ZZ4 Cam Valve Guide Clearance
 

Hello all,

I'm in the process of dropping my L98 TPI into my RS. (SLP Runners, ported plenum, gasket matched, 2055 headers, 3" catback, AFPR

The engine is sitting in the garage and I'm thinking, why I have it out why not do a cheap cam change. Looking around the ZZ4 cam comes to mind for cheap and some have had luck running it off of the stock tune.

I know my factory valvetrain is not up to the challenge and I'm trying to do this on the cheap as motor funds aren't exactly great right now...

Anyhow, I'm going to put the screw in studs myself (MRG-1075). Vader has a great tech article on that and kudos to him.

Also, I'm going to put in the Comp 981-16 spring set w/ associated locks and retainers.

QUESTION!

Has anybody here from experience done this and NOT machined the valve guide bosses? I've heard varying opinions from they /have/ to be machined to it will be fine?!?!?!?!?!?!!?!?!?!

Also, How do you check clearance with the springs installed?!?!

Lastly, if they do need clearancing is their a DIY way or cutter that I can do this myself as again - funds are not permitting a trip to the machine shop and honestly I don't want to pull the heads if I can get away with it. Any help will be appreciated. Thanks!

When I did the ZZ4 cam swap, i redid the valvetrain as well. Although my machine shop guy actually did the rebuild, I bought all the parts and had him simply do the labor. I never mentioned anything about the valve bosses, and for that matter, this is the first I've heard of the bosses needing to be machined for the ZZ4 cam.

Unless maybe it's a given, and he did it for me anyway, I dunno.:confused:

Anybody have experience with the ZZ4 Cam and the STOCK prom on Speed Density. I'm getting into PROM burning, but can't foot the money right yet (getting the Autoprom). Anyhow, I plan on advancing the timing to about 10deg and giving it maybe 50psi of fuel pressure.

Anybody got any helpful hints???

Someone on here told me it ran pretty good with the stock tune but ran a little rich at idle. I'm looking at the zz4 also. i have the autoprom and just need to learn how to tune it. I already burned a chip and just changed the rev limiter but i never put it in the car.

o yeah and if your looking for a cheap zz4 there is alot on ebay for $140 and $15 shipping for brand new take outs never ran

I am kinda interested in this also.

I think you're going to have clearance problems. If you had the bosses machined for positive seals, you may have some more room.

I don't think you can check the clearance with the springs installed. They have to come off.

You need to check make sure you have the spring seat shimmed for your spring to reach the appropriate installed height of the spring. From there you can measure from the spring seat (shimmed if necessary) to the top of the bosses and see if you have enough movement for .510 with 1.5 rr + clearance for the valve stem seals + clearance for variance.

FWIW, from what I understand, the stock clearance is ~.480 and it's best to stay at ~.460 lift for cams with absolutely stock heads.

Here's a relatively cheap valve spring micrometer you can use. http://tinyurl.com/6tkeu . First you must shim up the seat so that with the locks and keepers on, the valve fully pulled up only has 1.700" measured on the micrometer. To measure the height of the bosses with seals, you can use a straight edge or machinist's ruler over the micrometer and see at what height it touches the valve stem seal. Round up, if need be. Subtract that from your installed height (1.700 for the Comp 981 springs) and you'll know if you have the right clearance.