Its all gone quiet - can we talk about intakes?....
Discussion
Hi All
Seems to have gone a bit quiet on the forum so thought I'd ask a technical question about choice of intake.
Class rules aside for a moment; on a non turbo, non supercharged V8 motor used purely for racing (actually a big block ford but same applies to any large displacement V8 race engine I guess) what are people's views on stack injection system versus carburettor and manifold? I've done a fair bit of browsing but can't find any definitive stuff that would enable a decision either way (apart from assumed higher cost of stack injection).
It would seem logical to me that a well set up stack system e.g. Kinsler, Hilborn, Weber etc. would provide a perfectly equal fuel charge to each cylinder, which would enable you to throw as much fuel into each cylinder as it can take given the capacity of the valves, cylinder head and exhaust. Whereas a carb and convoluted intake manifold must have some compromises built in due to the different length runners so some cylinders would receive a slightly different supply of air and fuel and the different geometry would cause the mixture to swirl about in different ways as it enters the combustion chamber. Looking at pro stock engines with 2x4 barrels & sheet metal high rise manifolds, surely this is effectively a stack system by any other name and only uses carbs because the pro stock rules say so.
However, on the basis that there aren't many stack systems in use in the UK, can anybody impart some experience on why my assumption that a stack system must be better is possibly misguided? Also are there any issues applying nitrous to a stack system?
Seems to have gone a bit quiet on the forum so thought I'd ask a technical question about choice of intake.
Class rules aside for a moment; on a non turbo, non supercharged V8 motor used purely for racing (actually a big block ford but same applies to any large displacement V8 race engine I guess) what are people's views on stack injection system versus carburettor and manifold? I've done a fair bit of browsing but can't find any definitive stuff that would enable a decision either way (apart from assumed higher cost of stack injection).
It would seem logical to me that a well set up stack system e.g. Kinsler, Hilborn, Weber etc. would provide a perfectly equal fuel charge to each cylinder, which would enable you to throw as much fuel into each cylinder as it can take given the capacity of the valves, cylinder head and exhaust. Whereas a carb and convoluted intake manifold must have some compromises built in due to the different length runners so some cylinders would receive a slightly different supply of air and fuel and the different geometry would cause the mixture to swirl about in different ways as it enters the combustion chamber. Looking at pro stock engines with 2x4 barrels & sheet metal high rise manifolds, surely this is effectively a stack system by any other name and only uses carbs because the pro stock rules say so.
However, on the basis that there aren't many stack systems in use in the UK, can anybody impart some experience on why my assumption that a stack system must be better is possibly misguided? Also are there any issues applying nitrous to a stack system?
Issue with stacks is pulsing and uneven pressures due to lack of a plenum. They look awesome but are very dated now, an injection system on a tunnel ram manifold will make better power than stacks and be easier to tune.
Regarding carbs, I don't know to be honest I know squat about them. As an educated guess if allowed pro stocks would have been running injection for a long time.
Regarding carbs, I don't know to be honest I know squat about them. As an educated guess if allowed pro stocks would have been running injection for a long time.
Just located this bit of background reading on the subject for anybody interested.
http://www.chrysler300club.com/uniq/allaboutrams/a...
http://www.chrysler300club.com/uniq/allaboutrams/a...
I am not familiar with the design of drag-racing-specific systems.
But I love engines so that won't stop me rattling off my 0.02
For a decade or two I was an engine designer and developer and I can just about remember a few basics.
Four stroke naturally aspirated pure racing engines running on gasoline or methanol nearly all use a stack of individual intake pipes.
The length and diameter of the pipe determine the resonant frequency of the system. The engine cylinder and the pipe act as a helmholz resonator. When the resonance causes a pressure increase timed just before intake valve closing, the trapped mass is increased, usually leading to a volumetric efficiency of over 100%. On racing engines the pipes are usually tapered and one effect of this is to broaden out the resonance over a slightly wider rpm range.
Air boxes or plenums are usually sized large enough NOT to link or dampen the pulsations between cylinders. The plenum allows ram air to be effectively ducted to the intake pipes, not possible with the 'hilborn-style' stack pipes.
So ram intake feeding a huge plenum into a stack of pipes for the air ....
Fuel: The selection of fuel metering systems is often governed by race regulations. The goals are air fuel ratio control, minimised air flow reduction and minimised charge temperature. If permitted and affordable GDI is best, then port EFI, then port mechanical, then carburettor.
I also learned that everyone else one knows this too, so the competitive difference is all in the little details ...
I'm looking to reading others' contributions so I can learn about the drag-racing-specific aspects.
Cheers.
But I love engines so that won't stop me rattling off my 0.02
For a decade or two I was an engine designer and developer and I can just about remember a few basics.
Four stroke naturally aspirated pure racing engines running on gasoline or methanol nearly all use a stack of individual intake pipes.
The length and diameter of the pipe determine the resonant frequency of the system. The engine cylinder and the pipe act as a helmholz resonator. When the resonance causes a pressure increase timed just before intake valve closing, the trapped mass is increased, usually leading to a volumetric efficiency of over 100%. On racing engines the pipes are usually tapered and one effect of this is to broaden out the resonance over a slightly wider rpm range.
Air boxes or plenums are usually sized large enough NOT to link or dampen the pulsations between cylinders. The plenum allows ram air to be effectively ducted to the intake pipes, not possible with the 'hilborn-style' stack pipes.
So ram intake feeding a huge plenum into a stack of pipes for the air ....
Fuel: The selection of fuel metering systems is often governed by race regulations. The goals are air fuel ratio control, minimised air flow reduction and minimised charge temperature. If permitted and affordable GDI is best, then port EFI, then port mechanical, then carburettor.
I also learned that everyone else one knows this too, so the competitive difference is all in the little details ...
I'm looking to reading others' contributions so I can learn about the drag-racing-specific aspects.
Cheers.
@ Jonermart; when you're talking about racing are you meaning drag racing or circuit racing ?
Traditional drag racing mechanical stack injection is constant flow (Hilborn/Kinsler etc) which has limitations and is really suited to wide open throttle use.
See http://www.kinsler.com/page--Constant-Flow--14.htm...
The old F1 cars used Lucas fuel injection which operates better in transitional throttle use.
See http://www.kinsler.com/page--Lucas--11.html
It is now possible to use the stack plenums to control airflow and fire in the fuel via throttle mapped EFI controlled injectors to get the best of both worlds whilst retaining the look of stacks.
Traditional drag racing mechanical stack injection is constant flow (Hilborn/Kinsler etc) which has limitations and is really suited to wide open throttle use.
See http://www.kinsler.com/page--Constant-Flow--14.htm...
The old F1 cars used Lucas fuel injection which operates better in transitional throttle use.
See http://www.kinsler.com/page--Lucas--11.html
It is now possible to use the stack plenums to control airflow and fire in the fuel via throttle mapped EFI controlled injectors to get the best of both worlds whilst retaining the look of stacks.
The Kinsler site is very interesting.
Here's a nice EFI-over-stacks example.
Air box and scoop are not used on dyno test so it lets us see the injectors in action.
Yeah I know its a roundy engine but its not actually doing its daft circular thing in this clip.
... and its all music (even if the music is a scraping violin to a fueler's pride of angry lions).
http://www.youtube.com/watch?v=m27xXVgg1nc&fea...
Here's a nice EFI-over-stacks example.
Air box and scoop are not used on dyno test so it lets us see the injectors in action.
Yeah I know its a roundy engine but its not actually doing its daft circular thing in this clip.
... and its all music (even if the music is a scraping violin to a fueler's pride of angry lions).
http://www.youtube.com/watch?v=m27xXVgg1nc&fea...
So that clip shows an F1 Renault engine with the intake box removed and the EFI just squirts the fuel over the mouth of what looks like a relatively short stack. The lack of a plenum doesn't seem to prevent the engine performing so it makes you wonder how important the 'sonic supercharging' effect actually is The misting that develops at high revs is presumably the sonic resonance issue. Seems incredibly simple (although the tech behind the efi is obviously pretty clever) and if its good enough for F1 you wonder why equivalent set ups aren't used in drag racing.
As you say, no scoop on the dyno but that's normal - same on a pro stocker.
http://www.youtube.com/watch?v=khIFvU1QPiE Nice.
Scoops do give a benefit. At 200 mph the stagnation pressure theoretically recoverable from the scoop equals about a 4-5% increase in plenum pressure. Quite a ram effect. So its no wonder racers have ditched the traditional 'organ-pipe' look - cool though it was.
Where to put the injectors - Injectors above the stack pipes (like the Renault) do keep the airflow unobstructed by bosses and the also give the fuel more time to atomise BUT as you say there's quite a fuel fog hanging over that F1 unit!! ... I think an injector lower down is fine - a big block Ford is not going to be running 15-20,000 rpm so there will be plenty of time for the fuel to atomise properly and a well designed EFI injector boss does not create much airflow loss at all.
But what do I know? You are actually doing it and I'm just typing.
Speaking of doers, one pair of contributors on here who strike me as knowing their pulse widths from their elbow ducts when it comes to induction and EFI is Slinky and Frosty.
http://www.youtube.com/watch?v=khIFvU1QPiE Nice.
Scoops do give a benefit. At 200 mph the stagnation pressure theoretically recoverable from the scoop equals about a 4-5% increase in plenum pressure. Quite a ram effect. So its no wonder racers have ditched the traditional 'organ-pipe' look - cool though it was.
Where to put the injectors - Injectors above the stack pipes (like the Renault) do keep the airflow unobstructed by bosses and the also give the fuel more time to atomise BUT as you say there's quite a fuel fog hanging over that F1 unit!! ... I think an injector lower down is fine - a big block Ford is not going to be running 15-20,000 rpm so there will be plenty of time for the fuel to atomise properly and a well designed EFI injector boss does not create much airflow loss at all.
But what do I know? You are actually doing it and I'm just typing.
Speaking of doers, one pair of contributors on here who strike me as knowing their pulse widths from their elbow ducts when it comes to induction and EFI is Slinky and Frosty.
Edited by CH3NO2ADDICT on Saturday 14th January 18:02
Re: stack efi systems
No idea which ones are best but I think this looks cool!
http://force-efi.com/stacks.htm
This Hilborn tech paper looks informative (if brand-biased!) ...
http://www.hilborninjection.com/tech_elect_manifol...
OK, I'll go off and find a life now ...
Cheers.
No idea which ones are best but I think this looks cool!
http://force-efi.com/stacks.htm
This Hilborn tech paper looks informative (if brand-biased!) ...
http://www.hilborninjection.com/tech_elect_manifol...
OK, I'll go off and find a life now ...
Cheers.
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