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DCOE Throat Sizing?
https://mail.slantsix.org/forum/viewtopic.php?t=67064		 Page 1 of 1
Author:  Greg Ondayko [ Thu Feb 02, 2023 9:41 am ]
Post subject:  DCOE Throat Sizing?
I will probably be getting my DCOE Throttlebodies soon.

It will go on an NA Street car, but they will be fuel injected.

What size would be appropriate? 40, 42, 45, 48, 50 and 55 are offered.

Would bigger be better as there is not an air velocity issue pulling the mixture through the chokes and customization tubes / venturi like a carbby?

Cheers, Greg
Author:  ProCycle [ Thu Feb 02, 2023 11:01 am ]
Post subject:  Re: DCOE THroat Sizing?
The downside of going too big is it can make it difficult to modulate power delivery at small throttle openings.
Author:  Greg Ondayko [ Thu Feb 02, 2023 11:57 am ]
Post subject:  Re: DCOE THroat Sizing?
Quote:
The downside of going too big is it can make it difficult to modulate power delivery at small throttle openings.

ahh yes, the Motorcycle mechanic speaketh wise words... Thanks Jeff,

What would be good for a 1.5" Intake valve size Jeffery head on the slant?

I was thinking 45, and that is on the big side for an actual DCOE Carb for the slant.

Greg
Author:  ProCycle [ Thu Feb 02, 2023 12:16 pm ]
Post subject:  Re: DCOE THroat Sizing?
I don't really know what size would be most appropriate. I guess if i was doing it I'd try to translate the DCOE size into CFM and choose based on max realistic airflow. If you were putting a 4-barrel on it would you go with 350 CFM or 500 CFM?

I also don't know anything about the Weber carbs. Most modern 'big' automotive throttle bodies have a progressive cam (or drive by wire) that opens the throttle slowly in the first 1/3 of travel. Do the Webers have that or is it an option? If so, go big!
Author:  Greg Ondayko [ Thu Feb 02, 2023 12:44 pm ]
Post subject:  Re: DCOE Throat Sizing?
Current configuration has a single 4 barrel edelbrock 500 cfm on it. I could try the 750 cfm edelbrock from ruster on there sometime too.. but have yet to do so.
Author:  CNC-Dude [ Thu Feb 02, 2023 3:47 pm ]
Post subject:  Re: DCOE Throat Sizing?
40MM throttle bores is more than adequate for the small cubes of a Slant. If you go too large, the airspeed and low end throttle response will suffer, just as if you have too large of a plenum for a carb'd engine. I designed and cast (2) side draft intakes a few years back and know quite a bit about sizing DCOE's on inlines.
Author:  Rick Covalt [ Thu Feb 02, 2023 4:32 pm ]
Post subject:  Re: DCOE Throat Sizing?
Quote:
1.5" Intake valve size Jeffery head on the slant?
Why did you downsize your valve? :D :D

Honestly, On a street motor I don't even think you need a 45. That is all we are running in all out race motors. My car went 12.80's with 45's and 38mm venturi's. You could probably get by fine with 40's on it fine. Run some 34 or 36mm venturi's to keep your air speed up some.
Author:  Greg Ondayko [ Thu Feb 02, 2023 5:46 pm ]
Post subject:  Re: DCOE Throat Sizing?
Oops. :shock: Good catch Rick. :!: Thats the exhaust Valve.
My dyslexia is active that's for sure.
It's more like a 1.8" intake valve.

I don't think there is a venturi on it as it's just an air valve for EFI.
Author:  Dart270 [ Sat Feb 04, 2023 3:50 am ]
Post subject:  Re: DCOE Throat Sizing?
All I can add is that Tilley tried several sizes from 40-48 on this roadrace Slants and found 48 was too big and 45 was just right and made max power. His with 45s did not seem to have any throttle response issues from him driving it around, that I could observe. If it were me, that's what I would use. Of course, he had 38-42 mm venturis in his too and IIRC 40s were best.

That said, I have a set of 40mm DCOEs that I pulled all the guts/venturis out of and had Gill modify them and the intake for EFI. Maybe I will try that this summer? Come down and help me put them on Project V some weekend and you can test/feel for yourself!

Lou
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