Piston depth in hole - '69 Roadrunner

OK, I know that piston choice sucks for the 383 with stock heads but my best option seems to be the Speed Pro 2315. I have been told that these have a slightly shorter compression height than stock (~.014"). So that will put this piston ~.014" further down in the hole than my stock pistons.

Million dollar question: How far down in the hole are my stock '69 383 pistons in my Roadrunner?

Now, I know what some will say... "there all over the map!!" and I understand that I'm just looking for an average WAG, .005", .020" or ???

A lot of them are 20-40 in the hole stock. Some even more. I sure wouldn’t make any big decisions till pulling the heads.

Stock pistons at .040" in the hole would put the currnet engine at about 8.5:1 compression (assuming 90cc heads).

the stock pistons in my '68 road runner were very close to zero deck with nothing touched. 2315's will be close to .010" below the deck.

I have never seen off the shelf pistons for a 383 that was .010 below, they have been .040 or more that I have seen

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Same here. The stock pistons in my '69 Bee were about .005 in the hole.

stock '68's were +.020" out of the hole when decked to nhra specs. the 2315's I did for a friend were about .010" below the deck in a stock un-milled block. IIRC the '68 piston has a 1.935 pin height. KB's are 1.908, 2315's are 1.915 IIRC, generic 8:1's are 1.86 IIRC.

Compression height on a stock 383 piston is 1.934 (for '68 and '69). The compression height for the speed pro 2315 pistons is 1.92.

2315 link.

So if no machine work is done the 2315s will be .014 further in the hole than the stock pistons.

I knew the hp 68.69 had + or close deck, I was referring to replacement pistons [Shelf pistons] that said I still dont recall the 2315 being that close to the deck, BUT I have been wrong at least once in my life.

I was surprised at the deck height with the 2315. they would make a good street performance piston with zero deck easy; down side no valve reliefs. pretty sure the '68-'69 piston is no longer available.

I’m not finished with the build yet but I’m building a 66 383 right now with 452 heads. It had kB pistons in it. They are way down the hole with Grand Canyon valve reliefs. I can remember the exact specs right now but they are written down on my build sheet at the shop. The compression ratio was way low. I bought the sealed power 2315s as replacements. My machine shop had to equalize the deck because they appeared to have been mill slightly off previously. He did not take much off to correct it. Knowing how these blocks can shift around with heating and cooling cycles, it may not have been milled at all. I have only installed one piston to degree the cam and check valve to piston clearance with my choice of cam. From my memory right now, I think my final deck height was-.006. I’ll double check, I’ve got three builds going right now. Going from my pre-build notes, this should bring a compression ration of 9.0:1. I had plenty of piston the valve clearance with comp camps 262H cam. I’ll post the lift and duration numbers later today.

Great information guys. Thanks!

You may want to talk to member mike s. IIRC he had zero deck 383 pistons available.

Piston choice does not suck.

The 2315 is a good replacement. Depending on what your goal is, you can get it to zero deck pretty easy and use a aftermarket head of your choosing and have good quench with a 0.040" head gasket. Or cut less, and use a thinner gasket to get the quench. Valve to piston will become an issue with bigger cams.

The best piston IMO is the ICON IC687. It will requiring decking to get it to zero (if that's what you want) but has valve reliefs and a slight dome (4.5 cc) so you can get to 9.5 CR easily and not worry about piston to valve.

I've owned and have been around several 68/69 383s. They come in betweem zero (0.000") and 0.005" below the deck.

why not just call Diamond and have a set made?

Mostly becaust for what the OP is doing, it would not be any better than the IC687, and probably cost almost twice as much.

Good to know.

My engine is matching numbers so I don't want to deck the block and loose the numbers on the pad. Even without decking these pistons show a bump of about 0.2:1 over the 2315's. Definitely an option.

Go to class racer.com, register, then go to 1969 383 RR blueprint specs. All the pistons they show are good ones that will be up at the deck, all have 5/64 rings but thin ring packages are available $$. If using high lift or long duration cam it will need valve reliefs.

I did a matching numbers 383 a few years ago and didn't want to mill the block although it really needed it. used the 2315 piston with 84cc 906's and a fel pro 8519 gasket. also used a summit 6400 cam, stock intake/carb, re-curved stock distributor. no detonation and drives very nicely.

BE CAREFUL which pistons you use ....

I had 1970 TRICK SHORTBLOCK go together with the EARLY PISTONS !

Now if only I had had DECKED the block and had a decent set of 915 heads ...

Something is not quite right in your math. The IC687's net 4.5 cc volume above the 2315 flat top will be 0.4 increase in compression.

Like Lew stated, or was implying, watch your head volumes and gasket thickness. You'll be better at 9.2 or 9.3 verses risking detonation with 9.6 or more, IMO.

Also, if you are on a budget, you can probably use the 2135s without balancing the assy, the IC687 you will.

There are posts-one very recent from myself here about great power from smog era OEM pistons. In this case it was the smogger 360. Several members here are running in the 12s with the deep down in the hole factory mopar pistons and a good but not radical cam. with a good round bore with great seal - Id just use the lower comp piston unless your goal is greater than 12s?

i don't remember the exact numbers but I think the compression ratio for the 383 I did with the 2315 pistons was 9.1-9.2. I wasn't sure they'd work with a non-quench but they did. overbore sizes are heavier than stock and I wasn't sure they'd work without a re-balance but they did fine; smoother than my balanced 440. down sides to the 2315's are no valve reliefs and weight. only down side I can think of for the icons is noise when cold. I use a set of icons in one 440 I have and they're pretty noisey cold but that's just the nature of a true performance piston.

Just for a data point. My '69 roadrunner 383 had stock pistons 0.010" in the hole. The 2315 pistons are now 0.022" in the hole.

Since this old thread was dragged back up and I was not on the board much back when this was posted let me chime in ...

I have looked at this subject a lot because I have raced pure stock drags with my 69 383 GTS and planned to do the same with my 69 3383 Superbee .

Stock 68-69 HP compression height is 1.932, in a CHRYSLER BLUEPRINT SPEC deck block with a Blueprint spec crank stroke and Blueprint spec rod, the piston sits .0025 in the hole. ... this is not the same as NHRA spec which is .020 ABOVE the deck which is what Chrysler tells them and is not actual factory production spec.

KB pistons are 1.908 and the 2315 is 1.920 , Diamond also has a piston which I think is 1.915. I never measured, or looked into, pre 68 or 70-71 because I had no interest in them.

The aftermarket doesn't make a 68-69 piston because they make a one size to fit all years of 383 production, the 2315 is the closest to 68-69

That says your deck height was .0075 over factory spec . I know it's too late know but you could have had the block decked by a shop that uses a machine like a Rottler CNC for decking blocks , that can stop shy of the the numbers and move up and down at the stop point to finish the cut square... I've had it done to a couple of 383's

I was able to get the CR I wanted (9.0:1) without decking the block.

That's good but my reason for decking the block is that after thousands of heat cycles the block has settled. I take one rod and piston combo and put it in the 4 corners of the block and measure how deep the piston is in the hole , it is NEVER the same side to side or front to back. I usually pick the deepest pick a corner and when the block is cut the cutting confirms the warpage that has occured. For a mild street build what you did is just fine ... it's what most people do ... I'm building for zero deck and a certain squish/quench number so I spend the extra time and money.