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Old 06-13-2008, 02:58 AM   #41
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Originally Posted by AbeFM View Post
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. :-)
And the force required to stop a piston moving in a cylinder at higher RPMs would be measured in the thousands, where valve spring's are rated in the tens. As Jason said, the piston/rod assembly is connected to a crankshaft.

Dunno about you hydraulic lifter guys, but my car doesn't float 1K RPMs after peak power.

Magna I know people like improving things. I said what I said with the "vtec" conversation in mind. Our motor was not designed to be a high RPM screamer. Suppose you could drop a B16 vtec head on it. It bolts right up. It STILL won't make the power it could because the cylinder diameter, combustion chambers, valves, seats, and every aspect of the head is too small. The head simply can't more that much air. Out motors are long strok already. Simple fact is big bore, short stroke, long rod engines make hp at high RPMs. Our motors are the opposite of this.


And Zabac, what's with 9K? I don't think ANY miata engine would make peak power at or above 8K, much less 9K. Even if it did make power at 9K it would be a race motor. No way could you pound it to 9K daily. Piston speed would be way too high, rod loads would skyrocket to failure from piston speed, crank would break your OP gears or the weak cast aluminum case your overbuilt billet gears are in, or perhaps before that the transmission or clutch assembly will grenade because it too should not turn that fast. Better put a nice scatter shield around that sucker if you like your legs.
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Old 06-13-2008, 09:47 AM   #42
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...they might "ski jump" off the lobes if the RPMs are too high...
Horray for extra lift
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Old 06-13-2008, 10:19 AM   #43
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I am pretty sure it is possible, I still think the power will come with proper cams.
I am not gonna just set the rev to 9K and hope for the best, it will be a gradual increase with lots of dyno time, if I make all the power by 8K, 8K it is, if there is more past that, I will keep going until I'm there, but I am not just gonna sit here and beileve that it is not possible and not try...someone has to do it. And I am sure there are people that have done it, just gotta find them.
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Old 06-13-2008, 05:33 PM   #44
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From some emails with MarkP, when I asked about his 8500 rpm redline (motor seemed to be pulling strong in the dynos, so I asked him why he stopped there:

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I just picked 8500 RPM out of the blue because it gave me a 200 MPH rev limit in 6th and made sense that if I can pull a 133 MPH trap speed in 4th. I would be more than likely in the 10's if I turn the boost all the way up.

Mark
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Quote:
Originally Posted by Markp
Quote:
Originally Posted by AbeFM
Wow, nice set up. Too bad when I started all this I was on the FM warpath. The turbo is certainly priced right, no? I'd love to see where your spool up is, what the powerband is like, etc. Sounds sweet, anyway.
Somewhat dependent on the gear I am in, top gear it will make boost at 4000 RPM, in 3rd around 4500, 1st and 2nd around 5000 RPM. This is with a six speed and a 3.636 rear diff.

At the bottom I include the dyno chart. It pulls really hard.

Quote:
Where did you get the springs, and how much were they? Do you get float at 8500 now?
R and D Spring in Hesperia CA. I purchased them a while back specifically for a high RPM build. They are probably good to 12,000 RPM according to Don there. Who was pretty old and probably dead now. Belfab had a neat setup, which is close to what I have:

http://www.belfabracing.com/product_...oducts_id=1252

However they offer a whole setup with pistons, rods and everything you need for $1625.

Quote:
Any rods or anything? I mean, is all you did for high RPM's is change valve springs? I almost got some last time I had the head apart, but wimped out, and I didn't know where to get them.
Ya, I have SCAT rods and JE Pistons.

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Do you just get more time till shift, or do you get more power up there? I'd love to copy a bit of this.
peak power is at 7000 RPM, because I need to switch cams. I can rev it out to 8500 but power falls off above 7300 RPM. Still it lets me rev it out when needed and it's still wicked fast. Gives me about a 3,500 RPM powerband with the longer gears it's impressive.

That means the power band in each gear is as follows:

1st: 26-44
2nd: 43-74
3rd: 54-101
4th: 70-133
5th: 88-167
6th: 100-198

Yes, 8500 RPM in 6th gear would be 198 MPH. I wouldn't want to try it..., makes a nice overdrive and runs like a 5 speed with a 4.44 rear diff and an overdrive.


Hopefully Mark doesn't mind me sharing this, if so let me know I'll take it right down.
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Old 06-13-2008, 05:44 PM   #45
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Torque at 8k: 150
Torque equivilent at the wheels from 4th-5th transition: 185

So, when you shift at 8,500 rpm, you get the same torque at the wheels at 6,480 where you come in as where you left. Which means that only in gears more closely spaced than 4th/5th would you want to shift earlier (on Mark's set up).

Shifting from 4th at 7500 rpm (brings you in at 6k in 5th), give you a 23% reduction in torque at the wheels, verses staying in it longer.

So, a higher redline is totally worth it, viable, etc. If you can hold the motor together, there's no reason not to. Cause you'll be a hell of a lot faster.

If you disagree, please start shifting at 5,500 and I'll race for pinks. :-)
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Old 06-13-2008, 05:56 PM   #46
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Thanks for sharing Abe...Once Mark gets some better suited cams, his power will not drop of like that and he could run more boost there. This is what I have been hoping to accomplish with my build. I hope Mark gets his cams and shares some info by the time I am done with all my prep to take it there myself.
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Old 06-13-2008, 06:49 PM   #47
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Yeah - I have a small amount of headwork, and if throwing in valves would help, I'd be all for it. Us solid lifter guys are lucky. Probably, Matt's right, with more aggresive cams and the higher spinning rates, shim-over-bucket starts to be a realistic way out.

My point in asking Mark in the first place was what I can do, here and now? If it's between cams or a manifold, I dunno which way I'd go.

If it's "new springs for $100 and a few hours of my time to throw them in" or "spend the $100 on cold stone ice cream for the girlfriend" I might be tempted to throw them in.

Really, I wonder when my stock pistons will give up. FM has told me they won't last too long at high power levels....
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Old 06-13-2008, 06:52 PM   #48
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Well, it's a combination of things that makes it most usefull, but both individually will help obviously.
I would get a mani first, and then the cams, just cause it will cost less for me to build a mani. I want to do the valvetrain all at once, valves, springs etc.
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Old 06-14-2008, 01:41 AM   #49
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Quote:
Originally Posted by JasonC SBB View Post
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..
...A phenomenon known as valve float, and the reason Ducati spends so much money on their fancy Desmodromic valve system.
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