650 or 750 Carb For My 357, That Is The Question!!!!

[5.0 Mustang Man]

Hi, I have been trying to figure out what is going to be the best carb to buy for my 357. Right now Im using a friends 825 demon and it is obviously too big. Here is my combo:

351 .30 over, stock bottom end with girdle, je pistons, out of the box Track Heat heads, Stage 2 Trick Flow Cam, Victor Jr Intake, 1 3/4 long tubes, 3" exhaust, full MSD etc...

The compression is about 10 1/2-1. The motor spins to about 6300 RPM's. The rest of the setup consists of a C4 with 4000 rpm converter, 3.55 gears, and Im running a 28/10.5 ET Drag. One of my friends with a very similar combo is running a HP 750 and it does very good but I have heard that it might actually do better with a 650 HP. I will be getting a Holley double pumper either way. Any opinions would be greatly appreciated as this will finish the car for now. Thanks.

 

[85_SS_302_Coupe]

650 double pumper, jetted up if necessary. Unless you're running a monster cam and high RPM, that should be plenty of carb. If you're buying new, get a nice chokeless carb, or better yet buy a Proform chokeless main body and make your own carb.

 

[89MustangGX]

I'm no carb expert -- but I would think a 750 might be the way to go.

 

[Ourobos]

I run a 750 quick fuel on my 351w, and it's perfect.

 

[crazypete]

750 will make a tame lower end. The dyno will look good but it wont feel really zippy on the street. The 650 DP will wake it up all across the board and perhaps choke off 3-5 hp at the very top. You'll be too busy going WEEEE to notice though. Trust me, with carbs, smaller is better. It's ALL about vacuum signal and air velocity on carbed motors. I went 670->600 and it's amazing how much difference that made.

 

[srothfuss]

750 will make a tame lower end. The dyno will look good but it wont feel really zippy on the street. The 650 DP will wake it up all across the board and perhaps choke off 3-5 hp at the very top. You'll be too busy going WEEEE to notice though. Trust me, with carbs, smaller is better. It's ALL about vacuum signal and air velocity on carbed motors. I went 670->600 and it's amazing how much difference that made.

I totally agree with pete on this. No bigger than 650!

 

[85_SS_302_Coupe]

That's why i suggested the 650 jetted up if needed...you'll pick up the top end that you lost from the 750 but you won't lose much on the bottom end. If you get a chokeless carb or a Proform main body you'll also flow more than the advertised 650cfm anyways.


I've got a 650dp on my 302 right now because i KNOW there's a stroked 351W in my future, and i wanted to spend 400 bucks on ONE carb and not have to buy another in the future. CrazyPete and everyone else, if you havent looked into Proform main bodies yet, you can nab one for about 100 bucks and they're very nice, all Holley parts swap over, so for 100 bucks you can turn your 650 into a 750 if the need ever arises.

 

[tjm73]

I'm not going to say one or the other is better, but I am going to say you should call Holley and/or Barry Grant and ask one of their tech's what they would recommend.

A flowed 650 would be best I suspect. It would preserve throttle response and low end power while being able to support the top end needs as well.

 

[crazypete]

The holley 0-80540-1 carbs are just as good (IMO of course)! Chokeless, dogleg boosters, adjustable bleeds, 4 corner idle, 4 corner transfer slots, only 1 passage underneath (ie...rtv friendly), the works. Brings a tear to my eye just thinking about it. Check em out:

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/0-80540-1.html

 

[Uber5.0]

According to Holley's own website, your engine revving to 6300 RPM's should do just fine with a 650 CFM unit. Even if you had 100% volumetric efficiency (which you're more likely running between 90-95%), you'd only need 651 CFM.

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/FMSC.html