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RRich 09-13-2005 01:02 PM

Crank sensor position?
'03 Rubicon, 4.0, Direct ignition.

Has anyone tried slotting and repositioning the crank sensor a little to gain a bit more power?

If so, which way, how much, what kind of gain - enough to notice?

How 'bout the cam sensor?

Haven't touched either - yet.

I did the "adjustable MAP sensor" trick, it richened it, but no performance gain detected by the seat of the pants method.

Thanks in advance, Rich

elusive 09-13-2005 01:55 PM

Re: Crank sensor position?
when I built my stroker and I swapped cams, I had to re-index the cam sensor so it didn't jump time. it actually didn't matter performance wise where the sensor was.. the computer just adjusts the sprk to where it want's it anyway.

Junk Yard Genius 09-13-2005 06:32 PM

Re: Crank sensor position?

You can do the MAP sensor thing, but the O2 sensor will negate most, and you will wind up only slightly more rich.
Your emissions however, will kill you at the testing station...

LEVE 09-13-2005 11:32 PM

Re: Crank sensor position?
Has anyone tried slotting and repositioning the crank sensor a little to gain a bit more power?

[/ QUOTE ]

The thought is not a bad one, until you think about the results. If you mill the bell housing to accept the slot for the adjustable CPS, you're going to really hit a wall.

The CPS sends the ECM a signal telling it where the crankshaft is at all times in relation to the rest of the engine mechanics. But, the problem is that there's a window that the ECM expects the signal.

If the signal is late/early outside of the window of the ECM you'll get a MIL code.

If the signal is within the acceptable window, then the ECM will adjust accordingly...

So, as you can see, you really can't do a whole lot unless you also move the window parameters by reprogramming the ECM PROM.

That's not a real easy task.

NIX 09-14-2005 06:27 AM

Re: Crank sensor position?
The sensor can be moved a bit. It's an original option for high altitudes . As the article shows it can also be used the other way round to solve pinging problems at the later type FI. On the Renix system (on '87-'88 cherokees) the HA CPS can gain a few HP and torque with the pingsensor setup to prevent damage...

Another thing I haven't figured out yet, is a bit richer mixture. The adjustable MAP only works effectively in open loop. As soon as in closed loop the O2 chimes in it will correct the mixture. So for the closed loop the O2 signal might be adjusted a bit, as the O2 sensor on the Cherokee acts as a variable resitor in the 0V - 5V range. 2,5V is stoichometric. I'm not sure how to manipulate that signal exactly. But I'm sure it's doable without frying sensors or ECM and it's the only trick to really get a richer mixture during closed loop...

The cam sensor only tells the ECM wether the first cilinder is taking in or firing, if I'm correct...

RRich 09-14-2005 07:07 AM

Re: Crank sensor position?
As was mentioned, a window.

Before anyone wastes their time with it -
The adjustable MAP sensor as they call it - the way I did it was to increase the voltage to the ECM a little. Essentially that "tricked" the ECM into thinking it was under more of a load than it really was, so it would richen slightly.
A dash mounted switch enabled me to switch it in or out, increasing the voltage a little.
It did richen it, CO emissions went up. Performance-wise it did nothing that could be felt in the seat of the pants. I'm sure that the fuel consumption went up as well. That in itself would help at todays gas prices, the seat of your pants would feel the lighter wallet.
Don't bother.

As stated above, the O2 sensor tried to compensate for the richer mixture as well. But the O2 sensor only has a little influence over the mixture, so with enough "fake" MAP voltage, it was able to override the O2 input. Still no increase in performance.
The conclusion is that performance was not being limited by too lean a mixture, else richening would have shown good results.

But I'd seen some crank sensors with slotted mountings, made me wonder. But as LEVE said, it can only be moved in the hole slightly without milling the hole bigger. That would entail removing the bellhousing - I never even thought that far ahead, thanks.

As far as breathing goes, tossing the stock air filter box and replacing it with a snout type filter did make an increase that could be felt. I went with the Rock-ette snout with a K&N. Noise increased too.

The little throttle body spacer under the TB. It's supposed to "swirl" the air. I doubted it would do anything for PORTED injection, but I tried it anyway.
Don't bother, did nothing. They work on carbs and TBI where fuel is in the air at that point, but not where fuel is injected right by the cylinder.

I've already put on a better exhaust system - a "cat back." That made a big difference too. He He -- Not sure if it was the better flowing or the elimination of that 2000lb stock muffler!

I've just been looking for another simple, easy, external "bolt-on" HP increase. Maybe it's pretty much "maximized" as it is.

Any more suggestions?

NIX 09-14-2005 07:30 AM

Re: Crank sensor position?
I think you pretty much did what's doable and noticable. Maybe a bigger TB gains a few HP. If you want more you're getting in the stroker range I guess...

LEVE 09-14-2005 08:02 AM

Re: Crank sensor position?
I think you pretty much did what's doable and noticable. Maybe a bigger TB gains a few HP. If you want more you're getting in the stroker range I guess...

[/ QUOTE ]

Some of these HP gains are Horse feathers. In thinking about this... the concept is to bring in more unrestricted air. The bigger air gulp... the denser the air... the bigger bang during igntion in the cylinder.

That's the logic... of course. But then there's the little pesky ECM that gets in the way... it will trim the darn air/fuel ratio back to 14:7 unless you start fooling around with the fuel maps burned in the Eprom. (Whew... that was a long sentence!) So, in reality, you're bustin' your chops against a wall that ain't going to move unless you move all the bricks in one, or another direction.

Oh.. lets say that the larger TB does help. For giggles we'll look at the logic! <ul type="square">[*]The engine will gulp more air[*]The air gets combusted in the cylinder[*]The air now has to be exhausted into the manifold and the exhaust system[*]The engine is designed to exhaust A amount of spent plasma in B amount of time[*]A has increased[*]B has not changed[*]There is now a choke point that's been introduced into the system[*]The choke point decreases available HP over the OEM TB[/list]
That's my thoughts, and I'm stickin' with 'em.

NIX 09-14-2005 08:39 AM

Re: Crank sensor position?
You're probably right But Rich already changed C the resistance in the exhaustroute...

But in all, you're starting to mess in a well designed setup, that's true, so it's not garanteed to create a better situation. Maybe some trail and error will make that clear. The way Rich changes his stuf 1 thing at a time shows what mod has what result. I'm interested...

John_Strenk 09-14-2005 09:38 AM

Re: Crank sensor position?
Just my opinion.

Depends were the choke point is. If the choke point was the TB then the bigger TB will help a little. If it's the exhaust then a better flowing exhaust will help. You'll might get more a/f into each cylinder and the ECM will make sure it's the correct ratio for the demand.

From what I read the Airclear/TB/intake/valves was designed to be a long tapering intake path with the valves at one end. Kinda like a long smooth velosity stack. Change the Air cleaner/TB or Spacers and you've messed up an optimized system.

It would now be time to change the cam timing but becareful you don't mess up the tuned length. I know when I was running dual 45DCOEs on a Gordini motor a change in cam timing could lessen output until you adjusted the length of the velocity stacks and get more HP. But this is with independent runners for each cylinders so a log type manifold may not make any difference.

Fiddling the MAP will just make it run a little richer thinking it's under load but not realy improve performance because nothing else has changed. A richer mixture will only help if it was to lean to produce any power.

The O2 did little because the ECM thinks it's under a load so the rich mixture is OK.

So cams, valves or stroker or blower is next. Leave the EPROMS alone until you reached a point were the program cannot compinsate for the modifications.

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