Heads, Cast Iron vs Aluminum

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   I can't speak to putting GT40P heads on an older non-GT block.  However, my previous boat was a '96 with a GT40.  The heads developed hairline cracks on the water jacket channels and eventually I had to replace them (apparently a common problem with the original heads).  I replaced them with remanufactured GT40P heads, and was very happy with them.  I got a good 200RPM and almost 2mph at WOT over the standard GT40 heads I replaced.
The PCM GT40 engine required 89 octane, but I get my gas at a Costco that is five minutes from the pond so I just put premium in it.  I don't know if the change from the GT40 to GT40P would have resulted in needing premium (I don't know what the combustion chamber was on the original).

My current GT40 has low compression in one cylinder and a squirt of oil showed me it's the head, not the rings.  So when I get around to it, I'll most probably get the same GT40P heads I got for my old engine.

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slmskrs Members Profile Send Private Message Find Members Posts Add to Buddy List Gold Member Joined: January-03-2012 Location: SF bay area, CA Status: Offline Points: 522	Post Options Post Reply Quote slmskrs Report Post Thanks(0) Quote Reply Topic: Heads, Cast Iron vs Aluminum Posted: April-27-2021 at 3:13pm
	I can't speak to putting GT40P heads on an older non-GT block. However, my previous boat was a '96 with a GT40. The heads developed hairline cracks on the water jacket channels and eventually I had to replace them (apparently a common problem with the original heads). I replaced them with remanufactured GT40P heads, and was very happy with them. I got a good 200RPM and almost 2mph at WOT over the standard GT40 heads I replaced. The PCM GT40 engine required 89 octane, but I get my gas at a Costco that is five minutes from the pond so I just put premium in it. I don't know if the change from the GT40 to GT40P would have resulted in needing premium (I don't know what the combustion chamber was on the original). My current GT40 has low compression in one cylinder and a squirt of oil showed me it's the head, not the rings. So when I get around to it, I'll most probably get the same GT40P heads I got for my old engine.
	Gordon '97 Ski Nautique, GT40

Slydog Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: August-24-2020 Location: Georgia Status: Offline Points: 17	Post Options Post Reply Quote Slydog Report Post Thanks(0) Quote Reply Posted: April-27-2021 at 11:10am
	JQ, The Edelbrock heads look promising with the 60cc combustion chamber and angle plugs.Unfortunately they are not readily available. I was able to find a single head at two vendors. Thanks for your thoughts!. Sly
	Always looking for glass on the lake... Sly

Jonny Quest Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2979	Post Options Post Reply Quote Jonny Quest Report Post Thanks(0) Quote Reply Posted: April-26-2021 at 4:44pm
	I like the GT40P heads. For cast iron it’s a good way to go. You will boost compression ratio a bit but performance will also increase. Not sure, but you may need 91 octane with the CR boost. I would also consider Edelbrock Performer RPM heads (#60259) for hydraulic flat tappet application...along with a Performer RPM intake. Good combo and you will shed a bunch of weight going with aluminum. JQ
	Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum

Slydog Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: August-24-2020 Location: Georgia Status: Offline Points: 17	Post Options Post Reply Quote Slydog Report Post Thanks(0) Quote Reply Posted: April-26-2021 at 9:00am
	I am rebuilding a 1988 SN 351W and the original heads have damage. I thought about replacing them with GT40P heads for the slight increase in compression and performance. However, the price of the GT40P in the used marketplace is quite high and usually without a warranty. I can purchase new aluminum heads for a slight bit more $$. I’m interested in experience and thoughts on the cast iron vs aluminum head being used on a late 80’s SN. Any issues or concerns? Original heads have a ~64cc combustion chamber. Aluminum heads have a 61cc combustion chamber. Thanks! Stuart
	Always looking for glass on the lake... Sly

Heads, Cast Iron vs Aluminum

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