91-93 240sx 5500rpm power surge theory

[Xero]

okay, after reading past posts, and putting 2 and 2 together, I believe I have a theory as to what is happening.

We've already figured out that there is a power surge on 91-mid93 240sx's that had the 8-port head with the vacuum controlled butterflies.

Here's a dyno sheet from Injen showing the blatant VTEC like power surge:



My theory is this:

the butterflies are opening at 5500rpms, which is giving that large power surge, since it's essentially allowing twice as much air flow to get into the engine. So playing with this vacuum, in theory, you could move this surge down to a more usable level, of 4000-4500rpms. HOWEVER, some may say that they don't have a power surge, 'cause some don't. I theorize that there are 3 possibilites, 1)your car was made after mid 93, or is using a newer KA24 2)your vacuum hoses need replacing, and you are running on 4 ports all day long 3) I'm COMPLETELY wrong

any ideas? proof? amendments?

[trpower7]

I believe we have determined that this power surge is due to a cam difference between DE S13s and S14s, which is why alot of S14 owners swap in the S13 cam. The S13 cam allows the engine to continue to breath in more air past about 5.5K. People have entirely removed the butterflys and experienced minimal effect, I tend to believe if it had this drastic an effect on airflow totally removing them would produce a more pronounced effect across the board......these are all just conjectures though......also I would really be hesitant to trust Injen's dyno graph.......

[Nismo1182]

I dont feel a surge in mine, but i do hear the intake get louder 500 rpms before redline on my SOHC KA.

[slw240sx]

they are talking about Ka24DE's with variable intak butterflys

[syka24et]

they are talking about Ka24DE's with variable intak butterflys

ka24e have butterfly intake manifolds http://www.sdsefi.com on the project page or you can look on the 240sx.org site in the install section.

[Xero]

I wouldn't expect cams to create a power surge like that, since the lift on them doesn't change like a VTEC cam, it has that lift and duration throughout the whole entire rev range, it wouldn't create a jump like that.

[trpower7]

I think that graph is not exactly accurate first of all, but the cam does allow it to breathe at that point where the S14 KAs tend to run out of breath. The point I was trying to make that people removed the butterflys altogether and didn't see that kind of a jump across the board. I think the consesus among most people is that all KAs really start running out of breath and power in that range.......

[Xero]

but what I'm getting at is that my KA doesn't run out of breath, it HAS that power surge, I CAN FEEL IT. I'll try and get it dynoed soon, and get a real accurate graph, but it's there.

[trpower7]

Your butterflys may be gummed up and not opening till that point. I wasn't ever quite sure, but I thought they opened gradually over the RPM range. Lets see if we can get a few other stock dynos together from actual people to check this out, having that "Injen" dyno graph up in the first place kind of bothers me........

[Xero]

^^sounds good to me, yeah, that's also what I thought happened with the buuterflies, since they were under vacuum, it should open gradually,

[p00t]

ummm... has anyone looked at the entire torque graph of that "spiked" run?

there is a spike at around 3500rpm that is almost as high... the only reason the hp didnt shoot up then is because its dependant on rpms ... not just raw power... its a fictional number... remember?

although i dont doubt it spikes alittle... i doubt its enough to make a big fuss about.

[Xero]

but the butterflies would create a DROP in torque, not a spike

[Zebrahead]

but what I'm getting at is that my KA doesn't run out of breath, it HAS that power surge, I CAN FEEL IT. I'll try and get it dynoed soon, and get a real accurate graph, but it's there.

Agreed. I feel it to. The funny thing? I don't always feel it, just every other time or so I hit that rpm. Wierd.

Nick.

[Nismo1182]

they are talking about Ka24DE's with variable intak butterflys

yup, sohc ka's have them too.

[Nismo_Freak]

I've heard about this surge from alot of S13 owners... never has a S14 owner said anything about it.

The injen was tested on a 95 S14 BTW and the cold air extension does give a considerable bump in torque at 3500 rpms.

[trpower7]

My guess if it's only S13 owners still kind of rests with the cam thing, maybe the butterflys being open and the slightle extra breathing space those S13 cams give lets you keep pulling through to 6.5 or so.

[MrFox]

the butterflies are opening at 5500rpms, which is giving that large power surge,

From the FSM, the SCV (the butterfly valve everyone is referring to) changeover point is 2400RPM. (EF&EC157). Not at 5000RPM+.

Furthermore, the injen dyno graphs only show a power spike for the green line run. The other runs - blue and red, show no such spike.



So the cause that power spike is attributed to what they have done differently during that green run. and no I don't believe for a second that some injen plastic tube is the curpit for a 14 hp increase. There are simply lots of other things (tricks) that can be done to make dyno runs look good.

Driving a 91 S13, I notice no power surges like the others have mentioned. There is simply a powerband plateau from 4500-6500, confirmed by the dyno data.

cheers

[trpower7]

Injen Dyno = BullJunk. We should ban using it for anything. I think the power spike is a figment of most's imagination, or some funny thing with your car, every S13 I've driven has a plateau from 4.5 to the end.

[toy turbo 2]

I get the exact same power surge, its like terribly timed Vtec or some crap.

My MR2 turbo spooled up more gradually then this...so I'd kind of like to know what it is.

but then i don't like N/A power anyway

[Xero]

fine, we all agree that teh Injen one is junk, here is PDM's run WITH OUT their cams:

w/ intake, pulley, header and tuning,



the jump isn't as drastic in this sheet, but it is still there,

[mickee]

I was told it was the RODS... i dont know if thats true or not, but whne i dynoed my car (89) fully stock on 91 it was a horrible 100hp and 120trq and htere was downfal at about 4000rpm im not sure if that would be the same with yours??

[s14]

for what its worth... i have a 95 s14 and every once in a blue moon i feel a "surge" starting at roughly 3000 rpms and keeps increasing , sometimes its so signifigant i lose traction to my wheels when its raining due to this "surge", quess im just hitting my powreband plateau, imostly feel it while accelerating on inclines... p.a. what a hilly state

[s14]

correction it is 4000 rpms i feel a surge... sorry

[Nismo_Freak]

At 4k the S14 gets a little bump in torque, thats what your feeling.

As for the PDM dyno the header on the KA causes a VTEC like power surge at 4k on the S14. You even hear the difference in the exhaust tone.