I'm at the point of rebuilding my head for my new motor. After getting new valves installed I need to re-shim my BP4W.

I'm at the point of deciding $100 in shims vs $450 in SUBs. What would you do?

For my build i'll be revving to 7400rpm with ST light double springs with +1 Manleys, BP5a intake, stock exhaust cam.

-I have read conflicting info on what rpm necessitates SUBs (8K seems to be average). What is the de facto point at which SOBs don't cut it anymore?

-For my lower Rev limit, would I see a marked performance difference? Do SUBs rev quicker, smoother, or just wear less than heavier SOBs?

-Major difference between Mazdacomp and Supertech SUBs? I vaguely remember the Mazdacomps use 6mm lash caps on valve stem, Supertech SUBs use 5.5mm lash caps on bucket stem.

Also : Measuring out, I'll be needing shims on the thicker side of the spectrum (3.2-3.3mm) Do thicker SOB shims pose a greater risk of "shim pop" than Thinner (2.8-3.0mm) SOB shims??



tl;dr : Validate me wanting SUBs for my non-race motor.

 

In for info on this too. I'm curious to see if anyone has actually had a shim shoot out of some sort of issues with a stock solid lifter setup.

I understand how less reciprocating weight helps but it's hard to justify the cost.

This is a good read for a simple explanation http://www.revzilla.com/common-tread...alve-adjusters

 

I'm doing the conversion right now because I'm N/A with no plans for boost, ever, and need all the little things I can get to make power without sacrificing reliability, and doing a cam upgrade anyway. Unless you're spinning 8k, and actually making power there, there really isn't a "need" for it, especially when turbo guys can just turn up the boost.

 

Less reciprocating mass requires less force to open and close. You can rev higher with a little less spring and still have the valves close correctly. It would reduce the force the cam needs to exert to get the valve moving and would reduce the propensity to float the valves.

If you stacked all of the SOB shims and weighed them against the stack of SUB shims, there would be a pretty good difference. And valves move very quickly. I can see where the SUBs would free up wasted horsepower.

 

In theory I can easily see how the lighter valvetrain would help free up HP, but is the difference significant?

Is it akin to knife-edging your crank? Couple hundred dollars in work, for minute gain?

I'm also very curious if there is a measurable cam wear difference. Less inertia of the valve and spring assembly could help maintain a proper oil film at peak accelerations, but I'm not sure if the difference would be significant in comparison to the spring-rate to make a difference.

 

In all the historic race engine's I've been involved with the upgrade is all about saving valve train weight to run a softer valve spring which increases reliability and also does make power [we're talking tiny % though, so have a s**t before you drive and you'll get the same power to weight affect].

As for the BP engine…

The shim lifting off the top of the bucket is what usually causes issues. This can happen because of too quick a change in direction causing the inertia of the shim to lift itself off the follower [either through an over-rev or because a new cam profile increases ramp rates]. Valve float is the real enemy because it generate a large enough clearance for the shim to get flung around - but your ST springs will stop that.
In reality if I were re-building a head that's likely to re-use stock cams and was in a road car never really likely to see north of 7.5k for long then I'd stay with stock lifters.
If stock cams and track work where running into an 8k limiter can be useful I'd move to SUBS.
If you're going to change to uprated cams at a later date wait until then - you'd need to pull it all apart to re-shim anyway so best to keep the money in the bank for track time and/or BBQ food & beer.

 

I always thought the main reason for going to SUB's was to make high lift cams safe.

 

We have a pretty hard time keeping intake valves happy in these motors at higher revs. I suspect that its in some part due to such a tiny amount of valve float that its not audible nor does it show itself in the map signal on your data log. The lighter subs would help that. Even lighter is the zetec shimless setup, but you've pretty much got be on the highest end of the mazda stock shims to be in the range of the zetec lifters. The shortest one is equal to basically the largest oem shim, 3.4mm. But if you somehow have the need for lifters that long you can drop 3/4lb out of the valvetrain for $240.*









*No one has ever done this and lived to post on the internet about it, I have confirmed that the lifters do fit properly in the lifter bore, so there is no reason it wouldnt work with short enough valve stems.

 

I am very much on the upper end of the shim spectrum, but not at 3.4mm. These Manley valves are a bit shorter then stock my machinist said, and I need to order all new shims. 3.2-3.3mm across the board.

Zetec lifters sound interesting, I've heard about the option before. My concern is that if I go that route, I'll end up needing them ground to height which will put them right up next to SUBs as far as cost. SUBs still retain an ability to be re-shimmed which is a plus to my primarily street application.

 

Couple questions...

Are you having the machine shop set up the head either way?

Where can you find SOB shims for $100?

Are you estimating labor into your figure of $450 for the SUB, because the parts are only barely over $300?

 

Clarification :

I need 12 out of 16 new shims. I can move some of my old ones around to suffice. I know I said "all new shims", I just rounded up in my head

12 x $9 = 108 from Rosenthal. I had a free shipping coupon.

SUBs: I was looking at the Supertech SUBs as I prefer the design of their 5.5mm lash caps on the stem of the SUB, as opposed to 6mm lash caps on the valve stem for the Mazda ones. Might be wrong on that. I remember reading it somewhere. Is there any reason for those have used them to prefer one design over the other?

$350 SUBs + 16 x $6 lash caps = $446

My machine shop cleaned, decked flat, and unshrouded for new valves, 3 angle, installed new springs and OEM seals. I am installing cams + lifters and shimming lash. Easy enough (famous last words).

 

Mazdaspeed lifters from miataroadster are $213 & $96 for the ST caps. If you want clearances to be exact, you'll have to do some surfacing of either over or under shims. What are you planning to set lash at?

 

The shimless zetec lifters actually come in smaller height increments than the mazda shims. So less likely to need grinding to get just right.

 

Didn't know ST caps fit Mazdaspeed lifters! I should probably up my reading comprehension.

Setting lash at upper side of FSM recommendations (so as the valves 'tighten up' initially it'll work out right in the middle of the range). I think it was .009 intake and .012 or .013 exhaust. I'll have to look at my notes. Always heard that the 'loose' side was safer then the tight side. Again, not a race motor so maximum lift isn't top priority. If I want more lift I'll get bigger cams.

I ended up ordering the shims for stock SOBs from Rosenthal, but this is a NA build, and cams are on the horizon. So thank you all for knowledge!!

 

Yeah but the ST caps come in increments of .05mm.

 

So do Mazda SOB shims .

I made this massive excel spreadsheet where I input existing shim thickness, measured lash, and goal lash and it calculated what thickness shim I should use.

Using Mazda SOB shims I can get all my lashes (theoretically) within .0012" of each other. Sooo I would think I could get that same level of precision with ST lash caps. Maybe? Is that too much variance valve to valve? Thanks for the help. 1st time building a motor. Always learning something.

 

The problem is knowing your exact initial lash you are using to calculate. And yeah, there can be large variances from valve to valve. I had very few that matched.

 

I used some go no-go feelers on my test-assembled head. Cleaned bucket/shim interface real good with brakleen. Lobe positioned 180* from shim surface for measuring. Hope I did it right.

Sooo at any rate, as I'd like to keep this thread about SUBs as possible : Are there reduced wear characteristics of running SUBs? Decreased chances of valve float would help keep valves happy. Which is the wear item in the BP valvetrain, Cam or lifter?

 

Ok so I have a valve grinding machine I built, I can tip valves, removing 1/2 a thousandth with decent accuracy. I have aftermarket supertech valves. Can I do this? Is it basically just keep tipping the valve till it's short enough to use these lifters? And are you serious about the 3/4 lb part?!

 

I've seen lifters and cams on a 180k mile head both look absolutely fine. Don't think the wear is a concern as long as spring tension is correct.

To keep you off track for just a minute longer......
Let's say you're checking intake which you want at .009". You can get a .011 gauge in but not a .0105. How do you know if you're closer to .0105 or .011? If you assume you need .002" additional shim to get to .009", you could end up as tight as .00851. This is the struggle I had and had to surface several lash caps and actually had to order 2 additional. However, now they are all .0095 and .0115.