I pulley'd "down" to 7/2.75 with an UltraGrip today that seems to have at least helped my belt slip.

I checked the pressure before my intercooler, where I see 11psi. At the intake I see only 7psi. The intercooler is the ATI Corvette LT1 air-air, which isn't very big.

I know some pressure drop is normal from the increased density, but that seems like a lot to me.

Thoughts?

- Dave

 

That sounds about right but a little low. I believe your combo should be making 10PSI of boost normally without the I/C. With a little belt slip 8-9PSI should be normal. Since the intercooler is acting as a restriction you are seeing 11PSI (compression against restriction) at intake to I/C and 7PSI at T.b.

I have an ATI intercooler on my LT1 and 3-4 PSI is a normal drop. The Intercoolers are very restrictive. When I had my 8PSI pulley on I was seeing 5-6 PSI of boost. I use this to my advantage as I currently have a 12 PSI setup and really only want 8-10PSI of boost at the intake side. So I prefer to have the pressure drop.

 

You prefer the pressure drop??? Ok...

I pitched the intercooler this afternoon, and am now seeing a full 11psi at the engine. And the air temp only increased from 90C to 110C, not much difference.

 

I suspect 10PSI is at the limit of what my motor can hold, I prefer the lower boost (via Intercooler) to a blown motor (still too many stock parts in it).

 

How much pressure drop in comparison to cooled/dense air vs. hot/thin air and how much power it produces is questionable. I've heard there is a threshold where a certain amount of pressure drop going through an intercooler is still better than non-intercooled higher psi because colder air still has more O2. Basically, it's not always about absolute psi that makes power, but how dense the O2 charge is.

But, if you're saying the air temps haven't really changed for you, I guess it really doesn't matter.

From what you are saying, is that the pressure drop is because of the restriction, not because of the cooling effect. Are these stupid ATI IC's doing anything for us?

 

The only real method of finding out if its a restriction or not is to purchase a Differential pressure gauge and connect the DP guage across the IC. The high side would connect on the blower side of the IC and the low side on the engine side. Then driving the car you can see exactly what the pressure drop across the IC is. It seems to me if Daves readings are correct that is a considerable amount of DP that he is seeing. I would have expected 2 PSI of drop but not what he got.

 

I think it's more complrex than that. It's all relative to how much CFM you're flowing. If he says he's seeing 11.5psi on the hot side, and 7 psi on the cold side, isn't that basically saying just what a diff. gauge would tell you? It's the air temp differences that make the equation a little more difficult.

I would be interested to know what the amount of O2 per cubic inch on the hot side vs. the cold side is.

Don't know how you'd do that. O2 sensor?

 

It would be nice if someone could just put one on a flow bench. That would help determine if its a temperature thing or not. I have the twin intercoolers, theyre pretty small so they probably dont flow well either.

 

No, its not really that complex. It is relevant to the amount of flow that the blower is building. But it would build as RPM goes up, and the DP across the IC would change with the flow. Dave is taking measurements at two different drive cycles. Pressure is pressure, if you a have the DP meter across the IC you can see the DP across it at the any given moment. Conditions could have changed when Dave stopped and made the second connection or he may not have driven the car as hard or may have driven it harder the second go around. You could even get a El-Cheap analog data recorder and record a 0 to 5v DP pressure reading during a test drive or a dyno run. Then you can recoder and analyze the DP during the whole run.

Hmm checking O2 content.....not sure how to do that one. In anycase I am sure it could be done, but at what cost?

 

Dave...what did you use to measure the before and after boost air temp? that will tell us weather an intercooler is needed and the density of the air. I've got no faith in the stock air sending unit......mine is only showing a 5 degree increase in temp at 9 psi boost and no knock counts. which is also suspect. also a heat soaked engine should increase the air charge temp vs a cold engine.

 

The air temp I difference agree is not that reliable, because I'm logging the FAST using the stock sensor.

However, the boost difference is repeatable and reliable. Its the same gauge, moved from one to the other, run 30 seconds apart on the same road in the same manner.

Probably the best way to do it would be to look at the MAF readings, but they're beyond maxed on my car. That would tell you the actual mass of air you consumed.

You can also obtain that with a HP reading.

 

A word of caution. 11.5psi of non IC boost is waiting to have a blow head gasket. Since you have good piston I hope and your blow head gasket is prone to happen with 11.5psi of non IC.

Few yrs a go, most of you guys don't know who is Shalin (Master blown LT1 tuners) his blown 355ci LT1 Vortech 12psi non intercool made over 550rwhp. His car blow head gasket because of high boost and not intercooled. He than later adapted a ATI IC to his Vortech, since than he never has any problem and the IAT drop about 70 degree. He wrote a lenghty post about IC is a MUST for 12psi of boost motor


Bruce

 

No, and IC is not a "must". Avoiding detonation is a must. You can do that with an IC, with retarded timing, with reduced compression, or with alcohol injection, or a combination of those.

I'll be going with alcohol injection and my current 9.0:1 compression.

I have yet to see a reasonably priced and effective intercooler for the Vette. There just isn't enough airflow, so you wind up with air-water. And that means battery relocation on a Vette usually.

What ever happened to Shalin anyway?

 

I'll go along with the above comments. My ATI intercooler/Vortech installation never saw the street. The horsepower losses before/after on the dyno were amazing. Water injection does the job well. Unless I'm mistaken, the average (and I stress average) low compression blown Lt1 puts out about 550rwhp.

 

There is a right way and a wrong way to control detonation. 12 psi of intercooled vs. non-intercooled air creates less cylinder pressure to keep compressed cylinder pressures down and has more O2=more fuel=more power. I believe that's what Shalin trys to explain. Retarding timing is necessary simply because the burn characteristics change under boost, but it can also be done to overcompensate for high air temps and/or high overall compression ratio. Cold/Dense air is the best way to harnass all of the power you can create. From what I've learned, an air/air IC is the most efficient way to do this. Water/alky injection only reduces the cylinder temps, but does nothing to actually add more O2.

Controlling detonation somehow is necessary, but making efficient POWER is what we're all trying to achieve.

Unfortunetly no, but people have made them themselves. I still am skeptical however that even if you can get a custom air/air IC in front of the car somewhere that you can get enough air flow across it....especially without blocking the radiator and inadvertently reducing your cooling systems efficiency.

 

I agree that 12 psi of cold air has more mass than 12 psi of hot air, and therefore makes more power.

However, alcohol injection also cools the intake charge due to the flash evaporation of the water/alky mixture. I can't document by how much, but until we know whether its more or less than an intercooler, its all bench racing :-)

For the purposes of this thread, however, I'm still confident that when it comes to the ATI intercooler for LT1 corvettes that 12psi of hot air has more O2 molecules than 7psi of warm air.

 

Guys,

You can build an intercooler for your sc vette for under $500.00 bucks. talk about great airflow, I mounted my intercooler horizontal up against the air inlet baffle. I'm running 3 inch diameter tubing and my charged intake temperature never sees above 100* F.

Want to see a pic?

Frank

 

HECK YES!

 

Well then I'm confused, because I thought that water/alky injection doesn't actually cool the charge by that much, but it slows the burn down to prevent detonation. Maybe a little of both, but from what I've been TOLD (bench racing until proven otherwise ) having both an air/air IC and water/alky is the best of both worlds, but they do distrincly different things. Maybe I'm wrong. Afterall, I'm still learning.

I would agree.

 

I too am learning and hopefully by not too many hard knocks...how does a swamp cooler work, it cools incoming air by evaporation...at a low boost level it will cool the charge and you add alcohol to increase the cooling and make up for the lost air density (oxygen) from adding the water to the charge, it won't work as well in a humid climates and with very high boost or turbo's it will not cool the charge enough but were taking over 300 degree charge air.....nether will a air to air intercooler, so they use both.....and it does slow the burn for detonation. but using the boost levels most are on the board were going to get more for the effort, not spining the super charger as high with water/alcohol injection. what do you think, this is just food for thought and what I have read...........I have one book by Dick Datson....21st century turbo and he says under 10 boost turbo or supercharged an intercooler is a waste, the air charge temp is not high enough to get any real benefit and then look at caroll supercharging they sell kits with water/alcohol injection with 12 psi boost. I'm not trying to offend any one, I'm just trying to not have a melt down or reinvent the wheel. I for one am getting a real bennifit from not having the intercooler...more boost and less air restriction for engine cooling, the rest out there having belt slip issues could add bigger pulleys to obtain the same boost levels and slow down the supercharger by removing the intercooler..........or am I up in the night. looking for experiance from water alcohol users on this board.