Hot Rods Intake question (intentional vacuum leak)

I'm currently toying with the idea of creating an intentional vacuum leak to get around a carb CFM rule. Basically limited to a stock reproduction head with a 500 CFM 4412 holly carb.
My idea would be a intake drilled and tapped (one hole per cylinder) to accept a jet of some sort for tuning the air side and adding additional fuel through the main jet circuit. This is a race only application I'm aware of the danger of unfiltered air and that's a calculated risk i'm willing to take for a few more ponys. Motor is a 350-355 CI SBC chevy with a EQ stock replacement head ( no porting allowed ) good piston rods and crank. Has anyone any input or seen this done? This would obviously need to be tuned on dyno with air fuel and egt which I have access to.

 

Apologizes if this isn't the correct place to ask I'm new to this internet posting stuff.

 

For a while, years ago. Some of the smaller stock class cars that were limited to carb size, left the carb somewhat loose on the intake manifold. For just what you are thinking. I guess is worked under the rules at the time.

 

For sure. same concept just would like to go about it a little cleaner than just leaving it loose. That couldn't make reliable power I'd think it would swing wild lean to fat.

 

Is the problem that you can’t run as good as the guys who follow the rules?

 

It wasn't against the rules. Perhaps they were using the throttle linkage at WOT to cock the carburetor base to a repeatable gap. And so were able to tune for it. These were drag cars.

 

Good question! No not the case at all. As with any class of racing as time goes by competition gets closer and closer just looking for a little bit more edge. There is a couple (2 ) guys that work the heads for this class of cars and the jig is up on the cylinder head work so its on to the next idea. You'd fall out if I told you what a competitive SBC for this class costs.

 

You would use springs around the carburetor base studs and have linkage set so when you went to full throttle it would pick up the carb.

 

I see what you mean! Absolutely could see that being repeatable. This is a circle track class were talking about!

 

The good thing about this is you can always plug the holes if you decide that is best. Go for it. Is this an oval car?

 

Yes Sir, Dirt oval.

 

I would think that in order to move enough CFM to have a noticeable gain on top end your holes would need to be 1/2" or better. No way that would idle or start worth a crap unless you a way to close them when throttle is closed.

 

Dirt track, not worried about unfiltered air. You must go thru a lot of motors.

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Drill your carb studs. Guys in NASCAR did that with wax in the holes and hopefully wouldn't be found at the end of the race when running restrictor plates. This way all the cylinders will share the air...

 

The restrictor plate NASCAR guys were milling the flanges to create a leak and then running the carb fat. They got caught. If you are going to cheat you have to plan on hiding it and then plan on getting black flagged when you get caught.

 

I think you guys are right the hole/holes would have to be fairly large to make a noticeable or significant difference. That being said...... I've been caught bending the rules before! If you aint cheatin you aint eating! Im going to do some math on the subject to see what kinda area it would take to say go from 500cfm to maybe 600-650. In this class 10-15 HP is a huge advantage. Thank you everyone for the ideas, will update as they come to fruition.

 

We used to run a 283/2 barrel 4 speed 59 Biscayne NHRA stocker in the late 60s & did exactly what Saltflats said. Spring loaded carb studs that tiled the front of the carb up slightly when the throttle linkage bottomed out. Lots of guys used uncapped vacuum tees but they caught on to that quickly. Eventually the sharp tech guys would make us change the spring loaded studs out too. I later saw this setup set the Orange Bowl Regatta closed course 280 hydroplane record with a 273 Plymouth engine too. Boats guys werent as sharp as NHRA guys.

 

What would Smokey do?

 

I see what you were doing there. You remember how high the carb base was coming up off the manifold or how much additional jetting was needed to compensate?

 

Yeah. Agreed, This would be more for a big money race where its justified to risk hurt/ hurting a motor, deff not a weekly tactic!

 

More to the point, what didn't Smokey do?

 

HAHA thats a good point also!

 

There is a 4-cyl class at the local circle track. The hot guys were using the spring loaded mounting bolts. Eventually everyone figured it out. It became illegal. That being said it was legal until they outlawed it.

 

What would Smokey do ? WIN ! Is my answer


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Thats what im saying! Creativity with the rules spawns competition! Per rules now its still legal!!!!

 

How about something like this one?



The story is here: https://www.museumofamericanspeed.com/cheatermanifold.html

 

When I saw this it was the first thing I thought of. If you are ever close to Lincoln it is worth your time.

 

Alchemy! My friend thats one of the coolest things ive ever seen!

 

Hmmmmmmmmmmmmmmm.What`s that old saying?OHHHHHHHHHH yeah"All`s fair in love and war".I think that was Smokey`s motto too.
Good luck.Have fun.Be safe.
Leo

 

All is fair in love and war but when a mans racing... IF you aint cheating you aint eatin!