Title says it all. How much of a drop in power occurs due to a lack of fresh/ cooler intake air - 60, maybe 70 HP? In a typical Chevelle, the only air in the engine compartment is what is sucked in through the radiator ( or at least the majority of it). I have a nice fat radiator that does a great job of removing engine heat and keeping the motor "cool". But if you place your hand behind the fan in the airstream while the motor is running, it feels like a blast furnace, if motor is running at 180, I assume this air temp is darn close to 180 - 200 deg. Most dyno numbers are corrected to 60 deg air - correct? - so is it correct to assume that you may need an additional 100HP built into the motor just for parasitic losses from the fan, alternator, power steering pump and hot underhood air?

I can remember reading info on this a long time ago, but don't recall the accuracy of the numbers.

It can cause alot of loss, but probably not 60-70 HP. It depends on the difference between the outside air temp (or at least, the temp of what you can actaully get into the intake), vs the underhood air temp. Typically it's in the 2 or 3% range, maybe as much as 5% in extreme cases; so you might expect it to be something like 10-20 HP off of a 400 HP motor.

A mechanical fan can cost you that same 15ish HP or maybe more also. That's probably the single biggest power-robbing thing you can have, except for maybe running with the A/C on. PS pump and alt use up alot less, maybe 5HP altogether. Of course, if you have an electric fan, the power to run that comes from somewhere, namely the alt; so the alt loss goes up while the fan is actually running.

I'd say RB69SS396Conv is right on about the engine losses alone. There is a lot more lost in the drive train though.

I have tried this a few times over the last 6 years and 3 different combo's with cold(er) air induction. Both ram air and cowl air. I just can't seem to come up with a solid repeatable and verified gain using cold air. As much as I would Love to "justify" my time and expense with these systems I have tried, I just can't prove it works to lower ET.

On the brighter side...

What it has done and is the reason I keep my system is that it has improved my consistency dramatically.

The generally accepted rule of thumb it that power drops 1% for every 10 degree rise in air inlet temperatures.

Jason,
I had thought the same number, but wasn't real sure.

Assuming 80 degree outside temp, inlet air at 200 (based on air flow through the radiator as the only real source of air), that yields a 12% power loss - 48 HP on a 400 HP motor, that's quite a bit. My engine produced trap speeds of 99.09 and 97 MPH on 14.24 and 14.09 ET's. So even with tuning and starting line problems being fixed and an achieveable MPH of 100MPH, the power speed calculator indicates a requirement for 340HP in a 4000# vehicle. Backing in a parasitic loss from 2 belts and a fan (20 HP) and the drop in power for underhood air (48HP) yields a gross engine output of 408HP, which is where we figured this motor would be on a dyno.

Now the big question then is what power level in terms of gross HP do I need to have to run this same combo in full street trim, including the reinstall of the factory AC in the 12's. Just for discussion sake I am going to use low 12's (12.10's). The number I have is 475HP net, back in the belts/fan (3 total including the AC comp. belt) = 30HP plus a 12% power loss for the underhood air and my gross power requirement comes in at about 560HP or about 500HP if I can get the carb inlet air down to ambient temp.

Bottum line is - it is probably foolish to expect my 408 motor to accomplish deep 12's and still be streetable (at least in my view of streetable, including having AC and a 6000 RPM max. If I get the inlet air temp to ambient (80 deg for this discussion I would pick up the 48 HP loss and get to 12.90's, definitely a step in the right direction. So realistically, I should probably be looking into a mild 500CI motor and a fresh air source.


Tom,
If you check back in, the pictures I have seen of your MC have the stock hood, what are you doing for fresh air?

Anybody else have any input/suggestions, please respond. I had originaly wanted to keep the stock SS hood for an original look. The only other option I see available is the Ram Air Box with ducted in air - just can't figure out where to duct these in from, there is literally no accessible free space under the hood of this car ['69 SS Big Block w/ factory AC]. I am not opposed to going to a cowl hood, but would consider this as a second option.

Thanks for the input.
Joe

Blocking the crossover in the intake is probably as important in keeping heat away from the intake air as is cold air induction. An oil splash shield such as that available for the big block Chevys also helps to keep heat away from the intake.

This is one topic which you can go to the moon and back, and still not get a satisfactory answer.
There are ways to duct cooler, outside air to the air cleaner. Probably the cheapest and easiest is to locate an air cleaner with a big snorkel or 2 snorlels, attach some flexible hose and position the open end near an outside air source.
I presume that your car is a 69, thus, a true cowl induction hood wasn't available until 70. BUUUUUUUUUUUUUUUUT, Cowl Plenum air cleaners were available. Unfortunately, a genuine or a repo cowl plenum air cleaner is SUPER BIG BUCKS these days. But, they WILL provide plenty of cool outside air! That would probably be the easiest, but NOT the cheapest, way to go.
Also, you could remove the hood.

I know that for cruising once the car is in bright sunshine for a while, it takes a bit more throttle position to keep a steady rpm. Underhood temps get pretty high. So it might be a MPG issue, and not an ET issue since the car isnt running in the hot sun for 1-2 hours straight.

Joe,

I have a 2" cowl Hood you can just see in the following pic. I have sealed off the underside with a piece of sheet aluminum and fiberglassed it in. Cut a circular opening in the Aluminum which seals to a pan that surrounds the carb and air cleaner. the pan has Moroso foam around it to seal to the underside of the hood when placed on the car.

Maybe a picture will help, will take some this week.

http://www.boomspeed.com/mc71454/June2004Nostalgialaunch.jpg

Assuming 80 degree outside temp, inlet air at 200 (based on air flow through the radiator as the only real source of air), that yields a 12% power loss - 48 HP on a 400 HP motor, that's quite a bit. My engine produced trap speeds of 99.09 and 97 MPH on 14.24 and 14.09 ET's. So even with tuning and starting line problems being fixed and an achieveable MPH of 100MPH, the power speed calculator indicates a requirement for 340HP in a 4000# vehicle. Backing in a parasitic loss from 2 belts and a fan (20 HP) and the drop in power for underhood air (48HP) yields a gross engine output of 408HP, which is where we figured this motor would be on a dyno.


On our 64 Nova race car, the underhood temps tend to be about 70° less than the engine temperature.
The radiator isn't 100% efficient in heating the air, and there is some air that enters the engine compartment without going through the radiator.

Nova,

I assume you have actually checked the temp. Interesting, I may have to "borrow" an Industrial Therm from the back isle inventory and try to establish this, maybe it is not as hot as I think. I do know, the 7 blade fan that I have running along with the Hvy Duty clutch moves a lot of air through the radiator.

I used a pair of indoor/outdoor thermometers from Radio Shack. I placed one right in front of the air cleaner and one inside the airbox of a dual snorkel setup. There was about a 25° drop from the underhood air temp to the airbox temp, and the underhood air temp was about 70° below the engine temp. With our hood scoop the air is even cooler.

I stumbled on a real good article about this awhile back. I was looking for alternatives to the OE SS cowl hood. It was an article written by one of the GM engineers that did some of the original research on what became the Z28 cowl hood. They looked at it as HP gained, not lost, because underhood snorkels were the norm (ie: they had to convince someone it was worth it). It was never a question about cooler air, it was about the BEST cooler air. Their research showed that there is a high-pressure area at the base of the windshield and that a cowl opening facing the windshield could take advantage of that. Even that distinctive Z28 cowl "lip" that sticks out has a purpose. It was not just for style. So not only was the air cooler, it had higher pressure. There is research that shows forward facing scoops can cause turbulence and affect mixture at the carb. Thus, the cowl hood. I believe their numbers were 1hp gained for every 10deg cooler air using this method. I will try to find it and post the link. Also, many NASCAR bulders used intakes that opened thru the firewall to the base of the winshield for the same reasons. You can by a replica firewall intake at RamAir. Check it out.

Do the Goodmark 2" steel cowl hoods come with the correct round opening in the underside frame?

running at night as we do picking up cool air down track seems to pick the car up a couple of hundreds or so thats one reason i started running my filter on the air pan to help consitantcy

yes.