Moparts

Cast Crank and 10 to 1 pistons

Posted By: cornet684me

Cast Crank and 10 to 1 pistons - 11/09/11 05:02 AM

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
Posted By: Alikazam

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:22 AM

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!
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:30 AM

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

Posted By: 70AARcuda

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:32 AM

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..
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:42 AM

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

Posted By: RapidRobert

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:43 AM

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
Posted By: DaytonaTurbo

Re: Cast Crank and 10 to 1 pistons - 11/09/11 07:55 AM

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.
Posted By: babarracuda

Re: Cast Crank and 10 to 1 pistons - 11/09/11 03:36 PM

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.
Posted By: Challenger 1

Re: Cast Crank and 10 to 1 pistons - 11/09/11 04:17 PM

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.
Posted By: dogdays

Re: Cast Crank and 10 to 1 pistons - 11/09/11 04:51 PM

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.
Posted By: MoparforLife

Re: Cast Crank and 10 to 1 pistons - 11/09/11 05:17 PM

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.
Posted By: Challenger 1

Re: Cast Crank and 10 to 1 pistons - 11/09/11 10:42 PM

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.
Posted By: dogdays

Re: Cast Crank and 10 to 1 pistons - 11/10/11 12:42 AM

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.
Posted By: pishta

Re: Cast Crank and 10 to 1 pistons - 11/10/11 01:26 AM

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.
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/15/11 05:28 AM

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.
Posted By: JohnRR

Re: Cast Crank and 10 to 1 pistons - 11/15/11 05:32 AM

Quote:



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



How many miles on it since the rebuild ?
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/15/11 05:41 AM

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.

Attached picture 6920111-resizedfullmotorshot.jpg
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/15/11 05:43 AM

another

Attached picture 6920113-resizedbottomend.jpg
Posted By: JohnRR

Re: Cast Crank and 10 to 1 pistons - 11/15/11 06:05 AM

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 ?
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/15/11 06:13 AM

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



Attached picture 6920139-resizednumbersshot.jpg
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/15/11 06:16 AM

the heads have new rockers/valves/springs etc.
Posted By: DaytonaTurbo

Re: Cast Crank and 10 to 1 pistons - 11/15/11 08:18 AM

Quote:

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.



Closest thing would be a set of trw2355's. Besides the smogger 440 pistons, the only other stock type 440 pistons being produced will only give you around 8.5 compression or so where those smogger pistons will be closer to 7.8.
Posted By: 1_WILD_RT

Re: Cast Crank and 10 to 1 pistons - 11/15/11 08:31 AM

http://www.summitracing.com/search/Part-...sion-Distance-i
Posted By: JohnRR

Re: Cast Crank and 10 to 1 pistons - 11/15/11 01:04 PM

Quote:

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





Wasn't that good of a deal if you have to replace the pistons ... ...

That said here is the rub , WHAT DO THE PISTONS in the engine weight NOW ??? You have an external balance engine , balance is critical .

Here is your main problem the true 10.0 piston, the piston that came in the 68-69 440's IS NOT REPRODUCED , you have 906's so that is the only piston that will get you close to the OVERSTATED 10.0 from the factory. The 2355 is the 70-71 6pk piston and in 70 at least the engine had a HIGHER than 10.0 rating from the factory , that replacement piston I am told is 40 grams heavier than the piston it replaces.

Good Luck in your quest to fix your good deal ...


Posted By: bboogieart

Re: Cast Crank and 10 to 1 pistons - 11/15/11 01:23 PM

If it's a street driver, you might want to leave the smogger pistons, and put the money into cam and carb. These motors can make tons of torque. That's what's needed for street fun. Just a suggestion.
Posted By: dogdays

Re: Cast Crank and 10 to 1 pistons - 11/15/11 06:25 PM

KB 236 is exactly what you need.

R.
Posted By: cornet684me

Re: Cast Crank and 10 to 1 pistons - 11/16/11 05:08 AM

Thanks for all the Great Input!!! now i have great options, i will post what i decide to do, right now money is the only problem.


Posted By: R/T1968R/T

Re: Cast Crank and 10 to 1 pistons - 11/16/11 02:52 PM

Factory 440 pistons (10:1) weigh in at about 867gr. the later smog motors are in the 850 range. TRW (Speedpro) 2355 are 872gr and 2266 876gr.
Posted By: JohnRR

Re: Cast Crank and 10 to 1 pistons - 11/16/11 07:16 PM

Quote:

KB 236 is exactly what you need.

R.



That's a step head , quench dome, piston. If he doesn't have the money to balance the rotating assembly he certainly doesn't have the money to make those pistons fit properly. The questions elude that he doesn't have the skills, or equipment available, to do it himself either.


Quote:

Factory 440 pistons (10:1) weigh in at about 867gr. the later smog motors are in the 850 range. TRW (Speedpro) 2355 are 872gr and 2266 876gr.



When and where did you get the numbers for the 2355 ?
Posted By: dogdays

Re: Cast Crank and 10 to 1 pistons - 11/17/11 12:19 AM

"Quench dome" height is 0.075". Take away the 0.015" the piston is below a stock deck, and the 0.020 of a steel shim gasket and the dome protrudes 0.040".I can't see that as being any worse than a flattop that lies at deck or below. Is it optimum? If he's lucky, but the heads are going to have to have been milled quite a bit for there to be any interference problems.
Piston weight of the 236 is 775 grams with a 190 gram pin. It's a lot heavier than I would suggest, but the OP is trying to get to 10:1 and this piston will do it. And a difference of 15-25 grams is going to be "good enough." Probably not a lot worse than Mopar original balance jobs.
So I stand by my recommendation.

R.

PS: The word you were looking for is "allude." Elude means to escape something.
Posted By: JohnRR

Re: Cast Crank and 10 to 1 pistons - 11/17/11 02:11 AM

Quote:

"Quench dome" height is 0.075". Take away the 0.015" the piston is below a stock deck, and the 0.020 of a steel shim gasket and the dome protrudes 0.040".I can't see that as being any worse than a flattop that lies at deck or below. Is it optimum? If he's lucky, but the heads are going to have to have been milled quite a bit for there to be any interference problems.
Piston weight of the 236 is 775 grams with a 190 gram pin. It's a lot heavier than I would suggest, but the OP is trying to get to 10:1 and this piston will do it. And a difference of 15-25 grams is going to be "good enough." Probably not a lot worse than Mopar original balance jobs.
So I stand by my recommendation.

R.

PS: The word you were looking for is "allude." Elude means to escape something.



I stand by elude , he is trying to escape both doing it right and spending money ...

P.S. one is also assuming the heads haven't been cut , are straight and equal depth across the entire head , I also stand by the assumption he would be in over his head.

Posted By: RBDART1

Re: Cast Crank and 10 to 1 pistons - 11/18/11 08:25 AM

Just pop out the smoggers and weigh them, then weigh the proposed 10-1's, the 10-1's should b heaviest,reduce them in weight to the smoggers weight, but 1st check comp dist b-4 u invest much time and effort u may b swapping in the same thing..chk how far down the hole the smoggers are,and the comp distance of new ones to determine how far down in hole new ones will be, then u need to know what cc ur heads r to determine comp ratio and u prob aint gonna see 10-1 maybe 9.3 or so but way better than 7.8...I had a early 70's blk advertised as 10.5-1 that when calculated the cc's of heads and how far down in the hole came out to be a true 9.69 comp ratio..only way to know 4 sure is chk it
Posted By: GTX MATT

Re: Cast Crank and 10 to 1 pistons - 11/18/11 09:05 AM

If you dont want to bore it or rebalance it just swap in some earlier high compression slugs. It will be more like 9.5:1 but it'll cost you 50 bucks for some old pistons.
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