My '95 Z with about 140k has developed a head gasket leak and I'm looking for input on my best options.

The engine has always run very well (strong) and has a good bottom end, no oil consumption issues, no noise, no excessive blow by, good compression, oil pressure, etc

It's stock except the quick. cheap mods (cold air intake, cleaned up intake elbow, TB airfoil, bypassed TB coolant, re-programed ECM tune, & edelbrock cat back exhaust). I was pleased with the noticebale power gain from these simple improvements. The car was a lot of fun to drive and felt very "lively".

My time and budget dictate a quick top end rebuild, but I would like to add more HP while I'm in there. I'm planning to do most of the work myself, except machine work if required. My goals are to add enough power to notice and feel the difference (at least 40-50 HP), keep the driveability factor high and not have to mess with it again for at least 40k miles.

I am aware that, when adding power mods, the total power output will always be limited by the next most restrictive component in a system, i.e a larger TB might gain you some power, but the "power limiter" then becomes the intake manifold. If you upgrade the TB and the intake, the next power limiter becomes the heads, etc, etc. In other words components need to selected based on their compatibility with the other components in that system.

here's my plan so far;

1. Pull the intake and heads and check the heads for warping, damage, etc.
2. If the heads are in good shape I plan to de-carbon them and re-use.
3. I'd like to add a high performance cam, probably a good quality new style fast ramp cam with decent daily drivability and idle.
4. Inspect and re-use stock LT-1 lifters if in good shape
5. Add hi ratio (1.6?) roller rocker arms
6. Change the mechanical water pump with OEM or hi po version, but not electric
7. Use a good quality gasket set to put her back together
8. Add a hi po (MSD?) coil to increase spark energy

My initial questions are;

1. What is the downside and risk of re-using stock heads with 140k on them?
From what I've gathered on this site most folks seem to agree the stock heads are good up to 375 -400HP. If they're not warped or cracked is it worth $500-600 to rebuild them? (new guides, multi angle valve grind, re-surface)

2. What are the biggest power limiters, in order of magnitude, on the stock LT-1? My local rebuilder suggested the stock intake manifold will become my power limiter after a hi po cam goes in and suggested the Edelbrock LT-4 style intake. Will this gain me any power with just a cam and hi ratio rockers on stock heads? Is "opening up" (extrude hone or machining) the stock intake manifold a viable option?

3. Am I making a mistake re-using stock LT-1 lifters if they inspect and test OK. I know enough to never re-use non roller lifters on a new cam, but I'm told you can re-use roller lifters on a new cam.

4. My budget can stand one or two more major components beyond cam and rockers. What is my best bang for the buck, 58mm TB and aftermarket intake? head rebuild or aftermarket heads? MAF sensor? MSD aftermarket opti? (my opti has never given me any trouble)

5. My impression is under drive pulleys, electric water pumps and opti replacements won't gain me much HP. What top end mods haven't I considered?

thanks guys, great site, keep up the good work!

 

Are the lifters ticking now? I just did my intake and didn't notice till after I put it all back together that the lifters tick. I mean I barely drive it and usually just get in and crank the stereo. Either way I would probably just go ahead and replace the lifters with LS7 (about $120). Also, if there is oil in the front of the engine check to see which bearing that is coming from (wp or opti or both). I guess it's already a vented opti or else it probably would not have lasted this long. Maybe swap that out with a delco unit from Partslady on ebay.

The intake is not a problem. I'd go with headers and worked heads with good springs (Comp beehives) first. I would certainly go to a builder that knows what he is talking about because anyone who suggested the intake first does not know what he is talking about.

Hal

 

Ok, I'll answer in the order you asked 'em

1) Reusing the stock heads will be fine after a rebuild.
2) The stock intake manifold is fine well past 400 horsepower. Switching to the LT4 style intake will require switching to LT4 heads as the ports are different.
3) You can reuse your stock lifters but replacements are inexpensive and yours have 140K on them.
4) If your budget can stand one mod then I suggest getting your stock heads ported to go with a good aftermarket cam. Stick with the stock intake manifold but open up the throttle body holes to 58mm. Buy a 58mm TB to go with it. There are lots and lots of options here.
5) Underdrive pulleys won't do much because you aren't driving the waterpump with the belt. An electric water pump is worth about 6 horses and worth it in my opinion when your sitting in traffic or on the strip. A cold air kit is worth about 10-12...not the amazing amount they all claim. A TB coolant bypass is worth 6 hp and is free. An aftermarket ignition doesn't gain you any power at all. Don't bother with a different MAF...it'll just cause you headaches. Headers will be a big help at about 15 horsepowerr.

I hope that helps. I would suggest you consider rebuilding the bottom end as well. 140K is a lot of miles to be starting mods on.....

 

UGGHH lost my first reply for some reason.....

Hal & BW, thanks for your responses

Hal, the lifters aren't ticking now and there's no external oil leakage

BW, curious about your comment on stronger multi spark not gaining me anything. i thought conventional wisdom was that the OEM coil was weak at high RPM? I do sometimes get a very slight stutter as the RPM goes through 5k. I had thought an MSD coil would solve that and gain me a little high RPM power back

It appears both of you favor spending $ on machining my stock LT-1 heads and intake for better flow vs, buying after market. I'm good with that since I like to keep OEM parts on it when I can.

So $500-600 for head rebuild is worth it? what might I expect to pay for porting the heads? How about maching cost for the intake for 58mm TB and ported to match the heads?

my revised plan then is;

1. pull and rebuild stock heads, plus machine them for better flow/porting
2. pull and machine stock intake for 58mm TB and port matched to heads
3. aftermarket cam, new lifters, 1.6 roller rockers, properly set up and degreed
4. aftermarket 58mm TB (summit?)
5. new OEM timing chain set and mechanical water pump (I don't take it to the track and the temps always stayed nice and cool with the OEM pump even in heavy traffic. I have low temp thermostat and good radiator)

what else should/must I do while in there?

I'm willing to go top end only because I just want to have fun driving it for another 40k and by then I'll be ready for a new toy. I have faith the bottom end will hold together until closer to 200k. I'm not going to beat the hell out of it....often.

 

I know...lots of people think a new ignition is going to generate tons of horsepower. The truth is that it really doesn't. A hot ignition can help you light off that new mixture from your new cam but, by itself, it isn't worth any power. If you have a weak ignition..breaking up at high rpm, for example, and you replace it with a new stock coil, you get the same hp as if you used a new msd coil and ignition. Start adding adding nitrous or a supercharger or a big cam and you'll have to upgrade....

A few of things, based on your new list.
1) get a good tune for the setup you have to incorporate that low temp thermostat.
2) add a LT4 knock module when you get the roller rockers.
3) don't bother with the LS7 lifters, they aren't better than stock. In fact, they are stock on LS2, LS3 and LS7 engines. Cadillac racing lifters are lighter allowing high valve train speeds...especially when coupled with titanium spring keepers and locks. Don't worry, you don't need the Ti parts....
4)Porting costs vary alot between porters. Do some research and reach your own conclusions. A lot of guys on here prefer Lloyd Elliot's work but I'm not impressed.
5) Machine your intake maniold yourself. All you need is a 1-1/2" drum sander for your drill and you can easily do it. Use the gasket that comes with your new 58mm TB to mark the manifold and sand away. It really is easy. Same thing with the ports..mark them using the new gasket as a template sand use a rasp to remove metal and get a smooth port shape. Nothing to it.