I am sure this has been discussed before, but I couldn't find one in a list form. So today I was really bored in my Human Resource Managment class, and decided to make a Pros and Cons list of buying a Jspec engine or getting an existing blown engine rebuilt. Although this is

for my 87 TII, this can be a guide for all rotarys alike.

Rebuild/Reaman:
Pros
1. "New" engine
2. No modifications needed (direct drop in)

Cons
1. More expensive (altough "new")

Jspec S4/S5 (same series swap):
Pros
1. Less expsensive
2. Get whole kit and Caboodle (spare parts)
4. Have spare parts
5. Or sell extras and make a few bucks on the swap
6. Direct drop in

Cons
1. "Used" engine
Unknown actually mileage/compression
How it was taken care of

Jspec S5 in S4:
Pros
1. Less Exspensive
2. Overall S5 is better tha S4 (turbo, manifolds, block, etc)
3. Almost direct drop in if using S4 accesories
4. Easier/cheaper to modify (mainly electrical)
5. Have spare parts
6. Again, sell parts not needed and make a few bucks

Cons
1. "Used" engine
Unknown actually mileage/compression
How it was taken care of
2. Need wiring harness, ecu, etc
3. Need to modify existing dash harness (S4) to comply with S5 ecu

THE GIVEN:

Rebuild
This is the smartest choice. Really this is going to be the easiest way to get your RX7 back on the road, pull engine, send to get rebuilt, put back in.

Jspec (same Series)
Like above this is a pretty easy process, and you may beable to almost break even or make most of your money back. Or just have spare parts for when other things get tired. BUT, its USED, life expectancy will be unkown because it may have been abused.

Jspec (different Series)
Obvisously depending on how you go about this swap it CAN be SIMPLE or a HEADACHE. You can drop in the block and due minor modifications to fit, like TB, front cover, etc. And use the S5 Intake manifolds, turbo, etc. OR you could undergo a complete swap with harness, ecu, everything!


MY OPINION:

Rebuild
I guess I am not as smart as others, since I have been thinking about this so much. My ONLY problem is I will be tunning my engine once the break in period is over. Which may bring me back to where I am now, ie blowing the motor.

Jspec (same series)
Smart choice, It will be cheaper, so I will not feel as bad if it blows while tunning it. Plus you have extra parts, and while you are having fun tuning the car you can either try and sell what you don't need, almost everything, and try to break even. At the same time you could keep the short block, get it rebuilt and have a spare on hand to limit down time.

Jspec (different series)
Can be a smart choice as well, depending on how you under go the project. Orginally, before I blew my engine, I was going to get a S5 and swap everything in. Then it dawned on me that the dash harness from the ecu would not comply. I have heard of a few people that have found there ways around this, but I am unsure of how difficult this could be. Or I would just swap most of the parts, to have a hybrid S4.5. Again most of this is the same as doing a same series swap, by having spares or selling and making a few bucks.

Orginally like most other people, I wanted to get a S5 TII or NA. But after looking for a long while I could not find anything reasonable. So I decided to expand it to adding a S4 TII to the list, low and behold I know own a S4 TII. My biggest problem with the S4 is that most of the parts are more exspensive, and tunning can be alittle more diificult (lacking a few things compared to the S5), aside form the obvious of less power and exterior/interior looks. That is the main reason for wanting to try and convert it to a S5 Drivetrain. Plus I would like to have dual TPS, better turbo, Manifolds, TB etc so I would need to swap the harness and ecu for some of those. Maybe I am just stupid and really childish, but this is how I feel.

How difficult would it be to use a Jspec S5 harness and ecu in a USDM S4 or even swapping a USDM S5 harness and ecu in a S4? And what would need to be don? I don't mind splicing wires and ripping into the dash, because I am going to need to fix my heater core anyways. I might as well make it worth while.

Feel free to add or make comments on anything, but please don't flame. Maybe this could get archived for others in years to come.

 

you could get a j-spec and drop that in and rebuild ur old motor on the side... that way if anything happens you can swap motors... and rebuild the other one on the side... and always have a spare!

 

 

I went with a jspec. Its still holding up fine. I also watched them do compression so that wasn't a variable for me.

 

my answer, I went with a rebuild...

 

Let me know if you need it rebuilt. I do these engines for a living and can get you some good deals on parts.

B

 

Well if you go with a rebuilt you can always port it. With a Jpec you're getting the stock ports.

 

This isn't even a comparison. The differences between US and Japanese engines are trivial, so really you're comparing a used, unknown-history engine to an almost-as-good-as-new one.

No matter where it came from, any used engine you buy could last for years or blow the day after installation.

 

I say.......J-SPEC!!!!!

 

Same could be said for a new engine, really anything can happen. Its all about luck. Like my dad has always told me, there are no garuntees in life.

Yeah your right it is basically used v new, but don't forget you get more than just a block from a jspec. If it was just a used block, I wouldn't even consider it.

Jspec: 2
Rebuild: 2
Both: 2

Pretty even field.

 

and someone needs to make one of these posts a sticky maybe, or possibly link to it in the faqs. This question has been answered a million in one times, it all comes down to price, luck, and piece of mind.

Logan

 

Thats exactly why I took the time to do this, it gives basically all the pros anc ons, but again its all up to the person on which way to go....

 

i'm in the same postion, however i think i'm just going to go with the jspec cause of cost, the person that's doing this is going to rebuilt the jspec motor for me and put an aftermarket ecu on. so i don't know but i do know that you can get a used jspec engine for under 900 bucks if you look. shrugs.... but the guy that's selling me the engine is taking along time..... so yeah... don't know

 

I'm planning Jspec S4 if I can find one. I am VERY limited on money since my daily driver decided to blow a coolant seal.

I am hoping it will last me around 3-4 months because then I'll have enough to go with a rebuilt.

I say a Jspec is the foot in the door to the new engine.
A stepping stone for people like me which are about to do a NA to TII conversion.