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Cast Crank and 10 to 1 pistons #1109940
11/09/11 01:02 AM
11/09/11 01:02 AM
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Brandon, Ms
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cornet684me Offline OP
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cornet684me  Offline OP
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i have a cast crank motor with low compression pistons, can i switch out the low compression pistons with 10 to 1? a buddy told me that if i switch out the pistons on the cast crank to 10 to 1 that the crank rods and pistons will have to be balanced to make it work.

my question is, do they make a 10 to 1 pistons for the external balanced crank? or would it be easier and cheaper just to change out the cast crank with a forged crank? i have a good forged crank to use.

thanks

Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109941
11/09/11 01:22 AM
11/09/11 01:22 AM
Joined: Mar 2003
Posts: 571
Beaverton, OR, USA
Alikazam Offline
super gas
Alikazam  Offline
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Beaverton, OR, USA
I run 10.2:1 compression on my 360 with the stock cast crank and stock rods with good arp fasteners through out (main studs and rod bolts, arp pro wave 2000 for the rod bolts), with polished beam rods. Pistons are wiseco pro-tru series. Have over 200 passes on 150 shot of nitrous (440 whp) without issue. I did have it fully balanced when I was putting the engine together though. Hope that helps!

Re: Cast Crank and 10 to 1 pistons [Re: Alikazam] #1109942
11/09/11 01:30 AM
11/09/11 01:30 AM
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Brandon, Ms
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cornet684me Offline OP
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this is going into a 440, i think the key here is that i will have to pay the extra money and have the new pistons balanced. i was hoping to get by with just putting new pistons on the rods and getting by,

i should have known i could not get out the cheaper way,

thanks


Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109943
11/09/11 01:32 AM
11/09/11 01:32 AM
Joined: Jan 2003
Posts: 9,826
las vegas
70AARcuda Offline
master
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las vegas
Quote:

i have a cast crank motor with low compression pistons, can i switch out the low compression pistons with 10 to 1? a buddy told me that if i switch out the pistons on the cast crank to 10 to 1 that the crank rods and pistons will have to be balanced to make it work.

my question is, do they make a 10 to 1 pistons for the external balanced crank? or would it be easier and cheaper just to change out the cast crank with a forged crank? i have a good forged crank to use.

thanks




it all has to do with the weight of the piston...you need to know how much your existing pistons weight and how much the new pistons weight..

even if you change to a forged crank...it is all going to have to be balanced if the bobweight of the crank is off from your existing rods and pistons...

the balance is all based on the weight of the rods..pins..pistons..


Tony

70 AARCuda Vitamin C
71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield)
71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas)
71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)
Re: Cast Crank and 10 to 1 pistons [Re: 70AARcuda] #1109944
11/09/11 01:42 AM
11/09/11 01:42 AM
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Posts: 1,639
Brandon, Ms
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cornet684me Offline OP
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so what you are saying, the best thing to do when i switch out pistons, is have a machine shop balance my rotating assembly to make sure it is balanced? because i wld think that 10 to 1 pistons wld not be the same size as the smog pistons.

i think that i will send the extra money to have the motor balanced


Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109945
11/09/11 01:43 AM
11/09/11 01:43 AM
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Lincoln Nebraska
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RapidRobert Offline
Circle Track
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Lincoln Nebraska
I'm doing the same thing on an extremely low buck 318 DD. Have some std pistons/moly rings and some viper rods (.098" longer). I dont care what the bore taper/out of round/clearance is. Shooting for .035-.040" quench and will machine piston notches to reduce the static CR. I'll decarbon the pistons/pins and rods in carb cleaner then weigh em then deburr/polish/trim the new rods/pistons (they're heavier) until the new piston/pin/rings weigh the same as the old and slap em in w some new bearings. You can get a HF digital gram scale (on sale) for less than 10 bucks and it is (so far) as accurate as my high dollar one (might not stay accurate forever) EDIT adding 302 heads/1&5/8 headers. Keeping the eddy 1406/streetmaster. An over the fender overhaul to use these std pistons I have and the headers that are hanging from the rafters and... it never ends

Last edited by RapidRobert; 11/09/11 11:40 AM.

live every 24 hour block of time like it's your last day on earth
Re: Cast Crank and 10 to 1 pistons [Re: RapidRobert] #1109946
11/09/11 03:55 AM
11/09/11 03:55 AM
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
DaytonaTurbo Offline
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Manitoba, Canada
If you're going to buy new pistons, you might as well spend the couple hundred bucks to have your block bored. Then you might as well have your rotating assy balanced. You really only want to do this once and it doesn't cost that much more in the grand scheme of things to do it right. As said, cast or forged crank, your rotating assy will need to be balanced anyway. They do make pistons that are supposed to weigh close to stock 440 pistons, many guys have put in the trw 2355 pistons and ran without rebalancing. However you can buy lighter pistons for the same price so you can shave some rotating weight.

Re: Cast Crank and 10 to 1 pistons [Re: DaytonaTurbo] #1109947
11/09/11 11:36 AM
11/09/11 11:36 AM
Joined: Sep 2003
Posts: 1,465
Carson City, NV
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babarracuda Offline
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Carson City, NV
I raced my 360 with 14:1 for 3 years and sold it to a frend who is still running it. He put on W 2 heads a couple of years back. Now it only has 12:1. Same crank since 1998.

Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109948
11/09/11 12:17 PM
11/09/11 12:17 PM
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1 Offline
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Challenger 1  Offline
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Cincinnati, Ohio
I have done it twice lately, 340 and a 440.

Built my latest 340 in 2007 and used a cast crank that I had that was stock and KB 243 10-1 pistons and did not have it balanced. I have over 10K miles on it now and have driven it all over the country on vacations, including extended 120 MPH runs on the salt flats at Bonneville. This past summer drove it to the top of Pikes Peak for the second time in 95 degree weather and then in 115 degree weather in Vegas for 5 days.

Then back in 05 I bought a 440 short block that was freshly built with pistons that were .100" in the hole. I installed sealed power 10-1 pistons in it and did not re balance it. It runs great today. I hate to take my stuff places and try to do everything myself.

Why bore a block if it don't need it? MY 340 is standard bore with KB standard pistons in it. I honed it myself with a portable Sunnen hone when I built it.
So no it's not absolutely necessary to balance it, imo and experience.

This past summer my power brake booster started leaking causing my 340 to pop on decell, I did a compression test on it first and it had 165-170# on all 8 cyls and it don't smoke at all, none. So the the clys sealed nicely, the motor you see below. Replaced the booster and all is well.


It's idling in this picture at 13000+ altitude on the way down from Pikes Peak. It's a real test for a old car to make it to the top with a carburetor.

Re: Cast Crank and 10 to 1 pistons [Re: Challenger 1] #1109949
11/09/11 12:51 PM
11/09/11 12:51 PM
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dogdays Offline
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The real answer is that most replacement pistons are made to be the same weight as the pistons they're replacing. So you should be able to swap pistons as long as you don't spend big money for lightweight pistons. Chrysler Corp factory balance jobs were notoriously bad, but the engines still performed.

Now depending on how much $ you have to spend, it would make a better engine if you DID buy lighter weight pistons and have it rebalanced. But on the cheap, swapping stock replacement for stock replacement doesn't require balancing.
Think of the millions of factory rebuilt engines on the road and not one of those engines was rebalanced.

R.

Re: Cast Crank and 10 to 1 pistons [Re: dogdays] #1109950
11/09/11 01:17 PM
11/09/11 01:17 PM
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Posts: 25,200
Upper Midwest
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MoparforLife Offline
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Keep the RPMs with in reason and you will have absolutely know problem. Countless engines are put together this way all the time. They run on the street and track with no problem at all. Heck over the years there have been thousands of engines put together with 1 or 2 over size pistons and gone for many thousands of miles. Put it together and enjoy it.

Re: Cast Crank and 10 to 1 pistons [Re: dogdays] #1109951
11/09/11 06:42 PM
11/09/11 06:42 PM
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1 Offline
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Quote:

The real answer is that most replacement pistons are made to be the same weight as the pistons they're replacing. So you should be able to swap pistons as long as you don't spend big money for lightweight pistons. Chrysler Corp factory balance jobs were notoriously bad, but the engines still performed.

Now depending on how much $ you have to spend, it would make a better engine if you DID buy lighter weight pistons and have it rebalanced. But on the cheap, swapping stock replacement for stock replacement doesn't require balancing.
Think of the millions of factory rebuilt engines on the road and not one of those engines was rebalanced.

R.




Good info for sure. Thanks for posting Dogdays
I just looked and the stock 71 hi compression piston in a 340 weighs 758 grams and the KB pistons weighs only 507 grams. I'd consider the KB243 a stock replacement piston at only $263 dollars a set.

Definitly would need to be rebalanced for competition and hi rpm use.

My street driven 340 has been a reliable motor even though it has not been re balanced with the new lighter pistons.
I even own the fixtures and scales to determine bobweight. Just not the balancer...yet.

Re: Cast Crank and 10 to 1 pistons [Re: Challenger 1] #1109952
11/09/11 08:42 PM
11/09/11 08:42 PM
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dogdays Offline
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A Sealed Power, Silvolite, Ohio, Badger, Zollner, Hy-Duty, Nylen or Clevite piston would be a stock replacement.
KB pistons are supposed to be high performance and even if they don't cost too much, it is ASSUMED that the purchaser knows they will make rebalancing necessary. It's the same for the ring gap requirements.
I salute KB for making an affordable piston for a 340 that actually weighs like a smallblock piston and not a bigblock piston. But if your point was that a 340 needs to be rebalanced when using that piston you are absolutely right. No way is a 200+ gram difference going to go unnoticed, and probably right from idle and on up.

R.

Re: Cast Crank and 10 to 1 pistons [Re: dogdays] #1109953
11/09/11 09:26 PM
11/09/11 09:26 PM
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Tustin, CA
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pishta Offline
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oversized pistons from the same manufacturer of OEM replacement pistons weigh the same as the STD pistons they replace. Aftermarket performance pistons rarely weight what the stockers weighed. MP pistons, stock or HP/stroker whatever are not as close as Probe or other high end pistons. My stroker set were only within 7g of each other, some good manufacturer sets are within 1g or less. I had to lighten them all to the lightest one, 7g is alot to be taken off a short stroker piston. ended up taking a few g's off the pressed pin.


12 Grand Caravan
06 T&C
02 T&C
96 Breeze
65 Barracuda "S"
Re: Cast Crank and 10 to 1 pistons [Re: Challenger 1] #1109954
11/15/11 01:28 AM
11/15/11 01:28 AM
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Posts: 1,639
Brandon, Ms
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cornet684me Offline OP
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does anybody have the part number & name of pistons for the 10 to 1 pistons that i wld need to go with, looks like i wld want just to swap out the pistons that i have for the stock replacement 10 to 1 compression and not balance the motor.

trying to get by on a budget, i want to unbolt the heads, take out the pistons and rods, have the new pistons pressed on the rods and reinstall without taking out the crank.

the motor is already completely rebuilt , just has the smogger pistons.

this is going into a 440 with a cast crank.

Last edited by cornet684me; 11/15/11 01:35 AM.
Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109955
11/15/11 01:32 AM
11/15/11 01:32 AM
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Posts: 74,904
U.S.S.A.
JohnRR Offline
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Quote:



the motor is already completely rebuilt , just has the smogger pistons.




How many miles on it since the rebuild ?

Re: Cast Crank and 10 to 1 pistons [Re: JohnRR] #1109956
11/15/11 01:41 AM
11/15/11 01:41 AM
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Brandon, Ms
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cornet684me Offline OP
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none, i bought the motor off craig'slist., the motor was rebuilt 3years ago by a rebuilding company out of spokane wa. complete long block, 69 block, however, used cast crank , i am just wanting to get the motor back up to 10 to 1 compression.

the motor was still on the crate, has been oiled up and rotated every so often.

Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109957
11/15/11 01:43 AM
11/15/11 01:43 AM
Joined: Dec 2007
Posts: 1,639
Brandon, Ms
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cornet684me Offline OP
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another

Re: Cast Crank and 10 to 1 pistons [Re: cornet684me] #1109958
11/15/11 02:05 AM
11/15/11 02:05 AM
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JohnRR Offline
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Cast crank engine and you bought it as it is shown in that picture , no balancer and no info on how/what it was balanced ?

Re: Cast Crank and 10 to 1 pistons [Re: JohnRR] #1109959
11/15/11 02:13 AM
11/15/11 02:13 AM
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Brandon, Ms
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cornet684me Offline OP
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for 800.00 it was a deal, the heads are completely rebuilt 906, it is a 69 block with 906 heads, that is why i bought it, for the money i cannot go wrong


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