Thoughts on 390 engine performance? 1968 Mustang GT - Ford Mustang Forums
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post #1 of 38 (permalink) Old 11-30-2007 Thread Starter
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Thoughts on 390 engine performance? 1968 Mustang GT

I'm looking at a 1968 Mustang GT that has a 390 engine. What kind of hp and performance should I expect out of this engine and car? What kind of hp can I expect?... What can I do to upgrade it? Can I stroke it? If so, to what? Or should I just replace the 390 with another engine? Thoughts? Ideas?

P.S. Looking to get about 400 to 425 hp

Thanks,

Jadi
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post #2 of 38 (permalink) Old 11-30-2007 Thread Starter
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oh one last q... should i expect the same upgrades needed on this car as would be in a car that gets upgraded from a 302 to a 351?
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post #3 of 38 (permalink) Old 12-01-2007
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Yes using a bigger engine you have to make sure the car will take it.The 390 is junk to me small displacement and lacks power id use a 429/460 over any fe any day.400hp is easy with a 302 stick with a small block there cheaper to build.
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post #4 of 38 (permalink) Old 12-01-2007
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try placing a 428 crank in it (in your 390)... You may be able to bore your 390 to a 428 but I would be careful often the walls are too thin so I would just bore .30 over and change the crank out and then hit the top end ideas I mentioned, you will end up with 410 cubic inches about and that is a pretty ggod performer. You will want to probably go with an alum top end as well, unless you want that original look. I just a built a 428 for my s code and with 9.5 to 1 pistons, mild cam, carb 850 by demon, alum edelbrock heads/intake I am at 403hp and 488 in torque. Hope that helps Ask any more questions if you want-Edward
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post #5 of 38 (permalink) Old 12-01-2007
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The 390 in stock trim is a slug, but it has a lot of potential. Ford, true to form, saddled the 390 with junk heads. With a set of low/medium riser 427 or CJ heads and appropriate camming, intake, carb, etc., the motor wakes up and will run with any BB (396) Chevy. The 428 crank swap is a good way to get a few extra cubes too, with a little work the 390 can be a good motor.

The early 60's 390 Tri-Power Hi-Po was rated at 401 HP but they figured HP a bit different back then but it shows that 400/425 HP is very doable

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post #6 of 38 (permalink) Old 12-01-2007
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If its a true gt id do nothing to it just lock it up in a air tight room for 10 years then sell it.
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post #7 of 38 (permalink) Old 12-01-2007
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I'm not sure what some of this guys are thinking of, the 390 came with 320hp stock (that's what Ford told us), I sure with some mild !!!! changes you could get 400 +. Some of these guys are driving v6 & saying the 390 engines a slug!!!! Also racing rice burners??? I've got a 390 stock & it burns the tires thru 2nd gear

Last edited by Bob A; 12-01-2007 at 11:52 PM. Reason: lack of info
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post #8 of 38 (permalink) Old 12-02-2007
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Id never own a 4 or 6 banger mustang there slower then a import.The 390 needs better heads to make good power.
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post #9 of 38 (permalink) Old 01-20-2008
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well it depends on the 390 if it has the gt heads then they just need a little porting but I Have seen a lot of 390 engines that have pushed into the 500 and 600 range in horse power although at that point you want to see about having the block cross drilled so that it will keep the block from splitting
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The 390 mustang will run 14.50s in the quarter, stock, That’s what mine did any way. A 428 SCJ cam, 750 Holley, and 3.91 gears and it ran 13.50s.
Putting a 428 crank in a 390 is a little more complicated than just putting the crank in, The stroke is longer so the rods and pistons will also need to be replaced. And 428 cap screws for the rods, or the 390 type nuts will hit the block, and when replacing a crank the rotating assembly has to be balanced with the harmonic balancer and the flywheel.
The 390 looks great and sounds great, It's also heavy and gets baaaaad gas mileage, and wont make any more hp than a 302/351, The parts are hard to find and expensive for a 390 compared to a 302/351.
In the end it's up to you.
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There is the ? of what you want out of your motor first? As for my opinion the FE motors are better off in a truck really. But the most power i have seen out of one is not shabby at all 678 h.p. all motor single carb. and that is from the 2006 Engine masters competition. Note: the big boys on the block lol. But also remember FE parts are more $$$ and harder to find than small or big block Ford everyday motors. Not to put the FE's down but not the most power best build. But this is just my 2 cents lol not my car or project.
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Quote:
Originally Posted by Mustang Nazi View Post
Putting a 428 crank in a 390 is a little more complicated than just putting the crank in, The stroke is longer so the rods and pistons will also need to be replaced. And 428 cap screws for the rods, or the 390 type nuts will hit the block, and when replacing a crank the rotating assembly has to be balanced with the harmonic balancer and the flywheel.
Not quite right...The stroke is longer but the rods are the same. There were only two different length rods used in the FE. The first was 6.540 in lenght and used in early FE's (332,352,360 & 361 cid). The other measures 6.488 and was used in the 390, 406, 410, 427 & 428 cid motors. Swapping a 428 crank into a 390 is as easy as swapping the crankshaft, in fact that is exactly what Ford did to get the 410 Merc engine, There should be no clearance issues with this swap.

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I would spend the money on the 390 for nostalgia reasons. The car would be worth more money with the original block and engine type. If it was mine I would make it look somewhat stock under the hood and get the heads worked and maybe add some displacement if its cost effective. Also get the power to the ground with a limited slip rear end and aggresive gear ratio. Those cars are worth big bucks because that is what the original Bullittt car is so please don't totally resto mod it....

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I love FE's but just for those that don't believe that the 390 Mustangs were slugs in stock trim here's some numbers to chew on...

In December of 1966 Motor Trend road tests ran a GTA 390 Mustang the numbers were; 15.6 1/4 mile @ 94 mph

Motor Trend earlier ran a 66 289 auto (I assume it was an A code);
15.7 @ 89 So thats a 289 with numbers close to a 390.

And for you HiPo fans, in October of 64 Car and Driver squeezed a 14.0 @100mph out of a K code (4:11 gearing)

That stock 390 wasn't all that impressive, but it will respond nicely with some basic speed parts.

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P17
Your right and wrong. The rod length is the same but because the 390 block is not notched like the 410 the 390 type rods that have a nut will hit the block. the 428 used cap screws like the 427 except the 428 had a shorter head. There were two kinds of cranks used for the 428, a cast crank , that was in all 428s except the SCJ, and a forged crank used in the SCJ.

and you said "In December of 1966 Motor Trend road tests ran a GTA 390 Mustang the numbers were; 15.6 1/4 mile @ 94 mph"
The motor trend test was with a 4 speed with skinny tires, the times you post were correct but no traction and no power shifting relate to the high number for the ET. My 390 Auto would run 14.50s easy. After I put some L-60-15s.
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