05-26-2006, 05:35 AM
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Join Date: Apr 2003
Posts: 1,603
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 Quote:
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Originally Posted by joecautela
Have you guys had access to a wind tunnel? I was wondering also if under the hood temps were affected by closing off the bottom. How was air flow in the engine bay addressed? I follow your line of thought on downforce created by aerodynamics vs. created by added weight. Added weight I would imagine also helping traction. Is the 300hp figure what was required to move the "brick" to over 200mph? I wish I had paid more attention to my math. Most of these questions I'm sure have been dealt w/ before by engineers and mathmeticians. I still find it exciting. Good luck!, I follow what tidbits I get w/ great interest. I saw the car at Watkins Glen last yr but wasn't able to spend the time I had hoped for to study it, Joe
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The 300hp figure was bascially a calculated figure based on the boost pressure we generated and the engine speed. Jim had done some dyno work on that motor, which in Dayton, was capable of just around 400hp. But with an improperly sized turbo, the compressor map was not capable of matching that flow or pressure at Bonneville. Live and learn.
This time around, Jim and I really worked on finding the right turbo that is capable of producing the proper boost at the altitude. We have a boost system that is capable of somewhere around 600hp, we think. So far, the engine built has made somewhere around 500hp (brian, I can't recall of the top of my head). But unless some things really fall into place, we are going to trim back the boost to hit 220mph. If we CAN find the right hardware, the stretch objective is 240, which is faster than the other Spider out on the flats (a large block Chevy blown spider... a real monster 2 spiders long). But the important speed is 211+.
The motor is supposed to go into Jim's Lakester, which Brian aluded to in a previous post. This is an open wheeled, streamlined beast, that needs to go about 300mph.
As for the underhood flow.... We've have thought about it a lot, and if we actually owned the car, would change a few things. But at the moment, it has enough underhood flow to keep the engine reasonably happy in terms of cooling temp and intake flow. Most of the air comes out at the rear of the hood, where theres a large gap just for the flow. I would much rather divert this flow under the car (but above the floor pan) and have it exit at the rear of the car where there's a low pressure area. There are a few SAE papers that talk about this. If we could, we'd almost cut off the underhood flow, and go to a water tank heat exchanger to cool the engine- figure somewhere around 30 gal of room temp water will keep the engine happy for 7 miles. This is one of those times that I repeat that you MUST go to the salt flats to see some of the incredible solutions that these guys come up with. No package space for any airflow around the engine, and they are still doing 300-400mph. (and this is one place where you can see a 260mph full size diesel truck).
But for the ultimate, we need to keep all the air flow from coming out of all of the seams, which is hard, as we are not allowed to tape up the outside surface at all. And for stock openings, one can ONLY use stock sealing- hood, doors, trunk, etc- must use the stock seals. But sealing those will keep the air flow less disturbed as it travels over the car surface.
Even a digital buck that can be run on a super computer would be nice for flow view. But we are just making educated guesses on the aero.
I'm pretty conviced that with the changes we made to the body, we would be pretty close to the record with the old engine. With the extra power... Last year, we had massive wheel spin problems at 195mph. (think about that for a while- driving along at a nice and fast 195, and all of a sudden, the rear wheels light up...).
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