Snow Dog

iTrader: (3)

I'm sure this has been beaten to death as it's nothing new I imagine but I'm not finding the information I'm after. I'm in the process of selecting pistons for my 383 build and am having a hard time finding something that will work or that I was wanting to use.

The engine is a forged 383 with 6 inch rods. Ai 200cc heads and their cam. Heads have a 57cc chamber. I was shooting for an 11-11.5:1 compression ration while maintaining a 0.030-0.050 quench. I'll be running 93 octane. The car is strictly a street car/canyon carver. Ai supplied me with an 0.026 head gasket. I'm not opposed to changing this. I've just been using it in my calculations. Block is undecked at this point.

Looking through all the piston selections I'm aware of, I'm finding either flat top pistons with a 4-5cc valve relief or reverse dome with 15-16cc dish. I've been using this DCR calculator to figure compression https://www.uempistons.com/index.php...67524393fde667

In order to make the flat top pistons work, I end up with a huge quench. To make the dished pistons work, I end up with too tight of a quench. Ideally, a 10-12cc piston would work well for me but I'm not finding anything in that range. Does such a piston exist? I'm betting it would be custom which means more money. Considering I'm just a street car and have simple goals, I'm thinking I need to revise my compression goals. So does anyone have any suggestions on what I should do? I'd rather build a durable, long lasting engine than to push compression for the sake of a little extra power. That's why I didn't choose 12:1 as a compression goal.

Thanks for the help.

SS RRR

iTrader: (2)

I have a 396 that has an 11:1 CR. It has a .040 quench and the block is zero decked. Heads are between 58-60cc. I had to order custom pistons which have a -12 to -14cc relief in order to get that static compression. You building this yourself or having a machine shop do it?

Snow Dog

iTrader: (3)

I'm still debating if I want to assemble it or pay the machine shop to. They will be machining it to my specs though which is why I'm doing so much research.

Who did you choose for your pistons?

Thank you

SS RRR

iTrader: (2)

JE:


I would definitely get the block zero decked. Proper quench is then much easier to achieve.

Catmaigne

iTrader: (6)

A piston with a full dish like that has no real quench pad anyway.

Quench makes more sense when dealing with older motors with carb or TBI that are crap at atomizing fuel. We are lucky to have an injector in each port backed by high pressure to create a diffuse spray pattern. I could understand quench being a big deal when your whole fuel system is a vacuum controlled leak or half assed 80s EFI, but things have changed. There is probably a tiny bit of power to be had by having optimal quench, but it is not nearly as important as it used to be and I wouldn't lose sleep over it. Increasing CR is definitely more important IMO.

Nostang

iTrader: (4)

If you go with a zero deck and a .026 gasket you will be too tight for quench. If I were you, I would do a .006-.005 in the hole deck height to give you a little wiggle room in the future and run a .033-.035 compressed gasket which would get you a quench of .038-.040 which is optimal. My combo is a .027 gasket and in the hole .006 giving me a .033 quench which is really tight and if I were to do it over I would have went a little lower on compression and bigger on the quench for a greater safety factor. There is nothing wrong with a tight quench and it is supposed to provide the beast atomization of fuel, flame front, and detonation avoidance but when things are tight there is no room for variance/error.

BALLSS

FWIW exactly what I did. pistons .005 in the hole using the FelPro .039 head gasket. 6" rods & SRP pistons

Snow Dog

iTrader: (3)

True. The pistons I was looking at that had the 15-16cc dish are considered reverse dome pistons. There's more of a quench area but still not like a flat top of course. EDIT: Just looked at your build, you're running what I've been seeing called reverse dome pistons.

You're correct about the zero deck. That is why I say I'm too tight using the 15-16cc pistons. I was hoping to leave the piston 0.005-0.010 in the hole with whatever gasket I go with. What did your SCR end up being with your engine? 93 octane still?

What pistons did you choose, and what did your SCR end up being? Still run 93 octane?

To clarify, I was hoping to use an off the shelf piston instead of a custom one. I just can't seem to find one that meets my goals. So I'm open to suggestions on how to go about using an off the shelf piston and or what changes I'll have to accept while still being able to run 93 octane in a street car.

Thanks for the replies everyone. I do appreciate it.

KW Baraka

iTrader: (7)

Like others have stated.....you'll want quench in the .035" to .040" range for a regular, street driven car.

.050" = a bit too much for higher than 11:1 CR.....that is, if you're really looking for that stroker to perform.

KW

Snow Dog

iTrader: (3)

Thanks. I'll keep it in mind. The 0.030-0.050 number came from lots of searching in general around the web about all of this.

Catmaigne

iTrader: (6)

I use a -16cc dished Mahle Powerpak in my 383. The dish is D shaped so there is still a quench pad. Comes with rings too.

My comp height is taller bc 5.7" rods. The Mahle p/n for 6" rods in a 383 would be SBC125030i16.

Nostang

iTrader: (4)

My final SCR is 12.15-1 with a 58cc combustion chamber, .027 /4.060 bore gasket , .006 in the hole, and ~5ishcc valve reliefs. I had -3cc valve reliefs but had to get the pistons flycut for the cam I am running. My DCR is at 9.3-1 with my cam and I was told by multiple folks (including my tuner) that I need to run Sunoco 109 if I want the engine to live. I have run 93 pump gas but only putting around town and not getting into load but don't want to risk it at WOT. I was told if I retarded the timing back I could run pump gas but I would be down on power and not optimal. Cam is 259 267 @.050 108lsa .65x lift. 292 300 adv duration.

Catmaigne

iTrader: (6)

This is what the 1.425" version looks like.

Snow Dog

iTrader: (3)

Originally, I was hoping to run the Mahle flat top pistons as I've heard good things about Mahle pistons in general. Not sure that's possible now after crunching the numbers.

Thanks!

Snow Dog

iTrader: (3)

Well, I've found that Arias makes a 10cc dished piston for a 383 using 5.7 inch rods. I haven't bought my rods yet and my crank is for 5.7 inch rods so I could run 5.7 rods. Now I'm left wondering if it's worth it to go 6 inch rods. I know there's not much difference between the two lengths in terms of power. My reason for going 6 inch was cost, weight, and why not since every little bit helps.

Decisions decisions, lol

Nostang

iTrader: (4)

Why not get a set of custom pistons made to your specs? I did that for my setup with Diamond pistons and they were pretty quick to get them done and sent to me. They were not much more than off the shelf and I got exactly what I wanted. I would go with 6" rods as your crank can work with any rod length (pistons will not). Make sure you get rods that will not need as much work with block clearance and go with the best rod bolts you can get.

Snow Dog

iTrader: (3)

I didn't realize custom pistons weren't that expensive. I was expected that to be pricey. I'm not on a set budget, I just don't spend my money all ***** nilly.

SS RRR

iTrader: (2)

I bought mine about 10 years ago and it was in the $800 or so range? I've heard the price of metal has gone sky high and those same pistons would be well over a grand now.

Snow Dog

iTrader: (3)

Well, I emailed Arias asking for an estimate if they had to make them custom. We will see what they say. $1000+ is a lot IMO.

I also must be blind or just going cross eyed from looking through too many websites. Icon makes a 10cc piston in their FHR line for my application. It's a flat top but with 4 valve reliefs instead of the normal 2. Only problem is, I don't know anything about Icon's quality.

Thanks!

Nostang

iTrader: (4)

What about something like these? https://www.summitracing.com/parts/ros-90761/overview/

You could also look at hypereutectic pistons which would be fine for you if you never plan on nitrous.

From the lead time from Summit the Ross look to be made to order so a custom set might be the same pricing from Ross.