Differences in Northstars - '93-'97, also cheap head gasket fix...

97EldoCoupe · #1 (**permalink**) 06-26-07, 04:50 PM

I've got a beautiful 97 Eldo but someone has at one time, installed a 4.0 from an Olds Aurora. I solved my overheating problem by changing the head gaskets and retapping the block to 1/2" NC 13, then drilling out the heads to accept 1/2" head bolts. Loctight on the threads, and turned on many miles now without ANY overheating problems or coolant loss. The bolts tightened up well. The bolt heads are a tight squeeze under the intake cams and I had to remove the exhaust cams to get the ordinary 3/4 head bolts in there. The bolts are standard grade 5 bolts, 5.5" long, but I had to extend the threads on the bolts. My way of getting around the expensive timesert problem- $20 worth of bolts, and some time, $60 worth of headgaskets. I know it shouldn't be done this way but hey, I figured if it didn't work I was going to swap the engine out eventually anyway.

Anyway, since I've saved up a little $$$, and I want the power that the car originally came with, I found a great deal on an engine from a '93 STS- the L37 with 295HP. I know the intake/throttle body is different than my '97, so I plan on swapping the intake and TB (installing what came with my car on the '93 northstar). I'm pretty sure everything will interchange without any problems, and the sensors and all will be used from my '97 motor, but will it run right with the current computer? Will the injectors provide enough fuel to give it the extra 20HP over the stock setup? What other differences should I know about before buying this motor? (I've got an L37 in the garage with only 55,000 miles on it from a 2000 deville, but I have no wiring harness to go with it or PCM so it's sort of pointless to install)

Also, I've got a 4T80-E from an Olds Aurora that I tore apart, the 3.71:1 ratio, if I dropped this in my Eldo along with that '93 L37 how would it work together? My Eldo is originally an LD8 car. Will the final drive ratio throw the speedometer out, or shift points, or throw a bunch of codes?

Also, why does the '93 L37 have 5 HP less than the newer L37's? Just the intake setup or different cam profiles?

I'm new to Northstar Engines and controls but I'm learning...

97EldoCoupe · #2 (**permalink**) 06-26-07, 04:53 PM

Oh and if anyone else attempts to do this cheap head gasket fix, DO NOT drill out the block- the holes are ready to be re-tapped as they are. I wouldn't advise this repair but it's working good for me- so far.

**Ranger** · #3 (**permalink**) 06-26-07, 04:57 PM

Man, that is a BIG undertaking. '93 is OBDI and '97 is OBDII so you will have to change the PCM and wiring harness. The engine will have to be mated to the 3:71 trans. I am sure there are probably other problems that I am not aware of.

eldorado1 · #4 (**permalink**) 06-26-07, 05:14 PM

The 97 intake won't work on the 93 engine. It can if you're stubborn, but I don't recommend it. It requires drilling and tapping the heads in 6 spots. That's just to get the intake to bolt on. Then you have to deal with the "mouse holes" on the intake ports. You will need to use RTV for the intake gaskets to seal. Then you will have to figure out what to do with the knock sensor.

The reason for the 5hp difference is the "mouse holes"; the EGR passage slot that is cut into the heads. 95+ eliminated it and gained 5hp.

97EldoCoupe · #5 (**permalink**) 06-26-07, 06:04 PM

Alright, what if I decide to drop that 2000 300hp L37 in, with the 3.71:1 tranny, and if I can find the engine harness that connects to the coil-on-plug setup and injectors and all, and get the PCM from that 2000 DTS, will it work with the rest of the car? Like the digital read-out on the dash and the rest of the onboard electronics?

CadillacSTS2003 · #6 (**permalink**) 06-26-07, 06:42 PM

2000 is ALSO a different engine
you need a 95-99 N*

97EldoCoupe · #7 (**permalink**) 06-26-07, 09:27 PM

I know it's a different engine, that's why I was asking about the conversion- what changes are necessary to make it work.

danbuc · #8 (**permalink**) 06-26-07, 10:03 PM

Enough to make it worth just buying another car. Another 1k would probably get you another STS that isn't FUBAR.

97EldoCoupe · #9 (**permalink**) 06-27-07, 11:37 AM

That was an "Eldorado" by the way- and where there's a will there's a way to get things to work-

danbuc · #10 (**permalink**) 06-27-07, 05:18 PM

Eledo, Seville...they all use the same drivetrain. If I had a 1978 Chevy Caprice that had cracked valve seats in both heads, I wouldn't spend the time trying to adapt a set of heads off an LS1 onto the engine to fix it. I'd just buy a new engine. Sometimes you have to just cut your losses, and move on. Your trying to build one engine out of two, and that usually doesn't work very well, especially when the parts don't match. Your best bet is to just buy a new engine, or find another car for a decent price that runs well. By the time you finish adapting 93-94 intakes to 96-99 blocks..or whatever your planning to do, it would be easier to just start from scratch with a new or salvaged unit that works fine right off the bat.