aluminator with a supercharger

[K4fxd]

I'm not a FI expert.

It seems to me that if you use lower compression and more boost (air) allows more fuel in the cylinder this would make more power.

That is the reason for the low compression in top fuel engines.

I have no idea what compression ratio's the pro mod guys are using.

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[Jackson1320]

You talking air to air IC? 10deg over ambient while cruising sure, def not on a pull, absolutely not on a quarter mile pass.

If it’s a quick freeway pull 60-100 it stays pretty close to 10-15 maybe 20deg. As long as I don’t hot lap it iat at the track they stay low enough not to pull timing.

 

[Jackson1320]

There are definitely disadvantages to lowering the compression ratio, fuel economy being on of them. It's likely the tune will need a bit of work as well since all the Coyote tunes use high compression torque models and spark tables as a baseline. Some might also run into challenges with the supercharger drive system when attempting the necessary higher boost levels.

I've spent the last 6 months fiddling with my 12/1 10 psi Gen3 trying to extract every bit of power possible on 93 and keep hitting knock as the road block. I've learned a ton in doing so, but unfortunately most of the increases I've found happen below 5000 rpm. I actually have a Gen3 short block on the stand set up at 11/1, which is still a little higher than I'd like. I just don't know if it's worth it to swap out the pistons in order to get down to 10 or 10.5.

You can lower compression in other ways. Ported the combustion chambers. Mill the pistons

 

[engineermike]

Interesting...so it's IAT2 (I take it -460 Rankine is abs zero?) times some factor related to the ratio of post-compression pressure / manifold pressure? Dumbing it down for me, how did you calculate the post-compression pressure...does it depend on manifold pressure and IAT2 as well as CR?

The post-compression pressure is a function of the volume ratio (compression ratio in our case) the initial absolute pressure (boost + 14.7), and the specific heat ratio (~1.4 for air, but different when fuel is mixed in). Post-compression pressure is not a function of IAT2.

Post-compression temperature is a function of IAT2, the pressure ratio (post-compression pressure / (boost + 14.7)), and the specific heat ratio again.

So is that claim I've heard a hundred times about intercooling increasing air density therefore power a bunch of nonsense? The SC will pump what it's going to pump regardless of density afterwards, so intercooling is really only for knock prevention (and more power through more aggressive timing)? Sorry for all the questions...

Great insight!!! Only one thing....with intercooling, centrifugal compressors (both superchargers and turbochargers) will actually flow more air since you are changing the pressure ratio through the dynamic compressor. However, you are correct about PD style blower flow rate basically not changing when you change the downstream conditions (temperature or flow restriction). This is a controversial subject on this forum. Not long ago, I made some drastic changes to cam timing and the MAF flow vs rpm did not change at all even though boost level was different. But yes, in terms of PD-blown Coyotes, the primary purpose of the intercooler is actually to stave off knock.

 

[80FoxCoupe]

If it’s a quick freeway pull 60-100 it stays pretty close to 10-15 maybe 20deg. As long as I don’t hot lap it iat at the track they stay low enough not to pull timing.

Yea thats like a 2.5 sec hit. What rise over ambient are you seeing on a quarter mile pass?

 

[80FoxCoupe]

You can lower compression in other ways. Ported the combustion chambers. Mill the pistons

Thicker HG also

 

[engineermike]

That last sentence, did you mean post combustion?

Nope, post-compression.

Post-compression temperature absolute = (IAT2 absolute) x CR^(k-1)

Boost pressure doesn't play in at all. That said, high boost pressure usually leads to higher IAT2, so there's that.

However, knock is a function of both pressure and temperature, so just since we can keep in-cylinder temps well under control using intercooling, CR, and GDI doesn't mean we can run unlimited boost.

 

[engineermike]

You can lower compression in other ways. Ported the combustion chambers. Mill the pistons

Thicker HG also

Absolutely on both counts. I actually have a pair of .075 gaskets, which is what I was referring to earlier regarding a Gen3 at 11/1. I was also kicking around milling the pistons down to the bottom of the spark-plug clearance divot, which would get me where I want to be CR-wise. They'd still be hypereutectic, though. Seems like rather than doing all that I could get a set of 10.5/1 mod2k pistons and get the benefits of forged as well. I'm on the fence about it.

 

[Meatball]

Great insight!!! Only one thing....with intercooling, centrifugal compressors (both superchargers and turbochargers) will actually flow more air since you are changing the pressure ratio through the dynamic compressor. However, you are correct about PD style blower flow rate basically not changing when you change the downstream conditions (temperature or flow restriction). This is a controversial subject on this forum. Not long ago, I made some drastic changes to cam timing and the MAF flow vs rpm did not change at all even though boost level was different. But yes, in terms of PD-blown Coyotes, the primary purpose of the intercooler is actually to stave off knock.

Thanks. Actually, I think I read that on the Kenne Bell website so no credit to me, but good to verify.

Great information.

 

[Jackson1320]

Yea thats like a 2.5 sec hit. What rise over ambient are you seeing on a quarter mile pass?

Yea thats like a 2.5 sec hit. What rise over ambient are you seeing on a quarter mile pass?

About -20 to -30 degrees I have never gone a full 1/4 without the water/meth turned on

 

[engineermike]

@robmustang201528 apparently Brenspeed heard you. Here he dynos a 2019 A10 with the 9.5/1 aluminator and V3-JT at 14 psi:

 

[80FoxCoupe]

Good power on pump gas

 

[SolarFlare]

LOL I see some are still at it. Bless Ya’ll hearts.

 

[K4fxd]

The more air and fuel you can cram in a cylinder and burn the more power you will make.

The higher the compression the more efficient it will be.

So where is the trade off? Nitro 7 to 1

E85??

93 pump??

C-16????

Like I said I don't know what comp the turbo pro mods are running.

Most are running a meth nitro mixture.

 

[80FoxCoupe]

The more air and fuel you can cram in a cylinder and burn the more power you will make.

The higher the compression the more efficient it will be.

So where is the trade off? Nitro 7 to 1

E85??

93 pump??

C-16????

Like I said I don't know what comp the turbo pro mods are running.

Most are running a meth nitro mixture.

Start by focusing in on a specific power goal, fuel and a specific combo. You will then find your answer. Asking a general question while throwing out a list of fuels and engine combos from pump 93 coyote to nitro pro mod seems odd.

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