[bittles110]

This sorta goes with the MiniMe post in the Modifications section, but since it is on stock internals, I figured I'd post here.

If the P28 ECU does work out for my situation, with its 7600rpm limit, what should I limit my engine speed to? 6500 seems kinda low among Hondas... What can I expect to be safe with? I'm mainly looking for more room for the VTEC to do some good, but it's not worth a block with a rod sticking out of it.

 

[shorte]

The fuel cut-off on the 91 pm6 is 7500 or 7600 itself (up from 7200 on the earlier ones).
I beat mine regularly on it.

 

[bittles110]

Alright, so then what am I experiencing at 6500 on my 88 Si? Did they change ECU settings for 90-91? And is that not a true fuel cut? It sure feels like it...

What does a SOHC ZC redline at?

 

[akirarex]

The pm6 fuel cut off is 7413 rpms, and I don't think it changed through out the years. I can't find a 88-89 pm6 binary file to check.

The sohc zc vtec fuel cut is 7295 rpms (p70).
The sohc zc fuel cut is 7411 rpms (p29).

 

[akirarex]

One should note that the fuel cut can vary quite a lot. I have a friend who could touch 8k with a pm6 and other days it would stop at 7500.

 

[Synoptic]

One should note that the fuel cut can vary quite a lot. I have a friend who could touch 8k with a pm6 and other days it would stop at 7500.

I say tach issue.

 

[joshman]

I baby my car so I have rarely had it at 6500 and probably only a couple of times over 7K. But I also have an 88 Si like you but have never had the fuel cut of at 6500. So I don't think this is an 88-89 90-91 issue.

 

[bittles110]

Interesting... I was in second gear at the time, under WOT, and the motor didn't want to go above 6500...Very similar to our 99 Rangers 5500rpm limit. Am I misinterpreting a fuel cutoff and a redline? My definition of redline is the maximum engine speed a motor can safely handle, and a fuel cut limit is when the computer decides to cut the injectors, whether it be at a certain engine speed or vehicle speed. Am I wrong?

But I also have an 88 Si like you but have never had the fuel cut of at 6500.

So then why the difference? Is my car retarded?

 

[akirarex]

One should note that the fuel cut can vary quite a lot. I have a friend who could touch 8k with a pm6 and other days it would stop at 7500.

I say tach issue.

Nope, as read by stock guage and autometer, I have been in the car many times.... I witnessed it on multiple occasions.

Redline is the physical safe design limits and fuel cut is usually higher and is what cuts the ability of the engine (injectors in this case) from continuing up in rpms. There is a difference in fuel cuts as well, a cold engine one and an operating temperature one. Did you try it with the engine at operating temp? I can say that my 89 si would cut me out early many occasions, and sometimes way lower than normal. I couldn't figure it out so I just chipped it.

 

[bittles110]

I never really paid attention as to how warm the motor was, but I tested this out this morning. I'm not one of those idiots who runs a motor to 5000rpm+ on a cold motor, so I never thought about it being a cold rev limit. This morning on my way to school, I waited till the temp guage went to it's usual little-below-half mark, and it cut out at 6500 again. I also noticed that after I did that, the temp guage went down a bit, so I assumed the motor wasnt warm yet.

Anywho, after school I went to the local pick-n-pull to snoop around, and drove on the freeway for a ways. A truck was merging, so I figured I'd get out of the way and test it out again. Low and behold I could go to 6800! I guess it was just engine temp. My bad.