Exhaust options for 351W

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Re: Exhaust options for 351W

Gsmblue
You are correct.

Espy getting transmission, transfer case and rear axle treatment.
1985 F150 XL Explorer 5.0 EFI 4AOD 4x4 standard cab.
Daily Driver. I call her Eunice.
To do:  Rear fuel tank pump, replace door hinges, Front and rear windows need replacing, blue top steering box, front dampers, Interior panels to be painted, new carpet, seats to be recovered, some exterior paint work

1982 Bronco XLT Lariat 351 C6 4x4
Code name Esperanza, or Espy to her friends. Please see my Project page for details.
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
Oh

On my phone it looked like the jack was under the tank.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Rusty_S85
In reply to this post by ArdWrknTrk
I have heard lots of great things about AFR`s Renegade 165cc heads.  I havent used mine yet but thats the route I went.  I was looking at GT40 heads but then I started thinking about flow and the aluminum nature of the AFR`s and went with the Renegade 165`s for my build.  Everyone Ive talked to said those are amazing heads for a small ford engine for street use.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
Aluminum is ALWAYS nice if you can afford it.
Conducts heat so much better that you can get another point of compression all other things the same, and it's very easy to port.

Air Flow Research make a really nice product!  
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Gsmblue
Those are not cheap!!

Now i am questioning how much money i need to budget for an engine.. I was thinking $2.5k might be enough for a rebuild.
1985 F150 XL Explorer 5.0 EFI 4AOD 4x4 standard cab.
Daily Driver. I call her Eunice.
To do:  Rear fuel tank pump, replace door hinges, Front and rear windows need replacing, blue top steering box, front dampers, Interior panels to be painted, new carpet, seats to be recovered, some exterior paint work

1982 Bronco XLT Lariat 351 C6 4x4
Code name Esperanza, or Espy to her friends. Please see my Project page for details.
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Re: Exhaust options for 351W

Rusty_S85
In reply to this post by ArdWrknTrk
Yep my AFR Renegade 165cc heads were $1,800 for a pair assembled I got $200 off from jegs during their sale but it was right back at $1,800 as I had them custom ordered with springs AFR recommended as a very close match to the recommended springs by Crane Cams for the roller cam I got as well as the 7/16 rocker arm stud upgrade.

Im hopeful the aluminum 58cc AFR heads will allow me to run at least 89 octane mid grade fuel with 9.5:1 compression.  highest my compression I figure could be is 9.75:1 and lowest would be 9.0:1.  I wont know till i get my short block and do the math to figure what my compression would be.  I just know blueprint has 9.5:1 compression with a 60cc chamber head which will put me at 9.75:1 from my figuring.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

Rusty_S85
In reply to this post by Gsmblue
My 306 build with fuel injection for everything is going to be right at $10,000 when I am done.

This includes AFR Renegade heads, edelbrock performer intake, hedman shorty street headers, one magnaflow XL 3 chamber round muffler, tail pipe, Y pipe, one piece oil pan and valve cover gaskets, new timing set, new timing cover, new water pump, new balancer, new roller ford racing HD lifters, new scropion roller rockers, new ford racing valve covers, holley sniper stealth, new fuel tank, new fuel sending unit, new in tank fuel pump.

I am doing quite a bit for $10,000.  You can buy a prebuilt crate engine for around $8,000 but I find those are very generic hotrod engines and dont always fit nicely with a truck or a street setup.  That is why I opted to piece my own together using a short block.  That way I was able to select a truck performance cam from Crane and then build around that 1,400 - 5,400 rpm power band.

I also have another $2,800 set aside for a custom built C6 transmission with a E4OD planetary gearset to get a 15% lower first and 10% lower second gear.  I also have on my wish list a Currie 9inch center chunk with a detroit trutrak with 3.25:1 axle ratio for $2,800 as well.

It can run into money especially if you go all out like I am as I want it to be all new and done right.  Ive already had a engine built and it used oil from day one that the builders could never solve.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
In reply to this post by Gsmblue
Which is why I said GT40's and maybe a new crank.

Make decisions on what you need, what you want and what it's going to take to get there.
Then start picking those pieces to get you there and work together.

400/400 is way more than you need for a truck to drive to lake.
But (like I,said) this is a discussion you should have before you start.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Rusty_S85
Yep it is best to make a plan on what you want and then go from there.

Daily driver with long term reliability or all out performance.

I choosed a blend of daily driver with long term reliability as well as a slight lean towards performance.  Its why I would not use a flat tappet cam, why would I use a flat tappet cam when I can free up power, use a more agressive ramp profile by going with a roller cam.  Plus it prevents me having to run VR1 to make sure I have enough zinc for the flat tappet cam.

Just like with a street truck, have to decide like you said how much power you want.  My goal has always been 300 hp as that over double what a smog 302 was rated at for my truck.  That would basically make my truck run like I have two engines under the hood.  Some times you dont have to shoot for 500 hp like everyone wants to always go for.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

Gsmblue
“Daily driver with long term reliability”

My wife needs be confident she can drive 100miles round trip to a lake and be comfy and stylish.

Therefore 400/400 is way over. Honestly cruising with a nice sounding 250/250 with the 4OD tranny... she will be made up!

Sounds like I need to find an engine builder ...
1985 F150 XL Explorer 5.0 EFI 4AOD 4x4 standard cab.
Daily Driver. I call her Eunice.
To do:  Rear fuel tank pump, replace door hinges, Front and rear windows need replacing, blue top steering box, front dampers, Interior panels to be painted, new carpet, seats to be recovered, some exterior paint work

1982 Bronco XLT Lariat 351 C6 4x4
Code name Esperanza, or Espy to her friends. Please see my Project page for details.
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Re: Exhaust options for 351W

Gsmblue
Oh, and thank you all, what an awesome group of peeps!!
1985 F150 XL Explorer 5.0 EFI 4AOD 4x4 standard cab.
Daily Driver. I call her Eunice.
To do:  Rear fuel tank pump, replace door hinges, Front and rear windows need replacing, blue top steering box, front dampers, Interior panels to be painted, new carpet, seats to be recovered, some exterior paint work

1982 Bronco XLT Lariat 351 C6 4x4
Code name Esperanza, or Espy to her friends. Please see my Project page for details.
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Re: Exhaust options for 351W

Rusty_S85
In reply to this post by Gsmblue
Really dont need OD if you set it all up properly.  I will retain my C6 without OD, with a 3.25:1 axle ratio with 31x10.50-15 tires, my rpm at 75 mph will be with in the 2,400 - 3,000 rpm cruise range of my cam.  With 3% to 5% slip in my C6 after rebuild I should see 2,750 rpm at 75 mph.

Just have plan it out and think it through.  its why I am looking at the E4OD planetary gear set upgrade, a lower first and second gear will help the 3.25:1 axle ratio (or 3.00:1 in worse case) pull with my large tires but will still maintain a highway capability.

its really why I am leaning towards EFI now for my build cause it will help with fuel economy and should make my goal of 18 to 20 mpg highway quite possible.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
In reply to this post by Gsmblue
You can build it yourself.

250/250 is easily attainable, but I'd be shooting for more torque if you want to tow a boat.

Keep ports, valves, carburetor and exhaust smallish to make the best of low rpm filling.
Depending on how hard you want to push that new driveline and what fuel you want to use, decide on a cam and compression ratio.

The roller cam engine from a later Explorer is a great starting point.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
This post was updated on .
The '98-2000 -P heads have a little tighter chambers still.
But the 96-97 40's are still worth probably 30-40 Hp over what you've got now.

Consider compression.
It's the 'bang' that turns the tires... (torque)
... aside from things like flywheel, stroke and rod ratio that you don't want to get into without good understanding and deep pockets.

But you don't want to sacrifice reliability, long term.
So keep it mild while building the type of power you'd like.

Edit: P heads DO have a revised plug location though.
If you don't like the header access you have now you might want to table the idea of them.

Either one you're going to have to drill the bolt holes for them to fit a 351.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Rusty_S85
In reply to this post by ArdWrknTrk
250hp is pretty much a given no matter what kind of combo you piece together for a 302/351 engine.  Parts are so efficent today its hard to not make at least 300hp.

With a 351W, just like a 302, 9.0:1 to 9.5:1 is the goal one should shoot for.  I wouldnt go over 9.5:1 but some times its hard to not go over if you are dealing with a pre built short block that you are assembling yourself.

the Explorer cam is a good cam from what I have seen.  You can actually find aftermarket cams in the F4TE spec on ebay.

F4TE-6250-BA
256 / 266 Advertised Duration
186 / 197 @ 0.050"
0.422 / 0.448 Lift
116 LSA

Decent little cam for a street truck.

I actually looked at it quite a bit before I personally settled on a Crane TruckMax cam for the 302/351W

278 / 286 Advertised Duration
216 / 224 @ 0.050"
0.520 / 0.542 lift
112 LSA
107 ICL

When I talked with the engine builder next to where I work, he told me that 107* intake centerline will make my build quite snappy and responsive on the throttle.

Cam I went with isnt huge compared to a F4TE cam outside of lift, the lift on this cam is insane compared to the F4TE.

But for the poster, he might like the F4TE better as it will be a bolt in application where mine requires custom push rod lengths for my adjustable valve train.  Plus this came I got from Crane was pushing $550 by itself not including lifters, spider, pushrods, and rocker arms.  The F4TE spec cams I found on ebay brand new were in the $100 - $200 range.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
Rusty_S85 wrote
250hp is pretty much a given no matter what kind of combo you piece together for a 302/351 engine.  Parts are so efficient today its hard to not make at least 300hp.
.....
When I talked with the engine builder next to where I work, he told me that 107* intake centerline will make my build quite snappy and responsive on the throttle.

Cam I went with isnt huge compared to a F4TE cam outside of lift, the lift on this cam is insane compared to the F4TE.
Thanks for posting those numbers Rusty.  
A 1/10 of an inch doesn't seem like much to some people.
I understand your need for rollers with a ramp like that.

Yes, not many are looking to de-tune.
GSM is the one saying 250.

The tighter LSA on your cam = more overlap.
So perhaps you can get away with more static compression and you will have more of a sense of coming on the cam.
Not 'choppy dragster' idle, but the same effect is still there.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Gsmblue
So much info, thanks! I defo need to unpack all of this and work out how to proceed.

I mean, 300/300 will be fine, the new driveline should be fine for that!
1985 F150 XL Explorer 5.0 EFI 4AOD 4x4 standard cab.
Daily Driver. I call her Eunice.
To do:  Rear fuel tank pump, replace door hinges, Front and rear windows need replacing, blue top steering box, front dampers, Interior panels to be painted, new carpet, seats to be recovered, some exterior paint work

1982 Bronco XLT Lariat 351 C6 4x4
Code name Esperanza, or Espy to her friends. Please see my Project page for details.
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Re: Exhaust options for 351W

Rusty_S85
This post was updated on .
In reply to this post by ArdWrknTrk
Funny thing a 1/10 of a inch of valve lift doesnt really seem like much but when you look at AFR Renegade heads and their flow data you find out there is a good amount of difference.

For example the F4TE-6250-BA cam with a lift of 0.422"/0.448" or under 0.450" lift the AFR 165cc renegade heads I have is 240cfm @ 28" H2O at 0.400" lift.

Flow data for stock GT40 heads with the F4TE-6250-BA cam is 183cfm @ 28" H2O at 0.400" lift and 192cfm @ 28" H2O at 0.500" lift

My cam at 0.520"/0.542" lift or around 0.525" lift the AFR 165cc Renegade heads I have is 251cfm @ 28" H2O @ 0.500" lift and 255cfm @ 28" H2O @ 0.550" lift.  So I figure around 253cfm at 0.525" lift.  Running stock GT40 heads with this cam would not flow better I believe as the highest flow data spec for the GT40 heads I could find was 192cfm @ 0.500" lift.

I used DD2000 with all the specs that I could find to get an idea and I ran numerous combinations from the F4TE-6250-BA cam with GT40 heads to the F4TE-6250-BA cam with AFR 165cc Renegade heads down to the Crane TruckMax cam I settled on.

The build I have saved on DD2000 which is as follows

306 CID
Stock 1996 GT40 heads
9.50:1 compression
800cfm TBI Sniper Stealth
Small-Tube headers with Mufflers
F4TE-6250-BA cam (25* IVO ATDC / 31* IVC ABDC / 32* EVO BBDC / 15* EVC BTDC)

Peak HP : 245 @ 4500 rpm
Peak Trq : 365 @ 2000 rpm
Peak Vol Eff : 73.5% @ 3500 rpm

Next build

306 CID
Out of the box AFR Renegade 165cc heads
9.50:1 compression
800cfm TBI Sniper Stealth
Small-Tube Headers with Mufflers
F4TE-6250-BA cam (25* IVO ATDC / 31* IVC ABDC / 32* EVO BBDC / 15* EVC BTDC)

Peak HP : 308 @ 5000 rpm
Peak Trq : 373 @ 3000-3500 rpm
Peak Vol Eff : 77.3% @ 4000 rpm

Next build

306 CID
Stock 1996 GT40 heads
9.50:1 compression
800cfm TBI Sniper Stealth
Small-Tube Headers with Mufflers
Crane TruckMax cam (1* IVO BTDC / 35* IVC ABDC / 49* EVO BBDC / 5* EVC BTDC)

Peak HP : 300 @ 4500-5000 rpm
Peak Trq : 380 @ 3000-3500 rpm
Peak Vol Eff : 84.6% @ 4000 rpm

Final build and build I settled on

306 CID
Out of the box AFR Renegade 165cc Heads
9.50:1 compression
800cfm TBI Sniper Stealth
Small-Tube Headers with Mufflers
Crane TruckMax cam (1* IVO BTDC / 35* IVC ABDC / 49* EVO BBDC / 5* EVC BTDC)

Peak HP : 382 @ 5500 rpm
Peak Trq : 405 @ 4000 rpm
Peak Vol Eff : 87.9% @ 5000 rpm

What I like about this is from 2000 to 3000 rpm which will be highway cruising rpm listed by the cam and the rpm range I am setting mine up to operate in.

HP 141 / TRQ 371 @ 2000 rpm
HP 181 / TRQ 381 @ 2500 rpm
HP 224 / TRQ 392 @ 3000 rpm

So for me the torque builds up which means when I am on the highway and I nail the throttle I should have power to effortlessly pass compared to my smog 125hp 302 that at 75 mph @ 2750 and you nail it its like cmon lets go.

The interesting thing with overlap is it changes based off what stat you are looking at.  Advertised duration its almost doesnt exist, but at 0.050" its quite a bit of overlap as this cam has a very agressive ramp so the valves stay closed longer and pop open at a quick almost instant rate at the last possible moment.

Using this one interactive camshaft calculator that you punch all the data into it tells you overlap as well as map out how the cam opens/closes on the rate.

Putting in @ 0.050 and advertised duration it comes up with my overlap being -4.  But if you use advertised duration and do the math it comes up as some 77 of overlap.  This is the diagram with the proper 5* of advance that Crane cut into my cam to get the intake and exhaust timing at what the cam card says.



Thats why for me I am being very careful with compression and I am a bit worried if compression will hit 9.75:1 cause if the overlap is that little as it is indicating here then I may have a problem as I dont mind running 93 octane if I can get good gas miliage but preferably I want my fuel requirement to be 89 octane at the very least preferably 83/85 regular grade.

But you are right, with more overlap you bleed off dynamic compression and thus have to run more compression to offset the loss of compression due to valve timing.

Using Wallace Racing`s Dynamic CR calculator it comes up as the following.

Static Compression 9.50:1
Effective Stroke : 2.80"
Dynamic Compression ratio : 8.93:1
Dynamic Cranking pressure : 185.96 psi

This was done at 500ft which is roughly what my altitude will be driving around Texas from Houston to La Grange which should be around 25ft to 400ft but being the hill country of Texas, the elevation varies from 375 to 450ft.

But for me seeing the chart I posted above, it makes me seriously wonder with the aggressive ramp if it will have a different effect on dynamic compression ratio for me than what calculators are stating.

Idle quality I dont know what it will be I just hope my tach and truck idles smooth I dont mind a nice rumble to the exhaust I know I dont want a aggressive choppy idle.  That was another thing I thought about when I was in my planning stages.

There is quite a bit of planning one can do when custom piecing an engine together for what they want.  Ultimately price is the deciding factor.  If I did this build again I would probably go a different route as I didnt plan on spending $10,000 on this engine but it just got out of hand when I was piecing things together.  Then it didnt help I made the decision to switch from Summit 600cfm carb to the Holley Sniper Stealth.

~Update~

I am updating my post as I totally forgot to post the flow data I found for Stock 96 GT40 heads.

Intake @ 1.84" with 28.0" H2O
Lift / Flow

0.100" / 54cfm
0.200" / 107cfm
0.300" / 157cfm
0.400" / 183cfm
0.500" / 192cfm

Exhaust @ 1.54" with 28.0" H2O

Lift / Flow
0.100" / 47cfm
0.200" / 94cfm
0.300" / 119cfm
0.400" / 128cfm
0.500" / 128cfm

Compared to the AFR Renegade Heads (honestly you have to weigh the cost to upgrade personally I dont think its worth the upgrade unless you are trying to squeeze every bit you can out of your build as its quite pricy)

Intake @ 1.90" with 28.0" H2O

Lift / Flow
0.200" / 135cfm
0.300" / 200cfm
0.400" / 240cfm
0.500" / 251cfm
0.550" / 255cfm
0.600" / 260cfm

Exhaust @ 1.60" with 28.0" H2O

Lift / Flow
0.200" / 122cfm
0.300" / 163cfm
0.400" / 192cfm
0.500" / 208cfm
0.550" / 212cfm
0.600" / 215cfm

The CNC design does flow way more than stock GT40 as well as ported GT40 heads but its $1,800 for the heads, then you have to get push rods, rocker arms, head gaskets as AFR recommends two different specific head gaskets.  Ive seen GT40 heads picked up for under $1,500 rebuilt with new valves, seats, guides and springs.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
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Re: Exhaust options for 351W

ArdWrknTrk
Administrator
I don't have desktop dyno or any engine builder apps on my phone.
I can see the exhaust flow in the GT40's would be an impediment on a 351, but the runner volumes look good for torque.

I wonder how much is to be gained by grinding out the humps?
Maybe bigger valves if JY heads need a rebuild?
I know the 40's are pretty popular, and available mild to wild from rebuilders, relatively inexpensive.

Not sure how much Lightning headers cost, but those ports would be a big consideration for me if I even thought about going with with these heads.

Paul (Conanski) over on FTE was always good with Windsors.
Maybe ask him his thoughts.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Exhaust options for 351W

Rusty_S85
I believe the most ported GT40 heads I seen that were flow tested were still a good ways away from a good set of aftermarket heads out of the box.

Data I saw was GT40 heads with some port work flowed 225 cfm on intake @ 0.500" lift and 173 cfm on exhaust @ 0.500" lift using stock GT40 valves.

On Ford forums Ive seen home porting/polishing being done by individuals and seeing 213cfm intake and 163cfm exhaust.

I think with GT40 heads I think the max will be around 220-225 cfm Intake and 170 cfm Exhaust.

For the GT40P heads ive seen it claimed they can flow up to and over 240 cfm with full port work on the intake.  I dont know if I truly believe that as GT40 and GT40P heads have been made obsolete by CNC machined aluminum heads as they outflow a full ported stock head out of the box.  240+ cfm on intake on ported GT40P heads sounds a little too high considering AFR Rengade heads are 260 cfm intake out of the box.

I honestly thought about grabbing some lightning parts for my 306 build but dont think it would work out for me

DD2000 I actually got for free years ago when those filesharing sites were still up back in the 90`s.  So mine is quite old but I have learned how to use it and found it is pretty close when you put in accurate information.  Some times you have to tweak the Intake Center Line to get the valve timing to be correct.  You could punch in the valve timing itself but ive seen that actually result in a incorrect duration before, i see it more so on agressively ramped roller cams.

But the GT40 heads still are good street heads if you are not looking for all out power.  Can usually pick up a pair for around $1,200 - $1,300.  I justified it to myself by saying $1,800 is only $500-$600 more and I wouldnt have to spend any money on port work or adjustable valve train for my cam.
"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2
123