deMideon Posted July 10, 2005 Share Posted July 10, 2005 Well... I just broke the base of my Holley 750 double pumper... as it's an old carb (I got it used), I am going to get a new one. I wanted to find out what everyones opinion is. I want to go with mechanical secondaries and I have a 450 hp SBC 377. What should I use? I was thinking about the 750 speed demon with mechanical secondaries. Let me know what you think! Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted July 10, 2005 Share Posted July 10, 2005 Personally, I have never used Barry Grant Carb's, however I'm sure that they work fine. Anything better than a stock holley has to be good, right?!! 450HP is alot of ponies so a 750 might be alittle under carbed anyway. Keep in mind that a stock holley rarely, and I mean rarely flows 750, probably more like 700 actual wet flow numbers. You may try an 800 or even an 850 but it depends on what you are doing with the car. Don't knock a vacuum operated carb, they work good on some applications, although I prefer the DP carbs myself for my driving style and vehicle combinations that include high stall converters. I run a C&S 800 on the 350 and a 900 on the 406, both are wet flowed aerosol billet alky carbs. I have a stock 750DP, just doesn't work very well on anything I've ever tried it on. Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 10, 2005 Author Share Posted July 10, 2005 LOL I really like the feel of a mechanical secondary.... I get to choose exactly when I get into it. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted July 10, 2005 Share Posted July 10, 2005 I have a Pro form main body/Holley 750 dp with a modified base and love it on my 385 sbc. Mike Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 10, 2005 Author Share Posted July 10, 2005 I've never heard of a pro form... where did you get it? Quote Link to comment Share on other sites More sharing options...
Heavy Z Posted July 10, 2005 Share Posted July 10, 2005 Joe, The proform main body is a $100 direct replacement to upgrade (to 810-820 cfm if I remember correctly) your old cracked holley. Very cheap way to fix your problem and increase cfm. If yours is vacuum, I'm not sure if this includes what you'll need to go manual. Go to summit to have a look or google "proform main body." I used to have a holley 650 dp w/ mechanical secondaries but upgraded to a speed demon 650 6 months ago. Demon carbs are fantastic, they have great response and power once you get used to the differences in tuning over a holley. It is very adjustable - if you buy one get ahold of me and I'll save you some time by sharing what I've learned. Also, if your cam is above 240 duration @.050 then you'll need a mighty demon as the speed demons are set up for 220-240 duration cams. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted July 10, 2005 Share Posted July 10, 2005 So Brett, What have you noticed in terms of power increases...any? The Demon is better overall in terms of driveablility or also in power? (I don't mean to hijack the thread, I just want to see some more info ) Quote Link to comment Share on other sites More sharing options...
Heavy Z Posted July 10, 2005 Share Posted July 10, 2005 Davy, If I had to buy a new cab over, I'd do the same thing again. Having a holley and a demon carb side by side and you see all the cool stuff Barry Grant did to improve on the old design. Driveablity is noticeably better overall and there is definitely a power increase. I did have to run larger squirters over the holley to get it to be smooth all the way around. The transition from primaries to secondaries is seamless and it kicks you back into the seat more than the holley could. Especially noticeable at highway speeds. Not sure on hp gain, but down in second gear it moved the rpm at which my tires break loose 500 rpms lower than the holley and the car feels as fast as it used to be with just me in the car now when I have a passenger. Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 11, 2005 Author Share Posted July 11, 2005 Sounds like the way to go is the Demon carb... I'm going with a 750 Speed demon with mechanical secondaries, I should have it in a couple of days! While I have a cam that is at 244 @ .050 duration I really need to have the choke for winter. So I can't really go with the Mighty Demon... and I'm right on the edge so hopefully it will be Ok. So .... please let me know what you've learned about tuning it ect... I would really appreciate it! Thanks!! Quote Link to comment Share on other sites More sharing options...
Heavy Z Posted July 11, 2005 Share Posted July 11, 2005 I'm going with a 750 Speed demon with mechanical secondaries, I should have it in a couple of days! While I have a cam that is at 244 @ .050 duration I really need to have the choke for winter. So I can't really go with the Mighty Demon... and I'm right on the edge so hopefully it will be Ok. Just so you'll know how I got my speed demon 650...My friend Nick bought it for his mustang w/ a 390 and a 244 duration cam...car never ran right, lots of popping and unsuccessful tuning...Barry Grant told him speed demons weren't designed for his cam and to buy a mighty demon. He did and his problem was solved, and I got a barely used speed demon. I hope this is helpful as you may not want to deal with this sort of trouble. Below is Barry Grant's application guide to help you in the selection. As for the choke, I used to have(and need) one on my old holley. My speed demon has no choke, and I didn't need it as the car ran great all winter to the point that even if I had a choke I wouldn't have used it. Granted this is a Cali winter and not Illinois, but I thought I'd mention it anyway. A call to BG may help you out as maybe they have a better answer than mine. http://www.barrygrant.com/demon/default.aspx?page=5 So .... please let me know what you've learned about tuning it ect... I would really appreciate it! Thanks!! My speed demon was made before their new 'idle easy' screw was added, so yours will be easier to tune. The manual you get w/ the carb will cover basic tuning, here's more for you: 1. make sure initial timing is within the range of the above link 2. set prim/secondary butterflies so the fuel slot forms a square 3. set mixture screws to 1 1/2 turns out 4. bring in butterflies EQUALLY to lower idle (this is where your idle easy screw comes in handy). 5. adjust mixture screws for maximum vacuum w/o going lean 6. BG says keep jet sizes for the primaries and secondaries 8 apart (example: 70/78 ), so any sizeup should be uniform. I went from 67/73 on my old holley to 70/78 on the demon with no problems. Funny thing was I tried this combo with my holley before but it ran too rich. 7. any bogging or hesitation off the line or from primary to secondary can usually be remedied by going with larger squirters. I had to go up 4 sizes on the primary and 7 on the secondary circuit to get optimal smoothness on my application. The carb will include a video that covers a lot of info, let me know if I can be of any more help. Brett Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 11, 2005 Author Share Posted July 11, 2005 Thanks! When I get it if I do have any more questions I'll let you know! Quote Link to comment Share on other sites More sharing options...
John Scott Posted July 13, 2005 Share Posted July 13, 2005 I had a speed demon for a while. Pretty to look at, great construction, nice throttle response, but impossible to tune idle mixture. The Speed Demon is for camshafts up to 240 degrees @ .050. BG said they could recalibrate, for a fee and shipping. No thanks. Mighty & Race demons, are more suited to big cam duration. I ended up with an Ebay Holley 4150HP PRO 750. Comes with rear jet extensions, adjustable air bleeds. Useful if you are into squeezing out the last few hp, or have that funny rich spot on the top end due to your zero gap rings. Problem solved. You might check out the wise boys and girls at prestage.com. I posted a similar question a few years ago. Most will tell you you can't beat the classic holley 750 dbl pumpers, right out of the box. Plenty of big hp #s, (well over 450) and timeslips to back up their claim. John Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 13, 2005 Author Share Posted July 13, 2005 John did you have one with their new EZ Idle setup? Well since I just got I'll have to see what I can do with it. It really is pretty! LOL!!! I am mostly interested in great throttle response so this should work well for me. I do know I'll have a lot of work to do getting it setup properly. I don't expect this one to work right out of the box like the Holleys do. The 750DP I have right now is very old (out of production) and while I glued the base back together it's not something I want to use for very long. So at least I do have something I can swap back and forth while I am getting the Demon tuned right! Thanks! Joe Quote Link to comment Share on other sites More sharing options...
John Scott Posted July 13, 2005 Share Posted July 13, 2005 No mine is an older demon. My cam is 244 @ .050. which according to BG was over the recommended size. I started playing with the idea of doing the job myself of resizing metering plates emulsion holes and air bleeds to Race Demon specs. My BG manual has all the specs so it would be interesting to see what happens. Perhaps they are more flexible in the newer design. They are nice carburetors and see them often managing the fuel in the engine shoot outs. Nothing wrong with pretty either John Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 13, 2005 Author Share Posted July 13, 2005 Well yes it's supposed to be much easier to do the idle adjustment... I'll let everyone know what happens! Quote Link to comment Share on other sites More sharing options...
Heavy Z Posted July 15, 2005 Share Posted July 15, 2005 I had a speed demon for a while. Pretty to look at, great construction, nice throttle response, but impossible to tune idle mixture. Well, close to impossible. Without the idle easy feature I had my carb off way more than expected to get it right, but now I look at the frustration as a learning experience that was totally worth it. Best of luck Joe, keep us posted. Quote Link to comment Share on other sites More sharing options...
Turbo Meister Posted July 17, 2005 Share Posted July 17, 2005 I went from 67/73 on my old holley to 70/78 on the demon with no problems. Funny thing was I tried this combo with my holley before but it ran too rich. I'm not sure if it's true for your model but I read that the BG carb jets are sized differently than the Holleys and that's why the Holley was too rich. Hanns Quote Link to comment Share on other sites More sharing options...
Heavy Z Posted July 17, 2005 Share Posted July 17, 2005 I'm not sure if it's true for your model but I read that the BG carb jets are sized differently than the Holleys and that's why the Holley was too rich.Hanns Thanks for the info Hanns, it must be another model unless the tech guy I spoke with at BG told me wrong. He said jets and squirters were the same. I'll call them back at some point to settle it as you've got me curious. Quote Link to comment Share on other sites More sharing options...
deMideon Posted July 17, 2005 Author Share Posted July 17, 2005 Heh... well that was pretty easy! I bolted it on... and it works... really well too. I do have to pull the float bowls off and reset the floats, but otherwise it's amazing that it bolted up and runs well! Quote Link to comment Share on other sites More sharing options...
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