Hey just wondering if someone could stupid check my Compression Ratio maths.
Standard 350ci
Bore 4.00"
Stroke 3.48"
Rod length 5.7"
Combustion chamber vol 64cc
Deck height is pretty dead nuts flush I'm using a measurement of 0.0" for calculating purposes
Pistons have four eyebrow reliefs totaling about 1ci if I remember correctly.

Head gasket is a C5331-066
Thickness 0.066"
Bore 4.63"
Volume 1.1121/cylinder

STATIC C.R. 9.61:1

For dynamic CR
Comp cams 12-242-2
Adv dur 268/280
@.05 224/230
IVC 61 ABDC
IVO 26
EVO 72
EVC 27

LSA 110

When converted to 0.05 because it's a comp cam and they measure from 0.006.

IVC @0.05 38
IVO @0.05 6
EVO@0.05 49
EVC@0.05 1

Dynamic CR
8.32:1

Hoping this is in the limits for 91-93 octane with aluminum heads and a 180 thermostat.

I used gofastmath for most of this

I also realized recently that I have a non computer controlled cam on my 85 which now had a Holley stealth ram...not sure how much issue that will be. Worst comes to worst I'll pull the block back out and throw the equivalent comp XFI cam in it. Probably go with a roller cam at that point cause why not. So probably the comp XFI 218/224

 

I think you may have a few values that are incorrect.
Piston valve relief volume is more like 5cc. I've never seen a 1 cc piston top for a Gen 1 SBC.
The head gasket you've listed is for a big block Chevy.
If you're piston below deck is truly zero, then there's been some previous work done on the block. But let's go with zero. Minimum piston to head clearance is generally held to .040" so with a zero deck you want a .040" gasket.
That gets you about 10.25:1 SCR.

 

DCR can only be calculated from the advertised numbers (or in Comps case .006"). That's when the intake valve is closed (or very nearly so) and cylinder pressure can start to build.
Use the specs as listed, which are 268/280 with a separation angle of 110 degrees. If installed with a 106 intake centre line you have an intake valve closing of 60 degrees ABDC.
DCR works out to 8.46.
I suspect you'll find that a little difficult to manage.

A littler light reading for you if you're interested.

http://members.uia.net/pkelley2/DynamicCR.html

 

My 383 is well over that but it is SFI, has a LS computer and a massive cooling system that keeps it under 180°F. I tow a travel trailer while moving a 6,500 lbs Express van with it though. It also has 0.041" quench and a well tweaked timing curve with dual knock sensors.

I have however run 8.4:1 (10.4 static) with iron heads and a Q-Jet. 355 with 52cc 601 heads and a small 268/268 cam cut on a 106 LSA. Never knocked on 87. Takes a carefully planned advance curve, good quench and keeping it cool to work out.

 

[QUOTE=Fast355;6437219] Takes a carefully planned advance curve...]

That's the thing right there.
I like to tailor my advance for maximum output and don't want the risk of detonation.
If I feed it premium fuel I want to give it as much advance as it will handle before power no longer increases. If I can achieve that on regular grade gasoline, then that's great. But more than likely, with the higher compression, premium is required to keep it out of knock while utilizing a full curve. Not unlike locking it out at say 34 degrees for maximum output on premium, but only managing 30 before knocking on regular gas. That's power lost right there.

I've experimented with high DCR and was forced to dial back on the timing. There is a noticeable lack of output. From that I've determined, in my case anyway, is that timing is worth more than chasing a half point of compression.

One thing though, the higher compression can deliver better fuel economy and that's where a carefully crafted advance curve really comes into play.

 

[QUOTE=skinny z;6437259]Less timing does not necessarily mean less power with a different octane. Higher octane burns more slowly. Longer burn time means more crank degrees of negative pressure on the crankshaft before the piston hits TDC.

 

I also get 9.61 static compression but that's a big block gasket, wrong for your engine.
7.74 dynamic. Intake valve closes around 64° ABDC (at 0.006" lift).

Need to get the correct gasket and redo calcs. Will probably have a significant effect on compression ratio. Tight quench creates a better burn. Run the tightest quench you can safely run to improve tolerance to compression and resistance to detonation.

 

Rogue, if you use the specs you listed and enter -1cc for the piston head volume, I get the same 9.61:1 static compression that you did (and Qwk)– so your math looks OK, but some of the numbers you used are off.

You’re going to need to double check the piston head volume to properly calculate your compression ratio. If truly as you indicated as -1ci (cubic inch) that’s -16.4cc. Most 350 flat top 4-valve relief pistons are -6 or -7cc but they make 4-valve relief dish pistons, so I guess there is the potential for the volume to be -16.4cc?

Also as others pointed out the gasket you listed is a big block gasket. So, if you assume a zero deck height and 64cc heads, using a cost effective performance Felpro 1003 head gasket (4.166”bore .041” compressed thickness) and the 12-242-2 cam (110 spread +4advanced as recommended by Comp):
SEAT ----- .050
IVC 60 --- IVC 38
IVO 28 --- IVO 6
EVO 74 –- EVO 49
EVC 26 –- EVC 1

-7cc flat-top piston --- 9.94:1 static / 8.39:1 dynamic (using advertised)
-16.4cc dish piston --- 9.00:1 static / 7.61:1 dynamic (using advertised)

You’ll have no worries at all with that cam if it’s a flat-top 350 with the HSR – especially if you’re able to adjust the timing table yourself with the computer controlled ignition. I ran a 218/228-110 cam (installed 2-degrees advanced) with a HSR on top of a flat-top 355 with aluminum heads and was able to run a fairly aggressive timing table on GOOD 93 octane pump gas (170-degree stat). It ran 12.6s in 85-degree temps and 12.3s in 48-degree weather with the stock chip using just fuel pressure and base timing adjustments. It ran a good bit better (I’m going to guess at least .2-seconds better) after I played around with the timing tables and tip-in fueling, but I never got back to the track before selling it. Bumping up the timing at idle it had a mild bump to it at 750rpm.

 

I really appreciate all the input. I figured I boogered some of the maths and overlooked things. The eyebrows I measured like 5 years ago using a CVS brand graduated dropper...an extremely accurate method I am sure.
It may have been approximately 1cc/ eyebrow...which would match up more closely to what you all have been coming up with. That will widen the error margin quite a bit.

Also thank you for pointing out the HG error. I'll send that one back when it gets here or eat the cost (shrug).

I'm gunna rework the numbers and try to find a 040 head gasket with a decent volume. I had completed blanked that you could use the timing as well in this.

It's my first build so that's my excuse.

 

Happens all the time. Even to more experienced builders.
I would double check the piston below deck height. Unless the block has been machined, it's not likely to have a zero deck. Work your .040" piston to head clearance based on that. Rough dimension from the factory is .025" plus.
And I'd still go back over the 1cc piston eyebrow volume too. There's not a listing I can find for a piston with 1cc (other than the LS variety).
EDIT: Unless your meaning that each eyebrow measured 1cc. And then that would be x 4.
Much better.

 

Well. At least I'm in good company...
Yes, the edit is correct. Approximately 1cc per eyebrow. Now that I think about it, it sounds right. It's just been too long since I made these measurements.

The block was pulled 7 years ago (this went on the back burner several times) from an 88 suburban. The cylinders showed hone crosshatching. This was consistent with what the guy said about it being put back together recently with some machining work. So it is POSSIBLE that the block has been machined to zero deck clearance or close to it.

But my AFR heads showed up today...about 8 weeks ahead of schedule. So I'm tearing it down. I'll throw some sort of straight edge on it and try to slip a feeler gauge under it for a measurement.


Re-reading the comments about ignition tables. It looks like tweaking ignition tables that's another thing I get to learn how to do. Should be able to get it moving under its own power till then with base timing.
It's also an 85 so it has the super slow baud rate...so that'll be fun.

 

The feeler gauge technique works pretty good. It's nice to have a dial indicator so you can nail TDC precisely. Measure parallel to the piston pin so you don't have piston rock messing you up. On my original late 70's casting, I found the piston deck varied from .026- .036. So don't surprised by what you might find.

Which AFRs did you get?

 

That makes sense to measure across and not vertical. It would also make sense if I actually measure across all the piston to head clearances. Not just one.

195cc enforcer heads. https://www.summitracing.com/parts/afr-1001

Seems like a good deal for an as cast head with a brand I can trust.

 

Seems an interesting option from AFR. Plenty of talk about them web-wise. Looks to be a 500 HP capable cylinder head with the right complement of parts. I had to port my aftermarket Vortec castings to get similar flow numbers and that's my HP target (or thereabouts).

 

They seem to flow pretty decent for an entry level option with room for port and higher lift flow. Especially for the money. That's the kinda around price point for the cheap Chinese made aluminum heads.

I'm at the point where if this car moves under its own power after this I'll be happy.
Realistically I'm expecting 350-400 at the crank...and it's what? 20ish% parasitic loss to the wheels. So like 300ish to the wheels.

Which going from an 85 tuneport of like 215hp will be substantial.

 

You'll be limited on output with the cam but still 350 at the crank should be doable.
Next step will be to invest in a roller setup as you mentioned.

FWIW. With a stock Vortec head which is arguably about 220 CFM, it took 276(adv), 224 @ .050, (Comps XR276HR) to get my heap into the 12's. Estimates were about 330 to the tires.
Possibly less.

 

Yeah. I'd say those eyebrows are at least 1cc.

 

​​​​​​I'd say you probably have another 12cc is piston dish too.
What engine was that originally? L31? L98?.

 

FTR: This is a 5cc piston.


That particular engine was an original 4.00" bore with new aftermarket Speed Pro pistons. They were .030" below deck. With a 64 cc head and an .026" head gasket, compression was spot on 10:1.

 

OUCH. .056" quench.
But besides cutting the deck surface, there is not much else can you do.
Those rebuilder pistons assume that the decks get at least a clean-it-up cut.
The steel shim HG is only .015 thick.

 

That's not a rebuilder piston. It's a Speed Pro hypereutectic with a 1.560" compression height.



That deck is straight from the General. Block was a NOS 350 from a truck that had sat undisturbed in this guys garage from 20 years before I bought it (he was a auto shop teacher that plucked it from a donor vehicle to the local high school way back then). Then off to the machine for flat tops (to replace the crappy dished castings) and a general clean up. Did yeoman service for many years. A hundreds and hundreds of "drag strip" passes if you know what I mean.

Anyway, yeah, that was a brutal quench. A word, that when this engine built about 25 years ago, pre-dates the internet and all the buzzwords that are part of the lexicon today. Still, it was one of the best low buck engines I've ever been a part of. Eventually it ate a flat tappet cam and several lifters. One rebuild later, it milled the mechanical fuel pump eccentric off the cam (never seen anything like it before or since) and that put enough metal into the engine that it never recovered. Expensive too.

 

I have never seen the mechanical fuel pump eccentric get eaten.
But I have had camshaft shrapnel get circulated throughout the engine.
That trashes EVERYTHING.

 

First the cam and lifters went flat. That meant a crank cut, new bearings and an .020" overbore. Plus an oil pump. Not to mention a new cam and lifters and finally went retro-roller. The rest I washed and put into service.
Then the above happened. That took out what was left of the lifter bores and I couldn't keep them pressurized. Also mangled a couple of lifter internals. Eventually sold the short block off.
Live. Learn. Break other stuff.

 

WOW, just WOW.
You didn't find bits of cast iron imbedded in your piston skirts?
I sure did, but my pistons were KB Silv-O-Lites.
Hypereutectic with a surface hardening treatment.
That allowed me to pluck the cast iron out using a razor blade held 90 degrees to the surface and dragging it along the skirts.
I brought them to my machinist to inspect and he found nothing wrong that would prevent them from being reused.

 

That fuel pump lobe wipeout came after the cam lobes themselves went flat. So that was after all of the machining (.020" bores and 10/10 crank, etc). Different cam obviously And a new roller at that. But after the fuel pump lobe went away, I found that I couldn't keep a few lifters adjusted. A little post mortem revealed that the metering discs in the lifters had been sandblasted into almost nothingness.
​​​​​​So, all new rollers all around (Comps tool steel short travel versions) and I still couldn't get the engine quiet. My thinking is that the lifter bores took a beating too.
I didn't do any disassembly on that one. Just scrapped it and moved on.

 

Remember (when we were young and stupid), we just threw a new cam (and not necessarily all new lifters) into an engine where the camshaft failed?
No cleaning out the block or anything. We all figured that the oil filter would trap the debris. No cam lube, no 20 minute break-in, and sometimes not even an oil change. And it worked. How did we ever get away with that?

 

I was fortunate in that in my early days I had the very best of shop teachers both in high school and my auto technology college courses.
The high school teacher literally wrote the text book for the course corriculum.
College professors, in particular my engines teacher, were racers at heart. One fellow was racing V4's made from cutting a SBC in half. He helped with my first go round with "fuelie" heads. Another convinced me, when I proposed using a 350 crank in my new to me 400 block, by saying that if you want to go fast on the street, put the largest engine you can between the fenders.
Great people.
I was lucky that a lot of the mistakes other kids were making were things I learned not to do. Just like breaking in the cam you mention. Or drilling steam holes in those fuelie heads to put on the 400.
But now that I'm old and stupid, I can ignore all that good advice and break stuff all the time. Which I do.

 

I'm not sure of the specific engine code.
I did a bit of digging and this block is setup for a factory roller cam. So I'm puttin a roller cam in it. It's giving me almost a full 0.1 of lift with about the same duration. Bumping crank HP estimates to the 400hp mark. To be seen of course.

If I can do all the supporting stuff I need to get done alongside this.

I appreciate everyone's input on the math. I selected a head gasket about 0.036 thick and 4.2. calculator showed that to be about a 8.3 dynamic. Which should be manageable.

Hope to have this thing started before snow falls, but I've said that for 7 years running now.

 

I'm still thinking you might not have all of your measurements sorted out.
That piston in your picture is a minimum 12 cc dish.
And unless you've revisited and confirmed your piston below deck height, I'd say your .036" choice for a gasket is almost twice as thick as you might use otherwise.

Can you lay out what you've got so far?

 

A couple of screen shots showing SCR with a 12 cc piston and two different decks.


This is a zero deck
--------------------------------------------------------------------------------------------------


This is a "factory" deck

The above is using the spec'd .036" x 4.20" head gasket.