Ongoing Detonation Issue Help!!!!!
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Re: Ongoing Detonation Issue Help!!!!!
Isn't technology great? I have a RPM DL10 data logger with a G meter. Though the G meter trace is wavy as all get out. Unless I can figure out why it's useless.
Re: Ongoing Detonation Issue Help!!!!!
There must be some means in the software to apply smoothing to individual channels.
Re: Ongoing Detonation Issue Help!!!!!
Perhaps the G accelerometer sensor is vibrating because it is mounted some way that is less than ideal.
Re: Ongoing Detonation Issue Help!!!!!
It’s just so up and down. It’s screwed directly to the roll bar. The dark blue is the accelerometer. This is with smoothing about maxed out.
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Re: Ongoing Detonation Issue Help!!!!!
Contact Bruce the owner of RPM (I think that is his name). We run the same brand in our funnycar. He is great with support.
Paul
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Re: Ongoing Detonation Issue Help!!!!!
*Rolling out my jump to conclusions mat*Ishiftem wrote: ↑Mon Jan 16, 2023 2:58 amI'm not really sure how that would be accomplished or how it would help.Tom Walker wrote: ↑Fri Jan 13, 2023 5:18 pm It would be interesting to see if "softening" the top of that piston helped, it wouldn't cut the compression much as long as you were not too enthusiastic.
I think he was implying that with the large quench area that you could be getting very high quench velocities, which drives the turbulent flame speed too high and can itself be inducing detonation, so you "soften" the 3-dimensional chamber like in a nitrous engine, which includes your giant weird piston dome to get the quench velocity down and make the combustion less "rough" (and it reduces your CR a bit too, which obviously won't hurt).
Your thermal barrier coating is also increasing combustion temps and bringing it to detonation sooner than the DCR implies, too, AFAIK.
Adam
Re: Ongoing Detonation Issue Help!!!!!
I am going to do that. And yes they are very helpful. The RPM seems to be very popular among the funny car crowd.
Re: Ongoing Detonation Issue Help!!!!!
I'm pretty sure nothing can be done with the pistons as there is really no material in the crown to play with. In an N/A application, I've always read increased squish is a good thing. The faster the burn the less time for detonation to occur. And in this case maybe it's not really detonation prone, it just needs less timing due to the faster burn rate. Maybe......NewbVetteGuy wrote: ↑Fri Jan 20, 2023 4:00 pm*Rolling out my jump to conclusions mat*Ishiftem wrote: ↑Mon Jan 16, 2023 2:58 amI'm not really sure how that would be accomplished or how it would help.Tom Walker wrote: ↑Fri Jan 13, 2023 5:18 pm It would be interesting to see if "softening" the top of that piston helped, it wouldn't cut the compression much as long as you were not too enthusiastic.
I think he was implying that with the large quench area that you could be getting very high quench velocities, which drives the turbulent flame speed too high and can itself be inducing detonation, so you "soften" the 3-dimensional chamber like in a nitrous engine, which includes your giant weird piston dome to get the quench velocity down and make the combustion less "rough" (and it reduces your CR a bit too, which obviously won't hurt).
Your thermal barrier coating is also increasing combustion temps and bringing it to detonation sooner than the DCR implies, too, AFAIK.
Adam
As for the TBC, I've read two things. Number one, it increases temps and can cause detonation. Number 2, the piston stays cooler which in turn makes the incoming charge cooler and that reduces detonation. Either way, it seems the TBC coating on the piston doesn't make a much of a difference and this isn't a really good coating I used so I doubt it will make any difference. I did it as more of a "why not try it".
Re: Ongoing Detonation Issue Help!!!!!
Have you spoken to VP ?Ishiftem wrote: ↑Sat Jan 21, 2023 2:42 am . In an N/A application, I've always read increased squish is a good thing. The faster the burn the less time for detonation to occur. And in this case maybe it's not really detonation prone, it just needs less timing due to the faster burn rate. Maybe......
Their FAQs lack timing facts.
Everything is gunna burn fast at 13.3:1 but in your first post you said it wasn't excessive timing ??
Did you work up to 34 degrees ?
Considering the high comp and unusual chamber piston combination it would seem prudent to start your timing testing as low as 28 degrees.
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Nah, I'm not leaving myself out of the ignorant brigade....at times.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Ongoing Detonation Issue Help!!!!!
Yes, NewbVetteGuy, you pretty much covered my thoughts.
The 348-409 combustion chamber, or really lack of one, coupled with a massive domed piston is going to have some real challenges at high compression and RPM. Stable and smooth combustion is going to be something to always strive for.
All though challenging, they have the eye candy and history behind them to make it a beautiful thing for us to watch those who continue to race and collect the mighty W engine.
The 348-409 combustion chamber, or really lack of one, coupled with a massive domed piston is going to have some real challenges at high compression and RPM. Stable and smooth combustion is going to be something to always strive for.
All though challenging, they have the eye candy and history behind them to make it a beautiful thing for us to watch those who continue to race and collect the mighty W engine.
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Re: Ongoing Detonation Issue Help!!!!!
I think that's a good, slightly over-simplified rule-of-thumb.
My understanding is that Gordon Blair has said that max squish velocity should be between 15-20 m/s at max RPM, and as you start to go beyond that max squish velocity "speed limit", the rate-of-pressure-rise of combustion gets too fast and it causes rough combustion and potentially pre-ignition itself. The TSR tool recomends between 15-30 m/s and I think I've seen two David Redszus recommendations: one 25-30 m/s and one 25-35 m/s.
There's good few people who have reported adding piston top thermal barrier coatings and running into detonation problems that they couldn't get rid of without removing the coating -then the detonation problems went away. Right now I think of thermal barrier coatings increasing the effective compression.
Does anyone make any piston oil squirter jigs for your engine? If you've got a big hollow dome, oil squirters and an oil cooler should help pull heat out and maybe keep detonation away a bit longer...?
Adam
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Re: Ongoing Detonation Issue Help!!!!!
The 348-409 engines in my opinion, present such unique challenges relating to combustion processes, that comparing them too closely to another engine platform may not provide an accurate assessment as to what to expect in what we think is a similar situation..
In very high compression form, the resulting crevice volume on that side of the piston with the dome is going to have some "rough" or unstable combustion at time. There is so much room for fuel to play hide and seek!
In very high compression form, the resulting crevice volume on that side of the piston with the dome is going to have some "rough" or unstable combustion at time. There is so much room for fuel to play hide and seek!
Re: Ongoing Detonation Issue Help!!!!!
Well I've started at 32. The car picked up at 33 and 34. 35 was the same as 34 and it tanks at 36. So 34 was the best with locked timing. Now with a new perspective, it seems very plausible that it would be better with less at alower rpm.Tom68 wrote: ↑Sat Jan 21, 2023 3:16 amHave you spoken to VP ?Ishiftem wrote: ↑Sat Jan 21, 2023 2:42 am . In an N/A application, I've always read increased squish is a good thing. The faster the burn the less time for detonation to occur. And in this case maybe it's not really detonation prone, it just needs less timing due to the faster burn rate. Maybe......
Their FAQs lack timing facts.
VP.jpg
Everything is gunna burn fast at 13.3:1 but in your first post you said it wasn't excessive timing ??
Did you work up to 34 degrees ?
Considering the high comp and unusual chamber piston combination it would seem prudent to start your timing testing as low as 28 degrees.
Re: Ongoing Detonation Issue Help!!!!!
Well that could be. It would be interesting to know the quench area as percentage of the bore on this engine in comparison to a modern two valve head with a small fast burn chamber. I do have squirters. Basically drilled the main saddle and used brass set screws with a .025 hole. Pretty easy to do. I didn't notice any difference.NewbVetteGuy wrote: ↑Sat Jan 21, 2023 2:59 pmI think that's a good, slightly over-simplified rule-of-thumb.
My understanding is that Gordon Blair has said that max squish velocity should be between 15-20 m/s at max RPM, and as you start to go beyond that max squish velocity "speed limit", the rate-of-pressure-rise of combustion gets too fast and it causes rough combustion and potentially pre-ignition itself. The TSR tool recomends between 15-30 m/s and I think I've seen two David Redszus recommendations: one 25-30 m/s and one 25-35 m/s.
There's good few people who have reported adding piston top thermal barrier coatings and running into detonation problems that they couldn't get rid of without removing the coating -then the detonation problems went away. Right now I think of thermal barrier coatings increasing the effective compression.
Does anyone make any piston oil squirter jigs for your engine? If you've got a big hollow dome, oil squirters and an oil cooler should help pull heat out and maybe keep detonation away a bit longer...?
Adam
Re: Ongoing Detonation Issue Help!!!!!
The crevice volume is a killer. No doubt about that. What makes it worse is the counter bore at the top of the cylinder the factory added. The crevice volume is off the charts. The only way to get rid of it though is a stock block with eight sleeves or an aftermarket block. And you are right. All the info out there is based on a traditional wedge head as far as two valve stuff is concerned with some hemi stuff. There is more known about a flat head than a W engine. The best I try to do is take theory from other engines and see where I can apply it. Hell, I can't even get piston makers to see the design any different than a 90 degree deck engine. They either deny what is literally staring them in the face or when an alternative design is suggested, the reply is "that's not how we do it". That's a whole other topic unrelated to the situation at hand. I'm kind of left experimenting. It's rewarding when things work. Frustrating when they don't. Still even with the problems it does pretty good for an obsolete boat anchor!Tom Walker wrote: ↑Sat Jan 21, 2023 3:24 pm The 348-409 engines in my opinion, present such unique challenges relating to combustion processes, that comparing them too closely to another engine platform may not provide an accurate assessment as to what to expect in what we think is a similar situation..
In very high compression form, the resulting crevice volume on that side of the piston with the dome is going to have some "rough" or unstable combustion at time. There is so much room for fuel to play hide and seek!
Last edited by Ishiftem on Sun Jan 22, 2023 3:49 am, edited 1 time in total.