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madkaw

L31 street performer build

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Glad to back on Hybridz ! 

I have a block on the way to Rebello now and trying to make sure I am clear on my direction for this build. Yes , maybe I should have figured this out already but I have time since Dave is a ways out from working my block. I had a diesel block he wanted so I took advantage of the shipping and sent him my LD crankshaft and a N42 to prep along with the diesel block.

I'm looking for displacement number 1. This engine will be going in my DD - a car I drive whenever weather permits , to the store or a long leasurely drive or maybe to the track for some fun. 

I realize that Dave builds some really big HP motors , and I want HP , but I want longevity and reliability . I am also hoping for versatility also with the short block. For now I am wanting a NA motor , but I know I will want to pressurize at some point. 

Yes I know Dave is the one to talk to, but trying to educate myself as much as possible so I don't waste his time with dumb questions. I imagine most of his stroker builds are purpose build for high HP first priority , so my intentions might change his recipe. 

I know he offset grinds the crankshaft because he thinks the homemade stroker ( L24 rods) have an undesireable rod/stroke ratio. I don't know what length rod he uses but I imagine it's longer - don't see any negatives with this no matter what build. Forged pistons is in his recipe also, not sure if there is a street and race choice on this. Reading up on forged pistons I've read of pin offsets that quiet down cold running and help with excessive clearance noises. Forged are necessary for the rpms that his engines make power at compared to our stock cast counterparts. For a street friendly motor would I need forged pistons compared to quality pistons hypereutectic style. I could live with staying under 7k rpm and build the motor with that intention. 

In my dream world I would like to have a short block that would allow for a small chamber head for fun NA . Later on install a bigger chamber head for pressurized fun. Would forged pistons be required for this or just preferred or not?  I guess from what I read it's all about tune and detonation . Detonation will kill either cast or forged pistons. I guess the cast winds up being chatostrophic vs forged that might not take out the whole motor . Guys do very well with cast and turbocharging as proven on this site. Cast would be cheaper , but how much I don't know. Hell, Dave might not even have or offer a cast option .

Up for opinions and ideas before I chat with Dave. It will be months before he gets to my project , so I have time . He is a bit behind he said because he lost over a week taking care of his mom that was involved in a serious accident . He didn't have much time to talk but I wanted to get him this diesel block and get it out of my shop. I threw this up on FB , but really don't like that venue - glad to be back on Hybridz

 

 

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On 9/1/2017 at 9:12 AM, madkaw said:

Glad to back on Hybridz ! 

I have a block on the way to Rebello now and trying to make sure I am clear on my direction for this build. Yes , maybe I should have figured this out already but I have time since Dave is a ways out from working my block. I had a diesel block he wanted so I took advantage of the shipping and sent him my LD crankshaft and a N42 to prep along with the diesel block.

I'm looking for displacement number 1. This engine will be going in my DD - a car I drive whenever weather permits , to the store or a long leasurely drive or maybe to the track for some fun. 

I know he offset grinds the crankshaft because he thinks the homemade stroker ( L24 rods) have an undesireable rod/stroke ratio. I don't know what length rod he uses but I imagine it's longer - don't see any negatives with this no matter what build. Forged pistons is in his recipe also, not sure if there is a street and race choice on this. Reading up on forged pistons I've read of pin offsets that quiet down cold running and help with excessive clearance noises. Forged are necessary for the rpms that his engines make power at compared to our stock cast counterparts. For a street friendly motor would I need forged pistons compared to quality pistons hypereutectic style. I could live with staying under 7k rpm and build the motor with that intention. 

In my dream world I would like to have a short block that would allow for a small chamber head for fun NA . Later on install a bigger chamber head for pressurized fun. Would forged pistons be required for this or just preferred or not?  I guess from what I read it's all about tune and detonation . Detonation will kill either cast or forged pistons. I guess the cast winds up being chatostrophic vs forged that might not take out the whole motor . Guys do very well with cast and turbocharging as proven on this site. Cast would be cheaper , but how much I don't know. Hell, Dave might not even have or offer a cast option .

Up for opinions and ideas before I chat with Dave. It will be months before he gets to my project , so I have time . He is a bit behind he said because he lost over a week taking care of his mom that was involved in a serious accident . He didn't have much time to talk but I wanted to get him this diesel block and get it out of my shop. I threw this up on FB , but really don't like that venue - glad to be back on Hybridz

Hi Steve...  unless I'm misreading, offset grinding the crank is done to increase it's stroke, not to adjust the rod/stroke ratio.  For a given stroke and rod the ratio will be the same regardless of whether you acheived the stroke by offset grinding or not.  Or are you saying that he's offset grinding your LD crank for even more stroke?  That of course would be making getting a decent ratio even more difficult.  

You're pretty much stuck with having to fiddle with the wrist pin height in the piston (or increasing the deck height which is even more complicated) if you want to use a longer rod _and_ increased stroke.  This is most likely going to be what forces you down the forged piston route - it you can't find a decent hypereutectic piston that happens to have the pin height that you want you'll have to go custom, and I don't think I've seen anybody offering custom cast pistons...

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Tim,

I think I am confusing myself . I believe Dave was comparing the R/S ratio of using L24 rods compared to what he does with the Honda rods. I believe he did not like the R/S ratio of the LD crank with the 133 L24 rods - thus he offset grinds for his desired RS ratio

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2 hours ago, madkaw said:

Tim,

I think I am confusing myself . I believe Dave was comparing the R/S ratio of using L24 rods compared to what he does with the Honda rods. I believe he did not like the R/S ratio of the LD crank with the 133 L24 rods - thus he offset grinds for his desired RS ratio

Hi Steve...

This is what is not making sense to me - you offset grind the crank in order to modify its stroke - presumably to increase the stroke, which doesn't help the Rod to Stroke ratio unless you desire it to be smaller.  Decreasing the stroke by this means also wouldn't make sense since shorter stroke cranks are already available without modification.  Usually you accommodate a longer rod by raising the pin location in the piston.

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I believe the idea is that decreasing the size of the journal by offset grinding allows for a longer rod which increases the RS closer to a preferred 1.7 :1.

I don't know exact length of rod he uses so I can't do the math. But 133 divided by 83= 1.6:1 

So if he can get away with a 138mm rod, then your closer to 1.7 . Plus less side load on the piston walls .

This is my understanding - which might be way off, but no hard numbers to do the actual math. 

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The rod length is measured center to center, so the diameter of the journal would be irrelevant. My understanding is that he was welding and grinds the cranks to get more stroke (actually I think now I heard he's having cranks forged). He's also using diesel blocks now from what I understand, which allows more rod length because the deck is taller. There is a limit to how close you can get the pin to the deck, so taller deck, longer stroke and as long a rod and as high a pin height as possible.

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The key word here is OFFSET. If Dave takes the rod journal and cuts it smaller but to the outside of the center line then he has increased the stroke. He explained to me that the Nissan L24 rod with LD crank make for a crappy RS ratio. So he cuts down the rod journals smaller but OFFSET as to gain stroke at the same time decreasing weight. He then uses the Honda type rod which works with that journal size. He can use a longer rod which decreases side loading and gives more TDC time.

So basically the altering of the RS ratio is by the increased stroke and rod length.

And yes he is doing tall deck motors too. I sold him my diesel block for him to build some super motor.  

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Offset grind or completely different crank doesn't matter.  If you increase the stroke, you will have to decrease the rod length to maintain the same piston deck clearance.  If you  started with zero deck clearance and increased both the stroke and the rod length, your piston is going to come proud of the deck and slam into the head.   Unless, you change your pistons for ones with a shorter pin height or you alter the dimensions of the block.

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Keep in mind swapping to a modern forged piston from whoever along with rod if they put any thought into it at all is gonna drop pounds off the reciprocating weight in an L engine like the effect of a lightened flywheel

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On 9/12/2017 at 8:54 PM, madkaw said:

The key word here is OFFSET. If Dave takes the rod journal and cuts it smaller but to the outside of the center line then he has increased the stroke. He explained to me that the Nissan L24 rod with LD crank make for a crappy RS ratio. So he cuts down the rod journals smaller but OFFSET as to gain stroke at the same time decreasing weight. He then uses the Honda type rod which works with that journal size. He can use a longer rod which decreases side loading and gives more TDC time.

So basically the altering of the RS ratio is by the increased stroke and rod length.

This is what I've been getting at - yes increasing the stroke DOES alter the rod/stroke ratio, but by itself it moves it in the wrong direction.  The only two ways to compensate for this AND to get to your desired ratio are:

1) increase the deck height (this is why Dave is collecting diesel blocks)

2) decrease the piston's compression height (i.e., raise the pin location)

The L24 rod is already requiring this, since it is already longer than the stock L28 rod.  If you want to achieve increased stroke and a rod longer than the L24 and keep the stock block, your only option is to modify the compression height of the piston, and this is definitely what Dave is doing here.  If he's doing a really long rod then he's likely having to resort to some tricks like letting the pin bore impinge on the oil ring groove, like this:

images?q=tbn:ANd9GcTMhKwc8adqAAGpzaTdUTc

FWIW, I'm currently running 5.3" (134.6mm) rods with an 83mm stroke, and the pin bore on my pistons is pretty much as close to the oil ring as it can get without resorting to the above.  A 1.7 r/s ratio with an 83mm bore dictates a 141.1mm rod, which would require the pin bore to be 6.5mm higher than mine.

Sorry, couldn't find a pic of my pistons that showed this, but they look pretty much like this:

pinheight.jpg

Edited by TimZ
adding info

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