KA rev limits and ECU hacking

[AceInHole]

this is a copy of a post i made recently in FA. Just thought I'd run it through on here as well:

I'm looking at re-crystaling my ECU for a number of reasons right now:
1. All the (fwd) SR20 guys are doing it
2. Higher Redline
3. Less timing advance
4. Reduction in fuel

The big problem I'm having right now is finding the right crystal. I've been searching all over the web for something but I'm only coming up with 8.5, 9, and 9.2 as useable crystals (stock is 8). These leave me with 6900, 7300, and 7500 rpm redlines respectively. I'm looking for around 7000 ideally, so the 8.5 crystal, while being safer, isn't exactly what I want. A 7500 rpm redline seems overkill, so that leaves me with a 7300 rpm redline.

So, the ultimate question is: would the KA survive over-reving to a 7300rpm rev limit without a bottom end or top end build up??

Otherwise, I've been thinking about getting an aftermarket rev limiter and going to a much higher crystal. This would give me a lot more "tuneability" of the timing advance, although any changes would be linear, while allowing me to dial in whatever rev limit I wanted.

Edit: This would also help prevent killing clutches from staying on the harsh ass rev limiter on some of the higher speed autocrosses.... both letting me rev out 2nd gear longer and using a soft-touch rev limiter.....

Edit #2:
Upon a bit more thinking... the ECU overclock reduces injector pulse by the same percent the rev limit is increased, since it cycles that much faster. So, if one were to overclock the ECU enough, you could run 370's on it to "compensate". I did some simple math, and a 10mhz crystal would give that 25%, and if you pinned the 5th gear sensor shut (making the ECU think it's always in 5th gear so the rev limit is at 5500) your redline would be just under 6900 on an S14 KA. The only problem is your idle would be pretty damn high....... if you had it set to 650 (lowest factory setting) you'd end up at around 800rpm. I guess there's only 1 way to find out if it's do-able...... I'll probably just try my original less complicated idea first, and if it works use the ECU in the car to test out the new- fangled ideas.

[ryan hagen]

the jwt tune i got rev to like 7200 i think, my tach hits almost 7400, but form what i ve heard the tach can be off by like 200, cause the stock is suposed to be 6800 i heard and it used to look like 7200.

i came across a spare ecu for s14, not sure what year, maybe a 95? but i dried the ecu out and it looks good, it was in a stripped car with a cut harness, if u want i ll give it to u since not totaly sure it works, and because u are doing so much for us all......

[AceInHole]

thanks for the offer, but i've already got a spare ECU I'm working on (was gonna sell it but no one jumped on it). If you really just want to get rid of it, shoot me a PM and we'll work out shipping and cost (I wouldn't just TAKE it of course). It would be interesting to try out the latter idea I had with one of my friend's spare 9.54 crystals, or maybe just try and get an order of some 10mhz crystals later on. I'm gonna be on the dyno testing out 1 ECU... might as well try a few.

The thing I'm worried about is running the stock ECU at 25% faster than it's normally supposed to run, and if it'll overheat the same way an overclocked computer ECU might. As always.... only 1 way to find out!

[DuffMan]

I think I read somewhere that S14 valvespings are lighter/weaker than S13 ones. I would just get some mildly upgraded valvesprings and everything else should be fine.

[Def]

I'm not exactly sure what you are proposing... I think the results would be somewhat "not optimal" to put it lightly.

Since it seems you aren't afraid of going internal on your ECU, why don't you just tune it directly? This site is about 300ZX's, but the same techniques apply.

http://cherrypicker.tripod.com/turboupgradeforvg30dett/id10.html

A cheap burner and some more EPROMs and you're good to go after you slightly mod your ECU with a daughterboard and unsolder a resistor. You can change rev limiters, speed limiters, remap your ignition/fuel curves, compensate for HUGE injectors etc. etc. And it'll all run with factory smoothness if you tune it well.

[AceInHole]

I'm not exactly sure what you are proposing... I think the results would be somewhat "not optimal" to put it lightly.

Since it seems you aren't afraid of going internal on your ECU, why don't you just tune it directly? This site is about 300ZX's, but the same techniques apply.

http://cherrypicker.tripod.com/turboupgradeforvg30dett/id10.html

A cheap burner and some more EPROMs and you're good to go after you slightly mod your ECU with a daughterboard and unsolder a resistor. You can change rev limiters, speed limiters, remap your ignition/fuel curves, compensate for HUGE injectors etc. etc. And it'll all run with factory smoothness if you tune it well.

That's what comes next since it costs quite a bit more (exponentially more than what I'm trying to do right now). The nice thing about the theory behind my (2nd part) idea is that it may allow potential KA turbo owners to obtain a cheap (nearly free) and effective way to use 370cc injectors and reduce timing advance.

For the next step, I've been reading up on: http://ecu.ztechz.net/. It's a lot more complicated, and a lot more expensive.... although I think I could make up the cost just tuning local cars, so this summer I might give it a shot. The plus side is I picked up Bristol Dyno as a sponsor this year, so if this all went through I could get timing/ fuel maps for whoever wants to run whatever (assuming I can mimick their setup). But... I don't wanna get waay to ahead of myself here...

[sr240mike]

I dont know what you mean by recrystalling unless you have an msd ignition. I have tons of roms for ka24e, ka24de, and sr20's if you decide to start prograaming your ecu. You will need a badbiki daughterboard which is like $100 shipped from australia. Im working on a different type of daughterboard that doesnt use the odd even function and has a switch that you can mount anywhere to change fuel and timing maps. Im up on ztechz.net forums and my sn is myfairladyz. Ive been tuning 300zx ecu's for awhile and just started with my sr20det. Shoot me a pm if you are interested.
With a high rev limiter its very easy for the engine to overshoot it before the ecu catches it. I set mine to 7000 and it'll hit 7200 quite easily. There's not much power up there and I dont like to risk ruining my engine so I keep it down.

[AceInHole]

wouldn't you still need the eprom programmer to set your variables though??

[ryan hagen]

hey sorry its been so long but i offered that ecu to you for free, your pm box is full, but i ll tell yah waht, u can help me select my turbo for my ka-t and i ll even pay shipping. the turbo i m looking for i need to get me like 350hp, and i'm gonan get a bottom mount manifold like yours, from ssautochrome, i like the bottom mount better so i ll need the t25 flange. If you could let me know on this turbo i found, it would be huge and i ll get that ecu out to yah. i m not a drag racer, but not a track racer either, looking to build a multi puropse car. let me know what you think about it, the turbo i found and i think i m gonan get is this:


Specs: Dual Ball Bearing GT25/40-R Turbo assembly with specified ar. T25 style inlet flange with 5 bolt style exit. Large 60-1 style compressor housing with 4.00" inlet and 2.50" outlet. Very Good response turbo for 4 Cyl applications.

Turbine - Wheel: 53mm w/ 62 trim -Housing: .64 ar.

Compressor -Wheel: 60mm w/ 60 trim -Housing: .70 ar

Compressor maps can be found here: http://www.atpturbo.com/root/maps/gt2540r.htm

Full boost occurs around 3600-3800 rpms. This turbo retails new for ~1465 and runs about 1100-1200 at most places. Find it here for cheaper! There is NO shaft play at all. The compressor wheel is mildly worn from running w/ screen. Boosts very strong. With .64 a/r exhaust housing...good for peak ~400 hp.

[IKu]

wouldn't you still need the eprom programmer to set your variables though??

yes you would. and you would also need to know what's stored at each address or whatever, and i don't think that's been publicized anywhere for the KA. i've been looking. also, i don't think you need a daughterboard... just eproms.

[AceInHole]

hey sorry its been so long but i offered that ecu to you for free, your pm box is full, but i ll tell yah waht, u can help me select my turbo for my ka-t and i ll even pay shipping.

What you're looking at looks a LOT like the GT25R i was thinking about going with eventually, although I changed my mind in favor of a ball bearing T28 (which I'm still looking for). It looks as though it would work well, but the only problem is that 4" inlet getting past the distributor on the KA engine..... it barely gets by the CAS on the SR on my friend's car.



Anyways:
http://www.engr.uconn.edu/~corrales/carsIM/panda/IMG_8004.JPG
SUCCESS!!!

Ended up having to replace both crystals.... although I'd like to see if I can replace just 1. I also need to swap in some lower frequency crystals (i have 9.216mhz crystals in right now). A 7600 RPM redline is just waaaay too much.

[ryan hagen]

well some one else won the bidding, so i guess i m back to a t/3/4 top mount set up, iw as sooo hopeing to use a bottom mount so my turbo wasnt so close to my brakes.........

[1993240]

"yes you would. and you would also need to know what's stored at each address or whatever, and i don't think that's been publicized anywhere for the KA. i've been looking. also, i don't think you need a daughterboard... just eproms."

Ka24e you just need eprom. S13 ka24de needs daughterboard. Late ka24de, i have no idea. Open a ka24de file in romeditor and see what matches. You might be suprised.