Draw-through carb info?

-
Long

Long

FABO Gold Member
FABO Gold Member
Joined
Mar 1, 2023
Messages
12
Reaction score
17
Location
Bulgaria
Hi, folks!
I'm struggling to find good information about how draw-through carburetors work and what are the differences between those and the NA carbs.
Can you help point me to a decent source?
 
:popcorn:

I'm also interested in draw through setups.
 
Those two threads don't say much about the carbs other than:
1. No changes are needed
2. Minimal changes are needed

I see that Holley and QFT have designated "draw-through" carbs (up to 950cfm). There must be a difference... or is that just a "marketing trick"?
Problem is that with those I'm still limited to about 15psi and I need to go past that to reach 1000-1100HP.
 
When I was in school, me and a friend replaced the dinky draw through Quadrajet on a mutual friend's 301 turbo Trans Am with an early 70s 750. We did nothing to it and it ran really good. For what that's worth.
 
I'm not sure about other carbs, but with the Holley you need to have a separate intake vacuum/pressure line from the intake manifold to the carb. The stock Holley senses intake vacuum from the base of the carb. When used as Draw thru, it is possible for the base of the carb to "see" vacuum even if on boost if the throttle is only partly open. In that case the power valve might not open and the carb will be lean. Found that out the hard way. I used a 500 holley 2 bble on a Rajay F60 turbo on a 65 valiant 170 slant six.
 
RustyRatRod said:
When I was in school, me and a friend replaced the dinky draw through Quadrajet on a mutual friend's 301 turbo Trans Am with an early 70s 750. We did nothing to it and it ran really good. For what that's worth.
Click to expand...
Well if it works it works I guess. Thanks, man!
MiradaMegaCab said:
How To Boost Reference your Holley Carburetor

Article is based off of a draw through supercharged application but is the same for draw through turbo applications
Click to expand...
Great. Thank you so much.
I’ll be supercharging so that’s perfect!
 
MiradaMegaCab said:
How To Boost Reference your Holley Carburetor

Article is based off of a draw through supercharged application but is the same for draw through turbo applications
Click to expand...
Good article. I did mine slightly different, but essentially the same. Just have to remember if you later use the carb on a normally aspirated engine, you still need to connect that tube to the intake manifold.
 
67Dart273 said:
You WILL need a water exchanger for carb base heat
Click to expand...
I agree. I hade to water heat the carb to turbo adapter. Without the heat, the idle was like a big motor blown gasser. Surging up and down. The adapter had frost forming on it. My adapter was just a 3 inch "log" with a plate welded to the top for the carb. All I did was epoxie a piece of copper water tubing to the bottom of the adapter, and connected to the heater hoses. No more ice, and the idle smoothed right out.
 
Read a bit and I think I get it now. The draw-through carbs I mentioned have the power valves "fixed" out of the box basically.
I failed to find a source for the Holley 8082-3 that I have (and I'll need a second one) so I'll probably sell my 1050 and will buy 2 new draw-through Quick Fuel carbs. Gotta run the number again with BDS but it seems I can pull 20psi with the 950s and that should take me to 1170HP on the flywheel (and above 1000HP on tyres).
Thank you all for the great advice - you guys rock!!!

PS: I'll start a separate thread to discuss the blueprint in general and find out more about other details.

Rock on!
 
You must log in or register to reply here.
-

Back
Top