GM #458520 manifold on 78' SBC 305 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-26-2011, 06:39 AM
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GM #458520 manifold on 78' SBC 305

Hello guys,
I need some info and advises from you.
I have 78'Monte Carlo with SBC 305, 2bbl carb.
I want to put on it GM #458520 stock intake manifold and 4bbl Rochester carb.
Will this manifold fit the engine?
Do I need to make any modifications or it is bolt-on?

There are missing mounting holes on the manifold I would like to use, see the picture. On my current manifold, there is bracket mounted there. Can I weld some aluminium pieces there or the aluminum used is some spacial type?

Thanks for your help,
Ivo

PS I am in Bulgaria, there are no junk yards I can go and pick another manifold. I have to buy it from USA with enormous shipping cost. That is why I am trying to use what I have.
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Old 11-26-2011, 10:04 AM
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That manifold will bolt right onto your engine. They make those manifolds in both iron and aluminum. Someone already blocked off the EGR.
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Old 11-26-2011, 10:16 AM
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The manifold in the picture is a spread bore manifold which means the primary intake holes are smaller and the secondary holes are bigger. With this manifold, you are limited to using a spreadbore carb. The carb you mentioned should work, however you will not be able to put a Holley or Edelbrock carb on unless it is a spreadbore carb. Check to make sure you carb is a spreadbore carb before installing it. There is a square- bore which all holes are equal and the spread bore which you have. If you decide to use a square-bore carb, you'll need an adapter plate between the carb and manifold.

Last edited by kleen56; 11-26-2011 at 10:23 AM.
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Old 11-26-2011, 10:36 AM
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Hi guys,

I have rebuild Rochester Quadrajet, I plan to use. The secondaries are bigger.
Here is picture of it. I think it will fit, will it?

What do you think about missing mounts? Does someone removed them or there was this model as well?

Thanks,
Ivo
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Old 11-26-2011, 10:41 AM
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The missing mount on your manifold is for the throttle bracket. You should be able to make it work with a little bit of fabrication.
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Old 11-26-2011, 10:53 AM
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I am not afraid to fabricate
I just don't know if I can weld on this aluminum.
I also read the aluminum manifold wraps. How can I measure this?
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Old 11-26-2011, 10:57 AM
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GM had to put a warranty on it so I wouldn't worry too much that it might be warped.
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Old 11-26-2011, 12:46 PM
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Quote:
Originally Posted by V8&4spd
GM had to put a warranty on it so I wouldn't worry too much that it might be warped.
Sorry, I did not get that.
There is no warranty here, I bought it second hand.
Or you mean something else?
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Old 11-26-2011, 01:23 PM
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You wont have a warranty on it now, it's used. When it was on the car new it had to have an emissions warranty. GM would not have made that manifold it there was a problem of it not going the distance on the emissions and engine warranty. Aftermarket manifolds only have to last until they get sold.
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Old 11-26-2011, 01:32 PM
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Yes, you are right
That's why I want to stay on safe side, I don't look for high performance or so.
Thanks for the help,
Ivo
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Old 11-26-2011, 01:38 PM
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How much more performance do you need? It's going on a 305. The intake manifold is not going to be your problem. They used the same manifold on Corvettes. You would not have bought it if you didn't think it would work.
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Old 11-26-2011, 01:49 PM
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I have an Edelbrock Performer EPS manifold, and it does not have any bolt holes for a throttle bracket. I used the Edelbrock bracket 8031 for throttle and TH350 kickdown cable, and it bolts to the two rear intake manifold bolts. You don't need to add any fittings on the manifold.

Bruce
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Old 11-26-2011, 01:53 PM
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He won't need to weld the manifold to make it work. He just has to modify the throttle bracket.
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Old 11-26-2011, 02:28 PM
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Quote:
Originally Posted by V8&4spd
How much more performance do you need? It's going on a 305. The intake manifold is not going to be your problem. They used the same manifold on Corvettes. You would not have bought it if you didn't think it would work.
I don't need more performance. I am sure it will get much better than my current 2bbl setup. I just need to get as much info as possible before I start. I don't want to make some stupid mistake.
Thanks for the help,
Ivo
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Old 11-26-2011, 03:12 PM
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The manifold you have will work fine on a 305. Don't believe some of the hype that you need an aftermarket manifold to get more performance out of it.
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