jm93rx7

iTrader: (7)

Has anyone ever done a rebuild with one S4 housing and one S5 housing? What would happen if it were to be done?

Radial GT

iTrader: (16)

They are basically the same. They have a slightly different casting on the top that MAY make contact with your intake. What kind of engine/year are you running?

NOPR

which housing are you switching? if its an aluminum housing it wont matter, but if its an iron you have to be careful about EGR because it doesnt line up with the s4 lim

jm93rx7

iTrader: (7)

the car is an 88. The reason i ask is last night we were about to put my motor back together and realized that the person who had the car before when he did his rebuild on the car had used one S5 housing and one S4 housing. After looking at the housings it looks like the bottom spark plug hole on one of the housings is closer to the top spark plug hole. The guy doing the work didnt want to take a chance with it due to it might have timing issues and any problems that might occur with putting the motor togehter like that and decided tha we should re port 2 matching housings and use it. The new housings we used are in much better condition but i was just curiouse what would happen.

jm93rx7

iTrader: (7)

Plus the person who had ported the original housing did a big porting job . Now on the new housings the porting is a little smaller.

Radial GT

iTrader: (16)

Like NOPR mentioned in that year, your intake will not hit. But the EGR will not function correctly. It would run fine other wise.

If you are in a area that does not have emission testing be sure to remove all your EGR items. They may cause your engine to run a little strange with the different housings. Could end up building up carbon faster than normal.

Radial GT

iTrader: (16)

As long as the 2 housings your using have equal sized ports. You will have to even them out if you have to.

jm93rx7

iTrader: (7)

the car has no emmisions . It just has the bare essentials to keep it running.

jm93rx7

iTrader: (7)

well i guess i have a spare set of housings now.

RotaryEvolution

iTrader: (30)

S5 spark plug timing is different than S4 rotor housing spark plug timing due to the differences in compression.

DO NOT MIX THEM!

alexdimen

iTrader: (13)

s5 housings also have a more durable chrome coating. the s4 would wear faster than the other, though that is a long term concern.

NOPR

yup, i double checked this tonight, i never knew!

although, im not sure mixing them would be a huge deal because if you think about the timing its still sparking at the same point during the rotation of the rotor, just sparking a different spot on the rotor. that said, i dont think i would do it in my engine, but its probably not worth tearing an engine down for.

RotaryEvolution

iTrader: (30)

believe me you don't want to mix them...

i rebuilt a jspec S4 engine, well long story short... the S4 Jspecs use the same timing as USpec S5 and S6 engines, his particular engine blew the rear rotor and housing so i replaced it with a good S4 housing. after about 8 months the car started having idle issues and lack of power, i tore the engine apart and found it had eaten a side seal and this was a stock port motor so it was not a porting issue nor have i had this happen with my ports either so i could only relate it to this mixed housings. luckily all i had to do was reman the rotor, swap the housing and replace all the side seals, the damage was all superficial.

so after hearing my story i suggest not toying with the idea.

NOPR

thats really weird...... i guess i wont be mixing any housings any time soon

rx7man13b

I just put a S5 block into a S4. With the spark timing being different, am I hurting anything using the S4 wiring and ecu

NOPR

no, it should be fine as long as both housings are the same series.

jm93rx7

iTrader: (7)

I had an S5 short block with all S4 wiring , manifolds and turbo and it ran fine.

alexdimen

iTrader: (13)

i was wondering the same thing, but mine runs fine as well. perhaps the ignition fires at the same time due to the CAS, it's ust the placement on the housings is different. the ignition placement is apparently specific to rotor compression.

now that i think about it, it might make a difference if you used S5 housings with S4 rotors. maybe drop some effeciency/couple horses.

jm93rx7

iTrader: (7)

before it failed the motor ran fine with those housings. I was just curiouse of the effects that set up would have. On the new motor i did use matching housings