Long story short:
My cylinder head has been dismounted completely (not by me), and the amateur has put everything in a box.
So when he's mounting it again, he discovers that "wow, the valve springs aren't identical. wtf do I do now?"

So he calls me wondering, and I sure don't know. There's a reason I had him do the job..

Do any of you know?
The difference between them is that one of them is more "pointy" or "sharp", and mx5parts.co.uk differ on the part number. They don't show what is what though..

SI4517 is for the inlet valves
SI4508 is for the exhaust valves

I need a visual description of the difference, and the answer to which valve springs to on which valves.

Oh yeah, did I mention that I need the info fairly quick?

 

Here's everything I can find:



This is from the '92 FSM.

 

Yeah, sadly it doesn't give the information I need :(

Got a picture of it btw..

 

Could it be that the previous owner just swapped 8, and they're from a different manufacturer?
From what I've heard, there should be no size difference between the OEM springs..

 

all the performance springs I have looked at are all the same, not sure about oem...

 

The specs on them are different- read what I posted above.

Here's a guess: they're both spec'd to nearly the same extended length, but loaded to 40mm, the intakes are spec'd to 168 lbs vs. 134 for the exhausts. Which ones are thicker / stiffer?

 

From 3 different sources I've gotten 3 different answers. (Here, FM and Mx5parts)

I put the stiffest springs on the intake valves. Start praying.

 

Hi Loki79

I know it's an old question, but I was in exactly the same situration. It was imopssible for me to find any helpful info on the internet. So maybe this ínfo could be helpful to others in the future.
I have a spare motor, and is working on the head to optimize it (porting, polished, 3 angel cut). When I was checking the springs, I got suspicion that they maybe had been monted in the wrong location.

By checking on another head we found out that the "pionty" and stiffer ones is for the intake.
That also make good sense to me, because this valves is the biggest and heaviest.
So your head hopefully had been running fine for the last 2 years :-)