390 or 428 build for a '69 mach I?

[70SWGR]

Hello,
I'm trying to get some information for a friend.
Sammy owns a '69 mach I 390/4sp and will pull the numbers matching 390.He wants to build a stout 390 or a 428 and already has a 390 out of a truck.Can anybody suggest what would be needed for 400 to 450 hp?Are there aftermarket 428 cranks?

 

[D.Hearne]

Yea there's aftermarket cranks out there now ( Scat I believe) but they're damned expensive at about $500 a pop. That doesn't include all the other prep work needed to use it though. The 428 stroke ones use the stock rods, and there's, I think, two other stroke sized cranks that use aftermarket rods. For the cost involved, I personally, don't see the benefit of a crank with only a 2 tenths longer stroke, unless someone gave me a good 410/428 crank to start with. To get 400 hp with a 390, is fairly simple. Just requires a 10 to 1 comp ratio, a little port/polish work on the stock heads, a bigger cam, a better intake ( like the factory 428PI intake) a 750 carb and headers. And that in a Mustang is a handful. I've had both a 390 and a 427 in a 67 Stang and the 390 was streetable enough for everyday driving, but the 427 wasn't. The 427 was an awesome motor though, but just not something you'd want to put up with everyday. ( they love to break parts and consume high octane gas)

 

[70SWGR]

Would the edelbrock heads be worth the cost over rebuilding the stock heads?
Are there any lightweight forged pistons you would recommend to make the a quicker revving 390?
On the rods just resizing with new bolts?
What cam?

I know Sammy wants this car to run deep in the 12.0's plus be street driven.He has 4.11's in the car now but I'm not sure if he will stick with that gear or change to a 3.89 or a 3.5.

Opinions welcome!

 

[D.Hearne]

If his heads need springs, guides,valves and seats, the Ed heads are a good trade off. With the rods, just have em resized and install ARP bolts. They're good to 6500-7000 grand there. Cam ? That's going to be his personal choice there and how high he wants to rev it. Anything with a 290 degree ( advertised) and .500 lift is going to get you ( close to at least) 400hp, with either Edelbrock or ported stock heads. My 67 ran high 13's with a pretty much stock GT 390 with a 4 speed and 3.00's out back. Pistons? I wouldn't worry about it reving faster. If he wants that, just use an aluminum flywheel.

 

[Timmy]

Here’s the 390 I just built and dropped in my 69 “S” code Mach 1. I dropped it in a few weeks back. I got advice from D.Hearne and others. I was shooting for the 400hp mark. Don’t know if I made it or not but it sure runs strong. The cam I’m using make power from 2200-5200. Figured that was good enough for an A/T street car. I may have gone with something different if I had a 4 speed.

I ended up with:
390 block .040 over decked to zero
oiling mods (chamfered oil feed holes)
Standard 390 crank with 10/10 grind
SpeedPro forged pistons
Rods reconditioned
Compression is just over 10:1
Crane cam 343801 Hydraulic Flat Tappet, 114 lobe separation Duration 278/290, Lift .548/.580
Crane adjustable rockers
Crane pushrods and lifters
New rocker shafts
Ebrock RPM heads (.090 restrictors installed)
Ebrock PRM intake
Ebrock water pump
Windage tray
HV oil pump
ARP bolts through out
MSD 8595 distributor (has vacuum advance)
MSD high vibration coil
MSD 6AL (6000RPM limit chip installed)
Hooker Super Comps
Top off with a Holley 770 Street Avenger

 

[D.Hearne]

Not having detonation problems with that 114 LSA cam are you? Seems like a wide LSA for that much compression. But then again that's about what the Z303 roller I have in my 331 is also and it, combined with the 10.4 to 1 ratio, it's happy with 93 octane , maybe a tad less in a pinch.

 

[Timmy]

It's good to go so far but it's on a 93 octane diet. I haven't ran it too hard yet. I'm still tuning on it. Playing with timing and such. I'm setting at 14 initial and all is good. The powermaster starter spins it when hot with no starting issues. I may move up to 16 this weekend and see how runs.

 

[D.Hearne]

Had fun with the headers? I think that if I had to do that again with a big block 67-70, I'd spring for the few extra dollars FPA tri-y's would cost. I've dealt with Hookers in my old 67, and the FPA shorty's on my 68 Merc's 390 have been trouble free. Ain't had to touch them in the two+ years they've been there.

 

[Timmy]

The headers were a nightmare both taking them off and putting them back on. I got lucky and only had one bolt that was stuck. Took two days or soaking it in PB Blaster to get it out. If they had not been in good shape, I would have gone with the FPA’s