local Fiat specialist here in Australia who has them made to his specs.

[pgilling]

Folks, despite all the conjecture about what the real under bonnet (sorry hood!) temperatures are, surely we can all agree that the temperature under the bonnet is warmer than ambient, and higher intake temperatures reduce performance and increases the likelihood of detonation due to the reduced charge density. And this is why manufacturers normally have air intakes from the front of the car.

I've just had a 2L engine built by Guy Croft put in my 1977 Spider. I didn't go for a radical state of tune as I wanted it to be a drivable, torquey cruiser. Therefore Guy suggested just using a Weber 32/36 DGV (good for at least 170 bhp), although the engine does have his race quality HC pistons, a ported head, a custom built exhaust and one of his high-lift cams on the inlet side. Consequently, despite this relatively moderate state of tune, Guy did warn me that high under bonnet temperature (and therefore high intake temperatures) may cause detonation. So he suggested I would benefit from an ambient-fed airbox. After some thought, Guy believed we might get away without one so I just put a normal K&N filter on the carb. However, funnily enough, on nice warm days (yes we do get them in the UK sometimes!) I got slight oinking at 4000 revs in 4th gear under hard acceleration. We then put in race standard plugs (the lower temperature ones) and this did improve things, but it was still there. So therefore the only thing we can think of is the intake temperature being too high – as Guy had originally warned me!

So before I have the final Rolling Road tune done I'm going to fit one of these from Webcon UK:



That, coupled to a ducting hose and filter to the front of the car through this hole I created will hopefully provide the perfect solution.



So I will let you know how the fit goes and if the pinking stops. Unfortunately, I'm not going to waste time doing before-and-after rolling road runs as I need to cure the pinking first as I don't want to damage the engine! But of course I will say if the new intake cures the pinking issue or not.

[Thunberg]

When it is 9¤ C outside it will be around 11-16¤ C on top of your carburetor (40 idf, Lynx ramflo, 1995, 124 SC -73) while driving in 70- 80km/h.

[racydave]

When you are dealing with only 100HP, controlling all the optimum ranges does make a difference. And unless it is race only, you need to tune for overall performance. The stove pipe that is on our original set up is a great help in cold temps, as the fuel atomizes best at the correct temps. But it must work correctly. The same goes for hot temps as the engine requires cooler air than what is probably supplied under the hood. I like the thermal switch idea, as it can adjust to changing temps, and give better overall performance. I guess you can try and calculate what might happen under the hood. But using a temp sensor at the intake should be the easiest way to judge what is really happening. A Lambda sensor might help provide some info as to whether any of this really makes a difference, as it could analyze the results thru the exhaust gasses. I may end up with the ability to prove this whenever I can get my new lap-top to recognize the Mega-jolt program, and I can actually monitor and graph the lambda sensor with the ign system. But it might take several dyno tests to actually prove this theory. The ECM in a modern vehicle can control all this thru all the inputs and controlled outputs. I like my carb, and continue to do some guess work and seat of the pants calculations based on theory, history, and comments from other like minded fiat friends. A little science is helpful. Great thread.

[vandor]

> I like the thermal switch idea,

I think the carb'd 2000 Spiders had a thermal switch built into the air intake to switch between outside air or pre-heated air.. My Volvo 240s had it too.

[Daniel]

1 thing to consider about density and cool air while driving/testing/racing a car nothing can add density to the air
that we do we're just trying to avoid the hot air produced by the exhaust and radiator. If your starting off with more
dense air to begin with your going to have a better result even if it's warm then thinner cool air in the end.
A buddy of mine saw a few tenths of a sec difference in his drag car's time slips while running at sea level down in
carlsbad. Many car magazines and other articles talk about this topic and of course the aftermarket companies would
love for you to buy their gadgets and for us to believe the % numbers in gained power they boost of. I believe cooler
air makes a difference how much is the question.

[Thunberg]

This article (link) by J. R. Sodré and S. M. C. Soares with the title "Comparison of Engine Power
Correction Factors for Varying Atmospheric Conditions" measaure acceleration at different temperatures and at different atmospheric pressures.

http://www.scielo.br/pdf/jbsms/v25n3/a10v25n3.pdf

[pgilling]

I fitted the plenum from Webcon on my 32/36 DGV Weber and connected it to a K&N Apollo universal filter. Unsurprisingly I was getting pinking due to a combination of the warm weather, the high compression of the engine (race standard pistons & rods) plus the extra heat generated by the fabricated exhaust manifold. This has cured the pinking. Of note, I recently did a dyno run and it showed hundred and 148 BHP at flywheel.

The next job is to fit a Computronics ignition system from Alison's as I have been having problems with the upgraded standard type distributor.

[MrJD]

i was just thinking... Our cars pipe hot water through the intake manifold to warm it up. So, isn't the cold air concept kinda wasted being that the manifold warms the air anyway?

[RRoller123]

LOL I was wondering the same thing. The FI has a throttle plate heater too.

[chrisfiat]

as anyone who lives in a 4 season area, ie new england for instance, knows. cold air makes a huge difference. i live in New Hampshire, and on days like last week, and this week, where our daytime highs are 85, and our 10:00 to 11:00 pm temps are in the high 50's there is a noticeable difference in power going up my hills in the evening / night temps