General 5.0 Modification: cylinder head milling?

[spamynator_1]

I drive a 1985 Mustang GT Convertible, 5.0, and i intend to do some modifications to it's current motor. I do intend to replace the motor all together with a custom build one. What i intend to do to the current one is: replace the cam with a .450 .450 lift, and replace the **** throttle body injection with a holly 570 street avenger or 650 double pumper and mill the cylinder heads. NOW i know milling cylinder heads is something that is kind of hack and one would normally only do that to a gokart or something (I have done that) but my curiosity is i dont need to mill them much to reach the desired 10:1 cr i desire. I am just curious if anyone has done this with the stock heads, and what room i have for the ptv clearance to do such a thing. I am new to this forum and thank you for your help. It is the fi-ho btw

[mustangxtreme]

Milling the heads is a time honored way to raise the compression ratio. That said, you should always check piston to valve clearance with the cam you will be running. This is the only way to be certain you won't have any issues. If it were me, I would at least swap the stock heads for GT40s or GT40P and then mill them to get the compression ratio you want. They are the best factory heads Ford produced for a 5.0 and will work much better for your project.

[bwguardian]

To get the stock heads down to a chamber size to reach 10:1 will probably not be possible as they are in the upper 60cc's. As stated above, get some GT40p heads as they are in the upper 50cc's and will put you around 9.5:1 to start with, plus they flow better. That being said, you need more cam than what you are looking at as the stock cam is not much smaller. The cam you will want should be somewhere around .500" as that is where the heads will fall off. For the carb, I think you will have too much...there is nothing the 600 cfm can't handle, even in vacuum secondary form.

I too have an 85 GT vert and above is purdy much what is in mine, except I have a tweaked factory carb. This, in conjunction with a good breathing exhaust and a little more gear out back and she runs really hard for a weekend toy.

[JACook]

The stock '85 CFI cam already has .416"/.444" lift, 260/274 duration, on a 114.5 LSA. The stock heads
spec 68cc chambers. You won't be able to mill off enough material to get anywhere near 10:1 with the
stock piston compression height because the decks are not thick enough. Nor would you want to. The
stock heads do not have particularly well behaved chambers.

The stock pistons are cast four eyebrow flat-tops, that sit about .016" in the hole.

I'm with the others, you will be far better off starting with at least some GT40 or GT40p heads. Given
you've got an AOD, you should be conservative with your cam and carburetion choice. It's very easy
to kill off low-end torque in a 5.0, and I don't see any mention of gears or torque converter in your wish
list.

Likewise a 650DP is not a good choice for a mild 5.0 with an AOD behind it, in a relatively heavy convertible.
The 570 SA would be the better choice here, but either way you'll need to come up with a spacer ring for the
air cleaner, or swap one from a 4V car. The CFI uses a larger hole in the air cleaner with different locating
tabs, than the air cleaner used on the carbureted models.

I know you said this engine is not your end-game, but the entire combination still matters.

[spamynator_1]

To get the stock heads down to a chamber size to reach 10:1 will probably not be possible as they are in the upper 60cc's. As stated above, get some GT40p heads as they are in the upper 50cc's and will put you around 9.5:1 to start with, plus they flow better. That being said, you need more cam than what you are looking at as the stock cam is not much smaller. The cam you will want should be somewhere around .500" as that is where the heads will fall off. For the carb, I think you will have too much...there is nothing the 600 cfm can't handle, even in vacuum secondary form.

I too have an 85 GT vert and above is purdy much what is in mine, except I have a tweaked factory carb. This, in conjunction with a good breathing exhaust and a little more gear out back and she runs really hard for a weekend toy.

If the gt40 heads will give me 9.5:1 straight out the box, then i may reconsider milling at all. As for the cam, i was unaware that it was that large. I intend for this to NOT be an off idle car, What is it that would be best for my cam profile? given a <1200 idle

[bwguardian]

If the gt40 heads will give me 9.5:1 straight out the box, then i may reconsider milling at all. As for the cam, i was unaware that it was that large. I intend for this to NOT be an off idle car, What is it that would be best for my cam profile? given a <1200 idle

You will want the GT40p heads...the GT40 heads have a slightly larger combustion chamber, being in the low/mid 60cc's. I don't know what cam might work with an AOD but you will need a good converter with a high stall given what you are wanting. I am not sure that AOD can take the power you are looking at and you may want to consider a T-5.

[brianj]

What are your end goals for the car? Cruiser, street strip,?

[BMW Rider]

My engine is a 68 4V 302, .040 over with flat top pistons and with the 53 cc 4V heads it does have 10.0:1 compression so I doubt you'll get there with your set up. Don't forget all the other factors that affect clearance volume such as the deck clearance of the pistons, gasket volume, relief cut volume of the pistons, etc. Those little numbers add up quickly. Milling the heads is good practice as far as ensuring surface flatness for sealing, but it will be hard to make sufficient difference to get that much compression increase.

One of the biggest limiting factors with small block engines is flow, so improving the porting is as valuable as increasing compression. I did a lot of work to my heads to do just that; significant porting particularly on the exhaust side and enlarging the valves to 351W sized ones. A big cam will also aid in improving flow so long as the porting can handle it.

[spamynator_1]

What are your end goals for the car? Cruiser, street strip,?

Any track i can get on next spring. And but for this build i want budget, and daily derivable while i pull together the parts for my custom engine. With the custom engine i am going to t-56 swap. But for now i even intend to keep the AOD

[brianj]

Honestly, an 8.8 rear with a set of 3.73 gears, or even 4.10 with the aod, would be a huge improvement, and fairly cheap. '85, i think, might already have the 8.8 instead of the 7.5 rear. If you are planning on swapping out the motor, i wouldn't put too much into it that won't swap over to the new set up, such as headers and exhaust upgrades. You will notice a nice bump up in power with the 4bbl and exhaust upgrades, but you will rapidly get diminishing returns on money spent with cams, milling heads, etc. My motor is as complicated as an anvil, and cheap, and puts down a touch over 270 at the rear wheels.

[JACook]

'85 GT still used the 7.5". My '85 AOD Vert came stock with 3.27 gears in it. I believe that's fairly
typical for '85 AOD Verts.

The 307 (4.03"x3.01") in my '68 has 9.89:1 compression ratio, using flat-top pistons at zero deck, a
.042" thick head gasket, and Twisted Wedge heads milled to reduce the chambers to 57cc. The short
stroke of the 302 engine makes for a fair bit of work to actually get to 10:1.

[quickshift]

When I was building my 88 roller motor for my 84 Cougar, I played with the stock CFI motor just for S+Gs. I tore off all CFI and related wiring. I left just enough wiring to run the the 2 pumps and fire a Duraspark. I installed a Holley 500 2bbl on the stock manifold, used a Mallory 4309 return regulator to utilize the stock fuel system, and installed a re-curved dist with a Duraspark. I took the stock tube headers off the donor car (88 LX, HO) as well as the T-5 and the 8.8 with 3.73s. All I can say is , If for some reason I had to stop there, I'd be happy as the difference was night and day over the stock set-up without even having to pull a VC!

[Walking-Tall]

When I was building my 88 roller motor for my 84 Cougar, I played with the stock CFI motor just for S+Gs. I tore off all CFI and related wiring. I left just enough wiring to run the the 2 pumps and fire a Duraspark. I installed a Holley 500 2bbl on the stock manifold, used a Mallory 4309 return regulator to utilize the stock fuel system, and installed a re-curved dist with a Duraspark. I took the stock tube headers off the donor car (88 LX, HO) as well as the T-5 and the 8.8 with 3.73s. All I can say is , If for some reason I had to stop there, I'd be happy as the difference was night and day over the stock set-up without even having to pull a VC!

You just answered a couple questions I've had rolling around in my head with one fell swoop, thank you!
The questions are: "I wonder how or if a returning adjustable regulator would handle 40+ psi coming from electric pump/s down to around 7 psi for a carburetor?"; and the other, not really a question, "I am certain I can make this car ('86 CFI 3.8L) run better with a Duraspark and a Holley 2bbl, being that that's what was in my '83 Cougar and I had it working very well..."
So you had both internal and external, high and low pressure electric fuel pumps, and still ran them both?
I'll be checking out that Mallory. Thanks again.

[JACook]

Why not just bypass the external pump, and run off the lift pump only? Several here have done that
with good results.

One thing to keep in mind WRT the Duraspark ignition, the TFI cars do not have any ballast resistor
in line with the coil, and the E-core coil is also not the best choice with a Duraspark module. A red-
grommet module would deal with both of those issues, but those aren't exactly growing on trees
anymore.

[Walking-Tall]

That's exactly what I would do if I were so lucky to have the two pump scenario, lol
This '86 of mine has a single internal high pressure pump. I felt/feel pretty certain a consistent 7psi should be able to be had, but absolutely only with a return-style regulator. I may go that way, or I may fabricate a pickup in the tank and run a mechanical pump. Depends what I locate, when. These 3.8's sure seem quite difficult to find used parts for.

If and when I line up the parts, it'll be 100% Duraspark-ed, and I'll use a blue grommet module.

Thanks Jeff

[JACook]

Without naming names, there are a couple guys here who have recently upgraded to the single-pump
setup in order to install dual exhaust. The swap requires changing the pump hanger to the style used
with the later high-pressure in-tank pumps. Just sayin'...

[Walking-Tall]

Single internal low pressure? Great tip, thanks again

[quickshift]

Why not just bypass the external pump, and run off the lift pump only? Several here have done that
with good results.

One thing to keep in mind WRT the Duraspark ignition, the TFI cars do not have any ballast resistor
in line with the coil, and the E-core coil is also not the best choice with a Duraspark module. A red-
grommet module would deal with both of those issues, but those aren't exactly growing on trees
anymore.

The low pressure pump is hit and miss. I tried it and it wasn't enough. I'm using both pumps with the 4309 regulator at 6psi and have no drop, even at 5200 in 4th.I will say that I had to relocate the frame pump to a spot on the front of the tank where the filter is.

[JACook]

The low pressure pump is hit and miss. I tried it and it wasn't enough.

Did you bypass the ballast resistor wire in the fuel pump ground lead? The low-pressure pump won't deliver
full volume unless you do. The pump itself is rated to produce 6-9 PSI / 54-63 GPH free flow.

Here's a link for Walking-Tall what the low-pressure pump and hanger assembly looks like -
http://vb.foureyedpride.com/showthre...=1#post1666888

[quickshift]

Did you bypass the ballast resistor wire in the fuel pump ground lead? The low-pressure pump won't deliver
full volume unless you do. The pump itself is rated to produce 6-9 PSI / 54-63 GPH free flow.

Here's a link for Walking-Tall what the low-pressure pump and hanger assembly looks like -
http://vb.foureyedpride.com/showthre...=1#post1666888

This explains a lot. I was unaware of the restrictive circuitry in the in-tank pump. This explains the varying results people have had.
Since I'm 62 and retired, I have to explore this further to cure my curiosity (thanks a lot Jeff....LOL). It sounds inviting as to not having to run the external pump. I like simple and this would be one more thing to take out of the equation of "things that can screw up...will).

[Walking-Tall]

Did you bypass the ballast resistor wire in the fuel pump ground lead? The low-pressure pump won't deliver
full volume unless you do. The pump itself is rated to produce 6-9 PSI / 54-63 GPH free flow.

Here's a link for Walking-Tall what the low-pressure pump and hanger assembly looks like -
http://vb.foureyedpride.com/showthre...=1#post1666888

Thanks very much for that, Jeff!

[83gtstang]

Honestly, an 8.8 rear with a set of 3.73 gears, or even 4.10 with the aod, would be a huge improvement, and fairly cheap. '85, i think, might already have the 8.8 instead of the 7.5 rear. If you are planning on swapping out the motor, i wouldn't put too much into it that won't swap over to the new set up, such as headers and exhaust upgrades. You will notice a nice bump up in power with the 4bbl and exhaust upgrades, but you will rapidly get diminishing returns on money spent with cams, milling heads, etc. My motor is as complicated as an anvil, and cheap, and puts down a touch over 270 at the rear wheels.

The 8.8 was out in 86, but roller cam was 85. My 85 had the weak 7.5 which I upgraded with 3.73s in an 8.8.

[854vragtop]

Milling the heads is a time honored way to raise the compression ratio. That said, you should always check piston to valve clearance with the cam you will be running. This is the only way to be certain you won't have any issues. If it were me, I would at least swap the stock heads for GT40s or GT40P and then mill them to get the compression ratio you want. They are the best factory heads Ford produced for a 5.0 and will work much better for your project.

I also have an '85 GT convertible, but with the 4V and 5-speed. I rebuilt my bone stock motor two years ago with 192k miles on the odometer.
I was able to hone the cylinders and use stock size rings and bearings. The original cross hatching was still inside the cylinders and there was no ridge worn into the top of the cylinders. Very little wear on the crank and rod bearings and the crank looked pristine and all within B/P tolerances. The cam bearings were also pristine, so I didn't even have to replace them. Pistons were in great shape, and since they're forged, I re-used them too. I home ported a set of GT-40P head and took them to a machine shop to have a 3 angle valve job and minor milling clean up on the bottom. See my sig for the cam and intake that I went with. I don't have anything else to compare it to, but I'm extremely happy with the results. Pulls hard to redline. Improved low end torque. At 4300 RPM it pulls HARD. Not sure if that's all the cam or both that and the secondaries coming into play. These motors are very durable. I see no need for you to have to get a new motor. Pull yours apart on an engine stand and learn how to rebuild it yourself. It was a great learning experience for me!