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DET again

R
Jan 8, 2019
73
4
8
Nome, AK
Ok so I got basically a multirace winning shell/B.motor for free and completely built it up with all new and aftermarket:

Billet head (sea level)[new](87 octane here in Nome, AK, we add octane boost, maybe I need to mix some AVGAS 100oct? Head I think is very high compression [I'll re-test psi] and this is the first time I burped the throttle to 6g rpm = DET. Could be fuel pre detonation? I'll do some more testing and get back, maybe switch it to premium plug for the oct.boost)
Aftermarket bigger gauge stator (more accessory wattage, better spark, no electric lag)
Pro x pistons because SPI is trash, no offense. They suck. Wisecos are expensive, but I'm porting some old SPI f'd cylinders and after the renikasil will wisecos it.
Good crank
2013 CFI2 rebuild from 2010 CFI4, everything good/NoDET
AAEN fat pipe & muffler (need Y)[noDETissues]
Fuel commander (set for SLP pipe map)[new](not plugged in)
Dynojet autotune w/ wideband Bosch[newest](not plugged in)
I love my br9ecs, especially because the billet head is shaped differently and bpr9es are projected into the cylinder... br9ecs provide a better burn and are rather flush with the top of the head and pregapped to .18", br9ecs-5 is .24" I think. (NoDET).
Fuel pump is actually overcharged I think, or my $100 fuel pressure tester is wrong, @64psi.
For the last couple months of winter and all that new power my Track exploded, literally broke the steel-riveted-on track tensioner and blew my cogs I think. I have all new bearings on the way while I get a new cog.
Either way though, did I miss any ideas about my DET? Anything helps.
 

Scott

Scott Stiegler
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It doesn't have to be a compression or octane issue to trip DET sensor.
Make sure your motor mounts are new.
Make sure NOTHING is rubbing on the bulkhead under the pipe.

BTW, check the knock sensor.
And make sure the wire isn't kinked.
 

diamonddave

Chilly’s Mentor
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Apr 5, 2006
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Wokeville, WA.
2013 CFI2 rebuild from 2010 CFI4, everything good/NoDET

Not sure what's going on here. This entire post scares me. I agree with TRS but I think you're asking what might be causing DET?

Aftermarket bigger gauge stator (more accessory wattage, better spark, no electric lag)

Why? Never heard of this. Spark doesn't come from the stator. Coil output doesn't change with a stator.

Billet head (sea level)[new](87 octane here in Nome, AK, we add octane boost, maybe I need to mix some AVGAS 100oct? Head I think is very high compression [I'll re-test psi] and this is the first time I burped the throttle to 6g rpm = DET. Could be fuel pre detonation? I'll do some more testing and get back, maybe switch it to premium plug for the oct.boost)

Fail. You cannot run more than stock compression at sea level.

Also, what premium plug are you talking about? There is none. There is an ethanol plug.

Also, if you aren't loading the motor hard enough with your current clutching and gearing, then you could be tripping the det code from an over rev or too quick of a rev.

And why on earth are you using a plug made for a BRP???

Scott has some good points in his post.
 
The first thing you have to consider is what causes detonation.
1. Not enough octane for your compression,simply saying high compression head doesnt tell you what you need. You need to know your compression..
2. timing, to much timing reguardless of compression will cause detonation then mix that in with a high compression head and you sir could have a time bomb.
3. A lean condition will cause detonation, The fuel filter on these units suck to put it lightly. they MUST be changed yearly to flow properly...

Thats it in a nut shell, the issue is that youve messed with everything can cause DET. However wile I was typing out #3 I remembered you saying that your fuel pressure was 64lbs which is a bit high, so if your filter is plugged it will cause a high fuel preassure reading and a drop in fuel flow which stated earlier will cause your DET code. I would start with a filter cause you need one anyway then go from there....
 
R
Jan 8, 2019
73
4
8
Nome, AK
The first thing you have to consider is what causes detonation.
1. Not enough octane for your compression,simply saying high compression head doesnt tell you what you need. You need to know your compression..
2. timing, to much timing reguardless of compression will cause detonation then mix that in with a high compression head and you sir could have a time bomb.
3. A lean condition will cause detonation, The fuel filter on these units suck to put it lightly. they MUST be changed yearly to flow properly...

Thats it in a nut shell, the issue is that youve messed with everything can cause DET. However wile I was typing out #3 I remembered you saying that your fuel pressure was 64lbs which is a bit high, so if your filter is plugged it will cause a high fuel preassure reading and a drop in fuel flow which stated earlier will cause your DET code. I would start with a filter cause you need one anyway then go from there....

Thank you!
Apologies I didn't type it better, was nervous about the issue and pressed on time while at work. This is exactly what I wanted to hear though. My mind has been wrapped around most those points because I know everything else is new. Literally a used/all-new precisely torqued race motor, if I can finish tuning it. By myself/you guys. I have new fuel socks in the P.O. new gasket too. I still have my old pump but I'm not using it cuz it's a long story. I'll get a new fuel filterline too. What kind of timing advance should I have? I'll check my compressing right now...
Holy F@#%!!! 160psi mag... 160 pto
120 is stock.
I knew I should have checked it sooner, but yeah I need some AVGAS to mix up our trash 87 oct. Airport. Living in Nome, AK its all we get, crap 87.
Anyways thanks a lot man!
 
Last edited:
Thank you!
Apologies I didn't type it better, was nervous about the issue and pressed on time while at work. This is exactly what I wanted to hear though. My mind has been wrapped around most those points because I know everything else is new. Literally a used/all-new precisely torqued race motor, if I can finish tuning it. By myself/you guys. I have new fuel socks in the P.O. new gasket too. I still have my old pump but I'm not using it cuz it's a long story. I'll get a new fuel filterline too. What kind of timing advance should I have? I'll check my compressing right now...
Holy F@#%!!! 160psi mag... 160 pto
120 is stock.
I knew I should have checked it sooner, but yeah I need some AVGAS to mix up our trash 87 oct. Airport. Living in Nome, AK its all we get, crap 87.
Anyways thanks a lot man!
ABSOLUTELY DO NOT CONFUSE CRANKING COMPRESSION WITH YOUR COMPRESSION RATIO!!!!!!
The only way to tell what your compression ratio is to know how many cc your domes are. They are two different numbers, but with 160 good luck starting that thing on a 5* day...lol.....Anyway if you google " how to calculate compression it will how to do it. Once you get your number you can then determine your octane requirments, or if you should change your domes or if your stock head was milled maybe get a OEM head to return to stock...
 

Scott

Scott Stiegler
Staff member
Lifetime Membership
Nov 1, 1998
69,618
11,737
113
51
W Mont
ABSOLUTELY DO NOT CONFUSE CRANKING COMPRESSION WITH YOUR COMPRESSION RATIO!!!!!!
The only way to tell what your compression ratio is to know how many cc your domes are. They are two different numbers, but with 160 good luck starting that thing on a 5* day...lol.....Anyway if you google " how to calculate compression it will how to do it. Once you get your number you can then determine your octane requirments, or if you should change your domes or if your stock head was milled maybe get a OEM head to return to stock...

Yes, don't confuse running compression with cranking compression.
 
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