# 600 or 750 Carb



## joesweeting (May 8, 2011)

All,

I’m rebuilding a 455 I have purchased the following from Summit Racing:

-	Federal Mogul Premium Engine Rebuild Kits, MHP202-300
-	COMP Cams Xtreme Energy Cam and Lifter Kits, CL51-223-4
-	COMP Cams Magnum Double Roller Timing Sets, 2112
-	Pioneer Street Performance Balancers, 872011

For an intake I will purchase:

-	Edelbrock Performer RPM Intake Manifolds, 7156

I’m trying to decide, should I get a 600 or 750 carb? 

-	Edelbrock Performer Remanufactured Carburetors,9913 - 750 carb
-	Edelbrock Performer Remanufactured Carburetors 9906 – 600 carb




Thanks, 

Joe


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## BearGFR (Aug 25, 2008)

750, minimum.... although if you happen to have the original Quadrajet it probably came with, that would be better. All QJets were at least 750 cfm. Some were 800. 

Also, save your money on the intake. For a street motor that spends most of its time below 5000 rpm and rarely, if EVER, spins above 5500 - fact is none of the aftermarket manifolds will work as well as the factory dual-plane iron intake. That XE268 cam you're getting has a sweet spot that's a good match for street use, and it should still make plenty of vacuum for operating accsssories like power brakes and factory a/c.

Take the money you would have spent on the carb and intake, and instead get yourself a good set of h-beam forged connecting rods. (Eagle, Scat, etc.) Factory rods are the weak link in Pontiacs - you'll sleep better at night. 

Bear


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## ALKYGTO (Mar 29, 2010)

:agree Q-jet and good rods. If you don't have a factory intake or just want an aluminum one then the Performer is fine, but Bear is right, the Performer is pretty much a copy of the factory Pontiac intake mani.

Funny story, Tuesday of this week a friend of mine called and told me of his "score" of two "like new" Eddy 750 carbs for $200. He went on to say that he's the third owner of these shiny carbs and niether of the previous owners could get them to work on their dual quad applications.

Then he wants me to tell him how to make them work on his motor, a blown 468 Chevy .

Really?


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## geeteeohguy (Feb 2, 2008)

X3. What these guys said. 600 cfm carbs belong on 327 Chevies. For a 455, hard to beat the oem intake and carb.


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## 68greengoat (Sep 15, 2005)

x4 lol. 750's were even on the poncho 6 bangers........


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## joesweeting (May 8, 2011)

Thanks for the info guys; I will go will a 750, and upgrade the rods, just a little over $450. 

I bought the block, rods and crank, no intake, carb or heads(working). 

Putting it in a 69 GTO. I had a 400 in it and the crank broke.


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## Eric Animal (Oct 28, 2007)

What heads do you need? You should be able to find a stock intake fairly easily. A Q-jet is the way to go...if you must go aftermarket with a carb, try QFT....very nice carbs...... Eric


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## joesweeting (May 8, 2011)

Eric,

I have 4X heads, I haven’t done the math to see what size heads to replace with I know it want it close to 10 to 1 compression ratio. I’ve had the GTO just over a month; it will be my daily driver. I’m building the 455 with a four speed. I also need to check my gear ratio. I will research the carburetor you suggested along with the forged rods. Thanks


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## 68greengoat (Sep 15, 2005)

Those are low compression heads, around 8/8.5:1 I believe. 114cc This has been discussed before. I'm trying to remember, but I think you don't want to go lower than 86cc on pump gas anyway... Which should bring you just under 10cr.


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## SDGoat619 (Mar 21, 2011)

You should try and find some 6x-4's and convert the ex. Valve to 1.77 or find some 96. That is what I am looking to switch my 4x's to in my 455. 

Sent from my PC36100 using AutoGuide App


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## BearGFR (Aug 25, 2008)

joesweeting said:


> Eric,
> 
> I have 4X heads, I haven’t done the math to see what size heads to replace with I know it want it close to 10 to 1 compression ratio.


Umm... not really. If you're going to be running pump gas with iron heads, 10:1 is pretty risky. Around 9.3:1 would be much safer in terms of keeping the motor from having detonation problems. Consider this: on this 455 you're building, the difference between 9.3:1 and 10.0:1 will be less than 10 horsepower. Is it really worth riding the razor's edge and risking ruining the engine for 10 HP?



> I’ve had the GTO just over a month; it will be my daily driver. I’m building the 455 with a four speed. I also need to check my gear ratio. I will research the carburetor you suggested along with the forged rods. Thanks


That'd be a wise move. I've heard of people who "wrote the book" (no really, he did write a book) on how to build QJets who gave up trying to get an Edelbrock carb dialed in where it wouldn't bog. If you really want a good running "plug and play" carb and don't mind it not being close to original, I hear good things about these guys: AED Performance Racing Carburetors, Holley Carburetors, and Performance Holley Carburetor Parts
"Bear"  in mind though, no Holley-style carb is going to be capable of delivering the part-throttle gas mileage that a QJet can, they just don't have enough fine-tunable systems in them.
In case you're curious, I'm running an 800 cfm QJet with factory iron manifold, iron heads on my 461 (stroked 400) - here's the dyno sheet: http://www.garrettfamily.us/gto/docs/bestdyno.pdf

Bear


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## Eric Animal (Oct 28, 2007)

:agree he's smarter than the average bear......just went through the whole process...E


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## 68greengoat (Sep 15, 2005)

Here's some info I saved from someone on this forum awhile back. Where they talk about 4x being 98cc, that's for a 400.

_Green Goat: with your .030 over 455 (462cid) engine, you need one of the 87cc 1970 455 heads for about 10.25 compression (good luck finding the heads, and that's a little too high for pump gas in these engines). The BETTER solution is to get a set of 98c heads, which are waaaay more common, and will net you 9.4 compression. I put the 87cc heads on my 400, and It gave my smaller motor 9.2 compression and I love it. Good power, economy, and it does not detonate. Check out some Pontiac Head charts to determine the casting numbers you can use on your 455. Some heads that measure 98cc are: 4c, 4x, (1973), and 46. 6X are ok too, and have 101cc chambers. You could also install the Edelbrock 87cc heads, and have 10.25 compression WITHOUT pinging due to the aluminum head's ablility to dissipate heat. That's more $$$$, tho'.
Good luck!_


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## joesweeting (May 8, 2011)

68 Green Goat/SD Goat 619/Bear GFR,

Thanks for all the info, looks like I have a lot more research to do. I heard the 4X heads are not the best for my car, but I was going use them to get her on the road until I could afford better gear. I’m active duty and trying to do a budget build. I have two other divers I work with who are motor heads and been helping me out a lot.


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## BearGFR (Aug 25, 2008)

That's great, and also - thanks for your service.

One gentle caution about working with your friends, and this is not in any way meant in a derogatory fashion. Building a fast Pontiac is significantly different from building a fast chevy. chevy's tend to be higher rpm engines and don't make a lot of torque down low in the rpm range. Pontiacs on the other hand are low rpm torque monsters. What works well on one doesn't necessarily translate to the other.

Merry Christmas...

Bear


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## joesweeting (May 8, 2011)

Bear,

Thanks for supporting us. One of my friends is a chevy guy the other a Pontiac (has 69 firebird). They have both been a great help. However the chevy guy tried to talk me into putting a chevy engine in my. GTO, but I told him I would go to [email protected] for putting a chevy engine in a pontiac. 

Also, I have to check the numbers but I think the heads are might be 4X (1973) since the block was 1973. Again will have to go to storage unit and get the numbers to verify.


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## 68greengoat (Sep 15, 2005)

joesweeting said:


> 68 Green Goat/SD Goat 619/Bear GFR,
> 
> Thanks for all the info, looks like I have a lot more research to do. I heard the 4X heads are not the best for my car, but I was going use them to get her on the road until I could afford better gear. I’m active duty and trying to do a budget build. I have two other divers I work with who are motor heads and been helping me out a lot.


For now, use those heads to get her on the road like you said. I'm using them for now too, with a highway gear. It will still put a smile on your face when you get on it.....



joesweeting said:


> Bear,
> 
> Thanks for supporting us. One of my friends is a chevy guy the other a Pontiac (has 69 firebird). They have both been a great help. *However the chevy guy tried to talk me into putting a chevy engine in my. GTO*, but I told him I would go to [email protected] for putting a chevy engine in a pontiac.
> 
> Also, I have to check the numbers but I think the heads are might be 4X (1973) since the block was 1973. Again will have to go to storage unit and get the numbers to verify.


If you put a chevy in, we might have to "ban" ya! J/K


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## SDGoat619 (Mar 21, 2011)

Check the secondary boss marking that is the dead give away. Assuming the heads haven't been milled down. The boss on my 4x show a 1H which is 114cc. From all accounts good for boat anchors. The 4x off of 400 were 3H and 7H I believe which were the smaller 98cc. Just Google pontiac head codes and there are some good resources like Wallace racing, and year one that break down the head codes. My 73 455 came with 4x-1H 

Good luck. 

Sent from my PC36100 using AutoGuide App


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## 68greengoat (Sep 15, 2005)

I have the same head. A boat anchor is a stretch..... Not that I don't want a higher compression head eventually....

Edit:

Compression ratios have been mentioned by the OP. Here is a chart to give an idea of what the heads need to be chambered to acquire a desired compression ratio...

Pontiac Cylinder Head and Engine Compression Ratio Chart


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