Engine Build Tech Help

[HTMLmopars]

So I'm trying to rebuild a 318 to throw into my Valiant. I've posted a couple other threads about this build and this is the latest update with me feeling like I'm either in over my head, or just got too excited about parts and didn't spec the correct parts.

Basically I picked up a .020" over 318 block for 800 bucks, it came as essentially a disassembled long block with a ton of parts. Freshly machined, new cam bearings. I've verified that the machine work is a consistent .020" and am fairly confident with the bearing side of the equation in terms of mains and rods. The block came with .020" over KB167 pistons and Hastings rings, as well as mystery rings installed onto stock replacement .020" over pistons.

Right now I'm a bit stuck designing the engine, I figured that my '69 block I was running before had about 9:1 compression or thereabouts, so I figured a bit more was a bit better. I'm reusing the heads from the old motor, they measured out to 63cc. Per my thread about ring gap a few days ago, it came up that my dynamic compression ratio might be too high to run iron heads and pump gas, so now I'm second guessing myself.
Hastings Ring Gap?
I have a Hughes engines hydro roller cam to put into the motor, I failed to break in my cheap cam swap earlier this year, so I decided it was worth my money to not worry about breaking in a cam. PN: HUG SER1822ALN-10. Since the only numbers I have for this cam say it intake close is at 35* ABDC, I plugged that into the dcr calc. With the static compression ratio right around 9.0:1, I am getting a dcr of 8.4:1 at sea level (I will be able to drive the car to the ocean, so this is a realistic worst case).
According to the wisdom of the forum (and I don't mean that jokingly, most of the advice I'm getting is coming from guys who have been building motors longer than I've been alive) I want to see less than 8.0 dcr. I might be able to get there by moving cam timing (assuming piston to valve clearance is sufficient), or by changing my build path to the stock replacement pistons.
Any guidance on what the best path forward is? Goal is for a fun cruiser that I can occsasionally take to the autocross, so pump gas is important, and I'd rather have the car be driveable than super highly strung and hard to tune.

 

[MOPAROFFICIAL]

Sounds like you picked all the parts and pieces.
8.4 dynamic, 87-89 octane motor. Nice.
I don't mean to sound like this.. but whoever told you that you want to build an 8.1 dynamic or lower... is a...eh.. 'someone you shouldn't listen to'.

I edited out '******* idiot' to be considerate.

 

[67Dart273]

Have you CC'd the block? Or measured piston height? Do you KNOW whether the block has been decked? That will also affect compression ratio

 

[HTMLmopars]

Have you CC'd the block? Or measured piston height? Do you KNOW whether the block has been decked? That will also affect compression ratio

Block hasn't been decked, kb pistons measured .030 in the hole which was part of my 9:1 calc.

 

[HTMLmopars]

Sounds like you picked all the parts and pieces.
8.4 dynamic, 87-89 octane motor. Nice.
I don't mean to sound like this.. but whoever told you that you want to build an 8.1 dynamic or lower... is a...eh.. 'someone you shouldn't listen to'.

I edited out '******* idiot' to be considerate.

What kind of guidance on dcr to octane requirement is there? Rule of thumb on that?

 

[MOPAROFFICIAL]

What kind of guidance on dcr to octane requirement is there? Rule of thumb on that?

8.4 if you dont wanna a "fussy" motor is fine.
You have bozos telling you what they've run but I'll just tell you what works not about what I run because what I run might not be what you want to run but basically anything after 8.4 dynamic becomes a delicate animal on '91 octane' . Whatever the instructions for the Piston Ring Gap say I would probably add another .005 to it for good measure.
So if you're going to get them at say .029 to .030 ...may as well just go .034
When hyoereutectic pistons are exposed to pre detonation and damage themselves... you'll hear a clack noise upon said predetonation. There's the typical ping but with these there's not much of that before you get to that clack and that's a ringland coming off as you do with too tight a ring gap. Say you have one cylinder that's lean and lightly touching pre detonation and you don't really hear it but it gets that cylinders piston and ring even hotter than normal and the 'just enough' clearance becomes not enough..then it pops a ring land and gets into the valve or closed chamber then the entire piston SHATTERS...that's kind of where I'm going with that.
So 8.4 is great.
If the Cam's the right cam I would put it in straight up too if it closes at 35 or 36 make it close there.
If you want to get tricky like some of us who account for chain stretch you could put a degree or two into it remember those timing chains stretch ...and when they do..they retard.

 

[Ted265]

I have a Hughes engines hydro roller cam to put into the motor, I failed to break in my cheap cam swap earlier this year, so I decided it was worth my money to not worry about breaking in a cam. PN: HUG SER1822ALN-10. Since the only numbers I have for this cam say it intake close is at 35* ABDC, I plugged that into the dcr calc. With the static compression ratio right around 9.0:1, I am getting a dcr of 8.4:1 at sea level

Hang on - the Hughes cam timing is at 0.050" lift, the valve will not be closed at 35* so it will be inaccurate for DCR calculations. Call Hughes they should be able to tell you what the actual closing point is if the 0.006" timing is not printed on the cam card.

 

[dano]

Block hasn't been decked, kb pistons measured .030 in the hole which was part of my 9:1 calc.

Did you add the head gasket thickness as well? For your "in the hole" measurement, was that takes from the short block assembled? Are your heads closed chambered?

 

[HTMLmopars]

Did you add the head gasket thickness as well? For your "in the hole" measurement, was that takes from the short block assembled? Are your heads closed chambered?

Gasket thickness included, heads are open chambered. Piston measurement was taken with the old bearings I received the block with, rod and main bearings just snug, not torqued.

 

[HTMLmopars]

Hang on - the Hughes cam timing is at 0.050" lift, the valve will not be closed at 35* so it will be inaccurate for DCR calculations. Call Hughes they should be able to tell you what the actual closing point is if the 0.006" timing is not printed on the cam card.

Hughes says 35 dABDC is the actual closing point
Edit: have seen some articles that say to add 15* to a .050" lift point. That math gives me 50* and 7.99dcr

 

[mgoblue9798]

Sounds like you picked all the parts and pieces.
8.4 dynamic, 87-89 octane motor. Nice.
I don't mean to sound like this.. but whoever told you that you want to build an 8.1 dynamic or lower... is a...eh.. 'someone you shouldn't listen to'.

I edited out '******* idiot' to be considerate.

To be considerate? Looks like someone has hijacked your account.

 

[Ted265]

Hughes says 35 dABDC is the actual closing point
Edit: have seen some articles that say to add 15* to a .050" lift point. That math gives me 50* and 7.99dcr

The 15* is generic and will depend on the ramps on that lobe, but will be more accurate than the 35* you were using.
Here's an example of a hydraulic roller from howards - 50* between 0.006" & 0.050" lift, so 25* each side of the lobe. Yours could be a bit more or a bit less, but if the 0.006" timing is not printed on the card you would have to measure to be sure.

 

[mgoblue9798]

So I'm trying to rebuild a 318 to throw into my Valiant. I've posted a couple other threads about this build and this is the latest update with me feeling like I'm either in over my head, or just got too excited about parts and didn't spec the correct parts.

Basically I picked up a .020" over 318 block for 800 bucks, it came as essentially a disassembled long block with a ton of parts. Freshly machined, new cam bearings. I've verified that the machine work is a consistent .020" and am fairly confident with the bearing side of the equation in terms of mains and rods. The block came with .020" over KB167 pistons and Hastings rings, as well as mystery rings installed onto stock replacement .020" over pistons.

Right now I'm a bit stuck designing the engine, I figured that my '69 block I was running before had about 9:1 compression or thereabouts, so I figured a bit more was a bit better. I'm reusing the heads from the old motor, they measured out to 63cc. Per my thread about ring gap a few days ago, it came up that my dynamic compression ratio might be too high to run iron heads and pump gas, so now I'm second guessing myself.
Hastings Ring Gap?
I have a Hughes engines hydro roller cam to put into the motor, I failed to break in my cheap cam swap earlier this year, so I decided it was worth my money to not worry about breaking in a cam. PN: HUG SER1822ALN-10. Since the only numbers I have for this cam say it intake close is at 35* ABDC, I plugged that into the dcr calc. With the static compression ratio right around 9.0:1, I am getting a dcr of 8.4:1 at sea level (I will be able to drive the car to the ocean, so this is a realistic worst case).
According to the wisdom of the forum (and I don't mean that jokingly, most of the advice I'm getting is coming from guys who have been building motors longer than I've been alive) I want to see less than 8.0 dcr. I might be able to get there by moving cam timing (assuming piston to valve clearance is sufficient), or by changing my build path to the stock replacement pistons.
Any guidance on what the best path forward is? Goal is for a fun cruiser that I can occsasionally take to the autocross, so pump gas is important, and I'd rather have the car be driveable than super highly strung and hard to tune.

From what you have posted in this thread you have a good combo. With a good tune you will not have any issues running low grade pump swill. Just make sure you set the piston ring gap to whatever KB says is needed for their pistons for your intended usage.

 

[Bewy]

In my opinion, the DCR calculation is about as useful as a sun roof in a submarine.....
A myriad of factors are going to affect the weight of air drawn into the cyl, & the weight of air that will be compressed by the piston will determine the actual or running comp ratio.

 

[rumblefish360]

In my opinion, the DCR calculation is about as useful as a sun roof in a submarine.....
A myriad of factors are going to affect the weight of air drawn into the cyl, & the weight of air that will be compressed by the piston will determine the actual or running comp ratio.

It’s a minor help IMO. For some, it’s a big thing. For decades it was never used or thought about when we did our engines. We were told and just knew by being told or making the mistake as it was, that a certain static would work well with a certain advertised duration. If your engine was pinging on 87, move up to 91/93 and not worry. Bigger cams required bigger compression. The old timers had it figured out really well and passed on that knowledge.