Hey All,

I am a new Z28 owner looking for advice on the LT1. My car is nearly bone stock, with the exception of a K&N air filter and a close-throw Hurst shifter. Other than the dreaded OptiSpark issues, is there anything else I should stay away from or know about before diving into the deep end of the pool? I read somewhere not to use synthetic oil in these cars. Is that true?

Thanks in advance!

 

Changing to synthetic depends on the miles on the engine and how well it’s been taken care of, quality of oil used, quality of filter used, frequency of oil changes, etc..

I ran my 94 Formula (purchased new) on Mobil 1 synthetic from the 1st oil change. No problems for 80,000 miles. At that point the engine underwent a serious, high HP (+300 shot of nitrous) rebuild, and I used the specific conventional oil and change intervals the engine builder specified. There's nothing inherent in the LT1 engine that should cause you to avoid synthetic for stock or even moderately modified applications. If the engine hasn’t been treated well, it may develop leaks with synthetic, but that's true of just about any engine.

The LT1 engine installed in the 1993-1997 F-Bodies is virtually identical (except for 4-bolt mains) to the LT1 engine installed in the 1992-1996 Corvettes, and the Corvettes left the factory with Mobil 1 synthetic.

What issues you should address are highly dependent on the history of the car and how much you know about that history. On a 28-year old car, replacing all fluids, filters, plugs/wires should be considered. Unless there is evidence of problems with the Optispark distributor, leave it alone. At most, consider inspecting the cap/rotor and replacing if necessary due to wear, carbon tracking, etc. In 1995 the Opti was upgraded with a vent system to eliminate the corrosive ozone generated by the high voltage discharge, and minimize moisture. That was a significant upgrade from the unvented unit used in 93/94. Replacement caps are available that add a vent feature.

If the SES light is on you have to scan the PCM for codes, and eliminate the problems causing the diagnostic codes.

Good luck with your new purchase. These cars can be a lot of fun ! ! !

 

Thanks, Fred!

I feel like I got lucky with this one. It was pampered. It's a one-owner car with all the service records since purchased in '95, and the previous owner had all the fluids changed about 6 months ago (I have the receipt for the work).

I will probably keep it as is for a while before making any changes to it since it's in such nice condition.

Do you have any experience/opinion on the bolt-on aftermarket PCMs, specifically the JET Stage 1? They seem to be a pretty common swap for $250, as long as I install the correct one that doesn't require headers, new thermostat, and exhaust work. I just bought the darn thing, and I am not quite ready to tear it apart yet.

Thanks!

 

IMHO, you would be better off avoiding the Jet chip. It will have minimal, if any, performance gain. You can do a "mail order" tune by sending your PCM to a tuner. On stock motors typically that requires installing a 160 T stat as the tune will have fans come on earlier to maintain a lower engine temp operation so more timing can be programmed in. The HP increase is generally about 10-15hp so not much as the real power upgrade is heads and cam along with tuning to support that which can net a good 100hp increase. I will add though that modifying a 25+year old motor with 100k mi will have its downsides without fully rebuilding the motor

Adding 1:6 RR with new, better, valve springs and a mail order tune is about as far as I would modify a high milage motor. cold air intake and CAT back exhaust

While the tuner who has done all of my tunes as mods progressed has passed away, I hear good reports about mowhorsepower. Fred may be able to recommend one also.

If your Opti is an original AC Delco, never get rid of it as it has the Mitsubishi sensor in it. Service for it, like any distributor, is replacing cap and rotor every 100k mi

 

Thanks for the advice. Even though the engine only has 56k on the clock, considering the age it sounds like I would be better off staying with the existing PCM and just enjoy driving it until I am ready to do a full rebuild.

 

at 56k mi sounds like your car has had an easy life....it will be a nice driver you should enjoy as is. Just do a good maintenance of changing fluids, hoses and belts. More because of age vs miles if those items are original. You mentioned good service records, so it sounds like you are ahead of the curve. Enjoy the ride

 

The JET module does not replace the stock PCM. It simply inserts between two of the PCM harness connectors and the harness. As noted above, it's not of significant value. A "custom" mail-order tune will gain you more, and probably cost less. On a totally stock engine the mail order tune might pick up 10-15 HP. The tuner does this (most likely for less money than the JET) by leaning out the overly rich stock target A/F ratio at wide open throttle (WOT). The 160-degF t'stat will pick up a couple more HP when the fan on/off temperatures are lowered.

It isn't going to hurt to stick with the stock tune for a while. The best "starter" mods are a cold air intake and upgraded exhaust - first a full 3" mandrel-bent cat-back system, and then headers. These changes improve the engine's breathing, more, denser air in the cylinders. Fortunately the MAF sensor picks up the change in mass air flow, and the stock tuning adds the required fuel to match the increased mass air flow.

There's a "free mod" that can pick up a dyno proven 6 HP - removing the hot coolant that flows through the base of the throttle body:

http://shbox.com/1/tb_bypass.jpg

Modifications #8

Before making any mods, ask here first. There are a lot of things that are not worthwhile, and can cause issues with the engine.

 

I will absolutely ask here first. You guys are the veteran owners. I know what I know, and it isn't much so I will ask a lot of questions. Thanks for the reply and the valuable info.

 

Thanks, I appreciate it! She is super clean and straight for a 28 yr. old ride.