383 Rebuild - New Piston Suggestions

[Cerberus]

I hope that I'm not duplicating a previous question, but I couldn't find the answer I was looking for on the forums.
The engine shop called me today and said the '69 383 is rebuildable, but they will need to bore it 40 over and deck it. No surprise there, as it was locked up when I get the car and began the project. That being said, I'm shopping for new pistons. The originals were flat top, with a slight indent in them. I intend on reusing the original crankshaft and connecting rods (assuming they check out at the shop), and am looking at this top-end kit from Edelbrock: https://www.edelbrock.com/performer-rpm-top-end-kit-for-b-b-chrysler-2086.html

All that to say, my primary concern is making sure the valves don't hit the pistons, so what am I looking for in the new pistons aside from the correct diameter? I'm open to any and all suggestions as this is my first engine build. Thanks!

 

[radical rob]

Flat top with valve relief are the usual ones.
Biggest problem I see with this kit is it is marked out of stock. Isn’t that how it works lately, you find something you like and you can’t have it!
No specs on cam listed either. Hydraulic flat tappet. Will need a lot of extra attention to detail on startup.

 

[Cerberus]

Is thing along the lines of what you're referring to?

KB Performance Hypereutectic Piston Set

 

[65CopCar]

Be real careful. Really hard to get off the shelf 383 pistons that will have useable compression. I shaved my heads ALOT and ended up with like 8.9:1 compression. and that was a closed chambered head. What is the cc of the heads? Pick a piston and heads and I can run some compression numbers for you.

 

[HawkRod]

I hope that I'm not duplicating a previous question, but I couldn't find the answer I was looking for on the forums.
The engine shop called me today and said the '69 383 is rebuildable, but they will need to bore it 40 over and deck it. No surprise there, as it was locked up when I get the car and began the project. That being said, I'm shopping for new pistons. The originals were flat top, with a slight indent in them. I intend on reusing the original crankshaft and connecting rods (assuming they check out at the shop), and am looking at this top-end kit from Edelbrock: https://www.edelbrock.com/performer-rpm-top-end-kit-for-b-b-chrysler-2086.html

All that to say, my primary concern is making sure the valves don't hit the pistons, so what am I looking for in the new pistons aside from the correct diameter? I'm open to any and all suggestions as this is my first engine build. Thanks!

A competent machine shop should make sure that there is no piston to valve interference during overlap. Plus, if this is a street engine with .500 or less lift, I'll almost guarantee you that you will be OK.

It goes without saying that the pistons you get should be the right size and compression for your car (I haven't checked out options), but I have a couple of other things to suggest you consider:
1) Piston material. There are cast, hypereutectic and forged pistons. Most engines are built originally with cast pistons. Choose replacement pistons based on how you plan to drive your car. Cast are a budget choice, while hypereutectic are stronger than cast but also offer tighter tolerances (piston to wall) than forged pistons. Forged pistons are the strongest, but they also grow when they get hot more than others, so you need more clearance and they will make more noise before the engine gets warmed up. Not a big deal, but many walk around like forged pistons are the ONLY thing you should put in a rebuild. For a street engine, hypereutectic will be plenty strong. Bottom line: I suggest either a hypereutectic or forged piston.

2) Piston weight. Shaving piston weight will help to make the engine rev higher and faster, and helps performance. If you have a choice, go with the lightest piston available.

3) Rings. Ring technology has come a long way, and many pistons are now made for rings that are now 1 mm thin, and they are stronger and exert less drag than larger rings. Bottom line here: If you have a choice, choose a piston that has a narrower ring.

 

[RJRENTON]

I hope that I'm not duplicating a previous question, but I couldn't find the answer I was looking for on the forums.
The engine shop called me today and said the '69 383 is rebuildable, but they will need to bore it 40 over and deck it. No surprise there, as it was locked up when I get the car and began the project. That being said, I'm shopping for new pistons. The originals were flat top, with a slight indent in them. I intend on reusing the original crankshaft and connecting rods (assuming they check out at the shop), and am looking at this top-end kit from Edelbrock: https://www.edelbrock.com/performer-rpm-top-end-kit-for-b-b-chrysler-2086.html

All that to say, my primary concern is making sure the valves don't hit the pistons, so what am I looking for in the new pistons aside from the correct diameter? I'm open to any and all suggestions as this is my first engine build. Thanks!

Definitely use round ones.....unless you are broaching the bore and using square or hexagonal pistons......
BOB RENTON

 

[65CopCar]

So those are the pistons I used. My block was not decked. The pistons are 0.037" in the hole. Heads were reduced to 72cc. Calculated CR with these pistons was 9.08:1 and actual measured (with liquid) was 8.87:1. With 72cc heads the piston website says 9.8:1 compression. If I change the deck height to zero my calculated CR is 9.86:1 so the website is assuming zero deck height. Are you going to deck your block?

And here is the kicker - put your stock 906 heads (assume 90cc which I measured on one set of 906 heads before) on my setup and you are at 7.84:1 compression. No go.

 

[Cerberus]

Holy smokes, that was a lot of information to process. Thank you to everyone who has replied so far!
To answer a couple of the questions so far:
Yes, the block will be decked, but I don't know the final number they'll need to shave off just yet.
The heads I'm looking at, assuming they'll ever be available, appears to have an 84cc combustion chamber. So I'm assuming that translates to a 8.8 CR based on the pistons I shared?
@HawkRod thanks for the explaining the materials. I had seen a lot of terms thrown around and hadn't brushed up on them yet.
@65CopCar (or anyone else) what is considered a "useable" compression? Factory CR was 9.2 for the 2bbl 383, right?

 

[65CopCar]

So CR depends on what you want to do with the car. My daughter's 67 coronet tips in a little over 4000 lbs. Has a mild can RPM intake and a 727 and 11 inch converter. Otherwise stock. It is a street car that occasionally see the track. With the 383 (measured 8.87:1) compression it went 14.30's at 95 mph. It will do better once I give it some traction. Not bad for what it is. I made a big mistake and put too much cam and wrong intake on it. Changed it and oh my - much more fun to drive and faster. It now has low end torque. I was shooting for 9.0 - 9.2:1 compression.

So depending how much you deck it, on my setup 84cc would be between 8.4:1 (0.025" in the hole) or 8.82:1 at zero deck. So you are correct at zero deck you would have 8.8:1. Of course you could shave the head some or use a thinner gasket. I use the 0.039" felpro gaskets. If you went with the Cometic 0.027" gaskets at 84cc you would have 9.13:1 at zero deck.

 

[65CopCar]

Looked at that kit. I don't think that price is fantastic. You might consider something else that has smaller head chambers. You can get good aluminum heads at 78cc. All depends what you want to do.

I strongly recommend you talk to Dwayne Porter. Tell him what you are trying to do and he will give you great feedback. Pretty sure he lurks around on this board. He is in VT. You can google him.

 

[BSB67]

Start with the Icon IC687 piston and build around it. With decking, head gasket and the options in aluminum head chamber size, you can dial into anything from 9.5:1 to 10.5:1 CR. with quench.

Diamond has a decent 383 piston too.

 

[Budnicks]

Yeah they have 4.290" 0.040" overbore
& that IC687.040 Icon piston is 1.912" (IIRC) for compression height
org. 1968 383 10.25:1 maybe 10.5:1, 335hp (rated) RR engines 383
(with a thin steel 'shim style' head gasket & 906 heads like 88ccs)
is 1.935" for compression height "allegedly"
& the OE gaskets (MoPar Performance or Direct Connection, after market used to sell them)
were steel shim like 0.020" & like 0.018" compressed

need to deck the bock for sure to get it up a bit
& use a steel shim/multi layer Cometic gasket & closer to the size of the actual bore diameter
without getting into the combustion chamber
IIRC they can be had in like 4.350" bore, maybe smaller (maybe ? 4.320")
like 0.025" compressed thickness

not the 0.039"-0.040" (Fel-Pro, Perma Torque) or thicker stuff,
most people use, don't know any better

they make the RPM heads in 75cc (or is it 78cc ?) Combustion Chamber too

every lil' bit helps

 

[65CopCar]

Yeah they have 4.290" 0.040" overbore
& that IC687.040 Icon piston is 1.912" (IIRC) for compression height

I didn't look at all the available ICON pistons, but the one I saw I believe had the 1.912 compression height but it had a slight dome (4.5cc). Are they all domed? That makes a huge difference in CR.

 

[Cerberus]

Looking at the ICON pistons now and noticed that they are designed for Indy, Edelbrock, and OE style heads. Seems like a good starting point.

Im making notes of all of this to bring to the engine shop and get their recommendations as well. They're doing the cleaning, inspection, and machining, but I'll be doing the build.

Hoping for something driveable (400-425HP?) that will be paired to a Tremec 5-speed (yay overdrive). Once I'm done restoring her, I want it to be my daily. No sense in doing all this work for a garage ornament.

 

[BSB67]

If you cut the deck about 0.020 - 0.025” and use the IC687 you’ll be close to zero deck. Add a 0.040” gasket and 82 cc Stealth heads and you’re at 10:1 CR. Use the 75cc eddy heads and you’re are close to 11:1 CR.

 

[65CopCar]

If you cut the deck about 0.020 - 0.025” and use the IC687 you’ll be close to zero deck. Add a 0.040” gasket and 82 cc Stealth heads and you’re at 10:1 CR. Use the 75cc eddy heads and you’re are close to 11:1 CR.

10:1 is not a bad target. My 9.0 - 9.2:1 target was for stock cast iron heads. My street/street pump gas motor is 11.14:1 CR with TF270 heads. We overshot our target a bit. OOPS.

 

[1 Wild R/T]

As far as the first piston you posted... KB Pistons are hyperutectic... They require a lot wider ring gap as the top ring gets very hot & expands more than normal... Not a fan of them, at all....

The Icons are a great choice... Building cylinder pressure is tough do to the big bore & short stroke... A smaller chamber would help...

The Edelbrock E-Street 5090 is 75cc

DODGE Edelbrock 5090 Edelbrock E-Street Cylinder Heads | Summit Racing

The Trick Flows are bice but literally twice the money....

But as mentioned above if your gonna deck the block to get zero deck height & .040 quench use the 84cc head...

 

[Virg464]

Looking at the ICON pistons now and noticed that they are designed for Indy, Edelbrock, and OE style heads. Seems like a good starting point.

Im making notes of all of this to bring to the engine shop and get their recommendations as well. They're doing the cleaning, inspection, and machining, but I'll be doing the build.

Hoping for something driveable (400-425HP?) that will be paired to a Tremec 5-speed (yay overdrive). Once I'm done restoring her, I want it to be my daily. No sense in doing all this work for a garage ornament.

Listen to these guys, and do the research, I didn't take that route. I bought the heads first and then had to get a custom set of pistons (.350" dome) to get to 10:2 CR in my motor.

 

[65CopCar]

As far as the first piston you posted... KB Pistons are hyperutectic... They require a lot wider ring gap as the top ring gets very hot & expands more than normal... Not a fan of them, at all....

They do but I like them as a cost effective stock alternative. They do have advantages over stock pistons, but they do hold more heat in the glands so the ring gap does need to be larger. They are somewhat cheaper than the ICON pistons. I have the KB pistons in 2 or my 383s. In retrospect, if I were doing the Coronet 383 over again, I would be very strongly looking at the ICON pistons. I wasn't aware of them (or were they even available then?) when I did that motor.

 

[1 Wild R/T]

They do but I like them as a cost effective stock alternative. They do have advantages over stock pistons, but they do hold more heat in the glands so the ring gap does need to be larger. They are somewhat cheaper than the ICON pistons. I have the KB pistons in 2 or my 383s. In retrospect, if I were doing the Coronet 383 over again, I would be very strongly looking at the ICON pistons. I wasn't aware of them (or were they even available then?) when I did that motor.

I too had them in a engine... They were working but when I had the heads off they showed visible signs of detonation damage on a level I'd never seen before on cast or forged pistons... The engine had never been hot, never been audibly pinging, it did run lean one time when the fuel pump failed but it was only maybe twenty miles & I put the car on a rollback....

Having heard enough stories about them & then seeing what I saw I wouldn't run them or suggest them ever again...