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Good quality Rotating Assembly kit

Old 01-08-2019, 06:44 PM
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Originally Posted by Summitracing View Post
Cast pistons break due to tight .011-ish ring end gaps most often and take out everything. Gaping worn rings on stock pistons is odd if everything comes apart anyway. Putting new rings that need gapped anyway on an old piston also not a good way to go and the ring grooves in the piston are worn. So that leaves new forged pistons with extra thick lands and file to fit rings and *usuallyĒ aftermarket 6.125 length .927 rods being a logical upgrade and one considered a good value. Factory cast crank is ok at that, but not a lot more money for another 40 cubes with a stroker. Less reciprocating weight for faster acceleration and something that can take a serious beating.
I'm not talking about rebuilding a motor with stock pistons. I'm talking about taking a known good running motor and just boosting it without rebuilding it. No need to take apart a good running motor to gap rings for 600 whp. My current motor is at the 600 whp range with nothing but a cam change, headers, and a procharger at 12 psi with a completely stock as it came from GM bottom end.

I'm with you on putting good pistons and rods in if you are going to rebuild it anyway like the OP is doing. For the other guy with a good running motor I'd go ahead and put the procharger on it without any worries. Stock cranks have been way beyond 600 whp with no issues. I will never tell someone not to use the best parts they can afford even if it's overkill for their goals, but lets not mislead someone into thinking a forged crank is necessary for 600 whp either. If it gives you piece of mind then sure go ahead and put a forged crank in it, but can a thin sleeved ls1 block actually handle more boosted power than a stock crank anyway? Boost doesn't really care about the extra 40 cubic inches either. If you are producing 1500 cfm with a procharger they say that will support 1000 horse power. It doesn't matter if it's a 347 or a 383 that 1500 cfm will support the same 1000 horse power. The larger cubic inches will move that dyno curve to the left in other words making more power at a lower rpm. The issue then is at the 600 whp and above level is that extra low end from the longer stroke even needed or useable? Also at what power level does the longer stroke due to the effect on piston design actually become weaker than the pistons in a 347? There is a reason some high power boosted guys prefer 3.9" or shorter strokes over the 4"+ strokes.
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Old 01-08-2019, 08:55 PM
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3.900 is for people that cant do math and canít be bothered to measure piston skirt, ring land real-estate, and cylinder length. This has been settled over and over again for 15 years now.

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Old 01-08-2019, 09:41 PM
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Originally Posted by Summitracing View Post
3.900 is for people that cant do math and canít be bothered to measure piston skirt, ring land real-estate, and cylinder length. This has been settled over and over again for 15 years now.

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Old 01-08-2019, 10:31 PM
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Originally Posted by BCNUL8R View Post
680 rwhp was huge for a sbe ls back then. Enough people have laid the groundwork for tuning procharged ls engines now itís not as big of a deal as it was back then.
Agreed. Doing a SBE LS with a Procharger, good heads, reasonable cam at ~600 whp much easier now and probably last way longer too.

The Procharger and a SBE LS or Forged 347 sound like choices that meet the OP's goals. Definitely a lot of good choices and paths forward.

I will confess l like that instant response and torque on the bottom end at low rpm the stroker gives in a daily driver. Most of the Procharger sets ups I've ridden in are pulling vacuum on the boost gauge at cruising rpm on the street.

Originally Posted by Summitracing View Post
3.900 is for people that cant do math and canít be bothered to measure piston skirt, ring land real-estate, and cylinder length. This has been settled over and over again for 15 years now.
Well said!!! +++.

​​​​​Agreed 100% based on experience with two 4 inch crank strokers.

Math is scary to some folks.

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Old 01-08-2019, 11:01 PM
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Originally Posted by 99 Black Bird T/A View Post
Agreed. Doing a SBE LS with a Procharger, good heads, reasonable cam at ~600 whp much easier now and probably last way longer too.

The Procharger and a SBE LS or Forged 347 sound like choices that meet the OP's goals. Definitely a lot of good choices and paths forward.

I will confess l like that instant response and torque on the bottom end at low rpm the stroker gives in a daily driver. Most of the Procharger sets ups I've ridden in are pulling vacuum on the boost gauge at cruising rpm on the street.



Well said!!! +++.

​​​​​Agreed 100% based on experience with two 4 inch crank strokers.

Math is scary to some folks.
This wasnít to disparage people that donít know the particular math behind this. Its actually fairly simple math. The problem is those whoíve been offered guidance...including those that design pistons for a living...who frankly are too lax or ignorant to keep machinists, engine builders and racers out of trouble.

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Old 01-09-2019, 05:04 AM
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Originally Posted by Summitracing View Post
3.900 is for people that cant do math and can’t be bothered to measure piston skirt, ring land real-estate, and cylinder length. This has been settled over and over again for 15 years now.
I've had 4" stroker engines everyone knows that can be done, but rather than actually address my comments you'd rather just insult me that I don't know math? The issue is you are trying to sell parts he doesn't need. For 600 rwhp he doesn't need a forged crank what so ever. My comment was in relation to the fact that at the power level in which a forged crank becomes necessary a 3.9" stroke motor allows a stronger piston. At 1000+ horse where a forged crank is actually needed boost cares less about 0.1" of stroke and more about stronger piston ringlands.

Go ahead and insult me I don't know math blah blah blah, but I have nothing to sell. I don't want people wasting money on parts they don't need while I'm over here making 600 rwhp on a stock motor. I've had cars with a lot more power than my current one as well and various combos NA, nitrous, turbo v6, and now procharged ls. I get the value of low end torque in a street car, but at a certain level it become unusable anyway as you just blow the tires off on the street. The proper gear and/or stall for the combo goes along way also, but I don't know math so you all enjoy selling this guy stuff he doesn't need to reach his 600 rwhp goal.
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Old 01-09-2019, 05:45 AM
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I bet my friend with his 390Ē motor with over 1200 rwhp running high 4ís in the 1/8th with a true street car driven to and from the track is really missing that extra low end torque that 0.1Ē extra stroke would have given him. My point is at the high boost levels that would actually require a forged crank squeezing every cubic inch possible out of it becomes less important.

People donít put a 3.9Ē stroke in a high boosted LS because they donít know math.
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Old 01-09-2019, 09:26 AM
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Originally Posted by BCNUL8R View Post
600 whp is not too much for the street at all, but you just have to respect the power and don't drive over your head. Forged internals aren't necessary for that power. That's where I'm at with a stock bottom end, but it's a low mileage weekend toy with occasional drag strip visits. I'm of the mindset of not taking apart a good running motor so don't be afraid to boost your stock motor. Just understand it will not last forever at that level and I wouldn't push a daily that far. Power potential is based upon the CFM the blower is producing. Boost is measured at the intake and is a measure of resistance. If you have a good flowing motor it will make more power at a lower boost number. Their 50% increase is based upon a stock motor with the pulley they supply with the base kit. The rpm you spin the blower will determine how much power it's capable of supporting period. The boost number will vary based upon how well the motor flows. A cammed 346 with really nice heads and high flowing exhaust might make 600 whp at 10 psi while a stock ls1 with the same blower and pulley combo might make 600 whp, but be at 15 psi.
No offense intended. As we stated, the factory crank with forged rod and piston are desirable at the O.P.'s power level. You'll notice that Dart shortblocks come in 387 Cid to suit people with the need for the powerband and 4" stroke 427 Cid. as well. Cubic inches for blower cars do the same that they do for N.A. cars, namely allow the rpm to be turned down to keep the valvetrain in control. The car doesn't need to be geared as hard or require as much of a stall converter. You could accomplish this with a smaller pulley (and less belt wrap), but then you're just adding heat and running it closer to the limits of the fuel. For Turbo people, going to a much larger Turbine housing and A/R can be used and still spools more quickly. This reduces reversion and makes more power there as well.

Here's the math many people don't know. We've attached a (very) rough sketch of a typical 1.110 Compression Height Wiseco piston with a 1.2 1.2 3mm ring pack in a factory iron block. These have the shortest cylinder lengths of all the blocks at 5.430 effectively and aluminum are typically 5.550. The ring lands are maximized at nearly .300 top and .165 second. The third land could be pulled back to .070 without issue and add more meat to the top or second land. A .928 pin bore is within .009 of the top of the oil ring groove and the rest of the oil ring groove hangs below. From there we have piston skirt that remains riding in the bore at BDC. Skirt taper varies not only in the amount, but more importantly where it's introduced. A piston needs to have at least .080" of piston skirt at full diameter up above the liner at bdc with taper being introduced above there. This avoids the sharp intersection that would occur, act as a razor blade, and destroy the skirt in short order.

Wiseco's typically have a break point .650 below the oil ring groove or .525 depending on the model. The .525 is always found on the 1.050 C.H. pistons used with 4.125 strokes and serves well with 4.000 in. as well. From there, it adds a slight amount more stability too, but most of that comes from the amount of taper above the break point.

Herein lies the rub. Many piston companies didn't have a high enough break point with 4" strokes first became popular. This is what wiped out peoples engines 15 years ago. Wiseco and Diamond were the first to start publishing the actual reason for this skirt profile to be correct. Other companies were behind (and may still be). A lot of piston companies used the same break point for non-strokers as their stroker pistons at about .900 in. below the oil ring groove. You can see that didn't fare so well with either a 4.000 in. (or 3.900 in. for that matter) as it was definitely introduced far below the bottom of the cylinder liner at BDC.

This break point theory applies to all stroker engines. Ford, Chevy, Chrysler. etc. It's pretty simple for a good piston designer to look at the ring stack and the intake pocket etc. and determine the maximum stroke an engine builder should pursue. As a side note, we've done 2.200 rod journal/.990 pin 1.5/.043/3mm assemblies for the 2k hp plus guys, but the same theory applies and they're often tall deck, raised and larger cam journal anyway. The industry sells a ton of 4" stroker rotating assemblies a year and the cars aren't mosquito foggers or breaking ring lands.
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Taper.pdf (47.5 KB, 9 views)
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Old 01-09-2019, 11:13 AM
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Originally Posted by Summitracing View Post
No offense intended. As we stated, the factory crank with forged rod and piston are desirable at the O.P.'s power level. You'll notice that Dart shortblocks come in 387 Cid to suit people with the need for the powerband and 4" stroke 427 Cid. as well. Cubic inches for blower cars do the same that they do for N.A. cars, namely allow the rpm to be turned down to keep the valvetrain in control. The car doesn't need to be geared as hard or require as much of a stall converter. You could accomplish this with a smaller pulley (and less belt wrap), but then you're just adding heat and running it closer to the limits of the fuel. For Turbo people, going to a much larger Turbine housing and A/R can be used and still spools more quickly. This reduces reversion and makes more power there as well.

Here's the math many people don't know. We've attached a (very) rough sketch of a typical 1.110 Compression Height Wiseco piston with a 1.2 1.2 3mm ring pack in a factory iron block. These have the shortest cylinder lengths of all the blocks at 5.430 effectively and aluminum are typically 5.550. The ring lands are maximized at nearly .300 top and .165 second. The third land could be pulled back to .070 without issue and add more meat to the top or second land. A .928 pin bore is within .009 of the top of the oil ring groove and the rest of the oil ring groove hangs below. From there we have piston skirt that remains riding in the bore at BDC. Skirt taper varies not only in the amount, but more importantly where it's introduced. A piston needs to have at least .080" of piston skirt at full diameter up above the liner at bdc with taper being introduced above there. This avoids the sharp intersection that would occur, act as a razor blade, and destroy the skirt in short order.

Wiseco's typically have a break point .650 below the oil ring groove or .525 depending on the model. The .525 is always found on the 1.050 C.H. pistons used with 4.125 strokes and serves well with 4.000 in. as well. From there, it adds a slight amount more stability too, but most of that comes from the amount of taper above the break point.

Herein lies the rub. Many piston companies didn't have a high enough break point with 4" strokes first became popular. This is what wiped out peoples engines 15 years ago. Wiseco and Diamond were the first to start publishing the actual reason for this skirt profile to be correct. Other companies were behind (and may still be). A lot of piston companies used the same break point for non-strokers as their stroker pistons at about .900 in. below the oil ring groove. You can see that didn't fare so well with either a 4.000 in. (or 3.900 in. for that matter) as it was definitely introduced far below the bottom of the cylinder liner at BDC.

This break point theory applies to all stroker engines. Ford, Chevy, Chrysler. etc. It's pretty simple for a good piston designer to look at the ring stack and the intake pocket etc. and determine the maximum stroke an engine builder should pursue. As a side note, we've done 2.200 rod journal/.990 pin 1.5/.043/3mm assemblies for the 2k hp plus guys, but the same theory applies and they're often tall deck, raised and larger cam journal anyway. The industry sells a ton of 4" stroker rotating assemblies a year and the cars aren't mosquito foggers or breaking ring lands.
Thank you for the detailed reply. Iím not an engine builder Iíve always bought short blocks and taken it from there. My statements before on stroke were based upon what Iíve learned from friends and explained to me by my previous engine builder. I tried to phrase what Iíve learned in the form of a question to get input from you and others on those details to hear other opinions. Thatís why the initial response of knowing simple math rubbed me wrong and your current reply was more what I was looking for. Itís a forum and itís sometimes easy to misinterpret replies though.

My last 408 was built in 2006-07 area. It ran well, but used a little oil. I wouldnít say it was excessive and the only time I saw blue smoke was if I got on it before letting it warm up. The piston skirts were scuffed when we tore it apart for a rebuild.

After having a turbo v6, heads and cam cars, and a stroker ls with nitrous I wanted to try a procharger this time around. There is something to be said for high compression big cubic inch motors for the fun factor on the street. For my current goals the procharger fit the bill and itís alot of fun also. At low boost with a procharger itís definitely peaky power, but going from 8 psi to 12 psi really woke it up while making a lot more up top it really helped the midrange as well.

I will also also say I always buy from summit if you have what I need and Iíve always been happy. Itís nice getting my order in 2 days. Thanks again for the detailed reply.
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Old 01-09-2019, 11:16 AM
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Originally Posted by BCNUL8R View Post


Thank you for the detailed reply. Iím not an engine builder Iíve always bought short blocks and taken it from there. My statements before on stroke were based upon what Iíve learned from friends and explained to me by my previous engine builder. I tried to phrase what Iíve learned in the form of a question to get input from you and others on those details to hear other opinions. Thatís why the initial response of knowing simple math rubbed me wrong and your current reply was more what I was looking for. Itís a forum and itís sometimes easy to misinterpret replies though.

My last 408 was built in 2006-07 area. It ran well, but used a little oil. I wouldnít say it was excessive and the only time I saw blue smoke was if I got on it before letting it warm up. The piston skirts were scuffed when we tore it apart for a rebuild.

After having a turbo v6, heads and cam cars, and a stroker ls with nitrous I wanted to try a procharger this time around. There is something to be said for high compression big cubic inch motors for the fun factor on the street. For my current goals the procharger fit the bill and itís alot of fun also. At low boost with a procharger itís definitely peaky power, but going from 8 psi to 12 psi really woke it up while making a lot more up top it really helped the midrange as well.

I will also also say I always buy from summit if you have what I need and Iíve always been happy. Itís nice getting my order in 2 days. Thanks again for the detailed reply.
That probably should have been our first reply, but it was late. Thanks for the opportunity to explain the rationale more fully and thank you for your Patronage. Let us know when you're building your next bullet.
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Old 01-09-2019, 11:28 AM
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Originally Posted by Summitracing View Post
Here's the math many people don't know. We've attached a (very) rough sketch of a typical 1.110 Compression Height Wiseco piston with a 1.2 1.2 3mm ring pack in a factory iron block. These have the shortest cylinder lengths of all the blocks at 5.430 effectively and aluminum are typically 5.550. The ring lands are maximized at nearly .300 top and .165 second. The third land could be pulled back to .070 without issue and add more meat to the top or second land. A .928 pin bore is within .009 of the top of the oil ring groove and the rest of the oil ring groove hangs below. From there we have piston skirt that remains riding in the bore at BDC. Skirt taper varies not only in the amount, but more importantly where it's introduced. A piston needs to have at least .080" of piston skirt at full diameter up above the liner at bdc with taper being introduced above there. This avoids the sharp intersection that would occur, act as a razor blade, and destroy the skirt in short order.

Wiseco's typically have a break point .650 below the oil ring groove or .525 depending on the model. The .525 is always found on the 1.050 C.H. pistons used with 4.125 strokes and serves well with 4.000 in. as well. From there, it adds a slight amount more stability too, but most of that comes from the amount of taper above the break point.

Herein lies the rub. Many piston companies didn't have a high enough break point with 4" strokes first became popular. This is what wiped out peoples engines 15 years ago. Wiseco and Diamond were the first to start publishing the actual reason for this skirt profile to be correct. Other companies were behind (and may still be). A lot of piston companies used the same break point for non-strokers as their stroker pistons at about .900 in. below the oil ring groove. You can see that didn't fare so well with either a 4.000 in. (or 3.900 in. for that matter) as it was definitely introduced far below the bottom of the cylinder liner at BDC.

This break point theory applies to all stroker engines. Ford, Chevy, Chrysler. etc. It's pretty simple for a good piston designer to look at the ring stack and the intake pocket etc. and determine the maximum stroke an engine builder should pursue. As a side note, we've done 2.200 rod journal/.990 pin 1.5/.043/3mm assemblies for the 2k hp plus guys, but the same theory applies and they're often tall deck, raised and larger cam journal anyway. The industry sells a ton of 4" stroker rotating assemblies a year and the cars aren't mosquito foggers or breaking ring lands.
Excellent post. Are there any drawbacks to raising the major diameter higher in the skirt?
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Old 01-09-2019, 12:18 PM
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Originally Posted by KCS View Post

Excellent post. Are there any drawbacks to raising the major diameter higher in the skirt?
It can and has been done and it's a balancing act as the top of the piston is undergoing a lot more thermal expansion (from combustion) than the bottom (mostly subject to oil temps). Basically the piston needs to be straight up and down when it's up to temp.

You don't want to make a big change all at once and seize a piston due to lack of taper. This takes careful reading of used piston skirts to evolve the design over time. You would think it was all done through FEA, but with the differences in blocks and sleeve materials and thickness...good old fashioned skirt profile reading is still the primary method of getting it right. The better companies have in-house dynos to get it right the first time, but others work through evolution. This works too, but at a slower pace. Often based what customers send back from the field as they develop engines.

The skirt profile (cam and taper) can be affected by things like water jacket temperature differences across all 8 cylinders. Because of this, pistons are made to be happy in the cylinder that has the least heat transfer. #7 in a LS often to blame for ring butting because the top ring cant transfer heat out quickly enough, but we've seen evidence of 6 getting hot as well.

The very top of a piston's top land may be .054-.060 smaller than the bore in many cases. This can be more of less depending on the app. and bore size. The arc to the bottom of the break point up isn't constant. This is because the top, second, and oil rings are all transferring heat into the water jackets with the top ring doing the most work. You'll usually see round lands that are tapered from the bottom of the third to the top of the top. Sometimes you'll see stepped lands, but his takes a little more development.

On high end pistons used in Pro Stock, Nascar etc., oval ring lands and even other shapes can be found. This is based on structure (mass) through the pistons differing (like the pin towers at the sides for instance). It requires a lot of testing over many many successive builds to get this level of resolution.

Some engine builders will have a go/no-go for cold piston rock before they start seeing signs of oil consumption. This is something easily modeled and there are guidelines that create a stable piston whether it's a tall standard stroke piston or shorter stroker piston. A company's stocking piston will have this all worked out (usually).

Thanks and let us know if you have any more questions.
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Old 01-09-2019, 12:30 PM
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Originally Posted by Summitracing View Post
That probably should have been our first reply, but it was late. Thanks for the opportunity to explain the rationale more fully and thank you for your Patronage. Let us know when you're building your next bullet.
Iím in the planning stages now because my current 600 whp isnít enough...lol. Iíve got the fuel system and driveline to support 800 rwhp and my D1x procharger should get me there as well. The built 4l60e is a question mark, but Iíll just run it till it breaks. The motor build is what Iím planning now and just trying to learn more every day.
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