Stock vs 1.72 rockers AGAIN

[jb89coupe]

Well some of you may remember my thread from a while back about my car being slower after I put a set of fms 1.72 rockers on it. I had a bunch of issues, one of which was the valves weren't closing all the way giving me about 60psi compression in a few cylinders. Well I put another shim under the rockers (they're all shimmed .090" now), and now my compression is between 155-165 where it belongs. My car is still a dog with these rockers on. I've re-installed the stock rockers and gotten a 2nd and even 3rd opinion - with the stockers, my car feels like it has 40hp more, not exaggerating. At 3k in 3rd gear if you floor it the car will lunge out and throw you back in the seat. With the 1.72 rockers, it just bogs down. With the stockers, flooring the car at 2k in 2nd gear will spin the tires, with the 1.7's, again it just bogs down. My low end is GONE with the bigger rockers. I can't really tell if the top end is worse or not.

So, why are the 1.72's (properly installed, checked, and re-installed several times) making my car such a dog? Could I be leaning out.. should I need bigger injectors? Keep in mind I run a 100 dry shot and have never leaned out on that. Bad fuel pump/regulator? I just removed and cleaned all of my injectors, then reinstalled them and ran a cleaning machine through them for 20 minutes.. the fuel filter is about 4 months old.. I'm drawing blanks here. I don't have a way to watch my fuel pressure while I drive, but it behaves normally if I rev it in nuetral. Could the higher lift of the stock cam (.478 vs .445) be murdering my low end?

 

[RickyB]

is your valvetrain up to the task of handling the increased lift, specifically springs?

 

[jb89coupe]

The springs are trickflow duals rated for .57" lift. They have about 10k on them.

Now I definately don't think I'm leaning out.. I bumped my fp up to 48 today and the car ran much worse like that. I was kinda hoping it was a fuel delivery issue, because now I have no idea what it could be.

My timing is at 16* right now.. I've tried playing with it from 10-20. Lower than 16 and the bottom end is worse, higher than 16 and I start losing top end.

I guess the smart thing to do would be just stick the stock rockers back on and sell the 1.72's, but I'd really like to figure out why I'm losing so much power with a part that should definately be adding a few hp if anything.

EDIT: untouched 100k bottom end (155-165psi compression), stock pushrods, heads/valves/springs have about 10k. I have a pretty complete rundown of my setup on my cardomain page. o2 sensors are new bosch units.. act sensor was cleaned when I swapped the intake.. can't think of anything else right now.

 

[jb89coupe]

.

 

[SilverFoxbody]

Hmmm.......sounds like we better find someone that has done the mod and accualy GAINED power.....we need to find proof that it works.

 

[jb89coupe]

Well theoretically all you're doing is increasing the lift of the cam (from .445" to .478" in this case) and reducing valvetrain friction. Neither one of those should cost you any power. If I had no gain, I would be fine with that.. but the car seriously feels 40hp weaker when I put the 1.72's on. I've swapped the stockers back in and out 2 times now, and every time the same result..

Now why is it that I can throw my stock 1.6 rockers on without shims, torque them down, and my car runs strong.. compression is good. But if I try to run the 1.72's without shims, my valves won't close all the way.. I end up with sub-60psi compression readings. As it stands I need .090" in shims to get the compression up, but no shims with the stock rockers - that's a huge difference!

 

[ALMOSTFINISHED]

Maybe there is something with the pushrods, possibly need longer ones? Does it feel like it is valve float??Where-abouts in CT are you? Maybe I can come by and help you out in person. Its alot easier than doin it over the internet.


Nick

 

[Mean86GT]

bad set of rockers?

 

[goesquik]

I wonder

Most likely the problem lies in the valvetrain geometry, in other words the pusrods are the wrong length and shimming is not going to fix it.

I have 1.72's on mine and used to run a B303 w/ 480 lift then i installed a TFS stage1 with 499/510 lift. I was able to keep my pushrods(not stock) because my rockers are adjustable. You can buy an adjustable pushrod tool that can help determine proper length.

The biggest thing is that you have stock heads and even with aftermarket springs they are limited to the amount of lift possible with out the valves staying open. So for now leave the stock rockers in or buy diff pushrods, either way though lift will not be that much different. I found that duration is what controls cam power not so much lift.