Holley or Demon?
Discussion
Just a quick straw poll to see how many of you run Holley and how many run Demon carbs?
I've had Demons in both my Ultimas and whilst they should be 'better' engineered (apparently), I haven't been overly impressed with them in practice.
I guess it's one of those things that divides opinion. You're either a Holley-man or a Demon-fan?
I've had Demons in both my Ultimas and whilst they should be 'better' engineered (apparently), I haven't been overly impressed with them in practice.
I guess it's one of those things that divides opinion. You're either a Holley-man or a Demon-fan?
Used two Demons without any troubles. They are very accurate and easy to set up. However I do recommend dismantling and cleaning a BG carb before installing it. before fitting my new one, I read on a US website that machine swarf can be trapped which manages to escape BG's cleaning and QC. From memory, I think their was a reference to this on BG's website at the time also.I checked mine and found some alloy swarf.....
Keep between the green bits!
Keep between the green bits!
Am sticking with the Demon for the time being. Have just ordered a rebuild kit and a load of jets from the US to give it a tune-up 
I prefer the billet engineering of the Demon (and the looks), but I've heard about the swarf thing on other sites. I think like most things, regular maintenance is good practice.
I prefer the billet engineering of the Demon (and the looks), but I've heard about the swarf thing on other sites. I think like most things, regular maintenance is good practice.
I have used a Demon and a Holley carb on mine. The Demon is made of proper billet ali, while the Holley looks like it's made from recycled milk bottle tops 
. Also, a lot more adjustment on the Demon.
I could'nt get the Demon to run on my rebuilt engine, no idea why. I even took it to pieces, made sure all the passageways in the metering block were clear and rebuilt it. Did'nt make a blind bit of difference and yet the engine runs with the old Holley?
No need to go to the U.S for spares though, all Demons use Holley bits. They are all interchangeable. Real Steel do a "repair kit" for Demons and Holleys, comes complete with all gaskets, a selection of power valves, needles and seats, accelerator pump diaphragms and jets. I also bought a selection of cams for the accelerator pump (which I have yet to play with). The wrong cam could cause the engine to stumble when pulling away.
Don't forget to get some gasket removal stuff and a can of carb cleaner!
One thing to be aware of on the Demon, Charles Dunn told me the sight glass on the fuel bowls has been known to break! No need to tell you what that could mean!!
Best thing is to replace them with the plugs from the Holley.
. Also, a lot more adjustment on the Demon. I could'nt get the Demon to run on my rebuilt engine, no idea why. I even took it to pieces, made sure all the passageways in the metering block were clear and rebuilt it. Did'nt make a blind bit of difference and yet the engine runs with the old Holley?
No need to go to the U.S for spares though, all Demons use Holley bits. They are all interchangeable. Real Steel do a "repair kit" for Demons and Holleys, comes complete with all gaskets, a selection of power valves, needles and seats, accelerator pump diaphragms and jets. I also bought a selection of cams for the accelerator pump (which I have yet to play with). The wrong cam could cause the engine to stumble when pulling away.
Don't forget to get some gasket removal stuff and a can of carb cleaner!
One thing to be aware of on the Demon, Charles Dunn told me the sight glass on the fuel bowls has been known to break! No need to tell you what that could mean!!
Best thing is to replace them with the plugs from the Holley.
gtr-gaz said:
One thing to be aware of on the Demon, Charles Dunn told me the sight glass on the fuel bowls has been known to break! No need to tell you what that could mean!!
Best thing is to replace them with the plugs from the Holley.
Some Holleys come with sight "plastics" with an O ring and they definitely leak. The plastic goes hard/brittle with the fuel and heat cycling causing them to leak!!! I ALWAYS change mine for brass plugs. The consequences don't bear thinking about. Best thing is to replace them with the plugs from the Holley.
gtr-gaz said:
I have used a Demon and a Holley carb on mine. The Demon is made of proper billet ali, while the Holley looks like it's made from recycled milk bottle tops . Also, a lot more adjustment on the Demon.
I could'nt get the Demon to run on my rebuilt engine, no idea why. I even took it to pieces, made sure all the passageways in the metering block were clear and rebuilt it. Did'nt make a blind bit of difference and yet the engine runs with the old Holley?
No need to go to the U.S for spares though, all Demons use Holley bits. They are all interchangeable. Real Steel do a "repair kit" for Demons and Holleys, comes complete with all gaskets, a selection of power valves, needles and seats, accelerator pump diaphragms and jets. I also bought a selection of cams for the accelerator pump (which I have yet to play with). The wrong cam could cause the engine to stumble when pulling away.
Don't forget to get some gasket removal stuff and a can of carb cleaner!
One thing to be aware of on the Demon, Charles Dunn told me the sight glass on the fuel bowls has been known to break! No need to tell you what that could mean!!
Best thing is to replace them with the plugs from the Holley.
. Also, a lot more adjustment on the Demon. I could'nt get the Demon to run on my rebuilt engine, no idea why. I even took it to pieces, made sure all the passageways in the metering block were clear and rebuilt it. Did'nt make a blind bit of difference and yet the engine runs with the old Holley?
No need to go to the U.S for spares though, all Demons use Holley bits. They are all interchangeable. Real Steel do a "repair kit" for Demons and Holleys, comes complete with all gaskets, a selection of power valves, needles and seats, accelerator pump diaphragms and jets. I also bought a selection of cams for the accelerator pump (which I have yet to play with). The wrong cam could cause the engine to stumble when pulling away.
Don't forget to get some gasket removal stuff and a can of carb cleaner!
One thing to be aware of on the Demon, Charles Dunn told me the sight glass on the fuel bowls has been known to break! No need to tell you what that could mean!!
Best thing is to replace them with the plugs from the Holley.
Doh! Wish I'd got that reply yesterday Gaz. I popped into Real Steel and they couldn't tell me whether the rebuild kits were compatible between the Demon's and the Holleys. I'd suspected that they were, but ended up just buying a pair of bowl gaskets in case they got duffed when I changed the jets. Then again, it took me three attempts to explain that it wasn't a double-pumper and had mechanical secondaries!! I think my Demon (which I'm now sure is a 750cfm Mighty Demon) is an equivalent to a Holley HP ie. no choke assembly at all. It's probably a 'bit' big for the engine, but made 402hp according to the dyno so I reckon it's worth sticking with.
Have read so much on this subject in the last week my head is crammed full!
I've ordered a complete BG rebuild kit and jet kit from the US to be safe. It worked out cheaper than buying them here even including the shipping!
I'm going to leave it be until after its first trackday outing this weekend at Rockingham (and maybe the one after as it's the open day), then it will be completely stripped and rebuilt with smaller jets.
The daft thing is, other than being a bit rich (always, not just idle), it runs really well. The drilled butterflies concern me a bit (can get replacements easy enough), but I'm wary of trying to 'fix' it and ending up with it running worse
It's been a hugely informative exercise though. Learnt a shedload about EFI systems too.
PS. Apparently, Demon's a far more sensitive to compression, cam duration and lift etc. than Holley's (but they supposedly give better power when tuned in properly). That may explain why it didn't want to run right?
Edited by stig on Thursday 27th July 21:53
"The daft thing is, other than being a bit rich (always, not just idle), it runs really well. The drilled butterflies concern me a bit (can get replacements easy enough), but I'm wary of trying to 'fix' it and ending up with it running worse"
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
Boosted LS1 said:
"The daft thing is, other than being a bit rich (always, not just idle), it runs really well. The drilled butterflies concern me a bit (can get replacements easy enough), but I'm wary of trying to 'fix' it and ending up with it running worse"
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
I know Boosted, but the drilled butterflies are making it hard to adjust idle speed. The Demon's have the transition slots and whilst they should be adjusted to 'square' them, at the moment they're bottomed out just to keep the idle below 1000rpm. That's why I might change the butterflies - to give me adjustability back on the screws.
stig said:
Boosted LS1 said:
"The daft thing is, other than being a bit rich (always, not just idle), it runs really well. The drilled butterflies concern me a bit (can get replacements easy enough), but I'm wary of trying to 'fix' it and ending up with it running worse"
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
They are only for idle air bypass. So only really effect the engine at idle. Out of interest, has the demon got transition slots machined into the chokes like the holley? If rich all the time you probably have main jets that are to large. Mains are for cruising on and not WOT. UK tuners don't always know that. You need bigger pvcr's for WOT. Also the wrong power valve will make it rich at certain vacuums.
Boosted,
I know Boosted, but the drilled butterflies are making it hard to adjust idle speed. The Demon's have the transition slots and whilst they should be adjusted to 'square' them, at the moment they're bottomed out just to keep the idle below 1000rpm. That's why I might change the butterflies - to give me adjustability back on the screws.
I see. Could you solder the holes up like we used to do on rv8's back in the good old days
Or is is just easier to change the butterflies? Boosted.
BogBeast said:
As a carb related type thing I has installed a 1" phenolic spacer that has helped alot. Idle used to be hard work to setup and keep at one speed, noticably worse as the engine got hotter... 
I can now actually touch the carb after a hard run...
I has installed a 1" phenolic spacer that has helped alot. Idle used to be hard work to setup and keep at one speed, noticably worse as the engine got hotter... I can now actually touch the carb after a hard run... Already got a 3/4" one in place
Not a lot of room under a Can-Am deck for anything thicker than that - see you tomorrow mate.My experience with Demon carbs is considerable. I have NEVER seen a 'good' one. I have had poor build quality (including a small 390 baseplate gasket stopping the blades from opening!) all the parts left loose, floats that touch the metering block & don't move, exremely lean situations, extremely rich situations, (neither of which could be tuned out.) I had to abandon testing of one engine when two successive new BG 750 carbs gave an air fuel ratio that went up to 17:1 -total meltdown zone- and even a set of #100 jets wouldn't put it right. They would not accept there was anything wrong. There is NO technical back up. BG systems do not give refunds, but will offer to 'repair' your new faulty carb. If you have one on the dyno that doesn't work, it's always the fuel system, dyno or engine that's wrong. However, putting a Holley on it always solves the problem....
I have now resulted to giving them the dyno sheets with air fuel ratios, Brake specifics, lambda readings, V.E. Etc, with the BG, and with another carb. When presented with all the info they need to sort the problem out, they say they'll call you back, but they don't. At least one major parts house in the USA has dropped the line completely due to complaints.
You will never see anything other than a Holley (usually highly modified by a specialist) or EFI on a serious racing engine.
I would avoid them like the very plague itself, and wouldn't sell one to my worst enemy.
(If by some chance I have sold you one, you know who you are.....) Only Joking...!
I have now resulted to giving them the dyno sheets with air fuel ratios, Brake specifics, lambda readings, V.E. Etc, with the BG, and with another carb. When presented with all the info they need to sort the problem out, they say they'll call you back, but they don't. At least one major parts house in the USA has dropped the line completely due to complaints.
You will never see anything other than a Holley (usually highly modified by a specialist) or EFI on a serious racing engine.
I would avoid them like the very plague itself, and wouldn't sell one to my worst enemy.
(If by some chance I have sold you one, you know who you are.....) Only Joking...!
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