383 Rebuild - New Piston Suggestions

[monaco66coupe]

Am I in deep doodoo?
We are just finishing my 69' 383 engine with the .030 over KB162 pistons, stock 383 magnum cam, using the 67' 915 closed chambered heads, and .025 (mancini said the .020 was no longer made)steel head gaskets. anything to do to avoid any problems with the setup?
any problems to watch out for?

 

[1 Wild R/T]

Am I in deep doodoo?
We are just finishing my 69' 383 engine with the .030 over KB162 pistons, stock 383 magnum cam, using the 67' 915 closed chambered heads, and .025 (mancini said the .020 was no longer made)steel head gaskets. anything to do to avoid any problems with the setup?
any problems to watch out for?

You will probably be fine... There are tens if not hundreds of thousands of engines running KB Hyperutectic pistons...

Run big ring gaps, don't run nitrous, be careful about running to much timing of running lean & you'll be fine....

Just cause I'll never build another engine with them doesn't mean most owners aren't happy with them...

 

[monaco66coupe]

Thanks! I feel better. This a bone stock original 383 Barracuda down to the hubcaps. No racing, but maybe to Salt lake or Flagstaff this summer to see kids. No abuse allowed!
would you hazard a guess as to what my CR will be?The 915 heads I am using have the larger valve, if my memory serves me, the cam is 450/442 somewhere abouts. It was as close as we could get to OEM.

 

[1 Wild R/T]

Thanks! I feel better. This a bone stock original 383 Barracuda down to the hubcaps. No racing, but maybe to Salt lake or Flagstaff this summer to see kids. No abuse allowed!
would you hazard a guess as to what my CR will be?The 915 heads I am using have the larger valve, if my memory serves me, the cam is 450/442 somewhere abouts. It was as close as we could get to OEM.

View attachment 1796738

The KB 162 pistons are listed as having an 8cc valve notch volume...
Stock 915 chambers are around 82CC
If it measures 9.98 deck height
Stock length rod, stock stroke 1.908 C/H
the numbers say 8.5-1

Actually a little higher, I used .041 for the head gasket.... with the .025 your still getting some useable quench effect as well which helps..

 

[monaco66coupe]

The KB 162 pistons are listed as having an 8cc valve notch volume...
Stock 915 chambers are around 82CC
If it measures 9.98 deck height
Stock length rod, stock stroke 1.908 C/H
the numbers say 8.5-1

Actually a little higher, I used .041 for the head gasket.... with the .025 your still getting some useable quench effect as well which helps..

That is Less then I hoped, but it is what it is.The stock hp was 10:0,and 2bbbl was 9:2. at least the car is a four speed.
I also have a redone set of the original 906 heads, as a spare set, but I thought that would lower the expected CR? I haven't Installed the heads yet, so I can go either way if one is better than the other.
I am also building another original 68 383 from a roadrunner next, and I hope to have a standard bore. I will also be asking for advice a bit quicker the next time around!
Thank you Wild R/T!

 

[1 Wild R/T]

That is Less then I hoped, but it is what it is.The stock hp was 10:0,and 2bbbl was 9:2. at least the car is a four speed.
I also have a redone set of the original 906 heads, as a spare set, but I thought that would lower the expected CR? I haven't Installed the heads yet, so I can go either way if one is better than the other.
I am also building another original 68 383 from a roadrunner next, and I hope to have a standard bore. I will also be asking for advice a bit quicker the next time around!
Thank you Wild R/T!

Well, just because Chrysler said it was 10 or 9.2 doesn't make it so....
But the stock 4bbl pistons were slightly higher C/H.. The 906's will lower the C/R and you'll lose any hope of quench...

Chrysler lists 906's as having 81cc chambers but most measure between 88 & 92cc's
915's are listed as 72 cc's but most measure around 80-83CC's..

If you want a little more have the heads milled .040... But know the better approach would have been to deck the block .025 off the block & a .040 head gasket gets you ideal quench and 9-1
Take another .040 off the heads and you get 9.4-1

 

[BSB67]

383, A-body, 4 speed car. Nice. Not really sure how you don’t drop the hammer on that every time you get a chance.

 

[BSB67]

And for an iron head 383, the 915 head and Speed Pro 2315 piston is a great match, with a reasonable street cam.

 

[Cerberus]

You all are amazing! Thanks for all of the input!

 

[65CopCar]

Well, just because Chrysler said it was 10 or 9.2 doesn't make it so....
But the stock 4bbl pistons were slightly higher C/H.. The 906's will lower the C/R and you'll lose any hope of quench...

Chrysler lists 906's as having 81cc chambers but most measure between 88 & 92cc's
915's are listed as 72 cc's but most measure around 80-83CC's..

If you want a little more have the heads milled .040... But know the better approach would have been to deck the block .025 off the block & a .040 head gasket gets you ideal quench and 9-1
Take another .040 off the heads and you get 9.4-1

Pretty much totally agree with everything you have said. My 67 915s measured 81cc on average. My 65 516 heads were in the 75cc range.

My 67 383 is basically a clone of yours with the KB piston. But I used 0.039 gaskets. I shaved the heads (and the intake to correspond to the head shaved) 0.045". As I stated before, that got me to 8.87:1. Should of used the Cometic 0.027 gaskets (I don't like the steel gaskets) and that would of got me to 9.18:1.

The calculated piston height from the advertised piston compression height should of put the piston 0.027" in the hole. My actual is 0.037" in the hole. That lowered my compression some.

It is best to actually measure everything you have and then see what you need to do to get reasonable CR.

 

[qkcuda]

I run the KB 240 pistons in my 400. With the 8cc valve reliefs, .015 deck height, 88 cc 346 heads and a .040 gasket, I am right at 8.5:1 compression. The good news is that I can run regular gas, which is a major cost savings here in Canada.

 

[monaco66coupe]

I had hoped the KB162 was similar to the originals, as the manufacturer advertised. But they aren't.
However, I do have these lower compression pistons in another 69 383,9(Possibly,2008) and it runs very well. not the quickest, but after 20 years it still runs great.
I can say an original 383 HP I have in another car runs like an HP engine,
and the second with the KB'S run like a 383 2bbl with a four barrel carb.(same Identical camshaft)


In the end I really feel lucky That I get to own and drive these old Mopars,regardless of performance, and I really appreciate the response of the members here.

I may start a post with the progress of the car if anyone is Interested, as it has a build date of 8/1/68 and is a formula S car as well.
In my receding years, since I have not assembled a four speed car in 40 years,(1985)I may need some members help refreshing my Memory as to what parts go where. I do have all the parts, plus a B body four speed car to refer to for help.

Unfortunately, the original engine was stolen in 1976. On the good side, the engine i have is a 5/3/68 from a totalled late year 68 GTS 383 car. So all is good!

 

[1 Wild R/T]

If you post a thread I'll be watching... FB 67-69 Barracudas are on my short list of favorites... I appreciate the power of the big block but if I were shopping it would be a 340 4 gear....