Demon or Holley Carb for 306 Ford? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-25-2006, 11:52 AM
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Demon or Holley Carb for 306 Ford?

This is my first post on this forum, but I've been reading posts for quite a while and am always impressed by the knowledge and experience on this board. I'm going to be doing a carb swap over the winter on my 5.0L Ford. I'm considering a Demon carb and would like your advise. The engine is a normally aspirated 306 with 10.5:1 compression ratio, ported TFS Twisted Wedge heads, full-length headers, and a 224/232 @ .050" hydraulic roller cam. I haven't bought it yet, but I'll probably end up using an Air-Gap RPM manifold. The car is a Mustang LX notchback with a 5-speed manual and 3.73:1 rear. The car is a street-driven in the spring, summer, and fall so I want a vacuum secondary carb with electric choke (for the cooler mornings).

Based on similar combinations from old magazine articles and word-of-mouth, I was thinking of using a 650 Speed Demon or 670 Street Avenger. Recently I've been reading more and more about the benefits of annular discharge boosters for hot street engines and how they can allow the use of what would traditionally be thought of as too big a carburetor. For this reason, I'm now considering using the new 750 Annular Discharge Speed Demon. Do you think this carb is just too big for my combination? Does anyone have experience using this carb in a combination that would "traditionally" call for a 650cfm carb?

Sorry for the long post, and thanks in advance for any feedback.

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Old 11-25-2006, 12:31 PM
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Welcome to H B B !!!!

although i currently use a Demon carb i would recommend you use a Holley. if you do a search on this site you will find there are/have been a lot of problems with Demon/Barry Grant carbs. on some other sites i visit there is a number of negative comments about Demon carbs.
here`s an example
http://www.streetrodding.com/sr/inde...395&forumid=11

Trouble with Barry Grant Tech Support?

there is so much bad feed-back that i feel VERY fortunate to have not experienced any trouble.
however, it`s your money, spend the way you want.
good luck with your STANG !

Last edited by FASTFORD; 11-25-2006 at 05:53 PM.
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Old 11-25-2006, 01:10 PM
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As for the BG issues, I have a 625 cfm vac. sec. Road Demon on my wife's 331 stroker in her '66 Mustang and it has been great right out of the box. I verified all the initial settings and adjustments, per the instructions, and adjusted it after I started the engine for the first time. It started right up. After the engine broke in and ran a few times I reset the timing and adjusted the idle mixture with a vacuum gauge after setting the idle speed again.

The carb has performed flawlessly and the throttle response is better than the fuel injection on my truck.

Some people that you read talking about problems with BG carbs are only repeating what they have heard already. I understand that BG had some issues with aluminum chips in some passages and that was supposedly addressed by BG about the time I was buying this carb. All I can say is that this one has been as perfect as anyone could hope for, basically right out of the box.

After putting the car on a chassis dyno I found it is a little rich at WOT but great at all other throttle positions. I'm going to tweak the jets on the secondaries and be done.

Not to say that there is anything wrong with a Holley, there is a reason for the long history and storied reputation, but my next carb for my next engine build will also be a BG.

Steve
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Old 11-25-2006, 05:07 PM
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Demon or Holley Carb for 306 Ford?

Earlier this year I replaced my old Holley 800 dp with a new Mighty Demon annular booster 800 dp,this was the model recommended to me by the Tech @ BG guy here.I partially disasembled it to check for foreign materials,it was perfectly OK.The only thing I had to do was go up 4 sizes all around in the jets,otherwise I have been very pleased with my new carb.I would recommend a Bary Grant to anyone,but you must make sure to get the proper one to match your application.
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Old 11-27-2006, 10:29 AM
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Are you guys using single or dual plane manifolds? I've read recent articles that say dual plane manifolds require a carburetor that's up to 25% larger than what you'd use on a single plane manifold. Ordinarily I'd think that a 650cfm carb would be fine for my 306, but since I'll be using a dual plane manifold, I'm wondering if I'd be better off going to a 750 with annular boosters. Any more thoughts or experiences?
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Old 11-27-2006, 01:12 PM
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Dino Boreanaz,

The Air Gap style intake manifolds act much bigger (more similar to an open plenum intake), you'd be better off with a 650 on this combination.
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Old 11-28-2006, 06:24 AM
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I've been reading another thread on this forum about the supposed advantage of the Air-Gap manifolds and how they still heat soak on street-driven cars. For this reason I am now wondering if I should go with an RPM or Stealth manifold rather than the Air-Gap.

Several people stated that the real advantage of the Air-Gap manifolds is their taller height, but according to the Edelbrock & Holley websites, the Air-Gap manifold has the same height as the non-Air-Gap style dual-plane manifolds (like the Performer RPM and Weiand Stealth). Would your carb recommendation be the same if I go with a non-Air-Gap style dual-plane manifold?
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Old 11-28-2006, 06:43 AM
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Dino Boreanaz,

If everything else in the combination is staying the same yes a 650 would be the way to go.
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Old 11-28-2006, 08:29 AM
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I don't want to be "another guy" to knock a Demon, but I have tried both on my camaro with a 406.

The 750 mighty demon with annular boosters I have now is a pain. I have a LM-1 wideband tuner, and I log TPS, MAP, fuel pressure, AFR, RPM, and I still struggle with strange symptoms.

Look on the Innovate website and you will see where most people that have problems with the Demons are having a high speed leanout condition - that is basically due to the HUGE main air bleeds in the carb. .039" bleeds on a Demon, .028" bleeds on a "normal" HOlley. This causes all sorts of problems on many motors - but you may get lucky. I finally changed mine out to .028" like the HOlley and the carb no longer has that problem.

But the emulsion holes in the metering blocks are also oversized. They are .031" instead of the normal .028 or .026 on a Holley. That doesn't look like a huge difference numerically, but do the math on the area and it is a large percentage of difference. I'm not going to get into the theory of why this hurts the stability of the carb, but believe me it matters. Some people find themselves drilling and tapping the emulsion holes in the metering block, installing brass set screws, and drilling the proper sized holes to restore the performance. Plus, the bottom set of e-holes usually needs to be plugged so that the low speed mixture isn't so rich.

From one hotrodder to another, if I had it to do over again, I would buy a Holley. The Demon can be made to run very well if you have the patience.

And BTW, the problem with the metal chips is not fixed. Mine had all sorts of stuff in it. I bought the carb 6 months ago.

Again, I don't mean to dig on Demon - I just don't understand why they calibrate them the way they do. And neither do most of the other tuners out there. WHen I had my 750 vacuum secondary Holley on the camaro, I didn't have these sorts of issues with it. I thought going to a Demon was going to make the car perform better. And it has, but it has taken a long time to get it close to being right on tune.

If you have a datalogging wideband and like a challenge, get a demon.

Increasing the jet size on these carbs is a way to crutch the lean out condition on the top end, which is what some people end up doing to fix it- but you will have HORRIBLY rich part throttle, which no one can afford these days. A wideband reveals a bunch!

If you want more info PM me.
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Old 11-28-2006, 10:35 AM
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I would not reccomend a Demo for a garbage truck!!!!!! I bought a new Demo and they left a plug out and ruined my 383 motor when I contacted BG about they said send the carb back and they would install a plug. Big deal what about the cylinders that are washed down and the ruined parts and machine work?????
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Old 12-09-2006, 06:04 PM
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My vote is for the Holley.

I tried a new Speed Demon last year and here are a few facts that were let downs:

1. The metering blocks were filled with aluminum chips out of the box.

2. It had the wrong size main jets in it out of the box. BG said they would send the right jets and never did.

3. The design of the primary throttle arm allows allot of flexing against the idle screw. The vacuum on the primary butterflies can flex the arm and change the idle RPM every time the primary arm is returned against the idle screw. When I questioned BG about this their response was that they have heard that before but didn't have a fix. The design of the Holley arm does not allow this to happen.

4. The air cleaner base circle is blocked by the choke rod. Would be nice if the marketing info would mention that the customer will have to modify their air cleaner base pan to clear the rod.

Chris
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