Re: how much timing are you guys running on pump 93??
Will meth injection on a stock air/water setup (with a johnson high flow pump) help to combat the heat soak? Will it get it as cool as an air/air setup with meth can? ---
Methanol will help combat heat in all scenarios. Obviously, water injection is best for strictly heat removal, but methanol provides considerable heat removal while introducing an additional combustible fuel into the chamber. This is why methanol is usually the cooling agent of choice for those with undersized injectors, because of it's fuel "band-aiding" capabilities.
As for your actual question, it depends on the efficiency of the air-water setup. Hypothetical here, but lets say you have an A2A setup that's capable of keeping IATs at ambient + 10% (200 degF comp outlet temp resulting in 93% efficiency) and an A2W setup that can achieve IATs of ambient + 30% under (200 degF comp outlet temp resulting in 79% efficiency) at static cooling levels (road speed, no boost, just cruising). Now, let's say it's an 80 degree day, at 15 psi, resulting in 200 degF ....you'll have static temps of:
A2A - 88 degF
A2W - 104 degF
But that's not the real issue.....the problem is with heat retention and thermal transfer barriers.....and here's where the real downside to A2W systems show when used outside of ideal situations (ice assistance, rest time, etc...). A2W systems must enact 4 thermal transfers to expel intake charge heat to the atmosphere (where you ultimately want the heat released). Each of these transfers occurs through a barrier which provides resistance to the thermal transfer and, thus, reduce efficiency. A2A systems only have to enact 2 thermal transfers and this increases efficiency. The downside is that you can't (easily) introduce a supercooling principle to one of the barriers in an A2A system, whereas you can (easily) introduce it to the A2W system.
Now, back to our hypothetical.....let's say that the A2A has a minimum efficiency of ambient + 40% (73% efficiency....pretty much the industry average). That would mean that at full boost, no rest period, and significant time under boost, the IATs would be around 112 degF. However, the A2W cannot achieve this level of efficiency on it's own, and loses efficiency as heat is retained. So , while you can achieve 79% efficiency static, you could fall to 50% or 30% or even 10% as heat soak sets in and heat is continually introduced to the system. So, let's imagine you're on a back road doing a launch to 120 mph blast and you've allowed both systems to rest down to (near) ambient.....well your run might look like this (again, hypothetical here):
A2A
- 1 second: 90 degF
- 3 seconds: 95 degF
- 5 seconds: 100 degF
- 8 seconds: 105 degF
- 10 seconds: 110 degF
- 12 seconds: 110 degF
- 15 seconds: 110 degF
A2W
- 1 second: 90 degF
- 3 seconds: 90 degF
- 5 seconds: 95 degF
- 8 seconds: 105 degF
- 10 seconds: 115 degF
- 12 seconds: 125 degF
- 15 seconds: 140 degF
Now let's pretend you wait a minute and make the same run again. Here's what you might see:
A2A
- 1 second: 100 degF
- 3 seconds: 100 degF
- 5 seconds: 105 degF
- 8 seconds: 110 degF
- 10 seconds: 110 degF
- 12 seconds: 115 degF
- 15 seconds: 115 degF
A2W
- 1 second: 120 degF
- 3 seconds: 120 degF
- 5 seconds: 125 degF
- 8 seconds: 135 degF
- 10 seconds: 145 degF
- 12 seconds: 160 degF
- 15 seconds: 175 degF
So as you can see, for the first little while, the A2W actually retains a more stable temperature pattern, UNTIL heat soak begins to overwhelm the system and the lower heat exchanger cannot keep up with the demand of heat being introuduced. All of this is simply a byproduct of the type of system the A2W is and the thermal barriers present in this system. Sadly, the same component (water) that allows the A2W to be supercooled (iceing upper IC or using an ice chest) and retain that cooling for the needed period of time becomes the crux of the system when that cooling has given way to heat soak.
[Disclaimer: This is all out of my own head (efficiencies and thermal results) so ignore any inaccuracies or contrary results to what you have encountered.]
