Heads & motor

Cut my teeth on these-Im old school - so bear with me = Id port & clean the heads up- use 454 valves-yet - look closely @ the pistons- must be for closed chamber heads -!!- very diff chambers . Back in the day these were factory engines - usually had 10-11 - 1 comp ratios too. as for the 6000 rpm range - it will do that even wit a hydraulic cam & some nice valve springs - dont nessaraly nheed that expense of a roller cam. That motor should make the HP your after easily too.Id guess the 396 crank is due to having that? Easy to get a used marine setup with all the good parts cheap id guess? if needed.You dont mention what type intake carb ect you will be using? With that motor -likely need to use the higher octane pump gas also. Should be ba nice easyly done motor too-hap-y Roddin

 

The 396-427 crank will make it a 427+.030 with the correct pistons. You will have to use closed chamber piston. If you use a factory 427 closed chamber forged piston it will hit on the head around the exhaust side of the piston. As these pistons were designed for the rect port heads that were more open in that area.

You will be able to rev the thing 6000 rpm with all factory parts. Just a re-bolt and resize job on the rods. If you can get the labor $$$ low. The heads will respond to a 2.19/1.88 combo. If the bowls and shrouding on the intake wall are correctly delt with.

It is wise to run a roller cam on these. Modern oils and the seat pressure/ramp rates make for short lived hot rod flat tappets..

 

dang that sucks, well maybe i can sell the pistons on craigslist. Any experience with an ls5 head? i can get a set for free in rebuildable condition and keep the pistons maybe. I couldnt agree more on the roller cam, plus itll give me more turnover time if its hard to start on break in and it will be peace of mind. Thanks for the info so far guys!

 

How do i find a closed chamber piston on summit racing for example. Because their is no sub category that says "closed chamber piston". Are they defined by their compression distance or dome volume or both? If so, what would they be to fit a 454 .030 over block. thanks guys

 

Not many affordable new closed chamber piston sets available for 427. KB-176+.030 can be ordered. Closed chamber Keith Black hypers. Also has open chamber piston listed..

Fed-Mogul/Sealed Power/Speed Pro list a couple different pistons. But, many are no longer available since production was moved to India/Pakistan a few years ago. Maybe some in an obscure warehouse somewhere.

 

Well if i cant get pistons for under $750 i'll just find different heads cause they need a rebuild anyways, i just figured they were decent and i got them for free but oh well. Is it a clearance issue with the smaller combustion chamber or a compression issue? Are ls5 heads decent cause i can get some for free probably

 

awesome those keith blacks run only $360, not bad at all. Will i have to get my rotating assembly balanced again???

 

just read the whole build, very inspiring. Im not sure if those are 390 casting heads though because they are open chamber...

 

Okay, after much debating i have decided to ditch the 390 heads as i would have to spend 400 bucks on pistons, 250 on rebalance and still have to rebuild the heads and this is after i spent 6 hours porting one head.... BUT!!! i can get a set of 781 heads bare for free. I have heard these are some of the best oval port heads gm ever made. Are they all the same or are some different? are the exhaust ports rough on these and could use bowl blending and typical porting?

 

while you at it, get a 454 or 496 crank.

more cid = more power

 

that would be great, and if i had built the engine then i would have no doubt went with a 4" stroke but i didnt.... and this setup is ready to go all balanced, just needs heads, cam and intake. If i got a long stroke (496), would i have to get different length rods? id think so. Im pretty sure i could use the same rods depending on journal size if i were to go with the 4" stroke crank... correct me if im wrong. Thanks for the input, im considering it even though money is tight!

 

If you use the 781 heads. On a 427. Only aftermkt domed KB type open chamber pistons will work and they will have to be checked for dome clearance. (not TRW/FedMog/Sealed Power/Speed Pro/Manley/2308).

The 2308 style piston is the factory style L-88, 12-1 compression design. Hits in various places and is a hollow dome piston with not much meat on the top to cut on..

781 heads respond well to larger (and longer) valves..2.19+.100 long and 1.88+.050 long..

Yes, most 496 cranks require +.250 long rods unless you are using a tall deck..

 

why do only kb open chamber domed pistons work? Idk what it has yet unfortunately.... Thanks for the info, i was unaware big blocks had to be so strategically put together. way different ball game then the small blocks where almost any part will work on any size engine.

 

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.

 

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.

 

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.

 

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.

 

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..

 

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

 

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

 

check out this 496 build

http://www.superchevy.com/technical...vetrain/completebuilds_testing/sucp_0901_496_chevy_big_block_build/viewall.html

summit as rotating kit for 1200.00

 

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..

 

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

 

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!

 

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???