L28 Stroker crank shaft questions

[Immortal]

Well I am new and have tons of questions as I do my research pulling from every end of the Interwebs. I am going to be doing a stroker build starting next weekend with pulling the motor out of my 77 and I have some questions since this will be my first motor but I have tons of resources (people not wallet).

 

the main questions I have is about the crank it seems like everyone that does the stroker wants the LD28 and I have one that I can get if thats the route I want to go but It raises questions in my mind if that is really the best choice or if so why.

 

correct me if any numbers our wrong please because again this is from the research I have done and I have 0 first hand knowlege on any of these subjects.

 

from what I gather:

stock L28 crank has a storke of 79mm

the LD28 crank has a stroke of 83mm

 

so the reason you would want it is to increase your stroke since all the rest of the stats our the same (should fit right in)

 

using the Ozdat calculator (to estimate) I have some questions about Bore/Stroke v.s. Rod/Stroke

 

the typical build from what I have read is LD28 crank F53 Block head seems to very and then 240 rods with most likley custom pistons

 

with this build I see 2 things that are appealing the Rod/stoke is very high 1.6xx range displacement with the 89mm pistons is the 3.1L and then the second highlight I see is the Max Rod Angle... as this number is lower than stock less friction and from what I gather more efficiency

 

my question is rather than going with the LD28 crank and that setup I want mine to be more custom for one (rods and pistons on my build will be custom forged) but I was thinking what if I got a crankshaft Made for me... if I could keep all the journal size and such the same... so it would fit the same as a LD28 or a L28 but the stroke was something larger than 83.... at first I stumbeld on this idea because of an error in my searchings... I was looking into custom cranks and seen a custom SR20 crank that was 92mm and thought that sr20 was what I needed... but its not. Is it posible to have a Bore/Stroke ratio of over 1.... basicly with a custom crank thats above 88mm (the bore I am going for) with a custom crank at 92mm it would put me at a much larger displacement.. 3.3L

 

the conserns I have is 1 that means i would need a shorter rod... so the Rod/Stroke Ratio suffers and would be closer to 1.4 and the max rod angle is closer to a stock L28 engine... the compression Goes WAY up I think too high from what ive read.... but I want a very hot cam.... like .495 lift is what I was looking at. should I dish my pistons since they will be custom to get my compression down from high 11's and if all this would potentially work would pump gas even be possible?

 

I do have a complete build that I have thought up before this Idea but as the motor is coming out next weekend I need to start from the bottom up and find my crank.

 

any help / ideas would be helpfull and I thank you all in advance

[ctc]

I looked into the same issues when building my stroker. Crower could cut me a custom crank for about $5000-6000 a couple years ago, Scat wouldn't even talk with me.

 

I decided to go with a stock LD28 crank with 240Z rods and had minor clearnce issues with the connecting rods hitting the bottom of the cylinder bores. Had to relieve that area a little bit. I would assume a longer stroke crank would have more issues with bottom of the cylinder bores, but if you use custom rods with a smaller journal size on the big end, you might be ok.

 

I am no expert and am just relaying on info that I gathered. There are more knowledgable people on this board than me.

 

If you are more concerned with HP than "WOW" factor, I would look to the JDM guys and replicate their builds or what others on this board have done. If you are building an unlimited budget show car, then more power to you and be sure to post a build tread, the community would appreciate it.

 

Remeber, just because someone hasn't done something yet doesn't mean it can't be done. It just might not be pracitcal.

[Xnke]

Wow, you've got a LOT of learning to do before you even start this. Spend some time and money getting the How To Modify Your Datsun/Nissan OHC engine book, Nissan Part Number 99996-M8012, and the How to Rebuild Your Datsun/Nissan OHC engine book, the part number which escapes me. Read both of these books through three or four times, take notes, and study before you start spending any more money on parts. It'll save you time, money, and junked parts in the end.

 

First, the L-series connecting rods and cranks (ALL OF THEM) are factory forged.

 

Second, you can buy an 85mm stroke crank from Kameari for about five grand. This is the biggest commercially available crank for the L series six-cylinder.

 

Another manufacturer that makes/had made custom cranks for the L-gata is Moldex.

 

The L31 and L32 stroker motors are popular because they are simple to assemble, parts wise. You use the LD28 crank, L24 rods, and KA24 pistons, in various combinations, to get the compression ratios and bore sizes where you want them to be.

 

Third, if it fits in the block, it fits in the block. If it doesn't fit, then clearance the block. If you can't/won't clearance the block, it doesn't fit.

 

Fourth. A .495" lift cam is not nearly as hot as you seem to think from your post; there are cams out there with .600" and higher lift, and valvetrain components to match. The important number is the duration. Valve lift is all fine and dandy, but the duration is just as important, if not more.

 

There are people on this board that run cams in the .495"-.530" lift in daily drivers, if i'm not mistaken, or cars that are driven daily.

[ezzzzzzz]

Dollar for dollar you're much better off looking at a V8. I built a 2.8 stroker for my 240Z SC project. The cost of the long block including parts was around $6000. I used the LD28 block (85mm bore) and V07 crank, L20B rods and custom JE pistons. The head happens to be a mechanical P90A but could be any head you choose. This engine is nearly square with a rod ratio of approximately 1.7:1. A possible option on your crank would be getting the V07 piece welded up and reground to a greater stroke. You will experience clearance issues on the rod big ends though. Just custom crank, rods and pistons will likely set you back about $7000. That doesn't include the machine work or top end! Personally, I love the sound of a L6 winding up. The challenge of building my unique L6 was the motivator. Had I realistically looked at the cost I would have done a LSx for the cost, power and reliability.

[josh817]

Wow, you've got a LOT of learning to do before you even start this. Spend some time and money getting the How To Modify Your Datsun/Nissan OHC engine book, Nissan Part Number 99996-M8012, and the How to Rebuild Your Datsun/Nissan OHC engine book, the part number which escapes me. Read both of these books through three or four times, take notes, and study before you start spending any more money on parts. It'll save you time, money, and junked parts in the end.

 

First, the L-series connecting rods and cranks (ALL OF THEM) are factory forged.

 

Second, you can buy an 85mm stroke crank from Kameari for about five grand. This is the biggest commercially available crank for the L series six-cylinder.

 

Another manufacturer that makes/had made custom cranks for the L-gata is Moldex.

 

The L31 and L32 stroker motors are popular because they are simple to assemble, parts wise. You use the LD28 crank, L24 rods, and KA24 pistons, in various combinations, to get the compression ratios and bore sizes where you want them to be.

 

Third, if it fits in the block, it fits in the block. If it doesn't fit, then clearance the block. If you can't/won't clearance the block, it doesn't fit.

 

Fourth. A .495" lift cam is not nearly as hot as you seem to think from your post; there are cams out there with .600" and higher lift, and valvetrain components to match. The important number is the duration. Valve lift is all fine and dandy, but the duration is just as important, if not more.

 

There are people on this board that run cams in the .495"-.530" lift in daily drivers, if i'm not mistaken, or cars that are driven daily.

Yah I'm using a standard "stage IV" .495" 290º cam. Comes in around 3200 RPM. The duration is important because that is what affects the location of the power band. More duration, power at the higher RPM, lower duration, power is down low. Braap explains the reasoning behind this pretty well in the "Big nasty head work" thread. If I remember correctly, it widdled down to dynamic compression ratio/cylinder pressure. With high duration cams, you lose cylinder pressure at lower RPM due to the valves being open while the piston is coming onto its compression stroke, essentially dropping your power output. It isn't until you hit higher RPM

where the valve timing works for you instead of against you because cylinder pressure is higher. I don't think the compression ratio changes though.

 

I'd love to contact Moldex especially since our long L6 cranks like to break right before the flywheel. My dad was getting some cranks from them, but at a price. Like $2000... Group buys can save you a couple of hundred. Even without a Moldex crank, you can probably get away with a heat treated crank, very well balanced, and get your reciprocating masses to a minimum! I wouldn't hesitate to buy a $1200 clutch/flywheel setup that weighs like 10 pounds all together if you are going to be seeing more than 7000 RPM on a regular basis. I think I spent around $3000 on my motor but I did everything myself. Obviously the positive thing was that it cost quite a bit less, but you also have to make sure that you are a competent worker. I'll admit, I wasn't ready to do certain things like porting my head. I didn't know what I was doing really...