Hey folks, my Aussie track car build is a deliberate copy of Andrew's Acamas, except with a GTX2867R instead of the EFR turbo. I have recently developed a big case of the "yips" (self-doubt/second thoughts) about the stock valve shim arrangement. When I did the research, it basically indicated that the criteria for whether or not shim-under-bucket lifters were needed was if the engine is going to see “sustained revs over 7500”. I figured it was a high-rev NA race engine strategy, and that I would not need them because I was planning to draw the hard-cut redline at 8000, with a soft cut starting at 7500. I am hoping that the new engine will have enough torque that most gear shifts will be around 6800-7000 most of the time. The other reason I decided against shim-under-bucket was that they added another $1500 to the build cost (yep, things are that expensive down here).




But now I have seen a case where an engine failure occurred at around 5000rpm, caused by the exhaust valve not following the cam profile perfectly due to exhaust pressures. Will post more info about the context and specs of the engine when I find out more, all I know at the moment is that it was in a fully prepped drag car.

Is anyone out there using shim-under-bucket for track cars with a max of 40psi, and a redline of 7500? I've been reading MT.net solidly for over 2 years now, and the shims just don't seem to come up as a widely-identified area of failure. I am just being paranoid, right?
Cheers

 

$1500? Maybe, if you are targeting lightweight buckets. My Gary Stewart race engine used gutted hydraulic lifters with SUBs, ran very aggressive cams to 8000 with no worries - even when I buzzed it to god knows how many revs (twice), nothing bad happened. When I had to replace them (welded cam failure damaged the lifters), I replaced them with more of the same. Buckets cost me stuff all, plus a bit of my time to gut them. Shims were pretty cheap AFAIR, got them from Melbourne. In fact, I must have a bunch in my workshop that you can have if you do go down that path.

I'd say do it, but don't spend $1500 unless you are building a screamer where a lightweight valve train is a high priority.

 

Thanks Gee Emm, that is an alternative I had not thought of! Which parts below are you messing with when you talk about "gutting" a hydraulic lifter, and are you just sticking the large over-bucket shims up inside, or are you using the little 6mm Supertech under-bucket shims?

 

Update: All I was able to find out about the 5000rpm failure was that it was running a lot more boost than 40psi, no one will tell me anything else because Racing Car Secrets (heavy sigh). I know we deal in facts here, and was hoping to have some comparative specs to share, but not possible. So does that basically mean the answer to my question is something like "without more info its impossible to say whether that failure has implications for me"? I think it might...

 

I think you should do it if you are building the head. On my built motor I'm doing +1 valves and SUB just for more flow to maximize the rest of the system

 

I did shim under bucket on my spare vvt head. Used Supertech valves which where slightly longer. Made it impossible to find shims and the builder wasn't confident about tipping the valve as it'd eliminate the hardened surface and could put it out of lash over time. Base circle on stock cams was too large so I ended up buying Tomei cams to finish it.

Now it sits unused because I don't know if it'll interfere with my pistons and have yet to clay a yet to be built short block to find out.

If you want a fully built, pnp vvt head with +1 valves, Supertech dual heavy springs and Tomei cams, lmk.

 

Most kind, Psyber. But was hoping to avoid the (relative) complexity of VVT and non-stock cams

 

It was a long time ago, but as I recall everything comes out, and you are left with a post inside what that photo calls the 'main HLA body'. The small shims sit between the post and the valve tip. I have no idea of the valve stem length, because I was replacing like for like.

You could measure the depth of the gutted lifter (end of post to top surface), and compare it to the same measurement for a solid lifter. That will demonstrate whether substituting one for the other will be feasible for your setup.

 

Thanks Gee Emm, I have a couple of HLAs, I might muck around witrh the dremel on one for giggles.

I guess my logic here is pretty simple - if Andrew, Emilio and the other S1 head honchos are not doing SUB, and they are pounding out lap after lap, then surely my modest track car doesn't need them either?

 

A bit off topic but that site in Australia basically plagiarized our entire post in September 2015 after we published ours on miata.net March 2015. Laid out the same as ours, same topics, same sequence, same warnings, same numeric values. Saddens me that they weren't able to simply ask me to republish my post but that's life. So you can ignore the Australian blog post as 3rd party confirmation because it's just a copy of my forum post
And I own Supermiata so the second two references are also me. So basically one source for all those references.

Building a Naturally Aspirated Mazda BP Engine (copyrighted!)

Ours

https://forum.miata.net/vb/showpost.php?p=7386298&postcount=1

 

Thanks for clearing that up Emilio, and it sucks that Aussies plagiarized you. But some good has come out of it... by virtue of a completely circular line of self-referential logic, I now have irrefutable proof that I do not need what I never wanted all along.
Sometimes one source is enough when the source is reliable