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Discussion Starter #1 (Edited)
I have the setup below in my sig. I have replaced the springs on my 68k, 1996, TFS-TW stud mount heads with new TrackHeat springs, which AFM said should be fine with their B-25 (218/226,.544/.544,112) cam. However, I still get a SHARP drop off in power from about 290 to 250 hp from 5800 to 6000 rpm. I have readjusted the pre-load on the lifters from 3/4 turn to 1/4-1/2 turn, with NO effect.

The only other thing I can think of is that the valve guides on these heads are worn out and contributing to the problem. However, I burn no extra oil, pass emmissions, get 18-20 mpg, and still knock down 295 rwhp. Everything is fine up till about 5800 rpm. AFM says that the cam shouldn't float the valves until about 6400 rpm with the 1.7's that it is designed for.

I know that the Cobra will fall off after 5400 rpm, but I've seen lots of dyno pulls, and they don't fall off any where as sharp as mine does. I just want to be able to shift 1st and 2nd at a decent rpm to optimize my 1/4 times. Can you help me out? Thanks.

P.S. Air fuel looked fine and dyno operator said ignition "sounded" right.
 

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If they are pumping up I would thing that they can affect it. Also are you still running the stock ignition coil?

Greg
 

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I had rhe same problem after installing my X-303 cam. 5700 and then the valves floated. High lift cams need more spring, I installed some Crane double springs with a damper and now it runs to 6500 easy.

Dan
 

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Discussion Starter #5
84GT350VERT,

I have installed the TrackHeat upgraded 0.6 in lift springs, and that moved valve float from about 5600 to about 5900 rpm or so. It's more than just the spring on my car.

bigredstang,

Do you really think that the stock ignition is letting go up there? Wouldn't my car be puffing black smoke and the air fuel going to pot if it was the ignition?

Thanks all for helping out.
 

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I just wondered if the spark was getting blown out at the higher RPMs. A PS-91 coil is only $50 and is a nice upgrade to the ignition system.

Greg
 

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Discussion Starter #7
Chirs/Kim or anyone else have some insight on my 5800-5900 fall of a cliff dyno curve?

Bigredstang,

Thanks for the PS-91 coil suggestion. I guess I could try the ignition upgrade, and AFM actually suggested the ignition could be the culprit as well. Hmmm...
 

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Having done countless engine dyno pulls and valvetrain evaluation...

Your Hyd. Roller lifters are collapsing and inducing "LASH" into your valvetrain. Thus reducing lift and duration as rpm increases. They are not "PUMPING UP". A valvetrain that has been put thru this abuse for any length of time can be recognised by that fact that the retainers and locks have been wedged together thus requiring striking with a hammer in order to disassemble. This is due to the valvetrain "springing apart".

If you don't believe it...

Pull out your Hyd. Rollers, Install Solid Rollers and Adjust for .003" to .005" lash and Re-Dyno !

I think we've been here before...
 

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Discussion Starter #9 (Edited)
This is interesting. I thought running solid lifters with a hydro cam was a no-no. Since I don't have any class rules, I would love to run solids if they would fix my problem. Here are some questions, if you don't mind:

0) Won't the extra lash reduce the effective duration of my cam? Wouldn't I then have to run a bigger cam?

1) What solid rollers can I run on my car, which sees commuting once a week and the track a few times a year? What brand do you recommend.

2) After I adjust this lash to your specs, how often will I have to readjust it?

3) How noisy will it be ... not that I care that much, but give it to me straight?

Thanks.

P.S. I may as well swap in an RPM intake and do the Tweecer/Tuner/PMS/Chip rev limit extension if I go this route. I'll shift her at about 6500 rpm, until she blows!!! If this old gal is going to go, then she'll go out in style :evil:
 

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Understand the following...

1.) You MUST have enough spring pressure: 140#-160# on the seat and 350# to 400# on the nose as minimum to reach say 7000rpm.

2.) YOU ARE PLAYING WITH FIRE ! The Hyd. cam does not have a "clearance ramp" as do all solid lifter cams. Thus the imparting initial acceleration of the lifter is SEVERE. This is why you only set lash to about .003". Any more than this and you may start to break valvetrain components.

3.) This valve lash setting must be maintained MORE often than a normal solid due to the very small lash setting and the above point. THUS...

4.) Even thou this little trick is being used on some race cars with good results I can't say I could recommend it for a street driven car.


The decrease in duration is not significant. And noise will be minimal to the very tight lash.

Some would just buy a Solid Roller Cam...
 

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A valvetrain that has been put thru this abuse for any length of time can be recognised by that fact that the retainers and locks have been wedged together thus requiring striking with a hammer in order to disassemble. This is due to the valvetrain "springing apart".
I thought this was normal with 7 degree locks/retainers. The 10 degree locks/retainers seem to disassemble easier.
Would increasing the oil pressure via a high pressure or high volume pump help prevent lifter collaspe?
My E-303 cammed 302 with 1.72 ratio rockers could have suffered from lifter collapse. The Crane conical springs were only set at 125 lbs. seat pressure (approx. 1.910 installed height). Open pressure was around 330 lbs. At 5,100 rpms I could hear valvetrain clatter and a noticeable drop in power. Maybe this could have been lifter collaspe in my combo. Or the crappy 5/16th pedastal mount rockers from Omega.
 

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Discussion Starter #12
CStraub, you out there? Kim, anything to say on this subject?

I remember reading an MM&FF article by Richard Holdener, in which a car fell off a cliff on a dyno pull like mine. He blamed it on old lifters, since his springs were new, and replaced them. The next dyno pull was cured of the fall off, and the car pulled like crazy.

I'm thinking of trying the lifter swap ... and possibly an RPM/RPMII intake swap (I could always go back to a Performer, if my cam and valvetrain can't cut it). If this doesn't work, then I'll just stop messing with the 302 and start saving for the 347.

Thanks.
 

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I am not a fan of the hyd. roller lifter due to the simple fact it is heavy. 1bad50 is correct about what he has stated. During testing on marine engines we finally upped the spring pressure and got some more rpms out the engines but not much. Old lifters may have "varnish" and just plain dirt in them which will affect the valving and may cause the lifter to perform worse. The replacing of the hyd. roller lifters with solids is a rememdy for those who have to have more rpm but a light lash setting is a must and your going to have more maintenance. The restrictor pushrod that we manufacture does work, basicly backs the oil up and keeps the lifter pumped up. This is an option. You can ask Ed about them, or Houston, Bennett, Keith Craft, or Wynne.

A good stock ignition is good to 6500. After that the aftermarket will be a must.

Now off to work to solve some more of these problems.

Chris
 
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