whats the difference? i noticed different specs on both of them... i have a 1990 iroc-z and my engine lost compression and im going to need a new motor. found myself a deal on a 94 LT1 engine with computer, wires and everything for only $500... i just wanted to know the difference between the two so if there was a major difference, i'd just look for a 96-97 LT1 instead. thanks guys... if i get the LT1, i'll probably be talking to you guys more often

 

94' is non-vented opti
275 give or take hp
ODBI

96' is vented opti
285 give or take hp
ODBII

 

The main differences between the two is the PCM (computer) and the optispark (distributor). The 97 has the newer vented style opti which is typically more reliable than the older style, but it also has the OBDII pcm which is harder and more expensive to have programming done for mods. The 94 has the older opti, but uses the OBDI pcm which is cheaper to reprogram, it also has hardened pushrods which isn't a really big deal but is a plus.

If the 94 motor is in good running condition and includes the PCM and harness $500 sounds like a really good deal to me, good luck and you'll get plenty of help here if you need it.

 

From what I've been told, the 96/97 LT1's have a little bit stronger bottom end. The OBDII computers are more expensive to tune, LT1 edit becomes $550 as oppossed to $150. I'd say go with the 94 since you're doing an engine swap. My motor, it's a 97, has held up to a LOT of abuse, including 3 bottles of nitrous before I bought it and now 8 lbs. of boost from a supercharger.

 

could i use the distributor from my 350 tpi instead of the one on the 94 LT1? whats so bad about optispark? thanks guys

 

Their identical motors. The only difference is the non vented Opti on the 94. The only reason 96-97 had 285HP is they changed the exhaust to dual cats which added an extra 10hp. You could get the 94 motor and do a vented opti conversion before you drop the motor in, but I wouldnt worry about the vented opti too much.

 

I dont think that would work, but the opti are famous for giving out close to 100K. Id say maybe just put a new one on before installing the motor and be done with it.

 

No. The LT1 opti mounts behind the water pump (no joke! ) and is driven off of the end of the camshaft through the timing cover. I wasn't trying to say it was that bad, just that the earlier versions seem to have had more problems than the later 95 and up vented optis. I would go with the one that comes with the 94 motor if you get it, it's not that hard to replace down the road if it goes anyway

 

i have the G92 option on my iroc which has dual cats, but i had them replaced with straight piping... what would i need if i want to swap engines. im going to get it from a crashed f-body... name me all the parts im going to need to take from the crashed LT1 to my iroc so i make sure to get everything all at once. u think there are going to be any problems installing it? you guys suggest on me getting a new distributor while im at it as well? any help i can get would be awesome! im going tomorrow to pick up the LT1. thanks guys for all your help... anyone got some websites i could go to to learn more about LT1's, how to mod them up, and any specs and info on the engines?

 

The LT1 engine"evolved" over the years. Many of the parts had minor changes, but the part numbers were never changed. The earliest engines had forged rods, late in 94/early 95 they switched to the powder metallurgy rods. There are subtle changes to the intake manifold and heads over the years. Cam profiles varied slightly. The obvious change is the vented Opti, as mentioned in several posts above, and the changes it engendered in the timing cover. OBD-II added several items, the most notable a crank position sensor for misfire detection.

All things considered, the Opti is probably the biggest difference.

And, if you are keeping the EFI, you can't substitute your old mechanical/HEI distributor for the Optispark distributor. The LT1 PCM requires the pulse signals from the Opti optical sensor for spark timing and injector timing.

This article covers a lot of the differences. But many are too minor to even be noted in the article.

This book covers "Rebuilding the LT1.....".

And if you go to this post on the Project TransAM bulletin board, you will find some additional reference links.

 

You can get a complete opti with cap and rotor from Jason Cromer for $200. Or you can reuse the cap and rotor and buy an Opti from O'reilly's for $140. But DONT go to a dealership, they charge about $600 for the complete opti.

Some people have had problems with the O'reilly's opti, but it does come with a lifetime warranty. Ive never had a problem with mine.

 

This is one of the best places for info that I've found on anything from general repairs to serious modding of the LT1.

I've never done the swap your talking about but I know a lot of people have. Check out this site if you havn't already for info on the swap:

http://www.thirdgen.org/techbb2/foru...php?forumid=20

It's a very popular site for third gens, it looks like they have a lot of good info.

 

would it be a lot harder to change the distributor once the engine is already in the car? and since i have an A4 tranny, do you think it would be wise of me to do a t-56 conversion later down the road? i know the stickshift lt1's are quick, but i wasn't sure about the auto's. thanks

 

If you plan on keeping this car for a while then I definitely recommend putting a new optispark on the motor before installing it. If it was me I would even put a new waterpump on it as well, cause if the water pump starts leaking it will ruin your brand new opti. Contact Jason Cromer as mentioned before, do a search and you will find his number and he should be able to get you a water pump and opti for about $350, which aint bad at all and well worth the hassles that you will have if you dont replace them now. I know because I just replaced mine.

These engines are notorious for having leaking manifold gaskets. When you get the motor, check if there is any oil on the back of the block below the manifold, if there is, get a new gasket set. That covers about all the notorious problems on these motors, maybe throw in a new rear main seal, only like $20, just for added insurance (its a bitch to do when the motor is in).

I assume you are not doing a cam or having eth heads ported based on teh way you are talking, but now is the best time to do so. Something like the Hotcam kit (do a search) will net you maybe 30-50 rwhp and is somewhere around $400. You can have your heads ported, valve job, cleaned, milled, etc by a very reputable guy (Lloyd Elliott), do a search, for about $600 if you keep the stock valves and dont have any poliching done. Just things to consider while you have the engine out.

Best of luck to you and let us know how it all turns out.

 

well... here's the deal. im jobless right now and im going to have to use my visa to do all of these at my mechanic's shop. i was riding around in my iroc-z (350 L98) and it just died on me. tried to fix it, spent about 100$ trying to fix it, but to no avail, it wouldnt work right. i took it to my mechanic and he told me it has to be rebuilt... so it comes out cheaper for me to get an LT1 and just swap it than having him rebuild it. im really low on cash right now so im just going to have it dropped in and have him get it running for me. the cam, heads, and all that good stuff will come later but for now i just need to get her running. if there's anything i need to FIX now before it goes bad on me later, i'll put it on my card and get it fixed before it cost me twice as much to do it later on, you get me? so far it looks to me that im going to have to get a new distributor, and a new water pump. ill have my mechanic look over all the seals and to see if the engine is in good condition before he puts it in. all i can say is "damn, what a bad one"... cant believe all this crap is happening to my car right at christmas. don't even have money for gifts for my family cuz im spending it on my car, lol. thanks guys for all your help.. any other suggestions would be greatly appriciated