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Discussion Starter · #1 ·
Hi all, new member (Lou)

I’ve been working on my wife’s 65 coupe for 3 years. About 95% complete. I’d like to get a little more hp out of the rebuilt stock 289. Already has edelbrock performer intake and 500 cfm carb and magma flow exhaust. Suggestions greatly appreciated.
 

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Welcome, & x2 on some pics. When it was rebuilt did you use a stock cam?.
 
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Your biggest semi-easy mod will be to swap the cylinder heads. After that....cam.

You'll need to do a little research with the heads though. The stock heads have 54 cc combustion chambers, so you'll want to stay close to this to NOT kill your compression ratio. Also, some stock pistons will hit the larger valves in aftermarket heads because they don't have valve reliefs.

One fix to both issues is to replace the pistons at the same time with something like a KB116. I had AFR 58 cc heads (AFR165) on my 289 and it ran great with them and a mild performance cam. Those heads and pistons work out to right at 10:1 CR on a stock bore 289 IIRC.
 

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67 Fastback T5 331 TCI Frt End, Canted 4 link rear susp
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Hi Lou, welcome. An "easy" way to get more "fun" from your Mustang is changing the rear end gear ratio. While it doesn't add more power, it can give your car more "zip" which can have the same effect. Tell us more about the car as far as current gear ratio, engine / trans, and what type of driving (around town versus highway) that you do.
 

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1970 Sportroof Mustang Grabber Value Package
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Welcome and ditto on the pics
 

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Discussion Starter · #9 ·
Thanks for the reply’s

I did change the rear gear to 3:10 with posi and it has a rebuilt C4 transmission. I was thinking about changing to aluminum heads with a cam but I read it might be a waste of 2k for a daily driver. I’m also thinking maybe put some header on it. Idk.
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67 Fastback T5 331 TCI Frt End, Canted 4 link rear susp
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Headers alone may not be very effective, since the heads are probably a bigger restriction for flow than the exhaust. Tough decision as far as what upgrades you can do to a stock motor, and when it needs to come out to go to the next level. Like you mentioned...where's that point on a daily driver.
 

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When I first bought my 65, it had a Holley 2bbl carburetor on it with a dual exhaust using stock exhaust manifolds. One long road trips, I would get 25+ MPG on it, and it was my daily driver. Everything else on it, as far as I could tell, was stock.
 

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1966 289 3-speed
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Welcome and nice car!

Yeah I don't think there's more you can do short of heads and a cam as mentioned. And to me that seems a little much for a driver. But its your car so have at it.

Also, headers by themselves wont add much if anything with stock heads.
 

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The Edelbrock Performer intake is no better than stock other than being aluminum.
Performer RPM would have been a better choice, or air gap if would fit.
 

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Discussion Starter · #14 ·
Thanks for the information guys. I call it a daily driver because I like to drive it regularly and my work is only 6 miles away and no freeway. Not concerned about gas mileage. What heads and cam would work best with a stock bottom end? Should I also do headers? Long short or tri y?

thanks again for all the help!
 

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If your plans include headers, I suggest you avoid the long tubes as they typically hang pretty low and may scrape speed bumps, driveway aprons, and other road hazards encountered on the paved streets here in the Golden State. The tri-Y models usually tuck up inside the front frame rails thus clearing the road "hazards" present in your daily commute or cruising route.
 
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^^^^^ that’s why I chose tri-y’s , it was that or cast iron hi-po’s.
 

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The tiny exhaust ports were the restriction on the stock 289 heads. "Porting" those exhaust ports would add as much power to a basically stock engine as aluminum heads.
 

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1966 Mustang 289/306 3spd coupe, 1966 Mustang 289 C4 coupe, 1965/64.5 Mustang 289 4spd convertible
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Hi all, new member (Lou)

I’ve been working on my wife’s 65 coupe for 3 years. About 95% complete. I’d like to get a little more hp out of the rebuilt stock 289. Already has edelbrock performer intake and 500 cfm carb and magma flow exhaust. Suggestions greatly appreciated.
While not a huge power gain, a carb spacer could be an easy to install and budget friendly add on, if you can tune for it.
I also agree on a rear gear change, however it sounds like you added 3:10 already. For a 6 mile commuter car, something deeper could yield better "push you into the bucket on take off" feel. Headers and exhaust would be the next suggestion. Long tubes will give you the most HP gains, but mostly at higher revs. Tri-Ys will also gain HP, but work best for low end torque as the design improves exhaust scavaging. Performer intake is the baseline upgrade. As someone stated, a performer RPM or air gap will yield more, but anything that helps the 289 breath in and out more with less restriction will gain output, and anything that will support an upgrade will yield more. Which is why it's rare to see someone install aftermarket heads and then re-install the factory cast manifolds (non-hipo) into the single pipe muffler system. Just my $0.02
 

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1966 Mustang 289/306 3spd coupe, 1966 Mustang 289 C4 coupe, 1965/64.5 Mustang 289 4spd convertible
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I also noted the engine picture shows the car has P/S, if you decide to add headers at some point, different bracketry, or P/S compatible headers would be needed.
 
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