Most can't believe this but it worked for me.Back in the Year 2000 I got my 1968 Chevy II Nova SS396/375HP 4 Speed 410 car from Stockton California.Anyway it was family owned since new and eventually the original block was put into a 1969 Corvette thats still in Stockton California. So instead of building a 396/375 I built a 427. I used Superior Machine shop in Allentown PA with Jim the owner doing all the work. Anyway all my GM parts were ordered from Pace Chevrolet. I bought a Brand new 427 4 bolt main GM block ,Eagle crank,GM 7/16 Rods,Speed Pro 12 1/2 to 1 Pistons,GM 119CC Open Chamber Aluminum Heads,Double roller timing chain,7/16 GM push rods,Roller tip rockers,Mehanical 630 Lift cam,Victor Jr intake,850 Holley Double Pumper,MSD 6AL,Hooker Super Comp headers.Rotating Assembly was completely balanced. What I found out was this motor runs real good on Sunoco 93 Octane ,never pings,never runs hot and never fouls plugs. People can't believe how good it runs on 93 Octane Sunoco. The Old days it was Cast iron heads and crappy GM single point GM dist. Backin the 70's I use to do weekly plug changes and car ran hot. Aluminum Heads make a HUGE difference in High compression 12 1/2 to 1 Dome pistons with keeping the heat down. Also the cam Jim at Superior Machine spec out for this 427 bleeds off Compression. This MSD 6AL is way better then the GM single points. This motor is probably one the best motors I've had.Honestly I can't believe how good this motor runs! I have all machine shop receipts and parts invoices used in this awesome combination.Yes 112 runs even better but 93 Octane Sunoco is fine.It never hurt the motor.I have probably 5000 miles on engine and it fires right up and holds a constant 45LBs of oil pressure at idle. I love this combo and love the sound of this radical 630 lift cam at idle.
427 12 1/2 to 1 Motor GM 119cc Aluminum Heads-It runs on 93 Octane!
1968Motion427SSNova
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Most can't believe this but it worked for me.Back in the Year 2000 I got my 1968 Chevy II Nova SS396/375HP 4 Speed 410 car from Stockton California.Anyway it was family owned since new and eventually the original block was put into a 1969 Corvette thats still in Stockton California. So instead of building a 396/375 I built a 427. I used Superior Machine shop in Allentown PA with Jim the owner doing all the work. Anyway all my GM parts were ordered from Pace Chevrolet. I bought a Brand new 427 4 bolt main GM block ,Eagle crank,GM 7/16 Rods,Speed Pro 12 1/2 to 1 Pistons,GM 119CC Open Chamber Aluminum Heads,Double roller timing chain,7/16 GM push rods,Roller tip rockers,Mehanical 630 Lift cam,Victor Jr intake,850 Holley Double Pumper,MSD 6AL,Hooker Super Comp headers.Rotating Assembly was completely balanced. What I found out was this motor runs real good on Sunoco 93 Octane ,never pings,never runs hot and never fouls plugs. People can't believe how good it runs on 93 Octane Sunoco. The Old days it was Cast iron heads and crappy GM single point GM dist. Backin the 70's I use to do weekly plug changes and car ran hot. Aluminum Heads make a HUGE difference in High compression 12 1/2 to 1 Dome pistons with keeping the heat down. Also the cam Jim at Superior Machine spec out for this 427 bleeds off Compression. This MSD 6AL is way better then the GM single points. This motor is probably one the best motors I've had.Honestly I can't believe how good this motor runs! I have all machine shop receipts and parts invoices used in this awesome combination.Yes 112 runs even better but 93 Octane Sunoco is fine.It never hurt the motor.I have probably 5000 miles on engine and it fires right up and holds a constant 45LBs of oil pressure at idle. I love this combo and love the sound of this radical 630 lift cam at idle.
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10,475 Posts
Is that compression calculated or measured? How did you come up with 12.5:1?
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Royce good questions.I started digging up my paperwork on this awesome running 427.First off the TRW Speed Pro 12 1/2 to 1 Pistons were bought from Summit Racing on 7/03/00 for $447.00. Part number was L2308AF.The aluminum heads are GM part number 12363400 with 118CC Chambers,2.25 Intake 1.88 Exhaust on Valves.Heads bought from Jim Pace May 5 2000.Mechanical cam is Federal Mogul CS1110R. Cam specs-Solid-Lobe Center Angle-108.0-Intake Duration 264-Exhaust Duration-274-Intake Center line angle 106-Intake lift 0.612-Exhaust lift 0.637-----427 4Bolt main block from Jim Pace is GM part number 12550307---GM part number 12496661 427/396 Rods also from Jim Pace--Push Rods were GM Premiun 7/16 10134305 Exhuast and 10134306 Intake.---Intake is Victor Jr ED2927----Holley 850CFM 0-4781C Carb------Engine Calculations with above combo brought the Compression Ratio to 11.28 with Deck Volume,Head Volume.Gasket Volume Dome Volume Dish Volume at 9.8 Deck Height.---Peak Horse Power using the Computer was 580HP at 6500 RPM with best torque at 5500 RPM being 496. .....I gotta tell you Aluminum Big Block heads are the only way to go in my book,lighter and they cool the top end of the motor way better!
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10,475 Posts
From whay I see you are at 11.39:1 at best that would be with zero deck. Now add in how far in the hole your pistons actually are, your true combustion chamber size (the only way to know that is to measure/cc it), now add in your head gasket volume. From my experience when you actually measure things they are not "as advertised". 11.5:1 with aluminum heads is do-able, 10.5:1 with iron heads is do-able.
You are still claiming 12.5:1, but I don't see it.
Not sure I am following your logic or post. I don't doubt you have a great running engine, but would hate to see someone less experienced read this and think they can build a 12.5:1 engine and run it on pump gas.
Yes aluminum disipates heat, but that is also why you NEED to run a little higher compression to make up for the heat loss. Everything being equal iron heads will make more power, the thing is they are heavier and you usually can't get them as fancy as aluminum heads.
Cam timing will play a large role in all this as well.Read up on DCR (dynamic compression ratio). Here is a link: http://cochise.uia.net/pkelley2/DynamicCR.html download the calculator and plug in your numbers, then post back with your DCR.
Bottom line looks like you have a nice combination and a good runner.
You are still claiming 12.5:1, but I don't see it.
Not sure I am following your logic or post. I don't doubt you have a great running engine, but would hate to see someone less experienced read this and think they can build a 12.5:1 engine and run it on pump gas.
Yes aluminum disipates heat, but that is also why you NEED to run a little higher compression to make up for the heat loss. Everything being equal iron heads will make more power, the thing is they are heavier and you usually can't get them as fancy as aluminum heads.
Cam timing will play a large role in all this as well.Read up on DCR (dynamic compression ratio). Here is a link: http://cochise.uia.net/pkelley2/DynamicCR.html download the calculator and plug in your numbers, then post back with your DCR.
Bottom line looks like you have a nice combination and a good runner.
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1,629 Posts
Royce,Again Good info.The specs on 427 L2308AF TRW Speed Pros in my motor are 50.0cc 585 Dome.The 427 L2268AF TRW Speed Pros are 35.5cc 266 Dome. My pistons call for using a open chamber 118cc heads because of the larger dome size.Yes I agree once you factor everything in doing what I did it drops the compression down. Yeah Royce this baby runs AWESOME!! Build it,Use it and Enjoy It='s 
BUE Car! Thanks!
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