NO TOP END!??? no cat, plus headers.

[mackdaddy240]

Ok over the summer I did a complete motor swap I have a 90 240sx. I bought a 92 ka24de tore it appart bored it 20 over and bought some ka24e pistons to go in. I port and polished the intake side of the head myself. bought obx headers, injen intake, and electric fan. from the headers back it is straight 2.5" pipe all the way back to the magnaflow muffler. Now it has really weak bottom end which I expected from running straight pipe. Real power doesnt kick in till about 3000 rpm. However once I hit about 6000rpm I actually feel the gas pedal slightly start vibrating and it loses hp at 6000. The only thing I can figure is that the coil might have somthing to do with it. I kept the coil from my ka24e when I did the swap and spliced the ka24de wiring harness to the ka24e coil plug so it would work. Does anyone know if this has anything to do with it or has anyone had a problem like this before??Any info would be great I have to fix this before I go to NOPI NATIONALS.:help

[corn322]

heh heh, intake manifold? only thing I can think of. it's kinda pounded into my brain.

how about fuel filter? if you didn't, drop in a 300zx fuel filter.

[mackdaddy240]

I dont think it could be the intake manifold. unless taking the butterflys out and port and ploshing the manifold and the head could somehow hurt your hp. The fuel filter is pretty new but it is a 240 filter. I'll try putting a 300z filter in but I doubt that could the problem, but it couldnt hurt

[mackdaddy240]

Oh I did take off all the egr systems on the back of the intake, and pluged all the hoses. I also pluged the hole on the ehaust pipe that circulates exhaust to the AIV. think it could have anything to do with it?

[InsanityInc]

KA's have bad top end because the intake manifold cannot support high-RPM breathing. There is an aftermarket one in the works.

[InsanityInc]

though, with all those mods, you'll probably want an aftermarket coil. You've probably changed the volumetric efficiency of your engine enough that it warrants one.

[mackdaddy240]

thanks for the input I was about to buy a msd 6AL but I just found out that they only have chip sets for 7000rpm, and I just checked the factory limiter which cuts fuel at 6800 so I'm trying to decide which system to get. Does the MSD SCI have a manual rev limiter knob or does it use the chips as well??

[InsanityInc]

The ignition rev limiter stops spark after a specific RPM, it has no bearing on the factory fuel cut rev limiter. Not that you should ever be revving it above 6300 or so in a KA with a stock manifold, as doing so will just make you go slower.

[:: orion ::]

heh heh, intake manifold? only thing I can think of. it's kinda pounded into my brain...

That's the funniest s*** I've read today...hehe.

(if you don't understand why, check the "most HP from a KA" thread, and you can follow our intake manifold debate)

[/no help]

- - - - -

But as another counter point to the intake manifold debate, here's my 2nd best N/A dyno...



Notice the TQ continues past 5000rpm...hell, it's pretty flat from 4000-5500.

- - - - -

Now, as potential problems...I'd start with checking your base timing. It should be 20 BTDC, but a few extra degrees will help up top.

And the things that tell the ECU how much extra timing advance are the TPS and the MAF (versus RPM). Sounds to me like your problem is that the ECU is not feeding you enough timing advance up top, so check the TPS is set properly, and that the MAF is clean...

Check the air filter, make sure it's clean as well...

It could be a spark issue, but the OEM ignition system is pretty stout, so I'd look at the MAF and TPS first.

- Brian

[InsanityInc]

you seem to have a magical KA. I've never seen any graphs besides yours that look anything like that. Seriously, try to find another KA dyno that makes anywhere near peak torque past 4300. Even ones with different cams. What else did you do to that engine, and why are your other turbo graphs so different from that one and your turbo graph that you posted?

However, for the rest of us with non-magical engines, a legitimate problem exists with the intake manifold.

[:: orion ::]

you seem to have a magical KA. I've never seen any graphs besides yours that look anything like that...

...What else did you do to that engine, and why are your other turbo graphs so different from that one and your turbo graph that you posted?

No magic...just a list of carefully chosen parts that seems to have worked well together.

Mods: JWT N/A ECU, S13 cams (240/248), base timing at ~21BTDC, Injen intake, HS header, GReddy MX exhaust (60mm), ASP pulley, E-fan, no cat...that's all i think...it's been a few years!

Seriously, try to find another KA dyno that makes anywhere near peak torque past 4300. Even ones with different cams...

1997 240SX: JWT ECU, JWT Cams, Injen intake, N1 exhaust, HS header:



This is from 'Sport Compact Car'...they had a "Project 240SX" way back in the day...like 1998.

- - - - -

And I'll say it again...there's a market for a KA intake manifold...but it's not the most needed part when building a KA. First there needs to be cams, and I/H/E...at least...then a KA may see gains from an intake manifold.

- Brian

[corn322]

orion, how much did that ECU help on your car? also, I've got another question: Are there any negative benifits from using a bigger throttle body?

[InsanityInc]

Wrong graph. I think the one you're looking for is this one:



This is the before/after cams/ecu graph. Unfortunately, since they added them both, it's kind of hard to determine what did what.

HOWEVER, people usually see just as much of a peak gain from JUST an ECU. To me, it looks like the cams are mainly responsible for lowering low-end power, and making extra power after the manifold has already started killing airflow, while the ECU is most likely what's causing the torque to be slightly more level, though it still drops like a rock after 5000.

The fact that the horsepower peak happens at the same RPM, and that adding an ECU and cams only raised the peak horsepower by 6 should probably tip you off to the fact that the cams aren't at fault.

[:: orion ::]

Wrong graph. I think the one you're looking for is this one...

...This is the before/after cams/ecu graph. Unfortunately, since they added them both, it's kind of hard to determine what did what...

...The fact that the horsepower peak happens at the same RPM, and that adding an ECU and cams only raised the peak horsepower by 6 should probably tip you off to the fact that the cams aren't at fault.

No, that was exactly the graph I was looking for...

I wasn't trying to illustrate before/after with just cams....I was merely posting another dyno chart that showed TQ continuing past ~4300.

- - - - -

And it's easy to determine what did what...an ECU cannot increase top end airflow like that. It can maximize spark and fuel trim, which helps...but it's a linear increase...i.e. you'll gain 3-5rwhp across the board with an ECU. Same curve, just higher on the "y" axis. Similar to how pulleys "make" power...

Cams extend it out past it's previous drop-off spot.

And IMO, peak power means very little when compared with max gain...especially when you're looking at the effects of cams...the point of running hotter cams is to change the usable RPM range. So you increase airflow and upper-RPM torque, and that leads to more HP, and more usable revs...faster on the dragstrip, faster on a road course.

15.4rwhp is a HUGE gain...

Basically, more area under the curve makes a faster car...peak HP means nothing.

- - - - -

Anyway, we're starting to "beat a dead horse..."

We need some dyno evidence of a KA with a new/improved intake manifold to continue this debate...once you get it done, come back and show us what happened.

For now, lets agree to disagree.

- Brian

[mackdaddy240]

OK I just installed a MSD digital 6 plus ignition with a blast 2 coil. Didnt help top end much but it did help bottom end. Next I'm going to put in a 300z filter and maybe a 300z MAF anyone know if the 300z MAF will help any??

[corn322]

it will once you're running over like 250 hp. you also need a new computer to use the 300 mafs.

[:: orion ::]

...maybe a 300z MAF anyone know if the 300z MAF will help any??

Don't bother. Unless you maxed you stockMAF with ~250 or more RWHP, then there is ZERO performance advantage to a Z32 MAF.

Plus, as ^^^ that guy pointed out, you need a retuned ECU or an S-AFC to make it idle and drive anyway...

- Brian

[toptechracing]

So all these good answers here but I gotta ask. You put ka24E pistons in the motor. What are you running for fuel? If just running 92 octane pump gas is the knock sensor kicking the timing back at high rpm. The other thing would be is the Exhaust restricting the exit flow.

[nab911]

Put a good can of octane booster in a take of 92-93 or get some toulene and see what happens...

[:: orion ::]

...If just running 92 octane pump gas is the knock sensor kicking the timing back at high rpm...

GOod thought...but the factory knock sensor is ignored by the ECU above the TQ peak.

Basically, at ~4700 and above, the factory knock sensor does no good. ECU no longer "listens" for knock in the high RPM.

Nissan ECUs aren't cool like DSM ECUs, where there's active knock control and timing is pulled gradually as knock is detected. If the knock sensor reads knock, the ECU pulls about 8 degrees all in one shot. Nothing more.

It's an old Nissan safeguard...like the "tip in retard".

- Brian

[mackdaddy240]

I'm running 93 octane when Im just driving around town, then when i want to race I advance the timing a little and run 93 with a $7-10 octane booster. I changed the fuel filter for a 300zx filter and it did help the top end quite a bit, I think the top ends pretty much normal for a ka motor now. I can tell anything above 6200 doesnt pull much and thats with a complete 2.5" exhaust headers all the way back with no cat. I'm going to have to get a JWT ecu or something. I ran a 16.2 in the quarter this weeknd. I figured I'd be running low 15s. does anyone know how much some underdrive pulleys take off the quarter?. I also had a little wheel spin in 1st so I figure if I had a better launch it would be high 15s but I want low 15s high 14s!