[terminal_crazy]

Hi all.

I'm still planning my 383 LT1 build but still struggling with pistons.
I'm planning on 3.750 stroke & 6" Rods and stock 54.4cc heads.
Pistons appear to be either 5cc flat tops or 16-19cc dish
CR works out to around 12.5 with the flat tops or 10.9 with the 16cc

I was looking for around 11.5+ but still not sure what the max i can run on the street. Any suggestions please.

Thanks
Mitch

 

[ShowNoMercy]

Are you looking for brand suggestions or what SCR to go with?



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[terminal_crazy]

Are you looking for brand suggestions or what SCR to go with?

Either. Every time i read that 12.5 runs fine with flat top pistons they seem to running with different heads.

I've found Probe do a 12cc dish top which works out at 11.3 but is forged from 2618 rather than 4032. Are these still suitable for a Road Going car?

Thanks
Mitch

 

[cocobolo95]

Could not upload the original zip file for the dcr calc, because it exceeded the upload limit.

If anyone still wants it, pm me with your e-mail address and I'l send the 1.5 mb file via mail.

For my upcoming build I'm using 11.8 static compression pistons. According to the calculator, it should run fine on pump gas.

 

[Mystery Bird]

You can also control compression with deck height and/or gasket thickness.

 

[USMC]

I will be running 12.28 car on 91pump gas. I will be fine and so will u. Flat tops forged.

 

[terminal_crazy]

Here's a handy little program called the dynamic compression calculator. You plug in the static compression, cam info, and other info and it will give you the dynamic compression, which is what is important.

For my upcoming build I'm using 11.8 static compression pistons. According to the calculator, it should run fine on pump gas.

I've tried to run setup but setup can't find LST (1ST) file. Only setup/exe is in the zip.

Thanks
Mitch

 

[terminal_crazy]

I will be running 12.28 car on 91pump gas. I will be fine and so will u. Flat tops forged.

Thanks, that's what I was hoping to hear.

What pistons/material do people prefer.

Cheers
Mitch

 

[Dynamic396]

What camshaft are you planning on running? Without this information, static compression numbers are meaningless.

I have used Icon forged pistons in some very abusive situations (Super 4 Modified, Limited Late Model, Super Late Model). All of the off-the-shelf Icons I have used are 2618 alloy.

 

[terminal_crazy]

What camshaft are you planning on running? Without this information, static compression numbers are meaningless.

I have used Icon forged pistons in some very abusive situations (Super 4 Modified, Limited Late Model, Super Late Model). All of the off-the-shelf Icons I have used are 2618 alloy.

I'm planning on the Comp Cams XFI 280. (Closes at 69 Deg). I think the 292 (75 deg) might be bigger than I need, harder to tune for our emission test but would lower the Dynamic Compression to about 9ish

Thanks
Mitch

 

[Dynamic396]

Yeah, your chamber size is going to limit your setup options. I'd much rather run a flat-top piston than a dished one, but with that cam and stock heads you're kind of stuck. Some 60cc heads would make a new ball game out of things, though...

 

[terminal_crazy]

Yeah, your chamber size is going to limit your setup options. I'd much rather run a flat-top piston than a dished one, but with that cam and stock heads you're kind of stuck. Some 60cc heads would make a new ball game out of things, though...

My nievety i suppose. I presumed there would be more choice/range in pistons.

Would opening the chambers up be better than a fatter Head gasket especially if cc'd?
Each 0.010 drops CR by about 1/3. I'm working on Zero Deck Block and 0.040 Gasket.

Thanks
Mitch

 

[Dynamic396]

Do not adjust compression ratio by going with a thicker gasket. The quench distance should be kept at about .040-.042" on a street engine. A zero deck height with a .039-.040" head gasket is just about perfect. Using a thicker gasket will kill your quench.

You could open up the chambers, but at that point you become the combustion chamber design engineer. The shape of the combustion chamber has a tremendous effect on flame propogation, burn rate, detonation resistance, etc. If you start opening things up, who knows where you'll end up. Better, worse...who knows?

If I were in your shoes, I'd save my coins for the correct sized heads...

 

[USMC]

And the Phantom returns. Hows it been Dynamic? Okay here it is..if I were to take anyone's advice it would be Dynamics. The man knows what he's talking about. Listen to him. Heck I bet he would love to build the engine your speaking of. Follow his advice and u will be just fine. Also, I have a combo that I just had built that and I will glady give you my specs plus a few cam choices. No secrets over here

 

[ShowNoMercy]

You can hog out the stock heads to ~60-64cc chambers, but as dynamic pointed out, you want to be sure you know what you are doing. Most guys do that for cheap lower SCR when boosting, but with NA stuff you can't make as many shortcuts.

On the piston topic, I run JE stuff, think mine are -28cc :lol:



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[terminal_crazy]

After getting Pat Kelly's Compreesion Calc of Cocobolo95 I'm getting virtually the same figures.

I'm Looking at PROBE's 12345-030 piston 12.8cc Dish
Gives me 11.36 (8.76 DCR) ( 11.38 - 8.78 DCR &179psi with Wallace)

Is it worth looking at some custom Pistons (Recommendations) or am I getting hung up on this for a street engine ?

A 10cc dish would get me 11.76 & 9.06 DCR
8 12.07 & 9.28
6 12.38 & 9.5

Mitch

 

[terminal_crazy]

I've also noted that some of the given CR by manufacturers don't always match up to the calc.

PROBE Flat Top Moleculite -4cc Shows 11.81 with 58cc Chamber. I get 12.1

Mitch

 

[PA94Z]

If you are willing to spend the money Diamond will make you a set of custom pistons. You could choose any dish size, ring package, material you want. 2618 requires a larger side clearance than 4032 but is a superior material in performance motors. If your machining is right there is no reason you could not run them in a street car.

 

[sweetbmxrider]

I would also keep in mind the prices. How much more would you spend on a set of good heads, pick up some good power, and use a shelf piston so in case something happens, its not a huge burden to replace.

 

[Dynamic396]

And the Phantom returns. Hows it been Dynamic? Okay here it is..if I were to take anyone's advice it would be Dynamics. The man knows what he's talking about. Listen to him. Heck I bet he would love to build the engine your speaking of. Follow his advice and u will be just fine. Also, I have a combo that I just had built that and I will glady give you my specs plus a few cam choices. No secrets over here

Doing great, Devil Dog... I literally cannot remember a time that I have been this busy in the shop, though. No time for much of anything fun these days! My 396 sits there on the stand...patiently waiting for some love. Thanks for the shout out and kind words...!

As for the question about custom pistons...no, I wouldn't go through the hassle (and $$$) of custom pistons. It looks like the numbers with those Probe dished pistons will work just fine. If it were my project, though, I would run a flat-top piston at about .040" quench, and the get a good set of heads with the right chamber size. Dished pistons work just fine...don't get me wrong, but I much prefer a flat-top because it forces all of the mixture up into the chamber, which has been extensively engineered down to the last detail for optimum combustion efficiency. When you run a dished piston, the "dish" becomes part of the combustion chamber. Will the shape of the dish and the shape of the chamber work optimally together...? I don't know, either...