I have a '67 mustang coupe with a 289 V-8. It has an Edelbrock Performer manifold and matching edelbrock performer 4bbl carb. It is an automatic. The car runs great but seems to top out at about 75-80 mph. A buddy of mine thinks it may have to do with the fuel delivery system.
Two questions: Does anyone know what the proper compression should be for a 289? I tested all cylinders yesterday and want to know if they are low or average.
Secondly, Any ideas on why this thing is not doing 120 or at least 110 mph?
Any gearheads who might have experienced something like this? Let me know what you think.

 

your kidding right? these cars were never ment to see those speeds.........not trying to sound rude....just honest. If you are hitting 75-80mph and still have control of the car you are in good shape. I am interested to hear the pro's respond here.

 

What is the ratio of your gear set?

 

i got it figured out he is looking at the numbers on his speedometer. hes probally wondering why his car wont reach 140.

 

like they said, these cars are not meant for anything faster than highway speed. they could do 100+ but you need a lower gear set on your rear end, im guessing its like a 3.00 or 3.25 which isnt too bad, but with a 3spd Auto, thats all you can expect. the maybe with a few more mods to the engine you can expect a slightly higer speed, but the easiest thing to do is spend like 150-250 on a new rear end gear set and lower it down to like 2.5. only prob is the lower the gear the worse your accleration is going to be

 

are your rpm's really high at 80??? if so, you may have really low gearing. If not, it sounds like you aren't getting enough fuel.

"these cars were never ment to see those speeds"
I'm not going to encourage this guy to go faster, but i have a 289 with an auto and still have plenty of juice left at 80.

 

red.....what suspension upgrades have you done where you can suppot that speed? i have a 289u auto as well....stock suspension at the moment and I do not have fun at that speed. I am getting ready to upgrade/rebuild the spring seats, upper arm bushings, link pins and strut bushings. Also considering strut bar/monte. Any tips?

 

i previously had mostly stock suspension other than bigger sway bars and gas-a-just shocks. I have brake equalizers installed near the master cyclinder that helps keep the car straight when braking.

i say previously because my car is currently in my driveway with half of the suspension torn off. i am replacing damn near everything in the front end. your car probably feels bad at speed because of the steering box. I know that's the weakest link on my car right now. Next stop Flaming River and SSBC brakes!!!!

 

You folks that think a stock 289 with a 4 barrel should only do 75-80 on the highway are smoking something. Even a stock 289 2V with just about any stock gear set should do 100 easy!

 

check you throttle linkage compared to your gas pedal. Sometimes you are reaching the floor with your foot before the throttle is open fully.