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Microtech Fuelling above 6500rpm

Old 05-07-07, 10:54 AM
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Fuelling above 6500rpm

I've been looking at posts on this Forum to see what Fuel Maps other people have been using on their 13B's. I have an LT8S and have tuned my own FD (running GT35R turbo and 550cc and 1000cc injectors, 40psi constant fuel pressure) on the road using (PLX) wideband logging software. I haven't changed the ignition timing maps much from the base maps I was given. But I have used both NORMAL and MATRIX mode for the Fuel maps. I found that MATRIX is better as the mapping is much more accurate.

BUT what's really bugging me is that (when I'm tuning to a target AFR eg. 11.5 at 7000rpm 10psi boost) the Fuel injector times (in ms) want to be set to LESS at RPM's over 6500rpm. Why does this happen? Is it because Peak Torque is max at approx. 6500rpm? I would expect it be at approx 5500rpm anyway as my engine has only a mild street port. Could it be due to Ignition Map values over 6500rpm being too retarded!?

Anyway, I'm including the Fuel / Ignition Maps for my FD as attachments, as well as couple of high speed runs I logged (via PLX-500) yesterday.

BTW my boost controller (Blitz SBC-ID3) is causing a lot of fluctuations in boost (see PLX log), but I have logged other runs when its switched off and still get AFR's dipping into the 10's at the top end of the rev range.

Can anybody offer me an explanation as to what's happening above 6500rpm?

Thanks,

Adrian
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Old 05-07-07, 11:04 AM
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injection times log

Here's a separate log of of the LT8S injection times. See rows #78,79. these are above 6500rpm.
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Old 05-10-07, 07:58 AM
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Is there anybody out there, that has some good technical knowledge on fuelling and timing at high rpms? Silverotor? Rice?
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Old 05-10-07, 08:08 AM
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You're correct.
Most rotaries with your setup use the most fuel somewhere between 6k and 7k rpm with 6.5k rpm being the norm for peak. It's also the area you want to run the least ignition timing especially when dealing with low octane pump fuel. On the dyno you'll also noticed that in that area you can actually richen it up without any great loss in power for safety purposes.
Happy safe tuning!

Last edited by crispeed; 05-10-07 at 08:13 AM.
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Old 05-12-07, 09:07 AM
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Thanks a lot Crispeed.
I guess I'll have to alter my T_RPM map again. I originally backed off the timing advance around 5000-6000rpm cos that's where I thought peak torque would be. Now I'll change this 'dip' to be around 6000-7000rpm. I haven't had a chance to put the FD on the rollers yet, I just want to get my mapping in a decent state before I do.

Thanks again,

Adrian
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