gt40p in a 66'

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bigarchie

New Member

Jan 17, 2004

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Jan 17, 2004

#1

• Jan 17, 2004

• #1

i just bought a set a gt40p heads without really researching them (stupid) just from what i heard they were an improvement over stock, but now im finding out that they may not fit and i may need special headers, has anyone used these heads and will they work in my 66? any help would be appreciated.

 

B

bigarchie

New Member

Jan 17, 2004

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Jan 17, 2004

#2

• Jan 17, 2004

• #2

i just did a search and found out some info. sorry guys.

 

12sec67

Active Member

Oct 6, 2003

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36

San Diego, Ca

Jan 17, 2004

#3

• Jan 17, 2004

• #3

not only will the p's require other headers but athey also have bigger cc chambers than your 66 289 heads which will lower your compression.i believe 289 heads are 53cc's - 55cc's and the new heads are 64 cc's.

lower compression=lower horspower and torque

 

6

'69Stang

Founding Member

Sep 28, 1999

1,130

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38

Metro Detroit

Jan 17, 2004

#4

• Jan 17, 2004

• #4

They are good heads and a nice bump up in performance over stock. If you can live with the special headers they should be fine. Otherwise a set of regular GT-40's are really the same thing. Also, you can mill the heads down to 54cc's with no problem for about $100 to get the compression to where you want it.

The GT heads aren't as good as other aluminum performance heads, but are a great value and should net you a good 20-30 hp over the stock ones.

 

Glen's 1965 5.0

Founding Member

Feb 5, 2001

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Tomball,Texas

Jan 17, 2004

#5

• Jan 17, 2004

• #5

I have the World heads that are basically the same head. I had them milled also to keep the compression up. I finally had to bite the bullet and buy the ceramic Powertrain headers that are made to fit these babies and all is now good in Mustang land.