Mazda Valve springs
I took some time and checked out some valve springs for the Mazda 1.8 BP engine.
For a base line I checked the SBI catalog.
SBI replacement valve spring
Part # 160-1250
46 lbs @ 1.600
1.831 free length
AERA, Automotive Engine Rebuilders Association
States the spring installed height is 1.555
The spring pressure is 50-57 lbs closed
OnDemand5 lists the spec as
39.5mm/1.550 installed @ 19.9kg/43.87lbs
I started off by checking 8 valve springs from 2 different heads.
All testing was done using a installed height of 1.555/39.5mm
I found they fell in the range of 37-40lbs
When the factory .020 spring seat was used they came up to 40-43 lbs.
So close enough to be put back into use for a stock rebuild.
Next up are SuperTech,(ST) and Brian Crowder (BC)
I know the ST is widely used on this fourm.
I started with the ST Dual springs, that are advertised to be 74lbs @ 33.75mm/1.329
The ST is a bit light, when the math is done, Keep in mind ST supplies a .250 thick spring seat.
So 1.555 - .250 = 1.305 So .025 shorter installed height
So I tested, I found the springs will install 90lbs @ 1.555
This is a bit off still, due to the inner spring not being fully compressed from the Ti retainer not being installed.
Now I pulled the inner spring, so it would be a ST Single spring
On the ST Singles, ST advertised 56lbs @ 34.2mm/1.345
But here again, with the thick seats, the installed height is shorter by .040
When I pulled the single spring with the thick spring seat, I measured 70lbs
At this time, I have not checked the ST Ti retainers against a stock retainer to see if they step up or not.
Now on to the Brian Crower valve springs.
These install 80lbs @ 1.420
If the same .250 thick ST spring seat is used, the seat pressure is a whopping 110 lbs
That is a bit high, so I need to drop some seat pressure.
Now with two .060 thick shims, .120 total
I get 80lbs on the valve seat.
I like this for a boosted application.
The math works out better also
1.555 - .120 = 1.435
If I add a .015 thick shim, I will have 84lbs on the seat.
Since these are a cost effective spring, that does not require a custom spring seat and will work with the stock retainer, I can see this set up going into use on a wide range of builds.