i like Steve Morris view.. https://www.stevemorrisengines.com/v...d-chamber-mods

 

Swapped from a 0.036 quench setup d-dish with a quench pad to a 0.052 quench d-dish with a quench pad and softened chambers. Car made more power on pump gas due to the better timing window. Also, 0.036 setup ate itself due to timing/pre-ignition. I insist on a softened chamber now - seems to help with tunability if you are planning on going up to the octane limit.

If you aren't taking it up to the octane limit, I'm not sure the difference is that notable though.

 

Exactly correct.

 

So, all else being equal in terms of quench since there's only so much you can about that a 317 head would be more ideal than a 243 head since the 317 has a 70cc chamber versus 64cc for the 243.
Or do we then get into a chamber efficiency conversation and does the 317 inherently have a less effective chamber due to the larger volume?

 

I definitely appreciate the input...

But what you have just described is an Alan Johnson Hemi headed 481X combo. Unfortunately most of us have closed chamber heads (which means a quench pad). If I was to mill the chambers to meet these "big open chamber" requirements, it would be a 100cc chamber and a 7:1 SCR engine....lol.

I say all of that with a bit of humor.

Seriously though...
All great info you provided.
And I do get the point you were making about peaky cylinder pressure and tuning windows, makes sense.
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Mr NoLiftShift

Great addition to the conversation!! And great read.

Guess I will just softend the chambers (5°-7° layed back angle) and put some BTR small bore LS9's in her and see what happens.

Will net me roughly 9.5 SCR and a 0.047" quench.

I will quit trying to over think it...like the N/A racer that I WAS.

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sbe 6.2 summit tt cam, twin vsr 6762 made 817 shutting off early at 16ish psi through t56 and 2.73 gear. goal is 1000whp if i ever put it back on the dyno but ls doesnt interest me anymore so it just sits in the garage.

 

Is that a manual mill? If so would love to hear how you performed this job, I am working on the same.

 

its a manual converted to cnc with mach3. i have a vf2ss now so next set will be a tiny bit easier and quicker.

 

Depends what the goal is. If the goal is maximizing peak power potential on that specific combo, then yes—317s are better, especially the softened versions. The bigger the chamber, the better for “performance potential.” That doesn’t mean, at a given boost, a 243 won’t make more power. It means that at some point, the cylinder pressures will be high enough to risk head sealing issues with the 243. So if you plan to go beyond that point, a larger CC makes sense. You’ll have a cooler chamber with less peaky pressure. On the flip side, you’ll need more boost to hit the same point, and you give up some response. If you don’t plan to push that far, there’s no reason to sacrifice the response and efficiency of a smaller chamber.

 

I see your point, but I don’t agree 100%. There are lots of ways to eliminate quench and soften the chamber on an OEM LS head — aside from just going with an aftermarket larger-chamber, thicker-deck unit and dished pistons to match (which is always best).

Cometic makes tons of thick head gaskets. Paired with softened or enlarged combustion chamber modifications, that will make a huge difference. Or, as mentioned above, you could simply run the larger-chamber 317 heads that no one wants.

The latest trend is to run high base compression because E85 tolerates it. I don’t agree with that at all. Amateurs (like me) would stop seeing so many failures if they simply ran 8–9:1 compression instead of the 10–11+ that is so popular these days. There’s no real reason for that in a drag car or street-cruiser toys — just more heat, wear and tear, and a tiny tuning window. I had zero issues getting up on the converter with an 8.6:1 5.3 S475 combo that ran in the 8’s. Plenty for most weekend warriors. Gen 3 dished piston 5.3 with 317’s and LS9 gaskets — sounded like a minivan out of boost!

To make a point, I really want to put the short 5.3 rods in a 4.8 and run it — .177″ in the hole assuming zero deck. That would make it about 6.8:1! You could deck the block ~0.020″ or so to get it back up to ~7:1. Probably make ~200 HP naturally aspirated! But it would be fun to run silly amounts of boost through it to see how far it could be pushed — in theory, pretty dang far, especially on E85.

 

Just to beat a dead horse...lets say 1000hp is the goal.
I believe in a volumetric efficient N/A engine before boost is ever added (thats why I'm into quench and good healthy compression).

Just some basic math...based on 70% compressor effeciency and 90° underhood temps (no intercooler to keep it simple with discharge air temps)

300hp N/A engine + 14.7# = 600hp @ 260° air temp

500hp N/A engine + 14.7# = 1000hp @ 260° air temp

For the 600hp engine to make the same 1000hp would require an additional 15# of boost. Which would make the target boost pressure (29.7#) at 390° air temps. Thats a 120° difference in air temps between the two engines, that are both making 1000hp.
The intercooler has to work harder on the less efficient N/A engine and more than likely become heat soaked sooner in the process.

Now, let me ask, which combo would be more prone to detonation at the targeted 1000hp ?

Now add that 15# that the 600hp engine got to the 1000hp combo...we get 1375hp at the same 390° air temp.
Not to mention how the compressor map favors the more efficient N/A engine...lots more breathing room.

Guess I should have called the thread..
Lets make max power N/A before boost, but have a large tuning window.

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An iced air-to-water intercooler can easily keep charge temps in the 30–40°F range for a full 1/4-mile pass on a 1000 HP setup—whether you’re running 15 psi or 30 psi. For a drag car, outlet temps aren’t a limiting factor if you’re using the right intercooler and turbo system with the proper fuel.

When chasing power, boost is far more effective than compression ratio.
A one-point increase in static compression might gain ~4% power at best, even with good quench and tuning. That’s minimal compared to what boost delivers—an efficient iced turbo setup can yield 7–8%+ HP per pound of boost.

So, if an 11:1 engine is at its knock limit with great quench at 10 psi, dropping to 10:1 may lose a small amount of off-boost response and power, but it lets you safely add more boost. Even a single extra psi makes up the power loss, and the lower compression opens the tuning window for 3–5 more psi before detonation becomes a concern.

In short, the lower-compression, higher-boost combo will make the same or greater power with less heat, less detonation risk, and less stress on the engine—a much safer and more flexible setup overall.

Not claiming you should run a 6:1 setup either. Only that in general for the largest tuning window, you want to run the least amount of base compression needed to light the turbo(s) at a reasonable time. So quench doesn't even need to be in the equasion if you are looking for longevity and the quickest pass.

 

I was referring to an A2A intercooler in my example. I have zero experience with A2W and somewhat believe those are for "racecars". To be honest, I wasn't planning in running an intercooler at all. With an Ethanol based fuel, I was planning in spraying Methanol upstream for cooling and "extra" fueling. From my reading...I feel the distribution should be adequate with the Proflo manifold.

I love quick cars and attend a lot of the x275-ish and NHRA events. But I am not interested in building a trailer queen. If I can't drive it out to dinner on Saturday night, I'm not interested. The trailer is for when your streetcar breaks down driving home from the track....lol.
I just enjoy seat time, not enough driving for me...with a trailer queen.

That being said, I've been reading a lot about A2W and trying to decide if it fits into my build combination. I'm on the fence about it, I often feel that its only for trailer queens and short bursts on "big" boost.
I can only imagine the water capacity needed to keep 400° air happy in anything more than a 1/4 mile burst. And the weight penalty and complexity involved in such a setup(Complexity raises the probability of failure).

Change my mind with facts ??

And just to be clear, this is my first "performance" based turbo build. Have build turbo propane rock buggies and such. Just not big power builds.

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Forcefed86, I see your KISS method. And I don't disagree with it "most of the time".

I'd like to take a different approach on the compression idea.

But just so I can understand your point of view better.

What is the Effective compression (boost + static) limits of E85 (not pump, for discussion sakes), or knock limits before MTB is compromised ?

I'm just looking for the general consensus because we know there are lots of variables. Its not a trick question.

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A2W is absolutely for the street, my current car runs A2W and it works amazing. Setup is a Frozen Boost 2,000HP cooler, 5 Gal. reservoir, Rule 2000 Pump and 3/4" hose.
With ambient temp water my IAT's rarely get above ambient air temp, and I only run the pump when I know I'm going to be beating on it. With the pump off I might see a 20 degree increase on a pull at 14-15 lbs., with the pump running my IAT's will actually drop down. I haven't even put ice in it yet to see what that will do but I'm sure it will do well. The cooler filled with water is an insanely effective heat sink even when the water is not flowing.
Don't write off an A2W for the street.

 

You make some great points...I will checkout the FB kits.

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Lets say E85 has a effective compression ratio knock limit of 22:1

Does the engine care in which form its delivered?
8.5:1 + 13.5# = 22:1 ECR
Or
11.5:1 + 10.5# = 22:1 ECR

When the valve closes and the plug fires, is there a differences in tunability in the chamber dynamics if both combos are seeing the same 22:1 ECR?

I see the difference in how the compression effects other parts of the cars overall characteristics. But does the engine care how its delivered ?

Btw, I just picked 22:1
we could make the discussion any number, just asking if cylinder pressure is cylinder pressure when the plug fires?

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The math on those is not even close to being accurate. Either way the same principal applies and yes it most definitely matters how you get there for all of the reasons mentioned in the previous posts in this thread. The answer 99% of the time is less compression and more boost when you are up against a knock limit of the fuel.

 

Methanol is the only fuel I would even consider not running an intercooler on. E85 even with added meth injection will still be way better with an intercooler.