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GT40 HEAD UPGRADE

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waterboy View Drop Down
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    Posted: March-22-2006 at 9:41pm
I'M INTERESTED IN UPGRADING MY 92 SN 351/240HP
WITH A SET OF GT40 HEADS TO GET THE EXTRA HP.
HAS ANYBODY OUT THERE DONE THIS? IF SO, WAS THERE A NOTICABLE DIFFERENCE IN PERFORMANCE?
HOW ABOUT LOW END TORQUE AND TOP END SPEED?
I WOULD GREATLY APPRECIPATE YOUR HONEST OPINION.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: March-23-2006 at 6:56am
My dad added GT40 heads to his '92. That boat ran very strong- you will like the upgrade. I want to say it added almost 2mph on the top end, and improved the holeshot. With a 4-blade acme prop (#422) it would pull a 200lb barefooter at 41-42mph, if my memory is correct.

You should also look into an acme prop. We noticed just as big of a difference going from an OJ Legend 4 blade to the 422 as we did from the heads.

I loved that boat so much that I got my own '90 that looks just like it (dad upgraded to an '03 196). Im going with an Acme 612 3-blade this spring and will report back with my impressions... so stay tuned.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pmt2234 Quote  Post ReplyReply Direct Link To This Post Posted: March-23-2006 at 11:24am
I converted my 1984 351 in my 2001 to GT40P heads, a performer intake, and a 207/217 cam. I already had an electronic ignition conversion. It pulls significantly harder off the line.

Top speed is also increased, but if you cared about that you wouldn't own a Nautique.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote waterboy Quote  Post ReplyReply Direct Link To This Post Posted: March-23-2006 at 5:51pm
Thanks for the feedack! I really appreciate the input. Know anybody selling a good used set of GT40 heads?

By the way, i just bought my 92 last September from the original owner in Ft. Myers FL. 600hrs. I towed the boat from Florida all the way home to NE ohio! The boat runs strong and looks almost new. It also has what I would consider one of the finest custom built wakeboard towers and top I've ever seen. He spent about $3000 on it. Also, it does have a 4 blade prop. Not sure who makes it. It tops out at around 43-44 mph. Thanks again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote duffnit Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 7:13am
Welcome waterboy.

The GT40 upgrade made a huge improvement on my cousins 97 176 SN.

The hole shot is better, the top end went from about 43 to 50ish. The thing I've noticed the most is how much better it maintains a set speed while the skier is making hard cuts.

Lets just say it has me thinking about doing the same to mine.

As for the heads, try SkiDim. FWIW, sometimes PCM has "used" stock for sale too. That's where my cuz got his. d
Danny





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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 8:09am
If you get the GT40 heads make sure they are the "P" version or cast iron and not the aluminum GT40 heads. Also keep in mind that the GT40 heads are not the best heads available for the 351W engine. They work well for the stock motors but if you are planing on adding a cam then there are better choices for heads and the GT40's would not be my first choice.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David F Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 9:45am
The GT40 heads started life as an automotive head (fairly sure). I would look at salvage yards for the best price on a set of used heads. Then take to a machine shop and have them rebuilt.

IMHO, the GT40 heads at skidim are overly pricey. I would think you could get both heads via salvage yard for the price of one head via skidim.

Local (Austin, TX) has a set of GT40p heads (brand new, never used) for $500.00 ready to go. (about 60% less than skidim)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote waterboy Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 9:57am
Thanks again for the feedback. Are there any better heads than the GT40's if I keep everything else stock ? What about a set of aftermarket aluninum heads ? Would I have to remove the engine if I replaced the cam?

I have a good friend who is a mechanic. He would be doing most of the work. He ownes a formula with dual engines. He said if I do the heads I might as well do a performance manifold. What do you think?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote waterboy Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:09am
David F.,
I've been told that there is a difference between the automotive GT40 and the marine version. I would be Very interested in the heads for $500 from (Austin Tx)If they are the right ones and are complete.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David F Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:14am
There is NO difference between automotive and marine cylinder heads...unless someone proves me wrong.

If you want them, you are the first to show interest, so I am inclined to reserve them for you...at least get you in touch with the seller. Yes, they are complete, ready to bolt on. Remember, they are the "P" heads and thus a bit different than the plain GT40 heads. I forget the difference, but you should do a bit of homework.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:14am
you don't have to remove the engine to replace cams you will have to remove the sky pylon though. The aluminum heads will give you trouble with a cast iron block, the engine doesn't get hot enough for the aluminum heads to work right. Get a performer or airgap from edlebrock or a professional products intake off of e-bay, you can get a polished PP intake for the price of a cast edelbrock and it has a cross over for the water jacket.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:16am
The "P" is for cast iron all others are aluminum that's the only difference auto or marine, most marine are "P"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David F Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:29am
I do not think you have it correct. The GT40 AND GT40p heads are both available in cast iron. I believe the "P" version has a smaller combustion chamber and slightly smaller exhaust valve over the GT40 head...yet it flows better.

In other words, the "P" flows better and raises stock compression a bit over the GT40 that lowers compression a bit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:32am
Oh you'll have to have the mounting holes drilled out to use on a 351, GT40P heads ar for a 302 or 5.0L engine which uses 7/16 head bolts compared to 1/2 head bolts for a 351. Also you'll need new head bolts, you don't won't to re-use torq to yield bolts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote waterboy Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 10:32am
Thanks again guys!. $500 for a set of new GT40's sounds cheep. New ones from Mid West Correct Craft cost $695ea. Any idea why he is selling them? Where they came from?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeinNY Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 11:43am
79 is right about having to have them drilled out if you want to use them on 351, best to let the machine shop take care of that for you. We just had a pretty long running thread
that ended up covering the differences between the various GT-40 heads pretty well.
I need new cylinder heads for a 351w

I have a 302 and ended up buying these slightly improved GT-40ps, I haven't run them yet but the guys were very helpful, the heads got here within a couple days packed well. They are new and shiny looking and dialed out correctly.. Unfortunately the boat is no where near done so I won't get to try them on the water till the end of may...

tristate cylinder heads
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David F Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 11:52am
Yes, someone ordered them a long while back and never picked them up or paid for them. $500.00 is a fair market value for heads.

and I believe 79 is correct in having to drill out the bolt holes. probably a nominal cost addition. I did not think the 351W uses torque to yield bolts. True for my aluminum BMW V-8, but the Ford? Never heard this before. I know I did not replace the head bolts on the 351W in my '77 way back in '89...still going strong. With torque to yield bolts, you first torque to a low setting then tighten the bolts a certain number of degrees (of the compass) further, regardless of torque. This is not the case with the 351W that I remember...hmmm.

One more thing...I believe the spark plugs are in a different location over the GT40 heads, but I am not sure if the new plug position works with the exhaust manifolds. Can anyone remember and verify there is not interference. I do not think so, but better safe than sorry.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 12:41pm
"Ford Racing GT-40 Cylinder HeadsPerformance heads for your Ford.

The Ford Racing GT-40 "P" high-flow cast iron cylinder heads flow 185 cfm of air right out of the box, giving your small block Ford greater power potential. Designed for Ford 289-351W engines, the complete assemblies have 60cc combustion chambers, 1.84 in. intake/1.46 in. exhaust valves, and work with stock or aftermarket intakes, rockers, and valve covers."

this is the listing from summit even though you cannot buy the cast iron heads from them or Jegs, you can get three different aluminum versions. If someone is trying to sell you GT-40 "P" heads and they are aluminum then they don't know what they are talking about and have there information wrong.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AWhite70 Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 1:44pm
There isn't a difference between marine and automotive heads except for some ports for emissions equipment that may need to be plugged.

GT40 and GT40P heads were originally used on 302's and if used on a 351 will need to have the head bolt holes drilled larger.

There are several aluminum GT40 variants made by Ford Racing Performance Parts (FRPP) but the OEM GT40's and GT40-P's were both cast iron.

The GT40 head I believe was orignally used on the 1993 Mustang Cobra, and then used again on the Explorer when it got the 5.0L engine. Later model Explorers with the 5.0L got the GT40P head. I believe this head was developed for improved emissions but features a smaller combustion chamber, smaller intake valve, and a different spark plug position. The "P" head does flow better than the standard GT40.

Most iron GT40 heads have disappeard from junkyards but you may get lucky. GT40P's are a little more plentiful and less expensive. If you use GT40P's be conscious of the increase in compression ratio you'll get from the smaller combustion chamber...this may force you to use higher octane fuel.

You can identify GT40 heads by three cast bars on the ends of the heads and "GT" cast into the head. GT40P heads have 4 cast bars in the end of the head and "GTP" cast into the head.

There is definitely a large selection of aftermarket heads out there but be careful not to spend too much money and buy too much head. Our marine engines will seldom run much over 4k rpm and a lot of the high dollar heads are meant to flow tons of air at 6-7k rpm's.

I think $500 for a set of GT40's or GT40P's is about all you'd want to spend. If you go for a fancier head than that you'll likely not see much of an improvement over the GT40's. I chose to rebuild my stock D8OE heads, had them cut for 1.94/1.60" valves and mildly ported them myself. It cost me far less than a new set of heads and I've been more than happy with the increased performance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 2:11pm
Well said, AWhite70. I have read all of that info before, and you summarized everything quite nicely.

I am curious- what are your thoughts on running aftermarket aluminum heads on our marine engines? Will there be issues with the aluminum vs. iron? Many seem to run aluminum intake manifolds without issues, right?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AWhite70 Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 2:52pm
Iron vs. Aluminum. Well I don't have any hard data so I'll give you my educated opinions.

The problems with aluminum are 1, corrosion, and 2, thermal expansion. I think both problems can be overcome with a closed cooling system. You'll note the 6.0L ZR6 engine has aluminum heads but has a closed cooling system.

With raw water cooling your engine is going to be subject to more thermal cycling. The difference in expansion between iron and aluminum is going to put more stress on your head gaskets and probably cause them to prematurely fail. As for corrosion you will definitely rot out aluminum components at a much faster rate than iron. I would have guessed that you could easily get 5-10 seasons out of a set of aluminum heads but someone once told me they heard of aluminum heads corroding through in 1.5 years. With that said I've run an aluminum Edelbrock intake on my '79 for two seasons now and it is showing no signs of corrosion.

Personally I would stick with iron heads because heads are hard to change and expensive. I think the perfomance increase you get from aftermarket intakes is worth the potential corrosion effects. Intake manifolds are relatively cheap and easy to change.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jim_In_Houston Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 8:17pm
The GT-40 and GT-40P are two completely different heads with different origins:

"The GT-40 Irons were Fordís high performance entry into the small block marketplace, and they feature a bigger exhaust valve than the P heads. The P heads were a last minute change to keep the 5.0 Explorerís passing emissions into the near future because the 4.6L SOHC engine wasnít yet available in the Explorer. Ford didnít want to make the P head. To speculate why it was made the way it was, Ford didnít want to lose a leading market share in the most profitable line of vehicles in production. The market was crying out for a V-8 offering in the mid sized SUV market, and Ford only had one engine that was available to squeeze under the hood. The 35 year old 90* based 5.0L V-8. The 5.0 was being phased out because Ford didnít want to invest the money to keep it up to par with emissions. That would, and eventually did, require a head redesign. The result was the GT-40P series head. Ford was forced to pump technology into the 5.0ís head to increase the burn efficiency so the Explorer would pass more stringent emissions standards. They did a good enough job so that they could get rid of the large exhaust thermactor bumps that plagued the GT-40 Iron and E7TE heads. This freed up a lot of space in the exhaust port, and all the technology going into the head design helped out the burning properties of the air/fuel mixture."

The above info was stolen from MustangNet

PS: I am running GT40Ps with a small Holley 450CFM 4V on my little 289 and the little small block never fails to get a WOW! out of everyone that rides. It will put you back in the seat when you kick it.

(Of course it could have something to with the fact that right before "I kick it" I hand my speedo to the rider and say "here, hold this").
Happy owner of a '66 and a '68 Mustang
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeinNY Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 9:46pm
Jim,
Drill that hole and mount that speedo, in a couple months once you see all the crap I am mounting in my dash and how I am going to do it you won't feel soo bad about one little 3.5 inch hole...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 11:26pm
AWhite well said, I doesn't suprice me from someone that sweat the details the way you do.

I'm looking to trade in my D80E with stock valves for a 1.84/1.54 seventies head with larger runners, what's your thoughts on runner size increase with the same combustion chamber size? for instance the 178cc vs 158cc int on the gt40 aluminum's?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: March-24-2006 at 11:27pm
where's the spell check????
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jim_In_Houston Quote  Post ReplyReply Direct Link To This Post Posted: March-25-2006 at 4:42am
I agree with Awhite 1000% about the aluminum vs iron although I am considering trying an aluminum intake. What is it everyone seems to rave about? An Edlebrock Performer? Is that the one?

I hate to admit it to myself about aluminum and salt water. The engine in my lake ran '68 was emaculate when I bought the boat. Now the aluminum parts are begining to corrode and there is rust forming on the engine mounts.

Is there some kind of coating that can be applyed to aluminum parts to protect them? Can engine moumts be powder coated or some such thing?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AWhite70 Quote  Post ReplyReply Direct Link To This Post Posted: March-25-2006 at 8:28am
JIH, The Edelbrock Performer is pretty popular, that's what I've got on my '79. Others have used the Air Gap which I understand to be a better performing intake but it's quite a bit taller. The Performer is probably 1-2" taller than stock and I had to go to a 1.5" spark arrestor to get my motor cover to close fully. I know I couldn't fit the Air Gap under my cover. As for corrosion on aluminum the best thing you can do is keep the metal covered. Paint, Powder Coating, etc. are all good options.

'79 I don't have a lot of experience with intake tuning since I work exclusively with turbocharged diesels (and turbo's negate a lot of intake tuning effects) but I have had some coursework in it. Basically your intake runner cross-sectional area and runner length can be tuned for optimum performance at a given speed (both in length and area). You set the length so reflected pressure pulses in the runner reach the intake valve just as it opens, this pressure pulse pushes more air into the cylinder. On the contrary if the pressure pulse is moving away from the valve when it opens less air will enter the cylinder. Intake port area can be adjusted to get the proper air velocity into the cylinder. This aids in mixing the fuel/air. With a well tuned intake you can actually achieve over 100% volumetric efficiency. It's a pretty complex question to answer which is better. It depends on the engines intended use, camshaft, cylinder head, intake manifold, etc.

In general I think longer smaller x-section ports are better for lower speeds and shorter larger x-sec ports are better for higher speeds. You can probably search the net and find some pages as to what head/manifold combinations work better for what you want to do.

This link explains this fairly well Intake Tuning
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