Cam gear tuning + excessively retarded timing
12-27-2008, 05:03 PM
#1
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Cam gear tuning + excessively retarded timing
Car idles fine, runs fine, makes a bunch of power, but the absolute timing in MS is retarded way too far, even worse than my car was with the intake cam retarded 30 degrees. The car is a 1990 Miata with a built 1.92 Protege BP, Bell mani/DP, GT2560R, 3" exhaust, and MSPNP with RC440s.
Anything more than this and we both hear knock.
The car has DIYed adjustable cam gears from the previous owner of the motor. I am not convinced they were lined up correctly at all. What I'm looking to find out is what kind of mistake when installing the gears could cause issues like this, whether it's installing both gears a full tooth off or just one of the gears. 1 tooth = 15.x degrees, and 21 degrees at 16psi is WAY too much for CA gas, so I don't think it's just that they are both off a full degree, unless the crank pulley itself is off?
Also, once we get that figured out, how should we go about tuning those cam gears? I know retarding the intake cam will increase top end power and kill the bottom end, but what does the exhaust do?
Anything more than this and we both hear knock.
The car has DIYed adjustable cam gears from the previous owner of the motor. I am not convinced they were lined up correctly at all. What I'm looking to find out is what kind of mistake when installing the gears could cause issues like this, whether it's installing both gears a full tooth off or just one of the gears. 1 tooth = 15.x degrees, and 21 degrees at 16psi is WAY too much for CA gas, so I don't think it's just that they are both off a full degree, unless the crank pulley itself is off?
Also, once we get that figured out, how should we go about tuning those cam gears? I know retarding the intake cam will increase top end power and kill the bottom end, but what does the exhaust do?
Last edited by Savington; 01-04-2009 at 05:01 AM.
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12-27-2008, 05:33 PM
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Jerry (DIY Autotune) was telling me that the built engines he's tuned like to run stupid fall-on-your-face retarded timing. But it looks like you're running pretty advanced until 183kpa, then you're running so little it might be dangerous for the exhaust valves and/or manifold. I'm not sure what that means.
I'd think if the cams were off, it would be really noticeable in vac. You can always have a look.
Plenty of cam gear tuning info on m.net.
I'd think if the cams were off, it would be really noticeable in vac. You can always have a look.
Plenty of cam gear tuning info on m.net.
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12-27-2008, 06:37 PM
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I backed it off to 14psi and on high load pulls in 5th and 6th gear we THINK we still hear a touch of knock, but we aren't sure. I took another degree out, but we are down to like 6 or 7 degrees up there which is just foolish. I told him to buy an EGT gauge so we can look at where the EGTs actually are.
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12-27-2008, 07:06 PM
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Going to have him (thesnowboarder) order this:
Megasquirt EGT Interface Module - SymTech Laboratories
and this:
Chief Avionics Inc - MGL Avionics - Senders and Probes
since he doesn't really have room for another gauge (oil temp+boost on a-pillar, WBO2 in the left vent) and Autometer wants $200 for their matching EGT gauge. That will also let me log it in MS which is way better than trying to watch a damn gauge. I will probably duplicate this setup. I assume I can use two of the spare pins in the MS, one for the EGT input and one for +5v hot to the interface box. I know MSEFI has a diagram to build your own EGT circuit but neither of us are very comfortable with fine soldering like that (hence why we both own MSPNPs). I will probably do the same EGT setup. Anyone know where to pay less than $40 for a 1000°C K-type thermocouple? I could have sworn I saw one somewhere but Google turns up nothing.
Megasquirt EGT Interface Module - SymTech Laboratories
and this:
Chief Avionics Inc - MGL Avionics - Senders and Probes
since he doesn't really have room for another gauge (oil temp+boost on a-pillar, WBO2 in the left vent) and Autometer wants $200 for their matching EGT gauge. That will also let me log it in MS which is way better than trying to watch a damn gauge. I will probably duplicate this setup. I assume I can use two of the spare pins in the MS, one for the EGT input and one for +5v hot to the interface box. I know MSEFI has a diagram to build your own EGT circuit but neither of us are very comfortable with fine soldering like that (hence why we both own MSPNPs). I will probably do the same EGT setup. Anyone know where to pay less than $40 for a 1000°C K-type thermocouple? I could have sworn I saw one somewhere but Google turns up nothing.
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12-27-2008, 09:04 PM
#8
Car idles fine, runs fine, makes a bunch of power, but the absolute timing in MS is retarded way too far, even worse than my car was with the intake cam retarded 30 degrees. The car is a 1990 Miata with a built 1.92 Protege BP, Bell mani/DP, GT2560R, 3" exhaust, and MSPNP with RC440s.
Anything more than this and we both hear knock.
The car has DIYed adjustable cam gears from the previous owner of the motor. I am not convinced they were lined up correctly at all. What I'm looking to find out is what kind of mistake when installing the gears could cause issues like this, whether it's installing both gears a full tooth off or just one of the gears. 1 tooth = 15.x degrees, and 21 degrees at 16psi is WAY too much for CA gas, so I don't think it's just that they are both off a full degree, unless the crank pulley itself is off?
Also, once we get that figured out, how should we go about tuning those cam gears? I know retarding the intake cam will increase top end power and kill the bottom end, but what does the exhaust do?
Anything more than this and we both hear knock.
The car has DIYed adjustable cam gears from the previous owner of the motor. I am not convinced they were lined up correctly at all. What I'm looking to find out is what kind of mistake when installing the gears could cause issues like this, whether it's installing both gears a full tooth off or just one of the gears. 1 tooth = 15.x degrees, and 21 degrees at 16psi is WAY too much for CA gas, so I don't think it's just that they are both off a full degree, unless the crank pulley itself is off?
Also, once we get that figured out, how should we go about tuning those cam gears? I know retarding the intake cam will increase top end power and kill the bottom end, but what does the exhaust do?
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12-27-2008, 09:06 PM
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MICRO-1000 EGT PROBES - 1/8 NPT from Aircraft Spruce
******* knew I saw them somewhere for less than $40.
******* knew I saw them somewhere for less than $40.
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12-27-2008, 09:10 PM
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I'm assuming the "DIYed adjustable gears" are home made adjustable gears? Please elaborate. IE-do they have the "I" and "E" marks that are on the factory gears? Got a set of factory gears handy for some testing? Have you Verified that the TDC mark on the harmonic balancer is actually TDC?
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12-30-2008, 02:56 AM
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I'm assuming the "DIYed adjustable gears" are home made adjustable gears? Please elaborate. IE-do they have the "I" and "E" marks that are on the factory gears? Got a set of factory gears handy for some testing? Have you Verified that the TDC mark on the harmonic balancer is actually TDC?
Yes they both have "E" and "I" marks on them, they are modified factory gears.
Today i check with the pully and TDC, When the mark on the harmonic balancer is at "T" #1 is dead top
What do you guys suggest as my next step in solving this issue? Adjusting the gears, and if so intake or exhaust cam and which way? Swapping to a set of unmodified gears?
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12-30-2008, 09:05 PM
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On the EGT probe question -- I have bought a number of different thermocouples from Omega Engineering (omega.com) and the prices are very good. They can make just about any kind of thermocouple you need with any kind of connector and cable assembly. I have had good luck with their exposed junction probes post-turbine -- they have super fast response time.
This BX cable like sheath was overkill but pretty cool...
This BX cable like sheath was overkill but pretty cool...
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