Getting Good Cold Air Flow Into A Set Of 45s On A 205.

[Guest Megster]

I'm in the last stages of converting my car to a set of twin 45s and was wondering how I could improve the airflow into them without putting a scooby style bonnet scoop on the car (My production class rules do not allow the cars shiloutte to be changed - but we can cut holes etc in the exhisting 205 shape).

 

 

I have seen a car with a half sized ally radiator and a ram -air type tunnel arrangement feeding into the carbs where half of the original rad used to be. But I can't afford to do this.

 

Any alternative ideas? Lowering the existing rad slightly and removing the cross member (replacing it with a custom made bar - a bit like a strutbrace at the front ) is an early idea we've come up with. Will doing this have a knock on effect on the cooling system? Any thoughts?

 

 

 

 

Cheers -AJ

[16v205 9]

Hi

 

Had my car mapped in september running throttle bodies and the intake temps were rising up over 65 degrees. I took it back for mapping again end of october, in the mean time id dropped the rad and made a new bracket up to hold the rad fans. The intake temp was then the same as ambient around 20 degrees and didnt rise once.

 

You can drop the rad and make new brackets for holding the rad fans and not have to move any of the cars original bodywork.

 

Rich

[mfield 20]

Carbs have a problem with direct air flow iirc. They can suffer from freezing at high speed and if the inlet pressure raises to high it can start to push the fuel back up the jets must be bloody rare though. I've always understood the best thing is an airbox with the inlet somewhere nice and cool

 

Must add TB's dont suffer either of the above and work great with direct airflow .

[Martin@PRD 0]

Be cautious with direct air flow with twin carb set-up as carbs are set on a rolling road with a fan that can not produce air flow more than 80 Mph (in some cases), therefore with direct air flow over 80+, carbs will start to run lean and this courses serious damage to valve etc.

 

In colder whether I experienced carb freezing at 90+ which resulting in misfiring, so I fitted a plate in front of the carbs so that cool air could pass into the engine bay.

 

On the other hand throttle bodies perform better with direct airflow as fuel can monitored by the Ecu and adjusted to suit via lambda sensor were carbs are at set values

 

EDIT: Mike you beat me to it!!!

Edited January 14, 2006 by Martin@PRD

[mfield 20]

who's Mike ? my names Mark but ill forgive you

[crogthomas 0]

This is what you need to but or make:

 

 

Then duct air from infront of the radiator similar to the way the original setup does it (or infront of the windscreen). That way you get clean, cool, high pressure air without sucking up stones, rain, small fury animals or mucking up the aerodynamics of the car. Jobs a good-un.

[Martin@PRD 0]

who's Mike ? my names Mark but ill forgive you

 

Sorry Mark

[Jonmurgie 2]

This is what you need to but or make:

 

 

That's the new airbox from Pipercross... looks good (saw it at Autosport) but it's only in 1 size so only good for small trumpets. Airbox is a nice way of getting lots of cold air to the carbs/tb's with a good equal pressure... here's what I'm currently fitting to my Mi:

 

 

[Guest Megster]

Thanks everyone.

 

Used to have carb icing problems on my old GSXR.

 

AJ

[Sandy 191]

What is that strpped onto the strut brace? Not a fuel conditioner I hope!!

[Jonmurgie 2]

What is that strpped onto the strut brace? Not a fuel conditioner I hope!!

 

LOL, I think it was... but it's coming off anyhow

[Sam 4]

http://dcoe.net/gallery/hillclimb/Tregrehan4.JPG

 

Ideal?

[crogthomas 0]

http://dcoe.net/gallery/hillclimb/Tregrehan4.JPG

 

Ideal?

 

I wouldnt call it ideal. There are a few points that could be improved. For a start the opening in the front looks to be far too big for the amount of air that is required. All it will do is increase drag on the car as a whole and therefore negate any power increase. Also the forward opening going directly into the trumpets will cause a lot of turbulence, just where you want a nice smooth flow. It also requires the radiator to be lowered, which would decrease ground clearance and increase drag.

 

A similar large volume airbox fed by a tube from a high pressure region would be much better.

[Sam 4]

The rad issue can be solved many ways, a thicker core shorter rad or do as colin has and use a TU rad tilted back. Its not really "direct flow" either as the trumpets point at a higher angle if you look at it. Ok maybe its not the perfect solution but it certainly works and I bet temps are pretty low. He seems to do ok with it

 

Worth noting the touring cars seem to use a similar setup.

Edited January 16, 2006 by Sam

[crogthomas 0]

The rad issue can be solved many ways, a thicker core shorter rad or do as colin has and use a TU rad tilted back. Its not really "direct flow" either as the trumpets point at a higher angle if you look at it. Ok maybe its not the perfect solution but it certainly works and I bet temps are pretty low. He seems to do ok with it

 

Worth noting the touring cars seem to use a similar setup.

 

Indeed he does go quite well with it, but it could be improved.

You are quite right, many touring cars use a similar set up but usually with slight detail differences. The entrance to the airbox will be much smaller, usually like a post box just above the radiator. As explained above it only needs to be big enough to supply the engine with enough air. Too big and it will increase drag, although thats probably less important with the relatively low speeds on a hillclimb.

 

I have seen some airboxes with a panel filter at the very front, just behind the grill, which in my opinion is a very poor design for drag reasons. Although it is possible that it is like that for other reasons, possibly a lack of underbonnet space.

[number2301 1 1 Cars]

Something I've always wondered, surely having an airbox such as that Lotus one on TBs would just give the same effect as the standard inlet system? In that while multiple cylinders are 'sucking' from a limited air supply you're not achieving maximum air flow?

 

I'm probably wrong but wouldn't mind that explaining

[DrSeuss 0]

The throttle body itself forms the major restriction to an engine. So assuming the filter isn't restrictive you still have the same gains. With a reduction in inlet temps from not exposing the bodies to a warm air supply.