Smitty275

On a factor olds head it ends up being .0055"/CC. On Edelbrock and ProComp its .006"/CC. Believed me when I tell you that I've CC'd and milled enough heads that these numbers work out to being as close to perfect as your gonna get.
Also keep the grease sealing ring for the plexiglass as thin as you possibly can. Its easy to have .006" of grease to give you an added CC that really isn't there.

rcktdoc

If you use to much grease when you put the cover over the chamber the excess grease will sqwish into the chamber and you wont have accurate data.Also make sure that you fill the burret even with the line and not over as in the pic.
accuracy is key or it doesnt make sence to even do it.

Greg

67 Cutlass Freak

Thanks for posting that information Smitty, now I can do the math. Greg you are 100% correct. Accuracy is key or why bother doing it? As I said this was my first ever experience with doing this. It wasn't hard, but I do realize there's little tricks to everything.
So using the information we have, we believe these #6 heads were shaved .030" so .030/.0055 = 5.45
We take the stock chamber @ 70CC - 5.45 = 64.55
The current combustion chamber is 67CC - 64.55 = 2.45CC
So guys, I know my methods may not be 100% accurate, but I'm just trying to get an idea of how big of an affect polishing the combustion chamber will have on your final compression ratio. Ideally we should have measured the combustion chamber before, and after work. We're still assuming the heads had a .030" shave. The heads may have started out closer to 2.220" which would have been a .050" whack. Copper's engine has been zero decked, with flat top pistons, bored .030 over, and assuming FelPro head gaskets @ .040". So if I plug these figures into the compression ratio calculator-


https://www.rbracing-rsr.com/compstaticcalc.html


At 67CC it calculates out to be 10.62:1 ratio. That's pretty ideal for pump gas performance.
At 64.55CC it calculates out to be 10.94:1
So in conclusion this tells me just polishing the combustion chamber will result in a compression ratio drop of .3:1 that seems like a lot.
What amazes me more is how easy it is to bump the compression ratio back up by using a thinner head gasket. With the 67CC formula if we used the .025" thick Commetics that would put our static compression ratio at 11.05:1

coppercutlass

I have 3cc probes dave. That's why I got that 10.25 to 1 figure. The flat top piston engine is in my 72 right now that has the pistons sitting .025 in the cylinders. Also .030 over

Lars

I figured the cc would drop a few points after the polish, and using a thinner head gasket would loose the perfect quench (if that is actually something). A lot of people say it matters... what say you??

rootney

It's more than a quest for good quench and higher comp. You also need to observe
a min piston to head distance. A piston to head gap of .040 to .045 would be a good number for quench and piston to head clearance. A gasket of .020 would put you right where you want to be. The gap allows for piston rock, rod stretch, rod bearing clearance, etc.
It's insurance that the piston doesn't smack the head.

67 Cutlass Freak

Lars I'm not so sure we have a perfect quench with our Olds heads. In my opinion, after polishing the chamber, you're basically moving it slightly further away from the piston. By using a slightly thinner head gasket, you're just putting it back where it originally was.

67 Cutlass Freak

This is exactly why you need to be real careful with a block that has been zero decked. I'm putting together a high compression race 350 that has been zero decked, with BB heads. This is exactly why I chose to go with the thicker .040" head gasket.
113-1393_IMG.jpg

Smitty275

In dome styles of combustion chamber quench makes a big difference. On others not so much. On a chamber like the Olds which is shallow compared to most it doesn't seem to be as big a deal.

How far does the dome stick out of the block on that piston. I'd be sure to clay them all in a mock up to be sure you have clearance at all points.

Wise Performance

FYI~There are other ways to make compression other than a Mountain with sharp edges...Wow! lol

rcktdoc

Mock up your short block, put the head on it without a gasket, turn it over if you can and see where and how much contact it makes.massage the domes untill they fit each chamber without contact. Its also pretty impossible to get big compression on a small cubic inch engine without a dome unless your combustion chambers are very tiny.More so with a stock castiron head.

Greg

Wise Performance

Whats the application, Whats the desired CR, What fuel is being used are all factors considered?
Give me your engine specs and I'll do some quick math.

captjim

What are you calling "big"? Like Wise stated, there are other ways. Add a little bore, add a little stroke, do a little milling. Doing quick match, a 350 bored to 4.125 with a flat top .015 in the hole, .028 gasket, 3.5" stroke, and a 64cc head you get a tad over 11.5 to 1. How much do you need?? Not to mention the much better flame travel with a flat top, IMHO.

captjim

I'm glad someone else said it. Are you planning on de-burring those?? The whole thing looks like a nightmare in the making. No offense, but if you have never CC'd a chamber, are you prepared for the complications of running that piston? I am assuming a BIG cam goes with it. Your piston-to-valve better be right, your springs better be perfect, float a valve just a tad and it will suck a valve.

rcktdoc

13-1 and up I have done many high compression small blocks .Cutlass Freak was talking 350 cuin.

Greg

captjim

Lots of guys going plenty fast with less, but whatever works for you. Not sure the "was talking 350 cuin" means? I was talking about a 350 block and crank bored and the crank offset ground .115

rcktdoc

I have done a few 400- 406 cuin bored & stroked, to get 15-1 needed domes. Ive done plenty of small blocks with big compression. They all needed small chambers and domes. Im sure if hes got a dome as big as pictured hes looking for max compression. The dome needs to be finished and quench at the minimum or your just wasting your time.

Greg

rcktdoc

I guess it depends on what you consider plenty fast. I can build a 440 cuin small block that doesnt need domes also so whats your point?

Greg

captjim

My point is that depending on his goals, there might be an easier way to do it than those huge domed pistons and all the hassles that go with it. At some point, the heads will probably be the limiting factor.

rcktdoc

Well its completely evident that he already owns the pistons so instead of trying to reengineer his compolete project it might be simpler and cheaper for him to help him use what he has.

Greg

Smitty275

That's why I asked how tall that dome is.

cutlassefi

Seeing as how you'll need to run really good fuel anyway, I'd be much more concerned about flame travel than quench with those pistons.

rcktdoc

The flame will get there,I have run big domes like that before and made great power. Because of the flat valve angle of the olds you need to have large domes on smaller cubic inch engines with large cam shafts. The valve relief is such that it uses up a lot of ccs and you need to make up for that somewhere. They used domes exactly like that back in the day when olds was running in NASCAR.

Greg

67 Cutlass Freak

Ok guys, I appreciate all the concerns about this dome piston engine. I feel I should give you guys some back ground and details on this build. Two years ago I tried to sell this engine at a thousand dollar loss with no serious nibbles. Here's the story-------


Olds 350 High Performance short block


Back in 2004 a friend of mine wanted to build a drag car. He was fresh out of high school and worked at my shop as a clean up kid. He didn't know much about mechanicals, but he seemed eager to learn. I gave him a nice '86 Cutlass with a fresh Turbo 400 and a 12 bolt rear end. I also gave him a 1972 350 engine along with a 330 crank and some Ga BB heads. I showed him what needed to be done to port them but he didn't get too far. I finished the heads for him. I probably have close to 80 hours into them. I bought a bunch of parts for this engine and paid for all the machine work. My friend went into the military and lost interest. He came back from Iraq, got married and had two kids. The car was scrapped but I got the trans and I picked up the engine from the machine shop. I kinda lost track of how much money that I sunk into this thing, so I got out all the receipts and put together this spread sheet. The compression may be too high for pump gas, and I really think it's not going to be very streetable. My car is set up for a BB so I really have no need for this engine. The block is from 1970-1972. The crank and flexplate are original from my 1967 330. I have plenty of core heads if someone wants to purchase a complete running engine that can be arranged. For anyone who is really interested , I can e-mail all the photos taken and blue print data compiled during assembly. I will also throw in a stock oil pan, a split timing cover and an HEI distributor with low miles.
Olds 350 CI Race Engine
1972 350CI engine block core
1967 330 steel crank core
1967 Flex plate
1972 Damper
JE Pistons Custom 2300077 $680.75
Rings J100F84080-5 $100.00
Rod bearings 02-5029 $60.00
Main Bearings MS805P20 $60.00
Rod bushings 02-5029 $40.00
(2) Heavy metal slug 1”X1” $70.00
ARP rod bolt RB-200 $58.00
Freeze plug kit FP-640 $14.00
Race Cam Bearings RCB-499 $69.00
Gasket Set GS-550 $95.00
High Volume Oil Pump SP-754 $69.00
Bolt on pick up PU-3 $35.00
J&S 5 Main Halo $250.00
J&S Main Stud kit $85.00
Custom modern grind cam/ lifters $265.00
Machine Work Performed by LAM Racing Engines
Install rod bushings, Fit/ assemble rods & pistons,
final polish rod beams, Recondition rods with ARP bolts-
includes R&R bolts, machine oil relief grooves in rods,
deck block, piston height + .0001,
Balance rotating assembly, regrind crank
Rods - .020 Mains - .020, install slugs of heavy metal (mill),
Install main studs, mill for main girdle (halo) to 2.175 depth of caps
Dial bore gauge main bearing bores, low limit to middle of spec,
Final wash block and install cam bearings & freeze plugs, check main
bearing clearance and ring end gaps. Total machine shop services - $1311
Final assembly and measurement performed by Dane Lulling of
Mild to Wild Racing $400
total investment- $3825.75


So there you have it. I have decided to finish the GA heads with some Stainless steel valves and then finish with the mock up and clearance checking. I have everything parts wise needed to finish this engine. I have an MSD billet distributor, a ported Victor intake, and a Demon 850 CFM carb. Since nobody wanted to purchase this engine I'm going to break in the cam on a running engine stand and then I plan to sponsor a couple local racers to flog this engine and get some data. Mark (Cutlass EFI) set me up with the cam & it will be a race fuel only engine. Here's some data sheets on the build:
scan0001-1.jpg
Olds350cam001.jpg


Smitty this short block has been bagged in storage under my bench for the last two years. The assembler did smooth the sharp edges on the pistons before final assembly. I will dig it out real soon and do some measuring for you. The piston spec sheet sais the dome is 18CC. I find that hard to believe. I'm going to use clay to check my clearances. I was also considering making a clay casting of the dome to CC it for myself.
When I plugged in the numbers to the compression calculator I came up with 11.3:1 when using an 80CC combustion chamber. It will be 12.26:1 if I milled the heads down to 74CC. This is with a .040 gasket. I think I will need all the chamber I can get so I wasn't planning on milling.

rcktdoc

18cc sounds about right with the dome. You dont need clay just take a bare clean head casting,place it on the block with NO gasket turn the thing over and see if the pistons make contact,(which Im sure they will) you can use red dychem on the dome and that will allow you to see where contact is being made. A bit simpler than claying it. If it clears without a head gasket you should be good to go., but you still need to check and make sure the valves dont clip the valve reliefs, that will be a little trickier to make sure you have enough clearance around the valves. Domed pistons such as these are very rarely ever a throw in most of the time you will need to do some clearanceing and check ,check and check again for correct clearance .

Greg

Smitty275

No need to remove piston. Bring piston to TDC. With an indicator on it drop piston until dome is below flush. Record distance that piston was dropped into the bore. Now you can calculate the CC of the bore for that distance. Next put a little grease in the ring gap around the piston to wall for a good seal and put your CC plat on the block and CC the remaining area. Subtract that from total volume you calculated earlier and you have an exact measurement of your dome volume.

cutlassefi

That's right. But look at the difference in power output per c.i. then and now. That's why they don't do it anymore.

Wise Performance

Pretty simple to mill those mountains off to flat top and have a nice pump gas engine without any issues and you'll be suprised at the performance.
.02 carry on.

rcktdoc

Many more reasons why they dont do it. I made 770 hp and the car ran 9.50 @ 3400lb with 10" tire and 400 cuin small block with big domes in it. so I think I know what Im talking about.

Greg

cutlassefi

That's great I'm happy for you. But as usual people miss my point.
But maybe you could make 800 with the same compression, just with less dome via a different head and piston configuration. If that was the best way to go don't you think other builders would still be doing it that way? Chevy, Ford, whatever? Big domes with appropriate chambers vs flat tops and smaller chambers?
You have to do it that way because of what you have to work with, my hat's off to you. But that doesn't mean it's the best way by any stretch. That was my point.

coppercutlass

Diffrent strokes for diffrent folks. More than one way to skin a cat .

rcktdoc

And what Im sayin is sometimes you just have to play the cards your dealt.

Greg

cutlassefi

Hmmmm I'm pretty sure that's what I said, but it's not necessarily the best way.

67 Cutlass Freak

Best, or not it's what I'm stuck with. I do have a lot of cash tied up in this motor and it's really not doing any body any good sitting under the bench. So I say pull the pin and let's see if this rocket will fly or grenade. Thanks for your input guys - Mark, Greg, Smitty. I had thought about having the tops machined down a little. Who knows maybe I will still. The ProComps might work better with a bigger chamber. I really don't want to put any more money into this thing. Mark, Jeremy was asking what kind of vacuum this engine might have with that cam. Do you have any projections?

380 Racer

You have to remember piston-valve clearance with any piston. Just because it doesn't hit the head......doesn't mean it clears the valves. Not all domes are created equal. That's why you send the manufacturer a mold so you get the slugs you want/need.

rcktdoc

I never said it was the best way its just the way it is.

Greg

Smitty275

So far no one has posted anything wrong. But some aren't taking into consideration the era of what was done and when. The ability to take a mold of the chamber and send it to Diamond, have them scan it in, run it through a combustion analysis, and design the best possible piston top for the desired compression ratio, is really not all that old of a technology. From mold to finished piston in 7-10 days now. I can remember when they put them in a CMM and probed the mold to get the chamber shape and will worked from there and it took a while. Before that they cut it close and you had to finish it to the chamber on your own. A lot has changed in just the last 5 years. Probably more change in the last 5yrs than the 15yrs before them.

Smitty275

They can even hard coat a piston that you won't melt through on a lean N2O tune. Though something else most likely will give way. That was unheard of a couple of years ago. True N2O tuners no longer read the plug to see how much aluminum has transfered to it. They use a safe tune and go from there by the clocks & mph to know if their getting it right.

67 Cutlass Freak

Greg what ever happened to your iron Batten headed engine? That thing was a beast. It's been a while since you've posted up any progress on your race car. I know you've been real busy with restorations. The last thing I saw about your car, you were working on the frame in the back, for a mini tub. How's it looking? Do you think you'll hit the track this year? We met at Alston's when my chassis was being built.


Dave

rcktdoc

The 69 is sitting in the back of the shop. Dont think it will be out anytime soon.
Been trying to finish my 69 post 442 but trying to find the nos parts to complete has been tough, havent work on it for about 7-8 months.Still have the engine from the 69 .

Greg