650 or 750 ?!?!?!

1

10secgoal

Active Member

Dec 1, 2003

2,801

3

49

San Diego

Jan 2, 2004

#1

• Jan 2, 2004

• #1

I called summit asked them to send me the new proform carb main body replacement. I asked for the 650 because everything in my body and everything I know (that's not saying much) says that a 750 is too big. Here's the kicker. They don't make the 650 yet. Summit sent me a 750. I have a 650 double pumper holley now. Do I mill the choke horn and drop in downleg boosters and call it a day? Or try to get away with the proform which is the 750. Now I have a RPM AIRGAP gasket matched to a set of AFR 185's with a x-303 cam and about 9.5to1. It's getting sqeezed so it's got a 1/2in spacer more or less. But I want to keep the dual plane. The dual plane is why I think I might be able to keep the 750. OH I spin it to about 6500.

 

12sec67

Active Member

Oct 6, 2003

1,301

1

36

San Diego, Ca

Jan 2, 2004

#2

• Jan 2, 2004

• #2

i think you should post in race tech....sorry no help

 

gxnos

Founding Member

Apr 14, 2002

173

1

0

Birmingham, MI

Jan 2, 2004

#3

• Jan 2, 2004

• #3

dont use the 750.

 

M

mustangrfast88

Founding Member

Sep 22, 2002

330

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0

middletown ohio

Jan 2, 2004

#4

• Jan 2, 2004

• #4

go ahead and us the 750 i got a 750 on my car and it works fine if you want you can pm and i will tell you my specs

 

Dark Knight

Founding Member

Feb 1, 2000

2,578

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0

Chandler, Az.

Jan 3, 2004

#5

• Jan 3, 2004

• #5

750 will be fine.. to big of a carb isnt as critical on a dual plane.. and you have more than enough engine to handle the 750

might ask here
http://www.carbdford.com/forums/

nut they'll tell you the same thing

 

1

10secgoal

Active Member

Dec 1, 2003

2,801

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49

San Diego

Jan 3, 2004

#6

• Jan 3, 2004

• #6

Anybody had a similar problem? Tried both carbs ?

 

S

SmockDoiley

New Member

Jun 14, 2003

1,591

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San Diego, CA

Jan 3, 2004

#7

• Jan 3, 2004

• #7

I'm assuming its a 302? If so, thats a pretty large carb. I'm only running a 700 with a 342 and supercharger. There are sites that have cfm calculators and will tell you what size you need. The 750 will drop your low end but make good peak power. It may not be the best for a broad power band, and its not ideal for streetability. I had a 750 on mybuilt 350 and it ran out to like 6700, but it was a dog off the line. If its professionally tuned it will run and most guys here will say run it, but I would suggest a 650. Youd be surprised at what size engines really need. CFM really comes into play coming off idle and at peak rpm. Off idle if the venturis are too large the engine will be sluggish because the velocity will be slow, but too small venturis will choke an engine at high rpm. Youll love the 750 at 4000+ rpms. Hope this helps.

 

S

SmockDoiley

New Member

Jun 14, 2003

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San Diego, CA

Jan 3, 2004

#8

• Jan 3, 2004

• #8

I just punched in your numbers, 302,6500,.85 VE, and dual plane, and it gave me suggested carb size of 579 to 724 max. Taking the average, thats about a 650.

 

1

10secgoal

Active Member

Dec 1, 2003

2,801

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49

San Diego

Jan 3, 2004

#9

• Jan 3, 2004

• #9

Yeah I think you're right. I got rid of my victor jr manifold because it had nothing before 4500.
I'll only spin it to 6500 so I think yeah you're right. thanx guys!!

 

hllon4whls

BANNED

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Jan 17, 2002

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Covington

Jan 3, 2004

#10

• Jan 3, 2004

• #10

10secgoal said:

Yeah I think you're right. I got rid of my victor jr manifold because it had nothing before 4500.
I'll only spin it to 6500 so I think yeah you're right. thanx guys!!

Click to expand...

If you can swing it ($$$), get a demon 650 carb. Those are nice carbs. I did the 750 DP and the proform center section thing. The center section helped a lot on hp.

 

S

SmockDoiley

New Member

Jun 14, 2003

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San Diego, CA

Jan 5, 2004

#11

• Jan 5, 2004

• #11

Hell, even the Road Demon 625 will work. Its really cheap and even comes with the chrome dual feed line. I used it on my old 302 with exhaust, E303, stock heads, rockers, and RPM intake, and it was awesome. Its not a double pumper but sometimes you really dont need one. That thing was a charm to drive eventhough I didnt have the choke hooked up. Very streetable and very fast. The only thing killing the engine was the stock heads. Even with the stock heads and block and street tires, I ran 8.8's in the 1/8th. The guy announcing kept saying I had a stroker or heads but I said it was a stock block with cam, intake and exhaust. Nobody believed me. I also ran a vacuum secondary on my 12 sec. big block Javelin and it hauled ass. I ran that thing to 6 grand all the time. DP's arent always mandatory for power. Vacuum secondaries are much easier to use and very user friendly when it comes to street use and weather changes. But Demon by far makes the best carbs, and they look good too. I'd use one too but you cant with blowthrough supercharging.