Going back to NA

[randy 77zt]

Before i put the turbo motor in my 77 I did a litlle work on the stock l28.Put on new injectors and connectors.Made a good distributor out of 2 that had a good advance curve.Got rid of the cat convertor and put a 2.5" exhaust system on.the car was very fun to drive-would have drove better with a 280zx na trans and 3.9 rear gear.

[ComicArtist]

I'm actually thinking about doing the '81 - '83 NA tranny with a 3.9 diff. What kind of highway cruising RPMs do you generally get with that setup? I've seen it before, but I can't recall.

 

I'll be freshening up the L28 a bit. I've got a shaved intake manifold and a Pallnet fuel rail off my L28ET I'll be throwing on there. Probably end up doing a 6-2-1 header with 2 1/4 exhaust back. I'm not sure if 2 1/2 will let me go low enough.

[cygnusx1]

Alot of the engine response strangness comes from emission control devices like the BCDD valve in the older EFI cars. The turbo L28ET engines are riddled with vacuum controlling devices that really kill the engines response. You see, by making the engines "sluggish", they run far cleaner, from an emissions standpoint. When you bypass and disable all those devices "shave the intake", the engine does respond better, but they don't run as clean anymore..not that it matters to me. I fully concede with the flywheel, exhaust, and cam, to improve response.

 

My point is that a snappier engine is more fun to drive...and you are after more fun, less power. Focus on "snappy".

Edited October 7, 2011 by cygnusx1

[Tennesseejed]

If your looking for a little more MPG why not megasquirt it??

 

Second this.

 

Got 27MPG on a 300 mile roundtrip this Summer.

[Tony D]

"Alot of the engine response strangness comes from emission control devices like the BCDD valve in the older EFI cars."

 

INcorrect!

 

The sluggishness of the OEM system is DIRECTLY linked to it using a flapper-style AFM. There is an inherent delay of response due to simple inertia.

 

Almost EVERY SINGLE ONE of the emissions control devices comes into play when you CLOSE the throttle, not when you open it! As a matter of fact, during WOT NONE of them are functioning! Matter of fact, over 3500 not much is going on with them either!

 

The sluggishness goes away with aftermarket systems because they measure MAT, as well as having accel-shot functions. They all drive similarly to early GM TBI systems, which were MAP based as well, and didn't have response issues inherent in the Bosch system.

 

The key to responsiveness is to keep the flap close to open. It's why the cars are geared to run on the freeway around 3K rpms. This REALLY helps throttle response. And in fact, the response above 3000 for an aftermarket and stock system is hard to differentiate.

 

Most people drive their cars so poorly that they attribute ills to the system that are really inherent in their misoperation of the vehicle.

 

And of course the Emissions Bogeyman comes up and is blamed for it as well. I don't know where that comes from, they all go inop at WOT, and most function to decrease emissions on overrun (drop-throttle)!

Edited October 8, 2011 by Tony D

[cygnusx1]

When I use the term responsiveness, I refer to the engine's rev up as well as rev-down characteristics. There are plenty of devices in the factory EFI that keep the engine from dropping revs too quickly, for emissions purposes. Sporty driving , in my book, requires some engine braking, which is barely existent in the factory EFI setups. Call me old school.

Edited October 8, 2011 by cygnusx1

[Powerglide]

Agree with Tony on this one. Keep the rpms above 3000 on an EFI car. The flap in the AFM will be close to open and the car will respond nicely, not "rev slow" and you'll get PLENTY of engine braking. On surface streets around town, most poeople drop in to 4th gear. The car is sluggish when turning only 2400rpm at 45 mph. I cruise around town in 3rd gear a good percentage of the time. Above 50 mph or so I'll go to 4th gear. Or I'll use fourth at slower speeds if I don't need the "snappiness". Power band on these EFI cars is 3500-5800 rpm. Torque peak is 4400 rpm. The L series motors are NOT American V8s. Driving them well takes an ENTIRELY different tecnique.

[Tony D]

Agreed, engine braking is done above 3K rpm, if you are holding braking below 3K rpms, that's pretty extreme. For Emissions devices to affect the sporting driving characteristics of the car, you must drive it grossly incorrectly.

 

Powerglide hits it spot-on with the operational range.

 

" I refer to the engine's rev up as well as rev-down characteristics." Rev-Up is also dictated by the camshaft, rev down is not an issue the BCCD is driven by engine vaccum, if you are truly WOT there isn't any driving force for the hold-open function at 4000 rpms. The only thing that operates is the dashpot and that is as much a 'keep the throttle from sticking' function as anything else.

 

If you were old-school, you would realize it has to be driven as Powerglide suggests. If you learned on an Air Cooled VW you would realize this. Cut your teeth on American Iron and you find yourself upshifting at 3000rpms and complaining of the lack of 'low end' torque at 1700 rpms.

 

Engine braking exists on the early EFI systems. If you're driving it. It's not there on todays' CVT's unless you select a lower ratio...it's a complaint overblown IMO.

[Tony D]

Also, most people agree the old 'engine braking to save the brakes' is outmoded as a driving technique even in Endurance Racing. Using the brakes to slow the car has become the accepted method. Improvements in brake compounds and most importantly brake fluid have rendered the old concerns almost irrelevant. It can be used as a method for 'conservation' in some cases...but as a general rule it's not neccessary any longer.

 

Drive a stock EFI car through an Auto X and you find there's plenty of engine braking if everything is properly maintained. Even if haphazardly maintained...

 

 

In other words, if you think 'sporty driving' involves any of the areas where the Emissions Devices affect engine operation (below 3500 rpms)---you need to relearn the driving you are doing. You are loosing ALL the sporting characteristics of the car driving in that range. Emissions affects daily driving, not enthusiastic driving.

 

I have often said chances are for most people driving these cars, you could substitute a VW Jetta TDI engine and they would think it was the greatest thing since sliced bread! They always shift before 3500, and when they DO run the tach to 5000 ever so rarely the engine does seem to pull all the way there. Just like a Jetta TDI. Plenty of torque down low, and the ability to rev to 5400. "Performance Personified" for many of today's drivers.

Edited October 9, 2011 by Tony D

[cygnusx1]

Sorry for all the thread jacking! But IMHO an engine that drops revs in between shifts, to about the proper amount for the next upshift, in about the time I need to shift; and a motor that promptly revs up with a heel tap, to the proper rev for a downshift, is fun. Having rpm/s highly variable depending on where you are on the tach, is a bit annoying.

[Tony D]

That, sir, is again the function more of the flywheel than the emissions devices.

 

The NEW cars are FAR worse than the old mechanical only BCDD and Throttle Dashpot. They will physically hold/bypass air open to keep rpms up---that is on stuff like the Z32, not S30's.

 

If this is happening on your car, you got something adjusted wrong! It's not the emissions devices, they're transparent when driven hard. If maintained with a modicum of care (if that!)

[Powerglide]

If your 280z has "throttle hang"...look for vacuum leaks. Then check the BCDD. If it's out of adjustment, rpms will hold between shifts and perhaps even rise when the load is removed from the motor when you push in the clutch.

[Powerglide]

If your 280z has "throttle hang"...look for vacuum leaks. Then check the BCDD. If it's out of adjustment, rpms will hold between shifts and perhaps even rise when the load is removed from the motor when you push in the clutch.

[cygnusx1]

It has been at least 12 years since I drove a stock EFI S30. I have recently driven stock ZXT motors, and with only two data points, not really a good chart, I feel like I am driving an engine filled with molasses on the way up, and dealing with intake leaks on the way down. Disabling the various "wind intstruments" from the ZXT intake manifolds improved the situation on decel greatly. The light flywheel helped much as well. I was well versed in the 280Z EFI back when it was my daily driver, turned weekend warrior for about 10 years. The BCDD valve definitely "goes bad", but it could be corrected or eliminated to improve the engines feel. The L28 was way more natural feeling than the L28ET.