Carb Questions

[Guest mudbutt]

Im posting this trying to help a guy on another board, as I dont know shit about carbs.

 

I am having a little trouble building my carb... All I see in the books is "thinning the throttle shafts leads to better booster signal and airflow at top end, as well as less turbulence." Beond that noone seems to know anything. Here are my questions...

I am modifying a Holley 4500 Dominator 1050 cfm HP series carb for blow-through turbo. How much can I thin the throttle shafts before risking breakage? How large a fillet radius should I cut? Can I countersink the screws in the butterfly?

Right now I have the shafts cut to .100 with about a .060 radius. Can I go much more without risking breaking the shaft if I backfire through the carb or overboost?

[desperado]

Damn dude, seems someone's getting WAY extreem.

 

Now as far as your carb, you can clean off about half of the shaft and be ok, but you are going to want to run a plate under the thing to catch the linkage if it comes apart, i understand that happens from time to time and the parts und up in the cylinders, causing all sorts of bad shit to happen.

I will also say that mods like thinning shafts and going with button head screws are more pointed to N/A motors that need the extra boost signal. Not knowing how big you are going with the turbo and having any idea of how quick it will spin up, you may have some issues with booster signal off idle when you go WOT. But, because the restriction to flow is going to move up the intake tract to the turbo, it might have very little effect.

 

The other thing that you need to be considering with the shafts, again depending on the turbo size is the pressure down on the shafts/butterflys when you close the throttle under full boost. I assume that you are going to be running a BOV, but even then you are still going to have a pressure pulse hit the butterflys until the BOV see's the vaccum and has time to pop open.

 

BTW, just what in the hell are you putting a 1050 on that's gonna be a blow thru? Inquiring minds gotta know.

[Guest mudbutt]

Reply from the guy.

 

 

"Inquiring minds are going to have to wait until next season

 

I cut a plate to slip under the carb with holes under each barrel .030 undersized to catch any butterflies that try to fly away. I figure that should be enough. I am a little weary of the restriction to airflow, and may end up putting together a 1/2" spacer with venturi bores instead to cut down on the turbulence. Thanks for the input."

[desperado]

Reply from the guy.

 

 

"Inquiring minds are going to have to wait until next season

 

I cut a plate to slip under the carb with holes under each barrel .030 undersized to catch any butterflies that try to fly away. I figure that should be enough. I am a little weary of the restriction to airflow, and may end up putting together a 1/2" spacer with venturi bores instead to cut down on the turbulence. Thanks for the input."

 

No No.... it's not the butterflies that you need to be concerned with.... the linkage tying the secondary to the primary on a dominator is internal, right in the center of the carb. That is what you need to keep control of. The butterflies are not going to get into the engine, they may get down in and lunch a valve and valve seat, but that's all the farther they will get. make your holes the same size of bigger than the venturi, because it WILL screw with air flow, just make sure that the area in the center of the venturi is covered so that if that linkage comes apart it will not fall into the motor.

 

Jegs actually sells a plate for this very thing... but if your plate is already made just enlarge the holes so that there is no restriction.

 

Will you even hint as to the manufacture and rather it's a small or big block motor???