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I took my 396 block to the machine shop last week. I got a 402 back. They had to bore it .030 over. My next concern is compression ratio. 396 pistons .030 over will give me the stock 10.25:1 ratio. I think that is a bit high for todays gas, but I like the idea of the power it will make. Stock 402 pistons will give me around 9.0:1 compression. Good for power, but I think I will always wonder 'what if?". Any ideas or suggestions?
Getting proper fuel for a 10.25 motor might be a pain, especially if it's not fuel injected. I know I would always be asking what if as well, so don't know what to tell you....sorry.
rich
My buddy runs his truck at 11:1, but we are at 5000 ft, and wheel up to 9500 ft where the motor can really use the extra stroke space for the thin air. I'm sure it would ping like a mofo at lower altitudes- gonz
You could go with 396 pistons and get a little bigger cam to bleed off some of the compression. But for every day use I would probably use 402 pistons. Are you using early 396 heads?(larger washer seat spark plug) if so then 402 pistons will have more than 9:1 comp as they were designed for later open chamber heads. (small taper seat plug)
I have the 98cc closed chamber oval port heads. Good point and thanks.
mill the heads run 13:1s roller. Id go back and tell them you want your 396 back.LOL!you could have had a four bolt block. :lol:
stock 396 with 10:25 was a 325 horse motor and they ran pretty good on 91 octane. may have to back timing down a few degrees but I dought it. My 396/375 horse ran all the time on premium unlead (91) and I only had a problem once and that was when I ranway over 38 deg. total advance racing it and burnt a hole in a piston that time.
i have a 396 bored to 402 in my daily driver k-30 chevy... 9.5:1 compression, runs fine on mid-grade, runs like absolute crap on regular. works good for me, but the cam is not in the right RPM range, so i need to change that. it has a 270 or 280 (don't remember), but i'm going to put in a comp extreme 4x4 cam for that low end grunt. also going to put in pete jackson timing gears and MAYBE roller rockers.
i also need to mess with my advance weights because my MSD billet HEI distributor came out of small block in a fast-running car, not a BBC in a big 4x4, and i think the advance goes too high... i want all my advance by 4,500 RPM... not 6,000 like in a car.
i'm also going to swap in a TBI setup down the road...
have fun with your new motor! I guess my buildup all comes down to wether or not i buy a diesel dodge... if so, the M-715 is going on that chassis...
Pete Jackson gear drive.....nice touch....love that!!
bute4c
Actually, you want your full advance in around 2,000 to 2,500 rpm for help with the low end grunt.
The percentage power gained by the higher compression will probably not be worth the extra money you have to spend to safely run it like that. You have to keep your timing in check, your fuel has to constant (fuel injection makes this point mute though), and other cooling issues that arise as well.
Run a roller cam to get the best low end grunt.
With a sb 9.5 should be the max cr with iron heads, but with the larger bore of the bb you gain about .5 to around 10:1. Add thick head gaskets and you can knock .2 off the cr. Or you could just get the 402 pistons, they cost about the same.
my .02
Ron
You'll get really good power by running open chamber heads (120cc) and lower the compression down to a ratio that will run cooler, run on 87 if you keep the time 6*-8* btdc, you'll make up for the compression loss by having better flame travel (flame propogation) across the top of the piston, AND you can run a high torque cam and have it really work well! Unless you got a mass of money to burn don't go the way of the gear drive cam timing sets. The idler gears tranmit torsional vibrations (why you have a harmonic dampener) that you don't want in your engine...up to the cam, the consequently through the lifters. Run a chain or drop a hunk on a Jesel equivilent belt...but, personally, I won't run a PJ style gear drive.
Thanks for the advice everybody. I will sit down with the machine shop guys when I get the money collected for the pistons, after the FE, and figure out a combination of piston that will get me in the low to mid 9:1 range.
I think everybody knows by know that the block is great and the heads were done very wrong. Maybe I can look back in two years and laugh. Not now.
This flashback stuff is pretty crazy. And I'll laugh for you. . . or at if you prefer. Did you try the thinner trick by Bob?- gonz
I didn't need to try the thinner. I was looking over the guys shoulder as he finished them the other day. He did a leak test like it for me. I painted all the parts Thursday night and got it going Saturday morning.
It has more torque and power than ever. No noises either. The best way to describe it is like this. Just about any vehicle with a granny gear does not need throttle to be applied when you let out the clutch slowly in that gear. I used to have to give a little in second. Now, I can let the clutch out in second like it was a granny gear and third from a stop just needs a toe twitch to make it go. I only drove it up and down my dirt road, so I haven't opened it up yet. I have to get Jennifer to help me put the freshly painted hood back on before I get on the road. I will drive it to work Tuesday and play then.