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Old 12-12-2018, 03:05 AM   #1
kingkong
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Default Mechanical RPM limit ? (and yes i searched through all the BS)

Hi peeps,

I am no dreamer. My B23FK with a Holset HY35 is finally running, and goddamn its getting fast at only 1 bar boost.

My mods are :

H-beam rods
K-cam like, made by KG-trimning
Double valve springs
Aluminium spring retainers
TTV flywheel + 850R clutch + M90

Now the question : if i was to take to 8000rpm, what would break first ?

As of now i take it to 6000 at 1bar boost.
The plan is 2bar boost, but the thing is, the higher the rpm go, the more violent it is.
And i like it.

Thanks fellow brickers
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Old 12-12-2018, 03:56 AM   #2
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What's special about your cylinder head? Stock?
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Old 12-12-2018, 03:57 AM   #3
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Yes stock head. No porting.
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Old 12-12-2018, 09:17 AM   #4
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Throw them aluminum retainers in a river, or they WILL be the first thing to go, get some steel units it's worth a few grams
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Old 12-12-2018, 09:19 AM   #5
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How so?
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Old 12-12-2018, 09:28 AM   #6
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They will eventually split and allow the valve locks to separate,or wear out around the valve spring and allow a valve to drop, I remember those used to be the hot ticket but nobody uses them anymore,semi exotic steels,titanium are way to go, even simple tool steel will last forever and is only a few grams heavier, aluminum has a finite life span
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Old 12-12-2018, 09:58 AM   #7
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Does your cam make power at 8000? No point reving there if your cam profile isn't designed to make power there.
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Old 12-12-2018, 10:37 AM   #8
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That would be the real issue. Can it spin that fast? Maybe (although for how long - you're really yanking and flinging those stock cast pistons around *hard* at high RPM's). Is there any real point to it? Probably not. Unless you have a metric boatload of supporting mods to actually make it flow and produce torque at that RPM. And a cam that will make HP at that RPM won't be much fun at more reasonable revs, there's no variable valve timing or VTEC stuff on a redblock to help stretch a cam's range out.
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Old 12-12-2018, 10:55 AM   #9
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need cro moly retainers, and a cam that will do it. Also, an intake manifold that doesn't choke, and at that point you probably want head work, but eh.

as far as the bottom end, 8k is fine.
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Old 12-12-2018, 11:03 AM   #10
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How would the water pump handle those RPMs?
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Old 12-12-2018, 11:20 AM   #11
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An underdrive pulley would probably be a good idea. But certainly not a the top of the list of things needed to make it actually worthwhile revving that high.
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Old 12-12-2018, 11:21 AM   #12
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Definitely replace those aluminum retainers with some steel or chromoly ones. Aluminum has no fatigue limit, and they will eventually fail.

As far as rpm goes, the old b230 in the rally car got spun to 8k all the time, and spent minutes at a time over 7k rpm. It had a k-cam, upgraded valve springs, and some porting. Otherwise completely stock. Only issue when I pulled it apart was some scoring on the last two cam journals, which I assume was from poor oil supply to the back of the head. Fixed that on the 16v head with another oil supply line added.
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Old 12-12-2018, 01:08 PM   #13
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Thank you for schiming in guys.

I haven't taken it to the dyno yet but I agree, I will not take it up to a range it doesn't make power anymore.
But it just felt like it would benefit from 2000 more rpm, judging by how strong it feels at 6000.
Given the fact the K cam is high lift high duration high overlap, in my book it is the recipe for good cylinder filling at high rpm.

Since the spring retainers were avaliable in KG trimning catalog, I humbly thought it was quality durable parts.
I bought them along with double spring so I could explore this high rpm range.

Will let you know once I dyno it.
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Old 12-12-2018, 02:01 PM   #14
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Quote:
Originally Posted by kingkong View Post
But it just felt like it would benefit from 2000 more rpm, judging by how strong it feels at 6000.
By this logic why stop at 8? If 2000 is good 4000 must be great. 10,000 rpm red block with a stock top end, itíll make a ton of power Iím sure.
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Old 12-12-2018, 02:29 PM   #15
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Quote:
Originally Posted by Stiggy Pop View Post
By this logic why stop at 8? If 2000 is good 4000 must be great. 10,000 rpm red block with a stock top end, itíll make a ton of power Iím sure.
I was wondering when there would be a dick to say something like that.
I am so sad for you. Being a **** won't make your life less miserable.
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Old 12-12-2018, 02:34 PM   #16
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Quote:
Originally Posted by Stiggy Pop View Post
By this logic why stop at 8? If 2000 is good 4000 must be great. 10,000 rpm red block with a stock top end, it’ll make a ton of power I’m sure.
This one goes to 11:



1000 hp, normally aspirated, sounds like a blender.
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Old 12-12-2018, 02:37 PM   #17
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Quote:
Originally Posted by JohnMc View Post
1000 hp, normally aspirated, sounds like a blender.
pretty sure it's got a k-cam in it too!

(cool vid, thanks)
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Old 12-12-2018, 02:43 PM   #18
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spin it until it scatters valvetrain or shoots a rod through the side of the motor...then set the limiter 400-500rpm under that.
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Old 12-12-2018, 02:44 PM   #19
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Oh, the k cam is pretty much shut down after 6500-6800
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Old 12-12-2018, 02:54 PM   #20
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6800? then to shift at 7500 really wouldn't be outrageous....I wish someone with aluminum retainers would Chime in...I guess my experience had been in cam in block engines...I wonder if there's something I'm missing with ohc engines
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Old 12-12-2018, 02:59 PM   #21
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Quote:
Originally Posted by RvolvoR View Post
Oh, the k cam is pretty much shut down after 6500-6800
Yes. I ran for a bit with a k-cam in a stock head, Nathan intake, tube header, holset blah blah (a better flowing setup than being discussed here is my point). I set the rev limiter at 6900 and it was gassed out by then.

BUT I'm just the dick with first hand experience :p
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Old 12-12-2018, 03:07 PM   #22
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Quote:
Originally Posted by freevolvos View Post
...I wish someone with aluminum retainers would Chime in...
I did chime in, you either didn't read it or are ignoring what I (and others) have said.

I used to work in an engine machine shop (my dad still runs it), he primarily builds race motors and vintage motorcycle engines. I have removed cracked aluminum retainers on at least 2 occasions, and the run time on these motors were in the 20 hour range.

Once again, do not use aluminum retainers unless you're drag racing and replacing them after 2-3 hours of run time. They WILL fail.

K-cam revs out just fine when it's retarded a few degrees and the ignition timing is bumped up 5 deg or so.

Last edited by culberro; 12-12-2018 at 03:17 PM..
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Old 12-12-2018, 03:07 PM   #23
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I used to run my hy35cw powered car up to a 7100 limiter on a stock unported head without any valve train issues or block issues.

This was at 26psi.
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Old 12-12-2018, 03:34 PM   #24
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The mechanical limit is how fast your valves can open and close. YOu already got double valve springs so you got that covered. The aluminum keeps are race only and yes you change them all the time, every race. I used to have my old hot rod and no rev limit lh2.4 and rsi stage 3 turbo cam and double valve springs and would rev it to 7500rpm and more even. Valve float is when your valves can't open and close fast enough and that is what keeps the motor from revving faster. There is your final answer only took 24 posts to get there..

Zero to sixy watch the tach, goes below and around and past the 7k on the dial..



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Old 12-12-2018, 03:39 PM   #25
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I somewhat regularly zing my B20 (olde pushrod OHC motor) to 7500 rpm, with the carbs/cam/head/exhaust it's still productive there.

I've also replaced a cracked piston once in the past, and I currently have a cylinder with low compression that's leaking into the crankcase, so probably same thing again.

It's pretty fun to just keep your foot in it and let 'er rip.
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