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The differences you're seeing on compression height is to allow for decking the block. Many lower cost cast and hypereutectic pistons are made "short"..so the piston will remain down in the hole after decking. Fast rebuilders just want to cut everything to one measurement and know that whatever they put in there will run. Is it the right way? No. Often folks end up with pistons down in the hole .040-.060 and it just kills compression and likely to detonate worse. Most shops deck them to provide .005" or so deck clearance.....but since you probably won't be decking it...shoot for the tallest piston. Do the math.
You've got a 3.48" stroke. Divide by two.....and you get 1.74". Now add your 5.7" rod to it and you have 7.44". Adding the 1.562" compression height gets you 9.002".
"Nominal" deck height for a SBC is 9.025". So if using the 1.562" piston you should end up with around .023": deck height. But that assumes your block is 9.025"..which it may or may not be. As you can see that 1.540" piston would put you at .045" down in the hole at the best. Those are used for severely cut blocks.
I would suggest taking the block to the machine shop..let him measure it to determine how much it will have to be bored. And since it's a mild build...just let him get the pistons he trusts....but as mentioned I'd avoid the KB's for sure and I'm not a hyper fan either...but they will probably be OK for you...just keep it tuned well.
JIM
You claim it is a numbers match block so decking it is out of the question unless he has an X/Y Rottler all in one and knows how to use it. We tried it once on a big ancient Quik-Way and the stone being round made it impossible to make the cut up to the pad right......
So, knowing that....you will probably be .020 in the hole with a 1.562 C/D piston. A -5cc four eyebrow flat top will get you 10.3 to 1.......the Vortec fast burn chamber heads will be fine with that on 93 octane.
It may be further than that in the hole......measure it and do a compression ratio calc on it to be sure.
If you're not planning to go all-out, a shop with a machinist that knows what he's doing could probably hone to the next size. The bores may not end up quite as straight as if it were bored and honed, but they're pretty dang good, might save you some bucks. I've had it done and ended up with a good mill that didn't burn a drop of oil and ran fine.
It looks like it had water in it and was just cleaned up and assembled, the rust in those bores was a lot worse than you can see now. I've torn down blocks that had bores that look like yours and some of the pistons had to be hammered out.
I rebuilt the 350 in my '97 Tahoe with true flat top/4 valve relief hypereutectic pistons. Block was zero decked. Compression is at 10.1:1 with Vortec heads. I'm lucky in that I have a computer to control this engine but have never had any rattle that I could hear. Runs great with an LT4 roller cam. Last road trip in my 4200lbs rig got just shy of 18mpg.
thanks
pump gas, reg or premium?
have to re program / tune oe computer?
I would take it to a shop that you know you can trust to measure the bore and let them tell you if you can stone hone it and reuse the bore and or pistons. Very hard to measure with any precision from a photograph. If the bores/pistons are toast, you can make a plan from there. Much more money in new parts and labor once you cross over to a rebore but it will be 100% new if you do.
Measure before ordering parts. Some can be 40-50 thou down!
I really dont think a # match block will do spit for resale but hear what youre saying. If youre daydreaming about a 454 do it now put your old block aside.
If you did deck it there are companies who can CNC the deck so the #s arent touched. QMP racing in Chatsworth Ca is one they do a lot of vette stufff where guys trip out over it
not trying to ruffle feathers but unless you got a sub 10mi car with some ultra rare combot thats got all the ncrs certs I think all that will matter to most is its a properly rebuilt 350
When I sold # match cars the #s guys that came over just wanted to nitpick the car , get it for free then flip it.
Originally Posted by 427HotrodThe differences you're seeing on compression height is to allow for decking the block. Many lower cost cast and hypereutectic pistons are made "short"..so the piston will remain down in the hole after decking. Fast rebuilders just want to cut everything to one measurement and know that whatever they put in there will run. Is it the right way? No. Often folks end up with pistons down in the hole .040-.060 and it just kills compression and likely to detonate worse. Most shops deck them to provide .005" or so deck clearance.....but since you probably won't be decking it...shoot for the tallest piston. Do the math.
You've got a 3.48" stroke. Divide by two.....and you get 1.74". Now add your 5.7" rod to it and you have 7.44". Adding the 1.562" compression height gets you 9.002".
"Nominal" deck height for a SBC is 9.025". So if using the 1.562" piston you should end up with around .023": deck height. But that assumes your block is 9.025"..which it may or may not be. As you can see that 1.540" piston would put you at .045" down in the hole at the best. Those are used for severely cut blocks.
I would suggest taking the block to the machine shop..let him measure it to determine how much it will have to be bored. And since it's a mild build...just let him get the pistons he trusts....but as mentioned I'd avoid the KB's for sure and I'm not a hyper fan either...but they will probably be OK for you...just keep it tuned well.
JIM
You claim it is a numbers match block so decking it is out of the question unless he has an X/Y Rottler all in one and knows how to use it. We tried it once on a big ancient Quik-Way and the stone being round made it impossible to make the cut up to the pad right......
So, knowing that....you will probably be .020 in the hole with a 1.562 C/D piston. A -5cc four eyebrow flat top will get you 10.3 to 1.......the Vortec fast burn chamber heads will be fine with that on 93 octane.
It may be further than that in the hole......measure it and do a compression ratio calc on it to be sure.
Personally unless you are just itching to build a motor I would look into a crate motor. You will end up spending just as much usually rebuilding it as you would replacing it. Plus a lot of crate motors have warranties. This is a pretty good deal right now. https://blueprintengines.com/product...etor-bp3961ctc
Personally, I would build the motor with top quality parts including forged pistons, etc.
Why spend money and build a so so bottom end.
A 2 bolt main with cast crank motor can take a good amount of torque and horsepower if you decide to add a bigger cam, heads and up the performance down the road as long as you build the bottom end right with good parts now.
I think if you price it out good parts won’t cost much more.
If you need to deck the block don’t worry about the matching numbers.
Unless your car is all numbers matching and period correct, including “all” the parts and components, just the matching block really doesn’t add much value to the car.
Since my car was a base model 69 350/300 the motor was bored .030 over, mild cam like a 350/350, 4 bolt main and had Lar's rebuild the carb/distributor and the car really runs well with 3:08 gears. However I will change out the gears. I have a complete 4:56 rear and also 3:55 or 3:70 ring and pinions that I can go with. I get to the next red light pretty quick for a little base model but original motor car.
Just sayin................................... ........................................ ....................................
The easiest and usually the cheapest way to get a renewed engine for your car is a crate motor which usually has a warranty as well. HOWEVER, do not delude yourself into thinking that a crate motor is in any way near the same, as building your OEM motor with high quality parts....Building your OEM motor with top quality parts is more expensive BUT in the end you will have a more solidly built motor, that almost always will make more power (my L-82 355 build with the best parts will out power almost universally any bigger 383 crate motor due to the parts combo), and in the end will probably last longer and be more reliable. This statement is not a knock on crate motors, just an accurate opinion of what you are buying for cheaper money......crate motors are probably fine for most C3 that just want to cruise......
Machining, careful assy and a good balance job buys longevity. one can use basic parts but if those 3 items are done super well it will live.
Lots of motors out there blown due to a lazy hourly worker. Love the 1 man shops, few and far between. They cost more but you usually get something nice, they cant afford to screw up.
They tend to idiot proof motors sometimes too
thanks
pump gas, reg or premium?
have to re program / tune oe computer?
Pump ****, we usually get 85 - 87 octane. Factory tune, haven't done a thing to it. I've never run anything in it other than the lowest octane available at the pump.
I assume it has something to do with the Vortec head not needing a lot of timing for max power.
Pump ****, we usually get 85 - 87 octane. Factory tune, haven't done a thing to it. I've never run anything in it other than the lowest octane available at the pump.
I assume it has something to do with the Vortec head not needing a lot of timing for max power.
Thanks!
so cam is OE from stock LT4? Not Hot cam upgrade? And flat top 4 VR right ?
Thanks for all the advice.
This will be the first v8 engine I will rebuild, so I am trying to see this as a learning lesson. I really should not have bought all these parts before i had the heads off to see the condition of the block. It was truly a bad decision to just hope for the best after seeing good compression, oil pressure, and relatively good power from the motor.
I guess I am overrating the value of the numbers matching aspect. I'm sure that is more of a novelty when it's an L82 with all the forged bits.
In hindsight, I would have been better off just getting a used 350 vortec motor and freshening one of those up. At least it would have been a 4 bolt main and maybe I could have reused some of the computer controlled pieces. I see a couple for less than $500 on craigslist that maybe could just use a hone, clean and reassemble. This is the other option i am considering, but again, I'm not going up to 6000 rpm; it's an TH400 auto that won't shift that high in the rpm range unless i force it, so i'm not sure I really need a 4 bolt main. Of course, I could also open up this used motor and have it require the same machine shop costs.
But now, I have the heads, retro roller cam, retro roller lifters, and all the rest of the small things to add to the stock motor. I hate selling these because I know I'll only get peanuts for them, and it will take me a while to sell them. For this reason, the crate motor route doesn't seem like the cheapest option at this point because all the retro-roller parts would be essentially a sunk cost.
I'm trying not to focus on the past at this point, and only the costs moving forward.
I think I can get new pistons and get the stock block bored for less than $1k, and maybe I can (optimistically) get $500 for the parts. I don't think I can buy a crate motor for $1500 that will be of equal quality or performance.
This of course assumes I put it back together correctly. ha
But that's part of the fun with this hobby, right?
I'll post some more pics once I start pulling the motor and trans out.
Keep and use the parts you have already purchased and plan your rebuild as you had, but use forged pistons and quality parts.
If your crank, rods and other components are reusable then use them.
For what you have planned a cast crank and 2 bolt main block will work for you.
First, find a really good machine shop near you, who can give you advice, do the machining and maybe help you put together your motor or at the least assemble the short block.
I've been collecting the parts for my 496 build for over a year and it's been a great learning experience.
I will pay the machine shop helping me to assemble the bottom end because they have been building performance motors for over fifty years and I trust them to do it right.
Just make a plan and move forward.
Thanks for all the advice.
This will be the first v8 engine I will rebuild, so I am trying to see this as a learning lesson. I really should not have bought all these parts before i had the heads off to see the condition of the block. It was truly a bad decision to just hope for the best after seeing good compression, oil pressure, and relatively good power from the motor.
I guess I am overrating the value of the numbers matching aspect. I'm sure that is more of a novelty when it's an L82 with all the forged bits.
In hindsight, I would have been better off just getting a used 350 vortec motor and freshening one of those up. At least it would have been a 4 bolt main and maybe I could have reused some of the computer controlled pieces. I see a couple for less than $500 on craigslist that maybe could just use a hone, clean and reassemble. This is the other option i am considering, but again, I'm not going up to 6000 rpm; it's an TH400 auto that won't shift that high in the rpm range unless i force it, so i'm not sure I really need a 4 bolt main. Of course, I could also open up this used motor and have it require the same machine shop costs.
But now, I have the heads, retro roller cam, retro roller lifters, and all the rest of the small things to add to the stock motor. I hate selling these because I know I'll only get peanuts for them, and it will take me a while to sell them. For this reason, the crate motor route doesn't seem like the cheapest option at this point because all the retro-roller parts would be essentially a sunk cost.
I'm trying not to focus on the past at this point, and only the costs moving forward.
I think I can get new pistons and get the stock block bored for less than $1k, and maybe I can (optimistically) get $500 for the parts. I don't think I can buy a crate motor for $1500 that will be of equal quality or performance.
This of course assumes I put it back together correctly. ha
But that's part of the fun with this hobby, right?
I'll post some more pics once I start pulling the motor and trans out.
Almost ...But you can get a Brand New GM iron head roller Vortec L31 Long Block with pan & damper & valve covers delivered for $1600... read through it … with discounts it's $1596 delivered
Find a reputable machine shop and let him make some of these decisions like deck height and boring. Don't buy pistons until he has mic'd it. Where are you located? Maybe one of us knows one nearby.
On the pistons though, I would go with an inexpensive forged piston. Think of it as cheap insurance. If you ever get a tank of bad gas, get stuck with low octane gas, plugged carb, some body borrows it and beats on it, etc, it could detonate (ping) a few times and live. Might save you $1-2000 if that happens. Only $200 or so extra maybe. And if you ever change your mind, and want a bigger cam, you don't have to rebuild it all over again. The hypers are really just cast pistons and when they let go, it's very bad....
Before I committed to boring the block and the new pistons, I'd check the taper and out of round on all 8. Then figure out if it's more economic to bore and new pistons or another block.
It may be that a good hone will clean everything up.
I'd also look at the cost difference between the hypereutectic and forged, remembering that forged will take some detonation with out self destructing. And you're in there, check the crank dimensions- If things are worn to the point the crank needs turned, it may be that it'll be less cash to build a 383.
I'll admit up front I'm not a big fan of the hypereutectic pistons in applications that are not computer controlled. Too easy to make a mistake and go into the detonation zone.
You have some decisions to make on pistons. If you plan to reuse your rods and crank then you need to number the rods so they return to the same holes they came out of - even if your boring the block. Are your reusing the rods as is? Are you reconditioning the rods with new rod bolts? If just reusing the rods make sure they go back in the same holes they came out of.
For pistons you want to have at least one piston pressed off the rod and weight it. You will want to match the original piston weight with the new piston. So lets do some math for you to see how the compressed height works.
Most stock blocks have a 9.025" tall deck. Stock 350 stroke is 3.48" and divided by 2 gives you 1.74 crank throw reach. So 9.025-1.74=7.285" distance to block deck. Now 7.285-5.7" (rod length) = 1.585" remaining from the center of the piston pin to the deck of the block. So your piston with 1.562" compressed height still has 1.585-1.562=0.023" clearance. Most performance machined blocks will get "zero decked" such that the block deck height is 9.00" and those 1.562" compressed height pistons would be 0.001" down the hole - for good quench with a approx 0.040" head gasket.
This is something you need to sort out for yourself as there are soo many options for pistons and compressed heights - dish and valve reliefs too.
01-29-2019, 09:08 AM
The differences you're seeing on compression height is to allow for decking the block. Many lower cost cast and hypereutectic pistons are made "short"..so the piston will remain down in the hole after decking. Fast rebuilders just want to cut everything to one measurement and know that whatever they put in there will run. Is it the right way? No. Often folks end up with pistons down in the hole .040-.060 and it just kills compression and likely to detonate worse. Most shops deck them to provide .005" or so deck clearance.....but since you probably won't be decking it...shoot for the tallest piston. Do the math.
