I hear Demon Carbs are better on older mustangs than edelbrock and holley. I am looking at the following carbs (Demon 525, Demon 625, Holley 570, Holley 670, and Edelbrock Thunder 650. I will be running a 68 302 (Stock) with minor mods to exhaust, distributor, and coil. I hear the Demons tunability is much better. Any thoughts on the brand and CFM for my application?

 

Demons are modified Holley's basically. For your engine I'd use either the Demon 525 or Holley 570. Keep in mind that Demon tends to under-rate heir carbs, so a 525 is closer to 625, 625 closer to 725 etc. I had a 650 Thunder, didn't like it, throttle response sucked going to WOT no matter how I tweaked it. Other's I've talked to have also had a LOT of trouble dialing them in.A vac 2nd carb like the 570 Holley or the 525 Demon will both work well though. FWIW I'm building a pretty dang stout 302 street beast, and it's getting a 570 Street Avenger. Most poeople don't realize how much power you can make with a smaller carb, the CFM rating is actually somewhat arbitrary anyway.

 

I just purchased a Speed Demon 575..... totally impressed and worth the extra 100$ compared to Holley. I'd say it worked for my 67' 289 cid.

 

What sort of cam do you have in the 289? If I go with the Demon is it worth the extra money to go to a speed demon rather than a road demon on a stock engine? I cant imagine it would be for the extra money? Thanks Guys for the follow up.

 

Also, would I run into any trouble putting a Road Demon 625 on vs 525? I have found some around the same price and the the engine falls inline with the specs of both on Demons site. What are the pros and cons for the 525 vs 625 if they are they same price?

 

Those sound like more carb than you need. Here is a CFM calculator. You decide.
http://www.4secondsflat.com/Carb_CFM_Calculator.html

 

Thanks saoring. The calculator came up with 471CFM to 567 CFM. So it looks like I should go to the Demon 625 vs the Demon 525.

 

Holley 600 vacum. Get one on sale at Summit.

 

Get an Autolite 4100 carb (4 barrel) - make sure it is the short snout version (has todo with the accelerator pump)and then send it to Pony Carbs for a complete rebuild. Your engine will NEVER run better! You can do the spreadbore conversion on your car and you will increase gas mileage as well as torque...

http://www.ponycarburetors.com

 

i would go for the 625 road demon. i ended up with a 650 speed demon due to my cam specs but seriously considered the 625. if cash is an issue, a holley 4160 is pretty much the standard to which all other carbs are based IMO