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Yeah Mats is right, I scoop would be suitable for the back of the bonnet area to suck air in where there is a lot of pressure against the bonnet and windscreen.

Mats wrote:

Evert wrote: Its important to place the louvres as far back as possible, because the ridewind pressure at the beginning on the hood is high.

The louvres create a underpressure (talk to the airplane guy about wings) and stimulate a better flow of ridewind through the enginebay.

No more overheating problems.... Soon other problems followed.

This is totally contradictory to pretty much all I have read about automotive aerodynamics. The slat with louvres or deflector should be placed as far forward as possible to tap into the large low pressure area at the front of the hood. Further rearward towards the windscreen there is a big over pressure area that you need to stay away from.

Somewhere in my big photograph archive, I have some pictures which Alfa made from a 164 and a 75 with pressure buildup area's. I'll try to find them and post them.

Pressure towards the windshield is high relative to other areas on the hood. I seriously doubt it's a high as the underhood pressure. I suspect you could put louvers anywhere on the hood and air would flow out through them.

Lots of American muscle cars used a rear facing scoop for an air intake. It was almost always right at the base of the windshield (within inches), and it was ALWAYS sealed off from the underhood pressure. For examples look at a 60's Chevelle or Camaro with cowl induction, AMC's AMX, and many others.

I think venting the hood is more of a turbo thing. The underhood temps on a supercharged motor are not that high.

Greg

Yes, naturally the underhood pressure is always higher then on the topside but it was weather you want to put the radiator exhaust at the front of the hood or rearwards. Bigger pressure drop is naturally better for moving air through the radiators.

That's true. Now back to our regularly scheduled programming...

If you want to see something on underhood pressures in a GTV6, or other car with a rear opening hood, unlatch the hood then drive. At around 65mph the rear edge of the hood will be about 2 inches up. It doesn't get much higher if you go faster and it goes down if you go slower. I did notice a significant temp drop while doing this (my cooling fans had failed) over what the temp was reading at 65mph before unlatching the hood.

Car has a worn out stock 2.5, no turbo or supercharger. outside ait temp was about 80deg F.

hth
Scott

Greg Gordon wrote:Pressure towards the windshield is high relative to other areas on the hood. I seriously doubt it's a high as the underhood pressure. I suspect you could put louvers anywhere on the hood and air would flow out through them.

Lots of American muscle cars used a rear facing scoop for an air intake. It was almost always right at the base of the windshield (within inches), and it was ALWAYS sealed off from the under hood pressure. For examples look at a 60's Chevelle or Camaro with cowl induction, AMC's AMX, and many others.

I think venting the hood is more of a turbo thing. The underhood temps on a supercharged motor are not that high.

Greg

Any body here driven a GTV with the bonnet unlatched ?
At 120 km/h the bonnet gets pushed up at least 200mm.
Under hood pressures are WAY higher than what you get at the windshield.

I relocated the intercooler's heat exchanger and made ducting. It only made a slight improvement. I think the overall problem is the heat exchanger really isn't up the task. However it's the only off the shelf unit that would fit, and it works well enough. With the Milano this is not a problem, with an A/C equipped GTV6 a really good heat exchanger will have to be custom made.

It's going to stay just under 10psi because the next size pulley (only .1" smaller) put it up well over 11psi. I really don't want to exceed 10psi at this point.

I did run into a tensioner pulley problem which cost me most of they day and I will have to go out of town soon, so I may not be able to dyno for a couple weeks.

Greg

After delays due to bad weather and the need to go work at my real job, I finally got to the dyno shop today. Results were decent, although not quite as high as I had hoped.

The engine put out 231rwhp at about 6500 rpm. I will put the dyno sheet up tomorrow. I feel this is a respectable number for a 2.5 with 10psi and 8.5:1 compression. However I had expected about 240 and hoped for just a little more. I think I can squeak the numbers up a bit more with a better heat exchanger. Of course ditching the original catalytic converter would help power for track only event. The cat back system on this car isn't too good either.

After driving it, I think its performance is pretty close to the 265rwhp 3.0 we built. The 2.5's 4.10 gears and 7000rpm redline partially make up for the 34 horsepower deficit. The 2.5 also has a lot less torque which seems to make tire spinning less of an issue.

Note to Barry and Jim K. : I was very surprised how much timing this thing wanted. We ended up with about 36 degrees total advance from about 5000-7000 rpm. That's a lot of timing with 10psi.

Greg

thumbs up greg
your work is great.

Great numbers Greg!
Re. the advance thing, when I run the 3liter with my distributor curve I have ~23* at idle and ~32-35* high up.
Jim K.

Hi Jim, I actually started with your normally aspirated numbers for these cams, and they were darn close. However I was surprised it wanted even more timing, that's contrary to conventional wisdom.

Anyway, here is the graph. All testing was done in third gear to keep the tire speeds down. I didn't want to be standing next to an older tire at 4th gear 7000rpm speeds.

This is a photo of the dyno sheet so it's a little tough to read. Here are the numbers, max power=231.13 max torque=204.65 outside air temp 76.77F, atmospheric pressure 28.97"HG, humidity 12%. The dyno is supposed to correct for these factors.

I will put a video up soon.

Hey, do you guys think that torque curve is flat enough?

Greg

Here is a video of a second gear pull from 1300rpm-7000rpm. The red Nordskog gauge shows air temperature in the plenum. Notice how little it rises under boost. A lot of people ask, "how soon does it develop boost?". This video should answer that. It's pretty much right away. As you can see in the video the car pulls pretty well throughout the rpm range.

The green light comes on when the water injection starts spraying. It also stays on off boost if the nozzle clogs, which is highly unlikely. The red light is a low level warning for the water tank.

Greg

http://www.youtube.com/watch?v=mDuzCwfEM8s

Greg Gordon wrote:After delays due to bad weather and the need to go work at my real job, I finally got to the dyno shop today. Results were decent, although not quite as high as I had hoped.

The engine put out 231rwhp at about 6500 rpm. I will put the dyno sheet up tomorrow. I feel this is a respectable number for a 2.5 with 10psi and 8.5:1 compression. However I had expected about 240 and hoped for just a little more. I think I can squeak the numbers up a bit more with a better heat exchanger. Of course ditching the original catalytic converter would help power for track only event. The cat back system on this car isn't too good either.

After driving it, I think its performance is pretty close to the 265rwhp 3.0 we built. The 2.5's 4.10 gears and 7000rpm redline partially make up for the 34 horsepower deficit. The 2.5 also has a lot less torque which seems to make tire spinning less of an issue.

Note to Barry and Jim K. : I was very surprised how much timing this thing wanted. We ended up with about 36 degrees total advance from about 5000-7000 rpm. That's a lot of timing with 10psi.

Greg

Dam those real jobs, they always get in the way of fun .

Nice work again Greg! I would love to see the end results of a well made set of extractors and a decent exhaust. Surely you could get close to or even go past 245/250hp @ the wheels?
Maybe some more boost ? You know she wants it.....

Hi Duk,

I don't really want to add any more boost. Right now max boost is about 10psi. With 8.5:1 compression it's conservative enough so there is a large margin of safety. In other words, if the intercooler, or water injection system fail it should still be fine. If someone accidentally puts in lower octane fuel, it should be ok. I am pretty sure with good exhaust and a better heat exchanger it would be in the 240rwhp to 250rwhp range. The exhaust is chosen by the customer and not by me, so I don't have any say in that. I do plan to fit a better heat exchanger in a few months.

Like everyone else, I always want more, but compared to other cars, that 231rwhp number is really pretty good. For comparison a Mustang 4.6 V8 with an Allen kit using a M90 blower puts out about 257rwhp.

This car has at least 40 more horsepower than a Callaway on the same amount of boost. Now I know that's not an apples to apples comparison because the pistons, intercooler and engine management on this car are quite a bit better, but it's the closest comparison I can come up with.

Greg