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I found this posted on Speed talk and would like to hear the opinions of others on here.


Specifically what do you think a tapered squish would do for a naturally aspirated methanol injected (mfi) BBC? Would it hurt it or help it.
Say a 3-5 degree head "chamber cut" (softening) with a BBC 4.5 bore at 13.5-14.0 CR, 4"stroke.

Some quick mathematics gives the volume of 17cc for a 5 degree x 4.500" cone created by the taper cut. This 17cc cone volume is actually less and affects the CR less as the cut runs through the combustion chamber itself.

Thanks
 

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I found this posted on Speed talk and would like to hear the opinions of others on here.


Specifically what do you think a tapered squish would do for a naturally aspirated methanol injected (mfi) BBC? Would it hurt it or help it.
Say a 3-5 degree head "chamber cut" (softening) with a BBC 4.5 bore at 13.5-14.0 CR, 4"stroke.

Some quick mathematics gives the volume of 17cc for a 5 degree x 4.500" cone created by the taper cut. This 17cc cone volume is actually less and affects the CR less as the cut runs through the combustion chamber itself.

Thanks
I assume you’re talking about attaining more horsepower from this modification. There are many different ways to do the geometry and in all cases the piston tops should compliment the combustion chamber. Basically, the objective of these types of modifications is to promote a very homogeneous fuel-air mixture around the spark plug at ignition. This should promote a “fast burn” and lessen the chance for detonation by adding “mechanical octane” to the fuel mix. The results would be less parasitic loss BTDC by being able to run less ignition advance and the ability to support higher cylinder pressures at the right time acting on the piston ATDC. If those two things are accomplished from this modification Then you should have more horsepower. Compression ratio is a big factor in all this. If you are going to do this modification make sure you end up with the same compression ratio so you can determine if your modifications helped or not.
 

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I assume you’re talking about attaining more horsepower from this modification. There are many different ways to do the geometry and in all cases the piston tops should compliment the combustion chamber. Basically, the objective of these types of modifications is to promote a very homogeneous fuel-air mixture around the spark plug at ignition. This should promote a “fast burn” and lessen the chance for detonation by adding “mechanical octane” to the fuel mix. The results would be less parasitic loss BTDC by being able to run less ignition advance and the ability to support higher cylinder pressures at the right time acting on the piston ATDC. If those two things are accomplished from this modification Then you should have more horsepower. Compression ratio is a big factor in all this. If you are going to do this modification make sure you end up with the same compression ratio so you can determine if your modifications helped or not.

Lobes
Thank you for your reply.

Yes, the end result would be more power. I think a custom piston from a mold is the way to go to get the compression ratio desired.
The wedge shape just seems to make sense from a combustion point of view.
 

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What I don't quite get is that you are talking about "softening" the chamber with this "taper" which will slow the pressure rise and then you will have to put more timing in it to get back where you were. If in fact it does the opposite and speeds up the "burn" you may be able to take some of the timing out. The way I think is that I would have the head porter shape the chamber to flow as much as possible, in and out, allowing for as much "squish" area that you can get while running the piston as close to the head as possible and not having any more valve pocket than needed for the most compression/ect. Just me thinking out loud.
 

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What I don't quite get is that you are talking about "softening" the chamber with this "taper" which will slow the pressure rise and then you will have to put more timing in it to get back where you were. If in fact it does the opposite and speeds up the "burn" you may be able to take some of the timing out. The way I think is that I would have the head porter shape the chamber to flow as much as possible, in and out, allowing for as much "squish" area that you can get while running the piston as close to the head as possible and not having any more valve pocket than needed for the most compression/ect. Just me thinking out loud.
As you noted, horsepower occurs best with a rapid pressure rise ATDC. A properly designed piston top and chamber improves how this happens. An homogeneous mixture (meaning air and fuel molecules are evenly dispersed throughout the charge) with the best air-fuel ratio for power are key. However, something that can get tricky, is with a good design and a lean air-fuel ratio the burn will be "slow and cool." It will like a lot of lead and be good for emissions but is not good for making power. The tricky part is you won't see signs of detonation and power will keep increasing as you increase the lead. It just won't be the kind of power you make with a richer fuel/air ratio. You can test this at the track but a Dyno would be much, much better!
 

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What I don't quite get is that you are talking about "softening" the chamber with this "taper" which will slow the pressure rise and then you will have to put more timing in it to get back where you were. If in fact it does the opposite and speeds up the "burn" you may be able to take some of the timing out. The way I think is that I would have the head porter shape the chamber to flow as much as possible, in and out, allowing for as much "squish" area that you can get while running the piston as close to the head as possible and not having any more valve pocket than needed for the most compression/ect. Just me thinking out loud.
It just seems that a tapered quench pad would have a more complete chamber burn across the face of the piston than having two parallel surfaces slamming together. I realize the squish/quench raises the pressure exponentially when the two surfaces come together creating a crevice.
 

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Discussion Starter #11
As you noted, horsepower occurs best with a rapid pressure rise ATDC. A properly designed piston top and chamber improves how this happens. An homogeneous mixture (meaning air and fuel molecules are evenly dispersed throughout the charge) with the best air-fuel ratio for power are key. However, something that can get tricky, is with a good design and a lean air-fuel ratio the burn will be "slow and cool." It will like a lot of lead and be good for emissions but is not good for making power. The tricky part is you won't see signs of detonation and power will keep increasing as you increase the lead. It just won't be the kind of power you make with a richer fuel/air ratio. You can test this at the track but a Dyno would be much, much better!
I am probably using one of the worst induction systems and fuel for a homogenous mixture with the MFI and methanol! With the big dome I have now we run 40 degrees lead.
 

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What MBE is talking about/doing is different than what speed talk is talking about , and if you would notice he talks about the chamber allowing better flow as I talked about. Heavily NOS 4 cly motorcycle engines where running turbo dished pistons .100" or more down in the cyl at least 20 years ago, all to be able to "stuff" more "stuff" in the cyl by mechanical means. And Mopar has been using this concept with their no squish 440's and hemis, So just like a diesel, that loves swirl, you'd better have the "stuff" you put in the engine mixed up pretty good or have a means to mix it in the chamber.
 

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I am probably using one of the worst induction systems and fuel for a homogenous mixture with the MFI and methanol! With the big dome I have now we run 40 degrees lead.
When I dynoed my car we stopped at 32deg due to pepper on the plugs.
I’m surprised your running that much lead with a modern comb chamber.
I’ve been contemplating running more timing in 1st gear then pulling it out after high gear shift.
 

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Discussion Starter #14
When I dynoed my car we stopped at 32deg due to pepper on the plugs.
I’m surprised your running that much lead with a modern comb chamber.
I’ve been contemplating running more timing in 1st gear then pulling it out after high gear shift.
I don't know about a having modern chamber but we have a pretty big dome at .650 height and 44.3cc. With a 106 chamber that gives 13.5cr., so it takes some lead to get the flame travel across that dome. It will actually pick up mph gong to 42 degrees, but I normally leave it at 40.

I tried leaving with a higher timing and pulling it back for best mpg but it resulted in tire spin off the line. I will try it again.

My goal in digging around here is trying to find information for a future build. One of my goals is to reduce the dome volume for better flame travel and hoped the tapered squish would fit into the program.
 

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Discussion Starter #16
Interesting, only 32. Some type of gas?
 

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Darin Morgan talks about chamber roof taper in his second video posted yesterday( 3 total videos posted, 3rd was this morning)

Well worth the 1 1/2 hours of your time to watch all 3.




Sent from my iPhone using Tapatalk
 

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Discussion Starter #20
PmGRacer

THANK YOU very much for posting the video. I watched #2 already and will be watching the others. Again and again and again.

He touched on the two parallel surfaces at the 17 min mark and what happens when they come together at the 19 minute mark, This is what I was looking at with a tapered cut.

One thing I believe is that in a methanol engine (cylinder heads) need to be at a high operating temperature (180) to vaporize the fuel when injected. I found this to be the case with a friends 360 sprint car. They keep that engine plugged into a water heater and blanked all day long, if not they will be down on power the first few laps.
 
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