Question for the induction experts
Discussion
With a normally aspirated plenum fed engine is there any benefit to be gained from carefully choosing the inlet ducting size ? What I am thinking here is there is a fairly long and restrictive feed from the air filter at the front to the throttle butterfly. There is potential for making the ducting a lot bigger and less restrictive but before spending a lot of time making something thought I would ask.
The bigger the better seems to be the obvious answer, unless there is some benefit in increased air speed with a smaller diameter feed. Only other thing I can think of is if it is too big the air would have longer to pick up heat on the way.
The bigger the better seems to be the obvious answer, unless there is some benefit in increased air speed with a smaller diameter feed. Only other thing I can think of is if it is too big the air would have longer to pick up heat on the way.
steve-V8s said:
With a normally aspirated plenum fed engine is there any benefit to be gained from carefully choosing the inlet ducting size ? What I am thinking here is there is a fairly long and restrictive feed from the air filter at the front to the throttle butterfly. There is potential for making the ducting a lot bigger and less restrictive but before spending a lot of time making something thought I would ask.
The bigger the better seems to be the obvious answer, unless there is some benefit in increased air speed with a smaller diameter feed. Only other thing I can think of is if it is too big the air would have longer to pick up heat on the way.
The issue is one of transient response and it depends to a large degree on the placement of the mass airflow meter. The most ideal set-up you will have on a road car is an inlet manifold of around 2 to 2.5 times the volume of the engine, a single butterfly throttle, an airflow meter next to it and an airbox that can flow enough air when the filter has been exposed to extreme dirt for 20000 miles. It's not to say it's the best for absolute power but it's a very good starting point.The bigger the better seems to be the obvious answer, unless there is some benefit in increased air speed with a smaller diameter feed. Only other thing I can think of is if it is too big the air would have longer to pick up heat on the way.
Go up on inlet manifold volume and the responsiveness will drop off - as you open the throttle further the cylinders go lean and you need to compensate for it, which isn't easy when you need to meet emissions. Put the airbox and mass airflow sensor on the other side of the engine bay and you really make matters worse.
If you have a long plenum then reducing the volume is good, but do it by shortening it, not by reducing the diameter and therefore increasing the pressure drop along it. Covering it with a heat rejecting sleeve is no bad thing, but it's better to avoid it being in a hot area.
Thank you for the reply, I probably didn’t explain myself very well.
I am talking about the ducting between the air filter and the throttle butterfly. The engine has no Air Flow Meter, the plenum size and inlet headers are already optimised. The opening immediately before the butterflies (there are three feeding into one plenum) is 72mm and that is fed with 72mm pipe all the way from the filter, the pipe runs a fair distance and has some twists and turns which must be restrictive. My thought is to increase the diameter to more like 100mm and re route it to remove some of the corners. Plainly if the diameter is larger the air speed will be less for a specific air flow. So my question is about the filter to butterfly section. Is it a case of the bigger and less restrictive the better or not ? The optimum arrangement would seem to be a filter right at the throttle inlet but the air at that point would be rather hot.
I am talking about the ducting between the air filter and the throttle butterfly. The engine has no Air Flow Meter, the plenum size and inlet headers are already optimised. The opening immediately before the butterflies (there are three feeding into one plenum) is 72mm and that is fed with 72mm pipe all the way from the filter, the pipe runs a fair distance and has some twists and turns which must be restrictive. My thought is to increase the diameter to more like 100mm and re route it to remove some of the corners. Plainly if the diameter is larger the air speed will be less for a specific air flow. So my question is about the filter to butterfly section. Is it a case of the bigger and less restrictive the better or not ? The optimum arrangement would seem to be a filter right at the throttle inlet but the air at that point would be rather hot.
Shortest straightest coldest least restrictive is good.
Is there a vaccum in the intake tract now? Whats the air temperature delta? (intake to ambient)
Those will help answer your questions.
Take a read here http://autospeed.com.au/cms/article.html?&A=06...
Is there a vaccum in the intake tract now? Whats the air temperature delta? (intake to ambient)
Those will help answer your questions.
Take a read here http://autospeed.com.au/cms/article.html?&A=06...
Excellent autospeed article. Thanks for the link. I tried to find the next one where he was going to tinker with the boost controller but there was no obvious link and the archives are huge so I gave up. Might have another go later but it's certainly a website I'll be adding to my favourites.
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