Should I mod the 302 or run the 390?

Strangler Brett · May 19, 2020

What's up, Stangnet folks? I'm hoping to get some opinions here, help me make a good decision! I'm in the never-ending process of restoring a 1969 Mustang GT Sportsroof for my son. As it stands right now, we have a 302 that runs well, with the following add-ons; Performer 4-barrel aluminum intake, Holley Sniper, WC T5 5-speed tranny into a 9" w/ 3.0 rear gears. The boy wants more power (no surprise!), so the plan for the next phase was to go with AFR Renegade 165 heads or Trick Flow 11R 170 heads, and a roller cam & link-bar lifters. That should put us in the 370-400 hp range, I think.

But now, we have another option. My father just gave my son the 390 FE that he built 10 years ago for a Torino GT that is now off the project list. So the engine has sat on the stand for a decade, having only been run on the stand. All rebuilt, but all stock. Has all accessories, new flywheel, clutch, pressure plate & bellhousing, and the full exhaust.He's tired of it taking up space that he needs for other projects, so he gave it to his little gearhead grandson. The 390 has a reputation for being a torque monster, but not a really strong candidate for hp. And is aparrently a gas-hog, to boot. Now, I have no personal experience in a Mustang w/ a 390, so I'm only aware of reputations. It's heavier, so we'd want to go with aluminum intake & heads (which would make it roughly the same weight as a 351, as I understand). And, although it's not the most important consideration, I'm not sure what the mpg difference would be between the stock 302/EFI, the updated 302/EFI, the stock 390/EFI, and the updated 390/EFI.

So, the question. Should we 1.) Continue with the 302 build & store the 390 away to maybe make into a stroker someday, 2.) swap mounts, radiator, crossmember, etc. and run the 390 as is, w/ iron heads & intake, or 3.) keep driving the 302 and upgrade the 390 (heads, cam & intake), then do the swap? And if you favor option #3, do you have a favorite combo of HCI for the FE? Trick Flow, Edelbrock, BBM? If it were you, what would you do?

Olivethefet · May 19, 2020

If it was me.... That 302 that you currently have would be pretty tempting. Good power. Reasonable gas mileage. Already in the car. I'd love to own a big block one day just for the fun noises it makes! But I would think that you would also have some suspension work to do if you dont all the aluminum parts to the 390. I think I would keep the 302 and then work up the 390 over time if you decide you have to have it in the car one day. I barely get by tinkering with my fox, so I got no recommendation on HCI only an opinion on what I would do.

wicked93gs · May 20, 2020

I don't know what you mean the 390 doesnt have a good reputation for power...maybe stock they are anemic...but a 302 will split the block at 500HP(or less)...no chance of that happening on a 390.

How We Got Over 500hp from Ford's 400M Engine - Hot Rod Magazine

Check out how this Ford 400M engine was able to put out over 500hp with Ford, Chevy, Mopar, and Aftermarket products.

www.hotrod.com

Here is an article on the 400m...no one's idea of a performance engine....they built it quite easily to 500+HP. When you are talking modifying an engine, it really doesn't matter what you start with, you can always get more power, up to what the block can handle at least. The real decision here is torque...the 390 will always out-torque the 302 mod for mod(and probably out-power it mod for mod too). There is a reason they say there is no replacement for displacement....gas mileage will be atrocious of course...but it always is on big blocks. Everyone and their mother has a 302....the 390 is a much less common engine to see.

Strangler Brett · May 20, 2020

wicked93gs said:
I don't know what you mean the 390 doesnt have a good reputation for power...maybe stock they are anemic...but a 302 will split the block at 500HP(or less)...no chance of that happening on a 390.

How We Got Over 500hp from Ford's 400M Engine - Hot Rod Magazine

Check out how this Ford 400M engine was able to put out over 500hp with Ford, Chevy, Mopar, and Aftermarket products.

www.hotrod.com

Here is an article on the 400m...no one's idea of a performance engine....they built it quite easily to 500+HP. When you are talking modifying an engine, it really doesn't matter what you start with, you can always get more power, up to what the block can handle at least. The real decision here is torque...the 390 will always out-torque the 302 mod for mod(and probably out-power it mod for mod too). There is a reason they say there is no replacement for displacement....gas mileage will be atrocious of course...but it always is on big blocks. Everyone and their mother has a 302....the 390 is a much less common engine to see.

Oh, I understand the potential for HP is there, just not relative to weight in the opinion of some who advise to build a small block. What was appealing to me was the idea of simply swapping the crank for a very simple stroke, changing heads and intake (possibly cam), and surpassing 500 hp very easily. That's a hard & dangerous target with a 302. With an aluminum top-end, the weight difference would not be that bad. I'm just wondering HOW bad the fuel economy would be. I'd hate to spend time & money on an upgrade that ends up dissuading us from road trips. 331 & 347 strokers seem to be reasonable balances between power & economy. Not sure what a top-end swapped 390 or 410 would look like.

wicked93gs · May 20, 2020

Strangler Brett said:
Oh, I understand the potential for HP is there, just not relative to weight in the opinion of some who advise to build a small block. What was appealing to me was the idea of simply swapping the crank for a very simple stroke, changing heads and intake (possibly cam), and surpassing 500 hp very easily. That's a hard & dangerous target with a 302. With an aluminum top-end, the weight difference would not be that bad. I'm just wondering HOW bad the fuel economy would be. I'd hate to spend time & money on an upgrade that ends up dissuading us from road trips. 331 & 347 strokers seem to be reasonable balances between power & economy. Not sure what a top-end swapped 390 or 410 would look like.

That would depend on power output...but built for 500HP...I am sure a big block would be somewhere around 8-12mpg, unless you use a turbo to get there, then you might get as high as 17mpg if you can keep your foot out of it.

Strangler Brett · May 21, 2020

wicked93gs said:
That would depend on power output...but built for 500HP...I am sure a big block would be somewhere around 8-12mpg, unless you use a turbo to get there, then you might get as high as 17mpg if you can keep your foot out of it.

Man, I'd be all over that big block for 12 mpg! I have a 1995 Jeep Wrangler with a 4 cyl as my daily driver - it's an engineering marvel! No power AND god-awful fuel economy! I bet it gets 14-15 mpg tops. Highway! A 500 hp big block at 12 mpg? Sign me up all day long!!!

wicked93gs · May 21, 2020

haha....again, assuming you can keep your foot out of it, you might see that mileage. I base this off of an 8mpg 500HP SBF(351) a neighbor of mine once had though....so mileage should be similar assuming a similar volumetric efficiency

mrspeed · May 23, 2020

The 390 for the cool factor but IMO your best bang for the buck is a stroked 351. You can get a 408 Windsor for fairly cheap and have small block weight and big block power.

Adieu · May 23, 2020

If the car already has and is already set up for a Windsor, keeping a Windsor in it makes sense. To replace it with a 390 is a lot of work and money for very little gain. Sell the 390, use the money to build your 302 or buy and build a 351. Getting to 500hp with a 351 is nearly child's play, it can be done with a bolt-on kit from Edelbrock. 500hp on a 302 is doable, but you're pushing the limits of the engine.

wicked93gs · May 23, 2020

Back in the 60s, the 390 was most certainly considered a great performance candidate...but 74stang2togo is correct...a 351 might be what you want. FEs tend to be more expensive to build. I personally always wanted to build a Clevor myself...maybe one of these days. In the end, you should build for the most efficient way of reaching your goals. If your goal is 400HP(I no longer truly care about the top HP in my cars...been there, done that often enough) then a 302/351 is the way to go, but you could just as easily go the 390 route since you have the engine...the fact that it is a gift to your son that he is unlikely to use in another car has to mean something after all. The first question you should ask though...is why does your son need more power anyway? How old is he? How likely is high HP to get him or someone else killed because he gets into a street race?

Neuron · May 23, 2020

Had a 1967 390 GTA, smoke would come off the front tires during tight turns. Best compromise was my 1970 Cleveland 4 bbl., faster than the GTA and handled nicely. My 1967 289 GT toploader I miss the most, the handling with a few mods was fantastic. I would sell both and build a 351. Or keep the 302 and mod it. The 390 was Ford's band aid until the 428 CJ in '68 1/2, great in trucks and T-Birds though.

rbohm · May 24, 2020

personally i would build the 302 for the mustang, as i tend to prefer a balanced car that can go around corners. that said, the 390 is a excellent engine to build for performance, many racers are still using them, as well as other FE motors, in drag racing and doing quite well with them thank you.

yes the 390 is a heavy motor, all big blocks are, but with a set of aluminum heads and an aluminum intake, and suddenly the weight is down to that of a fully dressed 351w with iron heads, and that makes a big difference. and of course you can add fuel injection to the FE and improve fuel economy as well. it wont get the same economy as your average econobox, but it will approach the economy your modified 302 will get.

either way remember that building an engine requires a systems approach. you decide first what you want from the engine, where teh engine will spend about 80% of its time when running, and then select parts that fit that build parameter. for instance, if the engine is going to spend 80% of its time in the 1000-5500 rpm range, then pick your parts to work best in that range. choose wisely and you will be amazed at how well your engine build performs when done and tuned.

2Blue2 · May 24, 2020

The crowd chanting
BigBlockBigBlockBigBlockBigBlock

Just do it! your only young once, plenty of time for sensible shoes later.
390 is a great street motor and its paid for!
Every one here would give their eye teeth to have had a big block 69 when young

stormsedge · May 24, 2020

I've seen plenty of strong running 390 street cars, without getting bogged down in mythical HP guesses. BUT, if your Mustang is not an original 390 car, I'd stick with whatever is in the car x best cubic inch block.

mrspeed · May 24, 2020

Keep in mind that while a 390 with aluminum heads and intake will approach the weight of a 351 with iron heads, the 351 with aluminum heads & intake will approach the weight of a 302 with iron heads (may even be less). My 67 GTA has a Windsor and of course the air cleaner says 289 and most people don't even know the difference. I once got a big laugh from racing a co-workers recently restore high dollar 57 Chevy with a 383 and showing him my tail lights. =) He was crushed that his stoked small block Chevy got smoked by such a "tiny" SBF. I waited about a week before I let him off the hook LOL. My vote is still a stroked Windsor. Cheap to build, fits anywhere a 302 does, has big block power and can be passed off as a 302 to the average Joe. Your existing setup is already for a SBF so your motor mounts, transmission and most engine accessories will work with a Windsor.

Strangler Brett · May 26, 2020

wicked93gs said:
Back in the 60s, the 390 was most certainly considered a great performance candidate...but 74stang2togo is correct...a 351 might be what you want. FEs tend to be more expensive to build. I personally always wanted to build a Clevor myself...maybe one of these days. In the end, you should build for the most efficient way of reaching your goals. If your goal is 400HP(I no longer truly care about the top HP in my cars...been there, done that often enough) then a 302/351 is the way to go, but you could just as easily go the 390 route since you have the engine...the fact that it is a gift to your son that he is unlikely to use in another car has to mean something after all. The first question you should ask though...is why does your son need more power anyway? How old is he? How likely is high HP to get him or someone else killed because he gets into a street race?

Oh, he'll never drive the car, barring a miraculous medical advancement. He has Lesch-Nyhan Syndrome, is in a wheelchair, and has poor motor control.

The car is everything to him. All he asks for on Christmases and birthdays is car parts and mustang diecast cars. We drive the car 4-5 times per week, so we want to stay streetable and have at least SOME kind of decent mileage, but Nino wants more power because he has some things he wants to do. Nino wants us to take his car to the drag strip (just for fun, of course), and what he REALLY wants more than anything is to take his car to California and drive it at Laguna Seca. So if Nino wants a "go-fast car" that's worth doing that in, that's what I'm going to give him.

Strangler Brett · May 26, 2020

mrspeed said:
Keep in mind that while a 390 with aluminum heads and intake will approach the weight of a 351 with iron heads, the 351 with aluminum heads & intake will approach the weight of a 302 with iron heads (may even be less). My 67 GTA has a Windsor and of course the air cleaner says 289 and most people don't even know the difference. I once got a big laugh from racing a co-workers recently restore high dollar 57 Chevy with a 383 and showing him my tail lights. =) He was crushed that his stoked small block Chevy got smoked by such a "tiny" SBF. I waited about a week before I let him off the hook LOL. My vote is still a stroked Windsor. Cheap to build, fits anywhere a 302 does, has big block power and can be passed off as a 302 to the average Joe. Your existing setup is already for a SBF so your motor mounts, transmission and most engine accessories will work with a Windsor.

The 408 stroker or 347 stroker was ultimately what we planned to do. Then we were gifted the 390. I don't think it would be appropriate to sell what Nino's Papa Fred gave him, so selling the 390 to buy & build a 351-based stroker isn't in the cards right now.

mrspeed · May 26, 2020

OK - totally understand that! A 445 stroker can be built from a 390 and would be a beast! With Aluminum heads and intake with a roller cam and possibly fuel injection if the budget allows. FE's sound incredible too.

Strangler Brett · May 26, 2020

mrspeed said:
OK - totally understand that! A 445 stroker can be built from a 390 and would be a beast! With Aluminum heads and intake with a roller cam and possibly fuel injection if the budget allows. FE's sound incredible too.

We already have a Sniper, which will work fine up to 600 hp, so fuel injection is already a done deal.

Adieu · May 26, 2020

Strangler Brett said:
Then we were gifted the 390. I don't think it would be appropriate to sell what Nino's Papa Fred gave him, so selling the 390 to buy & build a 351-based stroker isn't in the cards right now.

Alternative take: Find an older Ford pickup (pre-1980) and drop the 390 in that. 390s make excellent truck motors in stock form, and he'd have Papa Fred's engine AND something useful to run around in to pick up parts, move furniture, etc.

Should I mod the 302 or run the 390?

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