Author Topic: XXO/BVGC '38 Chevy Coupe Build  (Read 1026869 times)

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Offline John Burk

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1275 on: August 19, 2012, 01:53:43 AM »
The efficiency of a rear is easy to calculate if you know the heat gain and the specific heat and weight of the parts . With 600 hp a rear that gains 30 deg / minute is loosing 1.3% . That's if the rear had 15# of aluminum , 65# of steel & 3# of oil and no air cooling .

Offline desotoman

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1276 on: August 19, 2012, 01:15:21 PM »
Buddy,

It was nice to finally meet you. The car looks great, and congratulations on the records. I did not hang around too long since you had just lost a freeze plug and everyone was busy. Your car will go much faster after the bugs are sorted out.

Dale, it was great to see you again, I think it has been at least 25 years since I last saw you when you lived in Lomita. You did a great job on building the motor, keep up the good work.

I hope you guys make it to El Mirage this year, it would be great to see you again.

Tom G.
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Offline Jack Gifford

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1277 on: August 20, 2012, 02:19:40 AM »
Oops- I see that you only said that a "taller gear" is needed, and then were asking about overdrives, not a different ring/pinion ratio. I still have the same question though- why can't you simply use the appropriate quickchange gearset?
« Last Edit: August 20, 2012, 02:39:27 AM by Jack Gifford »
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Offline Jack Gifford

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1278 on: August 20, 2012, 02:22:59 AM »
... easy...
... and no air cooling...
So you'd need to do this on a chassis dyno- to simultaneously run the rear under load while attempting to not lose heat to the surrounding air. "Easy" is subject to different interpretations, I guess. Even then, the result will only be a ballpark figure, since there WILL BE heat conducted away (axles, housings, etc.) and temperatures will vary widely throughout the mass that sees a temperature increase.
« Last Edit: August 20, 2012, 02:36:21 AM by Jack Gifford »
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Offline Peter Jack

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1279 on: August 20, 2012, 02:33:02 AM »
Jack, different rear ends have different degrees of efficiency. A quick change is particularly bad because of the extra gears, each of which causes some loss. Ford 9" rears tend to be poor because of the large offset of the pinion in relation to the centerline of the crown gear. This causes excess scrubbing.

As we all know quick change rear ends make ratio changes rather simple and the Ford 9" is probably the next easiest to change ratios especially if full floating axles are used. There's probably no reason to go to one of the more efficient rear ends until you're scratching for the last couple of mph to set a record. At that time it becomes more than worthwhile to gain every efficiency you can and at the same time you probably know very close what ratio you require.

Pete

Offline Jack Gifford

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1280 on: August 20, 2012, 02:38:47 AM »
Pete- I'm not sure you understood my post (about FlatCad's QC), since I'm already aware of everything you just said.
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Offline John Burk

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1281 on: August 20, 2012, 09:49:21 AM »
Jack questioned the accuracy of using rear end temp to gauge lost hp . The point is rears are more efficient than the 7% power loss we often hear . A good bit of lost energy is oil churning which is not related to power transmitted and pretty much constant for any rear . The drag in question is probably under 1% .

The temp to hp formula is :
(lb of steel x .11) + (lb of aluminum x .22) + (lb of oil x .5) x heat gain (deg F) / minute = drag in BTU
Drag in BTU divided by 42.4 = drag in hp
 


Offline Jack Gifford

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1282 on: August 21, 2012, 01:51:30 AM »
Another 'oops': please disregard my recent posts that mentioned FlatCad's ring/pinion set. I had to read all of his posts back to July 8th to discover that his term "rear end gears" is in reference to the overall rearend ratio (2.4, 2.55, etc.), not to the ring/pinion gears. Too bad I didn't realize this back in July, as I very well could have loaned him some QC gearsets that he was looking for.
« Last Edit: August 21, 2012, 02:12:17 AM by Jack Gifford »
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Offline Kiwi Paul

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1283 on: August 22, 2012, 02:06:33 AM »
Yes, Fellas, I was kidding about the Overdrive shift problems....I honestly don`t see any real problems with whichever route you take. That is one very Impressive Flathead..... :-D :-D :-D

Offline zenndog

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1284 on: August 22, 2012, 02:19:35 AM »
 :cheers: :cheers: :cheers: :cheers: :cheers: :cheers: :cheers:

Offline jdincau

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1285 on: August 22, 2012, 10:47:41 AM »
According to these sources a Hypoid (most popular third members) gear set is 92 to 96 percent efficient at power transmission. A spiral bevel (V-8 quick change) gear set and a single spur gear set are both 99 percent efficient. That makes a V-8 quick change 98.01 percent efficient . Tell me again why I should dump my quick change.
http://www.zakgear.com/Hypoid_worm.html
http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html
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Offline Rex Schimmer

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1286 on: August 22, 2012, 03:15:38 PM »
Interesting info jdincau, I am with you hard to beat a good QC. A note on the practical side, ever follow a rear wheel drive in the rain and notice that the diff housing is always dry?? Think it is because it is hot?

Rex
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Offline jimmy six

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1287 on: August 22, 2012, 03:33:24 PM »
I'm not a believer in OD's (but still have one in the roadster) and have 5 gear sets and 4 diameter of tires to make the changes and that does not include the OD.

The OD I use is from the 4 speed trans I bought from Tex which is now G-Force.  It was a T101A and I think it's a GF4A now. I use the 3rd gear position for a .96 OD. There are countless combinations and I really don't care about a low 1st gear. I currently have a 1.61, 1.23, 1.00, & .96 for gears. Most OD's have too much of a change because they built for street use. The only time we used OD at Bonneville we slowed .5 mph and the tach never showed to pick back up and that's with a .96.

OD is just incase the tail wind is good.... :lol:...JD
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Offline 38flattie

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1288 on: August 23, 2012, 03:01:23 PM »
Lots of ideas and opinions for me to sort through!

While I sort through them, here is the in car video of Dale's qualifying run in XXO/BVGALT.

http://youtu.be/lO8Poof9kL8
« Last Edit: August 23, 2012, 03:03:07 PM by 38flattie »
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Offline jpm49c

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Re: XXO/BVGC '38 Chevy Coupe Build
« Reply #1289 on: August 23, 2012, 03:20:15 PM »
Very Nice!