Air box trumpet with or without?

Dorchester2 · 31st July 2019, 15:55

I've just been told by a mate that the trumpet inside the air box 'improves the air flow'.

So far according several opinions I thought that reducing the entrance diameter it was only a restriction.

So far I assume that it's the ECU which does the mix, i.e. it's only the ECU that decides the appropriate need & proportion between air & fuel.
I've got a V6 2.5 auto and with a K&N panel & some additional holes at the bottom of the box, I feel an obvious improvement (very noticeable when kicking down), so much so that my engine is exclusively ethanol-fuelled (E85) which needs 25% more fuel.

Your opinion pals?
Thanks.

the dutch guy · 31st July 2019, 22:23

what you call a trumpet is what engineers call a venturi. also look up bernoulli effect.
its some black magic science but it creates a low pressure zone that speeds up the air so more air can get sucked in wich eventually means more air into the cyclinders. gross generalisation but i hope it helps.

Dorchester2 · 1st August 2019, 07:14

Thank you for your explanation.
I assume that your idea is similar to this one:
'It is there to improve pressure recovery and therefore reduce the restriction on flow ; the engineers who design induction systems have got CFD and flow benches and piles of experience.'

Hence in other words I assume you think it's better keeping the trumpet than taking it off? Am I wrong?

Thanks.

Dorchester2 · 1st August 2019, 07:15

Last question to the mighty owners of ZT 190: is there any difference between the 75 177 airbox & the ZT 190 one? Is there a trumpet in each car?

Thanks again.

RoverP480 · 1st August 2019, 07:25

Another reason for the trumpet is that it can have a very significant affect on intake noise. I was only talking about it a few days ago on a classic Rover V8 where the owner had taken it off to" improve" air flow and the noise had increased dramatically.

stocktake · 1st August 2019, 07:25

The 190 has a larger air intake for the shannon tube, cannot remember if the trumpet is present or not.

Dorchester2 · 1st August 2019, 07:35

Quote:

Originally Posted by RoverP480

Another reason for the trumpet is that it can have a very significant affect on intake noise. I was only talking about it a few days ago on a classic Rover V8 where the owner had taken it off to" improve" air flow and the noise had increased dramatically.

In the case of my V6 with or without the trumpet didn't make any sound related difference.

But drilling 7 nice holes in the air box bottom (with an hole-saw, same diameter as the holes in the back bumper for the parking alarm) dramatically increased the responsiveness.

I did that job before taking off the trumpet and it's true I didn't notice then any sensible driving improvement but a noticeable mpg decrease.
Could it be related with that Venturi effect?

Les4048 · 1st August 2019, 07:43

I’d leave it how it is, it is was designed to run that way. I’m always suspect of people saying things are better after modding without any concrete evidence other than saying it is better. Is it actually better or are they just convincing themselves it is?

rab60bit · 1st August 2019, 09:20

Quote:

Originally Posted by the dutch guy

what you call a trumpet is what engineers call a venturi. also look up bernoulli effect.
its some black magic science but it creates a low pressure zone that speeds up the air so more air can get sucked in wich eventually means more air into the cyclinders. gross generalisation but i hope it helps.

I've not checked my 'very old' text books but I recall it's all to do with resonance, reflection and back pressure. Early modern two stroke racing engines with disc valve technology used exactly the same science to increase inlet pressure and create a 'plug' at the exhaust side of the diabetic cycle resulting in improved efficiency which is one reason why the East German MZ's managed more bang for their Mark and wiped the floor with everyone until the Japanese copied (well, maybe came along later) with the same idea.
Another case of Britain lagging behind when we had all the advantages - a very clever guy called Joe Ehrlich (ex. German.....) who worked for De Havilland in the 50's developed the EMC racing disc valve two stroke motor cycle (and aerodynamically wind tunnel developed fairings) but no one spotted the investment potential and opted to continue with the BSA Bantam and Villiers - and we should all recall where that ended up....! MZ succumbed when the GDR withered and Suzuki/Yamaha/Kawasaki went off with all the spoils, and to be fair made a damn good job of it.

Dorchester2 · 1st August 2019, 09:45

Very interesting informations but rather a bit too far from my down-to-earth initial questions...

31st July 2019, 15:55	#1
Dorchester2 incurable Rover addict Rover 75 Saloon V6 2.5 1999 - Rover 25 1.4 2002 - Rover 214i cab 1994 - Rover P5b coupe 1968 Join Date: Sep 2017 Location: Bioule. South West of France. Posts: 1,643 Thanks: 612 Thanked 385 Times in 223 Posts	Air box trumpet with or without? I've just been told by a mate that the trumpet inside the air box 'improves the air flow'. So far according several opinions I thought that reducing the entrance diameter it was only a restriction. So far I assume that it's the ECU which does the mix, i.e. it's only the ECU that decides the appropriate need & proportion between air & fuel. I've got a V6 2.5 auto and with a K&N panel & some additional holes at the bottom of the box, I feel an obvious improvement (very noticeable when kicking down), so much so that my engine is exclusively ethanol-fuelled (E85) which needs 25% more fuel. Your opinion pals? Thanks. __________________ Rover 75 V6 2.5 Auto Connie born 1 July 1999, 24 kOhms resistor, 10 kOhms manual starter, full E85, modified airbox, full derestricted SS exhaust line, power & torque remap -> 202 bhp This vehicle was the 7,517th 75 to run off the production line, out of 112,381 This vehicle was the 1,190th 75 2.5 V6 Contemporary to be made out of 8,214 This vehicle was the 2,032nd 75 in Atlantic Blue Pearlescent (code: JEY) to be made out of 2,572 Atlantic Blue Pearlescent 75s

1st August 2019, 07:14	#3
Dorchester2 incurable Rover addict Rover 75 Saloon V6 2.5 1999 - Rover 25 1.4 2002 - Rover 214i cab 1994 - Rover P5b coupe 1968 Join Date: Sep 2017 Location: Bioule. South West of France. Posts: 1,643 Thanks: 612 Thanked 385 Times in 223 Posts	Thank you for your explanation. I assume that your idea is similar to this one: 'It is there to improve pressure recovery and therefore reduce the restriction on flow ; the engineers who design induction systems have got CFD and flow benches and piles of experience.' Hence in other words I assume you think it's better keeping the trumpet than taking it off? Am I wrong? Thanks. __________________ Rover 75 V6 2.5 Auto Connie born 1 July 1999, 24 kOhms resistor, 10 kOhms manual starter, full E85, modified airbox, full derestricted SS exhaust line, power & torque remap -> 202 bhp This vehicle was the 7,517th 75 to run off the production line, out of 112,381 This vehicle was the 1,190th 75 2.5 V6 Contemporary to be made out of 8,214 This vehicle was the 2,032nd 75 in Atlantic Blue Pearlescent (code: JEY) to be made out of 2,572 Atlantic Blue Pearlescent 75s

1st August 2019, 07:15	#4
Dorchester2 incurable Rover addict Rover 75 Saloon V6 2.5 1999 - Rover 25 1.4 2002 - Rover 214i cab 1994 - Rover P5b coupe 1968 Join Date: Sep 2017 Location: Bioule. South West of France. Posts: 1,643 Thanks: 612 Thanked 385 Times in 223 Posts	Last question to the mighty owners of ZT 190: is there any difference between the 75 177 airbox & the ZT 190 one? Is there a trumpet in each car? Thanks again. __________________ Rover 75 V6 2.5 Auto Connie born 1 July 1999, 24 kOhms resistor, 10 kOhms manual starter, full E85, modified airbox, full derestricted SS exhaust line, power & torque remap -> 202 bhp This vehicle was the 7,517th 75 to run off the production line, out of 112,381 This vehicle was the 1,190th 75 2.5 V6 Contemporary to be made out of 8,214 This vehicle was the 2,032nd 75 in Atlantic Blue Pearlescent (code: JEY) to be made out of 2,572 Atlantic Blue Pearlescent 75s

1st August 2019, 07:25	#6
stocktake Vis Whiz Rover 75 2.5 auto Saloon Join Date: Jun 2007 Location: LEEDS Posts: 20,587 Thanks: 2,057 Thanked 3,056 Times in 1,621 Posts	The 190 has a larger air intake for the shannon tube, cannot remember if the trumpet is present or not. __________________ Dave... Lost a few stones and a Gall Bladder and part of a bile duct and all of my dignity in the suppository incident

1st August 2019, 09:45	#10
Dorchester2 incurable Rover addict Rover 75 Saloon V6 2.5 1999 - Rover 25 1.4 2002 - Rover 214i cab 1994 - Rover P5b coupe 1968 Join Date: Sep 2017 Location: Bioule. South West of France. Posts: 1,643 Thanks: 612 Thanked 385 Times in 223 Posts	Very interesting informations but rather a bit too far from my down-to-earth initial questions... __________________ Rover 75 V6 2.5 Auto Connie born 1 July 1999, 24 kOhms resistor, 10 kOhms manual starter, full E85, modified airbox, full derestricted SS exhaust line, power & torque remap -> 202 bhp This vehicle was the 7,517th 75 to run off the production line, out of 112,381 This vehicle was the 1,190th 75 2.5 V6 Contemporary to be made out of 8,214 This vehicle was the 2,032nd 75 in Atlantic Blue Pearlescent (code: JEY) to be made out of 2,572 Atlantic Blue Pearlescent 75s

31st July 2019, 22:23	#2
the dutch guy Newbie 75 Join Date: Jan 2019 Location: Greenbridge, Essex Posts: 21 Thanks: 0 Thanked 4 Times in 3 Posts	what you call a trumpet is what engineers call a venturi. also look up bernoulli effect. its some black magic science but it creates a low pressure zone that speeds up the air so more air can get sucked in wich eventually means more air into the cyclinders. gross generalisation but i hope it helps.

1st August 2019, 07:25	#5
RoverP480 Gets stuck in None at the moment Join Date: Jan 2018 Location: Hereford Posts: 501 Thanks: 1 Thanked 165 Times in 146 Posts	Another reason for the trumpet is that it can have a very significant affect on intake noise. I was only talking about it a few days ago on a classic Rover V8 where the owner had taken it off to" improve" air flow and the noise had increased dramatically.

1st August 2019, 07:43	#8
Les4048 This is my second home Rover 75 Tourer/ MG ZT-T 400 Join Date: May 2012 Location: Lhanbryde Posts: 3,278 Thanks: 2,627 Thanked 1,523 Times in 869 Posts	I’d leave it how it is, it is was designed to run that way. I’m always suspect of people saying things are better after modding without any concrete evidence other than saying it is better. Is it actually better or are they just convincing themselves it is?