what r the diff between usa model 13bts and jdms?

 

there are minor differences.. like the vacuum line for the brake booster goes into different spots.. most everything else is the same.... most people can swap them out w/out any headaches

 

any power advantages?

 

nope... still the same as usdm.... s4 182hp s5 200hp.... id assume there was a slight advantage though w/ the delete of the precat

 

IIRC the J-spec engines have less emmisions equipment.

 

Yep, the only major difference is the lack of emissions equipment. As stated earlier there are a few other minor changes of locations of a few things, but nothing that really effects performance. The engine itself is still identical.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/us-vs-japan-fc3s-490591/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/jdm-13bt-450431/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/usdm-vs-jdm-13bt2-408897/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/difference-between-usd-jdm-299458/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/whats-difference-between-2-a-287616/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/jspec-horsepower-254724/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/difference-between-j-spec-us-spec-2nd-gen-74672/

 

so then why do some many people have trouble wiring jspecs up?

couldn't you just use a usdmspec harness with usdmspec ecu and fly?
(with a few little modifications to RHD)

 

Spark timing is different, no EGR on the LIM, brake booster line is in different spot on the manifold, fuel runs through the rails in the opposite direction from the Aspec...****, what else...

I think that's it...

I'd use the Jspec ECU if you can get one.

oh...and don't mix and match jspec and aspec housings...even though they may be from the same series engine. The leading plugs are spaced differently...
Ask Karack if you don't take my word for it.

 

don't remind me...

 

That's what you're supposed to do. Anything else is just creating unnecessary and pointless extra work. And the only RHD-to-LHD change that needs to be made is a new brake booster vac hose.

Why? There's no advantage to it.

Are you basing that on confirmed info or just your experience with one engine? I've seen no evidence that different rotor housing were used in different markets, but we all know S4 and S5 spark plugs are in slightly different locations and how easy it is to mix and match housings.

 

Correct and the they COME with Dual Pulleys I have one....

 

no egr and sub zero, some other things ummm brain fart ahha

 

They did not come with dual pullies stock. How would it, since they all come with air pumps?

 

yes the Jspec has identical plug timing as S5/S6. after about 8 months Funkspectrums engine lost a bit of compression on the front rotor which was still running the Jspec housing and a Aspec in the rear since that one had blown the rotor initially and i replaced it. this was a stock ported motor and after i tore it down i found the side seals had broken, a problem i had never found on any of the other engines i had built previously and still to this day have not had any issues like it, the only conclusion i could come to was the difference in spark timing. in any engine the power strokes need to be almost completely identical or the rotors would be working against each other, it appears the front rotor was working harder than the rear and let go under a hard load, luckily it was all superficial damage that was easily repaired but i replaced the Jspec housing with an Aspec housing so they match and now he has had no problems with it.

you can run an Aspec ECU with a Jspec engine but i would probably retard the timing a few degrees for safety due to the spark plug location differences.

 

Tell you what, I have downloaded the Training Manual that someone from down under gave us access to, and read the ENGINE section.

In that ENGINE section, page 1-5, it lists 8 major changes to the HOUSINGS. Number 7 mentions the "position of the LEADING sparkplug hole (Australia only).

So maybe that is a clue or I'm misunderstanding what I read. But it seems there is a front rotor housing for some model that has the front sparkplug hole located differently than some other front housings.

Or could it be KARACK had a front housing from an earlier 13B model that was in a first gen car at one time?

 

after i checked into it further both front and rear rotor housings had identical plug timing, if you line them up with an FD rotor housing they have the same exact spark plug timing front and rear as the FD has. i haven't seen many Jspec engines yet but from that experience i am a bit more careful now with checking the rotor housings.

 

That table is a comparison of the S4 engien to the S3 engine. It's saying that Euro-spec FC's got the old housings, and Autralian FC's got the new housings with revised coolant passages and spark plug locations. These were the same housing US and Japanese FC's used.

Like I said, is this one engine or all J-specs you've seen? It sounds to me like you had an S4 engine with S5 housings. That just means it was rebuilt, it doesn't mean all J-spec engines had different spark plug locations to US ones.

 

the housings had no knock sensor embossments(threads) but had S5 spark plug timing and S4 low comp rotors, i saw no indications the engine had ever been apart previously.

i haven't seen many Jspec engines so maybe this was just a fluke late model S4 engine, i have also seen S5 engines with rear irons with no added reinforcements at the upper rear dowel pin, the engine has gone through many stages so who really knows, it's pretty tough to know what you have with no serial #'s.

 

I was just speaking from personal experience as far as owning the god-forsaken engine...

I didn't mean to give out any mis-information but I felt the need to state the facts according to my experience...

It's true that you never really know what you're getting when dealing with an used engine. It may also be true that my Jspec was a bastardized hybrid...who knows?

I apologize once again for giving out any bit of misinformation if I did...