kilby94

I have searched and searched for similar problems as mine and keep finding people asking the same question but never saying how they fixed or if they fixed it. I have a 91 GT with a freshly rebuilt motor that is sporting 351 heads (casting D0OE), typhoon upper and lower intake, e-cam, 1.6 rr's, shorty headers, 70mm TB and egr, new 8.5 MSD wires, Blaster tfi coil, new plugs gapped .054, new ignition module, and some other little things as well. My problem is that the car will not rev past 5000 Rpm. It has great power down low and will eat the tires up through third, but when it gets around 4000 rpm you can notice it quits pulling as hard and hits a brick wall at 5000 rpm. No matter if its in neutral or any gear it still won't rev to the limiter. It has good fuel pressure, timing is set at 10 degrees, and overall it runs good. But i know it is lacking power up top. I have seen people asking the same question but neversaying how they resolved the problem. Any help greatly appreciated. Thanks Richard.

MikeVa

I see you have the Blaster coil, but did you upgrade the TFI module? The stock one will hit that wall at 5000.

kilby94

I put in a newfactory replacement ignition module. Have not upgraded anything.

AdderMk2

since when??? I run my car to 6500 on a stock module.

set you plug gap to around .045...

and when you rebuilt the heads, did you UPGRADE the valve springs, or did you use stock POS springs

kilby94

Thats one of the things i am worried about. I did not rebuild the heads, i bought the carwith those heads. With the valve covers off the rockers are definately aftermarket and the springs don't look like they are from 69', but i am not sure if they are still good. Do my symptoms sound like valve float? If so i will upgrade springs i guess.

67mustang302

If the car suddenly loses power at 5,000rpmit could be float. Do you hear any clacking or loud ticking from the engine when it loses power?

kilby94

No ticking or rattling or anything of that sort. A little popping in the exhaust, but at the motor everything sounds normal.

mjr46

no reason to be afraid if you find out you have to change springs you can convert a compresion tester by removing the schredor valve and using a inline regulator.... pump the cylinders with air and use a on the head valve spring removal tool....it works quite well but is quite time consuming cause you have to roll the motor over one by one until both valves are closed but none the less it is quite simple.....just check your installed/reccommended height and shim accordingly if necessary

kilby94

A mechanic friend of mine says he has the tool that fills the cylinder with air for on car removal, but i just wanted to run it by some mustang gurus before i drop that money on new springs. What springs do yall recomend? Do i just remove and replace or is there any measuring to be done?

my77stang

well you should be able to tell if you have upgraded springs by a quick visual. if they have stamped steel retainers and the intake and ex are different then they are stock. if they are all the same and most likely anodized them they are aftermarket.

sorry i dont have a part number for the e cam springs, but i bet the ford site lists a recommended number. off thet top of my head i'll say something with about 120 lbs of seat pressure should work just fine. stock springs have like 80 if your lucky