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Author Topic:   Carb Spacers
posted November 16, 2002 06:32 PM
Currently running a one inch open spacer on a 406 Chevy. I am thinking of trying a 2 inch spacer to see if there are any improvements.

My question is if I change to the 2 inch spacer will I need to rejet the Carb. If so how many jet sizes might I have to adjust.

KP Lugnut any ideas????


posted November 16, 2002 07:45 PM
A lot of what will determine that is what intake you have under the spacer, really. If you're on top of a good open plenum intake as it is, you'll be adding significantly enough plenum volume to need a change.
The real question, is will you LIKE what the 2" spacer is going to do to the torque curve on the motor. It will not give you more bottom end, I'll tell you that much. And in extreme cases, it affects throttle response in the normal operating range.
You have to determine if this kind of change is what will help you on the track. It's going to raise the peak torque up a bit in the rpm range, for sure.
To honestly answer the question the best I can, all I can say is that on average, only a slight boost in jet, maybe 2 at the most is going to be needed, but there is really so many variables involved that I can't tell you for sure.
Some spacers are far less efficient than others, especially at the 2" size, and they may actually wind up doing the opposite you'd expect as far as jetting and what it does to the power.

Let us know what intake, carb, etc you're dealing with and I can probably recommend something more specific.

Hope that helps.


posted November 17, 2002 10:26 AM
KP, we are currently running a edelbrock victor JR intake and a 750 CFM alcohol carb ( I didnt mention before that we are running alcohol)That Speedway Motors sells, It is made by Bill Mitchell.

I was thinking of just trying a 2 inch open spacer to see if we liked the results, from what you said above I may rethink that, but if you could offer any other advice I would appreciate it.

You mentioned throttle response, we have had problems with that before but I think it is more a product of our mechanical fuel pump than anything else.


posted November 17, 2002 02:10 PM
OK, horse of a different color there. The big plenum volume in a Victor Jr isn't anywhere near as limiting a factor as, say, a cast iron quadrajet intake. You've got a ton of top end power as it is with it.
Probably what will happen in your case, by adding the 2" spacer, is a need for a jet increase of about 2 on average, it'll be a bit more temperamental with regard to temperature changes that require jet adjustments too.
I think with the carb you have, the throttle response problem you mentioned is more in the carburetor than just in your mechanical pump. If your pump is functioning well, AND you have a regulator in the line adjusted properly so your boosters aren't dribbling at or just off idle, then any throttle response problem is usually in the carb. I'll not mention float levels, because that would be the first place to verify.
Anyway, adding that 2" spacer if you are having a throttle response problem is going to magnify it.

Also, don't think that in your case I'm saying don't do it. With your setup, I think it will flatten your torque curve a bit, raise it a tad on average, and the peak will move up in the rpm range just a bit. It goes without saying, too, that insulating the carb that much more from the heat is a benefit, too.

What I suggest doing first, tho, is to have the carb checked and improved such that throttle response is what it should be, verify your fuel pressure and supply issues, and add that 2" spacer and go win some races.

Good luck, and if we can help, gimme a shout.

Kinetic Performance

posted November 17, 2002 07:56 PM
KP Thanks for the help I really appreciate it.

As for the throttle response you may be right, but we adjusted the carb and idle settings and it is much better now.

The problem we had was a stumble in the corner when getting back on the throttle.

There is a regulator plumbed in.We thought the steady pressure needed with the alcohol and from the mechanical pumpo was causing the carb to load up in the corner when off the throttle. It is much better now.

Fuel did not nor does it now drip from the boosters though.

again thanks for the help


[This message has been edited by chief4car (edited November 17, 2002).]

posted November 17, 2002 08:27 PM
Glad you've been able to improve it some.
One thing we like to do to help eliminate stumbles in the corner is to make sure all our oval track carbs have the special oval track "cut" floats in them. Regular brass (or any other regularly shaped style) will allow the fuel that is sloshed over to one side in the bowls to greatly alter the float level, thereby overfilling the bowls temporarily in the corners.
Suddenly, as the driver just gets back on the throttle, all that extra fuel dumps over thru the boosters, etc, and causes that momentary "blubber" or overly rich condition you are seeing.

It could be something to check, anyway, just thought I'd mention it.


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