TimZ

Maybe do a leakdown test instead - if you already have an air compressor, the testers aren't that expensive.

Ya know... get a pair of butterfly valves from a Taurus SHO, splice in some short runners on the other side of the plenum and you could have a variable length runner setup. You're almost there - that plenum orientation would make it pretty easy...

Just to be clear - the "James Thaggard" design and the "TimZ" design are one and the same. James made that piece up for me after we had talked about it for some time. The "Spoolie Jobbie" in the pic above is the one that James made. The flange is mild steel. The throttle and shaft are made from Hastelloy X. We picked this material because of its ability to withstand the temperatures that were likely to be seen at the turbine inlet. I didn't want it either melting or binding as soon as the EGTs went up. The Hastelloy X material should be good to close to 2000 degF. Also, the throttle shaft rides in two stepped busings that were pressed into the flange, also made of Hastelloy X. When I was running the mild Isky cam and the T64, initial trials with the Spoolie Jobbie showed boost coming on about 600 to 800rpm earlier as noted above. However, when I went to the more radical Elgin cam, it appeared that the added backpressure from the closed throttle caused more problems than it solved, and boost response was actually worse than without it. This, combined with the problems I was having finding a reliable actuation method led me to shelf the project. I think that this should still be able to work, but you really need to think big on the turbine housing. With the T64, I was using a ~0.8A/R housing, so with the throttle closed it was 0.4A/R - too small. Also, I was originally thinking of this as an on/off application - it might be useful to look at performance with the throttle partially open. I'm thinking about resurrecting this project with the GT42 turbo, with a revised actuation method. I'm thinking that the much larger hotside might work better...

Agreed - at least you can tell why that particular car went for so much.

...same stuff he made the "bumpers" out of. He keeps talking about it being a Cobra, yet it's all stock Z body panels (in different colors to boot) and a missing hood.

Here's a really nice one for only $16k... Sheby Cobra kit car? WTF??? That crystal meth is one hell of a drug...

The injectors should always be seeing the base pressure - the regulator's job is to make sure of this by moving the rail pressure around to keep the pressure difference across the injector constant. So, even though you had 29psi in the rail, the injectors were still seeing 36psi since they were spraying into a vacuum (of -7psi in this case). This is why it's best to only talk about the base pressure - everything else just confuses things.

Base fuel pressure usually refers to the fuel pressure that you read when there is zero vacuum. The fuel pressure with vacuum varies, since not everybody has the same idle vacuum. Because of this, it's not a good value to use for comparison purposes. You guys do realize that injector flow ratings are given for 3 bar fuel pressure, right? If you are running with a base pressure of 2.5bar, then the injector flow is derated by ~9%.

2bar - as in 29psi?

Ummm - am I the only one that noticed that this didn't include forged pistons? I guess that this might be okay if you don't plan on a turbo, but I'd guess you'll be mighty pissed when the ring lands fail from detonation the first time you make a tuning mistake... At that price, I wouldn't even consider cast pistons.

I guess I'm not that familiar with MS, but in general the high impedance injectors have considerably lower dynamic range than low impedance ones (i.e. ,low Z injectors take less time to open and close, so they have a wider range of usable pulsewidth). Is there some idiosyncrasy with ms that doesn't work well with low Z? Looking at one of the MS help pages, it looks like one option would be to go to simultaneous injection if you start getting down close to the min on-time at idle. Even though this is not ideal, it will allow you to only have to open and close each injector once per 720 degree cycle, which should alleviate the min pulsewidth problem. FWIW, I was able to run 72lb low Z injectors with my TEC2 without much of an issue. One technique for leaning out the idle mixture when you are near the min on-time is to run less advance at idle - say 10 degrees or so. Less timing tends to slow the idle speed so to compensate you set the idle bypass to allow a bit more air, which leans the mix out. Another useful trick if you don't need the full capacity of your injectors is to run your fuel pressure a bit lower, say 30 or 35psi. This will make the injector act like a smaller injector - a 72lb injector at 35psi will only flow ~65lb, for instance. This will get your idle pulsewidth up a bit, and have the side benefits of getting a bit more flow capacity from the pump, stressing the pump less and heating the fuel less. I wouldn't go much lower than 30psi though - you might start having atomisation problems.

Doubtful - all of the stability control systems on the oem market have pretty sophisticated failsafe and plausibility algorithms, and wheel speed failures have been well understood since the early days of ABS. Any sensor failure that would cause the car to have a constant, repeatable oversteer problem would have long ago caused a system fault, shutting the system down and lighting a light on the dash. BTW, I realize that this was kind of a tongue-in-cheek answer, but thought I'd answer it anyway.

Did you ever say how far lean you are? I thought that the stock FPR was supposed to be 2.5 bar, or 36.25psi, so the difference between that and 35psi would only equate to a difference from 12 to 12.2 afr. Just want to make sure it's clear that the fuel pressure might not not be main contributor to your problem. For instance, if you are using stock injectors, they might just be gunked up and not flowing to spec. This would be a much more important problem to focus on, since this will most likely result in afr differences from cylinder to cylinder. If you "fixed" this problem by upping the fuel pressure, you could run into a situation where one or more cylinders are still lean, even though your wideband readings look okay.

That's right - the pressure that you see at idle really depends on how much vacuum you have at the time. The FPR simply maintains a constant pressure difference between the fuel pressure and the absolute pressure in the intake manifold. So, for instance, 18 in of vacuum equates to about 9 psi below the ambient pressure (the manifold pressure you see when the engine is off). So in this case if you are seeing 35psi with the engine off, you should expect to see 35-9 = 26psi with at idle. Also, fuel flow varies with the square root of pressure, so the actual difference you should expect to see between 35psi at the rail and 38 is about 4%. So if you would normally see 12 AFR at 38psi, you should expect to see more like 12.5 AFR at 35psi.

...and have you verified that the TDC mark on the damper actually comes up at TDC? The timing light will only tell you how you are aligned to the damper. Also probably a dumb question, but since nobody has asked it yet, are you sure that the block deck and the head are both flat? Surface prep looks good around #5?

The smashed head thing is more referring to trying to run a full cage on the street, without a proper harness and helmet. The problem with trying to use a 4 or 5 point harness on the street with that they are extremely restrictive to the point that they are really impractical. They don't retract, so if, for instance, you forget to close the door before cinching them down, you won't be able to reach the door handle to close it. Forget about tuning the radio, possibly even rolling down the window. If you leave them loose enough to be able to do these things, then they won't be doing you any good safety wise. They would be a giant pain in the ass on the street and are really only meant for track use, where the only thing you are doing is driving as fast as possible.

I stopped counting long ago. If you are already setup for the T5, you might want to look into the GForce T5 gearset - mine has been holding up really well. You'll need a WC gear housing (the datsun bellhousing and tailshaft house bolt right up), you'll need to modify the tailhousing for the larger output shaft, and of course you'll need a new drive shaft and clutch hub.

Just for reference, I'm running custom 5.3" forged Cunningham rods, not the stockers, so I'm not a good reference for what the rods can handle...

Seriously? Changing the flange is too much work? Really? ...oh, and http://forums.hybridz.org/showthread.php?t=121857

For 500rwhp, I agree. For 600rwhp, it just kinda looks like you're going to have to lean on those turbos pretty hard, and I think that's where the efficiency comments came from. Probably not out of the realm of possibility though - how much power have people been able to put down with the stock (single) turbos? I'm pretty sure I've heard of high 200's, anyway...

Is this the map you are looking for? 17psi of boost and 500hp would put you near the following: pressure ratio ~ 2.2 airflow per turbo ~ 34 lb/min 25psi boost and 600hp: pressure ratio ~ 2.7 airflow per turbo ~ 41 lb/min My assumptions for the airflow were 15% drivetrain loss, and 1.5 SCFM of airflow per HP, with air density of 0.0765 lb/ft² So ASSuming that this is the correct map and that I did my math correctly, the numbers that 1fastZ put down are right at the ragged edge of the compressor map for those turbos.

It's much more than that - Those look to be TWM ITBs integrated into somebody's manifold design (can't tell which offhand - Canon, maybe?). Jeff - did you fab those, or did TWM make a custom casting, or what? That's really nice. Those Wiggins clamps are really nice, and should make assembly/disassembly much easier, too. I looked into using those on my last buildup, but didn't have the cash to outlay at the time. That's just a beautiful layout all around - can't wait to see how it runs! On the original question - I was thinking packaging would be the main determining factor for square vs. round, also. Depending on what your plenum design looks like, the square horns might work out better, and if that's the case, I wouldn't be afraid to use them. Actually, now that I'm thinking about it, there might be a pretty good case for using the square horns. I haven't yet seen your plenum design, but I'll make the ASSumption that it's the "normal" asymmetrical log-style with the inlet at the front. Since the air is going to have to make the transition from the shape of the inside of the plenum into the horn anyway, the square horn should at the same time give you a greater area to draw from, and will allow you to have much better control over how the transition from the (probably squarish) shape of the plenum to the round shape of the runner takes place.

Cool - thanks Jeff.

Thanks for confirming - I was suspecting that perhaps they had changed the spec, so I was avoiding posting my old spec and causing even more confusion. Okay, so now I need still more clarification. I thought that the original question was about the main studs, not the head studs. Soooo... was that correct, and was Jeff's answer referring to the main studs or the head studs? Main stud torque was the one I was looking for, btw. Also - for the stock head bolts, I think the final torque was different depending on which bolts you had. As I recall the early L24 spec was 55lb-ft, somewhere in between the L24 and L28 it changed to 60 lb-ft, and then the turbo head bolts were 65lb-ft. If you don't know what you have, the 60lb-ft number should be safe, but if you are getting new bolts, you should just get the turbo bolts.

The stock fasteners are bolts, not studs. The main cap bolt torque spec is 33-40 lb-ft.