I have decided to completely rebuild my 225 for my 60 Val and was wondering on decking the block.Originally I was just gonna shave the head .090 but now that Im doing a complete rebuild I was wondering if I should cut the deck .045 and the head.045 or ??????? trhis will be my first engine build and I will be asking alot of questions so please bear with me.
thanks ,Slanted Attitude

hi, do both the deck and head. i just did a 68 225 and took off .060 off deck and .060 off head. i still have 1 thread below the rocker arm which is perfect. ron

Your suspicions are right. Take some off both surfaces. What ends up happening, is that you true up both of them, and ultimately get a better sealing surface.

You can take off quite a bit, but you run the risk of the pushrods ending up too long and screwing up the valvetrain geometry. You'd have to get some custom p-rods to correct it. It's also possible that the fuel in your area wouldn't like the higher compression ratio, and give you some pinging problems. You'll be ok with a .090 cut. That should give you a ratio of (roughly) 9 or 9.5:1.

Roger

Thanks guys,I think Im gonna take .045 or .050 off each but Ill know more after I talk to my machinist.

hi, how far down are your pistons? did you measure before you pulled engine apart? did you cc the head before you bring it to the machine shop? are you using steel .020 or composite .040 gasket? if you have more cc's on head <54 cc's standard, but can be 58 to 60 cc's> to begin with you need to take off material just to get back to stock specs. same deal with pistons. let's say you should be down in hole -.140 but yours are found to be down -.160. you are taking off .045 ,but .020 is being used to get you back to stock #'s. thats why you need to measure everything before and after. you are taking off .045 but do you want .045 off what you have now or off of what is stock? if you don't have the tools then bring it to shop and have them measure it first. post back your measurment specs. not giving you a hard time, but you cannot get an exact accurate compression ratio <i.e. 9 or 9.5-1 > unless you measure, then machine, and then measure when done.the machine shop should be willing to help you out. keep us updated. ron

Pardon me for jumping in here...
Assuming stock cylinder block height, what combustion chamber volume gives 9.5 to 1 compression? 10 to 1? Is it just doing the math of total volume at BDC/ total volume at TDC?

I just purchased a refurbed head, had .090 shaved and am going to do a little more than a moderate porting job. Is it ridiculous to run the stock valves and springs assuming street /performance cam, dutra duals, and the proline dual weber setup ?

I have another spare head and block to do a "real" buildup on and as of right now I'm not interested in touching the bottom end of the 1974 110,000 mi engine the head is going onto. Engine Has Pertronix ignitor II ignition, street/strip tranny kit and stock 3.23 7 1/4 rebuilt 10,000 mi ago (at 180,000 for the rear)

Will the head(stock valve size) be the weak link in limiting horsepower or the comp cams 252

Car is a 1968 four door Dart 270 with rallies and high back buckets, no rear seat.

Thanks for any advice ...

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STEALTH DART
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Mike--
Calculating compression ratio requires 4 numbers:
A) Head (combustion chamber) volume
B) Head gasket compressed thickness & hole diameter
C) Swept Volume
D) Piston-deck clearance

A=(combustion chamber cc's)/(16.387)
B=(Thickness)*(3.1416)*(Diameter)*(Diameter)/4
C=(Stroke)*(3.1416)*(Bore)*(Bore)/4
D=(Piston-Deck Clearance)*(3.1416)*(Bore)*(Bore)/4

Compression Ratio = (A+B+C+D)/(A+B+D)

On a "stock" slant (assumed numbers are 54 cc head, .140 piston-deck, stock bore & stroke, .040" thick head gasket), milling .060 from the BLOCK would result in 9.5:1 compression, a similar amount off of the head would be close to the same compression. Milling .090 from the BLOCK would result in 10:1 compression, similar #'s for the head, but you would probably need to take .100" from the head to get 10:1 (combustion chamber is not a perfect cylinder like the block bore, so the volume decrease by milling the head is not constant)

-S/6

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87 Ram D150

thanks for the lesson...

I'm still curious about running the stock sized valves with my above setup and just how detrimental they will be to overall output...

I'm expecting quite a bit of blowby...thankfully the car is not a daily driver anymore, -well, I still drive it almost everyday, but I don't have to...

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mike, you can go to prestage.com and look under engine math for compression ratio formula. put in your numbers and tell us what you have. my 68 225 has pistons down .110 with 51 cc head and .040 gasket for 9.25-1. just right for me. how much r.p.m. are you spinning? unless you rev it to the moon the stock valve size will be o.k. ron

I'm not sure about the exact RPM, no tach, probably not more than 4500 on the motor that's now in the car.

I should be completing a high-rev slant this winter...trying to decide if I should go with the 2.2 pistons and 198 rods...

I was basically trying to figure out if I should do some porting and bolt it on to what I'm running now, or wait 'til I get the bigger valves...

Think I'll bolt it on!

P.S I'll check the piston height when I bolt it on

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mike, cc the head before you put it on. just looking for what cc's you have.post back how low your pistons are. thanks, ron

will do, got my plexiglass all ready

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STEALTH DART
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