Let's say one wanted to build a BP to rev to the 82-8400 rpm range.
Beyond valve springs, a billet oil pump and engine management what items are absolutely needed, what items would be greatly benefitual and where is the line with regards to diminishing returns.
Let's talk naturally aspirated, forced induction, pump gas and E85 all as potential options/opportunities and the limiting factors or advantages of each with regards to spinning things faster.
(also I meant to post this is the grassroots section of the forum and not the off topic, if possible, could it please be relocated)
I mean, to turn those RPMs and to make it worth turning those RPMs, you are going to need airflow. So, ported head, better intake manifold, better cams. I know my BP-4W, with unported heads, stock cams, BP-5A "squaretop" intake and Rotrex supercharger falls off a cliff at 7000RPM.
You don't need better connecting rods if going NA (Quinn Kizis has been turning the kind of RPMs you want with stock rods on his 184whp ITB BP for years) but they definitely would improve piece of mind. If you are going forced induction you would need them though. Gary at Track Dog Racing in no uncertain terms told me do not go above 7500rpm in boost with stock rods.
You probably want to talk to Eric Anderson. He races a Miata in SSM named Lafawnduh. And he's broken nearly everything in the BP motor on a quest to see 500 hp out of it.
But the real question is: wouldn't it be easier to either change gearing or install a motor designed to handle ridiculous revs? (Honda K24 for instance) The BP design is pretty long in the tooth at this point and you can do a lot with it but it's sort of like building the worlds most accurate shotgun when the smart money just buys a rifle.
First you need a reason to rev that high. Can you make/sustain power in that range? Can the head support the flow needed there without sacrificing other things? Can you get/make cams that make the most of it? Is your transmission tight enough ratio that the shifts don't drop you into a bad space even with high peak power?
That being said I rev my boat anchor vr6 to 8200 rpm and shift, dyno peaks out at 7800-7900 even with stock cams but shifting a bit higher is a better powerband. I've done literally nothing to support revving that high other than good manifolds and welding the flywheel bolts on. 
I lose a rocker arm from time to time so springs and better cams are in the plans.
KyAllroad said:You probably want to talk to Eric Anderson. He races a Miata in SSM named Lafawnduh. And he's broken nearly everything in the BP motor on a quest to see 500 hp out of it.
But the real question is: wouldn't it be easier to either change gearing or install a motor designed to handle ridiculous revs? (Honda K24 for instance) The BP design is pretty long in the tooth at this point and you can do a lot with it but it's sort of like building the worlds most accurate shotgun when the smart money just buys a rifle.
Quinn Kizis, who has a Youtube channel called Slip Angle Media (formerly Garage Quinn Motorsports) is another good one to talk to. He has the highest HP naturally aspirated Mazda BP in his NB1. It made 184whp at 8400RPM and he has to run 4.77:1 gears with a 6-speed to make it a happy camper
I kinda went down this same train of though for my Miata , to try and get more RPMs out of my BP for more MPH in second gear. I almost made a thread about it even. The problem I hit was that I would need bigger cams, better oil pump, upgraded rods, ported head, and then I'm almost into overspeeding my blower as the car sits, so I would have to put a bigger pulley on the blower and maybe a smaller one on the crank. At this point, it'd be easier to either swap from a 6-speed back down to a 5-speed and see if the car has the guts to pull the 3.63:1 gears with a 5-speed (which would give me a 70mph second gear) or dump the complexity of the Rotrex-blown BP for some sort of Honda K24 screamer.
Trans is a 5 spd with a 4.1 final drive. Rods would be done prior to boost, boost would still be kept mildish, two intake manifolds are on hand that flow a higher CFM (the Kia sephia and a skunk 2. I'm staying BP as I have three of them, they're easy to work on and parts are plentiful, otherwise I agree that a K24 is the answer with regards to an inline 4 that does everything amazingly well.
So part of my thought process is the ability to move more air at a higher RPM to run a slightly larger turbo or a less modern turbo to be honest they can be obtained at a lower price point. And have the option to keep it happy and spooled with the additional RPMs.
The other aspect of this is that a larger turbo will make less power under the curve so that if shifting lazily and early it won't stress or strain the notoriously fragile G Series transmission of front-wheel drive BP powered platforms.
In reply to NickD :
My turbo build is getting the 3.63 diff and 5 speed trans. The VVT motor and T3 turbo should get me close to 250 WHP, that seems like enough without building the bottom end. The diff was $750 and that was a cheaper route than all the stuff needed to spin the motor faster. We'll see how it feels.
Admittedly have a bucket of KO3's in my basement but it's been over a decade since I've even checked to see what upgradable options there are for them if doing a rebuild on one. I have a real Evo 3 16G that I was planning on swapping a billet compressor wheel into. I have been debating whether to machine the compressor housing to accommodate a billet 18 or 20g wheel to swap into it.
Didn't catch the boost part. A k03 belongs in a trash can, especially on something you want to rev, it will choke and hard (maybe workable on a 1L motor?). Even a GT28rs is a bit small for those kinds of revs unless the boost is pretty low, the hotside isn't big enough. Cheaper turbo will fight you as well as those tend to be crappy at the exact things you are trying to do. I think more than revs whats your power/powerband goals? Big difference between 8000 rpm and 250whp and 8000 rpm and 700whp I agree that big hotsides save transmissions but it's gonna cost a lot of low end.
250-280 is realistically the goal. I have access to and injectors to run E85 which I'm hoping helps offset some of that low end sacrifice while helping with IATs as well. Though admittedly it will see a fair amount of 93 as well and I'll be running a GM flex fuel sensor (a lot of "moving pieces and parameters, I know).
Paul_VR6 (Forum Supporter) said:Didn't catch the boost part. A k03 belongs in a trash can, especially on something you want to rev, it will choke and hard (maybe workable on a 1L motor?).
Quad K03s! One throttle body per cylinder? Hah, one TURBO per cylinder! :)
For a turbo BP with 250-280 at the wheels IMHO there's really no better choice than a real Garrett GT2560. They've been around for a long time and there's fancier new turbo tech, but that's the sweet spot for that turbo and they're cheap. There's no need to rev it to 8K+ to do that either.
There have been a number of folks who've tried a "long rod" build on a BP in the past in order to improve the rod ratio and thus theoretically the "revvability". I don't know that I've ever actually seen someone document the results from it, though.
+1 on the gt2560. They just *work* on this engine. And since the VJ23's are getting really scarce, why not get what's available...
KyAllroad said:In reply to NickD :
My turbo build is getting the 3.63 diff and 5 speed trans. The VVT motor and T3 turbo should get me close to 250 WHP, that seems like enough without building the bottom end. The diff was $750 and that was a cheaper route than all the stuff needed to spin the motor faster. We'll see how it feels.
Daaaaamn, $750? That was a steal. I spent $750 just for the ring & pinion from Mazda. And then I had to get all the bearings and seals as well.
I wish someone would make a run of the vaunted 3.308:1 ring & pinion from the diesel Ford Courier. An original set may as well have been buried with King Tut.
captdownshift (Forum Supporter) said:In reply to NickD :
Is this close enough for you...
Supposedly these are pretty noisy. Fine for a race car, might not be a great choice for a street car.
BTW, the diesel courier thing is a myth. There was one with a 3.308, but it was a larger (7.5 inch?) ring gear and doesn't fit the Miata.
Duratec?
Rods, pistons, decent cams and springs, and a little work on the chain drive will get you 9400 or so with one of those, and it will breathe well enough to make it worth the while.
Esslinger had a recipe for Midget classes that require stock components that went something like 2.5l block, 2.3l crank (to meet a 2.4l displacement limit), and a direct injection 2.0l head (unported), and IIRC this with their cams/rods/pistons and methanol was a reliable 340hp. Knock off a fair bit for running on gasoline.
No matter the engine, I wouldn't bother with a plenum manifold. With the cams you'll be wanting to run, go straight to some decently sized independent throttles (45s, 48s?). The gain here is not with peak power, but powerband. Engines are far less peaky if you don't have a plenum manifold where all the other cylinders' intake pulses are interfering with each other.
How long do you want the BP to last? Everything I have read says when you take those engines higher in rpm, the engine life decreases drastically.
In reply to Countingcrowbars :
What's causing the failures when they're shortlived at higher rpms though? If solid lifters are used, stronger, lighter valve springs, a billet oil pump and stronger rods, then longevity shouldn't be an issue. A real oil pressure gauge as a precaution is also a wise idea.
A lot of things can fail if basic needs are requirements aren't met within developing a build. Which is actually in part why I started this thread.
codrus (Forum Supporter) said:captdownshift (Forum Supporter) said:In reply to NickD :
Is this close enough for you...
Supposedly these are pretty noisy. Fine for a race car, might not be a great choice for a street car.
BTW, the diesel courier thing is a myth. There was one with a 3.308, but it was a larger (7.5 inch?) ring gear and doesn't fit the Miata.
Doesn't fit as in it's not a 7", or doesn't fit as in someone tried it already?
Someone was telling me that the 7.5" fits where a 7" fits, because Mazda wanted a bigger ring gear without having to make another set of housings. I can see that for the banjo housing but never quite made sense to me for the diff case, because you'd think the pinion gear would have to sit further from the axle...
But Ford did make 9 3/8" rearend gears that fit in a standard 9" case, so maybe?
Pete. (l33t FS) said:Doesn't fit as in it's not a 7", or doesn't fit as in someone tried it already?
Someone was telling me that the 7.5" fits where a 7" fits, because Mazda wanted a bigger ring gear without having to make another set of housings. I can see that for the banjo housing but never quite made sense to me for the diff case, because you'd think the pinion gear would have to sit further from the axle...
I've never seen it myself, but I talked to someone who said he tried and it didn't fit.
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