Help selecting a rod stroke ratio for a turbo build

[turbobluestreak]

Thanks to everyone that has contributed, butthis was going in the right direction but seams to be more of a stroker build debate. I agree that a short rod makes for less detonation but you must remember that a short rod as it excleerated away and towards doesn't do so well for full combustion but it makes great vacume but in the land of turbo who needs vacume to do the work.

 

Stroking the L28 is a great idea but I don't see why to because you can't get the proper flow out of our heads to make the short stroke effective(with out lots of money and work) this isn't some 4 valve pent roof chambers its an old 2 valve heart shape. The more fuel I can burn in a tightly compressed area the more power that can be transmitted to the crank shaft, hench the increased dwell time at tdc of the longer rods. But then again the entire tune needs to be set up propperly because of the ignition timing needed for a long rod so trying to balance this with not detonating. I think the design needs to work around all the variables not just one or two. For N/A I would do a big stroker and be happy but time and time again the japaness with there small 2.0 turbo engine (4G63) make lots of power with a turbo.

 

Finally the rb26 has a small stroke and a realively good r/s and it makes Most of the L6s look like a bunch of toys. I would say that they figured out what needs to be done to make power out of a inline 6 but that just my opinion.

 

but thanks again for posting guys maybe if you concentrate on rod/stroke for a turbo we could be the sticky that DAW has been after.

 

tbs

[TheNeedForZ]

Mack,

 

I've read differently:

 

"All L-series engines share the same basic block design except for that used in the 280ZX turbo. The first L28 Turbo blocks have the front three and rear three cylinders Siamesed. Webs are cast between cylinders 1 and 2, 2 and 3, 4 and 5, and 5 and 6. Although this improved block rigidity, it was thought that the webs inhibited coolant flow around the Siamesed cylinders."

 

-How to modify your Nissan & Datsun OHC engine-

[JMortensen]

Pull a freeze plug on an F54 and shine a light DOWN in the block and you can see the siamesed web. F54 vs N42 has been dealt with here before, and apparently Sunbelt likes the N42.

 

I have a friend who built a 3.2 liter stroker with an N42 and it started blowing smoke within 1000 miles. He mic'ed the bores and they were definitely stretched in the middle causing the rings not to seal.

 

If I were doing a huge bore I'd go F54. Otherwise I don't think it really makes too much difference either way, but that's just MO.

[Mack]

eh, that how to hotrod and race book has been proven to give inaccurate information on more than one account.

 

We'll just wait for 1 fast Z to chime in, he has sonic tested both blocks and went with an N42 for his 3.1L build. must be a reason.

 

On the rod/stroke ratio.....

 

TBS>>> you would probably have a good motor is you went with a 1.75 rod/stroke ratio. You would have to get either FJ20ET rods or some LD28 rods, both bein 140mm. the LD28's would be your best bet for availability, but both sets would requitre custom pistons. This is porbably a moot point, because if you are building a bottom end for a turbo motor, the first thing you are going to do is toss the stock cast pistons.

 

Finally the rb26 has a small stroke and a realively good r/s and it makes Most of the L6s look like a bunch of toys. I would say that they figured out what needs to be done to make power out of a inline 6 but that just my opinion.

 

yes tehy did figure it out, and you figured it out in your post. What it needed to make power was a 4 valve pent roof head. these old side flow heads can make gobs of power, if you know what you are doing, but its not going to be close to an RB26DETT, or even the almighty RB30DET.

 

Electramotive was getting 600HP in race trim (road race, not drag race) but I think they changed their engine configuration, as it was almost a stock L28, but not quite. I think they went with a better rod/stroke ratio or maybe a shorter stroke/bigger bore.

[turbobluestreak]

I'm thinking about trying a set of stock turbo piston, 240 rods and crank for now and if I like it have a custom set of pistons made for it. I'm thinking maybe a 87mm and possible adding a few cc's on top of the piston in a off set dome shape, I guess more like a heart to match the chambers, to bring my compression up to the 8.5-8.8 range. This is of course is with the P90 head, because if I remember correctly, if I'm wrong someone please correct me, for and engine to be more volume metric efficiency you should go with a larger chamber but still have a higher level of compression, but a large chamber yields less compression hence my offset heart idea to keep the compression ideal for the turbo and maintain a large chamber. But then again this set up will change my bore stroke ratio and I'm just starting to gather info on that before I set any of my plans into stone.

 

Thoughts guys??

 

 

tbs

[Guest ON3GO]

i would use a N42 head and get it ported and worked.

 

mike

[Mack]

If you are looking to maximize your detonation resistance and keep a decent compression ratio, a piston dish that mirriors your combustion chamber is ideal. that being said..

 

If you are looking for a low to mid 8 compression ratio motor utilizing stock parts, just get a set of flat top pistons and un-shroud the valves on your head out to the fire ring on the head gasket. That should bring your compression ratio a bit lower, but not much than a factory flat top P79/P90 head combo, which is about 8.8:1 this will also improve off boost response. It will also be fairly detonation resistant because you are utilizing the high quech combustion chamber design by using the flat tops, as opposed to the dished ones. Im sure this will open up a whole new can of worms....

 

So, you are using an L24 crank?!? well then, that opens up a whole new realm of possibilities! LD28 rods and you could use some VG30E pistons, they had a 31.75mm compression height. which would be about perfect for an L24crank/LD28 rod combo. Granted you would have to bore out to 87m, and take about .7mm off the tops of the pistons, but I dont think thats TOO much work..... aside from getting the rods bushed or pistons bored out to make the piston pins work....

[JMortensen]

That's almost 1.9 rod ratio for Mack's setup. Not bad. I suppose the easier thing to do is run L24 crank and rods with L28 flat top pistons and P90. That gets 1.8 rod ratio with no fuss and all "normal" components. IIRC the pin height and all that is the same on the L24/26/28.

 

Wonder how low the compression would be that way though...

 

EDIT--According to Lengine.exe that would get you 8.05:1, with a .080 overbore you get 8.32:1. .080 over with a 1mm gasket gets 8.52:1.

[Cody 82 ZXT]

That's almost 1.9 rod ratio for Mack's setup. Not bad. I suppose the easier thing to do is run L24 crank and rods with L28 flat top pistons and P90. That gets 1.8 rod ratio with no fuss and all "normal" components. IIRC the pin height and all that is the same on the L24/26/28.

 

Wonder how low the compression would be that way though...

 

EDIT--According to Lengine.exe that would get you 8.05:1' date=' with a .080 overbore you get 8.32:1. .080 over with a 1mm gasket gets 8.52:1.[/quote']

 

 

That's an intreasting combo. So what would the displacement come out to?

[tfreer85]

According to OZDAT engine calculator:

 

displacement comes out to 2.569 Litres.

Rod/stroke of 1.805

Bore/Stroke .857

Max Rod Angle 16.085 degrees

Deck Clearance -.100 mm

Redline Piston Speed 1031.800 m/min

 

Using a L28 Block (non- F54). L24 Crank, L24 Rods, Late L28 Pistons, P90 Head (L28ET), L28 Cam.

 

All the same bored out +1mm;

 

Displacement 2.629 Liters

Rod/Stroke 1.805

Bore/Stroke .847

Max Rod Angle 16.085 degrees

Deck Clearance -.100 mm

Redline Piston Speed 1031.800 m/min

 

Tyson

[1 fast z]

Ok, the F54 Block provides BETTER cooling than the N42. Which is stronger? Well the N42 is. SOLID between the bores, 1-2-3, 4-5-6. Whats more rigid, solid form or webbing? No brainer there. I HAVE sonic tested MANY L series blocks, as we own a sonic tester. I use N42 blocks for ALL my builds, that require an overbore. I run a HOT 3.1 liter N42 block with a stock radiator, and see NO overheating problems. The cylinder thickness on F54 blocks is already .150" in ALOT of spots on most cylinders. It doest take a rocket scientist to realize that on a .120" over bore, that is .090 Walls. Which isnt that bad really, as some sleeves are that thickness, but Woule you rather have .150" or .200"+ like is on the N42 blocks? The casting content on the 75-76 blocks are ALSO a high nickel content, which is always stronger, than a regular cast iron low nickel content block. Your buddy probably didnt do something right on his motor build, and did not sonic test for core shift on his motor. I also offset bore my blocks to compensate for the core shift. My last bored 3.504" bore I moved as much as .025" in some bores, some needed no shift with the boring bar. To obtain MAXIMUM thickness, a sonic tester IS needed, and offset boring is optimal.

[Eric]

According to OZDAT engine calculator:

 

displacement comes out to 2.569 Litres.

Rod/stroke of 1.805

Bore/Stroke .857

Max Rod Angle 16.085 degrees

Deck Clearance -.100 mm

Redline Piston Speed 1031.800 m/min

 

Using a L28 Block (non- F54). L24 Crank' date=' L24 Rods, Late L28 Pistons, P90 Head (L28ET), L28 Cam.

 

All the same bored out +1mm;

 

Displacement 2.629 Liters

Rod/Stroke 1.805

Bore/Stroke .847

Max Rod Angle 16.085 degrees

Deck Clearance -.100 mm

Redline Piston Speed 1031.800 m/min

 

Tyson[/quote']

how well would these perform off boost? i'm looking to rebuild my engine soon, but get it all set up for boosting it once i have more money. i'd be running the stock 280z head(N47?) but will switch to the P90 later on, if this layout works well. i'm looking for a setup that requires little to no machineing, none would be ideal.

[tfreer85]

I think most of the machinest/builders will agree that you should at least hone your block if your cylinder walls are in REALLY good condition. However you might have to use oversized piston rings which IMO isn't the best for a boosted engine as you allow for more chances of blow-by or blow through (not the best for piston to cylinder wall seal). I think the best option for least amount of maching required would be bore the block out 1mm and get new pistons. If you use the N47 head you'll get 9.493 Static compression ratio, which will be fine for a NA motor until you go to turbo and the P90 head. Which will drop your compression back down to 8.231 which would be good for a street boosted L series motor. Some of the better engine builders can chime in and correct me if i'm wrong.

 

tyson

[Eric]

i hope u'r right, cause that will be awsome. i've been thinkin that a tad overbore would be a good idea since the engines at 160k and was beat up pretty good.

[JMortensen]

Your buddy probably didnt do something right on his motor build, and did not sonic test for core shift on his motor. I also offset bore my blocks to compensate for the core shift. My last bored 3.504" bore I moved as much as .025" in some bores, some needed no shift with the boring bar. To obtain MAXIMUM thickness, a sonic tester IS needed, and offset boring is optimal.

I don't know if they sonic tested it or offset bored it or what. He was a student at UTI at the time, and it was his roommate's project in his "performance engine building" class or something like that. They built it together, and it failed almost immediately. He always thought that if they had used the F54 it would have been OK since the bow in the cylinder was right in the middle, but I don't think that motor ever got fixed. I imagine if it was offset bored he would have said as much, and I don't remember him mentioning that at all, so I'm guessing they just did a straight .120 overbore. Not sure on the sonic testing either.

[TheNeedForZ]

1 fast z,

 

Great info and I stand corrected. If what you said is true then it is something every Z guy should know. One of the great myths about L series block is cleared up.

 

I guess "extra web" does not equal to "extra metal" as most of the info out there claims. Thanks again for the info.

[1 fast z]

" He was a student at UTI at the time"

 

 

This tells me alot, THANKS for clearing that up. No offence to any UTI guys here if there are any, but I have met MANY of them, and OMG. They dont know much, thats for sure.

 

 

Yea, I used to think the same when I first started in z's. I was building my turbo stroker motor, and I used the F54 block, cause Like you said, thats ALL I had read. Well, we sonic tested and offset bored, yada yada, and I could only go .050 over, to obtain 1/8" cylinder walls. So then I said, What the hey, and went out and grabbed one of the N42 blocks. So I sonic checked it just for the heck, of it, and I was like, WHAT!!!! Noooo, this cant be true, cause I have read on a dozen sites that the F54 is the SIAMEESED block, but sure enough, it ISNT. So I finished boring the last bore on the F54, just to complete the boring job. I then hot tanked the N42, then started boring that one .125" so I could still obtain .125" cylinder walls in the thinnest points.

 

 

 

YES I have sonic tested a V07 block. They have .150" walls already. Which means you could do a 2mm overbore safley, but that would be about it, unless you took extra percations then you could maybe get a .120 overbore out of it.

[crazy280]

1 fast z,

Are you saying that the f54 is not siamesed? Becuase that conflicts with all the published specs on these blocks (including manufacturer data, shop manuals, etc). Why would Nissan re-engineer their block to be WEAKER when they planned a turbo application? I've never cracked open an f54 myself, but maybe some of the turbo guys here could chime in.

[turbobluestreak]

I think you guys are looking at the extra webbing in the wrong light. Yah a solid block like 1 fast z pointed out on the N42 would be very strong, but how flexible would it be? With that extra strength in a solid part also comes brittleness. Yes I understand that it was an alloy block, but its not that the F54 block is stronger, its that for a turbo application Nissan designed it to flex to keep the cylinder from cracking.

 

I still stand by that the F54 is a perfect block for a turbo engine because of the changing pressures that is seen inside the cylinders Atmosphere, boost, Atmosphere, boost, ... (You know repeated loading and reduced loading) but I would say that an N42 would be ideal for a N/A build because the pressure inside doesn't fluctuate nearly to the extent that a turbo would see. At least this is why I think Nissan would have change there design.

 

tbs

[1 fast z]

Nissan changed the block design for BETTER COOLING, and yes, I guess that goes hand in hand with expansion and contraction. But the main reason is they figured the turbo would add more heat, and the block would then be more endothermic, and therefore, they figured they needed more cooling.

 

 

Ok, if it were me. If you were boring a block more than 1 mm over, for a turbo app, I would DEFFINITLY use a N42, if not, then yea, use the F54. But for overbore motors, I would use a N42.