Jump to content

Recommended Posts

i see in the post take a look under my bonnet that many have added ducting to the carbs for fresh air.

Dose this not restrict the air flow around the carbs with this crowding of the space available.  I was once told that it was more beneficial to cool the exhaust manifold by a dyno man .

Have any found a benefit with this ducting ?

I have gone with bonnet venting to encourage air flow.

Roy

Link to post
Share on other sites

With a shroud around the radiator the only air that can get to the carbs has been warmed by the rad on its way through. I installed the ducting to feed fresh air to the carbs. 

Rgds Ian

Link to post
Share on other sites

Like Ian I wanted my carbs to benefit from cooler more dense air so have a feed from in front of the rad through the fibreboard rad shroud. I did wonder if this would affect the carb vapour cloud that stands off from the carbs (I don’t run air filters :() and I still get the tell tale on the inner wing so it doesn’t affect it. 
 

I also added bonnet louvres to get the heat out. Heat rises and in sprint competitions you can spend a long time idling with no forward motion drafting. 
 

as to whether it make any difference - god knows- but if it looks Racy it must be racy :D;)

Link to post
Share on other sites
17 minutes ago, Hamish said:

but if it looks Racy it must be racy

:D

Link to post
Share on other sites
3 hours ago, Ian Vincent said:

With a shroud around the radiator the only air that can get to the carbs has been warmed by the rad on its way through. I installed the ducting to feed fresh air to the carbs. 

Rgds Ian

only if the floor is sealed.

Link to post
Share on other sites
58 minutes ago, roy53 said:

only if the floor is sealed.

True, but I'm not sure how much air is going to fight to enter the engine space when the air is being pushed through the radiator by the forward motion of the vehicle.

It's certainly true that on hot days the car won't idle very well and I have always assumed that is because the engine is having to breathe the heated air under the bonnet.  There are a number of TR owners that I am aware of who have solved their idling problems by installing a small fan in their fresh air line to feed air to the carbs when the vehicle is stationary and who claim smoother idling as a result.

Rgds Ian

Link to post
Share on other sites
13 minutes ago, ed_h said:

The idea is to provide the coolest air possible to the carbs.  There might even be a small ram effect at speed.

Ed

IMG_3833a.JPG

Nice job, but I fear your corrugated pipework causes the airflow to stall, you need smooth walls to keep the air flow delivery speed up to get even a small ram effect. That then has to be catered for the excess pressure pushing air into the carb and equalised, many tuners (Kastner even, thought it's too much bother, just give it cooler air).

Mick Richards

Link to post
Share on other sites
1 hour ago, Motorsport Mickey said:

Nice job, but I fear your corrugated pipework causes the airflow to stall, you need smooth walls to keep the air flow delivery speed up to get even a small ram effect. That then has to be catered for the excess pressure pushing air into the carb and equalised, many tuners (Kastner even, thought it's too much bother, just give it cooler air).

Mick Richards

Yeah, I'm not really counting on any significant ram effect, though it might be fun to try to measure it.

Ed

Link to post
Share on other sites

The tube's corrugations will reduce the effective bore of the tube to its smallest inside diameter and is then reduced further by surface air-turbulence (..like bow waves off those ridges).  So at a guess Ed's ducting would be as effective as a polished smooth sided tube of 50 - 70% of its inside diameter.  But it looks to be a generous size as is, and so whether full & generous radii ram pipes / velocity stacks have fitted within the air filter will make more difference to how much air is drawn in with each induction stroke.  

And the ram-air pressure effect of any such a crude * arrangement, even for a car traveling at 90mph, is insignificant compared to the piston speed / induction stroke velocity (m/sec) of air volume being sucked into the engine at speed.                        * absolutely no disrespect intended Ed. - I very much like your arrangement.

As such, when designing / configuring such a system, it is often useful to envisage how easily the air might be sucked (rather than pushed) into the tube, through the tube, and through a filter.  The pressure waves are generally very different.  And so like when designing an aerofoil ;  it is the very low pressure doing the work and not the just slightly higher pressure.

However, the difference in air density between hot and ambient cold air intake can be very significant.  Of course carburettor freezing is to be avoided but aside from that, when the fuel/air mixture is tuned ; the more dense air inducted into the cylinder - the bigger the bang (directly related to power).  And that can be felt by the driver, even with a crude cold air intake system.   

On my old Jag 3.8,  the standard air filter was ugly (resembling an exhaust silencer bolted across the top of the engine), and its intake was a tapered pipe with a sharp elbow, so that it could be poked towards the front of the car or else down to the exhaust manifolds.  I changed this to what looked like an aftermarket air filter, which was empty. The actual air filter used was from the larger capacity / 5.3 ltr Jaguar.  That was hidden away under the front wing besides the headlamp.  Cold air was drawn into that from the front of the car, through the large filter and ducted back under the wheel-arch, to then come into that dummy air filter canister ( you can see the clear ducting below ). . .  

      529974733_EnginebaylayoutP1170090.thumb.JPG.01b7a18b75c1e4a57425affbe9a1519c.JPG

^ The oval case for the apparent air filter was empty and served only as a distribution manifold / part of the ducting.

P1170156a.thumb.JPG.69437c3cc40cc4f13e3d7d194c99d93d.JPG

The air into the square black-plastic air-filter box faces forward but is sheltered from immediate road spray and rain, so no ram-air effect ..just as cool clean air as could be found at the front of any road vehicle.

P1170093a.thumb.JPG.9066ada124416291564bc3e84316f11a.JPG

That is a truly beautiful engine.  Even on a saloon car, it was criminal to bury it under an air filter.  

As you can see there was no way forward, around the radiator, to otherwise get fresh air ducting to the carbs.  Even though crudely executed, and using corrugated ducting., this fresh / cool air intake resulted in a felt improvement in mid-range power.   

I'm an advocate.

Pete.

 

Edited by Bfg
Link to post
Share on other sites

I dusted off a couple of old physics text books to refresh my memory on this.  Using the textbook calculations, it looks like even at 100 mph, the dynamic pressure of the intake air due to forward motion would only be a couple of tenths of a psi above ambient.  I'm sure this assumes no flow, so the fact that there is actually significant flow in the induction system would reduce that.

While the effect of this pressure increase might possibly be measured, it's unlikely that it could be felt.  It would be roughly equivalent to a drop of around 300 feet in altitude, an increase of about 10 millibars of barometric pressure, or a drop of around 5º F in air temperature.

When designing that intake system, I never really expected much ram effect, and this supports that.  Benefit from cooler outside air is more defensible, but even without that, I like the looks.

Ed

 

Edited by ed_h
Link to post
Share on other sites

The part of the duct which you cannot see in my photo connects to an in-line fan which is in front of the rad, above the front grill. It comes on at the same time as the main cooling fan, & is simply to provide cold air to the carbs when idling in traffic.

 966697201_Underbonnet3.thumb.jpg.2381353fc097e5e3f40ecdbf0b68d274.jpg

Bob.

Link to post
Share on other sites
1 hour ago, Lebro said:

The part of the duct which you cannot see in my photo connects to an in-line fan which is in front of the rad, above the front grill. It comes on at the same time as the main cooling fan, & is simply to provide cold air to the carbs when idling in traffic.

 966697201_Underbonnet3.thumb.jpg.2381353fc097e5e3f40ecdbf0b68d274.jpg

Bob.

Bob

interested in the in-line fan can you share the details/spec etc

thanks

H

Link to post
Share on other sites

Would need more ooomph than that surely 

I have seen inline bilge fans ?

Link to post
Share on other sites
On 4/21/2021 at 11:19 AM, Hamish said:

carb vapour cloud that stands off from the carbs (I don’t run air filters :() and I still get the tell tale on the inner wing so it doesn’t affect it. 
 

Hamish, it seems that Ali has measured a 1 AFR richening by capturing the stand-off in trumpets.

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.