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73-87 Chevy _ GMC Trucks => Performance => Topic started by: cyberxen on July 23, 2018, 08:59:28 AM

Title: 400 ci with Holley Street Demon 625
Post by: cyberxen 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.
Title: Re: 400 ci with Holley Street Demon 625
Post by: Rapid Roy on July 23, 2018, 09:04:39 AM
Welcome to the site.
Title: Re: 400 ci with Holley Street Demon 625
Post by: Stewart G Griffin 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.
Title: Re: 400 ci with Holley Street Demon 625
Post by: RossVE 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.

Sent from my ONEPLUS A6003 using Tapatalk

Title: Re: 400 ci with Holley Street Demon 625
Post by: Irish_Alley on July 24, 2018, 02:39:55 AM
a note about carb cfms (http://forum.73-87chevytrucks.com/smforum/index.php?topic=31379.0)
Title: Re: 400 ci with Holley Street Demon 625
Post by: cyberxen on July 26, 2018, 11:37:21 AM
a note about carb cfms (http://forum.73-87chevytrucks.com/smforum/index.php?topic=31379.0)

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
Title: Re: 400 ci with Holley Street Demon 625
Post by: cyberxen 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?
Title: Re: 400 ci with Holley Street Demon 625
Post by: RossVE 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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Title: Re: 400 ci with Holley Street Demon 625
Post by: Irish_Alley 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