Having problems with MAP sensor readings, possible because of location?

[Cardriverx]

Hey guys, I was wondering if any engine tuners here have a similar problem.

We have an intake that has around a 1050cc plenum volume, running a 600rr engine. I wanted to switch to MAP this year (from TPS), and so I attached the MAP sensor right near the middle of the plenum.

The issue is, I am not pulling much vacuum at all (not enough to run the engine MAP based).

Has anyone else had issues pulling vacuum with MAP sensors when dealing with he restrictor?

Thanks guys.

[Mikey Antonakakis]

It has more to do with cams designed for operation at 14,000rpm than anything. The best I've gotten at idle is around 80kPa.

[Cardriverx]

Didn't think of that. Guess I am just used to my miata where I am around 30kPa

[Mikey Antonakakis]

Yeah, it definitely threw me off when we first made the switch to speed density. Timing makes a pretty large impact (95kPa vs 80kPa).

[B Lewis @ PE Engine Management]

There are a couople of ways to deal with that.

-Use Alpha-N with Baro compensation.
-Use Alpha-N with MAP and Baro compensation.
-Use speed-density with a smaller range in the tables and a filtered signal (to reduce MAP fluctuations due to pumping)

[Some Guy]

The cams are going to make this an issue unfortunately. To add to the list of solutions you can up the idle RPMS a bit, we idled around 75-80kpa last year, that was idling at maybe 2500-3000rpm. I have found it is mostly matter of finding the right timing and throttle position if you dont mind the high idle. Lower RPMs and things get a little odd.

Our very first year we ran a log style plenum with the MAP source at the end of the log opposite the diffuser and had all sorts of issues. We went and swapped to running a small line right from each of the intake ports into a single line and got the results above. the stock throttle bodies may come with the line to do this.

[VFR750R]

Man, I've never tried it on a FSAE engine, but 80kpa absolute does seem really high for idle. The cams we use in pushrod land are actually waaaaay more aggressive (in total duration and overlap) than at YZF600 cams that I've measured.

I would expect 40-50kpa at 1500. Maybe 60+ at 800-1000RPM.

How much idle ignition timing do you have? I'm assuming the simple stuff like leaks in your MAP hose and swapping MAP's have been tried.

[Boffin]

On our CBR 600 RR, we have:
- 70-72 kpa for a 2800ish RPM idle
- 88-90 kpa for a 1700ish RPM idle
- 92-94 kpa for a 1300ish RPM idle.

Yes this is through a restrictor and yes that is a steady 1300ish idle.
The map port is in between the bell mouths on cylinders 3 and 4.

[Wagz]

Boffin, what was the BAP, or MGP for those?

The lack of vacuum surprised me too when first learning to tune our engines. Our CBR600F4i idles at 1550 rpm +/- 110 and does it at -7 MGP +/- 0.8. Ignition advance is at 25 BTDC.

[Boffin]

Originally posted by Wagz:
Boffin, what was the BAP, or MGP for those?
MAP. 2 bar sensor that is absoulte presure.

Advance is at 28 BTDC, for all of those idle speeds.

Also our plenum is 2.29L

[Nicky]

Originally posted by Wagz:
Boffin, what was the BAP, or MGP for those?

The lack of vacuum surprised me too when first learning to tune our engines. Our CBR600F4i idles at 1550 rpm +/- 110 and does it at -7 MGP +/- 0.8. Ignition advance is at 25 BTDC.

I think I got something from my understanding to clarify here. The minimum advance for the F4i is 13dBTDC. We need around 19dBTDC for it to start and around 15dBTDC for a smooth idle at around 1500(+-200)rpm. The maximum advance at around 9400rpm is 42dBTDC, that we run. Also, while accelerating, do you advance the timing from the "Base Map" or slightly retard it, hence reducing the load???

Now, I've heard a lot of stories of people blowing holes into their pistons with high advances. Do all run such high advances or is it just us trying to play it safe?

[Rex Chan]

Here are our (MUR Motorpsorts/Melbourne Uni) from 2010:

55-60 kPa @ 3700-4100 RPM, 20degress BTDC
Honda CBR600RR 03-06, stock cams, side feed log style plenum into cylinder 1 - see our website, we've used the same one since 2008. MAP sensor is between cylinder 3/4, just above trumpets. About 3L plenum.

Nicky: from memory, advance is from 20BTDC @ around 6000 to maybe 30BTDC @ 10000. That's for WOT/100kPa. At lower MAP (50 kPa), up to 40-45BTDC. Email me and I can send you the actual numbers.

[Simon Dingle]

If the F4i is as anything like the R6 (I've never worked on the F4i), then you can go to pretty insane spark advances without problems. The stock advance is 55°bTDC in the Yamaha but I've used values upto 70° without a problem (so far). I suspect that this is to do with the stock cams producing fairly high levels of EGR below 10,000rpm.

Has anyone sucessfully fitted a knock sensor to one of these engines?

[Mbirt]

Originally posted by Simon Dingle:
I suspect that this is to do with the stock cams producing fairly high levels of EGR below 10,000rpm.

I believe it was Queen's University (Belfast) that created the SAE paper attributing the EGR-like effect to high levels of overlap. If residuals are present in the cylinder when the intake valves open (quite early) and the pressure is lower in the intake than in the exhaust (due to the restrictor), it's no stretch of the imagination to imagine which of the two systems they're going to flow into. They then specced custom cams appropriate for a restricted engine and tested them with success.