RE: 401 heads on a 343 block?

["ROSS BLAIR" <bigbad69@xxxxxxxxx>]

Also, your 343 intake won't bolt up because they changed the centre mounting hole position. You would have to machine your existing intake or find a '70 & up 360/390/401 intake. Possibly the aftermarket intakes have the the centre holes already elongated so they will fit either setup, I'm not 100% sure on this.

You should also change your exhaust manifolds. The square port manifold on the 343 will leak when bolted to the dogleg port heads.

With all the negatives posted here, you might think this swap is a bad idea, but it is actually a fairly common one. You just have to know the differences between the two engine styles. I did this on my 69' 390. It has '72 360/401 heads, free flow exhaust manifolds and a '70 style R4B intake. I used the step dowels Todd mentions below with 7/16" head bolts. And yes, as Ken points out, I took a compression hit doing this, but 10:1 compression and today's pump gas don't mix well IMHO. So the performance drop due to loss of compression is less than you might expect because the engine wouldn't run to its full potential anyway (again IMHO).

Hope this helps,

Ross Blair
'69 BBO Javelin
Ottawa Ont.

>As below, it can be done, but why unless you don't actually have any 343/390
>heads? The increase in exhaust flow would be offset by the lower compression.
>But perhaps that's what you're after... :)

>Ken

>Quoting Todd Jesme <jesme@xxxxxxxxxxx>:

> Andy,
> you can bolt them on but you will need to buy a set of step dowels from your
> favorite AMC parts vendor, if you want to use the smaller 7/16" head bolts.
> If you want to use the more desirable 1/2" head bolts used on 70 and up
> V-8's you will need to have the head bolt holes in the block drilled and
> tapped.
>
> Todd
> MN
>
> -----Original Message-----
> From: raysinvegas@xxxxxxxxxxxxx [mailto:raysinvegas@xxxxxxxxxxxxx]
> Sent: Thursday, April 14, 2005 7:56 PM
> To: mail@xxxxxxxxxxxx
> Subject: 401 heads on a 343 block?
>
> Hi, can I put '75 401 heads on my '68 343 short block?  Thanks in advance!
>
> Andy Ray
> 64 440H (2)
> 68 Jav SST 343
>
> =============================================================
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>
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