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Discussion Starter · #1 ·
I am working on fabricating up a scoop tray to make my bolt-on factory scoop functional. I'm pretty certain that the extra air being forced into my stock 351W HO will cause my 4bl Holley 600 to run a bit lean.

I don't know how much air will be forced in and am trying to anticipate the mix. Should I just adjust the screw to run a little rich, or should I try bigger jets? I am plannin on rebuilding the carb soon anyway, so a jet change would not be really out of my way if it would help out more than adjusting the mixture.

Any experienced ideas?





MoocH
 

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As long as your carb vent is inside your scoop being pressurized you shouldn't have any problems with mixture.
 

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Discussion Starter · #3 ·
Chuck, I appreciate the response, but can you point me to some more info? I haven't been able to find anything in the KB.

I'm a little confused as to what the carb vent is. Is that the hollow pen thing that sticks up in the middle, or rear of the carb that is kinda shaved off at an angle? If so, does pressurized mean airtight with no vacuum?

Sorry, I'm a bit new to this.





MoocH
 

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Race it, Don't rice it!
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Yeah you are right,

Chuckie is talkin bout the vent tube. as long as it's in the ram air box surrounding the carb you won't see a pressure difference inside the bowls that will affect fuel metering through the air bleeds. You an resize trhe bleeds if needed but it might take a lot of experimitation to get them emulsifing right.
 

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Air vents on Holleys are positioned at the front and rear of the carb mounting flange, they typically have a 45 degree angle milled on the top of the tube but they also came straight cut on certain models. For your homemade ram air to work you need to seal off the carb flange directly to your scoop, a close fit isn't good enough since any clearance here will bleed off the very slight pressure differential inside your scoop box. I have had better luck running cowl induction type "ram air" systems since they are not as easily affected by wind, rain, or the disturbed air when following another car at speed. With a small "tripper" wing/lip ahead of the rear facing cowl scoop you can increase the ram air effect many times.

On my RX7 IP3 car I realized a 30 Km increase in top speed (about 160Km/hr) at the end of the 1/4 mile front straightaway at our road track, interestingly the folks that tech'd my car noticed the short piece of aluminum dryer hose running from the carb to a plastic fitting I had grafted into the firewall to pick up air from the cowl area and declared it legal?:eek: The tech inspector said it was just a fresh air pickup!:D

Needless to say I kept my mouth shut and the hood closed during pit sessions lest anyone see my cheesy "ram air" setup and call the tech inspector on it. I was worried because I went from running mid pack in IP3 to being hot on the heels of the leading GT2 cars running 2-3 seconds faster per lap than my class.

BTW it's not cheating if the tech inspector is an idiot.:cool: :thumbup:
 

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Discussion Starter · #6 ·
Thanks a MILLION guys. I'm gonna go over some designs and figure out what thickness I'm going to need to seal the tray to the bottom of the hood to account for torque movement.

My engine mounts are brand-spankin' new, but I still have a LOT of engine twist when I blip the throttle. I'm going for at least 1 inch of flexible clearance so I don't bang the tray on the hood.

Thanks again for the info. That's a big help for my carb questions. :thumbup:

I see what you're saying about starving out if I'm behind another car, but this is pretty much going to be used on the strip and maybe a few midnight cruises around town. HOPEFULLY if this works the way I want it to, I won't have to worry about riding tail ever again. :cool:





MoocH
 

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Thick foam for the pan and a chain on the left motor mount might help.:thumbup:
 

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I'm running a ram air system on my car, check my gallery. I'm also running stock motor mounts with an engine brace. I used a 3/8 grade 8 threaded rod cut to length with a spherical rod end at both ends. You can purchase the rod ends at a heavy duty truck part supply store. I made a bracket to bolt to the chassis for one end and used a bolt hole on the cylinder head for the other end. This gives a nice smooth vibration free ride and when I get on it the brace keeps the engine from torquing over. It basically eliminates any engine movement. Also, I went to one step thinner metering rods for my edelbrock 750 carb just to be safe as at high speed it'll be sucking in a lot more air than an open element air filter.

Steve
 
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