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Old 01-05-2012, 10:06 PM
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3904390 Heads

First check the bottom of your pistons to find a part #. You may even have to take one out. On my KB pistons the part# 203 was stamped underneath the piston. If you want to use the heads you have, KB360KTM should fit according to the website http://www.kb-silvolite.com/. Summit has them listed as UME- SKB360-030 for $327.95. It would be best to CC the head chambers to find out the cc to figure the compression ratio. Suppose to be 98.4cc but you don't know if they have been milled.

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Old 01-05-2012, 10:36 PM
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Quote:
Originally Posted by 1986c10
Okay here are my options

use the 390 heads, get closed chamber pistons, rebalance

use the 781 heads, (possibly change pistons? I dont understand this, these heads were used on 454's, my pistons should be same compression height, bore dome etc i would think as he was going to use 454 heads i believe, what am i missing?), rebalance if new pistons are used. IF! the pistons in the shortblock will work with these heads then this will be my head choice no question

Assuming i have to change pistons with either head. Which is better??? I believe the 781 gives me more options and seems to be much more popular

fbird- do those require the same special closed chamber pistons as the 390's? because the chambers look different that mine (i think). In regards to the solid roller. This will be in a truck that gets cruised in, alot. It will hit the strip a few times but will be lugged around. I know the topic is debated highly but can a solid roller withstand low rpm cruising. And no i am not looking for an rv cam, definitely set on a cam that makes power up high.
The 3904390 are a 427 ci closed chamber heads, you have to use closed chamber pistons for a 4.280 bore and 3.760 stroke. The 781 are open chamber head so you naturally would use an open chambered piston with the same bore and stroke because of the 396 crankshaft.
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Old 01-06-2012, 05:33 AM
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I would use a 454 crank, 454 pistons with a dome to get the desired CR, and the 781 heads.

you could also use the 454 crank with stock flat top 454 pistons with the small chamber heads.

496 kits come with stock or long rod configuations. It is just a different piston pin location.
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  #19 (permalink)  
Old 01-06-2012, 07:50 AM
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Quote:
Originally Posted by 454C10
496 kits come with stock or long rod configuations. It is just a different piston pin location.

Pin location and piston design. Most stock rod combo's will hit piston to crank counterweight. If not a specific designed kit.. and some of those get uncomfortably close..
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Old 01-06-2012, 08:09 AM
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thanks for the info guys and im glad those pistons are reasonably priced.
bobcrman- why do i have to run special pistons for the 781 heads? I believe the shortblock has domed pistons setup for 454 heads
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Old 01-06-2012, 08:27 AM
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Quote:
Originally Posted by cdminter59
First check the bottom of your pistons to find a part #. You may even have to take one out.
for me, this would be the first step
figure out what you have
maybe a pic would help, if you cant find a number on them

try asking the guy you bought it from?

buy heads to work with those pistons

or, plan on just starting over
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Old 01-06-2012, 05:06 PM
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check out this 496 build

http://www.superchevy.com/technical/...d/viewall.html

summit as rotating kit for 1200.00
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Old 01-07-2012, 11:38 AM
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427 pistons on 781 heads require a special dome. Because all factory style 427 forged pistons and mentioned clones are designed for rect port heads. Rect port heads, open or closed chamber, are factory designed with more open area around the exhaust side of the chamber.. Oval port heads ( 290, 390, 049, 781 included) will hit the factory style forged pistons on open or closed chamber.. Because of smaller intake/exhaust valve and tighter chamber in this area. Been this way since big blocks were first produced..

Used to constantly explain to customers, back in the day.. They would mix parts and have a terrible knock in the motor. (pistons hitting head on exhaust dome area)..

You have to watch Edelbrock designed pistons.. They are designed for Edelbrock heads. These don't follow GM design and will hit if used on many non Edelbrock castings..
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Old 01-07-2012, 02:16 PM
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okay, if they require a special piston to work with my head then chances are it doesnt have the correct one. The guy is a big local drag racer and knows his stuff but he probably was going to run an aftermarket head that wouldve cleared. Im picking it up in an hour so i'll get the numbers off the piston and report back.

IF the pistons wont work with either head. Which cylinder head is the best? The 781 or the 390 with cleaned up bowls, valve guide area, cleaned up exhaust and intakes and larger valves possibly? seems like the 781 is much more popular. Thanks again, i would be one of those guys *****ing about a bad knock if it wasnt for you guys! thanks again
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Old 01-07-2012, 08:26 PM
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Okay, got the shortblock today. Forgot to mention it has sat for 20 years.... it was oiled and kept in a heated garage but i will completely disassemble it and take it to the machine shop to have it checked out. for some reason their isnt hone marks.... it has not been ran though. I will get it honed.

The guys friend who builds engines said that it should work fine but check it out with puddy as you guys said and minor exhaust chamber porting may be needed. I'll let you guys know what happens and i'll list the piston number tomorrow. Thanks!
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Old 01-14-2012, 04:44 PM
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Okay, just got out and checked what the pistons were. L2300 .030. I believe this is a trw forged piston, don't know dome size or anything.... somewhat of a stock replacement i think???
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Old 01-15-2012, 09:07 AM
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L2300F pistons

Checkout flatlanderracing.com. They list the TRW pistons but they have some info on TRW pistons you should definitely read. This should change your mind about the build are working on.
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