Replacing Cold Air Box with Velocity Stacks

[Michael Oritt]

A few days ago I started the "Phenolic Spacer" thread as I was preparing to remount the Cold Air Box to my carbs I just rebuilt. I thought I finished the job yesterday until this morning when I pulled the choke cable to start the car and found that when I released the choke the car was running very poorly. On inspection I found that the front choke return spring was not attached to the choke arm and I will have to remove the CAB in order to get the hooked end of the spring into the hole in the arm--another couple of hours to be spent jamming my large hands into a tight space full of sharp edges, etc!

Though the CAB is iconic because of its connection to the M/Le Mans cars it is a major PITA and I have often thought of replacing it with a pair of velocity stacks. Without discussing the merits of the stacks versus a CAB I wonder if it is necessary to install "richer" carb needles to compensate for the alleged increased air flow that the stacks supposedly produce.

Advice/experience will be appreciated.

 

[HealeyRick]

I have velocity stacks on my bugeye and went to richer needles, but I also had a hotter cam, head and headers. You're going to want to use some kind of filter on the stacks, usually some kind of foam sock. By the time you do all that, you may find that you're still in the same range as the needles you have in there now.

 

[Michael Oritt]

Thanks Rick and since I already have the DW cam, AL head and tubular headers I would not be making any other changes that might affect mixture.

 

[steveg]

Michael,
Can you access the inside of the CAB?

The reason I ask is if you could, you could perhaps install the APT stub stacks inside the box.

 

[Michael Oritt]

Steve--

Yes, I could easily do that but what I am considering is to get rid of the CAB because it is such a pain to work around.

 

[Healey 100]

I have worked around one of those CABs and I certainly agree it is a pain to work with. I would put it aside in a minute if my car had one. Can't say what it would do to the engine performance, but I suspect the change would hardly be noticed.

Another dreadful feature of the 100M is the bonnet strap. It makes merely opening the bonnet to check the oil a tricky job, risking the paint job.

 

[DerekJ]

None of the racing 100s over here run with a cold air box so i assume it doesn't add power and may even restrict intake.

 

[Michael Oritt]

Bill/Derek--

Though my car is not an M it is an early (1956) owner-converted Le Mans and I would consider doing away with the bonnet strap sacrilege--plus I just had the car painted and what would I do about those holes! The CAB, however, is on the chopping block and the velocity stacks w/filter socks do provide an interesting esthetic, plus they may provide some performance benefit not to mention ease of access to the whole left side of the engine compartment.

 

[Bob_Spidell]

It's been many years, but a guy who tuned, and raced, 100s claimed he got more HP with velocity stacks than a CAB. I believe he had dyno data to prove it, and it seems feasible to me. With a CAB incoming air--while presumably cooler--has to make a sharp, 90deg turn into the carbs; not good for flow at all (and the rear carb may get 'robbed'). From what I've heard, the fancy CAIs often added to rice rockets and V8s only add a few honest HP, and this on a big V8 making 300HP+ to begin with. They are good marketing, however.

I got a pair of stubby stacks from David Anton at ATP when we were prototyping a K&N setup for BJ8/HD8 carbs. Can't say if they added any power, but they are well made. Can't see how you could possibly fit them inside a CAB.

 

[Randy Forbes]

It's been many years, but a guy who tuned, and raced, 100s claimed he got more HP with velocity stacks than a CAB. I believe he had dyno data to prove it, and it seems feasible to me. With a CAB incoming air--while presumably cooler--has to make a sharp, 90deg turn into the carbs; not good for flow at all (and the rear carb may get 'robbed'). From what I've heard, the fancy CAIs often added to rice rockets and V8s only add a few honest HP, and this on a big V8 making 300HP+ to begin with. They are good marketing, however.

I got a pair of stubby stacks from David Anton at ATP when we were prototyping a K&N setup for BJ8/HD8 carbs. Can't say if they added any power, but they are well made. Can't see how you could possibly fit them inside a CAB.

Well, if you made your own, and the top/front panel is removable...

But you should see the wild & crazy little 10mm wrench I had to bend up to snake around behind the flares to mount them!

Not a true cold air box, but more of a unified air filter assembly; standard 1-3/4" thick rectangle filter elements straddle each pair of velocity stacks and are sealed front and back when the s/s cover plate is slipped in and secured.

(no filter elements fitted in above pic)

 

[Michael Oritt]

This morning I removed the CAB and my wife lent her small hands to the job and reattached the choke lever return spring. I reinstalled the CAB and everything is now buttoned up and--I hope--fine. It only took about 10 minutes to pull the box and a similar amount of time to bolt it back onto the carbs, so though it still remains an obstruction I guess I was making a mountain out of a relatively small mole hill.

I use two bolts to fix the CAB to the carbs which thread through rivnuts in the inner face of the box and pass through the front mounting hole in the front carb and rear mounting hole in the rear carb (both of which have the threads drilled out of them to accept the diameter of the bolts) and are nutted from behind the carb ears. By removing these two bolts and using slightly longer ones to accommodate the thickness of the velocity stack I could install the short stacks inside the box.

I may order a pair of short horns and install them in the CAB as above. Or I may go for a more radical look, get some long horns and scrap the box. Or, as so often happens with these projects, I may simply continue to think about it and do nothing until the next time I must deal with getting my hands under/around the box and then rethink everything again--we'll see.

In any case it is good to have the car back together with the carbs rebuilt and not leaking air around the shafts. Spring is almost here and driving season beckons!