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Old 09-20-2010, 02:28 PM
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SBC 357 Crank suggestion

I am putting together a motor for a drag truck my machinist is letting me use. I started a thread under hotrodding basics about an idea i had for a couple years down the road when i had more money but looks like for now i will use what i have. I have 95% of the parts laying around so I realize some parts are not the best but will work. Its gonna be a .040" 350. I have a set of speed pro hyp pistons that are 5 cc flat tops. They are the 4 valve relief which don't promote good quench but ill be running 110 so not too worried about it. I also have a set of eagle I beams rods.

Motor will have a mechanical flat tappet cam
Howards: 112061-10
Vortec heads for now, i know these are not the best heads for this build but I have them already. I can machine them for more lift and i can do the valve job myself so no money spent on them.
CR should be just under 11:1

I imagine this motor will stop pulling around 6000-6500 due to the vortec heads so its gonna see some rpm but nothing insane. Will an aftermarket cast crank hold say 500-525hp at 6500rpm.

I have a couple stock cranks but I plan on putting 100-125hp shot of nitrous on this motor so I was wondering what would you guys recommend. I wasn't sure If I should use a 5140 steel crank or an aftermarket cast steel crank. I think a 4340 is more crank than what i need and out of my budget.

Rotating assembly will be balanced.

Thanks in advance everyone!
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Old 09-20-2010, 04:49 PM
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Quote:
Originally Posted by zildjian4life218
I am putting together a motor for a drag truck my machinist is letting me use. I started a thread under hotrodding basics about an idea i had for a couple years down the road when i had more money but looks like for now i will use what i have. I have 95% of the parts laying around so I realize some parts are not the best but will work. Its gonna be a .040" 350. I have a set of speed pro hyp pistons that are 5 cc flat tops. They are the 4 valve relief which don't promote good quench but ill be running 110 so not too worried about it. I also have a set of eagle I beams rods.

Motor will have a mechanical flat tappet cam
Howards: 112061-10
Vortec heads for now, i know these are not the best heads for this build but I have them already. I can machine them for more lift and i can do the valve job myself so no money spent on them.
CR should be just under 11:1

I imagine this motor will stop pulling around 6000-6500 due to the vortec heads so its gonna see some rpm but nothing insane. Will an aftermarket cast crank hold say 500-525hp at 6500rpm.

I have a couple stock cranks but I plan on putting 100-125hp shot of nitrous on this motor so I was wondering what would you guys recommend. I wasn't sure If I should use a 5140 steel crank or an aftermarket cast steel crank. I think a 4340 is more crank than what i need and out of my budget.

Rotating assembly will be balanced.

Thanks in advance everyone!
500 horse is on the upper end of what a factory crank will put up with. Given you want to use nitrous as well, I just can't see using less than a 5140 forging and some good rods as well.

Nitrous hit the crank real hard, it's not like a supercharger whether crank or turbine driven, a supercharger builds the power smoothly as RPMs and demand go up. Nitrous, on the other hand hits the crank hard, one revolution it's putting out 300 horses the next 500, the crank wants to become a steel pretzel. The rods are in the same boat having to react this sudden load while not bending caught as they are between a crank being held back by the weight of the vehicle and a piston driven by a sudden explosion.

Hyper cast pistons tend to be there one moment and gone the next. They don't like lots of force dumped on them real sudden, and they surely won't survive the detonation that often comes with nitrous.

This is all build-able, but the set up you propose is right on the upper edge of your parts selection, think more like 400-450 and no nitrous and the components you suggest will hang together at 6000 RPMs not 6500. Stresses go up to the square of RPMs so when you start spinning things over 6000, component strength gets really critical. Balance helps but you have to remember that we're balancing static weights so-called First Order balance. The Second Order is the whack the crank takes from the power stroke, that is not balanced and causes the crank to bend and snap back with every piston's power stroke. This is what the damper is there for to soak up these vibrations and those harmonics that form third and fourth and on vibrations. These vibrations are waves of energy flowing thru the crank. They can climb on each other which adds strength to them called "augment" or they can fall to opposite signs resulting in their reduction or elimination call "attenuation". Engine designers spend a lot of time working this issue. A good damper is also required as dealing with these vibs is a whole lot simpler if a device is used to just soak up their energy. There just is no way to build a cheap high performance motor and keep it together.

Bogie
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Old 09-20-2010, 05:03 PM
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Gonna need 59cc chambers w/a 0.041 quench for 11:1, all else as you printed above. W/64cc chambers, you're at about 10.4:1.
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Old 09-20-2010, 06:06 PM
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So definitely a 5140 forged crank, good balancer, and maybe a progressive controller to help the nitrous come on more smoothly? My machinist just picked up one for his nova and its for two stages and he said it only cost him a couple hundred. How far can Vortec heads be shaved to 62, 60cc?
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Old 09-20-2010, 06:30 PM
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Speaking of balancer, well on a 350 it's actually a damper, not a balancer, but anyway, in my opinion the best dampers are OEM. The crank bore is dead nuts on so that the press fit will be correct. If that dimension is too loose like I have seen on a number of aftermarket dampers, then the harmonics are not transferred from the crank to the hub properly for dissipation to the inertia ring. These guys do a good job of rebuilding your OEM damper (new elastomeric material pressed in and the hub properly clocked to the ring) or can supply you a rebuilt one from their stock....
http://www.damperdoctor.com/
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Old 09-20-2010, 06:45 PM
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Quote:
Originally Posted by techinspector1
Speaking of balancer, well on a 350 it's actually a damper, not a balancer, but anyway
I never realized there was a difference. Learn something new everyday. Has anyone known of sbc having two different balancers having the timing mark like 20* off. I noticed the other day when I was cleaning up my shed i had a bunch of dampers and stacked them on top of each other lining up the keyways and a couple were different. I have only torn down small block chevys 305, 350, and 400s.
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Old 09-20-2010, 06:49 PM
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The following is from another post I made on this:

There are several different dampers. Both the diameter and the placement of the line on the outer ring of the damper can differ. So you need to know what you have, to know what tab to use.

The three most common locations for the timing mark on the damper:

The pre-'69 damper has the TDC line on the outer ring at the 2:30 o’clock position- or 2º before- (i.e. to the LEFT of the keyway, looking at the front of the engine) the keyway centerline. The keyway is seen in the ID of the damper.

The damper used from '69 to mid-80's has the TDC line at the 2 o’clock position- or 10º before the keyway. You'll find that aftermarket dampers are the 10º type, as are the bolt-on tabs sold in the aftermarket, unless they're adjustable.

A third timing mark was used from about 1978 to about 1991-'92. It is at the 12 o’clock position- or 40º before the keyway. This damper uses a timing cover that has the tab welded on at about the 12 o'clock position.

If you're unsure, or just want to check the accuracy of the tab/mark for TDC, DETERMINE TDC and MAKE A TIMING TAPE will help you to see for yourself.

Last edited by cobalt327; 09-20-2010 at 07:02 PM.
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Old 09-20-2010, 06:51 PM
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Quote:
Originally Posted by zildjian4life218
I never realized there was a difference. Learn something new everyday. Has anyone known of sbc having two different balancers having the timing mark like 20* off. I noticed the other day when I was cleaning up my shed i had a bunch of dampers and stacked them on top of each other lining up the keyways and a couple were different. I have only torn down small block chevys 305, 350, and 400s.
There are 3 different timing locations used, 12:00 O'Clock, 2:00 O'Clock and 2:30 O'Clock. See all the different part numbers used here. Scroll down for 350's.....
http://www.damperdoctor.com/Merchant...egory_Code=CHE
Thanks for the post Cobalt, didn't see it before I posted....

Last edited by techinspector1; 09-20-2010 at 07:07 PM.
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Old 09-20-2010, 06:57 PM
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Oh man I'm gonna be a wealth of knowledge tomorrow. Thanks for the information
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Old 09-21-2010, 03:09 PM
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does anyone else have any suggestions? as of now I am definitely gonna go for the 5140 forged crank and possibly a nitrous controller.
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Old 09-21-2010, 03:19 PM
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I was just thinking about this yesterday. Aren't you going to be bracket racing rather than building for a particular pounds per cubic inch class in Competition Eliminator?

If yes, bracket racing, then why does it make any difference how much power you make? Pull your horns in and have some fun with a 350/400 hp motor using stock parts until you can get some experience and squirrel away enough money to build a high hp motor. Also, you know, 100 lbs equals 1/10th second, so get in there and start ripping out stuff that isn't necessary to the operation of the truck.

Spending money on a steel crank, nitrous and high-buck controller seems to me like hanging a string of pearls on a pig.
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Old 09-21-2010, 07:42 PM
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Quote:
Originally Posted by techinspector1
I was just thinking about this yesterday. Aren't you going to be bracket racing rather than building for a particular pounds per cubic inch class in Competition Eliminator?

If yes, bracket racing, then why does it make any difference how much power you make? Pull your horns in and have some fun with a 350/400 hp motor using stock parts until you can get some experience and squirrel away enough money to build a high hp motor. Also, you know, 100 lbs equals 1/10th second, so get in there and start ripping out stuff that isn't necessary to the operation of the truck.

Spending money on a steel crank, nitrous and high-buck controller seems to me like hanging a string of pearls on a pig.
Thats a great way to look at it. Maybe Ill just build it for now for whatever power it makes and use it and have fun. The truck is very light as it sits. I believe 2600 without driver so even a 400hp motor will let me have plenty of fun.
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Old 09-21-2010, 07:49 PM
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Quote:
Originally Posted by techinspector1
I was just thinking about this yesterday. Aren't you going to be bracket racing rather than building for a particular pounds per cubic inch class in Competition Eliminator?

If yes, bracket racing, then why does it make any difference how much power you make? Pull your horns in and have some fun with a 350/400 hp motor using stock parts until you can get some experience and squirrel away enough money to build a high hp motor. Also, you know, 100 lbs equals 1/10th second, so get in there and start ripping out stuff that isn't necessary to the operation of the truck.

Spending money on a steel crank, nitrous and high-buck controller seems to me like hanging a string of pearls on a pig.
I can't argue with this one bit.

I know for a fact Scat cast cranks will handle nitrous and motor combined HP into the mid 600's for several years without problems, I have several engines like this out there, some have 5+ years on them(500+ passes, 15,000+ street miles). I don't think forged crank is even close to necessary for what you plan.

The hyper pistons are the problem IMO, and by far the first piece that needs to be forged in anything stronger than a warmed over stock engine.
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Old 09-22-2010, 05:33 AM
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http://www.summitracing.com/parts/SCA-910526/

So like this. What about the cross drilled mains?
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Old 09-22-2010, 05:54 AM
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I would build it as is using a GM cast crank.
Open up the hyper piston ring end gaps some.
Bigger is better.

I'd have no problem hitting it with double the juice you plan, when
using 110 octane race gas.
Get a high stall converter (3500 stall at minimum) and a WOT switch
and a simple RPM window switch and it will be very hard to hurt this motor.
I'd go bigger on the cam. use the lunati solid cam with
256-270 .500-.515 112LSA install at 106 in c/L
If you want more top end.

A pro products hurricane vortec manifold +750

If you are going to use a aftemarket crank get a scat over an eagle.

The amount of nitrous you are planning on using is just a tune up.
You worry too much.

Last edited by F-BIRD'88; 09-22-2010 at 06:02 AM.
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