85 mph brick wall

[67coupestang]

wow didnt mean to start such a riot! but anyway. more specifics... The car WILL do more than 85, but not in 5th gear, Im pretty sure its the 750 just bogging out, thats what it sounds like, the motor is a recent rebuild from a late 70's t-bird, so its healty, not performance built (cam and heads). at high rpms and just off the line without wind resistance i have no complaints torguey as hell!! I guess i pretty much figured the problem just wanted to rant...

 

[skywalker]

750 cfm could do that if you motor isn't built for it...i have a 289 and the only majorengine change i have is intake...i have a edelbrock 650cfm 4bbl, You might want to change out that carb and see what happens.

 

[dodgestang]

Wow....I can't beleive this post took a gearing turn. It is unlikely and unless you are pulling like 1000 RPM or less in OD at 85....its not a gearing problem. If you have ever had your setup dynoed you would have a power curve and you would be able to confirm on the chart that you are still in the car's power band when you are at speed in OD (which you are most likely just at the bottom of the power band)

With that said....silly questions but....

1. Confirm you are really getting a full throw on the throttle. With car off look down carb throat and have some one IN THE CAR floor it with the pedal so you can visually inspect the primaries are opening all the way.

2. Are your secondaries opening? I just took a 770 VS of my mustang that sometimes the secondaries would stick and not open. The car would essentially just stop at 3500 RPM and not be able to go anymore (because it wasn't getting enough gas). I switched to a new carb and that problem was fixed. Along those lines...have you put in a new fuel filter to make sure it isn't a clogging issue?

3. Have you confirmed there is no vacuum leak? If you have a small vacuum leak with the RPMS you pull in OD you might not have enough vacuum to actually open the secondaries (pulling at straws here now ) while unlikely it is plausible.


And for the record....my CLEVELAND stroker with my .68 OD has no problem running it up from 1300 RPM to 4500 RPM in OD in about 2 heartbeats......but I generally keep it out of OD until I can keep it above 2,000 RPM consistantly.....to put it another way, I only use OD when I am on the freeway or a very long stretch of country road.

 

[67coupestang]

1. Confirm you are really getting a full throw on the throttle. With car off look down carb throat and have some one IN THE CAR floor it with the pedal so you can visually inspect the primaries are opening all the way.

yup a full sweep there.

2. Are your secondaries opening? I just took a 770 VS of my mustang that sometimes the secondaries would stick and not open. The car would essentially just stop at 3500 RPM and not be able to go anymore (because it wasn't getting enough gas). I switched to a new carb and that problem was fixed. Along those lines...have you put in a new fuel filter to make sure it isn't a clogging issue?

I think they are opening, i can definately hear a change in the exhaust when i punch it. it will rev fine in any other gear. oh and wouldn't a fuel filter clog be more evident at high rpms?? but yes a new filter is on the list...

3. Have you confirmed there is no vacuum leak? If you have a small vacuum leak with the RPMS you pull in OD you might not have enough vacuum to actually open the secondaries (pulling at straws here now ) while unlikely it is plausible.

no leaks heard...


And for the record....my CLEVELAND stroker with my .68 OD has no problem running it up from 1300 RPM to 4500 RPM in OD in about 2 heartbeats......but I generally keep it out of OD until I can keep it above 2,000 RPM consistantly.....to put it another way, I only use OD when I am on the freeway or a very long stretch of country road.