Weber velocity stack length

Eljaro · #1 (**permalink**) 08-07-2011, 12:20 AM

I did remove the phenolic spacer in order to get better hood clearance, but definitely the carbs were getting much hotter, so I had to put them back on.
Unfortunately the screen filter I have on the normal 2 1/2" stacks touch the bonet, and I have had one of them knocked of and lost it. The rocking engine keeps hitting the stack with the filter against the edge of the cutout for the scoop.
I have checked in Cobra Restores for a special wider scoop for Weber equipped Cobras, but they do not offer it any more. I am also concerned that the wider scoop will just not look right.
I wonder if shorter 1 1/2" stacks will work properly or if they will affect performance much.
Of course the auxiliary venturi would have to be milled off to the correct height and the upper radius be machined again.
Any experience or suggestion to this problem?

Gaz64 · #2 (**permalink**) 08-07-2011, 04:05 AM

I would try the short stack, but don't touch the auxilary.

It shouldn't matter if the auxilary is taller for a test.

The main thing is to keep a bellmouthed entry to the carb throat.

Have you thought about solid engine mounts?

Eljaro · #3 (**permalink**) 08-07-2011, 04:40 AM

Solid engine mounts? Better not.
But if it would be possible to have engine mounts which move the engine toward the left (driver) side, would make quite a difference.
The engine sits off center towards the right side, so one inch to the left would be fantastic.

bobcowan · #4 (**permalink**) 08-07-2011, 09:04 AM

How thick is the phenolic spacer? If all you need is 1/8" or so, maybe you could sand down the spacer a little.

Rick Parker · #5 (**permalink**) 08-07-2011, 09:41 AM

There are base gaskets that are about .125 thick this that help minimize heat transfer considerably. Have you tried this?

Eljaro · #6 (**permalink**) 08-07-2011, 10:51 AM

Hi Rick,
I did already turn down the phenolic spacers and they are now only 0.23" thick.

I tried the asbestos like spacers which came with the carbs, but they heated up a lot more.
I will remove the hood and cut the hole on the touching side as far close to the scoop as I can.
But if I could fit shorter horns that would be it. I only do not know how the engine will behave, because it now runs just fantastic. Dont want to spoil that.
Any experience how 1 1/2" horns will work?

cobrajeff · #7 (**permalink**) 08-07-2011, 11:04 AM

On my Cleveland, I milled 0.250 off the carb bases of the intake manifold. Kind of drastic, but, helped the clearance issue quite a bit (and I think that a quarter inch of phenolic spacer is probably a better heat insulator than an extra quarter inch of aluminum in the carb base on the intake manifold).

On a 289 Cobra without a hood scoop, we added the short stacks, and shortened the venturis, with good results. Seemed to run just as good as a similarly equipped 289 Cobra with a hood scoop and standard stacks.

Jeff

Full Throttle Al · #8 (**permalink**) 08-07-2011, 11:17 AM

I have the wider scoop from Cobra Restorers. In the 15 years I have had the car, never a single comment on the scoop being different. Nor have I ever had a problem with fuel boiling and I have no spacers. What temp thermostat are you running? You might try just eliminating the thermostat and switchin to waterless NPG coolant which elimnates any and all hot spots and makes cooling much more even. Also runs without any pressure in the cooling system.

Alan Sorkey
CSX4083
Shreveport, LA

Eljaro · #9 (**permalink**) 08-07-2011, 12:13 PM

Quote:

Originally Posted by Full Throttle Al

I have the wider scoop from Cobra Restorers. In the 15 years I have had the car, never a single comment on the scoop being different. Nor have I ever had a problem with fuel boiling and I have no spacers. What temp thermostat are you running? You might try just eliminating the thermostat and switchin to waterless NPG coolant which elimnates any and all hot spots and makes cooling much more even. Also runs without any pressure in the cooling system.

Right on. Thanks for the tip.
I must have been looking up an old link or their old page because I could not get the wider scoop to show up in the Cobra Restorers page. Now I have it. It is just the perfect solution. I am ordering it.
Are you runnig any type of filter on your Webers?

I am allready running NPG but the thermostat is in,because in winter it would take too long to warm up. I have no heat issues. The cooling is so good that as soon as I go fast the temp comes down to 160 ºF.

A bigger scoop would probably flow the air better over the Webers than it is now, where they are so close to the scoop that air is probably not evenly delivered to the eight throats. That has been an issue too, because the 8 spark plugs dont look the same.

dallas_ · #10 (**permalink**) 08-07-2011, 01:49 PM

I've got an extra set of 1 1/4" stacks that you could try to see if it would affect the performance.

Not sure what shipping would be to Spain, but would be willing to find out if you are interested.

John

Eljaro · #11 (**permalink**) 08-07-2011, 02:29 PM

Quote:

Originally Posted by dallas_

I've got an extra set of 1 1/4" stacks that you could try to see if it would affect the performance.

Not sure what shipping would be to Spain, but would be willing to find out if you are interested.

John

Thanks for your kind offer, but I will first change the scoop to a wider one and hope that the space is enough.

Full Throttle Al · #12 (**permalink**) 08-07-2011, 03:29 PM

To the horror of many at this site, I am not using any filters at all:

I can't understand why you would have problem with fuel boiling. I have owned many Webers and worked on many cars (including original Cobra's) with Webers and have never seen that problem.

Maybe you should consider an electric water pump that you can leave on with the electric fans for 10 minutes after shutting off your engine?

Alan Sorkey
CSX4083
Shreveport, LA

Full Throttle Al · #13 (**permalink**) 08-07-2011, 03:46 PM

Here is a better pic of the larger hood scoop:

Full Throttle Al · #14 (**permalink**) 08-07-2011, 03:48 PM

Shot of the Weber stacks as seen thru the larger hood scoop, plenty of room:

Eljaro · #15 (**permalink**) 08-07-2011, 04:59 PM

I also do not know why the boiling inside the carbs. The fact is that they are usually cool at the touch after driving, but soak up heat fast and then the boiling starts. I do shut off the fuel supply shortly before turning off the engine and the problem seems to be controlled that way.
Another problem could be the timing. I have to do a few tests with timing to see whether I can keep the engine cooler. I have 20º initial timing, which is a lot, but no problems whatsoever starting the engine. Maybe I could advance the timing more.
Al, How many degrees is your initial timing?

Dimis · #16 (**permalink**) 08-07-2011, 07:08 PM

Quote:

Originally Posted by Eljaro

Solid engine mounts? Better not.
But if it would be possible to have engine mounts which move the engine toward the left (driver) side, would make quite a difference.
The engine sits off center towards the right side, so one inch to the left would be fantastic.

Ummm... Not sure you want to go this route...

I suspect you might need to either re-align the entire drive-line (gearbox & rear-diff), or at a minimum it will put a hell of an angle (read - "force") on the ends of your short drive shaft. Definitely not a good thing!

I vote either:
Slightly bigger scoop... (easiest fix)
Or
Mounts that might drop the engine lower in the frame (this may require some fabrication, and you may need to re-check the ground clearance height of you bell-housing).
Or
As you suggested Short stacks - how much power will you honestly notice you've lost if your running a KC-482?
Seriously, try keeping your pedal to the floor for more than 3 seconds straight. Bet you or your tires run out of balls before your engine runs out of steam

Kind regards,

Disclaimer: I'm not an expert

Dimis · #17 (**permalink**) 08-07-2011, 07:16 PM

Quote:

Originally Posted by Full Throttle Al

To the horror of many at this site, I am not using any filters at all:

Thank you Al
I never get tired of seeing this pic...

But I'll bet that you're rarely at "Full-Throttle" with that beast under the hood.

Nice work!

Full Throttle Al · #18 (**permalink**) 08-07-2011, 07:20 PM

As I recall, more than 20 degrees, I think in the 26 degree range. I'm sure you've done this but any chance fuel pressure is higher than the suggested 2-3PSI for Webers or that the floats are set too high? High pressure fuel pump?

Full Throttle Al · #19 (**permalink**) 08-07-2011, 07:24 PM

Full throttle would be too much in this car, motor dyno'd with 629HP in 1967 with a single 560cfm Holley, more now. I have it rev limited at 6500 and the throttle limited to 3/4 throw to prevent sudden death, to the engine, car or occupants!

Car just won Best of Show at the Tulsa Shelby Meet in June, an unexpected honor. I hadn't even cleaned it up from 2 days on the track.

lemans24 · #20 (**permalink**) 08-07-2011, 08:05 PM

Jim Inglese says 38 degrees full advance on the timing. If you have a digital MSD, you might need a separate battery to power certain types of timing lights that will give a unstable reading.(per MSD Tech support)