MX_Eva

This is true. I think it can be overcome pretty easily though. If you are doing an engine build, you might as well make her love the revs.

I mean, engine wasn't technically designed for boost either. Even if it does have a close relative whose was.

On the list of ultimate miata plans. Revs to 9k are on there. I figure head work to match the high flow manifold, and a new oil pump gear. See how it goes from there. I don't intend to run much more than 12 psi. Though this may increase if I do end up running ethanol..but that's really speculative and not probable at this point.

magnamx-5

iTrader: (7)

IDK how diminishing your returns would be esp if your turbo can breathe the cfm's you need to hold boost on a extended rev range and you dont run into a flow reversion in the intake ports caused by a backlash in pressure differential. Ultimatley this is a game of how much we can breathe in and out, if you have a nice clear inroute and a nice effecient out route then the frictionnal looses will be moot. IDK why you are so hard on crankflex pat, we have a forged crank already, and given a proper balance and some op gears that wont desintegrate at that high a rpm/vibration lvl etc, and a head that will flow what we need in and out, i see no reason why we cant make every bit of hp you dream of and more. You as always are being abit to problematic with your hp developement man. Alot of the funn of building a super high hp motor and realy testing it is finding out why things go boomb and fixing them better. We cant do the whole excercise on a spreadsheet calculating the force equations and resonant frequenqys as they effect the metals at varius temperature ranges.

Duckie_uk

iTrader: (1)

Abe, Ive never really liked the idea of pressurising the cylinder to hold the valves in place. It does work and in most cases it works well, but if for some reason there is a slight leak and the pressure does release then the valve drops into the cylinder and you have to remove the head regardless.

A better method that I have used is to remove the spark plug from the cyl and rotate the crank using a socket on the pully nut so that the piston is at BDC then thread in loads of that cheap blue nylon rope through the spark plug hole. Force as much in as you can but remember to leave a tail that you can use to pull it all out with (dont ask me why I mention this) . Then turn the crank again untill it wont move any further and hold it in this position. I used a bungie on the end of my ratchet.

This will give you something nice and solid to push against without the risk of having to remove the head.

Cheers

Tom

y8s

iTrader: (8)

Zabac

iTrader: (39)

9K RPM, that's what I'm shooting for with my build.
The things you have to bring up to par.
-Rods
-OP gears
-rings
-bearings
-balanced rotating assembly (complete)
-cams/gears
-lots of headwork (the more the merrier)

Things in addition that will help further
-Knife-edged Crank
-shaved flywheel
reduced rotating mass iow
-Anything that will reduce friction and crank flex.
-Balance everything!!!

y8s

iTrader: (8)

see photo above your post.

Zabac

iTrader: (39)

I will be building a 99/00 head...so yeah

AbeFM

iTrader: (3)

That's one I hadn;t heard before. While a pain in the ***, it does seem like a good idea.

I guess you could put the motor at TDC, hold it, and use air pressure to hold the valves up, then if the seal breaks they only fall a cm. But that's not as clean as your method.


I agree in general that you want to work with the character of the motor, the squareness is certainly a factor, but if the rods will take it, you're fine.

I'm thinking with limited pressure driving it (no positive displacement (sc) or rising rate (tc + wastegate) air pump), your intake, throttle body, etc would all have been big factors, as well as the exhaust.

To a degree, the headwork must be an effect, clearly Mazda optimized it for sub-redline opperations, but that doesn't mean it can't be pushed further. The 99+'s have a much better head and I'm sure can be taken further. If you're not getting valve float, it means is doesn't hurt to try. It also means no need for springs yet.


Where does one get this OP ring? What does it cost, do they actually work? I'd heard of people putting them in and grenading anyway.

Cams would be the smartest thing to do in the quest for higher revs. Most of the rest is done already on my motor - pistons/rings excepted, I don't know what to do there. I guess get something lighter.

Someone on here, I forget who, MarkP maybe?, revs his motor to 8500, been doing it for a while. He makes quite a bit of power, and it doesn't look like the motor was starving up there. So, that set up, or Paul's, right now seem the best to copy as both are still pulling strong at 7+k

Zabac

iTrader: (39)

Abe, you mean OP gears? I don't know what OP rings are.
The oil pump gears are for sale by Bill at Miataroadster I think, but hopefully we will have our own source soon, I am relying on it. There was a big team effort to get them drawn up and a few guys worked their butts of to get that done, now we are waiting on a machinist for a cost estimate, etc. not sure when they will be available.
As far as them shattering, it is a widely discussed topic and there is a ton of speculations out there as to what causes them to shatter.

y8s

iTrader: (8)

and? they come with shim over lifters. that pic is a shim under lifter.

Zabac

iTrader: (39)

I wasn't sure what you mean by that comment.
From what I read so far, the solid lifters in the 99-00 heads are much better for a higher rev limiter. Are you saying it's the opposite?

AbeFM

iTrader: (3)

I, too, and curious of the advantage of the PITA shim-under-lifter mod. It seems a small reduction in reciprocating mass...... Is there anything else about it?

Heck, V-tech motors reving to the moon have big head screw adjusters and rockers, so I am not sure I see the big deal.



OMG! Yes, keep me posted on the oil ring thing. I wonder if a stand alone oil pump couldn't be made for testing gears - run a stock one to failure with an electric motor, then the "improved" one.

Zabac

iTrader: (39)

Abe, more testing? Go talk to Joe and make a video, haha
The Miata head is still a big mystery to me, damn lifters...

y8s

iTrader: (8)

the conversion is for two reasons mainly:

1. less reciprocating mass in the valvetrain
2. you wont spit shims out at high rpm.

AbeFM

iTrader: (3)

Matt, I like your sig. Could you do one for me? I'll polish the car, you tune mine till it has a dyno like that. :-)


Anyway, yeah - I can wiggle my shims out with (not inconciderable) effort without pulling the cams. Well, I loosen them. I have my doubts this would happen, but it's probably not a bad mod for a track beast.

Thankfully, the 99 head is pretty good, you can just run it, though a little deshrouding, etc, helps!

Zabac

iTrader: (39)

So, in a 99-00 head you want to swap over the shim under lifter? I read that somewhere on Mnet, ****, it's back to reading now...thanks for the info y8s.

y8s

iTrader: (8)

at high rpm... say if a valve floats or bounces... those shims get real loose real fast.

JasonC SBB

The big deal is because VTEC has a totally separate high RPM lobe with lots of duration, it can be designed for a slow ramp which means it can rev high despite a high valvetrain mass. Such a lobe profile would be terrible at low RPM, wihtout VTEC.

AbeFM

iTrader: (3)

Erm... Interesting. Sounds believable.

Although... My katana750, which revved to, I dunno, 12k or 14k or something, also had screw adjusters. And it idled just dandy. My lopiest idle was my old Kawi. You could argue the kan-a-tuna was giving up some top end, but it was making 98 hp on 1980 tech with only 750 cc's, so... There must have been some reasonable cams in there.

I'm just thinking maybe the mass in the head isn't such a big deal.

<edit>:
You figure, you've got 16 valves, total valves weight must be under that of just the rods or just the pistons. Then, they are going half the frequency of those parts. And to top it all off, they are moving like 1/4", not 4 inches.

Also, the shim-and-bucket is not light. They look very very stable, sitting all tight in that bore, but there have to be pumping losses and friction on the bore's circumference, etc. It seems to be the miata's set up would be more lossy than the honda's, even if it looks cleaner.

Show me a NA miata making 250 crank HP. :-)

JasonC SBB

The problem with valves is that spring force sets the max closing acceleration - they might "ski jump" off the lobes if the RPMs are too high. Rods are pushed and pulled by the crank pin..