383 build?

[Gary Stavely]

Hi I am getting my 67 383 built and I was trying to get close to a magnum in performance.
I have 915 heads but they are 1.6 exhaust valves, I know they are not the best but I think they will be fine for my purpose. I have a 1968 -69 4bbl intake, edelbrock 650 avs2 carb, a melling class 2 camshaft, and hp manifolds
I am in the process of rebuilding right now but my engine is going to be put together with silvolite 1271 pistons, this has got me a bit worried as I kinda wanted speed pro 2315's for the higher compression.
I am just a bit worried about the silvolite's being de stroked and too far in the whole? I just really just want a good running engine and maybe I am better of with the silvolite pistons but I don't want to suffer in performance at the same time...
Anyone got any suggestion? Probably not the only one using these pistons so any feedback would be great.
Thx!

 

[F4R/T]

Compression is a good thing no need for a tractor engine unless your going forced induction. A cam will play a big role in bleeding compression to a reasonable level. I prefer the forged piston to the cast/ hyperutectic. Bump the squeeze to a 93 octane level . Just remember it’s a package not a just one item it all must work together otherwise use big cam on a low comp engine stinks= unhappy owner. At the minimum I would shoot for stock compression ratios. 1970 I think the piston was down in the hole more than earlier. Call Bob Karaksian aka Mr. Six Pack he is sharp.

 

[PurpleBeeper]

"In general"
1. You don't need forged pistons without nitrous/blower/turbo
2. With lower compression, a cam with less "overlap" helps
3. With a small exhaust valve, a cam with more exhaust lift and/or duration helps

 

[Challenger340]

Hi I am getting my 67 383 built and I was trying to get close to a magnum in performance.
I have 915 heads but they are 1.6 exhaust valves, I know they are not the best but I think they will be fine for my purpose. I have a 1968 -69 4bbl intake, edelbrock 650 avs2 carb, a melling class 2 camshaft, and hp manifolds
I am in the process of rebuilding right now but my engine is going to be put together with silvolite 1271 pistons, this has got me a bit worried as I kinda wanted speed pro 2315's for the higher compression.
I am just a bit worried about the silvolite's being de stroked and too far in the whole? I just really just want a good running engine and maybe I am better of with the silvolite pistons but I don't want to suffer in performance at the same time...
Anyone got any suggestion? Probably not the only one using these pistons so any feedback would be great.
Thx!

Don't do it..... STOP !
I did some quick rough calculations and you are coming in around 8.26:1 CR in the real world even with the closed chamber 915's.... which depending upon criterions may start, idle and drive.... but you can FORGET anything even remotely close to a 383 "magnum" performance.
Bottom line is you need more cylinder pressure to attain anything even remotely decent midrange Torque characteristic with the relatively short stroke 383(3.38")

Most 915's after rebuild will CC around ~80's CC's
Composition style Head Gasket ~10 CC's
Silvolite 1271 will be around .085" down hole at TDC ~19.5 CC's
TOTAL Clrc Volume of around 109.5 CC's
.030" over bore383 of around 795 CC's
If you proceed as planned you are going to attain a 8.2:1 Engine that can not get out of it's own way with poor quench too boot.

IMO, you are well advised to wait... and save until you can afford a far better Piston offering to do things properly.

 

[Challenger340]

Step #1
CC your 915 Heads to acquire an accurate volume.
Don't listen to friends.... don't listen to keyboard cowboys(even me).... don't read/listen to what books say or any 'published' data on what the 915 Heads should be.... and don't listen to some dumbass NAPA store style so-called .machinst'
do this for YOURSELF.... and GET THE 915 HEADS CC'd ! or go BUY a damn burret for $15

Step #2
Armed with an accurate 915 Cylinder Head Volume in CC's..... now go select a correct style Piston, the KB162 comes to mind here ? and they will cost more.... however I highly suspect that once you have an accurate CC measurement on your 915's ? you will be lucky to attain even 9.5:1 CR with the KB162's ?

The pain of NOT doing the above will forever haunt you long after the glee of saving diddly-squat using the WRONG Piston right now !

 

[1 Wild R/T]

As Challenger340 said STOP!!! Your right to be concerned & you won't be happy with the engine built with those pistons....
I don't get why machine shops continue push low compression pistons the why they do...

 

[Challenger340]

Speed Pro 2315's with no Valve reliefs can be a PITA if using any Camshaft lifts approaching .500"

As Challenger340 said STOP!!! Your right to be concerned & you won't be happy with the engine built with those pistons....
I don't get why machine shops continue push low compression pistons the why they do...

IMO, because it's cheap and easy 'quick buck' turnaround ? That.... and they really dunno any better ?

 

[1 Wild R/T]

Speed Pro 2315's with no Valve reliefs can be a PITA if using any Camshaft lifts approaching .500"


IMO, because it's cheap and easy 'quick buck' turnaround ? That.... and they really dunno any better ?

That's always been my assumption but it really doesn't say much good about the industry when guys who build engines don't at least do the math on enough combos to see what they are actually selling...

 

[Gary Stavely]

Step #1
CC your 915 Heads to acquire an accurate volume.
Don't listen to friends.... don't listen to keyboard cowboys(even me).... don't read/listen to what books say or any 'published' data on what the 915 Heads should be.... and don't listen to some dumbass NAPA store style so-called .machinst'
do this for YOURSELF.... and GET THE 915 HEADS CC'd ! or go BUY a damn burret for $15

Step #2
Armed with an accurate 915 Cylinder Head Volume in CC's..... now go select a correct style Piston, the KB162 comes to mind here ? and they will cost more.... however I highly suspect that once you have an accurate CC measurement on your 915's ? you will be lucky to attain even 9.5:1 CR with the KB162's ?

The pain of NOT doing the above will forever haunt you long after the glee of saving diddly-squat using the WRONG Piston right now !

Thank you ! I was under the same impression but thanks for doing some quick math.
The heads have been rebuilt before so I think it is imperative we cc those heads. I am not sure why those pistons were ordered because he knows what CR I am wanting to obtain,
I will have a talk with him and find out the justification for wanting to use them.

 

[Don Frelier]

Just to give you some idea.
I have KB162's in my Charger my piston depth was about 0.025" on my 66 block I built a calculator in Excel to do this.
Assuming that number and an 80 cc head I come up with 9.0 : 1.
Cutting the head could be an option if you'd like to go higher, note that you can somewhat adjust your quench height milling the heads as well.
But to repeat you really, really need to measure everything the calculation is simple.

 

[Gary Stavely]

Just to give you some idea.
I have KB162's in my Charger my piston depth was about 0.025" on my 66 block I built a calculator in Excel to do this.
Assuming that number and an 80 cc head I come up with 9.0 : 1.
Cutting the head could be an option if you'd like to go higher, note that you can somewhat adjust your quench height milling the heads as well.
But to repeat you really, really need to measure everything the calculation is simple.

Thanks! I have looked at all my piston options and I am really looking at the speed pro L2315 nf, the CH is 1.920 and if they will work they advertise 9.77 :1 compression ratio with the 78 cc heads. I really want to get my heads cc'd but I think this will work and work well enough.

 

[Don Frelier]

You should think about an aluminum dual plane intake as well.

 

[Gary Stavely]

You should think about an aluminum dual plane intake as well.

Kinda trying to keep that stock look, I have the good 69/69 4bbl intake (can't remember the number off hand) but it's supposed to work very well.

 

[PurpleBeeper]

I'm with Don, but it's up to you. Many aluminum intakes offer surprising increases in horsepower and they don't "look" aluminum once painted.

 

[Gary Stavely]

Speed Pro 2315's with no Valve reliefs can be a PITA if using any Camshaft lifts approaching .500"


IMO, because it's cheap and easy 'quick buck' turnaround ? That.... and they really dunno any better ?

I am assuming you are saying the 2315 can be a PITA because of clearance issues? My cam is .444 int .466 exhaust , to me these pistons seem like the logical available choice to reach the right compression level.

 

[monaco66coupe]

any time you can lose weight on that engine is a good thing.

 

[1 Wild R/T]

Well with a cam that size if you truly get the head cc's down to 78cc & a true 9.77 C/R with iron heads your gonna need good tuning & good fuel or your gonna have detonation trying to destroy what you built... And as was mentioned no valve reliefs means a bigger cam will cause clearance issues...

My 383 has 915 big valve heads, I cut them .040 which took them from 82cc down to 74cc... I'm running the KB-162's, not by choice but I built the engine back in 95 & there wasn't many options
According to the Diamond Piston compression calculator using accurately measured numbers I have a true 9.6 C/R... I. run more cam then your looking at which helps bleed cylinder pressure & on hot days (above 90 degrees) if I'm being stupid the engine will detonate... I run what California calls premium, you may have better fuel...

 

[Gary Stavely]

Well with a cam that size if you truly get the head cc's down to 78cc & a true 9.77 C/R with iron heads your gonna need good tuning & good fuel or your gonna have detonation trying to destroy what you built... And as was mentioned no valve reliefs means a bigger cam will cause clearance issues...

My 383 has 915 big valve heads, I cut them .040 which took them from 82cc down to 74cc... I'm running the KB-162's, not by choice but I built the engine back in 95 & there wasn't many options
According to the Diamond Piston compression calculator using accurately measured numbers I have a true 9.6 C/R... I. run more cam then your looking at which helps bleed cylinder pressure & on hot days (above 90 degrees) if I'm being stupid the engine will detonate... I run what California calls premium, you may have better fuel...

Ya I am in Northern Canada and we never see Temps as high as you do, 94 octane is still readily available around here and the car won't be driven much past maybe a couple thousand kms per year once it is done.

 

[monaco66coupe]

With the KB162 and 906 heads what has to be done to be as close to 10.0 as possible? KB says 10.2 @72cc,,,,9.4@80cc, 9.0 @85cc

 

[1 Wild R/T]

With the KB162 and 906 heads what has to be done to be as close to 10.0 as possible? KB says 10.2 @72cc,,,,9.4@80cc, 9.0 @85cc

Well since 906 heads come in around 88-90cc And KB's advertised numbers are "Optimistic" 906 heads & 10-1 with the KB-162 isn't gonna happen....