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post #1 of 10 (permalink) Old 02-17-2019, 04:05 PM Thread Starter
 
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670 Heads

I just purchased a 1970 LeMans\ GTO conversion with a 400 from a dealer across the country. I'm currently waiting to receive the car. The dealer indicated to me that he thought it needed a bigger carb. It has an Edelbrock 450 cfm. When I received the title in the mail, it had the previous owner's name on it so I thought I'd give him a call and ask him about the car and restoration process. I had a great conversation with him and learned a lot about the care he put into the restoration.

When I told him about what the dealer said about the carb size he disagreed, but did say that the previous owner he bought the car from had fitted the engine with 670 heads and a mild cam and once he discovered he couldn't use Regular pump gas, he installed low compression pistons. He (the man I was talking to) felt that there was significant power loss as a result.

So, my question is, what is my solution to get this engine running as intended or better? Put the original heads and pistons back on? Keep the heads and put higher compression pistons on and take a beating at the pump? I don't know much about mechanics so any your thoughts would be very welcome.
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post #2 of 10 (permalink) Old 02-17-2019, 04:30 PM
 
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Originally Posted by bvcg1 View Post
I just purchased a 1970 LeMans\ GTO conversion with a 400 from a dealer across the country. I'm currently waiting to receive the car. The dealer indicated to me that he thought it needed a bigger carb. It has an Edelbrock 450 cfm. When I received the title in the mail, it had the previous owner's name on it so I thought I'd give him a call and ask him about the car and restoration process. I had a great conversation with him and learned a lot about the care he put into the restoration.

When I told him about what the dealer said about the carb size he disagreed, but did say that the previous owner he bought the car from had fitted the engine with 670 heads and a mild cam and once he discovered he couldn't use Regular pump gas, he installed low compression pistons. He (the man I was talking to) felt that there was significant power loss as a result.

So, my question is, what is my solution to get this engine running as intended or better? Put the original heads and pistons back on? Keep the heads and put higher compression pistons on and take a beating at the pump? I don't know much about mechanics so any your thoughts would be very welcome.
Well, I doubt it has a 450CFM carb. Edelbrock makes both the Q-jet and the AFB. The Q-jet is 750CFM. AFB comes in 500, 600, & 750CFM. Many dealers have no clue about cars they sell unless they are also mechanics and/or Pontiac enthusiasts.

You can figure out what carb is when you get it. Factory is the Q-jet along with a stock cast iron manifold which when set-up correctly cannot be beat.

The 670 heads are 1967 closed chamber. The '67 engine was rated at 10.75, but most likely 10.5 and required premium gas. To use them today, could not use pump gas and would then have to go the racing gas route or an octane booster.

The solution when using any high compression head, whether closed chamber or 1968 and up open chamber, is to use a dished piston or one having more cc's volume for the valve reliefs in the top of the piston. A pump gas friendly iron headed engine should be around 9.0-9.3 compression if set-up correctly.

You will lose some power by using a lower compression, but not a whole lot. Often times the timing and distributor curve can be changed and can wake up and engine. Many do not understand the function of timing and the advance curve with regards to a Pontiac - it is not a Chevy.

So at this point I would not be too discourage yet, but wait until you receive the car and then go from there. You may be able to make a few changes and fine tune the set-up and be pleased with how it runs. All to often people can mismatch parts when building a Pontiac engine and then it runs poorly, so a few changes may be in order.
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post #3 of 10 (permalink) Old 02-17-2019, 04:59 PM Thread Starter
 
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Thank you for your help! Also, I failed to mention it has an Edelbrock aluminum intake
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post #4 of 10 (permalink) Old 02-17-2019, 06:57 PM
 
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"...Edelbrock makes both the Q-jet and the AFB. The Q-jet is 750CFM..."


Some may consider this post a little picky. But, since I've been posting on Pontiac forums, I've been corrected, MANY TIMES, for stuff I considered very minor, almost trivial, at the time.

Edelbrock did, at one time, sell Q-jet carbs. I've read that they were actually made by Weber.

"...These spread-bore carburetors are manufactured by Weber USA with all new components. They are brand new carburetors... not remanufactured..."

Anyhow, they were rated at, 750cfm, 795cfm, & 850cfm. However, most say that the 795 & 850cfm models are basically the same size as a GM 800cfm Q-jet.

Edelbrock Q-Jet Carburetors

You can still usually find some E-Q-jets for sale on Ebay. The price of the #1910 850cfm rated carb has gotten ridiculous.

https://www.ebay.com/itm/Edelbrock-P...frcectupt=true

https://www.ebay.com/itm/Edelbrock-1...frcectupt=true

https://www.ebay.com/itm/EDELBROCK-1...frcectupt=true

https://www.ebay.com/itm/Edelbrock-P...frcectupt=true

Here's a 795cfm rated #1904 .

https://www.ebay.com/itm/REMAN-EDELB...frcectupt=true

And here's a 750cfm rated #1901 .

https://www.ebay.com/itm/REMAN-EDELB...frcectupt=true
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post #5 of 10 (permalink) Old 02-17-2019, 07:49 PM
 
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Good luck with that 1970! You will have some fun...solid advice from the guys here. And just to build on what was said. Think about getting the right size carburetor on it,...all too often carbs are oversized and the car runs poorly as fuel delivery depends on the vacumn signal from the engine to pull the fuel thru the venturiís....when the carb is way to big that signal is poor.....so not the right amount of fuel at the right time.

But letís say the carb is too small, then it will not be able to deliver the needed fuel under load.....and will feel real flat as rpm increase...

Also the power circuits of the carb have to be dialed in right, power valves, accelerator pumps and secondary jets....

Timing is everything we have all heard say,..but especially true on the V8ís.

The more info you can get from the previous owner will help you. If he can tell you exactly what pistons he installed you may be able to get some estimate of the compression for the build,..not exact but close. With the right info guys like BigD and Pontiac Jim can tell you right off what the chamber size was on the 670 heads etc.

Of course the heads could have been shaved the block decked the cylinders cut etc,....not exact but close.

Then when you have some educated idea of the compression you can set up proper carb and timing and try some pump gas....and see how she runs...you may be able to get it smooth with no engine work at all.....

Excited for you.....it will be a great car!
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post #6 of 10 (permalink) Old 02-17-2019, 09:00 PM
 
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Originally Posted by bigD View Post
"...Edelbrock makes both the Q-jet and the AFB. The Q-jet is 750CFM..."


Some may consider this post a little picky. But, since I've been posting on Pontiac forums, I've been corrected, MANY TIMES, for stuff I considered very minor, almost trivial, at the time.

Edelbrock did, at one time, sell Q-jet carbs. I've read that they were actually made by Weber.

"...These spread-bore carburetors are manufactured by Weber USA with all new components. They are brand new carburetors... not remanufactured..."

Anyhow, they were rated at, 750cfm, 795cfm, & 850cfm. However, most say that the 795 & 850cfm models are basically the same size as a GM 800cfm Q-jet.

Edelbrock Q-Jet Carburetors

You can still usually find some E-Q-jets for sale on Ebay. The price of the #1910 850cfm rated carb has gotten ridiculous.

https://www.ebay.com/itm/Edelbrock-P...frcectupt=true

https://www.ebay.com/itm/Edelbrock-1...frcectupt=true

https://www.ebay.com/itm/EDELBROCK-1...frcectupt=true

https://www.ebay.com/itm/Edelbrock-P...frcectupt=true

Here's a 795cfm rated #1904 .

https://www.ebay.com/itm/REMAN-EDELB...frcectupt=true

And here's a 750cfm rated #1901 .

https://www.ebay.com/itm/REMAN-EDELB...frcectupt=true

You are so damn picky! LOL I want a used 850CFM Edelbrock carb for $804. Man, what a friggin' deal. Wonder if it has a warranty.

Never looked that deep into the Edelbrock Q-jet offering with regards to CFM's. I'd rather, and have, purchase a $50-$75 factory Q-jet and rebuild from there - because I can.
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post #7 of 10 (permalink) Old 02-17-2019, 09:27 PM
 
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Originally Posted by bvcg1 View Post
Thank you for your help! Also, I failed to mention it has an Edelbrock aluminum intake

That might be your problem right there. Depends on which manifold you have.

The Performer has intake runners that are too small. Edelbrock lists them as 1.92" tall x 1.06" wide.

The Performer RPM is more like the factory size intake runners and ports = 2.06" tall x 1.10" wide

A factory Pontiac 400 blueprinted/gasket matched port should be 2.05" tall x 1.13" wide.

The Ram Air IV blueprinted/gasket matched port should be 2.18" tall x 1.16" wide.

Pontiac did have a smaller intake port that is more like the Performer as I do have a 1966 2 Bbl intake (389CI) having much smaller ports than the 1973 4X heads it was bolted to.
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post #8 of 10 (permalink) Old 02-17-2019, 10:04 PM
 
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"...Never looked that deep into the Edelbrock Q-jet offering with regards to CFM's. I'd rather, and have, purchase a $50-$75 factory Q-jet and rebuild from there..."



Yeah, we rebuilt all the Q-jets we raced. Most were Pontiac '69 models, with the slashed vent tube.

But, those carbs were not very old, back then. Now, they are 50 years old !

The Edelbrock Q-jets were made in the '90's & early 2000's. So, some of 'em are 30 years or so newer than the '69's like we raced. Makes sense that some of the cores would be in much better condition than a '69 Pontiac carb.

I was out of racing, working the family business, during all the years the E-Q-jets were being sold. So, I only learned of them after I started using a computer, less than 10 years ago.

I now own 2 of 'em--a 750cfm & a 795cfm. I think I have somewhere around $200 or a little over, in the pair. One of 'em came off a running 400 powered DD '79 T/A. Both should be real good cores for rebuilding. Might rig one up to run on my current bracket project.

Below is a pic of the Q-jet on my girlfriend's(now wife) 1st '68 Bird. She won lots of races with it during the '75 season, running E/SA. After the season, I swapped in a 4-speed Muncie, some muffs, a rear with street gears, & she used it as her DD for the next couple of years.
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Last edited by bigD; 02-17-2019 at 10:25 PM.
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post #9 of 10 (permalink) Old 02-17-2019, 10:42 PM
 
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"...The Performer has intake runners that are too small..."


A Performer should be OK for a mild street 400. Doesn't require a lot of flow.

I think it was Jim hand who tested a Performer against his iron Q-jet intake, on a 455, in his street/strip Lemans wagon. Don't think he noticed much difference.

Jim Hand Article #14
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post #10 of 10 (permalink) Old 03-13-2019, 08:41 PM
 
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hi bcvg 1,
solid info from jim, d, lemans, et al.
if the heads come off consider the following...the 670 heads (as well as others) from the factory will have many sharp edges in the combustion chamber. your pistons can have sharp edges. sharp edges promote detonation. use a die grinder and gently take all the sharp edges off. touch everything that is sharp with the grinder until it is smooth to the touch. you do not want to change the shape of the combustion chamber or go deep into the piston. just smooth things out. this is not a replacement for lower compression pistons but it definitely helps when using pump gas in an engine that is "on the edge" with compression ratio and existing fuel. also cometic makes custom head gaskets up to about .120 or .140 thousands thick that will lower your compression ratio significantly. of course your quench area will be enlarged. also prepare for sticker shock with these gaskets. i have done the smoothing thing on other heads and i recently finished the 670 heads that are going back on my 400. i did the badger pistons as well. i will keep you posted. good luck
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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