Don't exintake for FI - do BP-DE intake cam instead
 

Hello gents.

I figured I'd offer this up while I am busy making enemies over in the suspension area.

Here's a freebie.

If you are perusing your local junkyard and come across a 97-98 protege with a BP motor and an automatic trans you'd be smart to grab the intake cam. Well, and the crankshaft while you're at it (we'll do another post about that).

So, the intake cam. As you can see, some good lift but short duration. In stock location it'll give 13deg overlap (short overlap). This should be good for FI, and it's nearly free.
Also, it's solid lifter so it'll drop right into a BP4W.

BP-DE (US/Can) (MY1997-1998)

Intake cam duration
233° @ 0.003"

Intake cam opening
3° BTDC

Intake cam closing
50° ABDC

Intake cam lobe height
45.0mm (1.772")

Intake cam base circle
36.0mm (1.418")

Intake valve lift
8.9916mm (0.354")

Valve overlap [assuming stock rotation]
13°

(97-98) direct shim over tappet actuation, timing belt

Interesting find. Especially in a Protege and Auto only version

Overlap is used with both cams' Are you getting the 13 Deg with the Protege or BP4W exhaust(or are they the same)?

Edit I found this info:

"For the BP-ZE engines (I will list only the 99-00 Miata cams, since the 97-98
Protegé ones don't give real performance increases):
BP2Y-12-183 lifter bucket (need 16, and also 16 shims)
BP4W-12-420 intake cam
or BP5A-12-420 JDM intake cam (237° vs 241° duration @.003", either
cam maintains the same 17° overlap)".

The BP4W Exh cam has 0.004 less lift but a few degrees less overlap (can be fixed with cam gears). the MSM cam has a little more duration with the same lift. Protege cam might save you the trouble of repinning it but finding a cam in good shape 20 years later is tough.

for the Hydraulic lifter guys I also found this:

MazdaSpeed also have cams and cam gears
for the BP-ZE and BP-ZET engine. The part numbers are:
QEP6-12-420 intake cam (255° duration @ .003, 9mm lift)
QEP6-12-420 exhaust cam (255° duration @ .003, 9mm lift)

Yes exhaust in the BP-DE is the same as the BP4W so if you drop the DE cam into the BP4W head (in stock location) you'll get the 13 deg of overlap. The shorter duration of the DE cam enables the sorter overlap. Also it's an easy swap - no re-pin etc and what are you going to pay for it? $30 at boneyard?

How much do you need the shorter overlap? Don't know but should be a bit more efficient with boost.

I've got a lot of miatas. I've got one running na with this motor and it's fun in lower revs. But I'm anxious to pressurize it and find out if the less overlap helps in FI.

Yes I suppose where you pin a BP4W exintake will determine the overlap of that set-up. Then the question becomes one of shorter duration.

I run that crankshaft... Some have told me I'm a fool for doing it... The more you learn sometimes the more the masses think youre an idiot if you don't follow conventional "wisdom"

Is that another source for the lighter cast crank that was in the old B8 SOHCs? Asking for a friend.

Yes. 26lbs.

Makes a 1.8 rev like a 1.6

So.... slower? Seems backwards.


Is it the SAME crank as the old B8 SOHC? Or is it a different cast crank?

You've been wise. That crank makes good things happen.
I've got a 90 with the BP- DE motor (with the lighter cast crank) and it's a happy engine. Revs quick and eager. I just bought a BP4W head for it. I'll shave .080 off it and just go NA with the intake cam from the DE head. It's a really fun motor. I've got a FI'd '97 Miata with 220whp and the DE motor'd car is more fun (with nearly 100 less whp).

I didn't say less power like a 1.6, but the 1.6 is clearly more happy to rev than a regular 1.8. The lighter crank from the DE used in the 1.8 makes it rev quicker (obviously load dependent). I've got a picture of it somewhere with the casting number. IIRC it is same crank as B8 SOHC.

I'm making a joke at the expense of "Shit M.net Says." The 1.6 does not rev faster than a BP. It's not "happier to rev" than a BP. It just sucks that much worse below 5000rpm that when it finally decides to break triple digits crank HP, it feels like an event.

I like lighter rotating assemblies though, so i thank you. :) Would be interested in pic. Just has two counterweights, correct?

It has single counterweight at each journal (vs 2 per journal).

Also interesting on that crank. Half the counter weights eh?

Somethings tells me a BP4W w/ 10.5 pistons, B8 crank, MSM/BPDE intake cam and a Squaretop manifold would make a fun all-Mazda n/a motor

So like this?

http://i16.photobucket.com/albums/b2...6.jpg~original

It's a thing of beauty and a joy to behold
good for up to 300hp.

https://cimg4.ibsrv.net/gimg/www.mia...31836373a5.jpg

It's got oil squirters too (my motor).


https://cimg9.ibsrv.net/gimg/www.mia...4590033ed.jpeg

I'd need it to hold about.... 200hp.

ive always advocated the auto cams for a 1.6L for FI.

are we suggesting to put a hla cam and lifters into a bp4w?

"Also, it's solid lifter so it'll drop right into a BP4W."

"(97-98) direct shim over tappet actuation, timing belt"

97+ Protege BP's switched to solid lifters. Too bad the 97 Miata's didn't as well

missed that part. sorry it got messy with the mention of HLA guys

So lighter crank vs lightened flywheel? Does the lighter internal rotating mass have a different effect than a lightened flywheel?

The not fully counter weighted crank would increase main bearing loads.

By chance, do the cars that came with the lighter crank have a lower redline than a miata?

Why? Would the 4 cylinder crank not be balanced by the countering rod/piston combo going the other way?

I believe the purpose of the counter weight is to provide a centrifugal force in the opposite direction of the rod/piston assembly, and reduce the load on the bearings. Think about holding a weight in on hand extended straight out, and spinning in a circle. Your core is having to work harder to keep you spinning on an axis. If you held another weight in the other and and extended it in the opposite direction, it would help balance. The smaller the weight, the less it would help. At least, that makes sense to me...

Right, but you have less weight spinning as well. To my non-engineering brain, seems like a net zero in that regard.

Yes, but the loading on the bearing is determined by the net force about the axis; when you have 2 equal centrifugal forces in opposite directions, there's zero net force on the bearing, in a purely mathematical sense. In real life there's gravity, and you can never get perfectly equal centrifugal forces.

You're right that the other piston assembly is going in the other direction, but it's separated by a moment arm, so to rely solely on that is introducing a bending force into the crank. To continue the analogy, it's like holding the weight in one hand, and another weight on a pole in the other. It would counter the weight in theory, assuming a perfectly rigid structure, but you're not a perfectly rigid structure, and neither is the crank.

Spinning weight alone doesn't load the bearings, well, nothing more than gravity. The rod/pistons slinging back/forth puts thousands of pounds of force pulling on the crank throws up/down as it spins. The counter weights built into the crankshaft are designed to "counter the weight" of this force so that the bearing load is reduced and vibration is reduced. A fully counterweighted crank minimizes the loads on the mains by full counter balancing the reciprocating weight. As you can guess, a partially counter weighted crank only partially counters this weight.

Bear with me,

So to me, reading this... the counterweights are only truly SUPER AWESOME if they weigh the same as what's attached to the crank, right?

It's a balance of force. You want to minimize the maximum force on that area of the crank. So find the CG of the two counterweights, and calculate the force that puts on the crank. Then calc the CG of the throw accross from it, and then calculate the force the reciprocating assembly puts on the throw. Countweight force - throw force - rod/piston force should be about zero to minimize loading on the mains. I'm sure google can explain it better if that doesn't make sense.

Not necessarily weigh the same, but produce the same centrifugal force in the opposite direction. The rod and piston are not swinging freely on the other end. Only part of their weight is acting centrifugally on the crank.

It does, but in the context of using either of the stock cranks in a not-stock scenario, seems like they're both compromises.

If you wanted to maximize main bearing wear, you could run the lightest counterweighted crank possible, with heavier-than-stock beefy rods and heavy forged pistons. That would be worst case.

If you wanted to minimize main bearing wear, finely balancing the OEM parts is probably best, as mazda likely spec'd the miata crank to balance well with the miata rods/miata pistons.

Yes there are compromises when changing components around. Ideally you would adjust the counterweights on the miata crank to suit the reciprocating assembly bolted to it, that's a lot of work, nobody(very few) would ever do that.

Sure, anytime you use a highly engineered part in a context it was not designed for, it's not going to work as well. But if the 2 counterweight version is closer to the original design intent, then a single counterweight will be harder on the bearings.

And would probably result in projectile counterweights, unless someone really knows what they're doing and it's a bolt on weight.

Sounds like i'm going to make Nick come and hang out and drink beer while i go down this next rabbit hole. :lol:

Haha, sounds like a party! Engibeering...always a good idea.

Counterweights use centrifugal force to counteract the force (not centrifugal) from the inertia of reciprocating components without using a long lever of the crank that passes through the main bearing. A counterweight that's lighter still provides some of the benefit, just not as much. The benefit doesn't suddenly vanish when mismatched, since it still reduces crank bending, though not as much.

The downside of counterweights is cost and MOI. The SUPER AWESOME thing is to make a counterweight that provides a lot of counterweighting without a large MOI. This means making it denser and closer to the crank centerline. Like bolted-on tungsten counterweights.

Centripetal force of a counterweight (good) = mass * radius of CG * (angular velocity)^2

MOI of a counterweight goes up with the mass and the square of radius. Double the mass, cut the radius in half, and you get all the benefit with half the MOI increase.

No, centripetal force is the force acting on the counter weight keeping it from flying off into space. Centrifugal force it what's acing on the crank bearing to counter the force of the rod/piston assembly.

The only way to increase mass AND reduce radius without interfering with the motion of the rod is to use a different material of a higher density. What material is 4 times the density of iron? Black hole matter?

I think you're misreading what I'm saying. I'm not trying to open up a centripetal-vs-centrifugal discussion that adds nothing. I used the word centrifugal throughout my post, except in the mass-based calculation, where either is appropriate (the calculation is based on the mass of the counterweight, so it's kind of natural to examine the forces acting on it in that context).

By "not centrifugal," I mean exactly what I said. The force that counterweights counteract is predominantly the inertial force from the reciprocating masses. This is linear acceleration, not centripetal, centrifugal, or anything related to rotation.

Ok, yeah I misunderstood the first post, my apologies. The parenthetical "not centrifugal" confused me.

Having understood what you're saying, I'm still not sure I agree, but I need to think about it some more...I'm not sure how the centrifugal force of a rotating mass can counteract a linear force; they would only be opposed to each other at a single point in each revolution. Plus, the crank journals are offset from the axis of rotation, so that needs to be counteracted too, and the mass of the large end of the rod is also generating centrifugal force...so at the very least, a portion of what the counterweight it balancing is centrifugal and not linear.

Ok, so after further thought, I'm convinced that the counterweight is NOT counteracting linear inertial forces from the rod and piston. The reason is this: if you were to graph said inertial forces acting on the axis of rotation vs crank angle, you would get a sinusoidal plot. However, if you graph the centrifugal force of the counterweight acting on axis of rotation, you would get a straight line. You cannot cancel out a sinusoidal forcing function with a straight line.

If you tried to cancel the inertial forces with the counterweight, you would only succeed in shifting the load on the bearings to a different crank angle, because while the counterweight may cancel the inertial forces in the very narrow range of crank angles when it is mostly opposed to them, there would be nothing to counter the extra weight of the counterweight for the rest of the revolution, it would end up loading the bearings then.

One JDM/Canada version of the BP-DE actually had a 7250 redline IIRC. Main bearings were never an issue with the cast crank on EGT's and Proteges. Theory vs practice. I have been repeatedly reassured by the BP Protege crowd that the cast crank is good.

My normally aspirated experience in my white '90 is that the cast crank motor is MUCH more lively than my other 1.8 Miatas. You'd have to drive it to believe it. I suppose some of it could be the DE cams but the engine spins up much more freely and it has an eager "dog at the end of a leash" feel to it. It wants to rev. Oddly once it does rev up to 6-7k it doesn't feel like it has as much there, but it acts like it wants to get there faster (to redline). Does that make sense?

I put a MBSP with a NB2 oil pan on the engine before I swapped it into my '90 miata. I figured that couldn't hurt.

BTW, the cast crank isn't just a little lighter. It's a lot lighter. 36lbs vs 26lbs.

With the light crank and FW in my car it revs like a freaking motorcycle.

There's no such thing as a counterweight that perfectly eliminates bending moment. Even though you counter a sinusoidal reciprocating force with a centrifugal force, it still cuts the magnitude of the peaks.

Generally, counterweights can counteract bending moments from both linear acceleration and centrifugal forces. It gets more specific with inline-4 engines, and the relationship of counterweighting to "balance" (if any) is also different for every engine configuration.

What about US cars? Some JDM miata engines had a 7500 Redline, but not the US versions.

Theory vs practice, show me people making big power on cast cranks and spinning them at high RPM. In my experience, I can keep miata main bearings happy to 8500, but at 9000 they don't last. Do the protege cranks do 9000 reliably?

I wouldn't use one of these for big power. Madjak uses a cast crank in his car though.

No oem B series crank is going to buzz along happily at 9000rpms for any length of time.

It's a tradeoff. Wherever peak loading occurs, you'd want to minimize it.

If you seriously need to be at 9k I'd do this...
https://supermiata.com/Billet-Crank-Mazda-BP.aspx

Pat doesn't buy expensive parts, he makes them.

btw, I had a GTJ (Lou Fidanza) built XK 4.2 motor that was built to redline at 8500 and survive missed shifts at 9k. The old Jag had huge long stroke vs bore. We calculated that the piston speed was equivalent to 14k rpms relative to an oversquare motor! :) Oh the noise!

What are the final drive and transmission gear ratios in the Protege you are talking about being so lively?

Not protege, '90 Miata. Stock 5-speed and diff. The engine came from a '97/'98 Protege BP-DE AT.

FWIW that part number comes back NLA with some quick googling