Open chamber Pistons are not readily available for 396's anymore. You can get a piston made for an open chamber or you can use a closed chamber piston and fit it in the open chamber. I did a 408 with a 2287 speed pro piston and a 781 casting head. It's a little high in compression at 10.5:1 for pump gas and steel heads. But it has a decent cam in it so it survived. I am doing a 396 race engine and it's looking like I'll be going through wiseco for a custom open chamber 396 piston.

 

Is it possible to use a stock replacement piston for a later model 396 that used an open chamber head? Say like a 70 or 71 model year 396? If not then to use the closed chamber heads with today's fuel would the valve seats be the only thing that would have to be replaced to make it run right and last?

 

make life easy on yourself.stay with closed chambered heads.don't think a street build/small bore bbc really needs much more then the heads that you have already.saves a lot of extra money that could be spent elsewhere.just a thought.

 

Just for fun, I googled pistons for a 402 BB Chevy and got plenty of answers. So it would seem as others have mentioned, your going to have to know exactly what your working with. As an example KB has a list for both Closed Chamber, and Open Chamber, but again you are going to have to know exactly what you want to end up with. I hope this helps.

 

The nice thing about using open chamber heads with closed chamber 396 pistons is you can use the cheapest gas.

 

yes, at 7.9:1 CR you can run used cat pee.

 

I don't think I'll try cat pee in my 69 but it does run great on the cheapest gas I can find.
(but then I don't race)

I have no idea what the CR is now but it was 10:1 before I put the rectangular port open chamber heads on it.

 

If your thinking about changing heads & pistons you might as well think about changing the cam and put together a combination of parts that will work together in the 9.5, 10-1(iron heads) comp. area for pump gas and some performance, are you trying to make a replica Z16 ? seems I read on that.

 

The compression ratio goal here would be about 10:1.

As far for the Z16 thing, yes. I am in a sense recreating the motor. When I say that I mean the looks on the outside, and the 375 hp. I will never get it exact, but i want to get it as close as possible. The car is actually being done for my father. I want to use a block that has a 65 date code so that it will have the correct casting with the webbing above the timing cover that is visible. I also want to use the right intake and holley 3310 carb. If I cant find the 3310 then i will use the 3124 from the corvette. I am going to use the 70 camaro dual snorkel air cleaner assembly to mimic the actual chevelle one that is literally impossible to find.

The El Camino was originally a 283 3 spd car. I am going to the 396 and muncie 4 spd. My father is an old racer from the 60's and early 70's. He has no clue that this is all going back to him. He had the car before me, but needed help with some medical issues. He is the type of guy that flat out refuses to take something for nothing. It took me literally 2 months to convince him to sell the car to me just so he would take the money. When he had it the car just sat and collected dust and he had hopes of getting to it one day. That day never came and now due too his health it will never come.

Anyways, the point of all of this is that I get the car done how he always wanted to do it. The Z16 thing is just my own little surprise for him since he has always lusted after the Z16 Chevelles. One day I will lay all of this out in better detail in an actual build thread. I will be getting started about the first week in April. I just moved from Washington State to Lexington, Kentucky so things have been a little hectic.

Chris

 

Hi Chris, during the course of the year we do a number of the 396" builds, they are so popular here we just put in a bunch of Race-Tec pistons for about a 1/2 dozen various kits, some stock stroke and some 4.000" strokers! ALL will find their way into some 100% stock-appearing units!

Having said that, based on your 396" platform using the OEM Winter's castings (077's) or similar, we are past 500 HP on pump with 10.5:1 comp. We are actually at 510 with this setup.

This is WITHOUT really chasing HP numbers, it is on the (solid-lifter) flat-tappet, heavier (TRW-L2242F) piston/ring pack, and pressed-pin platform. The reasoning behind the 077's is these are the casting's most customers want to use, mainly due to the "Snowflake" on them. We can accomplish the same numbers easily with the Edelbrock line, again, with no porting involved.

Thanks, Gary in N.Y.

P.S. To add some to the above info, if you substitute a "lighter" piston/ring pack, use some bushed rods, and add a retro-hyd roller to alter the program you will see 550 or better. This is STILL on the 396" platform!

 

The goal here is to get about 375-400 HP out of this. It has to be reliable and be able to run premium pump gas. I am not chasing big numbers here. I was thinking getting as close to 10:1 compression as possible would be good. I need to use a set of rectangular port heads to use the intake that I want. So this leads me to the debate to use a closed chamber piston and find a set of factory heads to get redone, or to use an aftermarket head wether it be iron or aluminum. From what it seems the aftermarket stuff is all open chamber design. so from what I understand to use those I would need to change the pistons to get the compression ratio back up.

Chris

 

If I change the pistons they will be aftermarket either way so going with something either in open or closed I should be able to get something that will get the compression ratio where I want it to be either way i would assume? I have found a set on summit that is a stock replacement for the closed chamber that gets me the 10:1, and i am pretty sure there are some 71 or 72 402 open chamber design ones that will yield the same result.

 

I'd go closed chamber and minimize the required dome. I can't prove it, but I think flame propagation / detonation resistance would be better with a closed chamber head and a small dome. The closed chamber might shroud the valve a bit more, but I think the large dome requirement would offset any gains.

Also... never, ever trust advertised CR in catalogs when piston shopping. Too many variables. You really need to do the math with compression height, deck clearance, dome cc, etc to figure out where you really are.

 

That's really cool your doing this for your dad, my dad wanted to drive my chevelle when it was drivable but he passed away before that happened so I get it, my engine was put together by the help of guys here on TEAM CHEVELLE and a couple friends after I told them what I learned here they listened and helped, rick.:thumbsup:

 

Thank you, originally all I wanted to do was work on it with him. Before he got sick I was in the military and stationed far away all the time or deployed so there was very little time to do much of anything together. Now that I am retired I have moved closer to him, but as fate would have it about a year before I was done is when he became ill. Things just can't seem to align right for us. I wanted to just help him with some of the expense but my father's pride was too great to just allow me to do that outright. The ONLY way I could get him to agree to allow me to help was to buy the car that he had pretty much given up on. I love the car don't get me wrong, but I never wanted to take it from him. So I decided that I would get it done the exact way that he would have done it and surprise the hell out of him with a nice gift for either a birthday or fathers day or something.

 

FYI - this was 396/402 build for my 55 gasser

Raced this engine in a 3500lb 4 speed car on 92 octane pump gas
Best ET was 12.05 indicating about 395HP at the rear wheels.

Block casting: 3999290 1971 - 402 c.i.
.030 over = 4.154 Final bore (408 c.i.)
Block decked to .0043
Pistons - L-2242NF60...39cc dome
xxx781 Heads milled to 118cc
Final compression about 10.4

Lunati 20110549 Hyd Roller
232/242 duration
578/595 lift

GMPP HEI dist.
750CFM vac adv Holley

 

I like those pistons a lot, I have actually been looking at those for a closed chamber head. There is a set of Kieth Black Hypereutectic pistons that i looked at too but they were -17.00cc so a little shorter. Again all comes down to the heads and the combustion chamber volume. All of the heads I have looked at using are 106.8cc to 109cc.

 

Just to satisfy my curiosity, I know these are cheap, but to stay on a budget and to not have to hope i get a good core and go through needing to have all the work done to a set of factory heads what does everyone think about something like these BluePrint Engines Muscle Series Cylinder Heads PS8013 - Free Shipping on Orders Over $99 at Summit Racing

and coupled with a set of the pistons that dream66 mentioned above found here
Speed-Pro Forged Pistons L2242NF60 - Free Shipping on Orders Over $99 at Summit Racing

 

Cool story Chris and koodo's for what you are doing there. Just lost my Mom 2 weeks ago and it's a sick feeling afterwards thinking of all the things you should have done ....

 

Thank you, I have missed out on the last 15 years or so and I want to do all I can with the ol man before he leaves this earth. We are both die hard gearheads so this is right up his alley.

 

As much as I hate Ebay.......There is this.
Rebuilt BBC 396 427 454 Square Port Heads 3856208 3873858 | eBay

The 208 casting is the correct one that came on the Z-16. Even these are a mismatched pair if the combustion chamber, intake, and exhaust ports are all the same sizes as stated I wouldn't think that it would be an issue since casting numbers are not visible from the outside.
here are the specs:
3856208 1965 396 Closed 108.9cc
3873858 1966-67 396 Closed 108.9cc


Thoughts between this or something like a set of the aluminum ones I have posted above?

 

I may be wrong about this, but I remember reading on this Forum somewhere that you could use the "Square Port" Manifold on "Oval Port" Heads. No its not going to be optimal, but if this is the case, Any closed chamber head would work for you, and you could stick with closed chamber pistons. I would do a search both in the "Performance" section as well as here in the "Engine" section. The reason I remember this is I traded away a "Square Port" 3-2 Manifold and Carburetors for a bunch of 409 parts that I never got to use.

 

I may be wrong about this, but I remember reading on this Forum somewhere that you could use the "Square Port" Manifold on "Oval Port" Heads. No its not going to be optimal

You are not wrong and that combo works very well actually.

 

yes it does. you don't need square port heads at all, you can use the square port manifold on oval port heads, it's been done many times. Use the square port gaskets. The other way around won't work at all, but don't ask how I know this.

I don't know why this hasn't been mentioned already, but you can't just assume you can mix-n-match open and closed chamber heads and open and closed chamber pistons. Even with open chamber heads on CC pistons there's often problems with clearance around the edges of the domes. The shape of the dome and chamber are just as important as the size.

I recently went through this with a bone stock 66 396. neither the heads or block had ever been cut. The correct L2240F pistons hit the stock 702 heads (IIRC) around the corners of the domes. The engine wouldn't turn over on a trial assembly, clonk went the piston into the head. Had to trim the edges of the domes right down to the piston deck to get it to work.

pays to make a trial assembly with no rings or seals. if the pistons clear the heads with no head gasket they probably be OK.

 

yes it does. you don't need square port heads at all, you use the square port heads on oval port heads, it's been done many times. Use the square port gaskets. The other way around won't work at all, but don't ask how I know this.

I don't know why this hasn't been mentioned already, but you can't just assume you can mix-n-match open and closed chamber heads and open and closed chamber pistons. Even with open chamber heads on CC pistons there's often problems with clearance around the edges of the domes. The shape of the dome and chamber are just as important as the size.

I recently went through this with a bone stock 66 396. neither the heads or block had ever been cut. The correct L2240F pistons hit the stock 702 heads (IIRC) around the corners of the domes. The engine wouldn't turn over on a trial assembly, clonk went the piston into the head. Had to trim the edges of the domes right down to the piston deck to get it to work.

pays to make a trial assembly with no rings or seals. if the pistons clear the heads with no head gasket they probably be OK.

Good to know for sure on the gaskets. My question is by mismatching the ports this way won't this cause a major airflow restriction? Maybe even puddling of the fuel? On the other side of things, is there a benefit to doing this? Increases in low or midrange power?

As for the mockup, I am definitely going to be mocking everything up and checking all measurements and clearances thoroughly before any operation. The good thing here is that I am not going with a radical cam so that should help with piston to valve clearances. This will also allow me to keep the spring pressures down and the geometry of the valvetrain very reasonable. Here is a link to the cam that I was considering using.
COMP Cams Xtreme Energy Camshafts 11-246-20 - Free Shipping on Orders Over $99 at Summit Racing

 

Ok so after doing some searching and some reading about mixing square and oval ports I am seeing a lot of info. There is one common denominator that I am seeing, and that is the intake gasket fitment. Not so much a port seal issue, but a lot of coolant leak issues. Now i don't know if this is in relation to the gasket choice or a fitment issue of the mating surfaces being different slightly with each design. I am thinking that for what I am doing it might just be simple to just keep square with square in this case to avoid possible fitment issues. The parts are out there and not too hard to come by. Maybe looking at the aftermarket square port heads that are out there and being used someone can weigh in on this. It is a reproduction of the old Winters snowflake aluminum intake from 1965. A link to the intake that I will be using may shed some light on this a bit more, and it can be found here:

https://www.opgi.com/el-camino/1965/air-fuel-delivery/intake-manifolds/CH28538/

 

I have NEVER had any type of issue, coolant leak or other wise doing this. I have run 11 second ET's using a rectangular port intake on oval ports along with few other I know as well.The coolant ports are the same size whether oval or rectangular. Last combo we did using this "swap" has probably gone 10K+ street miles without issue.

Here are the gaskets that I use:
Mr. Gasket Standard Intake Gasket Sets 108 - Free Shipping on Orders Over $99 at Summit Racing

 

A large oval port head (open or closed chamber) will work much better on the small bore 396/402 motors than a rect port head. the runners are too big and you dont see as much benefit if any from the larger valves on the small bore motors. This will save you quite a bit of $$ over the 1965 208 big port heads.

If you happen across a 65/66 396 that has been bored a few times many times you can pick them up very cheap, most of the 65,66 or 67 blocks can be safely bored to 4.250 and you can make a cheap 427 out of them.

 

Any recommendations for a good oval port head that will work on a 65 block and still maintain a fairly stock appearance? If I am going to go with an aftermarket head I would prefer to use aluminum and paint them. Also when doing this with the rectangular port intake is there a preferred gasket to use that will ensure a good seal everywhere?

 

I remember reading a post on here 5-10 years back where a guy ran his big block at the strip that had oval port heads and an eddy performer RPM intake. His buddy had the same intake in rect port. One week they switched the intake and took it to the track and the car ran the same time as it did with the matching oval intake.

 

Post this build in the "performance" section and ask for an opinion on cylinder head and camshaft selection with your desired HP goal. Hopefully VORTEC PRO will give you his ideas on what to use. Read the BBC 410 build thread that was just posted on there. He recommended using JE 375HP pistons and GM closed chamber heads in #215, #063 or #290 castings and that was on a 600HP build

 

I just read through that thread. There is some good info there with the combo that he mentioned. I am not looking for a ton of power, but I will take what I can get. I am going to start a build thread once I get the car here and finally get to start on it. Probably won't be for about a month.