Author Topic: 400 ci with Holley Street Demon 625  (Read 790 times)

Offline cyberxen

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400 ci with Holley Street Demon 625
« on: July 23, 2018, 08:59:28 AM »
I finally got my hands on my dream truck - 1976 K10 heavy half with the 400 small block. The downside - its been sitting since 1999. The quadrajet is all jammed up, I'm not sure it can even be brought back.

I have my eye on the Holley Street Demon 625, is anyone else running this combo, maybe with a mild cam and a pair of longtubes?

Also, trying to decide on an intake. Currently the Jegs Champion is at the top of my list, it has the plenum notched which is supposed to be helpful if I upgrade to the Holley Sniper TBI some time down the road.

Offline Rapid Roy

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Re: 400 ci with Holley Street Demon 625
« Reply #1 on: July 23, 2018, 09:04:39 AM »
Welcome to the site.
1974 Cheyenne 10 LWB 350/TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline Stewart G Griffin

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Re: 400 ci with Holley Street Demon 625
« Reply #2 on: July 23, 2018, 11:49:59 AM »
1) Why not get a reman or rebuilt q-jet?

2) Who makes the Jeg manifold would be my concern.

i would go with an edlebrock performer rpm manifold (it's hi-rise) and q-jet, but that's just me.

Offline RossVE

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Re: 400 ci with Holley Street Demon 625
« Reply #3 on: July 23, 2018, 08:54:11 PM »
I'm running the 750cfm street demon on a Weiand dual plane intake on the 454 in my 75 C30. It's been a trouble free combination for me. The street demon was ready to go out of the box. I've got nothing bad to say about it at all.

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Offline Irish_Alley

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Re: 400 ci with Holley Street Demon 625
« Reply #4 on: July 24, 2018, 02:39:55 AM »
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline cyberxen

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Re: 400 ci with Holley Street Demon 625
« Reply #5 on: July 26, 2018, 11:37:21 AM »
a note about carb cfms

That was a good read, thanks. The Holley carb selector also indicated that the 625 Street Demon as the correct choice.

I do plan on rebuilding the QuadraJet though. It will be my first carb rebuild however, so I want to have a backup just in case  ;D

Offline cyberxen

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Re: 400 ci with Holley Street Demon 625
« Reply #6 on: July 26, 2018, 11:44:11 AM »
I'm running the 750cfm street demon on a Weiand dual plane intake on the 454 in my 75 C30. It's been a trouble free combination for me. The street demon was ready to go out of the box. I've got nothing bad to say about it at all.

Sent from my ONEPLUS A6003 using Tapatalk

That's good to hear. The YouTube videos I have watched also seem to indicate that only minor tuning for the idle mixture is required. Did you see a change in fuel mileage?

Offline RossVE

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Re: 400 ci with Holley Street Demon 625
« Reply #7 on: July 26, 2018, 11:51:35 AM »
I didn't see a mileage increase, but with a th400 trans and 4:10 gears mileage has never been a priority. I do agree that you would be better off with the 625cfm.

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Offline Irish_Alley

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Re: 400 ci with Holley Street Demon 625
« Reply #8 on: July 26, 2018, 12:18:28 PM »
cant remember the exact cfms but on my 79 with 38s, sm465 and 4.10 ratio i was got 8-10 mpgs if i was easy. think the cfms were either 600 or 625.  i agree with 625 is a nice conservative number to use also unless you plan on racing. also for the intake dont get one of those "high rpm" intakes get one that has low end tq and the same goes for the cam
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes