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 Street Single Plane with Spread Bore? 
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Is it possible that a small single plane intake could provide similar power under 3000 rpm to a dual plane just by using a spreadbore on the single plane?

I ask because I have a Holley Street Dominator/Contendor single plane for Chrysler 318. It's ports were match to the 340 gaskets, which may not have been the hot ticket for this purpose. It was designed to accept either pattern carb without mods. I'm currently using an LD340 dual plane. In spite of its legendary reputation, the runner entry from the plenums are big and open compared to an Eddy RPM intake. It looks to me like a lot of velocity is probably lost at lower speeds.

So, it seems like the easy answer is to try an Eddy RPM. But the Holley SD is much shorter (more hood clearance and room for phenolic spacer, taller air cleaner), lighter, and possibly better distributrion of fuel at high rpm (from the more even runners and shared plenum). Fuel distribution is not a top priority but I mention it because for 20 minute non-competitve sessions on a road course it will be in upper rpms longer periods than on the strip or autocrossing.

I've got a big Holley spreadbore discussed and, and am not adverse to experimenting with a used QJ or TQ.

I don't know anyone around here who has the experience and equipment to modify the runner entries and plenum floors like Vizzard has done. On the other hand, I see factory examples of single plane intakes such as came on the 273 4bbl Commando engines. My current cam has a fair bit of overlap, roughly 230 duration at 50, 108 LSA but a stock cam is more like 112 or 114 LSA and 52 degrees of overlap IIRC.

File comment: Street Dominator for Chrysler SB
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Wed Jan 29, 2014 9:00 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
Give it a shot or try it with a ThermoQuad or a QJet until you find the Holley parts you want. The Chevy Street Dominator is a good intake with either of those carbs. Not saying they’re not a good carb, but I haven’t used or tuned a Holley spread-bore in 30 years. ... ewall.html

Wed Jan 29, 2014 12:25 pm

Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Thanks. I guess I wasn't entirely clear in my question.
At its best, can a spreadbore like a QJ or TQ pick up the lower rpm range on a single plane?
I appreciate that the Holley spreadbore is crapshoot.

I understand the only way to really know is to test the combos. But no point trying something that folks with experience have already done or know enough to say. Dyno time aint cheap as you know, and its not close either.

PS. Neat article on the TQs. I hadn't seen that one. Also makes me think the Dusters have a little more room under the hood than the early and mid Barracudas. The LD340, Performer and too a lesser extend the RPM is gives just a little more room thant the Weiand 8007 I tried. Enough that I can experiment ith 1/2" spacers (using a 7/8" air cleaner drop base) and not worry about denting the hood. The AFCO? lid helps too.

Mon Feb 03, 2014 11:11 pm
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Just for fun. A 273 factory single plane is shown bottom right corner on "The Politician"
Full 1966 Carcraft article in post on FABO ... ostcount=5

Mon Feb 03, 2014 11:31 pm
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