: 94 to 97 Northstar interchange question

Joseph Upson
05-14-06, 07:05 AM
About to become a Cadillac mechanic briefly to do an engine swap in my brothers 94 Concours that runs but has a blown head gasket. We found a 97 but so far have discovered that there are intake and EGR differences that will render the EGR system non functional should the 97 be installed in the 94 body, is there anything else that would cause compatibility issues that someone can inform me of to further encourage purchase of the time sert to repair the current engine.

Thanks for any advice, that can be offered, I have plenty of engine building experience and am aware of the TLC required for the Cadi engine which is why I didn't want to bother with it initially.


Loose screw
05-14-06, 02:48 PM
Why not do a Time-sert repair instead of the head threads or better yet just rebuild it at least then you know your head bolts won't pull out. There aren't alot of part to repalace. Gaskets, seals, rings, rod bearing (not reusable once cap is loosened) new head bolts and a Time -sert kit. $1000 bucks and your done. You don't know if or when that will happen in the 97 which it may have all ready.

How many miles on the 94?

05-14-06, 09:09 PM
For starters '94 is OBDI and '97 is OBDII. That has to present some problems.

05-15-06, 02:39 PM
It is easier to just fix the 94 than trying to mix parts. Find a used timesert kit (if possible) and it'll only be as low as a few hundred for gaskets. More if you decide to do more than necessary.

05-15-06, 02:52 PM
...and the '96 and up Northstars have MAF sensors, where the older ones do not! Like other have said, it's better to get another '93-'94 Northstar long block.

05-15-06, 04:49 PM
What if you just pitched the 95+ intake in its entirety and put the 94 intake (Manifold, tb, cover, all)? I know you can put a 95 engine (OBD1) in a 96-99 car (OBD2) and you just have to swap manifolds (and TB).

05-15-06, 05:17 PM
you'd lose the egr, which he mentioned in his first post

Joseph Upson
05-15-06, 05:19 PM
Thanks all for your help, the majority of my engine building is with the small block and V6, I didn't have enough info to know for sure if trying to replace the gaskets was the best option with all of the becarefuls I've heard regarding this engine, for example I didn't know loosening a rod or main cap which ever was mentioned required replacement of the bearing. I was also told by the friend that lead me to this site that the EGR system is different and apparently non interchangeable.

I will take the time-sert approach as well as the main and rod bearings since the oil was contaminated and the engine has over 100K on it. Thanks a bunch and if there are sources on this site that will further help in the process please list them for me.

Thanks again,


05-15-06, 07:34 PM
From everything we have heard here and from what our old guru has said, you might want to leave the lower end alone. Rod & main bearings are supposed to hold up very well for over 300K. I'd just Timesert and replace the HG's.

Loose screw
05-15-06, 07:41 PM
with 100K on it yes do the whole show fortunately there is not that much to reworking of the engine or major parts replacements besides the Time-Sert, do them all head thread (no if, and or buts) the mains only if they look ruff and weak (they seldom need any work).

Do replace the rings, the cylinder will be like new and the pistons can be reused - clean the ring groves completely - you will probaby have to soak them to soften the carbon and sludge.

valve job unnecessary 95% of the time

Plaining heads and block surfaces ussually unnecessary.

rod bearings - on most makes of engines are all compression fit design (unless they have a steel back - rare) and should be replaced if the rod cap is even loosened or bearing will spin.

Crank bearing will not need replacing unless damaged (they are steel backed).

Replace front and rear seals for sure and halfcase/oil manifold and oil pan seals if they have never been done (common small oil leak source).

On the 94 the oil pickup tube will not match the new oil manifold they supply now and the anit-oil foaming plate (I forget the name but it is curved and has big holes) is now different, it looks the same but is a different hieght and the new one must be used with the new oil manifold. A couple hundred bucks for the whole the above. Note parts guy may not know this. but you will need all three of the new versions of those parts

So basically it all the gaskets and seals, rings, rod bearings and Time-Sert all head bolt threads. 1/2 inched drill required. Get the engine steam cleaned extremely well before you start, you will be glade you did and sorry if you don't. Allow more than enough time to take your time and it will be a good experience - you do have all the skills to do it and this forum to help. Get the factory service manual - a must! :thumbsup:

Joseph Upson
05-16-06, 05:12 AM
I'm usually pretty maticulous about engine rebuilds since they have all been for personal projects and not wanting to do it twice, so I will certainly time-sert all of the head bolt holes as well as several other things.

I'm currently working on a twin turbo project for my 86 Pontiac Fiero which I have a 2006 Pontiac G6 3500 V6 with ~7000 miles on it waiting for install. I had to remove the new style press on 58x reluctor ring from the crank to have one custom made 7x to work with the 90 Turbo Grand Prix ECM which will be used to run it. So obviously I had to disconnect the rods where in the bearings look like new, I'll use a magnet to test for a metal backing otherwise from the thread above if they do not have the metal backing they are compression fit and must be replaced unless the metal used is not magnetic, I didn't know that.

Thanks again for bringing me up to speed.

Loose screw
05-16-06, 11:45 AM
The the way thre cruch fit bearing work is they of course are compressed when you tighten down the rod cap but you could still remove the cap at this point - it is when the engine is run that the bearing fully deforms and relaxes or sets into the rod and binds under pressure with the contact surface. Once that has happened they are not reuseable, they have lost that oversized compression nature and will not be under the same compression to rebind or seat.
Steal backed bearings like crank bearings remain the same size and the steal will spring back again and again. But rod bearing bearing are softer and do not.

That is what Bbob a real N* engine engineering expert told us - recomend reading:

he also said: "Never, ever take a Northstar rod bearing apart unless you plan on replacing the bearings. You cannot reuse a rod bearing shell no matter how good it looks. They are crushed considerably upon assembly and once heated/used they bearing is set to that crush and will not have enough crush for dissassembly and reuse. Nature of the beast to handle 7000 RPM....."

05-16-06, 06:22 PM
Look at the Head Gasket thread in the Tech Tips section. It has most of the info you'll need.

05-16-06, 06:31 PM
I don't see why you would lose the EGR. I will investigate this.

I do agree though that fixing is always better in cases like this.

So about the oil issue... Does the original 1994 not have a windage tray? It;s mentioned that the oil pickup has to be changed because of it, so I was wondering...

05-16-06, 08:19 PM
The 93 and 94 heads have slots milled into the intake ports. They are the only years that have these, to facilitate EGR into the individual intake ports. Later models have the throttle body spacer that injects the EGR gases into the plenum. AFAIK, all northstars have a windage tray.

05-16-06, 08:49 PM
The 93 and 94 Northstars have the EGR ports in each intake port and the phenolic spacer plate between the intake manifold and the cylinder head. The intake manifold is the large box with the plastic tubes inside.

The 95-99 engines have the plastic intake with the external EGR feed into the manifold.

In order to swap a 95 or later Northstar into a 93/94 you would have to keep the heads, the intake, EGR system, water crossover, etc. from the 93/94. The later model short block would work but the rest of the engine would need to stay with the 93/94 parts.....


If you put the 95 or later engine into a 93/94 you could put the complete engine in but you would have to rework a lot of wiring including pulling the injector harness from inside the intake and using it on the external fuel rail for the 95 or later. It is possible to use the complete later model engine (95-99) in the 93/94 but it takes a lot of rework of the harness and other hardware.

05-16-06, 10:22 PM
Interesting. I didn't know the 93/94 had the EGR done in that manner.

Joseph Upson
05-16-06, 10:52 PM
I think I'll stick with the time-serts

02-17-08, 01:20 AM
I finally found this thread to be helpful .

In order to swap a 95 or later Northstar into a 93/94 you would have to keep the heads, the intake, EGR system, water crossover, etc. from the 93/94. The later model short block would work but the rest of the engine would need to stay with the 93/94 parts.....

So basically I'm doing the complete opposite but since I'm going to swap a 94' in a 96' I can use the 94 block and heads and just continue to use the 96 intake, plenum, TB,' INJ etc..

Or I may run into problems matching the 96' external EGR Fed plastic Intake manifold to that of the 94' Northstar.

Again sorry for the multiple posts but I think I'm finally in the right place.

I feel like I've been talking to myself all day. lol