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Author Topic: How to calc highest revs?  (Read 305 times)
StewRat
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« on: June 14, 2018, 16:36:28 PM »

Second question of the day before going racing on Sunday.

StewRat has only really been down the strip once for testing and I had a low rev limit on the tach light and the MSD box.

I'm not about to crank it up to "11" in one go, but as I add say 500 rpm per pass to the limits - how do I work out what my max should be?

We're talking 82x94, CB case and heads
35.5 x 40 valves
2 x DRLA 40 carbs
Engle W130 cam
SCAT forged crank and lightened flywheel
Balanced rotating assembly

... and a standard gearbox Roll Eyes

How do I know what max revs should be ? (apart from when things go pop that was too many)

Maybe I should add I'm as much interested in longevity of components as much as getting the last X% out of the engine.

Thanks
Stewart
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Fastbrit
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« Reply #1 on: June 14, 2018, 18:56:40 PM »

What rods/bolts are you running?

Your engine will start to run out of puff at 6500rpm due to cam/valves/carbs, but will breathe to 7000rpm quite happily. Won't be making too much more power at those revs, though.
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StewRat
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« Reply #2 on: June 14, 2018, 19:25:46 PM »

What rods/bolts are you running?

Your engine will start to run out of puff at 6500rpm due to cam/valves/carbs, but will breathe to 7000rpm quite happily. Won't be making too much more power at those revs, though.

Thanks - that's useful.
CB Unitech 5.4" rods and - erm - whatever bolts came with them.
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“There are three kinds of men. The one that learns by reading. The few who learn by observation.
The rest of them have to pee on the electric fence for themselves.” – Will Rogers

The Stew Rat build thread http://cal-look.no/lounge/index.php/topic,25365.0.html
andy198712
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« Reply #3 on: June 15, 2018, 10:43:19 AM »

And what valve springs.

I guess a dyno would show where the power tails off too
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StewRat
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Posts: 135


« Reply #4 on: June 15, 2018, 15:22:29 PM »

And what valve springs.

I guess a dyno would show where the power tails off too

Springs are what came with the CB 044 Supermag heads - singles, though it seems they are shipped with dual springs these days.
I do have a set of of dual springs not fitted.

At this early stage I'm not so concerned about wringing the last ounce of power from it, but trying to set shift lights/MSD limits appropriately so I don't get carried away and do damage by overrevving. But without throwing away too much potential Smiley

Thanks

Stewart
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“There are three kinds of men. The one that learns by reading. The few who learn by observation.
The rest of them have to pee on the electric fence for themselves.” – Will Rogers

The Stew Rat build thread http://cal-look.no/lounge/index.php/topic,25365.0.html
leec
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« Reply #5 on: June 15, 2018, 17:44:06 PM »

Single springs with an engle 130, I always thought a 110 was the most you could run with single springs. My 1776cc with engle 120 is dual spring
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StewRat
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Posts: 135


« Reply #6 on: June 15, 2018, 22:48:19 PM »

Single springs with an engle 130, I always thought a 110 was the most you could run with single springs. My 1776cc with engle 120 is dual spring

Sounds like I should probly get those dual springs on then.
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“There are three kinds of men. The one that learns by reading. The few who learn by observation.
The rest of them have to pee on the electric fence for themselves.” – Will Rogers

The Stew Rat build thread http://cal-look.no/lounge/index.php/topic,25365.0.html
leec
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« Reply #7 on: June 15, 2018, 22:54:05 PM »

Sounds like a good idea. The heads will probably need machining for dual springs
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