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turbo z24


Mr.Dean_Yates

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:w00t: HOLY SHITAKIES!!!! THAT IS SO BEAUTIFUL! POWER STEERING AND A/C!! Nice work, my new wallpaper for my ipod....INSPIRATION  :w00t:  :thumbup:

 

How much HP do you have now? EFI, how'd you do that?

 

But where's the screws to hold down that valve cover? Or is this just a mockup?

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:w00t: HOLY SHITAKIES!!!! THAT IS SO BEAUTIFUL! POWER STEERING AND A/C!! Nice work, my new wallpaper for my ipod....INSPIRATION  :w00t:  :thumbup:

 

How much HP do you have now? EFI, how'd you do that?

 

But where's the screws to hold down that valve cover? Or is this just a mockup?

 

Wharrs the dizzy?

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:w00t: HOLY SHITAKIES!!!! THAT IS SO BEAUTIFUL! POWER STEERING AND A/C!! Nice work, my new wallpaper for my ipod....INSPIRATION  :w00t:  :thumbup:

 

How much HP do you have now? EFI, how'd you do that?

 

But where's the screws to hold down that valve cover? Or is this just a mockup?

The truck is running.   This is a old photo.

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*snip*

Keep the stock cam if going turbo. Any extra overlap (that's when both intake and exhaust are open at the same time) will simply allow boost pressure to blow right into the combustion chamber and out the exhaust. A waste of boost and gas.

*snip*

 

 

I have been lurking here for awhile and before I say anything more, I want to say that I'm in awe of your all-encompassing datto knowledge here, Mike. Specifically about what works with what else and why. I seriously bow down to your knowledge.  

 

But coming from ~13 years of obsessively playing with all kinds of flavors of Japanese engines (7M-GTE's, 1JZ/2JZ's, 3S-GTE's, KA24E/DE/DET's, SR's, 4AGE's, 4AGZE's, BP, etc) I wanted to share a little of my own experience & reasoning that contradicts the common idea that bigger cams + turbo = blowing boost out of the exhaust. 

That *is* absolutely true for supercharged engines. On DOHC engines, a really hot supercharger setup tends to do best with a mild intake cam and a slightly more aggressive exhaust cam. To use the misleading but common nomenclature found in aftermarket Japanese cams, a 256* intake with a 264* exhaust cam tends to be the best setup on supercharged applications - precisely because trying to encourage a scavenging effect with a supercharged engine does indeed 'blow the boost out of the exhaust'. 

 

With a turbocharged setup though, the pre-turbo backpressure is ALWAYS higher than the inlet (boost) pressure. Because of this, you can even see upwards of 1.5psi of additional backpressure for every 1 psi of boost on non-optimal setups using small turbine housings at high RPM's, which can actually result in exhaust reversion back into the combustion chamber when the exhaust valves are open but the intake valves are closed. Depending on the stock cam specs, this usually starts happening in the upper 25% of the powerband where a turbocharged engine should be happily screaming along, and of course it puts the brakes on the fun and while boost will hold steady, HP and Torque falls off just as if it fell off from not enough cam. 

High backpressure brings with it higher EGT's as well, and of course higher EGT's bring a risk of detonation which is why it's so important to pick a good turbo for a given engine setup, and why it's better to be a bit on the 'too big' side. Most turbo setups reflect this somewhat even in older OEM setups.

 

With a turbocharger that's properly sized, particularly with large turbine housings & nice tubular manifolds, the backpressure ratio approaches 1psi BP per 1psi of boost. The presence of that backpressure guarantees that the 'blowing boost out of the exhaust' scenario is impossible while the turbo is spooled, and as a result, big duration for both the intake and exhaust can see big HP gains at the same boost level, because more cam = more head flow, and with more head flow on a turbocharged engine, you'll see lower manifold pressures for a given HP level, or more HP at the same boost level.

An extreme example of this can be seen when comparing the same T67 on a 2JZ-GTE cylinder head and an E46 BMW M3's S54 cylinder head. Both will max out the turbo around 670hp, but the 2JZ does it at ~30 psi with stock cams, ~25psi with a serious port job & 272* cams on intake and exhaust, while the BMW S54's would make that same `~670hp at 13-14psi.

 

The turbo is just an exhaust driven centrifugal air compressor, and like any other air compressor it can only flow so much. So a turbo will determine the max HP possible, but the cylinder head and  supporting stuff determines how much boost pressure would be required to make that kind of HP. Like any other pump or compressor, some turbos flow well with high pressures (a turbo sees boost pressure the same way a pump would see backpressure) while others flow their best at lower pressures. These 'happy' zones for a turbo can be seen on the efficiency island on a turbo's compressor map, which is why knowledge of your target HP as well as your cylinder head's flow characteristics can net you the most ideal results by picking a turbo that is happy supplying the sort of boost pressure your engine needs to achieve a target HP number. This pays off bigtime because staying in a turbo's efficiency range results in colder intake air temps, and as we all know from PV=NRT back in those shitty chemistry classes, hotter air at a given pressure will result in less air mass, and of course, less air mass = less HP. That is why 15psi from a tiny T25 won't make the same HP as 15psi on a HKS T51R. The other factor of course is that all of the engine's exhaust needs to flow through the turbo or wastegate, and smaller turbos = more backpressure = less total HP, even if the air mass at a given boost level was the same. 

 

 

Putting it simply, if you want big top end HP on a turbo motor, go with big cams too. Avoid big cams on supercharged engines, and it's safer & more reliable to run a slightly bigger turbo than you really need, as that will help keep EGT's low and help exhaust flow when in boost. There's a huge temptation to run tiny exhaust housings for the sake of a few hundred RPM of spool, and that results in more backpressure, higher EGT's, and more risk of detonation if everything else is the same.

 

Having seen my girlfriend's 98% stock NAPS Z24 powered 2wd 720 happily fly along at 110mph (GPS verified) for extended periods of time at near redline for that ~200k mile Z24, I honestly do NOT fear the idea of revving a Z24 to 6k or beyond, especially if it has been built appropriately. The only downside, again, is the lack of a 'big cam' for the Z24 to match a bigger turbo and bigger HP goals. It seems to me that something like the Nismo R6 or R4 for the KA24E would be perfect in a turbo'd Z24 if it were available, depending on the turbo setup & HP goal, as the stock Z24 seems to fall off a bit above 4500 rpm, and that tendency won't go away with a turbo, it'll just be masked by how you're making so much more power everywhere. 

 

My one reservation about a turbo'd Z24 would be the time/effort involved in setting up an EMS like a Megasquirt to get the most out of the turbo setup, which would need either a custom intake manifold or a Z18E/Z20E/Z22E intake manifold from the motherland. Being an old 7M-GTE guy, I'd also figure out if the ARP hardware for the old A12's works in the Z24, and I'd probably get a cometic MLS headgasket for the KA24DE and do the trimming/tweaking needed in the timing chain area for it to work on a Z24/KA24E and hope for the best. 

 

The crazy homebrew carb-turbo stuff I'll leave to you crazy Ratsun guys - but I will watch and admire your ninja skills. 

 

My Girlfriend is considering a newer cheap beater so that we can start playing with her beloved 720 as a project. Obviously, I'll start a build thread here with lots of oics when/if that happens

 

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