top end power is flat help with why

[newbe40]

Took it to the dyno and the numbers are ok but it looks like there is something holding it back at the upper rpms ? see graph lower numbers are at 15lbs higher numbers are at 17lbs of boost.I am looking for 300hp and tq out of the setup.I would like some feed back on a few things.1. Turbo is a t3/t4 50trim .48 exhaust, do I need to change to a .63 housing or may be another turbo?2.Could the exhaust system be holding it back ? It is 2.5 pipe all the way no cat with a magnaflow muffler.3.Should both of the above be changed ? The setup is 91 kadet with arias pistons, rebuilt motor, 50lb msd injectors, jwt ecu, z32 maf, jgs log maifold, t3/t4 50 trim .48 exhaust stage two wheel.

[SeVa-S13]

Ignition system and plug gap?

[MarkEmark]

Took it to the dyno and the numbers are ok but it looks like there is something holding it back at the upper rpms ? see graph lower numbers are at 15lbs higher numbers are at 17lbs of boost.I am looking for 300hp and tq out of the setup.I would like some feed back on a few things.1. Turbo is a t3/t4 50trim .48 exhaust, do I need to change to a .63 housing or may be another turbo?2.Could the exhaust system be holding it back ? It is 2.5 pipe all the way no cat with a magnaflow muffler.3.Should both of the above be changed ? The setup is 91 kadet with arias pistons, rebuilt motor, 50lb msd injectors, jwt ecu, z32 maf, jgs log maifold, t3/t4 50 trim .48 exhaust stage two wheel.

Hmm...that is strange...and you have a very similar build to me. I wouldn't think 2.5" exhaust would flatten the power curve that much....but if you can, try running it with just an open downpipe (if the dyno is near you), or disconnecting the exhaust past the downpipe at the dyno--if you make more power there's part of the problem.

What is your timing set at? And like Seva said, what kind of plugs and what are they gapped at?

The JWT's timing is very conservative; I set my base timing at 22 deg btdc as a result, and you'd be suprised how much 2 degrees makes a difference (for the record, I also have methanol injection, 93 octane gas, and a large intercooler to prevent any predetonation).

Also, I wouldn't think the turbo would cause that much flattening of power either...I know Rn240sx is running like 20+ psi from a .48 a/r turbine no problem, although the .48 a/r is definitely going to be choking the engine a bit at that boost level (I speak from experience). A larger turbine housing might help, but it'd be even better coupled with a larger turbine blade (e.g., stage III). You can usually pick up turbine housings for like $60 or so, so again, that'd be a relatively inexpensive way to see if you can make more power.

And do you have anything else to tune the car besides the ECU? Because it looks like on the graph that you're running at or below 11:1 for most of the rev-range, which is pretty rich. If you could get it to 12:1 you'd make more power...Although 11:1 is the "safest"...

Try some things out and see how it goes.

[newbe40]

Ignition system, this is a 95 240sx with a msd 6a and blaster 3 coil plugs are ngk iridium 6 heat range gapped at 28.When we dynoed the car it showed no sign of blowing out the spark if that is what you are thinking.I was really hoping to get some feed back on the turbo and exhaust but I am open to any suggestion.

[newbe40]

Thanks for your reply, I think you have given me some good advice about the turbo eg my stage 2 and housing. I was hoping to confirm what I thought to be the problem I will be calling the turbo builder on Monday !Would you have a good Idea of what total timing should be on pump gas 93 octane.

[Nismo_Freak]

http://www.texasracingscene.com

You should join up and post in the Nissan section.

[MarkEmark]

Thanks for your reply, I think you have given me some good advice about the turbo eg my stage 2 and housing. I was hoping to confirm what I thought to be the problem I will be calling the turbo builder on Monday !Would you have a good Idea of what total timing should be on pump gas 93 octane.

You didn't answer what you're base timing (at the distributor) is set at, nor if you have any tuning beyond the actual ECU...That'd be helpful in seeing what the problem is.

When I get home in like 2 weeks (where the car is, i'm at school), I'll data-log the timing at different RPMS/gears with my Blitz R-VIT to let everyone know what the JWT ECU programmed for 50 lb fuel injectors does for timing maps. (I'm using a Cobra MAFS, not a Z32, BTW).

I data-logged the timing when I had the JWT ECU programmed for 370 cc injectors, and even then the timing was pretty damn conservative, so I immediately advanced it 2 degrees to 22 deg BTDC. I believe one of the PRINCIPAL differences between the JWT ECU tune and the Enthalpy tune is the more advanced timing of the latter...it makes a big difference.

As for the turbo: does it hold boost consistently across the rev-range (in your case, up to 6000 rpm), or does it wane toward the upper rev-range (as was the case with my .48 a/r turbine)? Looking at your graph, the fact that the power does not drop but flattens out completely would indicate to me that you aren't losing boost...

I'm shooting for 300 whp @ 15 psi with a similar set up when I get home and dyno it so I hope part of your low power is due to the small turbo, conservative timing, and rich a/fs...My timing will probably be more advanced (yay methanol injection), and fuel pressure bumped down maybe 3 psi to lean it out a bit compared to yours though. If I'm able to get the a/fs in the 12 range, keep the timing at 22 or even 23 deg btdc depending on how much retarding the JWT ECU really does, and run with an open exhaust (I have an electronic cut-out after the downpipe, so it'd be like running just an open downpipe), I should be able to easily make 300 rwhp @ 15 psi, which is all I want. I also have an ASP crank pulley, fidanza flywheel, ACT street clutch, 1 mm oversized ferrea intake/exhaust valves, 3 angle competition valve job, and PDM stage II cams, and relatively high CR 9:1 wisecos....but the methanol injection will really let me run what others who don't use methanol would consider "lean" or "aggressive"....it really makes a huge difference. When I first turbocharged the car, I was running 10 psi (smaller T3) for over a year w/o an intercooler, just methanol injection, and it never once pinged. But I digress; this is all bench-racing...you need to make some changes with your set up and tell us how it goes.

For the record, S14tat made 300 rwhp from a similar set up as both of us (JWT ecu, Z32 MAFS), but with a larger turbo and an s-afc, but he said his a/fs were still mid-to-low 11's...and he's running base timing of 20 btdc as well. If his A/Fs were around 12:1 - 12.5:1, and he was running 22 deg btdc, I'm sure he'd have made around 320 rwhp, which is more like he should be making at 15 psi.
Modified by MarkEmark at 12:28 AM 4/30/2006

[newbe40]

It maybe a bit on the safe side, I would consider bumping the timing but it would make me feel better if I knew what total timing should be and a/f across the rpm maybe on the rich side but at wot it looks close.Base timing is set at 20 degrees and no tuning beyond jwt ecu. I am thinking a trubo change will make a big difference.My back ground is old school bigger is better olds 455 and then I bought a grand national and that started forced induction stuff and I got it to mid 12's, now I am liking 24 mpg and looking for 300hp.These forums a invaluable source of information and as everyone here the help is appreciated.

[newbe40]

registration is disabled and I couldn't find the nissan section.Nismo_ Freak please contact me at [email protected]

[9sec240]

Honestly, what your setup is missing is cams... You have the typical KA stock cam TQ drop... Your TQ is dropping 75 lbs from peak TQ and that is what is killing your HP... Cams will straighten out your VE and your HP will continue to rise...

[Chezedik]

I was thinking that, but I guess I was too late.

[SeVa-S13]

I'm no KA expert but I wouldn't think the obviously restrictive stock cams would cause the power to rapidly rise and fall like that, but rather be a steady decline. Or have more people had similar dyno sheets with otherwise well-tuned and setup engines?