legacycentral bbs

vrg3-

The density ratio would be <2 because the manifold temp would be higher than ambient temp.

This means less fuel, so it shouldn't matter.

Yes, and yes. This was just a quick and dirty attempt to get into the right ballpark. In actuality mass flow would probably be lower not only because of the imperfect intercooler but also because volumetric efficiency at redline is probably a good deal lower than 80%.

being im only a college freshman id have no way of knowing if you did it right. but it sounds good. this way hopefully i wont run rich till i need to. after all thats the point right

Yeah. Give 4:1 a try and see what your AFRs look like.

i was just looking at your calculations again and was wondering if the acutaly rise ratio is not quite 3 to 1 than if you bumped boost up to 20 psi wouldnt 4 to 1 still be sufficent.


btw i looked up fixed rates and their pretty cheap and so are the rebuild kits. the ones that are 300 are the adjstable ones. though they are really complicated to adjust

I wouldn't push it. Remember that this is just a band-aid. While I understand how you're achin' for high boost, I would suggest you keep things conservative, relatively speaking. Sure, fueling might be sufficient, but you still don't have reasonable control over it, and you still have no control over spark.

Even as it stands right now, you're gonna want to go over the entire pressurized portion of your fuel system and make sure everything is in tip-top shape for the sky-high fuel pressures you're going to be working with.

so true. that piggy back needs to get done soon for the sake of my nerves

just curious and because i suck as math, what afr would phil get on paper with the way he was running at the time of the dyno tests.

also when i was stock i was hittin 10-11 manifold pressure due to altitude so wouldnt 15 at sealevel be drasticly different up here. somewhere around 17-18 psi???

Well, let's see... He said he was running 16 psi in the manifold, and intercooler temperatures were about 125 degrees Fahrenheit, or 325 Kelvin. Let's assume intake air temps were equal to intercooler temps.

Ambient pressure = 14.7 psi
Ambient temperature = 293 K
Ambient density of air = 0.00125 g/mL
Engine speed = 6500 RPM
Engine displacement = 2212 cc
Volumetric efficiency = 80%
Fuel injector capacity = 370 cc/min
Injector duty cycle = 100%
Density of fuel = 0.7 g/mL

Density ratio = [(14.7 psi + 16 psi)/(14.7 psi)] / [325 K / 293 K] = 1.88
Volumetric airflow = 2212 cc/cycle * 3250 cycles/min * 0.80 = 5751200 cc/min
Mass air flow = 5751200 cc/min * 0.00125 g/mL * 1.88 = 13515 g/min
Mass fuel flow = 370 cc/min * 4 * 0.7 g/mL = 1036 g/min

AFR = 13515 g/min / 1036 g/min = 13.0

Hey, neat, that's the air/fuel ratio he actually saw.

Yes, barometric pressure differences due to altitude will affect the calculations, but it's not worth the effort to figure it out. Your density ratio will be higher but ambient density will be lower. Since we were doing the math so roughly anyway, just call it even.

wow that is neat.

call it even eh. well see. i just ordered a 4-1 and am going to test it out wiht the new pump. hopefully it isnt too much so i dont bog up top.

I don't think you'll experience bogging. The enrichment might be higher than you'd otherwise want, but it happens progressively and still isn't ridiculously high.