Can we all agree "tight" quench makes power and softening "slows" down the burn rate.

In a Turbo charged Ethanol/ Alcohol fuel combo, is one method a hands down winner ?

If so, why?

Because it seems I could make an argument for both methods.

.

 

So...things that I find contradictory or interestingly shared by the two methods.
~detonation
~flame speed
~flame propagation
~pumping losses
~mixture turbulence
~ignition timing
~maximum push angle ATC
~etc...the list is long.

the fuel used obviously plays a huge role in the method chosen.

 

Quench promotes turbulence, which speeds burn, which allows more dynamic compression for a given grade ( OCTANE) of fuel OR allows more spark advance.
The QUENCH itself is not the power adder, it is the power-ALLOWER.

 

Agreed, kind of splitting hairs on the language used. Quench is not the power adder, how about the power enabler.

Glad you brought up ignition advance. In my crude understand of it, we know each engine wants what the combo dictates. And every engine is different (to a degree).
But, I look at at ignition advance as something to improve on. More = worse chamber design/ burn characteristics. Thus, why I would lean towards quench over softening as quench "enables" more power potential, because of less advance, thus less puming losses we generate (because in a perfect world we would fire @ 15° ATDC for an immediate push). As we know, quench promotes flame propagation, burn rate via better mixture turbulence. Again, in an alcohol combo detonation is considerably dampened.

But, I have ran soften chambers with great success. But I have also ran a tight (0.025") quench on a steel rod engine with success.
Which begs the original question....which method and why?

.

 

It would be interesting to test this. Pretty easy if you have two pairs of stock heads.
I’d assume a CNC softening program for consistency.

One question would be do you mill the softened set to keep the same compression?

We could get Richard Holdener to test this. 😁

 

Holdners channel is great btw.

Thats another issue with softening, it adds to chamber volume, killing SCR. Unless your welding up the chambers beforehand.
The heads I had softend cost me about 2cc (per chamber). And they were not that "heavy" on the softening. I've seen cnced softend heads that looked way more aggressive than mine, I can only imagine the cc's lost.

.

 

Honestly, the person I'd most want to address this subject is David Vizard. He's probably already done testing of this sort.

 

.
...................(.025") Living Dangerously.
What RPM, and how many HOURS was this engine supposed to run?
Such a setup sounds--- TEMPORARY- haha

 

There's been some extensive discussions over on yellowbullet on this topic over the years, with fairly conclusive test results.

As it relates to detonation, increase quench distance did not meaningfully reduce occurrence of detonation, while even moderate softening did. That is to say that the shape change in the quench pad due to softening is the factor here, not the change in chamber volume or piston to head distance. Sinking the piston in the hole still showed detonation. Chamber shape change eliminated it. Said detonation had been occurring on the flat surface between head and piston, as evident by damage to the piston in this region. The two parallel surfaces (piston/head) were the pinch point without the taper provided by softening.

I have also run 0.0025" quench on a steel rod engine for many years, 8100rpm shift, street car. NA, nitrous, and turbo methanol. Made great power. I am now softening chambers to push it further. The tight piston to head was configured for NA application, it is no longer an advantage with power adder.

 

I've watched a lot of DV's stuff. Especially the quench information. But it seems to be always in the context of N/A applications.

.

 

Ran until I took it apart and changed the combo. Made 1.5hp per cube N/A to the tire on E (with lots of stock LS parts).

Spun it to 7300-ish with comp short travels 0.010 preload.
Think thats tight, should have seen the PtV...lol

.

 

All great info...and yes I've read every page I could find on YB and speed-talk about quench & softening and poweradders.

My only "what if" is...the whole idea on tight quench is to eliminate detonation, help turbulence, speed up the "burn" and increase chamber efficiency....thus less ignition lead.
So, in my mind those are all great attributes to a power adder combo. Again, I find it hard to believe I am going to detonate on M1 ?

Other factors that "may" make a difference, light vehicle (low load) also helps the engine stay out of detonation. And high SLR (mechanical advantage) all help the engine.

what I've read from some smart people is...if quench isn't perfect then softening is needed ?

I guess the way I envision it is...a softend chamber is a lazy chamber. And lazy to me is the opposite of efficient.

.

 

I'd be very interested in hearing about your tight quench boosted results as you talked about above.

The combo I'm on the fence about would be a very similar build as to what you described.

MLS 5 layer 0.027" compressed on a 0.006" out of the hole deal with under 0.010" rock (this is also the combo I ran, that I spoke about earlier "very" tight quench, but N/A). 11.1 SCR, 60cc chamber, radius all chamber edges (raw chamber casting), plug pad blend work. Bosch 210's on 50/50 E& M1, max of roughly 25-30# based on bsfc of the fuel blend and fuel system limits.

This combo will make 500 to the tire all day N/A (330-ish cubes). Now add boost and alcohol. IMHO, an efficient n/a engine...aka great VE...should make a great "low" boost engine.

when I've researched some great combos in the past. It seems all the great boosted combos were very efficient combos before boost (N/A). From what I've seen, I can pick out a well design combo by hp per # of boost (how the engine responds to boost). With the more efficient combos producing 30+hp per # of boost and the less efficient combos making in the low 20's per #.

And this is why I want a VE sound combo before boost. I'm not a believer in "just turn up the boost" as a band-aid for an inefficiency combo.


.

 

Some interesting points here, although I am not sure this thought process is fully accurate. The goal is not to speed the burn or affect "efficiency" of the chamber. The LS chamber already exhibits a rather quick burn rate, indicated by ignition advance for MBT. Furthermore, the improved resistance to detonation through softening is possible in many styles of cylinder heads (BBC to LS, wide variation in combustion speed). This is because the result of softening is a geometric change in the combustion chamber. By eliminating surfaces parallel to the piston top, regions which may act as a "pinch point" and produce isolated pockets of pre-ignition through pressure are mitigated. In doing so, one may increase average cylinder pressure through boost or ignition advance without the uncontrolled combustion events (detonation/pre ignition) spiking combustion pressure early. This is a reason big hemi combustion chambers outperform the others with boost. By lazy, I think you mean "requiring more ignition advance to reach MBT". This is not a problem. Controlling when the pressure peak occurs is the biggest problem to the engines in question. There is some really interesting combustion pressure analysis under different conditions which illustrates the effects of uncontrolled pre ignition. Cool stuff, check it out!

Regarding M1, it is very resistant to detonation. Like other fuels, it will still blow torch a hole through your head gasket if combustion process is not properly managed.

The so called "perfect quench" is probably a dish (concave hemisphere) piston with a hemispherical chamber. I am building this now! Big dish, softened LS7 chambers. Results to follow!

 

Sounds like a similar combo. NA i went bottom 10's at 130mph, 3300lbs. Now I run straight methanol. ID2000's at 115psi base pressure. Twin 7875's. 12gpm fuel pump. On 8lbs it made 800whp. On 18lbs, it went 8.6@160 @ 3300lbs. Stick shift street car on leafs. I wouldn't even consider mixing ethanol in the tank. Just turn up the base. Methanol is so much better.

 

Thank you for the great detailed response, much appreciated. Unfortunately this is a drag and drive/ no-prep build (2nd gen Syclone AWD) and thats why I'm blending fuels. But sounds like you know the deal, split mono & Caltracs ftw.

So from your previous experience you think I'll "hurt" the motor with my current vision of the quench combo I detailed earlier?
50/50 E&M1 on less than...realistically 25#'s.
With M1 liking a rich condition and tight quench I just can't see hurting it through the tune-up.

But I've been wrong before.

Do you think there is a boost threshold before "softening" becomes a requirement to keep the tune-up window manageable?

.

 

There are many ways to hurt something, but this has more to do with safety margin. Quench that tight means your range for controlling cylinder pressure with load and ignition advance is very small. You can stay on the conservative side, but as you creep towards the limit, you may find it quickly. Realistically the stock LS chambers go 1500+hp before these factors become limiting. You wont get there on 25lbs on stock castings, but if you are pushing these limits, then details like optimizing combustion dynamics begin to matter more and more. I enjoy working to optimize these details before they become a limitation.

I think mixing fuels will be a problem before the combustion chamber shape. But that is a separate discussion!

 

Again, thank you for the time. Very much appreciated.

In theory, I think in a compressor limit class, maximizing the N/A combo before boost is a combination for success.
I'm just detail oriented and like the attention to detail builds...to a fault.

So...just to understand your stance. The softend chamber will allow a larger tuning window and allow great room for error. And a tight quench "could" possible make more N/A power before boost, and have a greater hp per boost response, but will be more sensitive to small tuning changes "or misses"?

But honestly...at 25#'s and an E/M1 fuel, I'd have to seriously screw up to detonate this combo.

But I do understand the concern of mixing fuels, the good news is a have a local buddy whos had tremendous success do this. So I have a mentor on the topic.
.

 

Don’t get peak effeciency confused with peak power potential/performance. Can also be application specific... but for drag racing boosted peak power potential, you want zero “Squish or Quench”. You want a big **** CC that is “softened” for a nice controlled burn rate. Bigger the better for power potential, period. Response and effeciency are the only things you give up when you give up the quench pad. Neither are needed in drag applications.

Ideally run the least amount of compression necessary to light off the turbo and the biggest/softest chamber you can. (within reason of course). That will give you the most power potential for the combo. Will also have the biggest tuning window and least peaky cyl pressures.

How I understand it anyway.

 

It seems that the context has changed: in your application, which is not max effort, the softened chamber will offer a more tolerant combustion environment for timing and fuel mixture changes. But it is not at all required, as a normal combustion chamber will meet your goals, regardless of quench. I made 1100hp with the super tight quench, which was no where near max effort for the combo. I then doubled the quench distance, and the car performed identically at a given boost level. I would wager that the 0.025" quench change might be worth 5-10hp NA, if anything. Boosted, the humidity change morning to afternoon will swing power more than this.

In a max-effort application, you must maximize the amount of air you can reliably combust in the chamber for highest average tolerable cylinder pressure. A softened chamber allows you to do this, reliably. Lets consider three scenarios all with 200 lbs/min air flow (compressor limit):
1. tight quench may not be able to maximize the compressor. 15° ignition advance at peak power but exceedingly narrow margin for error (i.e 2-3% cylinder to cylinder fuel variation resulting in HG failure): 1600 hp
2. moderate quench allowing 15° ignition advance at peak power, marginally better reliability yet remains extremely sensitive: 1600 hp
3. softened chamber allowing 18° ignition advance, more fuel, and the ability to race the car without nipping plugs : 1900 hp

It is not detonation. I have seen many HG torched and pistons melted at lower boost levels - due to mismanagement of combustion energy. Combustion timing, piston speed, piston position are critically related and limiting factors related to pressure and heat vs time in the chamber. The combustion chamber doesn't care how much pressure is on the back of the intake valve (not to mention 25 psi on a 2" valve in a cathedral port head is wildly different than a 2.20" valve LS7 head). These factors are also why ethanol blends are more timing sensitive than methanol. The detonation resistance is one thing, but the thermal effects become critical with gasoline in the chamber: combustion temperatures shoot up. Many good papers which evaluate the effects of fuel composition, ignition advance, load, and engine speed on cylinder pressure, EGT, combustion efficiency, etc. Good stuff!