Hi,

Since there're to many oil leaks from almost every point of my L98 engine, I've decided to pull it out of my '89 GTA and do some mods by the way. I want to make it strong for street, with good mid-range and ~5.7-6k top rpm. Due to low budget, my plan is:

- stock TPI intake with all the parts ported and matching, AFPR;
- Flowtech shorties 1.5"/2.5" with 3" exhaust, no cat or other emmision stuff;
- stock iron heads ported,
- ZZ4 camshaft

So:

- how much valve lift can take stock heads without machining guides? is there any "lower" design of spring retainer, which allows more lift without cuttin guides?
- would it be reasonable to go into 1.6 roller rockers? would it require springs larger than 1.25" diameter? Valve lift with 'em is .507 in, .544 ex. How about stock valve covers w. centerbolts - should I replace them with higher ones?
- when changing rocker studs; is it better to use guideplates and n/a rockers or leave self aligning ones? (yeah, maybe it's a dumb question...)
- isn't max rpm overrated with this setup?

I'd be grateful if you've some suggestions - it's not easy do do even so simple work here, in Poland because we can't simply go to Summit or Jegs to buy the parts Thanks!

Mike (z_power)

 

The stock heads are good to abt .480" lift.
There are valves avaliable that are .100" longer than stock, which will help clear the valve guides.

I've seen 1.25" springs that were rated to .6" lift, but I've yet to see anyone recommend them.

There are also cone shaped springs that are 1.25" at the bottom and a little bigger at the top. Don't know of anyone running them though.

I'm hoping to run stock valve covers with my set-up (.530 and .560 lift) , but haven't got that far yet.

High lift will require high spring pressure. High spring pressure will require screw-in rocker studs.

IMHO, the guide plates will be more reliable at high RPM.

With your set-up, 5000-5500 RPM is abt the upper limit for any real HP.

If your going to keep the TPI, I'd be concentrating on pumping up the mid-range torque. That's where you'll be spending most of your time anyway.

While you have the heads off for porting , might at well upgrade to 2.02 and 1.6" valves. If your getting a valve job anyway, might as well.

 

I see there's going to be some serious work with heads: spring pockets, valve guides, rocker studs, porting, matching........ok, I'm starting to pull the engine tommorow

 

Well, I've just bought a new set of Comp Cams conical springs w. locks & retainers for $53 (ebay... )