L26 Turbo vs ITB

[NorthStar]

Hey guys, 

 

I have a bone stock L26 in my '74 260Z. I'm in the middle of upgrading the drivetrain with an OS Giken LSD, aluminum driveshaft and aftermarket ZCarGarage CV Axles in preparation for some power upgrades. I've decided to keep the L26 in the car, but I'm trying to investigate ways to get to 250 WHP. I'm looking into turboing the engine, but I'm getting a ton of mixed responses on whether it'll need forged pistons, ARP 9mm head studs etc. I want to overbuild this set up so that I have a comfy safety factor and won't be overloading any components. Can someone help me figure out once and for all exactly what stock engine internals may need to be replaced? I'm also debating just going with ITBs and calling it a day.

 

Thanks!

 

My 260 for reference.

Edited December 12, 2021 by NorthStar

[AydinZ71]

250 at the wheels, and reliable? Ok, here is what I recommend:

 

1) Custom forged pistons designed specifically for a turbo application. Rings are typically recessed to reduce overheating and premature wear. I assume you still have the N42 head? Get a piston with a slight dish so you get down to 8:1 or less. The lower the CR on a turbo application, the less off-boost response and power but you will have a wider margin to run higher boost before detonation on pump gas. I have turbo'd an L24 with OEM pistons and ~8.8:1 CR. It worked, but the rings wore-out in about 6-months of daily driving and i started getting considerable blow-by. 

2) OEM crank and rods are just fine up to 350 ft-lbs of torque. Some folks have taken it to 400 without breaking them. The rods will give before the crank. 

3) Independent EFI and an integrated wideband O2 to help you tune and ward off detonation in real-time. Go ahead and add a knock sensor while your add it, to automatically retard your ignition timing and dump extra fuel in. The forged pistons will give you some piece of mind if you detonate during tuning or a hot day etc. 

4) at least 400cc injectors. I still use the old-school Bosch 75' Mercedes 450SL injectors. I believe they are 420cc. 

5) convert to EFI fuel system. Consider a high-flow high-pressure fuel pump, quality FPR w/ manifold pressure reference. I have a low pressure pump near my tank, a surge tank in the engine bay, and the high-pressure pump is up-front as well. 

6) quality IC and 2.5" plumbing. 

7) T3 super 60 trim is plenty big enough to get you the power you want, but consider a modern more efficient small-frame turbo like a G25.

8 ) Weld a turbo oil return nipple onto your oil pan. 

 

In addition tot he upgrades you are already considering, you will need a clutch that wont slip at 300ft-lbs of flywheel torque (which is minimum what you need to get your 250 WHP. I am sure I am forgetting some stuff. 

 

I can go on, but those are the important items. Just FYI, the ITB's look super cool but they are not enough to give you appreciable power for an NA application. if you want to make over 200hp WHP on an NA L26, you will need a wild cam, up your CR, quality header, so on... The ITB's just "add" to the flow capability of an already heavily modified cylinder head, but they don't do much all by themselves. I assume you mean a weber side-draft type carburetor or EFI ITB's. Either way, they are an upgrade to the SU's and will certainly see more power, but their true potential is when you are flowing a lot more air through that head. 

 

ITB's certainly have the "cool" factor, but they are not the "source" for greater engine performance.

 

-Aydin 

[rossman]

Aydin gave you good advice.  I would also recommend that you do the cylinders 5 & 6 coolant bypass head modification (search) and plug the internal bypass in the block.  The cooling system on these old heads is marginal, even in NA form. The key to turboing them is to avoid detonation which can destroy the engine in a matter of seconds, especially if you're running stock pistons and rods.

[NorthStar]

13 hours ago, AydinZ71 said:

250 at the wheels, and reliable? Ok, here is what I recommend:

 

1) Custom forged pistons designed specifically for a turbo application. Rings are typically recessed to reduce overheating and premature wear. I assume you still have the N42 head? Get a piston with a slight dish so you get down to 8:1 or less. The lower the CR on a turbo application, the less off-boost response and power but you will have a wider margin to run higher boost before detonation on pump gas. I have turbo'd an L24 with OEM pistons and ~8.8:1 CR. It worked, but the rings wore-out in about 6-months of daily driving and i started getting considerable blow-by. 

2) OEM crank and rods are just fine up to 350 ft-lbs of torque. Some folks have taken it to 400 without breaking them. The rods will give before the crank. 

3) Independent EFI and an integrated wideband O2 to help you tune and ward off detonation in real-time. Go ahead and add a knock sensor while your add it, to automatically retard your ignition timing and dump extra fuel in. The forged pistons will give you some piece of mind if you detonate during tuning or a hot day etc. 

4) at least 400cc injectors. I still use the old-school Bosch 75' Mercedes 450SL injectors. I believe they are 420cc. 

5) convert to EFI fuel system. Consider a high-flow high-pressure fuel pump, quality FPR w/ manifold pressure reference. I have a low pressure pump near my tank, a surge tank in the engine bay, and the high-pressure pump is up-front as well. 

6) quality IC and 2.5" plumbing. 

7) T3 super 60 trim is plenty big enough to get you the power you want, but consider a modern more efficient small-frame turbo like a G25.

8 ) Weld a turbo oil return nipple onto your oil pan. 

 

In addition tot he upgrades you are already considering, you will need a clutch that wont slip at 300ft-lbs of flywheel torque (which is minimum what you need to get your 250 WHP. I am sure I am forgetting some stuff. 

 

I can go on, but those are the important items. Just FYI, the ITB's look super cool but they are not enough to give you appreciable power for an NA application. if you want to make over 200hp WHP on an NA L26, you will need a wild cam, up your CR, quality header, so on... The ITB's just "add" to the flow capability of an already heavily modified cylinder head, but they don't do much all by themselves. I assume you mean a weber side-draft type carburetor or EFI ITB's. Either way, they are an upgrade to the SU's and will certainly see more power, but their true potential is when you are flowing a lot more air through that head. 

 

ITB's certainly have the "cool" factor, but they are not the "source" for greater engine performance.

 

-Aydin 

 

Thanks for the super comprehensive rundown! This kind of detailed explanation is exactly what I've been looking for. I've been getting mixed responses varying from "if you turbo that engine you'll blow it immediately" to "oh you could turbo that engine bone stock to 350 HP easy don't listen to these people trying to sell you stuff!" Anyway, I feel like 250HP is a pretty modest power goal considering these builds you see on the internet hitting 350-450. 

 

So if I'm understanding you correctly, the pistons are really the greatest weak spot? And goal number 1 is to avoid detonation... got it. But where do you guys find parts that match these descriptions? Just call up Rebello and get a quote on a set according to your application? What are the trusted manufacturers of the components I'm looking for?

 

I'll use this rundown as a baseline. I'm very much of the mindset to overbuild now and not eat shit later when a component breaks from being overstressed.

[AydinZ71]

@NorthStar

IMO, the reason you get a broad spectrum of responses is that they are all partially correct and very few have actually done it themselves to understand or experience the nuance. Then, there is the ego to always need to be “right”. Premature ring wear is a thing, and it gets worse the higher your CR and boost on OEM pistons. 
 

Yes, pistons are the weak spot for

Modest boost.

 

Forget Robello. That’s for a full engine build or “kit” that is specific to an L-series. You can get the pistons direct from CP carillo, JE, etc. take your pick, but it will most likely be whomever answers your phone call or e-mail. Everyone is busy right now.

 

are you comfortable doing your engine math? You can use an online calculator. I believe your OEM CR is 8.3:1. Personally, I’d dish your piston a bit to get 8:1 or less, or get a P90 head which should drop your CR without changing piston geometry. There are plenty of sites that provide the OEM volume of various L-series heads. 
 

n42 is a decent flowing head so you can keep it. One thing you could do is go ahead and run your engine with the OEM 8.3:1 CR long block, do the cooling mod rossman recommended, and do all the other upgrades.  Keep your boost modest (8psi) and I’m sure she will be fine. As I said before, if you are not detonating, she will hold together and worst thing you will experience is premature ring wear. Not only will you gain experience on what it’s like to turbo an OEM long block, but it will give you time while your forged pistons are being made. 
 

OH, duh… you will need a turbo exhaust manifold and EFI intake manifold. For exhaust, OEM for around 350, or protuners for around a grand. OEM EFI intake manifold is just fine for the power you are looking for. 
 

 

 

[NorthStar]

On 12/12/2021 at 6:33 AM, rossman said:

Aydin gave you good advice.  I would also recommend that you do the cylinders 5 & 6 coolant bypass head modification (search) and plug the internal bypass in the block.  The cooling system on these old heads is marginal, even in NA form. The key to turboing them is to avoid detonation which can destroy the engine in a matter of seconds, especially if you're running stock pistons and rods.

Can you clarify what this modification does and why it's needed? As of right now I'm understanding it as: there is a stock bypass of cylinders 5/6 in terms of cooling and this mod gets rid of this bypass to maximize cooling and prevent detonation? 

 

 

 

 

On 12/12/2021 at 3:34 PM, AydinZ71 said:

@NorthStar

IMO, the reason you get a broad spectrum of responses is that they are all partially correct and very few have actually done it themselves to understand or experience the nuance. Then, there is the ego to always need to be “right”. Premature ring wear is a thing, and it gets worse the higher your CR and boost on OEM pistons. 
 

Yes, pistons are the weak spot for

Modest boost.

 

Forget Robello. That’s for a full engine build or “kit” that is specific to an L-series. You can get the pistons direct from CP carillo, JE, etc. take your pick, but it will most likely be whomever answers your phone call or e-mail. Everyone is busy right now.

 

are you comfortable doing your engine math? You can use an online calculator. I believe your OEM CR is 8.3:1. Personally, I’d dish your piston a bit to get 8:1 or less, or get a P90 head which should drop your CR without changing piston geometry. There are plenty of sites that provide the OEM volume of various L-series heads. 
 

n42 is a decent flowing head so you can keep it. One thing you could do is go ahead and run your engine with the OEM 8.3:1 CR long block, do the cooling mod rossman recommended, and do all the other upgrades.  Keep your boost modest (8psi) and I’m sure she will be fine. As I said before, if you are not detonating, she will hold together and worst thing you will experience is premature ring wear. Not only will you gain experience on what it’s like to turbo an OEM long block, but it will give you time while your forged pistons are being made. 
 

OH, duh… you will need a turbo exhaust manifold and EFI intake manifold. For exhaust, OEM for around 350, or protuners for around a grand. OEM EFI intake manifold is just fine for the power you are looking for. 
 

 

 

Thanks for the info. As of right now my build looks like:

 

Protunerz S30 turbo exhaust manifold

Protunerz intake manifold

Garrett GT3582R Ball Bearing Turbocharger (Apparently functional to 640 HP, but it's what Protunerz recommends. I'm going to study the maps and other specs more thoroughly)

Haltech 2000 ECU

Dished Forged Pistons at 20 over (Shop told me that Ross is a solid reputable maker of these pistons) (Also specify recessed rings???) to get 8:1 or less CR

(Possibly) H beam forged rods I think also from Ross. Not completely sold on this.

9mm ARP studs

I assume I can just get the fuel rail, injector, pump etc. from Protunerz

Associated sensors (I'll probably just get recommendations from my shop)

 

 

Any glaring holes I forgot? I've already got my LSD, aluminum driveshaft and aftermarket ZcarGarage half shafts on the way. I installed a Centerforce clutch about 1000 miles ago, https://zcardepot.com/products/centerforce-ii-performance-racing-clutch-240z-260z-280z-280z

I believe it's tolerant to ~282 ftlbs of torque? Cutting it a little close for my taste... but it's also brand new. I wish ZCarDepot would put product specs on their listings.

 

Edited December 13, 2021 by NorthStar

[AydinZ71]

If you are going for "easy" vs. "cost-effective", then you could just ask Hussein (Protuners owner) for everything he is willing to supply you. I know he sells injectors, ECU, etc. don't know about the rest. 

 

For pistons, you don't have to specifically ask for "recessed rings". That is a specific observation between the OEM L28et pistons vs. the OEM L24/L28 pistons. It is what Nissan did, and it made a difference on ring life. Just make sure they are clear on your displacement vs. power goals and that its a turbo application. They should have the experience to make the right piston for you. 

 

Most of the custom design work will be your electronics and fuel system. So, you should should sketch it out on paper until it all makes sense to you first. That way you don't buy parts you don't need and don't have missing parts. 

 

Here is an example of a robust fuel system design that will ensure high confidence you will not experience fuel starvation, regardless of HP (as long as the individual components are rated appropriately):

 

Tank (modified for EFI, or brand new fuel cell) -> low pressure fuel pump -> fuel filter -> new 3/8" fuel line (OEM is pretty narrow and no return) to engine bay -> empty into surge tank -> HP fuel pump picks up from bottom of surge tank -> fuel rail/injectors -> FPR with return -> surge tank again -> surge tank overflow into OEM fuel line used as a "return" back to tank.  

 

You should confirm ALL of your driveline components will meet the 300ft-lbs flywheel torque. That includes the new CV shafts, driveshaft, trans, etc. Hubs i believe are OK to at least 400 ft-lbs, and Nissan 4/5spd should be OK to 350 ft-lbs as long as you are not "launching" at a drag strip. Do you own research though, plenty of posts and experience on this forum. Just run your CF clutch for now and maybe it will hold up? Not a catastrophic failure point, the clutch will just slip if its too much torque. You will need to convert to a top-mount or solid bottom-mount for your R200. The OEM rubber mount on the nose of the diff "pulls up" violently with lots of torque. Best-case your driveshaft U-joints will wear out pre-maturely. Worst-case, your diff mount will fail and the driveshaft will bind catastrophically, assuming your OEM diff over-strap is worn too (do 260z's have these?). 

 

do some research on a quality intercooler. You can piece together your own plumbing with pre-made mandrel bent 2.5" AL tube, straight lengths, and silicone of V-band joints. I prefer silicone of IC plumbing and V-band for exhaust. You need a BOV too, but get a "real" one. One that actually dumps some decent volume, not those little squeaky ricer ones. 

 

On turbo sizing, if you are going for garrett than use their online sizing calculator. Its free, and shows you precisely where your airflow demand is relative to the curve. The goal is to stay in the highest efficiency zone for as much of the airflow/RPM curve as possible. 

 

I think the best way to go from here is to prepare a complete and comprehensive list of parts, upgrades, tasks etc. We can review and fill-you-in on what we see is missing. Unless you are paying someone bookoo money to build it for you, you will need to understand as much of this as possible. You will have troubleshooting to deal with when its all put together and you will want to solve it yourself, if for nothing more than convenience.

 

I don't have direct experience on a before-after on the cooling system mod, but the idea is to get the coolest water back to the last two cylinders. When done correctly, it can not hurt and will only help. the cooler the water jacket, the cooler the cylinder walls, the longer your rings will last, and the higher your detonation threshold will be. 

[NorthStar]

  

54 minutes ago, AydinZ71 said:

If you are going for "easy" vs. "cost-effective", then you could just ask Hussein (Protuners owner) for everything he is willing to supply you. I know he sells injectors, ECU, etc. don't know about the rest. 

 

For pistons, you don't have to specifically ask for "recessed rings". That is a specific observation between the OEM L28et pistons vs. the OEM L24/L28 pistons. It is what Nissan did, and it made a difference on ring life. Just make sure they are clear on your displacement vs. power goals and that its a turbo application. They should have the experience to make the right piston for you. 

 

Most of the custom design work will be your electronics and fuel system. So, you should should sketch it out on paper until it all makes sense to you first. That way you don't buy parts you don't need and don't have missing parts. 

 

Here is an example of a robust fuel system design that will ensure high confidence you will not experience fuel starvation, regardless of HP (as long as the individual components are rated appropriately):

 

Tank (modified for EFI, or brand new fuel cell) -> low pressure fuel pump -> fuel filter -> new 3/8" fuel line (OEM is pretty narrow and no return) to engine bay -> empty into surge tank -> HP fuel pump picks up from bottom of surge tank -> fuel rail/injectors -> FPR with return -> surge tank again -> surge tank overflow into OEM fuel line used as a "return" back to tank.  

 

You should confirm ALL of your driveline components will meet the 300ft-lbs flywheel torque. That includes the new CV shafts, driveshaft, trans, etc. Hubs i believe are OK to at least 400 ft-lbs, and Nissan 4/5spd should be OK to 350 ft-lbs as long as you are not "launching" at a drag strip. Do you own research though, plenty of posts and experience on this forum. Just run your CF clutch for now and maybe it will hold up? Not a catastrophic failure point, the clutch will just slip if its too much torque. You will need to convert to a top-mount or solid bottom-mount for your R200. The OEM rubber mount on the nose of the diff "pulls up" violently with lots of torque. Best-case your driveshaft U-joints will wear out pre-maturely. Worst-case, your diff mount will fail and the driveshaft will bind catastrophically, assuming your OEM diff over-strap is worn too (do 260z's have these?). 

 

do some research on a quality intercooler. You can piece together your own plumbing with pre-made mandrel bent 2.5" AL tube, straight lengths, and silicone of V-band joints. I prefer silicone of IC plumbing and V-band for exhaust. You need a BOV too, but get a "real" one. One that actually dumps some decent volume, not those little squeaky ricer ones. 

 

On turbo sizing, if you are going for garrett than use their online sizing calculator. Its free, and shows you precisely where your airflow demand is relative to the curve. The goal is to stay in the highest efficiency zone for as much of the airflow/RPM curve as possible. 

 

I think the best way to go from here is to prepare a complete and comprehensive list of parts, upgrades, tasks etc. We can review and fill-you-in on what we see is missing. Unless you are paying someone bookoo money to build it for you, you will need to understand as much of this as possible. You will have troubleshooting to deal with when its all put together and you will want to solve it yourself, if for nothing more than convenience.

 

I don't have direct experience on a before-after on the cooling system mod, but the idea is to get the coolest water back to the last two cylinders. When done correctly, it can not hurt and will only help. the cooler the water jacket, the cooler the cylinder walls, the longer your rings will last, and the higher your detonation threshold will be. 

 

So, a couple things. 

 

I'll openly admit, I understand a lot of this in concept, but actually doing it seems really daunting as this is my first project car (did I forget to mention that? lol)

 

As for the fuel system design, I have some dumb questions. What's a surge tank? I assume it's a tank to keep an amount of fuel on tap if you start beating on the car for a long time and to protect against starvation? How would I need to modify the stock tank? 

 

The 260Z has a R180 diff, no? That's what I researched and ordered to OS Giken LSD to be matched to. The drivetrain components are all confirmed to be plenty strong for this HP goal. What exactly is this top-mount/bottom-mount conversion? I've never heard it mentioned before. 

 

I'll check out Garrett's calculator, sounds like the best move. 

 

What's a BOV? I can look for a quality intercooler, I was thinking a standard air-to-air. 

 

All in all, I want to do as much of this as I can (minus actual tuning, of course) because I want the knowledge. But, I also don't want to destroy my very first project car by forgetting to install a wideband O2 sensor (I don't even know where it would go as of right now) or something trivial like that, so I'm kinda leaning towards having critical work done by the shop I've used all this time. Seems like the really worthwhile projects can be seemingly impenetrable to noobs.

Edited December 13, 2021 by NorthStar

[rossman]

3 hours ago, NorthStar said:

Can you clarify what this modification does and why it's needed? As of right now I'm understanding it as: there is a stock bypass of cylinders 5/6 in terms of cooling and this mod gets rid of this bypass to maximize cooling and prevent detonation? 

 

 

Go here:  

Google is your friend.  Type your search term followed by "site:hybridz.org"  to search only this site.

 

[AydinZ71]

5 hours ago, NorthStar said:

  

 

So, a couple things. 

 

I'll openly admit, I understand a lot of this in concept, but actually doing it seems really daunting as this is my first project car (did I forget to mention that? lol)

 

As for the fuel system design, I have some dumb questions. What's a surge tank? I assume it's a tank to keep an amount of fuel on tap if you start beating on the car for a long time and to protect against starvation? How would I need to modify the stock tank? 

 

The 260Z has a R180 diff, no? That's what I researched and ordered to OS Giken LSD to be matched to. The drivetrain components are all confirmed to be plenty strong for this HP goal. What exactly is this top-mount/bottom-mount conversion? I've never heard it mentioned before. 

 

I'll check out Garrett's calculator, sounds like the best move. 

 

What's a BOV? I can look for a quality intercooler, I was thinking a standard air-to-air. 

 

All in all, I want to do as much of this as I can (minus actual tuning, of course) because I want the knowledge. But, I also don't want to destroy my very first project car by forgetting to install a wideband O2 sensor (I don't even know where it would go as of right now) or something trivial like that, so I'm kinda leaning towards having critical work done by the shop I've used all this time. Seems like the really worthwhile projects can be seemingly impenetrable to noobs.

yes, surge tank is cheap insurance by keeping a small amount (1pt-1-qt) of fuel in your engine bay, and allowing your fuel-pressure-regulator to dump back into this ready reservoir instead of sending all the way back to the tank. Short run for your high pressure line to suck fuel from, and push to your dispensers. Mount the pump under the surge tank. 
 

stock (carbureted fuel system) tank only has a single fuel line and no return. You need to tap the tank somewhere to run a new fuel line, and use the existing line for your return. Most people just replace the OEM fuel tank with a new fuel cell with multiple nozzles available. 
 

BOV is a blow-off valve. Most of the acronyms, you can Google.

 

R180 is somewhat suspect at 300ft-lbs, but the weak spot are the spider gears. The LSD section replaces the spider gears so as long as the ring gear and output shaft bearings hold up, you will be OK. Double check with OS giken on whether the unit will handle the torque. That’s a super expensive part to risk blowing.

 

HP vs. torque. If someone tells you HP is a reasonable metric to use for determining drivetrain strength, they don’t know what they are talking about. Torque breaks drivetrain components, and it’s what gives you that “whoa this car is fast” feeling in your ass when you stomp on the gas. HP depends on torque AND RPM (therefore a close correlation w/ volumetric air flow) and is used to determine things like air flow through a head, through a turbo, through an intercooler etc. When you quote an HP number but you really mean torque, someone is assuming a torque number off your HP number. They are variables in the same equation. 

 

for diff top-mount, search “techno versions 240z”. Read their product description. Lots of ports on this forum about it.

 

I don’t know your personal finances, but il say this: if a shop does it all for you, they have to be “good” or your shit will fail often and be a headache. If they are good, they are expensive (thousands and thousands. Sung kang spent 250k on the fuguZ). Most of us here do it ourselves because we recognize we can barely afford the parts, let alone shop labor. We are also control freaks and want to understand why/how something happened and improve upon it, or we have serious trust issues. 
 

if all you need a shop for is to tune your equipment when done (and give free advice), that is affordable. 
 

O2 sensor screws into a bung downstream of your turbine outlet (exhaust). OEM L28et downpipe has one, so does the protuners downpipe. The wideband Meter uses the O2 sensor to determine how rich/lean your air-fuel ratio is. This lets you “rough” tune before you get to a performance dyno shop, and lets you troubleshoot while driving. Also helps to avoid running lean by accident if your equipment/fuel system fails. On-boost, 11:1 or richer is reasonable. Stochiometeic (sp?) is 14.7:1, but engines ALWAYS should run rich to a certain extent. NA will range a bit closer to stochio.

 

if this is all a bit overwhelming, I understand. Take your time, read, do your research. If you decide it’s not for you, I get it. Just remember, you can not get a 250 whp L-series without a turbo, or losing a ton of street daily-driving capability on an NA. A 3.1L stroker will get you there, but driving on the street will be rough, and all your torque will be up-high (race engine). 

As an example, an all-out race engine L24 competing at the top of its class in SCCA puts out about 260 flywheel HP and that’s on race fuel. Maybe 10% more w/ triple carbs. 
 

these are not modern engines, but at the time they were a marvel. 

[rossman]

7 hours ago, AydinZ71 said:

if a shop does it all for you...If they are good, they are expensive (thousands and thousands.

Yup, north of $15k just for labor (depending on the shop and your location).  Proper custom fabrication ain't cheap or easy.

 

To do it right and do it yourself, assuming you don't already have the knowledge (custom programmable fuel injection, forced induction, S30/L6 quirks, electrical circuits, wiring, etc.), skills required (welding, wiring, crimping, tube bending, etc.), and tools (welder, welding tools, quality crimpers, tube/pipe bending/flaring, DMM, grinder, chop/miter saw, sander, etc.)...the learning curve is significantly steep. Lots of reading/learning (mostly Googling and some books), practice, and trial and error, are required, not to mention the considerable investment in quality tools, which can make it into the multi-thousands of dollars depending on your tool preferences.

 

Personally, being somewhat of an introverted, gear head, mechanical engineer, and hotrodder, the love of all things Datsun, technical challenges of learning, skills development, trial and error, and tools ARE the reason I do it. 

 

YMMV of course!

Edited December 14, 2021 by rossman