Chamber size for large log on weekend driver? 50cc?

Well in a dumb move I managed to crack the intake manifold on my 2v-direct mount large log head for my '66 200 block... so while that's off at the shop to be repaired I figured I might as well mill the head a bit to get higher compression and see if I can get a little more power out of it. Is 9.5:1 still considered the high end for a reliable street car? I'm fine with using 91 gas.

The bottom end is a fairly stock rebuild, .030 over. If I did the calculations correct than with a Victor gasket (.044) I'd have to go to 47cc's to get there, and that seems like a lot to me. 50cc's would be 9.1:1, but not really high performance.

For the formula I used the stock numbers from the tech page and a 3.71 bore size. I wasn't sure what to use for piston dish size, because it says 6.5 or 13.. I picked 6.5. I believe the pistons I have are Enginetech, and it was whatever was considered OEM replacement by the builder.

Any advice?

-Nick

Howdy Nick:

With a stock cam at sea level (or close) 9.5:1 is pushing it a little. With 91 octane it should be OK. What trans.

13 cc pistons are for Calif/em engines with a lower advertised CR. All other 200s use the small dish of 6.5 cc.

So, What is your elevation? What Cam? What transmission?

Also, since the head is off and likely disassembled for repair, consider having the intake valves back cut for a little more performance.

Waiting to hear.

Adios, David

Ah good to know, this is an east coast car, so 6.5 then.. I'm basically sea level here (maybe 100-200 ft), running a '66 C4 with a '67-69 valve body and shift kit, and a COMP Cams 260H cam.

Thanks for the tip on the back cut, I'll ask the machinist about that. The head had some work done on it by the previous owner, so it actually might have already had that done... It has oversized valves, viton seals, dual springs with dampers, and some mild polishing at least.

Is there any low-mid range advantage with getting the 1.6 ratio rocker arm while it's apart too? Or is that mainly for top end power?

The piston compression height will actually be 1.50" instead of 1.511" listed. Both SilvOLite and Keith Black check in at 1.50". If you had the deck milled when it was bored, that will change things too. I wrote my own tool awhile ago to help me figure my design out. This is what I get when I plug in the numbers I could pick up from your post and signature. Based upon the cam card from Comp it appears that they grind in 2* of advance so I accounted for that. This made the cam events in my computation closely match the cam card.

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.71 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 6.5 cc
Piston Compression Height = 1.5 in
Cylinder Head Specifications:
Combustion Chamber Volume = 50 cc
Intake Valve Diameter = 1.649 in
Exhaust Valve Diameter = 1.38 in
Rocker Arm Ratio = 1.5:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.044 in
Camshaft Specifications and Events:
Intake Duration = 260 deg
Exhaust Duration = 260 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.293 in
Cam Exhaust Lift = 0.293 in
Ground-in Advance = 2 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 22 deg BTDC
Intake Closing Angle = 58 deg ABDC
Exhaust Opening Angle = 58 deg BBDC
Exhaust Closing Angle = 18 deg ATDC
Intake Valve Lift = 0.4395 in
Exhaust Valve Lift = 0.4395 in
Valve Overlap = 40 deg
================================================
OUTPUT
================================================
Engine Displacement = 202.76 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 0.03 in
Squish Distance = 0.074 in
Static Compression Ratio = 8.90:1
Dynamic Compression Ratio = 7.52:1



When I run the numbers with 48 cc, that puts you at SCR 9.13:1 and DCR 7.72:1. I don't know if you want to go lower than 50 cc on the chambers or not. If you ever mill the deck (or if it already has been) your SCR will start to climb. The real issue is that you're ending up with 74 thou in squish distance. If you could actually measure what your piston shortfall is while the head is off, we could figure that out more closely.

Hi, X2 on very good advice. Before you mill, cc a couple of combustion chambers to see where you are at. I wouldn't "go for broke" on my engines. I like a little more, not all I can get, if you know what I mean. Good luck

Wow, thanks cr_bobcat.. I was just using the simple static calculator on summitracing, but even the static numbers came out different from yours. I think the only difference is that I used .019 as the deck clearance (got that from the tech specs page). I can try to measure it while the head's off, but I'm not sure if I have anything that accurate for that small of a measurement.

I didn't have the deck milled unless the builder did it on his own... but as far as I know, it's stock. I'm ok with going smaller than 50cc chambers because the bottom end was just rebuilt maybe 1,000 miles ago so I have no plans on making changes there for a while... I'm just worried about taking more off of the head than is safe. According to the performance handbook you shouldn't go over .090, but the guy I got the head from said it was milled .060 already and cc'ed at 54. The shop is going to cc it before we do anything to double check, but if that's true then I'll likely have to go all the way to .090 to get to 48.

I guess the other option is use a steel shim instead. This company apparently sells custom .020 ones:

http://www.silver-seal.com/category/shop.engine_parts.cylinderheadspacershims.ford/

I'm running a C9 head that was milled 70 thou and I'm at 48 cc. I was starting 61 cc chambers if memory serves me correctly. I also managed to source some NOS gasket that is 35 thou. I think I'm in the 9.3 - 9.5 range. Would need to run my build through the tool again to confirm.

Or I could have just read my signature....

I plan to do the bottom end at some point and I'll probably need a different head or thicker gasket to keep SCR under control. I'm happy with the decision, just figured I better warn you what could happen for any future build that you might do.

kerb12":ww7vqf1c said:

Wow, thanks cr_bobcat.. I was just using the simple static calculator on summitracing, but even the static numbers came out different from yours. I think the only difference is that I used .019 as the deck clearance (got that from the tech specs page). I can try to measure it while the head's off, but I'm not sure if I have anything that accurate for that small of a measurement.

I didn't have the deck milled unless the builder did it on his own... but as far as I know, it's stock. I'm ok with going smaller than 50cc chambers because the bottom end was just rebuilt maybe 1,000 miles ago so I have no plans on making changes there for a while... I'm just worried about taking more off of the head than is safe. According to the performance handbook you shouldn't go over .090, but the guy I got the head from said it was milled .060 already and cc'ed at 54. The shop is going to cc it before we do anything to double check, but if that's true then I'll likely have to go all the way to .090 to get to 48.

I guess the other option is use a steel shim instead. This company apparently sells custom .020 ones:

http://www.silver-seal.com/category/shop.engine_parts.cylinderheadspacershims.ford/

Click to expand...

That shim can not be used by itself, it has to be used with a gasket...I may not of understood your intent.

Its a 30 degree backcut on the intake to remove the sharp edge from the seat to the underside of the valve.

Howdy Back Nick and All:

You are getting some super help. Bobcat's got it down. My suggestion to you, because you are assuming someone else's project, is to cc several chambers before proceeding with any additional milling of the head. I realize that you were told that the chambers cced out to 54ccs but IIWIYS, I'd recheck.

And if your deck height, distance from the top of the pistons to the block deck, is .015" it is likely that the block was milled/decked during the last rebuild. While the head is off is a perfect time to measure for yourself so you can proceed with accurated data. Stock 200 deck height is typically .025". That is another variable in the CR equation.

With those two pieces of information you can reassess what you have and what it will take to increase CR.

With the Comp 260 cam you can safely use 9.5:1 as a goal CR with high octane gas. On the hi-ratio rocker arms, the valve lift with the Comp 260 cam gives you .440" lift as compared to .348" with the stock '66 cam. The 1.6:1 arms would add approximately .030" more lift throughout the rpm range. That would help some, but be sure to check your current valve springs for binding problems first. Given the expense and compatibility issues, I'd be inclined to save my money. A back cut on the intake valves along with a performance valve job will be less expensive and very beneficial.

One more piece to compliment your performance engine, you didn't say what you're using for a distributor but, for sure, get it recurved to match your engine and situation. A proper ignition advance curve can be a big help in getting the most out of a performance engine.

On the head milling limit let me explain. My brother once used a C9xx head on a 144 engine. He had it milled .090" to get a decent CR on that engine. It did not show any signs of weakness, but it was an extreme case. Personally I would suggest no more than .075" to be the max. Head casting vary in casting quality. More is not always better- unless you're Dolly Parton.

You've got some great information and advice. One last "Measure twice, cut once".

You never did say what the damage was to the head. Care to share?

Adios, David

Thanks all, as usual you guys are awesome...

I'll report back after the shop takes a closer look at the head and cc's it, and I'll ask him what his opinion is of how much can be taken off. Something doesn't seem right to me about it being milled .060 and ending up with 54cc... if you did .070 to go from 61 to 48, then either the numbers I was given are wrong or this had to be way above the "stock" 62 originally. I'll take a crack at measuring the deck too.

cr_bobcat, good catch with the link I posted about the shim... didn't realize it was just a spacer.

David, I just realized you were THE David... thanks so much, your book has been invaluable. I'll probably reuse my rocker arm then, but I'll definitely ask the shop to backcut the valves. I looked through my old emails and it had a 3-angle valve job done already as well. As for the distributor, I'm using a DSII that was recurved by wsa111 and an MSD 6a.

So here's the story that started all of this... I was trying to chase down a vacuum leak that was probably due to the fact that I was stacking a few thick spacers to get the carb to clear the valve cover, so while I was taking it all apart I figured while I'm at it I'll put a new vacuum hose fitting in the intake too. It must have been jammed in there good though, because it sheared right off when I tried to take it out leaving me with nothing to grab on to to take it out.

I should have went with the slow and safe approach of trying to break it apart with a small chisel, but instead I put a spiral screw extractor in there and used too much leverage with my socket wrench... CRACK. I got 2 splits coming out of the vacuum hole. Maybe the metal got brittle from the brazing for the direct mount carb or something too...

Good thing is the shop seems hopeful in being able to repair it by putting some pins in it to stitch it up and pull it tight enough to seal again.

What kills me is I probably never even had to take that fitting out... should have just left it alone and dealt with sealing the spacers better.

My '63 has a stock Maverick C8DE 170 block/cam with D7DE 70's head milled @.070 and chamber matched to @ 48cc's by my machinist. This with the metal shim gasket yields <@ 9.5:1 CR (SCR-DCR?).

I hung the steel shim gasket and sprayed both sides with copper gasket sealant. Not RTV but an adhesive type spray like High Tack. After 11 yrs and lots of miles it still seals with no problems. The hi-comp 170 is reliable, drivable and gets good mileage as well as fun performance (on 93 octane).

D7 Head . Oversize intake valves, silicon springs. . Milled head w/ Steel Shim Gasket. CR= 9.5:1. H/W 5200 - 2.8 series (32/36) progressive 2Bbl carb., Exhaust ¾ siamese port divider, Champion racing spark plugs, Contact Point/Condensor distributor

Unfortunately steel shim gaskets for the larger bore 200/250's are apparently unobtanium.



have fun

what is the bore size on the steel shim head gasket? i know that on small block ford V8s the head gasket bore is about an 1/8" larger than the bore in the block to allow for over boring.

one place you might check is here;

https://egge.com/

they might make a gasket for you. contact them directly.

I checked with egge.. unfortunately they don't make head gaskets. There are a couple places that I'm planning to call around to though, maybe I'll get lucky somewhere. I've been searching for NOS ones for a while now, and never see them.

The NOS ones are out on flebay. Search for C9OZ-6079-A FORD. It's the valve grind gasket overhaul kit or something like that.

Nice! I snagged one, this should really help with my compression goal. All this time I've been searching for things like Ford 3.3, 200, 250, etc... none of those came up with a match until I searched for that part #.

On a side note, I reached out to Cometic Gaskets and they make a composite that's .043 (about same as Victor) and can also make a copper gasket at .027. Waiting to hear back on pricing just out of curiosity, but I'm going to go with the Ford steel one.

FYI, here's how you would play out with the 35 thou gasket, 48 cc chambers, and assuming a stock deck height.

================================================
INPUT - BUILD PARAMETERS
================================================
Block Specifications:
Cylinder Bore = 3.71 in
Centerline to Deck Height = 7.808 in
Rod Length = 4.715 in
Stroke = 3.126 in
Piston Dish Volume = 6.5 cc
Piston Compression Height = 1.5 in
Cylinder Head Specifications:
Combustion Chamber Volume = 48 cc
Intake Valve Diameter = 1.649 in
Exhaust Valve Diameter = 1.38 in
Rocker Arm Ratio = 1.5:1
Cylinder Head Gasket Dimensions:
Gasket Diameter = 3.81 in
Gasket Crush Height = 0.035 in
Camshaft Specifications and Events:
Intake Duration = 260 deg
Exhaust Duration = 260 deg
Lobe Separation Angle = 110 deg
Cam Intake Lift = 0.293 in
Cam Exhaust Lift = 0.293 in
Ground-in Advance = 2 deg
Camshaft Installation Advance = 0 deg
Intake Opening Angle = 22 deg BTDC
Intake Closing Angle = 58 deg ABDC
Exhaust Opening Angle = 58 deg BBDC
Exhaust Closing Angle = 18 deg ATDC
Intake Valve Lift = 0.4395 in
Exhaust Valve Lift = 0.4395 in
Valve Overlap = 40 deg
================================================
OUTPUT
================================================
Engine Displacement = 202.76 in^3
Rod to Stroke Ratio = 1.51:1
Rod Angle = 19.36 deg
Resulting Deck Height = 0.03 in
Squish Distance = 0.065 in
Static Compression Ratio = 9.34:1
Dynamic Compression Ratio = 7.89:1

Just an update, the repairs to the cracks ended up being more work than originally thought, since more cracks showed up when they inspected it closer... but, that work is now finally done.

He's going to back cut the intake valves next and do the milling, and I just realized something. If he can get it down to 48 cc's, will I need to switch from the current stock non-adjustable rocker arms to an adjustable set to account for the new height?