Re: Very high RPM on pump gas
[Re: Spaceman Spiff]
#2707204
10/16/19 09:32 AM
10/16/19 09:32 AM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
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New York
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Not sure I follow. If the venue in which that successful engine design stops, the design becomes invalid?
Boffin Emeritus
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Re: Very high RPM on pump gas
[Re: Spaceman Spiff]
#2707329
10/16/19 05:46 PM
10/16/19 05:46 PM
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Joined: Apr 2003
Posts: 3,570 Tulsa, Oklahoma
340Cuda
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there's no reason on God's green earth to ever build a 10,000 RPM engine To win races Not since modified production died. You can see them in Comp Eliminator.
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Re: Very high RPM on pump gas
[Re: polyspheric]
#2707331
10/16/19 05:54 PM
10/16/19 05:54 PM
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Joined: Jan 2003
Posts: 10,091 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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I Live Here
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A friend of mine has(had?) A 3.91 stroke 4.375 bore hemi that accidentally hit 9800 rpm last outing. Both valve heads in one cylinder went through the piston. Kinda made a mess. The valvetrain failed first. A Hemi spinning 7500 would be a challenge in the valve train department. 10,000 rpm would be insanely expensive.
8.582, 160.18 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Very high RPM on pump gas
[Re: gregsdart]
#2707353
10/16/19 07:14 PM
10/16/19 07:14 PM
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Joined: Jan 2011
Posts: 4,785 Utah and Alaska
astjp2
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JESEL or T&D would eliminate some RPM issues.
1941 Taylorcraft 1968 Charger 1994 Wrangler 1998 Wrangler 2008 Kia Rio 2017 Jetta
I didn't do 4 years and 9 months of Graduate School to be called Mister!
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Re: Very high RPM on pump gas
[Re: tubtar]
#2707437
10/16/19 11:00 PM
10/16/19 11:00 PM
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Joined: Jan 2003
Posts: 6,163 Melbourne , Australia
LA360
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I read an interesting article that detailed a lot of what went into a 9800 r.p.m. SS/AH motor and it was pretty remarkable. Narrowed cam bearings and re-located lobes was the part where I physically felt my wallet cringe in my back pocket. Spreading the lobes nearly 1 " also required custom bedding and rocker arms , and had to oil the valve gear through the push rods. If you can dredge up a February of 2011 MoPar Action , it is pretty interesting. And 8 years old. God only knows what they are doing now. Charlie Wescott moved the lobes around first, to try and straighten out the push rods. He also creatively interpreted the rules in regards to milling the intake flange, they later changed the rules
Alan Jones
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Re: Very high RPM on pump gas
[Re: hemienvy]
#2707444
10/16/19 11:32 PM
10/16/19 11:32 PM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
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Assuming using a stock block? Keeping the block & bits itself intact is the easy part: spend money. The rest is partially money: 7mm valves, biggest double-tapered pushrods that will fit, titanium? collars, beryllium? springs, Spintron test everything. Offset secondary rockers as jackshafts to correct pushrod angularity have been used successfully (but not in race cars, or recently).
The interesting part, to me, is to force someone to run an FEA program on the Barton rockers to isolate where mass can be safely removed without structural compromise, which may take many passes to get the lever ends slimmed down (as we say "make it all the same blue color"). Once this is done, no brain surgeons are needed, a small boy with a Dremel can duplicate the work. Wouldn't it be nice if Barton donated a (slightly used) set, in exchange for valuable data he may not have?
Boffin Emeritus
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Re: Very high RPM on pump gas
[Re: polyspheric]
#2707446
10/16/19 11:42 PM
10/16/19 11:42 PM
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Joined: Jan 2008
Posts: 4,274 Canada
WO23Coronet
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I was asking how you arrived at 9-10,000 RPM as a target? The rod-breaking stress level @ 10,000 RPM is double that @ 7,000 RPM.
Double the budget, much less power than stock stroke. The whole "the heads will work much better with smaller displacement" has been tried by everyone in the last 80 years. The heads will work very differently, but not necessarily better.
The rod ratio goes to hell. Unless you want a boat anchor for a piston, the rod gets longer by half the stroke change (more if low piston weight is desired): 6.86" ÷ 3.75" = 1.83:1 ratio 7.11" (+ .25" longer rod) ÷ 3.25" = 2.19:1 ratio Do you know what that does to vacuum? To air motion around overlap?
You're throwing 50 years of hemi cam development over the cliff, and starting with a blank sheet of paper.
Ask Barton for the price on a complete set of rockers (take a stiff drink 1st). What does a really long rod ratio do to vacuum?
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Re: Very high RPM on pump gas
[Re: WO23Coronet]
#2707567
10/17/19 10:33 AM
10/17/19 10:33 AM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
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Really stalls piston motion B/ATDC, initiates vacuum later, reduces piston to valve clearance. This is acceptable for an engine with small ports + large displacement (or no need for low speed power, like F1), but kills torque if the engine size drops. The opposite (big ports and short rods)? BBC, works very well. Reducing engine size by bore change is almost harmless as long as the new wall position does not significantly shroud the intake valve. By comparison, reduction by stroke change, even with reduced deck height, seldom does what you want.
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Re: Very high RPM on pump gas
[Re: hemienvy]
#2707649
10/17/19 01:09 PM
10/17/19 01:09 PM
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Joined: Jan 2005
Posts: 12,478 Kalispell Mt.
HotRodDave
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Those mazda's are kind of cheating when they say they have 16 to 1 or whatever, the fuel is directly injected into the cylinder after the piston is coming back down and the cylinder pressure is not so high as well as cam position being manipulated to increase or decrease overlap and retarding the intake valve timing to reduce cylinder pressure. At part throttle when cylinder pressure is reduced by the throttle restricting airflow then it may be injected closer to or even before TDC butt again, cylinder pressure is not as high under those conditions.
Motorcycles run high compression as a result of a typically very straight shot of cool air to the cylinders with very minimal if any heating of the air as well as small bores that tend to ward off detonation and very large cams that bleed off pressure. The individual runners also tend to run much smoother with a very large cam than multiple cylinders running off a common plenum with a huge cam, the cylinders are not interfering with each others air/fuel charge. Remember too that 1.9 inch stroke is not moving the piston any faster at 14,000 than a 3.8 stroke at 7000, twice as many cycles but nearly equal average piston speed. It is hard to compare a motorcycle valve train to a pushrod engine, the cam is usually pushing directly on a lash cap/tappet thingy with no pushrod or rocker arm weight to deal with at all and none of the weird harmonics that need to be dealt with that are associated with them.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Very high RPM on pump gas
[Re: HotRodDave]
#2707681
10/17/19 02:46 PM
10/17/19 02:46 PM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
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1.9 inch stroke is not moving the piston any faster at 14,000 than a 3.8 stroke at 7000
But the peak piston acceleration is much, much higher: Z (in feet per second, per second acceleration) = (N^2 × S (1 + (1 ÷ 2n))) ÷ 2189 (assuming 2:1 rod ratio for both engines) 1.9" stroke @ 14,000 RPM: 212,654 f/s/s 3.8" stroke @ 7,000 RPM: 106,327 f/s/s
Many current DOHC auto engines have variable valve timing, which uses... rocker arms. 2JZ (Supra) owners don't seem to understand what that is.
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