Effectiveness of c-fibre trumpets and insulating gaskets..?

[domV8]

Question:

Why are the plenum insulating gasket and carbon fibre trumpets supposed to increase horsepower by reducing the temperature of the plenum...?



Now, before you starting talking about temperature vs. charge density etc consider this..:


The plenum is alledged to be the same size in all engine variants (4.0, 4.3, 4.6, 5.0) - and is apparently the plenum from the 3.9l RV8.

Conventional wisdom has it that the plenum is supposed to be at least the same size as the cylinder volume, hence why people use the plenum expansion spacer.

So if the plenum is smaller in volume than the volume of the cylinders of all variants (3.9 plenum vs 4.0, 4.3, etc) - then once all 8 cylinders have filled (2 revolutions of the crank?), we will have entirely evacuated the air from the plenum.

So if, for the ease of calculation, we take a relatively low rpm - 1200 (just above idle), and divide this by 60secs - we get 20 revolutions of the crank every second.

If it takes 2 revolutions of the crank to fill all 8 cylinders - and evacuate the plenum of the original air - then we are looking at 10 plenums-worth of air every second.



So the plenum will be evacuated of the original air (before it gets refilled obviously) in 1/10th sec.



With air passing in and through the plenum so quickly, can the reduction in heat granted by the plenum insulating gasket and carbon fibre trumpets *really* have such an effect..?


And thats not even thinking about the heatsoak from the intake runners downstream of the gasket/trumpet, or the reduced transfer of heat from the plenum at higher RPM...


Surely the gains seen with things like carbon fibre trumpets have more to do with the shape of the trumpet, and a similarly-shaped metal trumpet would do just as well...?



Not intending on belittling any companies products - just wanting to get peeps thoughts on something that has been going around my head for a while...


Dom

[Dave 500]

domV8 said:

then we are looking at 10 plenums-worth of air every second.

Holy molly that's a lot of air.

Hmm might get a sticker made up "warning small children may get sucked into air intake keep clear"

[350Matt]

At full load you're quite right the air speed is very high and if you can keep the engine on full throttle then it'll help cool things down quite quickly.

But here's the rub when driving on the road you can't keep the taps wide open for more than a few seconds, consequently the temp of plenum tends to get pretty hot and air passing through at part and low throttles heats up.

In my experience the insulating gasket will tend to help prevent detonation occurring in hot weather and the recorded air temp inside the plenum dropped by 10-15°.

It may be subjective but the engine response tends to 'feel' sharper and you tend to notice it when rolling onto the throttle on the motorway

[Johno]

1200 rpm, 5ltr engine . . . so 6000ltr's of air every minute or 100ltrs of air per second . .

That's not at full throttle, a partial butterfly opening, but still the air has to pass at a high speed through the intake pipework, butterfly, plenum and inlet manifold.

I'm with the OP and always have been that the sheer volume of air and it's required velocity to satisfy such a large capacity engine even at low RPM negates the possible marginal benefits of a plenum insulator.

I know people may submit that it helps with pre-detonation, but I've not experienced this with a plenum that's powder coated black, in a black car, on a modified engine in 40 degree heat. So what effect it would have in UK climate I fail to see.

I submit different cars suffer with pre-det issues to different levels, but the maths do not seem to support the argument. However, I do not doubt that the plenum temp will be reduced, it's the thermal transfer of that heat to the air passing through it at such velocity that I do not believe an insulator plate/gasket etc would have anything other than a very very marginal effect on.

I used to run my old air temp sensor in SS housing where the AFM used to be located, due to it's location it would record temps over 60 degrees on hot days, but this wasn't the air temp, it was the ambient tempt the sensor reached due to the position. I have moved the ATS to the air box now and it reads exactly the true ambient air temp. Same conditions in the RR booth at Emerald recently it read 62 in the old location and 28 (which was the same temp as the therm on the wall) in the revised location.

Do I believe the actual air temp had been raised by 34 degrees over 1m of piping . . .. er no. I can now set up my engine better as the ECU properly understands the air temp it is dealing with, but I don't make any allowances for the a variance between the intake temp and the plenum temp as it is simply too marginal. If air was in a situation where it was 'held' in the intake somehow then I can see an argument, but the air speed and volumes suggest to me at least the benefit to be so marginal as to not stack.

Again, I submit that on some cars people claim it has solved their problems . . . But then I've never had a problem with my car overheating with a std rad and fan set up, but apparently you need an ally rad, uprated fans and a smaller number plate . . it's horses for courses I suppose.

The hottest air in the plenum is from the cross charges from the other inlet tracts, not the air entering the plenum, with higher lift cams there is a greater chance of the charge being contaminated by other cylinders being expelled as part of the normal cycle. A plenum insulator does not remove these charges or increase the potency of the now diluted charge entering the plenum . . . Perhaps it helps by reducing the ambient temp so the cross charges temp is reduced as well ? Again, feel rather marginal to me ?

It'd be good to see some back to back testing on a RR with all of these modifications to see whether it makes any difference to the charge temp, although how would you measure it consistently I don't know, perhaps someone has done it?

Edited by Johno on Wednesday 7th October 13:43

[spend]

I think just taking observed temps at face value can be misleading, temp sensors in the plenum area will be affected by conduction from the mating surface as well as a lot of the radiated heat. Thermally coating the inlet tracts to insulate makes far greater sense IMO.

Air is only moving by pressure differences from high to low areas you are not actually driving the air (unless using forced induction). Across each segment of the induction is a pressure drop, which affects how well the pressure equalization works. Minimize these and you get more air in (particularly at partial valve openings I believe). The air speed to get cramming due to the momentum of air after BDC is also a parameter, along with tuning the harmonics of the induction for given rpm ranges. I suspect these points may be a little esoteric in view of your original question, but still worthy note. Whilst many discuss the size of the plenum being required as a 'reservoir' concept to feed the engine, I would rather think of it in terms of waste recycling. If you have a small plenum the effect of the contamination on overlap would be much greater, whether port robbing or the waste charge spat back up the inlet?

Alternatively ditch the plenum and fit throttle bodies

OP, No trumpets will give you greater volume over any trumpets, and less area for thermal contact. The flaring of trumpets to smooth / accelerate air vs blending the base is pretty much an ongoing argument. I can't honestly see much difference between the 2, but grinding away metal makes things lighter and less things to fall out/go wrong IMHO.

[450Nick]

I don't think the only benefit of CF trumpets is heat management. I would think that their benefit is a combination of their shape (easier to achieve complex shapes), their smooth surface (lower friction and smoother flow) and possibly their weight(marginal, but they weight a hell of a lot less than even alloy ones, being only 2-ply thick). Together with their improved ability at resisting heat soak, I think they offer a slight benefit (though only slight) over alloy ones.

[spend]

450Nick said:

I don't think the only benefit of CF trumpets is heat management. I would think that their benefit is a combination of their shape (easier to achieve complex shapes), their smooth surface (lower friction and smoother flow) and possibly their weight(marginal, but they weight a hell of a lot less than even alloy ones, being only 2-ply thick). Together with their improved ability at resisting heat soak, I think they offer a slight benefit (though only slight) over alloy ones.

You can also form them into more complex shapes than is normally available with spun aluminium, so greater 3d flexibility.. But still people will try & set them at odd angles I suppose?

Still depends largely on whether you regard tuned length as more beneficial than open flow and lesser side wall resistance?

[spitfire4v8]

the trumpet thing is one of those issues that never seems to get settled. some people claim it makes a difference when you shorten them a set distance, how big the flare is etc etc .. other people like me say it doesnt matter one single jot as long as your trumpet (or lack of) is capable of flowing the aiflow demands of the rest of the system. Ive tested trumpets, blended bases, blended inserts, more trumpets. Other people have tried all manner of changes on cars in for mapping .. in all my testing I haven't found any consistent repeatable changes that tell me a certain length is any more beneficial than another. Just make sure the hole down the middle is big enough and you'll be fine

[450Nick]

spitfire4v8 said:

the trumpet thing is one of those issues that never seems to get settled. some people claim it makes a difference when you shorten them a set distance, how big the flare is etc etc .. other people like me say it doesnt matter one single jot as long as your trumpet (or lack of) is capable of flowing the aiflow demands of the rest of the system. Ive tested trumpets, blended bases, blended inserts, more trumpets. Other people have tried all manner of changes on cars in for mapping .. in all my testing I haven't found any consistent repeatable changes that tell me a certain length is any more beneficial than another. Just make sure the hole down the middle is big enough and you'll be fine

After doing a fair bit of work into resonant tuning on inlet manifolds for my final project at university, I can say that there is definitely a benefit to tuning your primary pipes to a desired rev band, though the results can be quite easily ruined by all sorts of things such as the height of the plenum ceiling from the trumpet causing reflections to interfere with desired rarefaction waves.

With a TVR, the inlet manifold isn't the best shape, and all ports aren't equal length. Coupled with the low plenum ceiling height and less than ideal side entry style, benefits aren't going to be huge. From experience though, it tends to have more of an effect on torque than it does on outright horsepower, as it is effectively putting a mild supercharging effect on over a narrow rev band.

I also have a graph somewhere of a 500 Griff on the rollers run back to back with blended base and trumpets. Sure enough, the blended base produced slightly more power at the top end at the expense of torque, whereas the trumpets produced the opposite, but gave a bigger boost in torque than the blended base did in horsepower.

From what I remember, equally important factors were the taper of the trumpet walls (around 2.5 degrees IIRC), and the amount of radius on the trumpet mouth - It wants to bend past 90 degrees, which is easier to do in CF than metal...

Having said all of that, larger gains can always be found from a tuned exhaust manifold then an inlet manifold - can't remember why though!

Edit: Here it is! - Was a Chim, not a Griff!

Edited by 450Nick on Wednesday 7th October 19:57

[crackedfinger]

Johno said:

1200 rpm, 5ltr engine . . . so 6000ltr's of air every minute or 100ltrs of air per second . .

Is the math fro a theoretical max not:

1200rpm = 600 refills on 4 stroke
600 refills x 8 cylinders = 4800
A cylinder is 0.625 of a litre
4800 x 0.625 = 3000 ltr's a min.

[spitfire4v8]

here's my most recent test of blended v trumpets. the blue line is the blended base, the red line some flared trumpets (not std TVR ones)

as you can see in this particula instance the blended base actually has more power low down, then loses out slightly then there's absolutely nothing to pick between either system. This lack of compelling evidence is something i've seen time and again and is the reason i say it doesnt really matter what you have in there as long as it flows enough air

Edited by spitfire4v8 on Wednesday 7th October 20:38

[v8 racing]

The reality is, the one thing that heats the intake charge up more than anything else is the actual intake valve, as air passes over the valve it does collect a lot of heat, the only cure for this is ceramic coating the valve, as for plenum insulators, the bottom line is anything you can do to keep intake temps down will work, are they worth the money each to there own, as for plenum volume, there is never a positive pressure in the plenum unless you have a well sorted engine at high rpm, it is allways negative, the bigger the plenum the less responsive the engine will be, the biggest factor here is making sure the the throttle size can flow the cfm that the engine will need, i have foam filled a trumpet base to decrease plenum volume to gain in throttle response.

[GreenV8S]

Johno said:

Do I believe the actual air temp had been raised by 34 degrees over 1m of piping . . .. er no.

Why not? How much of a temperature change do you think the air sees going through a 1" thick radiator matrix? The air has very little thermal mass relative to its volume and changes temperature very easily.

[Johno]

agree across a rad there is significant transfer, however it is designed with a significant surface area to transfer the heat to the air.

The intake piping is not designed in this way . . . The ATS was fitted into a metal pipe above the manifold so the ATS absorbs the abient temp transferred.

I don't think I can comment on air speed comparisons though . . .

[GreenV8S]

Johno said:

agree across a rad there is significant transfer, however it is designed with a significant surface area to transfer the heat to the air.

The intake piping is not designed in this way

Yes, but what it's telling you is that a slice of air (say) 0.1" high can be heater up substantially by travelling 1" over a hot plate. So if each 1" length of pipe is heating up say a 0.1" thick slice of air, then it's going to take about 15" to heat up the whole 3" diameter pipe. I know that's ignoring all sorts of effects but just gives you an order of magnitude feeling for the numbers involved. Air heats up very quickly and the density loss is important enough to be worth minimising.

Edited by GreenV8S on Wednesday 7th October 21:35

[Johno]

Agree Pete, not denying that air will be heated between entry at the air filter and the intake manifold, however, it's about the margin of benefit we're talking about here . ..

The question is whether there is a benefit, I am sure there is, I am also absolutely sure in my own mind that it so marginal I would not be able to notice the difference on my car. Perhaps it is differetn for other peoples cars, but seems to me to be so marginal to be inperceptible.

You'd do better to spend the money on a better air filter or reducing the run of the air intake piping . . .

[GreenV8S]

Johno said:

You'd do better to spend the money on a better air filter or reducing the run of the air intake piping . . .

It's all worth doing, but the question is which bit is most worth while? A 1C rise in charge temperature is likely to cost you around 1 BHP. With temperature differences in excess of 80C between fresh air and the heads, there's the potential to get the air quite hot. If things go wrong, you could easily be losing tens of BHP. Even quite a good air filter could still be costing you around 1 psi which equates to about 20 bhp. The longer and more tortuous the induction system the more pressure loss you'll suffer, but if shortening it means you pull in hot air you stand to lose a lot more than you gain - but find a direct source of cold air and it can really help. (Hint: there's a cold high pressure zone in the middle of the windscreen at the base.)

[Del 203]

GreenV8S said:

(Hint: there's a cold high pressure zone in the middle of the windscreen at the base.)

Oooooo





Or




Just need to sort a seal under the bonnet

[RussWood]

450Nick said: -
"Having said all of that, larger gains can always be found from a tuned exhaust manifold then an inlet manifold - can't remember why though!"

What leaves the exhaust is what enters the inlet plus the results of combustion, largely extra water vapour and Co2, it is normally at a higher temperature and hence larger volume flow. That's why looking at the exhaust system generally gives better rewards than the inlet.

Russ

[Bluebottle]

Del 203 said:

GreenV8S said:

(Hint: there's a cold high pressure zone in the middle of the windscreen at the base.)

Oooooo





Or




Just need to sort a seal under the bonnet

The possibilities are endless;
http://www.youtube.com/watch?v=vOey7ugadH8&fea...