Velocity Stacks on 40 DCNF's

Nice work Brad, I really like the home made bell mouths :thumbsup: ...I never got the hang of the metal shaping thing in high school metalwork class...if your ever thinking of making more let me know and I'll put in my order for some to suit 44's (without a cut off rolled lip between the throats)

I would agree that more "top" clearance would be preferable, but if you have the box as tall as you can for engine cover clearance that's about as tall as it can be...as always most things about engine building and prep are about reaching a workable compromise.

One small thing I would change is the fact you have a flat air box top. If you loook at "factory" items, like the 124BC air box (even though that has it's own design compromises) the lid is usually domed or rounded above the carburettors.

The top being domed assists with the actual "ram charge" effect due to wave action, as the sound waves emitted from the open end of the inlet tract don't hit a surface that is 90 degrees to their travel... getting pedantic I know, but all these little things add up... and can make a noticeable difference, just like the result you got from changing to an airbox in the first place.

Your absolutely correct with the "stand off" comment too.

Rough (minimum) rules of thumb for airboxes, if anyone is interested, is approx 2 x throttle size top clearance above any air horns, and approx 3 x throttle size to the air inlet away from the closest carb opening, and approx 3 x engine capacity in total volume... but usually all these are limited by the available space.

SteveC
 
Are you using a stock fuel pump?

:confuse2: I thought the stock fuel pump wouldn't provide enough volume to feed dual 40's. :confuse2:

Would love to see pics of the entire car. I don't remember seeing it. Engine bay does look good though. :clap:
 
Duel carbs only require 3-4 lbs of fuel. Stock pump is fine, as long as its not stock fuel injection pump.
 
You will NOT find a modern race engine with wire mesh screens on their V stacks.

Why?

Jet engines have basically the same inlet problem. In the case of Jet engines, they are very subject to sucking stuff in to the inlet (like birds) which can cause a multi-million dollar engine to fail. One simple solution to prevent these engine failures would be to put a wire or other mesh screen in front of them...But they don't. Instead, they rate jet engines for the number of bird strikes per unit time before they fail.

Why?

As I have stated previously, the wire mesh on intake V stacks are a relic from another era.. that has long since gone and should be used on vintage racers that are for show... complete with tire covers.

Bernice

 
I am glad to see some discussion on this. I have been considering putting these longer trumpets on the FAZA car. I want everyones oppinion on what to expect, Does and donts...

I would be attaching them to 2 40dcoe webbers side draft and they will stick out of the trunk...

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290377203776&viewitem=&sspagename=STRK:MEWAX:IT

that guys website has a bunch of options and all of them confuse me..

http://www.dellorto.co.uk/merchandise/products.asp?CategoryID=8&PartsectionID=41
 
Too small?

Inlet diameter or V-stack lenght?

Total inlet lenght including the V-stack, carb/individual throttle body lenght and intake manifold length becomes a tuned system that has a self resonate frequency or tuning peak for a given engine rpm range.

There are a number of engines today that have more than one intake system lenght. Most common is a double tuned system that has two basic self resonate frequencies that is controlled by a throttle plate or ball valve controlled by a ECU based on engine demands and rpm and etc... These resonant peaks over lap and can create a broader set of self resonant frequencies that can help the intake pressure wave work over a broader range of engine RPM.

In the case of Brad's V-stacks, they have a nice large inlet radii. Any taller and the V-stacks will not fit the air box and clear the engine cover.

Solution, modify the engine cover and make a differnt air box. Then one needs to figure what the optimum overall intake tract lenght needs to be for a given engine and how the engine will be used.

There is no simple answer or cure all, to this problem. All this is getting down to specific design details of the entire intake system.. And the exhaust will also have an effect on the whole system too.

Bernice

you don't think they're too small?
 
Leaf strikes

While not have a foam or paper type filter will shorten my engine life (so will see'in my tac at 5,000 rpm BUT I STILL DO IT!) a leaf or small stone coming in my side vents will end my engine life... me thinks?
While the major airlines can write off bird strikes I, on the other hand am concerned about the octane rating of an Oak leaf and while I can hold my own behind the wheel I ain't no Capt. Sulley. More importantly those unexposed stacks look really good so to cover with a black box? I DON"T THINK SO. For now the screens stay. Add to it the suggestion that there are jealous peeps that could "hock a lougie" down the open webers (probably an envious muscle head) is scary. But keep the opinions comin
Thanks.
Ron
P.S. MANN! does Bernice know allot, my only question is, does she know how to cook?:confuse2:
 
Nice thread - lot's of good conversation. Here is a little bit of information regarding the shape of the air horn and also a comparison of the effect that the length of the intake has.

The intake length is changed to reflect different length air horns. I did not vary the efficiencies (from a shape change of the air horn). Every parameter is equal except the overall intake length. As one would expect the longer design produces better in the lower RPM range and the shorter produces better in the higher RPM range. I included the intake port velocities as well as the ram effect (tuning pressures) in the simulation to help show what is happening. Hopefully it is legible.

effectfromintakelength.jpg


Here is a chart showing the basic effect of the shape of the air horn/s

RamPipeShapes.jpg


As mentioned it really comes down to a series of trade offs to best achieve your personal goal's for the engine/car. What is good for me may not be good for you and vice versa.

BTW thanks Steve and Bernice for the nice comments. Steve I had considered adding a domed cover but it was just a bit more complicated to fabricate than I was willing to take on. Do you have a design for the 44's I can look at? - No promises.
 
I couldn't agree more but on a different note...

Thanks for sharing your experience and photos and can I ask you why you removed the rear trunk floor? I'm not criticizing but am curious because I've often thought about doing the same thing but wondered if it would actually allow more heat from the exhaust up to the carbs or would you actually get more cool air having it all opened up like that.

All the air box talk on this thread has me doing my research and have found an airbox that I believe would be perfect for my setup and allow me to connect the drivers side intake hose to the airbox which is also connected to a blower motor so when sitting in traffic at the flick of a switch I can blow outside air into the airbox and leaving the passenger side intake hose free I can shorten it and leave it to blow outside air in the engine compartment. A win win in my head anyways.



I've re-done the sheetmetal removing the steel mesh and it is all closed up around the intake hoses and velocity stacks since this photo was taken.



'PeteX1/9
 
above my pay grade

Sorry guyz and chic! but some of this stuff is way above my pay grade. After reading all the dyno results stuff on this site in the past, I asked my head designer about it and he said dyno results are good ..but..they don't always translate into rubber on the road. He said he has had many of his engine who dyno low beat the shoot outa other cars on the track. So much where the opponents would protest the winners that he prepped. he said it's all about torque to hp transition. Something Carlo knew how to do IMO.
 
Stack and Screen Closure

OK a very spirited discussion on stack and screens
so the bottom line for me is the go pedal
and I can tell you I was stunned on how much improvement I got with the stacks from Pierce.
For those who don't remember I was very unhappy with my 2 carb's below 3,000 RPM so when met up with friends of my fathers who are serious amateur race drivers they both looked at the air filt's and said "too restrictive". I spoke to mad Matt who sent me to Piece and now we have stacks and instant strong pull as soon as I crack those butterflies. Now I called Pierce about the screens and they said "keep the screens on". They did extensive research on the stacks and ended up with the shared stack with the screens as the best result. I agree worth every penny for me. To everyone who weighed in thanks!
 
Stacks and screens, never noticed a diff with or without the screens as long as I had the stacks mounted. Just pulled like a b$#@h! Fiddley as the twin DCNF's were at my altitude, was never disappointed with power or the lovely sound.
IMG_0600.JPG
 
"Tigeravg", I'm glad you pulled up this old thread. Has some great info in it.
Hey 'mods', maybe this is a good candidate for the Wiki?
 
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