Sean73

I'll take a stab at this. The exhaust manifold pressure represents the total back pressure of the exhaust system, including the turbine, dowpipe, cat, muffler, etc.. If you reduce the pressure after the turbine by 1 psi, then the exhaust manifold pressure also drops by 1 psi. Some power would be gained through better flow efficiency, less reversion, and cooler combustion chambers. The power gains would be difficult to predict because of all of the variables involved.

Long story short, I have a broken thread tap in one of the injector hold-down holes on my N42 intake manifold. I tried drilling it out with a cobalt bit, but it doesn't even touch it. It's lodged in there real good. Should I just throw this manifold in the garbage, or is there something I can try?

I think Corky' Bells pressure ratio formula is only intended a simple guildine for planning purposes, such as injector & fuel pump sizing, compressor sizing, etc... For that, it works well. He never claims for it to be an accurate theoretical formula. Most of the time, it gets you in the ballpark, if you know the RWHP of your car at zero boost. If you don't know the base HP accurately, the error gets multiplied the more boost you run. If you're off by 10 HP in the base HP, you're off 20 HP at 14.7 psi. Since you guys disagree on the base HP of the L28ET by +/- 25 HP, this translates to +/- 50 HP at 14.7 psi, so no wonder there's no agreement on Corky's formula! Not knowing the base HP accurately aside, the real question is: Does power rise linearly with boost? If it does, then a simple formula like Corky's should work fine, assuming you know the right inputs-- a BIG assumption. Bastaad, I looked at your dyno charts on your website: 1) 200 HP / 234 TQ @ 10 psi (P=1.68 ) 2) 210 HP / 270 TQ @ 12 psi (P= 1.82) 3) 233 HP / 303 TQ @ 14 psi (P=1.95) Comparing runs 2 and 3 with the first run: +8% boost = +5% HP and +15 % TQ. +16% boost = +16% HP and +29% TQ. HP is anamolously down 3% in run #2. HP probably peaked early due to some other problem. But, with the exception of this data point, the relationship between boost and HP/TQ looks pretty linear to me! Given this empirical linear relationship, we could probably guestimate with ease how much HP & torque you'll make with higher boost (all other factors being equal). I noticed your HP dropped in the second 2 runs after 4100 RPM, but pulled to 5000+ RPM in the first run. If you could have tuned your A/F ratios, I think you would have yielded more consistent HP results. "All other factors being equal" assumption is an important thing to remember when applying Corky's formula. Increasing boost does not lead to predictable power increases, when lot's of other variables are changing (, ie. A/F ratio, charge temperature, IC efficiency, etc...). The formula works when implemented correctly. So to answer you're original question, Bastaad, 16% more boost got you 16% more HP compared to your baseline run. 'nuf said.

Bernard, - did you make note of when you reached full boost? In your dyno chart, torque is rising in parallel with HP, between 4000 and 5000 RPM. This seems to indicate that boost was also rising. Here is my chart, running 10 psi. At 4750 RPM, I am at about 230 lbs of torque. On your chart, you're making about the same torque at the same RPM. But you said you were running 20 psi? There's no way we could be making the same torque at 10psi and 20 psi respectively, unless you were not at full boost, or there is a big discrepancy between dynos.

Bernard - My torque was also low: 232HP / 232 TQ. I attribute this to dyno operator error / inexperience. He accelerated too gradually, failing to build boost at low RPM, resulting in a gradual torque rise, and late torque peak. Had he floored it, boost would have maxxed instantaneously, and I think I would have seen an earlier torque peak. I'm looking forward to seeing your chart. Sean

Nice. I have a similar setup (pending the injector upgrade), and it's good to see your dyno for comparison. Can't see the dyno though. Would like to see pics of your motor too.

The flat brackets are off 85-88 maxima and are a dime a dozen. Early 90's maximas also have flat brackets, but their radii is too small for the 11.4" rotor.

Here's what I did: 85-88 FWD Maxima Rear Caliper Flat Bracket- modified for S30 hub. 85-88 Maxima Calipers (similar to 240SX calipers) 84 300ZX 11.4" Brembo 4-lug rotors. Ok. A lot of you are probably wondering what I had to do to the flat bracket to make it work. Well, it wasn't trivial, and I would not have done it if I didn't have free access to a machine shop. So, here it goes: 1) Bore center hole to 82 mm. 2) Cut 4th mounting hole off, so bracket is removable without removing axle stub. 3) Mill down the hub mounting surface to 7.5-7.75mm 4) Mill down the caliper mounting surface to 7.5-7.75mm Edit:5) I also had to open up the holes on the mounting ears of the bracket slightly, since the rotor was rubbing the inner caliper a bit. The stock flat bracket is 12 mm thick solid forged steel. That leaves a lot of room for machining. I looked online for aftermarket non-Zcar caliper brackets, and most of them are 1/4" thick (6.35mm). Mine are 7.5mm thick at the mounting surfaces, and 12 mm thick in the rest of the bracket. I used the Maxima caliper because it has less of an offset on the hanger, thus it needs less offset on the bracket. Consequently, the angles are much less severe than if I were to use a 240SX caliper. In order for this mod to work with the 240SX caliper, the ears of the bracket would need to be cut and re-welded , because there is not enough material to merely mill down the bracket for the correct offset. I used SS lines purchased from MSA, that are the same ones they sell for the 4x4 front brakes. At first glance getting the e-brake to work should be easy.

straight out of the 1994 Q45 FSM, differential is R200V. No, it won't work with U-joint half shafts, not even close.

I think a LT1 is 100+ pounds heavier than the stock L-series, depending on what you've done to it. Maybe thats where you lost an inch on the front. According to the advertised spring rate of 140 lbs/in in the front, 140 lbs would bring the car down an inch, or even more, since the spring is progressive (assuming 140 is on the high side of the spring rate)

Wheelman: Did you get a 2" drop in the front AND rear? I just installed my rears last night, and got 1" drop. Will be doing the fronts soon.

Just curious, what size wheels/tires are those?

I bought the same kit off Ebay from jdmwerks. The front springs look nothing like progressives, so I am a little perplexed. I've also seen what a progressive spring looks like, (ie Eibach). I hope we can find a resolution to this.

I've also had recurring oil leaks at the pan, and I am convinced it's not the gasket but the pan itself. oil pans tend to get warped and bent around bolt holes, so the gasket doesn't seal flat. have you tried the competition oil pan gasket from MSA? the thicker gasket may help smear out imperfections in the pan.

If I were you, I would get a $7 can of engine paint and call it a day. I wouldn't want the stress of chipping the powdercoat on installation. With paint, it's easier to touch up in the long run.

Here's my setup, flowing from the fuel tank to fuel rail: Don't have pics now. 1) 240Z tank modified with 3/8" feed. (5/16 stock line used for return) 2) Low pressure electric pressure fuel pump mounted in stock location at rear of car. 3) AN-6 SS hose mounted attached under body to stock fuel lines feeds surge tank. 4) Custom surge tank mounted on the passenger side shock tower. 5) EFI pump attached to pass. side frame rail draws from surge tank above. 6) EFI pump feeds fuel rail through Fram HPG-1 fuel filter. 7) Fuel rail return goes to surge tank. 8) Surge tank overflow return goes back to fuel tank. Some might say that the safety of the surge tank in the engine bay is questionable. However, it only sees 3-4 psi. It doesn't hold that much more fuel than the HPG-1 fuel filter. I would be more worried about a 40 psi leak from somewhere else in the fuel system.

Did you break it in properly? I didn't break my stock clutch in, and it failed within 300 miles of 7-10 psi boost.

I have 94 Miata seats and love them. I searched all over for instructions on how to mount them in the Z. It seems most people end up modifying the seat bottom to accept Z tracks, but I didn't see a need for this. I cut the Miata tracks on each side down to the the flat portion, then installed a metric stud at the correct lengthwise distance to match the dimensions of the Z track. When the seats were ready to install, I had to "oval-out" the stock mounting holes ~1/8" in the Z to accomodate the extra width between the tracks.

Just thought I'd share my recent success with altering the stock 88 VG30T timing maps. Comparing the VG30 vs. the VG30T maps, one can immediately see the VG30 is much more aggressive in timing on the bottom end. I have no idea why. I don't see why the VG30T can't have a comparable timing curve off boost. I analyzed the VG30T maps, and noted each RPM/TP data point where the ECU begins to pull timing (for boost, of course). Then, I considered everything to the left of these points, fair game for timing adjustments. With both maps in Excel, I averaged the NA and Turbo timing values, and copied the results, into the off-boost section of the Turbo map. I could have simply copied the NA values, which would have resulted in more aggressive timing, but I wanted to start out conservative. What I end up with is a NA-turbo averaged timing curve off-boost, and a stock Turbo timing curve on-boost. The results are outstanding. Much better off-boost acceleration, and faster spool-up. I don't think I have compromised safety, but I have to wonder why Nissan made the VG30T such a slug for off-boost timing advance. After further testing I'll post the timing map, if anyone is interested. Another thing I did is reduce the cold-start enrichment values across the board by 8%, to account for the displacement difference of the VG30T vs L28T. I could have accomplished this with the K value, but this would have affected the entire fuel map. This modification seemed to resolve a "smokey" startup problem I've had in the mornings. Although, 8% might actually be a little to lean for the L28.

When the engine is over 3000 RPM, the ECU already switches to simultaneous injection (all injectors firing at once).

How do you define "NEED"? Let's say you have two guys that work the same job and make the same salary their whole life: Mister A makes 50K a year, and lives below his means. Shops at yard sales, pays cash for everything. Religiously contributes to retirement account every year. At 65, he has 1 million dollars in the bank. Mister Z makes 50K a year, and lives above his means. Pays double for everthing as his credit cards are constantly maxxed, and he only makes the minimum payment. Always buys brand new cars, and brand new stuff. Never contributes to retirement account. At 65, he is 100K in debt. Both Mister A and Mister Z paid the same amount of social security taxes. Who deserves a social security check? I don't think Mister A should have to forfeit his benefits, just because he was smart enough to save. I also don't think Mister Z should forfeit his benefits, even though he's stupid, because he made the same contributions through his salary deductions. For saving well, Mister A will already be punished through taxation when he withdraws funds from his retirement account to buy a vacation home. I don't think it's fair to force him to forfeit SS benefits, even though he doesn't actually need the money. I am by no means rich, but I aspire to have a nice nest egg when I retire. When I am 65, you better believe I'll be pissed if someone takes away my benefit, because some other dummy who never got his finances in order, "needs" it more than I do. If anything, I'll donate my benefit to charity.

From my own observations, the top ring land on the flattop L28 piston is the same thickness as the L28 turbo dished piston: I know of at least 3 people running this setup, including myself, pallnet, and Tony D. I have about 900 miles on my 8.8:1 CR L28ET, running about 10 psi normally. Dynoed at 232 HP @10 psi. Soon I will be upgrading to 460 cc injectors for more boost.

I am running 88 Z31 EFI. almost everything is from the Z31, including the wiring harness, ECU, and MAF. I use the ZXT distributor with the Z31 CAS wheel installed in it. I am also using the Z31 ignitor and a generic aftermarket coil. I mounted the ECU on the driver side kick panel, and trimmed the Z31 wiring harness to fit the L6 engine. I pretty much took apart the whole Z31 harness, and deleted the items that I didn't need. Having a wiring diagram helps. The advantage of using the Z31 harness is that they are newer, and in mostly better condition at the junkyards. Also, since the wires are extra long, you will only need to cut them once, and install new connectors. I made 232 HP at 10 psi on this setup. Will shoot for more power with an injector upgrade and ECU re-program. The 88-89 Z31 efi is the better choice over the earlier Z31, because they are relatively easy to re-program with an EPROM burner.

I've been playing around with a similar idea. The two main ingredients are: 1) an adjustable boost pressure switch (Ebay - $20) 2) an electric solenoid valve (off a junkyard turbo Saab; aka APC valve) Basically, plumb the solenoid valve so it blocks the wastegate boost signal. Wire the boost pressure switch so that it energizes the solenoid at a fixed boost level. When the solenoid is energized, the wastegate sees boost as it normally would, and opens accordingly. This is no different then a ball valve type wastegate controller, except it's done electronically. It may or may not work any better, but the parts are cheap and I might try it. I think the electronic solution may be more responsive to sudden changes in manifold pressure. I have a ball/spring type, and I frequently overboost when I smash the accelerator.

I looked into the HKS S-AFR, and I think the concept is flawed, especially for a turbo car. The way I understand it works, is that it intercepts the MAF voltage, and then sends the ECU a different MAF voltage, at various RPM points that you program in. Here's the problem. It has no idea what boost level you are at. It allows you to program +/- 50% more fuel at each RPM point. Let's say you program 25% more fuel at 3500 RPM. At 3500 RPM, you could be at zero boost (cruising) or full boost (full throttle) and everything in between. So, there's no validity in adding X amount of fuel at Y RPM. Here's another problem. By changing the MAF or AFM voltage, you're fooling the ECU into thinking you're at a different part of the fuel and timing maps. Let's say you program the S-AFR to reduce fuel by 25% across the board, to account for bigger injectors. In addition to the first problem (see above), now your ECU is now going to be in a less-than-optimal region of the timing map. So now your timing is screwed up, and you've defeated the purpose of the bigger injectors and put your engine at risk. You also lose dynamic range of the MAF. Let's say the ECU can interpret a MAF range of 2-4 volts. After making a +/-25% adjustment it will be 2.50-4 volts or 2-3 volts, depending on on which way you adjust. You should be able to use the S-AFR with just about any MAF or AFM injection system. But you would need loads and loads of tuning just to get it to be barely comparable to an OEM setup, and you'd need other aftermarket gizmos to address the timing issue. After all is said and done in parts and tuning costs, you might as well get programmable EFI.