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Bonneville Salt Flats Discussion => SCTA Rule Questions => Topic started by: Jack Gifford on October 30, 2017, 12:32:50 AM



Title: Exhaust
Post by: Jack Gifford on October 30, 2017, 12:32:50 AM
Rulebook says, in part,- "... directed away from... the course...". The exhaust will exit one side of my lakester, with no turn to the rear planned. The present stacks would be aimed 12 degrees down from horizontal. Must they be fully horizontal to be considered 'away from the course"?


Title: Re: Exhaust
Post by: MRK on October 31, 2017, 10:03:14 AM
If the exhaust exit is pointing downward past a horizontal plane, isn't that "towards the course"??
My suggestion is to run your design past the Chief Car Inspector and Committee Chair for approval. The contact info is in the rule book.
Cheers



Title: Re: Exhaust
Post by: SPARKY on October 31, 2017, 10:30:20 AM
As long as it doesn't make a big dust cloud I don't think it will be any issue---Jack you may want to visit your aero coach about the straight exhaust he may think that that is the same as sticking a 3' 4"x4" out the side of the car


Title: Re: Exhaust
Post by: Rex Schimmer on October 31, 2017, 01:07:39 PM
Jack,
I agree with Sparky, just having them stick out the side is not to "aero" and then not pointing them to the rear is just like throwing away horse power. Just to do a quick calculation with some easy numbers let's assume that your exhaust produces 25 lbs of thrust, which might not be to far off for a small supercharged engine, at 200 mph that is 133 horse power! Can you afford to do that?

I have always like what the Contrivance Engineering guys do with their exhaust.

Rex


Title: Re: Exhaust
Post by: Stan Back on October 31, 2017, 05:42:59 PM
Yeah, but what do they know.


Title: Re: Exhaust
Post by: ronnieroadster on October 31, 2017, 07:15:25 PM
Jack,
I agree with Sparky, just having them stick out the side is not to "aero" and then not pointing them to the rear is just like throwing away horse power. Just to do a quick calculation with some easy numbers let's assume that your exhaust produces 25 lbs of thrust, which might not be to far off for a small supercharged engine, at 200 mph that is 133 horse power! Can you afford to do that?

I have always like what the Contrivance Engineering guys do with their exhaust.

Rex




    Rex if the numbers are close to accurate using 25 lbs of thrust pointing rearward would it not be disrupted by the exposed rear tires rendering the hopeful push forward non existent? Or little if any noticeable.
  Ronnieroadster


Title: Re: Exhaust
Post by: Sumner on October 31, 2017, 07:46:28 PM
....I have always like what the Contrivance Engineering guys do with their exhaust.....Rex

I'm not a fan of the exhaust going straight out either.  We had it that way on the Stude, but were hopefully going to change it.

(http://1fatgmc.com/car/misc-pics-1/spit-1.jpg)

(http://1fatgmc.com/car/misc-pics-1/spit-2.jpg)

I like what they did on the prop planes during WWII and probably other times, as shown above, on a Spitfire.  Somewhat similar to Contrivance.

(http://purplesagetradingpost.com/sumner/bvillecar-3/02-18-09-14-chute-doors.jpg)

If I was ever to finish the lakester it has it exiting rearward and would also help the CP/CG as shown above, above the chute doors,

Sumner



Title: Re: Exhaust
Post by: Jack Gifford on October 31, 2017, 11:35:49 PM
Thanks guys. I'm still a long way from concerns about any thrust from the exhaust, but adding bends could definitely eliminate "exhaust directed at course".


Title: Re: Exhaust
Post by: jl222 on November 01, 2017, 03:06:20 AM
Thanks guys. I'm still a long way from concerns about any thrust from the exhaust, but adding bends could definitely eliminate "exhaust directed at course".

 We bend them back and up. Thrust and down force.

                 JL222


Title: Re: Exhaust
Post by: jacksoni on November 01, 2017, 07:22:51 AM
Though I don't know for sure I suspect this rule is directed at cars with under the car exhaust systems rather than special construction or others where fender exits are legal. My engine uses a very short header (so very hard to lengthen to direct toward the back of the car without messing up my exhaust tuning) and it was pointed more or less at the track, about 10" away. They made me put a deflector on the outlet. The prior suggestions are all valid but I don't think anyone is going to ding you if an exhaust coming out the side of the car is slightly pointed down (therefore "at the track") from 18" or more above the ground. But then again......


Title: Re: Exhaust
Post by: Jack Gifford on November 01, 2017, 10:47:34 PM
Historical note: this SCTA rule goes all the way back to 1948 (at least), so I'm guessing the main concern was kicking up more dry lakes dust.


Title: Re: Exhaust
Post by: floydjer on November 06, 2017, 08:37:29 AM
May as well add augmentation tubes while you`re at it :cheers:


Title: Re: Exhaust
Post by: SPARKY on November 06, 2017, 10:03:45 AM
notice the slight bellmouth on the planes exhaust----nothing like a little designed in low pressurer  to help extract the exhaust


Title: Re: Exhaust
Post by: wickedwagens on November 15, 2017, 10:31:25 AM
Back and slightly up on the Clark/Hall lakester.  They also make a great rest for tools ect.


Title: Re: Exhaust
Post by: John Burk on November 15, 2017, 01:27:47 PM
Eric Ahlstrom advised swept back and flush .


Title: Re: Exhaust
Post by: Jack Gifford on November 15, 2017, 11:55:10 PM
At least for now, I've put elbows heading back and up about 30 degrees.