GT40 Heads. Is this a good deal? - Vintage Mustang Forums
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post #1 of 36 (permalink) Old 02-02-2018, 01:39 PM Thread Starter
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GT40 Heads. Is this a good deal?

I stopped by the local performance engine machine shop to discuss and get an idea of what the cost would be for all the machining for my 1968 J-Code 302 4V engine. We talked about what is involved and cost to rework the stock heads and then I noticed they had quite the collection of heads on the shelves. I asked if they had any early 351 heads that may make more sense to recondition than my stock 1968 302 heads. He said no but he had a pair of reconditioned GT40 heads that a customer had them rebuild and then changed their mind and went with a set of AFR aluminum. He said they were the best of the old iron heads. I asked what he wanted for them and he said $575, He also said he'd throw in the new rockers the customer donated also. Does that sound like a good deal? They are freshly rebuilt (zero miles on them) ready to go in excellent condition all done by a professional shop. I asked him what it would cost to rebuild my 302 heads and would they be as good performance wise. He said I'd spend more than that on my 302 heads and they would not be as good performance wise as the GT40 heads. This sounds like the way to go to me and then shelve my stock heads for the next owner. What do you think?
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post #2 of 36 (permalink) Old 02-02-2018, 03:36 PM
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What was done to the GT40 heads? Just a stock rebuild? I have seen them anywhere from $250-350 for used ones. What kind of rockers, stock or pedestal? The combustion chamber will be bigger then your 302 so you lose compression but they have bigger valves for more air.

In my 89 I got 235RWHP through an AOD which is about 275HP at the flywheel.

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post #3 of 36 (permalink) Old 02-02-2018, 03:37 PM
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I just paid $650 to my local machine shop to have my STOCK '93 E7 heads rebuilt; nothing ported just everything measured, machined, repaired. So yea, $575 for a set of GT40 heads that have been completely gone through with rockers sounds like great deal. I mean it's not gonna blow your doors off but it's a solid plan if you don't want to step up to alum heads + rockers + pushrods + etc. You should confirm that the springs are rated to handle the cam lift you're running.

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post #4 of 36 (permalink) Old 02-02-2018, 03:43 PM
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hAVE BEEN LOOKING FOR A FEW years for some GT40 heads i didnt want reconditioned one . Prices for reconditioned ran around 475 to 575 in most cases. Some wanted 300 to 500 for used untouched ones.
Including the new rockers sounds like a good deal.
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post #5 of 36 (permalink) Old 02-02-2018, 03:55 PM
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Local mustang guy has them for better prices and can port them for less than what your guy is asking. Shipping may kill the "deal"

https://minneapolis.craigslist.org/h...436380175.html
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post #6 of 36 (permalink) Old 02-02-2018, 04:24 PM
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Another option are the GT40P heads. They have a smaller chamber at 59 CC. The P head is the next evolution of the GT40 head. Theyre suppose to have more efficient combustion chamber and exhaust port. Im using them and Im very pleased with them. The stock exhaust manifold will work just fine with a little minor grinding on the flange.

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post #7 of 36 (permalink) Old 02-02-2018, 04:34 PM
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i would say the heads the OP is talking about is a good deal. fresh heads with rockers for $575, i would be there in a heartbeat.
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post #8 of 36 (permalink) Old 02-02-2018, 04:55 PM
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The bottom line I think its a good deal too. Youd probably spend that alone fixing up your old heads. The GT40 will be a very noticeable improvement. Maybe you can talk him into resurfacing a bit to bring the chamber down slightly but not a deal breaker

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post #9 of 36 (permalink) Old 02-02-2018, 07:40 PM
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The "P" heads are the best Ford SB iron heads, period. Sounds high for a fairly common head unless you need them for this weekend or something. Would you pay that or slightly more for aluminum GT40's? Check dbay. purddy https://www.ebay.com/itm/Ford-289-30...5JIiJw&vxp=mtr
What was the cost to have your OE worked to that level? Id keep yours for even if it were more. Youll just have to work harder elswhere to get to the same level overall.
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post #10 of 36 (permalink) Old 02-02-2018, 07:55 PM
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FWIW, I bought a new set of Aluminum GT40X heads on the Corral with ARP bolts and shoulder washers for $800, but you have to be willing to wait for a deal to come around.

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post #11 of 36 (permalink) Old 02-02-2018, 08:54 PM
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just purchased 2 pair of untouched GT40 heads will clean them up, port them, install larger valves, machine for guides and studs, beehive springs, titanium retainers, guides if needed.
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post #12 of 36 (permalink) Old 02-02-2018, 09:03 PM
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dont really care for P heads their ok but the plug aimed at the exhaust valve should have been a bit less the plug boss is in the way they are spark limited because of it. ever see an aftermarket combustion chamber set up like that.
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post #13 of 36 (permalink) Old 02-02-2018, 09:26 PM Thread Starter
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The heads in question I believe have the stock valve sizes. He told me the heads were probably from a 1993 Ford Lightning. The springs, bushings, valves, hardened seats, etc.... are all new. No additional porting was done. I asked him what cam would be a good fit and he explained the way they determine what cam to use is by mounting the heads on a machine they have that measures the amount of air flow through the heads, that way they can tell what actually produces the best flow, which they'll do. He also said with the springs that were currently on them it would be right around a 500 lift. He also cross referenced some pistons and said I would be at 9.5 to 1 using a forged flat top piston using those heads as is. Also I know the ones in question are not the GT40P just because he made note of that. Also, I know my current 1968 302 4V heads have smaller valves but they have 10.5 to 1 compression ratio.

I think I will keep the original heads as is and store them for the next owner. The car is a nice clean original numbers matching car so I don't want to make any changes that can't be undone.

Last edited by lennyB; 02-02-2018 at 09:39 PM.
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post #14 of 36 (permalink) Old 02-02-2018, 09:47 PM
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if they are off a truck the head bolt holes are for 1/2 bolts you will need special washers or bolts. I use the washers and ARP bolts on my DOOE heads. the GT40s i just purchased are of an exploder.
The GT40s flow around 190 @ .500 lift as cast. Above that lift they dont do much better.
the rest is info on your intentions or other parts such as intake

9 to 9.5 compressionrange is about as much as i would go

In theory that could make 390 HP but intake selection gives a better estimate if you know its flow bolted to the cylinder head.

Last edited by turbo2256b; 02-02-2018 at 10:00 PM.
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post #15 of 36 (permalink) Old 02-02-2018, 09:58 PM Thread Starter
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He did mention I would need special washers since the bolt hole are different. Do you think these heads will be noticeably better than my 68' 302 heads. He said he thought it would be about a 40 HP increase.

Below are some specs I came up with to compare the difference between the two options.

1968 302 4V heads: 53.5 cc, 1.78/1.45, 10.5 to 1 compression 235HP factory rating (everything stock 600 cfm carb).

GT40 heads: 63.0 cc, 1.84/1.64, 9.5 to 1 compression, aftermarket cam to be determined, 600 cfm carb, HP unknown at this point?
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