maybe a stupid question, how to extend my torque band by 1000 rpm?

[Guest bastaad525]

Well... I still haven't ordered the parts yet for my 3" exhaust... my wife went on a couple small spending sprees this week (the woman has like 5000 people in her family and hence there is always some birthday, wedding, or other assorted occasion coming up where she needs to buy some gift for someone), so I'm holding off until I know I can do it w/o hurting at all.

 

Anyways... I've been looking at my dyno sheets a lot lately, and just boggling over the immense, rapid drop in torque after 4000rpm... it goes from 300ft lbs at 4000 down to 200ft lbs by 5500rpm... a very big drop!!!

 

Now I already know that part of that, at least, was due to boost slowly falling off as revs increased, about 1psi per 1000rpm. But no way 1.5psi is accounting for 100ft lbs lost over 1500rpm.

 

I figure that another part of that is due to my sorta-restrictive exhaust... a bastard 3" to 2.5" non mandrel bent lump that terminates in a crappy 2.5" glasspack, the kind with the fins that stick up into the airflow, causing even further restriction. Well, soon that will be taken care of, going to a full 3" mandrel bent system with a straight thru Dynomax bullet muffler. But will this be enough to get me that extra 1000rpm of torque?

 

if not, what else can/should I look at, to make it so that I can carry that 300ft lbs, or very close to it, up until 5000rpm? If I could do that, it would be worth about an extra 60-80 horses! Heck if I can extend it a measely 500rpm that would be worth 30-40 hp!

 

Is this even feasible or would it take big changes like a radical cam? Should a stock turbo motor and stock T3 even be able to breath well up to 5k, or even up to 4.5k, or is it really just the nature of the beast to fall of sharply after 4k like mine does? Do you guys think the exhaust will be the key?

 

Give me some recommendations guys... it seems like it should just be so easy to have it make that torque just a little bit higher into the revs...

[Tony D]

Got Dyno Time Reserved?

 

Get a Tomei, Arizona Z, or Kameari adjustable cam sprocket and start fiddling.

 

On our Bonneville car, playing with the timing 4degrees made a WORLD of difference in the N/A application by opening up torque on the bottom end (where WE needed it).

 

The Adjustable Sprocket gives incremental changes because slippingthe chain a full tooth is like 9 degrees. A combination of tooth slippage and camgear adjustability compensation would give a fairly large change on WHERE your power occurs.

 

But getting it on the top end is harder than getting it back on the bottom. Moving the camgear one tooth will make one heluva stout bottom end that drops FLAT on it's face at 5500. Slipping it in the other direction doesn't seem to have such a dramatic result with an N/A. But with a Turbo, you might have some hope.

 

Just check valve to piston clearances before any fire up---shouldn't be a problem with 9 degrees, but better safe than sorry!

[Guest bastaad525]

I was thinking about getting one of those... they're not pricey at all and install should be a breeze, but yeah tuning it is gonna take some serious time and $$$$$$$$$$$$$$$$$$... You think a Gtech would be of any real use here? I figure the $200 for the Gtech would be way less than the amount of dyno time it'd probably take to tune something like this.

 

I hope this 3" exhaust really wakes it up a bit... come onnnnnn 500 extra rpm!

[Clifton]

There is more of a restriction in the turbine side of your turbo than the exhaust at your power level. You will lower your post turbo back pressure with a 3" but pre turbo it will still be too high for good top end. Small turbos designed for fast spool just don't flow enough and power suffers. An extra 500 rpms before peak boost for an extra 500 rpms of a usable power band and alot more power too, isn't a bad trade off.

 

A G tech won't tell you if you are rich or lean. Spend the extra $150 on a wideband and not the G tech.

[Guest bastaad525]

So then the torque falling off at 4000rpm like that is likely a function/fault of the T3 itself then? 500 rpm i may not mind, but I dont think I'd like to trade 1000rpm of extra power for a turbo that spools 1000rpm later... this is why I haven't seriously looked at upgrading, I like that it kicks in full before 3000rpm.

 

About the Gtech, yeah I have already planned on getting a wideband for so long, was supposed to get one for Xmas but some circumstances made that one not happen. I was talking about getting a Gtech specifically for tuning an adjustable cam sprocket though, not tuning anything to do with a/f ratios, would adjusting a cam sprocket affect the fuel mixture?? I was thinking Gtech for tuning the sprocket because in that case I really would just want to see if it's making me any faster (meaning I've moved the torque band up and am getting more hp as a result). But if tuning a cam sprocket WOULD result in changing the a/f then yeah the Gtech would still be useless... no good going faster if I get dangerously lean and dont even know it.

[Clifton]

I misunderstood the reason for the G tech. Retarding the cam timing favors top end while advancing it gives more bottom end.

 

I like a turbo that makes full boost early too, but it's not possible to have both. My Z31 T feels real fast at half throttle as it makes full boost there but that's all it has and when I push more nothing more happens. It is a huge compromise. The torque falling off isn't just a function of the T3 but airflow. On a 1.6 liter it would be fine but on a 2.8 that isn't the most effecient and at higher boost levels it becomes a greater restriction.

[grumpyvette]

a few factors you might want to look into are the fact that the cam timing and the compression ratio and boost curve MUST ALL match the application, and then the voluumetric efficincy falls rapidly after about 4500-5000rpm simply due to the TIME available to fill the CYLINDERS, ESPECIALLY if the exhaust is restricted or the compressor flow map does not provide the voluum necessary and the cylinders dont scavage correctly.

at 5000rpm theres about 42 intake strokes per second per cylinder, you just don,t have a great deal of TIME to fill the cylinders above 5000rpm as the time available gets shorter and on a boosted engine the booost pressure tends to make closing the intake valve harder and without more spring pressure valve float comes in at a lower rpm

[Brad-ManQ45]

Plus, don't forget that the stock ECU starts going leaner around 4000 rpm.

 

Honestly, the first thing (aafter exhaust) would be to put an aftermarket ECU in there with bigger injectors to make sure you don't lean out.

 

I have an '83 ZXT with T3/T4 S-Trim T04B w/clipped stock turbine (put on in '94 before all the new stuiff was available) and 3" mandrell exhaust w/stock downpipe.

 

I haved been battleing the stock ECU shutting down when really getting on it, and the engine shutting off when underhood temps get hot at idle.

 

I don't want to throw any money at stock stuff any longer - I'm waiting for UMS to come out, then I'll get bigger injectors and do a good downpipe and upgrade the turbo to a TO4E w/stage 3 or 5 turbine and external wastegate.

 

I do have the advantage of not needing it or the '75 V8 project car for a daily driver though.

 

You may want to consider simply going with the 300ZX computer and mass air stuff with stock injectors - you'll probably get better gas mileage too....

[Clifton]

You can always run additional injectors to get more fuel and have full control of fuel under boost. I am still running a stock ecu, although not a Nissan one but it still has a restrictive AFM.

[Guest bastaad525]

I've already adressed the fuel issue, running an RRFPR, and have plenty of fuel, last time I dynoed with a W/B O2, I was right in the high 11-low 12:1 a/f ratio area up until about 5500rpm where it did lean out sharply to about 12.5:1. But from 4000-5000rpm I am nice and rich (not overly).

[cygnusx1]

I think the Sentra would have given you torque past 5000 rpms! LOL.

 

Just had to say that. Baaast nice to see that you are driving the Z again..or at least tinkering with it. I gave up some low end torque when I switched to the TO4B SuperV Trim. However, the torque hits so hard from 3000-5000+ now. I just don't rev much past 5K because of the stock ECU and the fact that I have my ign timing pushed ahead to get back some of the lost low end. I have to say, that with just switching to the bigger compressor, I lost speed in first, and probably second gears, because of the lag. The gears go by too quick to fully utilize the boost. BUT, 3rd-5th gears more than made up for the lost low end. On the highway, it is a torque monster with the larger compressor. I definitely miss the quick spool of the stock T3 but then as soon as I get into 3rd gear I forget all about it as it seems "nothing is going to stop me now". I think you will need to sacrifice some low end to get some high end...unless you go to a V8 or spend lotsa $$$ on the L28ET.

[Guest bastaad525]

eh... even if I was okay with giving up low end for high, I wont have money for doing a turbo upgrade any time soon. But I must state again how much I do like the stock T3 and how quickly it spools... I'd like to maximize what it can do..

 

but let me clarify here... torque falling off sharply after 4000rpm, that IS an issue with the turbo, right? I mean to say, is this exact pattern typical for the stock T3, to fall off like that? If it is then I wont bother looking for other ways to fix the problem.

 

I need to hunt down some dyno sheets for stock T3's and see if this is common or if it's just me... so I know if there are other things I can do or that I should look for other restrictions to try to free up some more RPM like this. You guys don't think going to a full 3" mandrel exhaust will let the torque carry on higher at all?

[GrayZee]

I need to hunt down some dyno sheets for stock T3's and see if this is common or if it's just me... so I know if there are other things I can do or that I should look for other restrictions to try to free up some more RPM like this. You guys don't think going to a full 3" mandrel exhaust will let the torque carry on higher at all?

 

 

I don't think raising the torque curve about 4000rpm is something that can be done easily (or cheaply) It's just the nature of the the L engine. I have a full 3" exhaust right after the wastegate, and my peak torque is about 4200rpm Until I had my ecu tweaked I was getting some bad detonation around there.

A bigger turbo would definatly give you a better top end, but that dosn't mean that it has to scream at 7 or 8k to do it. Just shift into the next gear and make that low end torque work for you.

[COZY Z COLE]

I agree with what's been said..... $$$ upgrade on your current engine or go V-8. That said have you read the link on optimal shift points??

 

http://www.datsuns.com/Tech/whentoshift.htm

 

I thought you posted here at one time about going to live overseas this year. You are at a crossroads on this car and all of us fall into the "not happy when we get there mode" with our set-ups. Stop awhile and enjoy the car as it is.....IMHO

 

 

LARRY

[Guest bastaad525]

well this post served it's purpose then I now know it is futile to really chase this one and try to 'fix' it when really it's not 'broken' but rather, just the nature of the beast.

 

So I'm not dissapointed... I can still make more HP by just raising the torque curve overall i.e. more boost and fuel Still hoping the 3" mandrel exhaust will at the least, increase spoolup time noticeably and at least that will extend my torque curve in the other direction = more power sooner. Yeah I guess it's no problem staying in the curve anyways by just shifting sooner... I tend to shift right around 5500rpm right now... I guess I kinda like that it makes the power early like that... one side effect is I dont have to rev the hell out of it to get all it has... hopefully that means less wear and tear as well?

 

I do hope that the 3" exhaust at least LESSENS the rate at which torque falls off after 4000rpm... that was really the main gist of my post, not so much that power drops after that point, but HOW FAST it drops... 100ft lbs dropped in 1500rpm seems just way too extreme and suggests there's a bottleneck there as opposed to just being the way the engine works. I remember my torque curve with the built up N/A motor I had was very similiar and did fall off right around 4000-4500 as well but it fell off MUCH more gradually and resulted in HP peaking much higher than with this motor. I was hoping there would be some way I could achieve that with this motor w/o major upgrades like a cam or turbo upgrade.

[GrayZee]

When I'm racing I usually shift around 6k. The PEAK torque may drop off earlier but the engine already has alot of momentem at 4k that the 2k difference passes by with a blink of the eye. Also when you hit the next gear and drop in rpm, then you're right back in the powerband. A bigger exhaust will definatly increase spoolup, I noticed a huge difference and even a extra 2psi without making any adjustments to the wastegate. N/a engines have been built to do 8k or so but those engine have alot of work done to them, particularally with the cam and valves. They would have alot of vavle overlap which would make them perform well at high rpms but suck in the low end. Such a design would not work well with a turbo at all as it would be blowing some of the air/fuel mixture out the exhaust valve.

[SHO-Z]

Instead of using a Turbo use a Supercharger. This will increase your torque at lower RPMs. There was a post about a month ago about the car that is in the Z car magazine. Supercharges do take HP away on the upper end but add HP and torque on the lower end.

 

There are plus and minuses to every system.

 

http://forums.hybridz.org/showthread.php?t=99330

[Guest bastaad525]

I agree with what's been said..... $$$ upgrade on your current engine or go V-8. That said have you read the link on optimal shift points??

 

http://www.datsuns.com/Tech/whentoshift.htm

 

I thought you posted here at one time about going to live overseas this year. You are at a crossroads on this car and all of us fall into the "not happy when we get there mode" with our set-ups. Stop awhile and enjoy the car as it is.....IMHO

 

 

LARRY

 

 

Larry - thanks a TON for that link that's something I've been looking for forever! The great little Excel spreadsheet they provide was very helpful and with my dyno sheet and tranny ratios from the Z design studio tranny calculator, was able to figure out my optimum shiftpoints in minutes! A really great explanation for when to shift and why you should shift at that point, many thanks! Funny thing is, I already did shift right around the recommended points anyways, dunno if it was just feel or coincidence... at least now the question of if I was doing it at the right times has been put to rest!