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Small Block Talk => 351W Small Blocks => Topic started by: brooksy on April 25, 2016, 01:22:10 am



Title: GT40P heads on a 351w. Possible ?
Post by: brooksy on April 25, 2016, 01:22:10 am
Is it possible to put gt40p heads on a 351w or should i put them on my factory 289 4v. Thanks. Mark. 


Title: Re: GT40P heads on a 351w. Possible ?
Post by: Jeff351w on April 25, 2016, 03:05:51 am
It's possible, but they would be better suited to the 289.  Do some research on headers that will work with P heads as well.  The spark plug angles are changed and can cause interference with some header brands.  That may be compounded by the extra deck height of a 351w.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: Outlaw Bill on April 25, 2016, 04:37:18 pm
They are better sized to the 289-302 but will also work on a 351W. It all depends on what you want for power.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: brooksy on April 26, 2016, 12:36:25 am
Thanks guys , its just that i was given the heads , just reconditioned and brand new gt40p headers ( JB headers ) for free . It seems a waste not to use them. I was told that using them on the 289 i would lose at least one point in compression. Is this true ?  Do you know of someone on SBFTech that has used them on a 289 and where i could search for their engine components and specs ? Cheers Mark.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: z-adamson on April 26, 2016, 11:04:57 am
I *think* that the gt40p heads are sized to accept a 7/16 head bolt where as the 351w block on the other hand has 1/2 threads for the head bolts. The holes that go through the heads may need to be machined to clear a 1/2 head bolt.

I know the 351w block has 1/2 head bolt threads. I have never seen in person the gt40p head but if it is like any other factory 302 head it is set up for 7/16 bolts and may or may not clear the 1/2 bolt.

Something to think about.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: Jeff351w on April 26, 2016, 01:08:07 pm
Thanks guys , its just that i was given the heads , just reconditioned and brand new gt40p headers ( JB headers ) for free . It seems a waste not to use them. I was told that using them on the 289 i would lose at least one point in compression. Is this true ?  Do you know of someone on SBFTech that has used them on a 289 and where i could search for their engine components and specs ? Cheers Mark.

Well you can't beat free, especially with compatible headers.  I don't know of too many guys that have done it on this site.  Maybe check out Vintage Mustang Forum and do some searches over there.  I have seen it come up over there in many posts. 

Good luck with the swap.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: Outlaw Bill on April 26, 2016, 06:47:20 pm
Thanks guys , its just that i was given the heads , just reconditioned and brand new gt40p headers ( JB headers ) for free . It seems a waste not to use them. I was told that using them on the 289 i would lose at least one point in compression. Is this true ?  Do you know of someone on SBFTech that has used them on a 289 and where i could search for their engine components and specs ? Cheers Mark.
GT-40P heads are 59 cc and 289 are 54.5 cc. For milling each cc is about .006 so you could mill them .024 - 030 if they have never been cut before, or cut less if you wanted. You will gain power either way but milling will gain the most from the swap.


Title: Re: GT40P heads on a 351w. Possible ?
Post by: tbirdtess on July 18, 2016, 06:35:45 pm
Hello

I have GT40p's on a 351W.
All info listed is correct.
Bolt up with 1/2 bolt size correction.
Spark plug angle different. I burn spark plug wires on drivers side only.
5 & 7 in think. i'm using factory Fox body manifolds(rule thing.)

These heads (GT40p's) flow better than the GT40's with a low lift cam.
GT40's flow better with higher lift cams + have the bigger sized valves.

I would run them until you find a good set of aluminum heads.
All are a flow improvement, Even the GT40X heads.

tbirdtess