Dual Quads with 450cfm or 600cfm?

PHM · #1 (**permalink**) 07-22-2008, 06:03 PM

I am putting dual quads on a genisis 427 and i am told that the 450's will give me much better throddle response over the 600's. The only down fall is I will loose a little HP. With the 450's i should get about 575hp and 600hp with the 600's. Does anyone have any insight on this. My gut feeling is go with the 450's since i will probebly never notice the HP loss.

blykins · #2 (**permalink**) 07-22-2008, 06:27 PM

I would vote on the 600's. I had two Demon Road Demon 725's on my Tunnel Wedge'd 428 FE. It was great.

Yes, the 450's would probably give you a little better throttle response and they're cheaper....but you only live once and it's a toy.

CobraMike · #3 (**permalink**) 07-22-2008, 06:29 PM

Hello,

All depends on the 'build', if it's a high riser 'type' motor with a '2000' rpm power band then the 600's are the way to go. If you're looking to be able to pull away from a stop light at less than 2200 rpm without every cop in town following you, and your build is more mild then go with the 450's.

Either way if the guy building your motor say's 450's, then it's quite likely you should trust him as he knows the motor build, cam shaft selection, rear end and transmission gear's. These cars are mighty fast and dangerious with 'only' 375 stock pony's. 575 HP is quite nice and if it's in a wide power band and you're street racing then a second gear start from a slow stop light roll out will be quite fun

. Either way there's a 1 in 10000 chance of anyone pulling up to you and 'winning' with either carb selection.

Cheers,
Mike

wtm442 · #4 (**permalink**) 07-22-2008, 06:34 PM

Fill in all the numbers for the Second Strike carb calculator. I think the dual 450's would be the best.

http://www.secondstrike.com/Technical/CarbCalc.asp

jwd · #5 (**permalink**) 07-22-2008, 06:43 PM

Quote:

Originally Posted by wtm442

Fill in all the numbers for the Second Strike carb calculator. I think the dual 450's would be the best.

Absolutely.

blykins · #6 (**permalink**) 07-22-2008, 07:02 PM

I really wouldn't put all my eggs in one basket with that site. It recommended a 685cfm carb for my 600hp 445ci Windsor.

SCOBRAC · #7 (**permalink**) 07-22-2008, 07:08 PM

I have had 450's 600's and 660's on my Medium Rise 427 with 550 hp (out of the 660's). I prefer the 450's to be completely honest. The 600's are fine but not great the 660's are over the top but FAST and very predictable. But for day in day out the 450's were my favorite.

Dwight · #8 (**permalink**) 07-22-2008, 08:47 PM

I was told the old 2 x 4s set up on the 427 were 390's. Is that true?

Dwight

REAL 1 · #9 (**permalink**) 07-22-2008, 09:03 PM

Split the difference. 550's.

My 427SO runs great with dual Holly 550s. Dual 600's too much for street use w/o a radical cam according to my builder who is one of the best on the east coast. He was right.

PHM · #10 (**permalink**) 07-23-2008, 10:59 AM

Thanks guys for the input, I think I'm going with the 450's

BOURRET · #11 (**permalink**) 07-23-2008, 12:07 PM

Having used the two 450 then the two 600 four-barrels on my FE, I had more satisfaction with the 450 mainly when I used the car on street/road.
And the 450 Holley seemed of a greater quality than the 600. They (the 450) also had a higher cost. I had greater set up stability with the 450.

CobraEd · #12 (**permalink**) 07-23-2008, 12:09 PM

Even with two 450's, . . . That's 900 CFM. Can't imagine anyone would need more than that unless you are spinning to 8 grand.

.

427 S/O · #13 (**permalink**) 07-23-2008, 01:48 PM

I run my 450's with straight linkage, very pleased and throttle response is awesome.

Seaman · #14 (**permalink**) 07-23-2008, 02:05 PM

I ran the 450's and now have the 600's. The 450's have a mechanical secondary actuation and the 600's are vacuum actuated. I think the 600's are much smoother through the entire band. The 450's seemed to be either on or off, but possibley I just didn't have them tuned correctly. With the vacuum secondaries, you can over size the cfm as the engine will pull only what it needs. Jet it correctly and all is good. I also switched from the progressive linkage to fixed, bringing both carbs in simultaneously. Much better.
Dave

427 S/O · #15 (**permalink**) 07-23-2008, 03:59 PM

I also had a pair of 600 vac. sec., and even with the spring kit's they never felt right. When you learn to control everything with your foot, it's great.

427 S/O · #16 (**permalink**) 07-23-2008, 04:00 PM

Oh! I forgot, sold them 600's to Ernie........

SCOBRAC · #17 (**permalink**) 07-23-2008, 10:40 PM

Quote:

Originally Posted by Seaman

I ran the 450's and now have the 600's. The 450's have a mechanical secondary actuation and the 600's are vacuum actuated. I think the 600's are much smoother through the entire band. The 450's seemed to be either on or off, but possibley I just didn't have them tuned correctly. With the vacuum secondaries, you can over size the cfm as the engine will pull only what it needs. Jet it correctly and all is good. I also switched from the progressive linkage to fixed, bringing both carbs in simultaneously. Much better.
Dave

With the 450's A little more progressive linkage will solve the on/off problem. I prefer 1/4 throttle on the front 2 barrels 1/3 throttle gets me most of the front carb, 1/2 throttle gets me 1/3 of the way into the third barrels and 3/4 to WOT gets me all in.

In "race" mode the 450's can be run without the progression and the front and rear carb are doing the same thing at the same time.

69boss429 · #18 (**permalink**) 07-24-2008, 06:15 PM

Quote:

Originally Posted by 427 S/O

I run my 450's with straight linkage, very pleased and throttle response is awesome.

I have the same straight linkage on 2 715 vaccum secondary carbs I purchased from Carl's ford parts.
Said to be repops of carbs used on the early 427 dual quad setups.
Very smooth street performance.
Can you tell me where you got the air cleaner tops for your setup?

davids2toys · #19 (**permalink**) 10-09-2008, 08:39 AM

I presently have a single holley 850 dbl pumper, 428, in a Unique Motorcar Cobra. It went on a Dyno at a car show this weelkend and only made 288 to the rear wheels at 5300 rpm. I am thinking it is starving for air, it has a 9 inchx 2 3/4 inch air cleaner. I called K+N and they said that filter was only flowing 470 cfm. the reason I am interested in a dual quad setup is two be able to run 2 air cleaners and double my cfm, also, if I have to get rid of the turkey pan which I love the look of, then the dual quads will also replace that WOW factor.
Any help or advice would be appreciated...Thanks, Dave

tmareina · #20 (**permalink**) 10-09-2008, 11:29 AM

I've got 2 660's on my 614 hp 428 with a tunnel wedge...it's awesome and no problems leaving the stop lights in a mild mannered disguise for those road dogs that want to cite you. Although how much of a disguise can you really hide behind. Also I get about 12mpg on the highway with my TKO in 5th gear when I don't get too foot heavy with the throtle. Response is excellent even at lower RPMs.

Tom