FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: cheeser on December 29, 2025, 08:57:14 PM
-
Cheers,
I'm picking up a stock 68 S code 390 Mustang, and planned to keep the stock heads with thermactor pump and exhaust to maintain the external looking originality, but CJ exhaust manifolds may be an option. I know this dramatically limits options and potential HP increase. I wanted the BT intake to help drop some weight off front end, but it appears it doesn't have the correct ports to maintain the original PCV balance tube system.
This would be primarily a car for cruising and car shows due to its originality, but would like a bit more power (who doesn't). I'm just gaining some input before working with someone on the rebuild in 1-2 years.
With those limitations, can I gain much in power (cam, head port?, etc.) in the event I do a future rebuild? I assume I'd be lucky to pick up another 50hp.
-
Cam change, modern piston/ring change, port heads, recurve distributor, there's all kinds of little tricks. I'd think you could pick up more than 50.
I did a 390 for a Thunderbird several years back that made 390-400 hp without port work, had a small-ish cam, etc.
-
I think the F-427 edelbrock intake has the same PCV system as the original intake. And it’s a good manifold.
-
Stangman,
Thanks for the info...I didn't know about that option. In the end, didnt know if a intake change was of much benefit for my situation.
Brent,
Thanks for the updates as I consider this for the future. My main drawback is in how much originality I want to maintain vs how much additional power I really want/need.
-
I bet that intake is 15 horse with that change alone
-
Stangman,
Don't you think the F-427 intake has too large a plenum for a 390 displacement motor? The "police Interceptor" intakes (or a/m copies) would likely work better due to a smaller plenum and the same PCV hook up ability (like the F-427 intake).
Mike
-
I don’t really think so Mike. IIRC the ports aren’t much bigger although the plenum is bigger. In the original post he does say he would like to install a cam. Even if he does a stock rebuild with better pistons like Brent says and a very reasonable compression of let’s say 10 to 1 with a more modern camshaft that manifold would be perfect. Stick a 600 or 735 carb on there and even with stock exhaust gotta be 375 HP and torque would be up to. I don’t think he’s looking for a lot just a good reliable motor with a little more bite.
-
Stangman,
I think you expressed it better than I did…a good reliable motor with a little more bite. The options Brent mentioned appear to fit the bill.
I was originally looking at the PI intake as it appears to have the same PCV setup with a similar balance tube.
If it wasn’t for the originality of this car, I’d do more and splurge on better heads and install the FPA headers. When opening the hood, Id like it to look stock.
-
If the police interceptor keeps it more original and you can use more of your stock equipment then it sounds like you will be happier that way. You have to do it the way you want it because in the long run the more you change it the farther away from stock looking it will be. That F-427 intake has that PCV tube though.
-
Hey there Stangman,
I just based my thoughts on the performance and longevity aspect. Thinking of when opening up the carb quickly with a smaller motor and a big plenum, there would be a considerable power bog at the start. I know this could be compensated for some with a more aggressive accelerator cam. Or a larger pump, but that could wash the cylinders more and could be a problem sooner than later. To be clear as I can on that thought, I’m not saying in a thousand miles the combo would ruin the engine! But it could shorten the life by 20,000 to 40,000 miles in comparison, in a longevity consideration.
I’m just keeping the conversation going for us to think about thus stuff. And in all fairness, Jay’s book stated the most power a 390 made was with an old school Streetmaster with plenum work and a 1” open spacer. That is an argument itself with my F-427 theory if you think about it…. That all said, the Streetmaster intake will not look original(!!) , and does not have the PCV hook-up provision.
Mike
-
After reading your post(s)…….why wouldn’t you put ported iron Cobra Jet heads and an iron Cobra Jet intake manifold on it? It could retain the smog lines and the OE pcv plumbing. You could do that, and a 445 rotating assembly which you cannot see, a well designed hydraulic roller cam which you cannot see, and CJ manifolds, and have a real runner. I did that for a guy a few years ago and it was real good and looked bone stock as a billy goat’s hind end.
-
CaptCobrajet,
That's always an option in using the CJ heads/exhaust/intake and stroker, but I'd like to see what could be done with what I have to help save on costs. A good rebuild and having it tested/broken in on dyno is already going to be expensive.
I think my driving style with this car will be fine with another 50-75hp, but will keep options open on mods you suggested that maintain that stock look.
-
I like Blair’s idea, if you really want to play with them get a good 427 or aftermarket block and add a big bore to the package. Most people who look at FE engine compartments don’t have an idea what it is or how original it is. Just paint it all Ford blue 😁
-
Yes Blair’s idea would be great and you wouldn’t see the mods and it could still pass for stock it just sounded like the original poster wasn’t looking to spend that much. Now being that he does want a reliable engine with newer parts inside a stroker kit would be a great idea.
-
Once the car arrives, I’ll have a better idea in how the current power level works for me. I’m in Colorado at around 5700’ and will lose power. I will have to tweak the carb a bit, and will pull the distributor and have it rebuilt/recurved if needed.
FYI-this a 56k mile engine and has never been pulled apart, but I trust the seller in being a well running engine. I went into this purchase thinking I may have to freshen the motor at some point (leaks, non-hardened valve seats) simply due to age, and while in there, make some changes to boost power a bit.
I know costs can quickly escalate as changes are made, but will work that with an engine builder I will need to find for a good “bang for the buck” configuration…thus reason to temper my expectations. Stroking to 445 is a consideration, but will need to see how that impacts costs.
Ive had variety of cars over time (2013 Mustang with 607 rwhp, 62 Galaxy with the 406/405hp motor, and a 71 Mach 1 with 351C-4V) and enjoyed their power, but know I won’t drive this car in the same manner as those.
After thinking about this for a bit, I’m tempted on using the FPA headers but understand I need to determine if I’m keeping stock heads, or migrate to the 428 heads while keeping existing thermactor system. I’m hesitant on installing headers now due to fear of breaking exhaust bolts and would probably wait until engine build.
Thanks for the groups input.
-
If your engine is truly a 57K mileage and never been into, then you should definitely think about changing the camshaft timing gears and chain. You can still find C6AE-9425-H aluminum intakes and C7AE-F intakes with the thermactor tubing holes and remove about 50# from the engine. 735 cfm Holley and FPA headers, and 2 1/2" exhausts and call it good for the street. Joe-JDC
-
Joe,
I’ll look out for C7AE-9425-F intake if I can find one for a reasonable price. They appear to be similar with PCV balance tube hookups as the S code intake, but tube is slightly different.
-
For me, if it was that original I wouldn't mess with it, especially if you are going to get into it in a couple years. I'd get the carb and timing dialed in, and I'd put a decent exhaust on it, meaning some larger pipes and mufflers of your liking, with the stock exhaust manifolds. You want it to feel more responsive put some 3.50 gears in the back and call it good until a time you want to really dig into the motor.
-
For me, if it was that original I wouldn't mess with it, especially if you are going to get into it in a couple years. I'd get the carb and timing dialed in….
That was my thought for now regarding carb and timing…just getting it dialed in for now. I may send the carb out to Air Fuel Spark for a quality rebuild, and distributor our for recurve.
I’m just gathering ideas in the event I want or need to do a quality rebuild in 1-2 yrs, and start gathering some parts.