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Old 03-26-2010, 06:40 AM   #1
sleepin cruiser
 
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Default 307 7A heads on a 79 350

Dad and I were looking this idea over and I wanted to get some thoughts from you guys. What we have is a 79 350 that is std bore and in good shape, we also have the pistons, rods, and a good crank which can be re-used. My dad has been the only ownner of this motor and it has always been taken care of. But any way the heads need quite a bit of work and we have a extra set of 307 7A heads that have been reworked laying around. Yes I know that the guide pins are not the same. I also have a aluminum intake that matches the heads to go along with it. We were thinking that it could either help or hurt the performance. Help since there is a smaller combustion chamber and bump the compression up a little, but also could hurt it since the valves are smaller.

What do you guys think? its only a idea, just looking for some opinions and thoughts.
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rides:
86 442 Parts Car

87 Cutlass Supreme Brougham.
307/200C / 72 350/2004R 3.23 14.5@94 2.1 60ft
(8.5" 3:73 posi 14.3@96 2.1 60ft)

88 Cutlass Supreme Classic Brougham. SOLD!!
Was: 307/2004R, now: 72 350/Th350 16.1@85 mph

88 Custom Cruiser.
73- 350/Th400

91 honda civic Lx.

67 Chevy Impala 4dr hardtop Family owned since 1967
Orig 327/Th400, going to be 327/700R4 or 2004R
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Old 03-26-2010, 07:17 AM   #2
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Default Re: 307 7A heads on a 79 350

I got the right 3a heads laying around my garage taking up space. They been tanked and reassembled (I went another route, but didn't manage to stop my machinst first)
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3 time G-body owner
86 Cutlass Salon 307/200-4r (salvaged May 04)
87 Cutlass Supreme 307/200-4r (stolen Oct 04)
81 Cutlass Calais 260/350 (purchased Nov 04)
never thought I'd say "I miss the power of a 307"
fixed that with an Olds 350/200-4r
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Old 03-26-2010, 07:58 AM   #3
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Default Re: 307 7A heads on a 79 350

I think one of the circle track guys on here tried that before. I have no idea what his results were though. Don't those 307 heads have visibly smaller ports too...like small and round?
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Old 03-26-2010, 09:22 AM   #4
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Default Re: 307 7A heads on a 79 350

smaller and an odd shape as I recall.
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3 time G-body owner
86 Cutlass Salon 307/200-4r (salvaged May 04)
87 Cutlass Supreme 307/200-4r (stolen Oct 04)
81 Cutlass Calais 260/350 (purchased Nov 04)
never thought I'd say "I miss the power of a 307"
fixed that with an Olds 350/200-4r
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Old 03-26-2010, 09:29 AM   #5
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Default Re: 307 7A heads on a 79 350

7As have the tiny swirl ports, and that 350 would run out of steam above 4K RPM. You *may* experience a bump in low-end torque, but that will be your only usable range. But since you have them and the engine, its cheaper to throw'em on and see what happens. I briefly considered doing the same.

Intake ports are squared, not rectangle, with exhaust ports being circular. Here, you can see the difference in size between the exhaust ports on the 7A heads, and the ports in the #17 cast iron exhaust manifold used on the 5A and possible earlier heads.
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Old 03-26-2010, 10:09 AM   #6
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Default Re: 307 7A heads on a 79 350

Depends on what you want the motor to do. The 7a heads with an A5 intake will provide great streetability, but you will get dusted by Geo Metro's. If I was building a high-mpg street-only car and didn't have access to a v6 I would do it. But from a performance standpoint it's a definite no-go combination without tons of work and $ into the heads. Rather I'd just grab a set of 5 or 7 heads. That way I'd have good flow and the small combustion chambers.
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'86 Cutlass Supreme with '69 Olds 350, .030 Flat Top Pistons, #7 heads, 10.1:1 compression, 1977 800 CFM Quadrajet, Modified A4 Intake, Dynomax headers, Cherry Bomb Turbo II Mufflers, HEI, TH200c. WIP.
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Old 03-26-2010, 03:39 PM   #7
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Default Re: 307 7A heads on a 79 350

We are just looking for a good get around motor with decent MPG and to have a little bit of performance. This was just a idea we had. Just figured it may be cheaper to do since all the parts were laying around.
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rides:
86 442 Parts Car

87 Cutlass Supreme Brougham.
307/200C / 72 350/2004R 3.23 14.5@94 2.1 60ft
(8.5" 3:73 posi 14.3@96 2.1 60ft)

88 Cutlass Supreme Classic Brougham. SOLD!!
Was: 307/2004R, now: 72 350/Th350 16.1@85 mph

88 Custom Cruiser.
73- 350/Th400

91 honda civic Lx.

67 Chevy Impala 4dr hardtop Family owned since 1967
Orig 327/Th400, going to be 327/700R4 or 2004R
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Old 03-26-2010, 05:10 PM   #8
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Default Re: 307 7A heads on a 79 350

I put on the 5A heads on the 350 in my truck with the small triangle port SP2P intake. With a stock Qjet, it plain overwhelmed the engine full throttle. Part throttle was like fuel injection. I now have TBI on the same motor, even better but needs exhaust and new O2 sensor.
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1994 c***y 4x4 Olds 350/454 TBI, rebuilt 4L60E, 3.73 gov lock
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Old 03-26-2010, 08:59 PM   #9
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Default Re: 307 7A heads on a 79 350

Quote:
Originally Posted by Synergic View Post
The 7a heads with an A5 intake will provide great streetability, but you will get dusted by Geo Metro's.
Damn!


Quote:
Originally Posted by sleepin cruiser View Post
We are just looking for a good get around motor with decent MPG and to have a little bit of performance. This was just a idea we had. Just figured it may be cheaper to do since all the parts were laying around.
If its doable and extremely cost effective why not. You will be able to fill in the blanks for some of us.
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1987 442 STOCK 307 - 15.179 @ 88.58 mph


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Old 03-26-2010, 10:16 PM   #10
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Default Re: 307 7A heads on a 79 350

Quote:
Originally Posted by olds307 and 403 View Post
I put on the 5A heads on the 350 in my truck with the small triangle port SP2P intake. With a stock Qjet, it plain overwhelmed the engine full throttle. Part throttle was like fuel injection. I now have TBI on the same motor, even better but needs exhaust and new O2 sensor.
So are you saying that the 5A heads on a 350 increased the performance, with or without the SP2P?
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Old 03-27-2010, 02:01 AM   #11
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Default Re: 307 7A heads on a 79 350

Can't see how putting parts that are restrictive on a 307, on a 350 as being anything but a bad idea....unless your goals are having an engine that starts to weez at 3500 rpm's. Personally, I wouldn't even consider doing it as I just don't see the point of it.

Did you calculate what your new CR would be with the peanut port 7A's?
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Botched Olds 350 build by the crooks at Rocket Racing. Lunati 207/213 Voodoo cam, 8.1:1 CR ( was supposed to be 8.8:1 ), Stock #7 heads ( was charged for work that was never done and what was done was done wrong ), American Racing headers, Performer RPM intake, Qjet with 1/2" 4 hole spacer, 2.5" Pypes X-pipe system, cowl induction scoop.

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Old 03-27-2010, 05:38 AM   #12
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Default Re: 307 7A heads on a 79 350

With the Corteco gasket it should be in the 8.75 to 1 range. Mine is right around 9 to 1. Part throttle with the Qjet was very good, full throttle not so much. I ran the leanest secondary rod I had, helped a bit. I was spinning tires when first installed in the 94 Z71. Added a gov lock since and the exhuast is shot and runs too rich now. The 3.73's in this truck helps a lot compared to the last truck's 2.76. Add the 4L60E's steep first gear and makes a snappy setup. I can simply get a A4 to help my top end, your heads will be your choke point. My engine pulls 4K no problem, just runs like **** for now. I will report how the new exhaust and O2 makes a difference. Coming very soon.
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1994 c***y 4x4 Olds 350/454 TBI, rebuilt 4L60E, 3.73 gov lock
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2000 Dodge Dakota Sport Club Cab 4x4 AEM filter,air box mod, Dynomax muffler, Accel coil,3.9 v6, auto, 3.92 no slip
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