BogusSVO

iTrader: (1)

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.

EO2K

iTrader: (37)

Neat!

What's the difference in price? I've not heard of BC, and I think the bias tword SuperTech around here comes from brand recognition more than anything else.

slmhofy

iTrader: (5)

One question and a couple of notes.

So you're basically doubling the seat pressure from stock?

You can look it up in your books, but I had heard that the earlier Miata engines, maybe 1.8 94-97 had slightly stiffer valve springs. I had also heard that volvo b20 engine valve springs were used as a hi-po upgrade.

BogusSVO

iTrader: (1)

I use a ton of the BC springs on the 4g heads I build. So I was talking to them one day and wanted to find a budget spring of sorts for the Mazda, so I gave them the spring specs from a used BP spring, and found these.

No as far as price, the ST single kit w/Ti retainers and thick spring seats is around the $325 range, The BC springs with commonly found spring shims along with using the factory used steel retainers will go about $125

I still need to check how the shims and springs fit on the head casting, from all I have checked to this point, it looks to be a solid set up.

BogusSVO

iTrader: (1)

Getting close to double the stock seat pressure, of 43-44lbs

Keep in mind that when the engine is boosted, the valve spring is given a second job, the spring now has to keep the valve closed against boost pressure.

Figure that there is 1 sq/in of area on the back side of the intake valve, now add 20psi of boost, you loose 20lbs of spring pressure just keeping the valve closed.


Ill check my books and look into the springs you mention.

BogusSVO

iTrader: (1)

Slmhofy

Checking my SBI catalog, the springs 160-1250 are for the 1990-1997

As far as the Volvo B20 spring, SBI does not have a listing for springs, it could be beacuse they are an older engine, B20B and B20E were made from 1969-1978 and is an OHV

slmhofy

iTrader: (5)

Roger that. I was just trying to throw out some information as it seems like you love knowing everything there is to know about what you're working on.

TNTUBA

iTrader: (1)

Do you have a part number for the BC springs?

miata2fast

iTrader: (2)

This is a very informative thread. A+

The question I always wanted to know is how do you calculate the desired seat pressure for valvetrain weight, camshaft specs, and rpm range?

Don't you want to have just the right amount of spring compression for your application? I have seen too many motors with springs way too big for a particular application, throwing horsepower away.

karter74

iTrader: (4)

Another question, can't too much seat pressure put unnecessary strain on the camshaft causing accelerated wear to the lobes? At what point is too much seat pressure undesirable?

18psi

iTrader: (76)

I'm wondering the same thing as the 2 posts above:
whats the perfect balance for your average boost setting (10-15) and/or a bit higher (20+)

Something tells me that you don't want to go too stiff, or you'll be putting excessive wear/tear on your valvetrain and/or throwing away power.

Some completely un-educated guessing here: if a stock motor operates at 1 bar and you're running 15+ psi (2 bar) then the double spring rates shouldn't be too bad? Probably doesn't work that way, just guessing

BogusSVO

iTrader: (1)

True, the more info I have, the better understanding of what I am working on.
Thats what brought me to this foum in the first place.

"Now you know, and knowing is half the battle!"
I would say I watched GI Joe a bit often growing up



Not at this time, this is a set up that I am working on with BC.

Honestly, I tend to be a tad heavy with spring pressures.

The springs first job is to keep the valve in contact with the cam, nasty things happen when it fails at that job.

Ramp rates and cam lift, have to be taken into account, along with boost pressure.

Also you have to allow for wear on the spring, after a season of track use,or a year or two of "fun" street use, the seat pressure will be a bit lower than new spring.

I do not know a fourmula for figuring spring pressures, it boils down to the head builders experiances.

But you are correct, they can get too heavy and cost HP, or be too light and cost HP and/or damage.

Efini~FC3S

iTrader: (4)

Can I ask a stupid question?

How did we get along before BogusSVO showed up here and starting posting Awesome

???

...

???

Please let me know ASAP when I can buy these BC springs for $125ish, I'll take a set!

BogusSVO

iTrader: (1)

18psi...A stock engine is NA, so it operates in a vacuume, springtions do not have to be as much as a Turbo engine.

When you add boost, the spring now has to hold the valve closed against the boost pressure.

With a stock 1.8 intake valve, there is appox 1 sq/in.

So the first thing you do is subtract boost pressure from spring seat pressure.

So with 18psi of boost, and 70lbs on the seat ( ST single if dropped in) leaves 52lbs of spring pressure to keep control of valve motion with the cam.

Factory spring is 43, so you have 9lbs more than stock.

Efini, Once I am happy with the set up, and get back with BC on them. I will let you know.

mcfandango

iTrader: (1)

Curses! A potential value option starts to form just after I had my 99 head redone with SuperTech

miata2fast

iTrader: (2)

Interestingly, I never though to account for boost pressure trying to keep the valves open. I always wondered about others having issues with valve float, when I was running the same valvetrain at a higher rpm. Them being turboed and mine N/A.

TNTUBA

iTrader: (1)

Ok. I have been using the Sealed Power ZVS855's. They are about $61 from Summit Racing. At 1.56" installed height they have roughly 66lbs seat pressure and work with the stock retainers and keepers. Just interested if these are a better option.

codrus

When is there less pressure inside the cylinder than there is in the intake manifold and you want the valve to be shut? During compression, power, and exhaust strokes there should be more pressure in the cylinder, right? During intake, the valve is open. Or is it just for the brief transition periods around overlap/etc?

--Ian

18psi

iTrader: (76)

Exactly what I was going to ask next.

I'm guessing he's talking about the split second transition

Der_Idiot

iTrader: (2)

So what you're saying is... backpressure from the exhaust manifold or intake manifold can apply pressure pushing the valve in, while at the same time having it beat on my the CAMs causing it to float and turn effectively into a torch, burning the exhaust valves, yes?