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Author Topic: Inline-four crankshaft  (Read 98070 times)
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Jack Gifford
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« on: December 04, 2011, 01:17:59 AM »

I need help with fundamentals of high-performance four-bangers, as I've never modified/built one before. This is for my F-class blown/fuel lakester (182 c.i., ~4" bore, a little under 3.75" stroke). To attain my goal of 4 HP/c.i., simulations show it needing to spin ~10,000 RPM (keeping boost within reason, vintage-look blower with no intercooliing, and on alky only). So... I need to learn about keeping this "vibrator" in one piece. Is it a 'given' that I use a flat crank, or does some arrangement of 90` offset throws have any "smoothness" advantage? If flat, is there any precedent for other than having #2 and #3 throws in-line?

Note: Think clean-sheet-of-paper with no restrictions, since crank and cams need to be from billets anyway.
Hmm... if there are literally no restrictions, I guess I shouldn't necessarily assume crank throws at multiples of 90 degrees, huh? rolleyes C'mon, help me think out-of-the-box on this!

Lots more questions, but that's it for now.
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« Reply #1 on: December 04, 2011, 02:34:12 AM »

I know you're just approximating at this point, but I'm showing you at 189 ci with the dimensions you gave.  This is the planning stage, so it's just numbers for now.

F/BFL record is 262 and change.

700 hp - 10 K, you're probably thinking a 3:1 rear end with 28" tires?  Wouldn't have to wind it that tight with different gears, if you can come up with an engine model that will get you your power at a lower RPM.

5 main bearings, I hope?  grin

How big of a bore do you think you could get away with and not have the walls so thin that they might flex?

Needless to say, I'm a fan of the low reciprocating weight, short-stroke idea if you want to keep it smooth.  You wind up with the advantage of a stiffer crankshaft, which equals less flex and vibration.  You also get a longer rod to stroke ratio, with less side loading on the bores.  You take a lot of pounding on the block out of the equation by going with a shorter stroke.

All generalities at this point.  You need to get specific.  More info, please!  cheers
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« Reply #2 on: December 04, 2011, 08:15:47 AM »

I would investigate an Offenhauser engine ... good starting point
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« Reply #3 on: December 04, 2011, 08:24:52 AM »

Give "jacksoni" a shout.....he is the architect and builder of our Pontiac G motor...
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jacksoni
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« Reply #4 on: December 04, 2011, 09:55:52 AM »

You might go read this thread on speedtalk which deals with a cross plane crank. Done in bikes. They shake your fillings out I understand. Done for traction not power. Uneven firing order. Need balance shafts etc. On a big four don't think good idea. Also on speedtalk a member "cspeier" who ran a comp elim 202" 4 based on same engine as mine (super duty pontiac). 465hp NA. Might ask his thoughts on the vibration issue. And of course, drag motor rpms and bonneville rpms may not be happy being the same. But there are lots of 4 cyls running comp eliminator. Gotta have all your valve train ducks in a row for that kind of rpm (your 10k) if you are running a 2 valve pushrod engine( I am and have some issues) Might think DOHC.

http://speedtalk.com/forum/viewtopic.php?f=15&t=29040
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Jack Iliff
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« Reply #5 on: December 04, 2011, 10:11:37 AM »

Other than a flat crank will not result in a cylinder firing every 180 degrees. That and a forged flat crank being inherently stronger than a twisted crank, that started out flat, pretty much rules out your plan.
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johnneilson
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« Reply #6 on: December 04, 2011, 11:10:04 AM »

The only way around the offset acceleration vibration problem (inline 4) is to configure the motor as a boxer type and problem goes away.
Using very long rods and the absolute lightest piston helps.

You didn't mention Vintage motor, what are you thinking about basing the motor on?

John
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« Reply #7 on: December 04, 2011, 12:09:22 PM »

I asked a good friend that designs cranks for some of the big engine builders and he mentioned that:

"This will be a bigger problem than he might expect, vibration will be
terrible even with a flat crank at that high rpm with a 3.75 stroke
unless the parts are super light.

When the Pro stock teams were running flat cranks at 3.72 stroke, WJ
said the car vibrated so bad the tack looked as big as a dinner plate.

It is possible to use a non flat crank but he will have to use an
external balance shaft. I don't know if there would be an advantage that makes it worth doing".

The record your after is held by a turbo Offy that can produce over 1000hp in the old Dick Russel lakester (maybe Rex will chime in with his "how to stop an runaway  Offy on the dyno story").  Unless you were really tied to what you want to do I would look for a last generation Chevy 3.0L IRL motor and put a turbo on it.  It will get you over 1000HP and you would be in it for a fraction of an Offy and less than a good SBC.  Tony
« Last Edit: December 04, 2011, 12:27:00 PM by maguromic » Logged

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« Reply #8 on: December 04, 2011, 12:56:23 PM »

I suspect what Jack has up his sleeve is a bit more interesting than an IRL motor . . . wink
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"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  rolleyes

We are NOT rebuilding . . . We are reloading.

GOD SAVE MG - The Queen can take care of herself!
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« Reply #9 on: December 04, 2011, 03:29:13 PM »

I may be wrong but I believe Russel Eyres runs, has run, a SBC using only one bank. I believe the engine has a standard V8 crank and so would be very much like what you discribe. Contact information for the Eyres clan can be found in the rule book. You might want to contact them and see what they think.
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jacksoni
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« Reply #10 on: December 04, 2011, 03:42:44 PM »

Of course, Fred Larsen and Cummins beautiful little liner ran a blown 4 cyl (of eight) in GBFS and a 3 liter V-8 in F.  This year, Don McMeekin had a half Ford motor in FGC. I think he had custom crank rather than just counterweighting it. So there are number of times has been done. And first time out with my streamliner took 2 pistons out of the G motor 4 to make a 2 cyl 1liter. Did set a record- which has been exceeded by 200mph! rolleyes cheers There are always ways.
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Jack Iliff
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« Reply #11 on: December 04, 2011, 05:53:13 PM »

I have seen several SBC V8 engines running the end two on one side and the center two on the other. I believe that's what Larsen and Cummins did. As did Solomen and Hartsok roadster. But Russel's one side Chevy. The other side blanked off with a flathead is a horse of a different color.
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Rex Schimmer
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« Reply #12 on: December 04, 2011, 07:33:38 PM »

Last time I was at Van Dyne Engineering Stu had a 200 inch 4 cylinder based upon current midget motor technology, it had a hair dryer on it and ran gas with an intercooler, I think, anyway it was for some guys sand rail but it made over 1200 hp on the dyno. That equals 6 hp/inch so you could back it down and probably get a reliable 4 hp/inch that would run 5 miles at Bonneville. If you are going to run alcohol even better. John Romero, was getting almost 650 hp from his 91 cu-inch Honda at the wheels and literally "hot lapped" that car at Bonneville a couple of years ago, so a high hp four cylinder should not be a problem. The cure for the vibration is to use rubber motor mounts to keep from breaking the motor loose from the frame and keep the instruments from being unreadable .  Trying to do some sort of trick weird offset crank is probably a waste of time and certainly lots of money.

When the old time sprint car guys ran Offys at 317 cu. inches the only way they could keep the motor in the frame was to use rubber motor mounts.

Rex
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Jack Gifford
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« Reply #13 on: December 05, 2011, 02:06:14 AM »

1) ... 189 ci with the dimensions you gave...
2) ... F/BFL record is 262 and change...
3) ... 3:1 rear end with 28" tires...
4) ... come up with an engine model that will get you your power at a lower RPM...
5) ... 5 main bearings...
6) ... How big of a bore...
7) ... generalities at this point.  You need to get specific...
1) I had only given approximate numbers. Bore will be 4.000", stroke 3.620" (or maybe 3.580" for more wiggle-room within the 'F' limit).
2) Which is one of the main reasons I've chosen 'F', since the car has already displayed good manners up to 260-something (on its GPS at Bonneville '08).
3) The quickchange box (my design and fabrication) has a huge range available, so no need to discuss rear gears and tire rollout.
4) With the constraints I've set I'm stuck with turning the engine that fast.
5) Yes. _____________________________[to be cont'd]
« Last Edit: December 05, 2011, 02:10:14 AM by Pontiac Jack » Logged

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Jack Gifford
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« Reply #14 on: December 05, 2011, 02:23:51 AM »

continuation of post#13 (I can't figure out how to create a loooooooong post?)

6) Although it would be advantageous, I can't do a larger bore-to-stroke ratio.
7) In the interest of being methodical, I hoped to avoid "distracting" specifics. Right now, I need to learn enough about the fundamentals of inline-four "shaking" to choose a crank configuration.
Thanks.
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