I should have been clearer with my previous statement. Supertech advertized spring rates are achieved using the factory shims. Without them spring rates are lower.

By measuring and shimming to your own spec you can use whatever shim(s) you need to.

 

Gotcha'. Thanks.

 

I'm going to ask a stupid question. I thought the BP5A cam was a stock cam in most of the world and a drop in replacement here in the USA. Why do you need more spring than the factory springs?

robert

 

Pretty sure more spring = more revs

 

"With the MS, Soft Cut (reduced timing to 10*BTDC) is 7000RPM and Hard Cut (Fuel) is 7200RPM." Yes, if he was turning more RPMs than stock, that would make sense, but he isn't.

robert

 

Stupid question, sorry...

Factory shims.. Are we talking about these? (With an arrow next to it)





I mean, these are only 0.02" (0.5mm) thick.
How would such a tiny height reduction make a difference in spring rate?

Yes, I just found all 16 of these in a box of parts (I had received from the machine shop) left over from the time when I switched over to Supertechs. Guess they did not think they were necessary.
And, I had bigger fish to fry at the time, so I never checked...

 

Yes godless commie those are suppose to stay. I forget the specs but kinda remember they are worth somewhere around 7lbs of seat pressure. I do remember they were a LOT more than I expected.

 

You're not missing anything. I'm having some real problems with this "fresh" engine -- and I shouldn't be. We're just trying to figure it out. It did exactly the same thing on ST valves and springs that it did on the OEM valves and springs (in other words, the OEM wasn't any better or worse). I'm obviously not a happy camper.

 

The spring rate is the same but the shims adjust the seat pressure (call it spring pre-load if you want).

 

Pretty simple - the spring rate on ST Singles is ~9.4lb/mm. 0.020" shim means seat pressure should rise by ~4.7lbs.

 

Gents, I just pulled the head and posted some pics and videos on the other thread:

https://www.miataturbo.net/engine-pe...en-warm-82232/

 

No shim

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Shim

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Thank you guys.
I really did not know this.
You live and learn, I guess.

 

Something else to keep in mind, the stiffer the springs, the more force you add with the shims. It's a linear relationship. So, adding that shim to ST light doubles has more effect than on ST singles which, in turn, has more effect than on stock springs.

And I can tell you that the shims were left out on my September head rebuild.

 

Bingo. That's why on my "supertech heavy doubles" the effect was 7lbs+, IIRC it was closer to 9lbs.

Now onto the next question. What spring pressure should you run with a BP5A cam?

 

Machine shop pulled my head apart today. ST singles without OE valve shims.

Curious along with K24madness as to what is the recommended Valve seat pressure for BP5a cam, and does anyone have the part number or place to acquire a set of OE shims?

(If anyone has a set laying around PM me!)

 

Is there a current discussion on this issue on a different thread as I am interested in what people have found out now that it is 4 months later. I am fixing to install some 1+ overs and was thinking about just using the inconel exhaust with OEM intakes. I would like to also use the 1+ intakes if the suggestions above fixed the problem.

 

I ended up going +1mm intake and exhaust, but Manley not Supertech. Supertech light double springs, stock shim over bucket, bp5a intake, stock exhaust cam. Will be a zippy N/A motor for now, eventual TSE turbo. Motor is being swapped this week. Will report on findings over next few months.

 

I run supertech undercut coated stock size intake valves, +1 inconel exhaust valves. I cut the seats myself, did a 5 angle on the intakes, 4 on the exhaust, kept the seat widths conservative. Stock shims/buckets, I just tipped the valves to adjust the clearances.

I run heavy double ST valve springs without the shims (opps). Reved the engine to 8,800 about 200 times, put about 2,000 miles on it. Broke a piston 3 weeks ago and checked the head, valves all seal perfect.

My guess is if you're vavles are tightening up, it's due to a machining error. Something is wearing in causing the clearances to tighten.

 

Any chance you guys are wearing out the valve guides and that is allowing the valve to move around a bit on the seat? This happened to me years ago on a honda engine.