Cam gear tuning + excessively retarded timing - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-31-2008, 12:26 AM   #21
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Quote:
Originally Posted by disturbedfan121 View Post
where exactly do you put the probe? exhaust manifold i'm guesing. tho in that picture you have it next to the o2 sensor and the wastgate? wouldn't that not be a good place for the 02? i think its the pic thats throwing me off
In the picture, it is post-turbo in the downpipe.
Best place for EGT sensor is in the manifold. O2 sensor must be in downpipe, can not be in manifold.
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Old 12-31-2008, 12:50 AM   #22
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Originally Posted by crashnscar View Post
In the picture, it is post-turbo in the downpipe.
Best place for EGT sensor is in the manifold. O2 sensor must be in downpipe, can not be in manifold.
actually, put the thermocouple 1.5xthe diameter of the exhaust port diameter from the head. That way you know the flame front is not passing through the valves. Going behind the turbine relegates the gauge to NBO2 duty.
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Old 01-02-2009, 10:48 PM   #23
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Picture taken @ TDC
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Old 01-03-2009, 12:44 AM   #24
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Yeah I highly doubt those gears are accurate. 99.9999% plus a spec sure they are your problem. Swap in some stock gears and problem solved.
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Old 01-03-2009, 01:00 AM   #25
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Nick, I'm going to have to agree, sadly. The good thing is that swapping to your other gears will be pretty easy because those gears are actually lined up like stock gears. Just ziptie the exhaust gear in place, loosen the tensioner, slide the belt off the intake, replace the cam gear, and then slide the belt back into place. Then repeat for the exhaust gear. When I slipped my belt, I was able to do this without removing the front nose, which means you won't need to replace the crank bolt. Shouldn't take you more than about 90 minutes. There's absolutely no way to look at those gears and know how much advance/retard you have.

Look at how close the marks are on this gear. Each white mark is two degrees.

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If you are even a third of a tooth off, it will wreak total havoc.
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Old 01-03-2009, 10:25 PM   #26
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Originally Posted by patsmx5 View Post
Yeah I highly doubt those gears are accurate. 99.9999% plus a spec sure they are your problem. Swap in some stock gears and problem solved.
100% right! Here is a picture to show the slop in the timing belt after replacing one gear.
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DIY cam gears=FTL :(
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Old 01-03-2009, 11:13 PM   #27
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Hooooly ****! That's nuts! Glad you found the problem. You should see a NICE difference in power if it was that far off. Man, I gotta build me a motor. Just hooked up the MBC to put boost to 10 from 7. Wastegate pressure lasted me.... 5 days.
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Old 01-03-2009, 11:15 PM   #28
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Oh yeah, and I've used those fancy "paper clips" that will pinch a large stack of papers to hold a TB on a gear. Used them on my dads V6 interference Isuzu Trooper. Only one per gear and it worked well.
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Old 01-03-2009, 11:15 PM   #29
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Yea savington and i were VERY suprised at how much it was off. We were guessing, maybe 10 degrees or so. Did a bit of tuning and got it dialed in nicely!

Thanks a ton for the advice on swaping gears over, really saved my motor!
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Old 01-03-2009, 11:26 PM   #30
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new:

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compare to old:

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Final map. About where I am with my setup, a little less advance on top since the 60mm compressor kicks harder above 6k. After tuning my car and Nick's car, I'm coming to the conclusion that you really can't push past 15psi on Cali pump gas.

Last edited by Savington; 01-04-2009 at 06:01 AM.
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Old 01-03-2009, 11:32 PM   #31
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Damn, that map still doesn't look right. What A/F ratio is he tuned for? What heat range plugs? What size IC and about what charge temps was he seeing?

I'm uploading what I'm actually running right now for comparison, and I'm running a bigger turbo than both of yall.

EDIT: And what boost. Spill the beans on the setup.
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Old 01-03-2009, 11:47 PM   #32
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What I'm running. I've been running this on a 9.5:1 99' motor with a lot of headwork, ported intake, GT3271, 3" exhaust wide open, 20x12x3 IC. Been running 7 pounds, but I ran 12 and 15 respectively when the wastegate was hooked up wrong. Never knocked. In fact I consider this map very mild and plan to add a degree or two to the boosted cells and then start tuning it in with a KnockSense.

And let me say again, that table is way retarded. I pulled 4* from everything above 70 kPa, then pulled a degree from boosted cells from 5K+, then another degree from boosted cells from 6K+, etc to 8K. I know I can run more advance.

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Old 01-03-2009, 11:49 PM   #33
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And that's on 93 octane. I could probably run 87 on that map. I might try it...
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Old 01-04-2009, 01:50 AM   #34
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we had that timing map up to 17 psi and it got a hint of knock at 5500 rpm in 6th gear.. I have the details of everything else, im at a friends house right now ill reply back with the details of intercooler size ect either tonight or tomorrow.
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Old 01-04-2009, 06:16 AM   #35
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Pat, the 3271 introduces a LOT less heat than the 2560 does. When you've got a T25 cranked up this hard, the timing drops drastically on pump gas, and our pump gas sucks *****. The old map was worse, too; I posted the 17psi map, and after I made my final "beat on it" pulls, I yanked a bunch more timing up top.

Here's my current timing map:
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compared to Nick's:
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Ben also said earlier that he had heard from Jerry that built motors don't like timing for whatever reason. Nick's about 4 degrees down from me, and I could probably improve on that if I were to get a little more aggressive (my timing is street-tuned with a Knocksense).

AFRs are 11.4-11.7, with a 20 degree delta (78F IAT). NGK BKR6Es, gapped to .035" on Toyota COPs.
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Old 01-04-2009, 10:00 AM   #36
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Ok this thread REALLY makes me want to check my cam gears now. My built motor is a torque monster down low but power flattens out way too soon. Extra timing up top did not help it either, and I'm running fidanza cam gears, who knows if 0 deg is really 0...
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Old 01-04-2009, 11:05 AM   #37
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Quote:
Originally Posted by Savington View Post
Pat, the 3271 introduces a LOT less heat than the 2560 does. When you've got a T25 cranked up this hard, the timing drops drastically on pump gas, and our pump gas sucks *****.
Well, actually, quite the opposite. The larger turbo actually introduces more heat as it's moving more mass of air. In the grand scheme of things, my 12 PSI is moving more kJ's, of heat than your 2554. However the temperature of the charges may be different after intercooling, but that's trivial in comparison.

The bigger turbo is moving more air. It will create higher cylinder pressures. Which means the mixture will burn faster during combustion. Hence I have to retard timing. Given the same intake temps after the intercooler and same boost pressure, you guys should be able to run more timing than I, all else being equal.
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Old 01-04-2009, 11:58 AM   #38
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that makes sense pat, I can see how even if you had a lower measured IAT than someone with a 2554, the bigger turbo would produce higher combustion chamber temperatures because of the raised (effective) compression. At the same CFM the two turbos would produce drastically different timings though, hence the powah
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Old 01-04-2009, 01:21 PM   #39
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Quote:
Originally Posted by patsmx5 View Post
Well, actually, quite the opposite. The larger turbo actually introduces more heat as it's moving more mass of air. In the grand scheme of things, my 12 PSI is moving more kJ's, of heat than your 2554. However the temperature of the charges may be different after intercooling, but that's trivial in comparison.
Yeah, you're right. I was thinking about your T3 at 10psi vs. a T25 at 17psi; you're just getting into the fat part of your compressor map and the T25 is beyond it. You're only running about 3-4 degrees of timing than I am in the 130-150kpa range, though, which 93 octane will let you do. I don't think that map is as retarded as you think it is (or 99 motors are amazing).
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Old 01-04-2009, 01:42 PM   #40
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Quote:
Originally Posted by patsmx5 View Post
Given the same intake temps after the intercooler and same boost pressure, you guys should be able to run more timing than I, all else being equal.
Is this in fact true?

This is one area of turbo math where I start to get a little hazy. We've basically got a closed system with three variables- temperature, pressure, and air mass.- all of which are related. If you increase temperature for a given pressure, mass decreases. If you increase pressure without an increase in temperature, then mass goes up. Etc.

It seems to me that for any two turbos on a given engine, if temperature after the intercooler is the same, and manifold pressure is the same, then air mass per unit volume is the same. This should hold true even for a GT25 vs. a GT40, assuming the hypothetical intercooler is 100% efficient.

So, if this is true, then any difference in power output, efficiency, timing requirements, etc., between the two turbos should be ascribable to some other factor. Maybe the back-pressure applied against the exhaust side of the cylinder by the turbine. It'd certainly affect scavenging and cylinder fill. Smaller turbine, more backpressure, less efficient exhaust cycle, more unburnable waste gas left after the exhaust cycle, less power. Kinda like EGR for boost.

Or maybe I'm completely wrong. But then, what's the real explanation? I've read many times that "X is true" but I really can't understand why in this case.
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