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they are used as an easy way to tune the intake runner length. They can add some hp or atleast modify the torque curve. Some engines like them some don't. There isn't much ryhm or reason as to if it will help or hurt your perforamce. It is just one of those things that you have to experiment and see what works.
 

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a 4 hole is said to improve torque, It actually gives the booster a better signal as the air is less turbulent coming off the base plate. It's also good to blend the bottom side to a knife edge like a "Wilson". I did mine myself! I think it improves most engines with at least a partially open plenum, then you can add an open one if you need more top end.


http://www.wilsonmanifolds.com/shop/index.php?l=product_detail&p=9
 

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super sucker

theres a spacer callled a 'SuperSucker' from HVH,,google it... makes good power,,,had 1 installled on my 489 on the dyno and made a huge difference..
dont get the plastic one,,, for the street use the alluminum.....
 

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All good comments, and all true. I'd just add that unless you are racing, I really don't see much point in using one for street driving.

Aside from the possible hood clearance issues, a few horsepower isn't going to matter much in a driver.

When I was racing sand drags years ago, we ran weight to cubic inches. Everything you could do to get 2 or 3 extra hp would help. There, it was a good thing.....gave me about 12 more. For street use, I wouldn't bother.
 

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My pipes are my music
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I believe that small improvements add up. Especially on a stock engine. I don't think your going to get much putting a spacer on a stock manifold with stock exaust. But, put a nice high rise and a set of long tube headers under it and it all changes. Like DALESY said, it all adds up.
 

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I think the 4 hole directly under the carb is the perfect addition for drivability even if it doesn't make huge gains in the hp/torque department. My point is the transition area under the base plate improves the metering of the fuel and improves the driveability. If you try one that has been ported or blended like the "Wilson" I think you willnotice the part throttle throttle response improvement.
 

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My pipes are my music
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Haven't I heard somewhere that with longer runners, velocity goes up and fuel atomization improves for a better "explosion" in the cylinder thereby adding power? I think that's the explanation for adding a spacer besides lowering the temp. of the carb. That's why they invented the tunnel ram intake. Uh, right? :D
 

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The 4 hole under the carb reduces the turbulence under the carb base plate providing a stronger signal to the boosters in the venturi. You can further improve that by blending the bottom edge to a knife edge where it goes to the open plenum. Why all the attention to porting and flow if you just have 4 holes dumping into an open area? Just think what the turbulence is like with a fully open area 1/8" below the throttle plates and transfer slots? All I am saying is the 4 hole spacer is a driveability improvement spacer and might not mean a hill of beans to a drag car but on the street I don't think you can loose unless you don't have hood clearance.

As far as velocity is concerned if it gets to fast the fully atomized fuel can go back into droplets and cause problems. One reason why intake ports are left rough and not polished to a mirror finish.
 

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People have learn't a lot over the years, they are the ones with less problems and going faster.... It's tough to change some people though.....

Only reason I can think of benifiting from pushing abrasive through a part is if you couldn't buy a part to do what you wanted it to do or because of rules wern't allowed to? Increasing the size of a port will lower velocity however the inside of a curve in an intake port can turn atomized fuel back into droplets.
 
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