Help me diagnose my low dyno numbers
#22
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I agree, some of it will most likely be the exhaust restriction. I picked up a ton of torque and spool when I went to a 3" exhaust from a 2.25" racing beat on my 2560. I imagine you have a similar restriction as at the same boost I was making 260ish hp if I remember right (with an NB head, mind). This was with the FM elbow coming off the turbo to their 4-bolt flange (that I hate) to 3" running the full length back. When I inquired with FM about the tube, I believe I was told it was 2.5".
#23
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If your exhaust is as-described (expanding from turbo outlet diameter to 2.5" in the downpipe casting and then at least 2.5" from there back with no cat or muffler), then it's not the exhaust. A 3" is definitely better, but a proper 2.5" can do 250 whp easy.
If there's a huge dent where you hit a rock, then that's another story.![](https://www.miataturbo.net/images/smilies/smile.gif)
Random thought: have you checked your spark hardware latency? Set spark to a fixed 10 degrees, use timing light to check at idle, now use it to check while holding at 6000 RPM and make sure it's still 10 degrees at higher RPMs.
--Ian
If there's a huge dent where you hit a rock, then that's another story.
![](https://www.miataturbo.net/images/smilies/smile.gif)
Random thought: have you checked your spark hardware latency? Set spark to a fixed 10 degrees, use timing light to check at idle, now use it to check while holding at 6000 RPM and make sure it's still 10 degrees at higher RPMs.
--Ian
#29
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Radial play would be bad, a small amount of axial play is normal. Sounds like yours is good.
--Ian
#32
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2560s are a ball-bearing center, which is not a DIY rebuild. "Rebuilding" one consists of sending the CHRA to a garrett authorized shop and they'll sell you a new one at a discounted price of $450 or so.
Radial play would be bad, a small amount of axial play is normal. Sounds like yours is good.
--Ian
Radial play would be bad, a small amount of axial play is normal. Sounds like yours is good.
--Ian
#33
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1993 1.6L running MS2PNP, gt2560 @16psi, 420cc injectors. BEGI manifold, FM downpipe and 2.5" straight pipe exhaust
Made 180whp/wtq on a Dynapack
As far as I can tell, the engine is happy. Doesn't cough oil and runs smooth (although I haven't gotten around to doing a compression test). AFRs are on point. Why are my numbers so low, when similar setups have been pushing 225+ with less boost?
I've attached my tune as well as a picture of my timing table.
Made 180whp/wtq on a Dynapack
As far as I can tell, the engine is happy. Doesn't cough oil and runs smooth (although I haven't gotten around to doing a compression test). AFRs are on point. Why are my numbers so low, when similar setups have been pushing 225+ with less boost?
I've attached my tune as well as a picture of my timing table.
Small update for everyone - warm compression tested the car, the mystery continues...
Cyl 1:
Inital: 90
Final: 190
Cyl 2:
Inital: 90
Final: 165
Wet: 180
Cyl 3:
Inital: 90
Final: 165
Wet: 190
Cyl 4:
Inital: 100
Final: 190
![](https://www.miataturbo.net/images/smilies/confused.gif)
#35
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Well, you have worn rings but I don't think you should be that down on power...
I see that you've checked base timing, but it's possible that your pulley has slipped. You could be running way less advance than you think you are. My pulley had slipped over 15° from stock. Drop a socket extension down #1 and check it against your TDC mark.
I see that you've checked base timing, but it's possible that your pulley has slipped. You could be running way less advance than you think you are. My pulley had slipped over 15° from stock. Drop a socket extension down #1 and check it against your TDC mark.