I keep going back and forth on what to do. I want to build an NA street motor for my car. I have ported TFS TW170 heads, JBA shorty headers, 1.6 roller rockers, Explorer intake, a stock short block that needs machine work, and other various parts like 65mm TB, 70mm MAF, etc. I plan on getting a custom cam made, TFS pistons and an RPM limit of 6k. This will also be going through either a built T5 or TKO500. A rough RWHP goal is 300+.
Is a stock block worth having any machine work done? Should I just save for a Dart SHP? I'd like to leave it a 306 or maybe a 331.
This car will never see a drag strip, no power shifting, etc. I just want a fun street, reliable street car that will cruise nicely.
Current mods to the car:
BBK X pipe
70mm MAF housing from a T-Bird
MAF sensor from a 94 Mustang
65mm Explorer TB
BBK upper and lower control arms
Other than that the car is completely stock, even the mufflers.
If that is the case then do not spend the money for a dart block.. I would look into a good short block from fordstrokers, this way you don't have to worry about the bottom end and put your cam and valve train in it.
Ok, so I'm back on using a stock block. I just see threads of split blocks even at relatively low power numbers and get scared. I broke the crank and block in my '85 GT and it only put down 220hp and 270ftlbs to the wheels. I was just driving it with the cruise control on when it went.
What machining operations are necessary vs optional? I priced out a full machine and balance job at a local shop and the price tag is $1200.
Is a torque plate bore and hone and an align hone necessary? I'm leaning more toward a 331 kit that's already zero balanced instead of having the money spent resizing rods, pressing on pistons, and grinding the crank and trying to zero balance it.
Zero balancing removes the need for counter balancing on the flywheel and harmonic balancer. This helps to reduce vibrations and wear on the crank, main bearings, caps, ect. It also helps to reduce crankshaft deflection.
I wouldn't worry about splitting your block at the power levels you are talking about, as long as the block has checked over (magnafluxed), everything is put together correctly, and you're not planning to run some crazy RPM. I'm not sure why you broke a crank and block at 220HP, but it usually takes much more than that to split a stock block and would tend to think something else let go to cause that. If you happened to read my most recent thread, don't let that scare you off.
I would have the bores both torque plate bored and honed as well as have the mains align bored. I'd also have the block surfaced of course. You will also probably have to have the block clearanced for your stroker kit. Zero decking and more race oriented machining doesn't need to be done for a street engine. Biggest thing I would suggest would be to find a local machine shop that you can trust, and work with them so they know exactly what your goals are so they can tailor the work to your needs. The $1200 you quoted is about what I would expect to pay around here for a full, proper machine job on a stock block and balancing of the rotating assembly. You can slap an engine together without all the "fancy" machine work, but you risk not having a perfectly straight main bore (main bearing wear and crank deflection), sub-par cylinder sealing (less power), ect. It's best to do it right the first time.
I also wouldn't go crazy on a forged crank and h-beams for a stock block. A cast crank and I-beams are just fine for any power level you will make on a stock 302 block.
This sounds to me like much agonizing over a street car engine. I agree with the line bore and torque plate bore/hone. Zero balance is a good thing but again, this is a street engine right? Balancing the reciprocating assembly is a no brainer. Now these are my opinions, I do not build engines, I stuff a used 5.0 in my ride and twist that dude to the red line on a regular basis, if/when it takes a dump I would grab a Jasper engine and get a 3 year 100,000 mile warranty and continue to spin it to the red line and punish that dude till the tires are bald, stuff another pair on the rear and do it all over again.
My junk is a half ton of fun to drive and I think dependable enough to drive anywhere.
At 300hp don't sweat the race engine dartblockI'mafraidtosplitmyblockonthewaytothelocalrodrun stuff!
Drive it like you stole it and have a good time doing it.
$1200 is what I paid for my 1969 351w block , fluxed, decked , bored, align honed and cam bearing installed (I'm in CT.)
Zero balance although nice probably isn't necessary for the ops build, use a reputable shop and you should be fine.
If I do go the stroker route I'll get a zero balance rotating assembly.
As far as turning RPM, 6k is my limit. My last car had a 6k limiter chip in the MSD box and I didn't see a need to spin faster. I've never turned my current 1993 stock motor past 5500 (what the stock tach shows anyway).
One of the reasons I was considering a Dart block is because as far as I understand it they are ready to assemble aside from final hone to fit the pistons. They are $700 more than the machine work quote I received for my current block, and I would never have to worry about breakage. I'm guessing that they hold their value better as well. I have my disassembled short block listed for $100 locally and I have received no responses.
Or I spend roughly $5k for an assembled 331 Dart short block from Fordstrokers built to my specs. An assembled CHP 331 short block is around $2400.