Hello all- I'm New Here - I have a question for Scottie-GNZ

[Guest Anonymous]

Scottie-

I've been doing some research on many of your previous posts. Ever since I saw a 280Z LT1 conversion on the corral (corral.net), it reminded me of my first car when I was 16 - it was an 83 280zx. I later traded it for a highly modded 280z (10:1 Compression / ported and polished / Holley 750 double pumper, etc, etc). I miss them both.

I got the grand idea to get a project z and discovered you beat me to the idea I had to drop in a GN engine. Anyway, the only thing is I really require with this future project car is a 5 or 6sp tranny. Couldn't the right tranny and rear end gearing solve the problems you mentioned about having to shift too quickly in 1st and 2nd?? Also, you mentioned that there are certain things you need to alter in you driving habits when driving a turbo to avoid breaking things. I have never owned a forced induction car so excuse my ignorance. Can you please explain what you mean by that?!

Thanks- I'm still learning.

Hopefully in a year or so I'll be well on my way to creating my GNZ!

 

Your help is appreciated.

Tony

[Scottie-GNZ]

Tony,

 

welcome to our little world.

 

This is an oft discussed and even debated topic here and on the Buick boards. It has been proven by those who have done it that the car actually runs slower with the manual box. However, this has always been from the drag racing perspective and in the big, heavy Buick. It is important to remember that this engine in stock form (I mean stock internals) is a low-revving, high-torque engine and it makes no sense pushing it pass 5300. As a result of those characteristics, Buick designed a special version of the 2004R for this application and that combo just flat works.

 

Another reason it works so well is because of the monster torque this little jewel generates. It seems to a lot of people, this is just not fully understood. This engine at 400+hp is pushing around 500lb/ft of torque at very low RPMs. People see 3.8L 6-cyl and it does not register, yet the thought of putting a stick behind a BBC in a Z and bombing it off the line would probably scare any Z owner. The whole point of that was to say you have to approach putting a stick behind this engine the same way you would putting a stick behind any big block.

 

No point in putting a stick behind any engine if the overall 1st gear ratio combined with the typically short tire a Z uses makes that gear usless. The thing you do not want to do is wind up this engine too quickly in the lower gears. I think my going from a 3.54 to a 3.08 proves that and I am just getting started with that combo . Now, if you build up the engine with ported heads, a cam and even bigger turbo, now you can wind it up to 6000+, BUT, you are now in the 525+RWHP range with torque approaching 600lb/ft and having to deal with another set of issues like a clutch, tranny and chassis that can withstand that. You could always turn the boost down, but then what is the point?

 

Well, I have rambled a lot but if you are considering the stick behind this engine, you have throw out conventional NA thinking of lower gearing and close-ratio gearboxes and go for the highest overall 1st gear ratio and widest ratios you can find. In the used OEM gearbox market, you are limited and that forces you to do what I did and that is go for the highest final drive ratio you can get. Stock Nissan will be a 3.36. Get the ratios of the tranny you plan to use and use the industry formulas to calculate overall ratios to get the max mph in each gear. 1st gear is the critical one and keep in mind that with the proper suspension setup, traction and 400hp, you will be in the 0-60 in 3-sec range. With the wrong combo (one that gets you only say 30mph in 1st) you could have a useless 1st gear or you will be a busy boy . Remember when Porsche first introduced the 930 turbo? Yep, it had a wide ratio 4-spd with Lonnng gears. Same concept.

 

Hope I did not muddy the waters or discourage you.

[Guest MegaShaft_2000]

Originally posted by 98blacksnake:

Anyway, the only thing is I really require with this future project car is a 5 or 6sp tranny. Couldn't the right tranny and rear end gearing solve the problems you mentioned about having to shift too quickly in 1st and 2nd??

As Scott mentioned, having a manual tranny in a turbocharged car with a slow spooling turbo slows it down.

 

In a turbo car, the turbo must spool up before it will produce boost. If you are shifting through the gears, your turbo will need to spool back up every time. The larger the turbo, the longer it takes to spool, and the worse your performance will be with a manual tranny. With an auto, the turbo only needs to spool once, and after that you keep it floored all the way down the track.

 

I have a twin turbo Z, and even with its tiny 2 turbos which spool up fast, the auto version of the Z (which only has 280 hp compared to the manual's 300) still beats the manual version to 100 mph. That's in stock configuration. With larger turbos the benefit of an auto becomes more apparent. Also, with bigger turbos the car seems to like longer gearing, I guess it helps if there is more of a load on the engine.

 

While you can eliminate much of the lag time by running small shots of Nitrous to spool up the turbos, on the street it will be a dog.

 

PS- The fastest turbo Z32's and Supra's are autos. I'd imagine that fastest GN's out there are auto also.

[Guest Anonymous]

Not to contradict megashaft as I totally agree with him, fact is fact, but the spool up in manual car problem can be dealt with to some moderation. A good blow off valve to dismiss closed-throttle back pressure (which is at root the problem with keeping the turbo spinning, as air "backs up" slowing down the compressor wheel. By relieving the pressure, and providing good shaft lubrication to the turbo, the built-up centrifugal force of both wheels will keep the turbo spinning freely in psuedo atmospheric pressure, the only "spooldown" factor would be the small amount of drag produced by the blades on the wheel and minute amount of friction involved. A BOV can create the ideal conditions for a manual shift turbo system. If I had a full drag race turbo car, I'd still go with a correctly stalled auto tranny, but for street, IMHO a manual is just more fun. Just my .02

-980mak

[Guest MegaShaft_2000]

Originally posted by 980mak:

Not to contradict megashaft as I totally agree with him, fact is fact, but the spool up in manual car problem can be dealt with to some moderation. A good blow off valve to dismiss closed-throttle back pressure (which is at root the problem with keeping the turbo spinning, as air "backs up" slowing down the compressor wheel. By relieving the pressure, and providing good shaft lubrication to the turbo, the built-up centrifugal force of both wheels will keep the turbo spinning freely in psuedo atmospheric pressure, the only "spooldown" factor would be the small amount of drag produced by the blades on the wheel and minute amount of friction involved. A BOV can create the ideal conditions for a manual shift turbo system. If I had a full drag race turbo car, I'd still go with a correctly stalled auto tranny, but for street, IMHO a manual is just more fun. Just my .02

-980mak

Yeah, I agree that manual is more fun, my Z is a manual. I also have blow off valves (Apexi), scares people when I let off the gas next to them.

 

I have BOV's and I don't notice much of a difference. They help more to prevent damage to the turbo than to enhance performance. When your throttle bodies close, the air pressure builds up behind them and a pressure wave can back up into the compressor blades. This can damage the turbo over time. Relieving the pressure prevents that damage.

 

But also, think of it this way- if you take a leafblower and block the nozzle, the engine will speed up because the fan isn't moving any air. The air might be backed up, but the blades aren't doing as much work as they would if you allowed them to catch air and pump it. By allowing the boost to leak out, you are making the compressor in the turbo do work, and this will slow the turbo down a bit. On the other hand, if you allow the pressure to stay built up behind the throttle body after every shift, that charge is available for when the throttle bodies open again. If you allow all the boost to leak out through BOV's, when the throttle bodies open again, there's no charge waiting and you get sluggish response after every shift.

 

When I first installed my BOV's, they weren't adjusted properly. You can set them to release the pressure at a certain pressure differential by tightening a set screw on the front of the BOV. Mine were allowing all the boost to leak out until there is none left after each shift. Performance suffered a lot, the car felt sluggish after every shift. After I tightened them up a bit they wouldn't release until there was a 10 psi or so pressure diff. That brought performance back up to where it was before I installed them.

 

I'm not sure if BOV's help or hurt performance, but I do know that it doesn't seem make much difference one way or another, and nobody has been able to measure the effect on the track.

[Guest Anonymous]

Thanks very much for all your replies!! As I said before, I am still new to the concept of turbocharging so I just want to get all the info I can before making a wrong decision.

 

Keep em coming-

t

[Guest Anonymous]

You guys let off the gas while shifting a manual? I just keep it buried, a bit hard on the clutch and rear end though at least on my N/A Chevy/Z...

 

This automatic vs stick which is faster in the quarter debate isn't limited to Turbo, I'm sure it has its own unique problems but... Automatics just plain shift faster, the amount of time taken to push in the clutch jam a gear and get back out of the clutch is all time where no forward momentum is being produced. A good built automatic shifts nearly imediately with little or no loss in power production. Add the time of three or four shifts for a manual, its easy to see the time loss in doing so.

 

That said, I still like manual trannies, theres something pretty satisfying slamming that gear and getting the push of torque from the next gear, maybe its just a mental thing, but it feels raw and primitive yet enjoyable...

 

When your talking about it being slower in a HybridZ, well slow is relative, gosh you mean I'll slow down running a manual tranny and only run 11's... Gosh that bites...

 

Regards,

 

Lone

[zero]

i found myself asking the same question, but I will probably not e drag racing, if i do any racing it will be road racing, where a manual is definately the better choice.So im basically asking if it is possible to bolt up a t56 up to a 4.8t

[clint78z]

Granted I love stick, and won't give it up. Yes automatics are usually much better for drag racing. While it does help all engines in a drag, it is especially helpful in a turbo car. In a manual when you launch you are basically launching it as a normally asprirated car. Since the turbo works off exhaust gas, it really doesn't spin that much when engine is revved in neutral. In an auto it allows the engine to build boost at a stand still, suddenly you are launching with mabey 150hp instead of 50hp at the low rpm.

 

Scottie makes a very good point about gearing often oevrlooked. Seems that some L6 guys want to put a T56 behind there engine. Well it seems good at first glance, but is it really matched for the motor. If first is too high or low it will either smoke the tires and you will have to shift right away, or huge bog and fall on it's face. Find the gear ratios of the 2004R and what diff gear ratios GN guys run. Then use a spreadsheet to try and find a good match for an different tranny/gear combo.

[Guest gprix1]

For a car that will be built for fastest 1/4 mile time I would go automatic for sure but if it's going to do any cornering give me a stick-shift please.

 

It's funny this came up because I literally just got of the phone with my friend who wrecked his automatic C5 Corvette. Seems he was going home tired, late at night, going around a corner that had just gotten wet from some sprinklers, and getting on the gas his car down-shifted and the car kicked out hard. This guy races side-cars and has a lot of track experiance but he was tired and caught totally by suprise and he did a rookie move; he slammed the throttle shut instead of easing off. The car whipped back the other way and he went backwards into a retaining wall.

 

If this had been a stick shift he would have been rolling into the throttle all the way through the corner not rolling on and WHAM downshift @ mid-corner.