GT40P questions

drummerboy5.0 · Feb 15, 2008

I was just wondering if the stock valve springs on the gt40P heads will need to be changed if I am running a B303 cam?

also does anyone know if my mac 1 5/8 equal length headers will clear the plugs without any major issues? I know most headers will not work with the gt40P's, but i have heard that mac's headers do.

any insight would be greatly appreciated!

jtfairlane · Feb 15, 2008

The stock valve springs on GT-40P heads are single springs with no damper. They are only rated to .450" lift and are not recommended to be run with just about any performance cam. If I were you, I would look at getting a Trick Flow valve spring kit. They work with most Ford iron heads, definitely including the GT40P, and are rated to .542" lift, and even include instruction, shims, and a gauge to measure installed height. You can't beat the simplicity.

Not ALL Mac Headers are made to work with GT-40P heads. You hear Mac's name come up because the happen to make a set of shorty headers that work, Part # 50158.

Also look at Ford Racing M-9430-P50 or P51.

earleys94gt · Feb 15, 2008

You need headers that are "P" specific.

Upgrading your valve springs would also be a good idea considering you will have the valve covers off anyway.

PUNISHER RACING · Feb 15, 2008

Crane 44308 spring kit works well on the cheap, also alot of people use reg. 302 headers with accell shorty plugs and high temp booties and get away with it!

allballsmustang · Feb 16, 2008

drummerboy5.0 said:
I was just wondering if the stock valve springs on the gt40P heads will need to be changed if I am running a B303 cam?

also does anyone know if my mac 1 5/8 equal length headers will clear the plugs without any major issues? I know most headers will not work with the gt40P's, but i have heard that mac's headers do.

any insight would be greatly appreciated!

to run my p heads with my b-cam i went with a crower dual valve spring...their 115lbers... which is what worked for that combo....as for the headers my mac's wouldnt clear the spark plugs so i bought the ford racing p headers (the polished ceramic coated ones) they were welll worth the money cause they make changing the spark plugs a breeze hope that helps

jim

PJC Racing · Feb 17, 2008

Change the springs.
FRP A50's will work well for the B cam.

madams74 · Feb 17, 2008

Do not just buy springs. You also need the new retainers and locks. The factory ones will not work. I purchased springs only. I went to the machine shop to have the head bolt holes drilled out for placing them on a 351w and figured I would have them slap on the springs while there. Did not happen that day, I had to place an order for retainers and the keepers. Factory springs are rated for .500 lift max.

PJC Racing · Feb 17, 2008

madams74 said:
Do not just buy springs. You also need the new retainers and locks. The factory ones will not work. I purchased springs only. I went to the machine shop to have the head bolt holes drilled out for placing them on a 351w and figured I would have them slap on the springs while there. Did not happen that day, I had to place an order for retainers and the keepers. Factory springs are rated for .500 lift max.

Very true, for the retainers and locks.

But as for the stock lift capabilty, this is not the concern here, it would be spring pressure/rate. Stock springs will fail/float with a B cam at higher rpm.

jtfairlane · Feb 17, 2008

madams74 said:
Factory springs are rated for .500 lift max.

As I already said in this thread, and will say again, the factory springs on GT-40P heads are single springs, no dampers, designed to be used on the Mercury Mountaineer's and Ford Explorer's they came on from the factory. The Ford Racing boxed up versions had the same components, they weren't different from the OEM heads at all.

The springs are only rated to .450" lift, and that figure comes from John Colletti at Ford Racing approx. 6 years ago when I ran the P heads for about a year.

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