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StuartG

Cold air intake

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My 6 always runs better in cool weather (noticebly more grunt) and I assume this is due to higher under bonnet temperatures in the summer putting heat into the air box. Has anyone tried insulating the air intake pipe/box and did it make any difference ?

Also I seem to remember water injection into the air intake n cars in the 1990s, or did I dream this ?

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Hi Stuart, I have just added a cold air intake to the 4A, do you have the flexible hoses to the inlets on your air box , these could be routed to an area open to cold air from the front of the car. As they feed the air box before the filter this should not introduce any pressure into the inlet which would adversely affect the mixture.

Chris

 

 

 

intake1.jpg

intake2.jpg

Edited by ChrisR-4A
Photos added

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I'm happy with the standard PI intake in the front RH  corner just behind the grille. 

Some of the blokes in the SLK forum I'm in use water/methanol injection to cool the charge - but they also have changed the supercharger pulleys to get more boost resulting in higher manifold temperatures. Don't know if it would be worth the trouble in a NA TR6.

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Hi Mike, I see your in Melbourne where summer temps are similar to a good U.K summer. I’m not expecting to notice too much difference in U.K. except on warmest days but each year when we go to France in July temps are often 29-35 deg and colder under bonnet air should be welcome .

I assume both you guys have the standard TR6 injection, the benefits of colder air would be more noticeable on a 6 with carbs and K&N filters more so with triple Webber’s.

Chris

Edited by ChrisR-4A

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1 hour ago, StuartG said:

My 6 always runs better in cool weather (noticebly more grunt) and I assume this is due to higher under bonnet temperatures in the summer putting heat into the air box. Has anyone tried insulating the air intake pipe/box and did it make any difference ?

Also I seem to remember water injection into the air intake n cars in the 1990s, or did I dream this ?

Hi Stuart,

your lack of grunt in hot weather is as you say the air temp under the bonnet is high.

This warmed/hotter air makes the air thinner so you do not get the same amount of air to do the business.

The water injection is an attempt to reduce the air temp and so make the air denser.  Used on aircraft a fair amount.

You could put an insulating jacket around the intake air box - but how long is our Summer :(

 

Roger

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The temperature increase should be regarded in Kelvin, 15 degrees increase from lets say 25C ambient to 40 degr.C inlet temperature as a result of heating up in the plenum/throttle bodies would be 14% increase (on the Kelvin scale) in temperature, so also about that % loss in mass flow (not exactly the same since other parameters change too). If mass flow would correspond to performance, it is significant.

Waldi

 

PS:

The true answer will come from Peter C.

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There are three problems the non EFI community is dealing with:

1.) As told warm air is less dense and transports less oxygen into the engine. This results in less feed.

2.) Carb and PI does not sense that and from that mixture is not correct.

3,) Due to weather and height the air pressure is different what PI and carb do not sense, too.

 

This is why racers had been set to perfect performance at the race track in the early days.

 

Besides the warm air that is sniffed in from the engine compartment or in summer from the outside, too

there is also the problem that the manifolds itself are heated from the exhaust and from the connection to cylinder head.

They give the heat to the mixture passing inside and increase the problems.

 

When making a dyno there is also a correction to be done where outside temperature and air pressure is needed for correction. This can be quite a lot in the range of +/- 5%

 

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21 minutes ago, TriumphV8 said:

Due to weather and height the air pressure is different what PI and carb do not sense, too.

 

I thought a constant-depression carb like SU and Stromberg does sort of compensate for air pressure. Lower ambient air pressure means the piston doesn't rise as far to maintain the depression and so keeps the mixture correct?

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There was a thread on one of the forums a while back where someone installed temperature sensors at various places under the bonnet.  One revelation was that, at road speed, underbonnet air temps were essentially the same as ambient.

Ed

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2 hours ago, RobH said:

I thought a constant-depression carb like SU and Stromberg does sort of compensate for air pressure. Lower ambient air pressure means the piston doesn't rise as far to maintain the depression and so keeps the mixture correct?

Yes,

But warm air has lower density even at same atmos pressure - see graph below  Between 20C and 60C density will fall from ca 1.2 to 1.05,  which is 13% - as Waldi posted earlier. So 13% richer mixture and 13% less power.

Water injection wont cool the mixture as very little will evaporate until towards the end of the compression stroke, It can lower the power taken in compression and add  a bit to the expnasion stroke, but at considerable effort and expense.

https://supertrarged.files.wordpress.com/2016/01/tr6se-35-water-injection-revisited.pdf

https://supertrarged.files.wordpress.com/2016/02/tr6se36-water-injection-effects-on-combustion-pdf.pdf

Heat picked up from the manifolds is undesirable so preventing radiant heat reaching the intake runners form the exhaust pipes can be an useful trick.

Peter

image.png

Edited by Peter Cobbold

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Thanks for all the replies gentlemen. I have a k&n air filter just in front of and to side of radiator. Sounds like exhaust manifold insulation would be the way to go ?

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3 minutes ago, StuartG said:

Thanks for all the replies gentlemen. I have a k&n air filter just in front of and to side of radiator. Sounds like exhaust manifold insulation would be the way to go ?

Maybe, But a simple ali plate between the manifolds will reflect almost all the radiant heat. Convected heat should be blown away by underbonnet air flow, and conduction is fixed by the manifold/ head bolts.

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4 hours ago, ed_h said:

There was a thread on one of the forums a while back where someone installed temperature sensors at various places under the bonnet.  One revelation was that, at road speed, underbonnet air temps were essentially the same as ambient.

Ed

I could accept that but only if there was ample venting between the engine bay and the front of the car. My gut feeling is that on a TR there isn’t as standard. Which is why I have added an  extra inlet to feed air around the carbs. I can also see Peters point on a heat shield between the exhaust and the inlet and will be looking into this as well.

Chris

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8 hours ago, ChrisR-4A said:

Hi Mike, I see your in Melbourne where summer temps are similar to a good U.K summer. I’m not expecting to notice too much difference in U.K. except on warmest days but each year when we go to France in July temps are often 29-35 deg and colder under bonnet air should be welcome .

I assume both you guys have the standard TR6 injection, the benefits of colder air would be more noticeable on a 6 with carbs and K&N filters more so with triple Webber’s.

Chris

I have a standard PI with a few mods for hill climbing. It does have more power on a cold, crisp morning. When the temperature's above 35 deg. C I'm usually heading home at a sedate pace.

If I was trying to get the temperature of the inlet plenum down I'd look at an aluminum heat shield between the exhaust and inlet manifolds or maybe  ceramic coating the exhaust manifold to reduce the radiation emissivity. 

Edited by Mike C

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I made heat shields for the injection bodies to try to reduce the radiated heat from the exhaust manifold.

image.thumb.jpeg.f1454bdf342e0311649ade8ab0fdaede.jpeg

 

 

 

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3 hours ago, Peter Cobbold said:

Maybe, But a simple ali plate between the manifolds will reflect almost all the radiant heat. Convected heat should be blown away by underbonnet air flow, and conduction is fixed by the manifold/ head bolts.

Peter, the heat shields shown  in the Moss catalogue appear to be vertical and fitted between the carbs and the inlet manifolds will stop exhaust heat reaching the carbs but not from rising vertically onto the inlet manifold. Is this good enough or is something else needed to do a "propper job".

Chris

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6 hours ago, ed_h said:

There was a thread on one of the forums a while back where someone installed temperature sensors at various places under the bonnet.  One revelation was that, at road speed, underbonnet air temps were essentially the same as ambient.

Ed

That was me !

i installed a sensor in the plenum and whilst driving along the air temp was indeed close to ambient 

but when ticking over in traffic the air temp went above  80c 

my pi car has the standard air filter arrangement , but with a k&n filter, which sucks cold air from in front of the rad.

steve

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24 minutes ago, ChrisR-4A said:

Peter, the heat shields shown  in the Moss catalogue appear to be vertical and fitted between the carbs and the inlet manifolds will stop exhaust heat reaching the carbs but not from rising vertically onto the inlet manifold. Is this good enough or is something else needed to do a "propper job".

Chris

Chris, I like Marcel's  arrangement as it reaches to where the two manifolds are closest. Maybe the Moss design was aimed at keeping the float chambers and jets cool ? Peter 

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I think you are right Peter as some cars have been known to suffer from fuel starvation causing difficult hot starting,  Marcel’s solution is practical but a detailed sheet of alloy with some judicial forming would look better and if stood off from the underside of the manifold on short pillars should be more efficient. Really need a spare manifold off the car to do this, I’ll put it on my “One Day” list. 

Chris

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37 minutes ago, Steves_TR6 said:

That was me !

i installed a sensor in the plenum and whilst driving along the air temp was indeed close to ambient 

but when ticking over in traffic the air temp went above  80c 

my pi car has the standard air filter arrangement , but with a k&n filter, which sucks cold air from in front of the rad.

steve

Hi Steve, I can understand from this discussion that the needs of an injected 6 are different from an engine on carbs with under bonnet air filters . The injected 6 at all times draws its air from outside the bonnet area but is affected when stationary by under bonnet heat being transferred to the plenum which will increase the air temp inside.
Whereas the engine on carbs is drawing its air from the under bonnet area at all times so will not have the same benefit of the injected car when moving;  therefore an additional cold air feed to the under bonnet area around the air filters looks like it should be beneficial, more so as the road speed increases.

Chris

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This is my fresh air induction arrangement on my carburetted TR6, and my version of a heat shield.  The heat shield has a reflective surface, an insulating layer, and an air space.  The graph is on the bench, not in the car.

Ed

IMG_3833a.JPG

IMG_0168a.JPG

Heat%20Shield.jpg

Edited by ed_h

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Ceramic coating of the exhaust manifold is meant to reduce intake manifold and under bonnet temps quite a bit.  I had it done but didn’t do before-and-after measurements so I cannot claim to be much of a scientist...my manifold needed cosmetic help so i went that route hoping to kill two birds at once.

c74

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16 hours ago, RobH said:

I thought a constant-depression carb like SU and Stromberg does sort of compensate for air pressure. Lower ambient air pressure means the piston doesn't rise as far to maintain the depression and so keeps the mixture correct?

The SU senses the pressure difference between outside (top of diaphragm or piston)

and pressure loss in the venturi built by the piston at underside of piston where air blows

by into the engine. So more or less it senses the air speed and lifts the piston to keep it

nearly constant. The needle gives at that position the correct amount of fuel by its varying

diametre.

 

From that some correction is done but the air that is sucked in is different, too.

As air changes density with low pressure air flowing through at underside of piston it

now has less oxygen per litre and so carb "sees" another air media than he was set before.

Mixture becomes richer like air is warmer what has same effect.

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Classy setup there Ed!

cold air to the carbs has to make a significant difference to performance.

steve

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16 hours ago, ed_h said:

There was a thread on one of the forums a while back where someone installed temperature sensors at various places under the bonnet.  One revelation was that, at road speed, underbonnet air temps were essentially the same as ambient.

Ed

Made similar investigations. on the highway all is in limits.

 

And the cold air intake itself and maybe the air filter robs some power.

 

With a crossflow head and air horns and some clean area from front to air horns

the race engines gave best results.

 

But at low speed and at traffic lights my V8 reported high MAT temps.

I changed the place of the sender several times but still found the results

did not make sense.

Anyway the MAT easily reached 60 degrees and often 80 could be found.

My EFI can correct a mismatch between measured MAT and calculated fuel.

Especially in traffic jam, at hot start or slow driving this correction is quite busy

showing me that the perfect place for MAT measuring is yet not found.

 

In our case it shows that under bonnet temperature has quite a large influence

on the mixture quality.

 

 

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