I have spent the last day searching threads to get a better idea if I need the Light or Heavy Double Supertech valve springs for my ~300hp 8000rpm VVT motor build. Stock valves, lifters and stock VVT cams. 95% street use with 1-2 track days a year (optimistic). The best info seems to be in Emelio's sticky stating "For any engine expected to see 8000 rpm whether intentionally or not, we recommend a heavier spring like the Supertech "light double" spring kit. Above 8000 sustained, the "heavy double"."

Since I am not planning on revving the engine over 8000rpm with stock cams and lifters, it sounds like I would be OK with light double springs. It sounds like heavy doubles would add more margin for an accidental downshift, but what is the real down side of the stiffer springs. I know there is the additional frictional load of the stiffer springs, but what does that mean in real world applications? If we are talking about a slight hit in MPGs then I wouldn't care, but I would not want valves, seats or cams to wear significantly faster due to stiffer springs. Long story short, why not just go with the heavy doubles?

I feel like this answer used to exist in a nice clean thread, but had no luck finding it!

 

It's on our product page. View it in desktop mode. https://supermiata.com/supertech-val...-miata-BP.aspx

Copied here:

Three kit options depending on usage. The below are estimates only and will vary greatly depending on valve weight, cam lift, and other variables.

Single spring - seat pressure 56lbs @ 34.2mm
Sustained revs to 7400rpm, mechanical over rev to 7800. N/A only

Light double spring - seat pressure 63lbs @ 34.2mm
Sustained revs to 7800rpm, mechanical over rev to 8200. < 8psi boost

Heavy double spring - seat pressure 74lbs @ 34.2mm
Sustained revs to 8500pm, mechanical over rev to 9000. > 8psi boost

 

Springs exert a lot of force against the bucket/cam interface, leading to wear. Idea is to match the force needed to keep valvefloat away, and wear to minimum. So heavier springs than needed just add wear without any benefit.

 

Need subs if it’s gonna live above 7500rpm.

 

Is there even much point in spinning stock cams that high?

 

Over 8? No. By that point you should be into different cams for sure.

 

I feel like you'll see it nose over well below 8k, no? From memory the stock cams are only making power to ~7400ish?

 

I mean it can be useful to turn 8k for other reasons but you're well past the power peak of stock cams at that point

 

If I understand this correctly, I should be running the Heavy Double springs just due to the fact that I am running over 8psi boost (15-17psi), even if I don't spin it up to 8000rpm on a regular basis. While I am not looking to make peak power at 8000rpm, it would be nice to eliminate an up shift or two at the end of the straights on the track that I run at most. I was not planning on running subs since I am not planning on running at or above 8000rpm on a regular basis.

Turbofan, is there any real measurable downside to running the 11lb stiffer Heavy Double springs? It would seem that it is a relatively small increase in seat pressure compared to the light doubles.

 

Yes, that's right. Many people get away with running normal valve springs but, say an NB1 running those boost levels may be floating valves occasionally without even realizing it. Worth the security in our opinion.

 

You cannot buy a valve spring for a Miata that has "too much" seat pressure.

I have NEVER seen a boosted Miata make less power with stiffer springs...actually quite the opposite. Every time we went up in seat pressure, we made more power and the valves lived longer.

So my advice (which is backed by a ton of experience with this specific application) there is ZERO downside (other than cost) to running the stiffest, highest quality springs you can afford. There is actually quite a bit of upside to running a stiffer spring.

 

That's what I am looking for. Thanks!

You guys had me wondering if I need to ad shim under buckets, but after pricing them I do not think I can justify the >$500 increased cost.

 

Shim over will definitely not like 8000rpm.

 

I wouldn't say definitely. I'd say more like not ideal.

On autox for short bursts, I hit 8000 often with stock shims / lifters (MSM) and the Volvo springs. 2 years with several co-drivers and still silly as can be. High comp, e85, 27psi silliness.

 

You should be able to get the Mazdaspeed SUB for about $200 from Mazda Motorsports, then you'd just have buy shims, so I think $300 is a reasonable estimate all said and done.

 

I think I have about $350 in my SUB setup along with a handful of spare shims.

unless you have a really good reason to spin 8k rpm, don’t bother. Probably a waste on stock cams bless you just have the parts laying around

 

With a ported head, ST single springs, S2 throttle body, flat top, Tomei cams, and RB header, I set rev limit at 7800RPM IIRC for safety, but power was flat lined around 7600. Stock cams give up the ghost around 6600, another 400-500rpm is just used to put the next gear in the power band.

 

This is of interest to me. I have stock ‘99 with TD04. On track, I run 7.5 psi @ 7000 soft red line. On street, up to 16psi.

This sounds like I should be replacing my valve springs if I want my head to last. Am I understanding correctly?

I suppose I could check to see if my clearances are tightening up.

Also, anyone besides Guido’s shop have experience with Comp Cam springs?

DNM

 

Nobody on this forum has access to the equipment required to measure the power difference between the light double and heavy double valve spring. Get the heavy double.

If you cannot justify the $500 for SUB lifters, I would strongly advise that you reconsider your plans to exceed ~7400rpm.

 

I will have to look into the Mazdaspeed SUBs, I have only looked at the Supertech option. I am planning at setting the rev limit around 7500 since I am running factory cams.