Power loss at around 2,500

[Anonymous]

I don't know if this is typical of the 3 speed auto or just the motor, but my mustang seems to have a dramatic hp dropoff at very low RPMs. The car doesn't seem to push anymore at this point. Is my car supposed to be this slow (all stock but dual out header)? Has anyone else encountered this problem?

Steve

 

[addo]

Without specifying what are the "low" values, it's difficult to say whether there is any kind of issue. Headers on a stock motor do very little (my experience has been they can quieten the motor (yes, really), and maybe improve fuel economy.

Perceived "lack of power" can come from an inadequate fuel supply curve, incorrect ignition base timing or faulty/inappropriate advance curve, misadjusted throttle linkage (surprisingly common), overheating, low compression (especially after a gasket change or head swap), retarded cam timing due to a stretched chain or emissions spec - the list goes on.

Start with the ignition; check the plug gaps and base timing. Then check the advance against factory specs as RPMs increase. When you've eliminated the ignition as a loss of power, move to compression, then induction/carburetion.

Regards, Adam.

 

[Anonymous]

I'd also suggest looking for a vacuum leak in the intake system, as this will have a more noticeable effect at lower RPM than at higher RPM.
These sixes pull off the line very well, fading as they rev up (stock).

One of the most common vacuum leaks is in the fitting where all the vacuum hoses connect to the manifold: often the caps on the ports have cooked, broken and fallen off. This is just under the carb, so it can be hard to see.

Another place is the brake vacuum booster, if you have power brakes.

The third most common spot is the base of the carb: they often have bad gaskets under them, cooked and worn from the heat.

 

[Anonymous]

has it always had this dropoff in power at low rpms? or recently has this occured for no apparent reason? or since you added headers? my fairmont had alot of power with the 3.3 but then I blew the tranny beating her and when I switched trannys for some reason now at low rpms I got no real boost no power power like when im at 55 and stomp where I can really feel the power

 

[CobraSix]

Just an idea...since it is an auto, what is the stall speed of the torque converter?

Slade

 

[Anonymous]

I appreciate all your help. I have only had the motor running since I put the header on, so I don't know if this was always a problem. This is the way it has been since I started driving it. How do I find the stall speed of the torque converter, also what is this and what does it do?

Thanks again,
Steve

 

[Anonymous]

If you have a tach, you can guesstimate the stall speed of your converter by driving in high gear at say, 30 MPH, and give it some gas. Watch how high the RPM jumps before the trans begins to strongly accelerate. This RPM is just above the 'stall speed' rating.

The C4 trans (common behind I6 engines) has 3 different ones I know of: 1100 RPM, 1500 RPM and 1800 RPM. Mine has a 1500 in the I6 Ford and my T-Bird, and the '67 LTD with a 390 engine has an 1800.