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Thanks for the spreadsheet, it’s great.
I beat my head against the wall for a long time trying to come up with the right ratios and build an engine so all would work the way I wanted it to.
Many shook their heads when I decided to go with the 3.08’s, but I wasn’t building a race car or something to run around town from light to light.
For me it was a nice cruiser I could run for hours on the highway.
Except to stop frequently for gas.
Yeah really. How bad is it? What do I have to look forward to?
I remember having an MPG contest with my Dad when I was learning to drive. 472 Caddy with 2.93 rear. He got 13 and I got 15 on a long Highway Trip at 70 mph cruise. And probably 2000 lbs heavier than the Vette! LOL
I don't have it on the road yet so I don't know what the MPG will be.
I'm not too concerned because it will be my toy.
I had a friend with a 472 Caddy and he ran a 472 Caddy in his family Sanger flat bottom drag boat.
"Sanger Jack", great guy and drag boating legend.
Last edited by OldCarBum; Nov 17, 2020 at 12:47 PM.
One of the members here, IIRC it was SteveG75, reported getting 30MPG as displayed on his EFI unit on his OD equipped 496.
I thought that was amazing!
Even if it was only an "instant" reading. Seems like he should be able to average over 20MPG on the highway.
That name isn’t familiar but there were so many people involved with drag boats back the the day.
I was not a professional racer but had a couple of Sanger’s and Cole’s I ran at the Colorado River, Lake Elsinore, Ski Land, Carlsbad Lagoon etc.
My family and Jack’s family used to get together for waterskiing weekends at the Parker Strip and other local So Cal lakes.
Last edited by OldCarBum; Nov 18, 2020 at 11:25 AM.
One of the members here, IIRC it was SteveG75, reported getting 30MPG as displayed on his EFI unit on his OD equipped 496.
I thought that was amazing!
Even if it was only an "instant" reading. Seems like he should be able to average over 20MPG on the highway.
Isn't that Fabulous for 500+ HP ?
That’s excellent.
If I get 15 mpg I’ll feel pretty good.
Anything approaching 20 mpg would be great. I currently get 11-12. Hoping with 200r4 modern HR cam and valve train will get me close to the best of both worlds.
Yeah I'll be happy if I can get 15 hwy. But I got that with my LT1 and my dad's 472. Neither had OD.
So with the OD it should help some right? Maybe a lot?
I see no reason it shouldn't get 18. Hwy.
In town of course will be bad, expecting like 9 there.
Last edited by leigh1322; Nov 18, 2020 at 11:38 AM.
How many miles are you guys running these per year? I historically run mine about 300 miles per year. Even if I went to 1000 miles/year at 10 mpg I would burn 100 gallons. Going to 15 mpg save me 33 gals/year or less than $100 dollars in the state with the highest gas tax in the nation (Pa.)
Agreed. When I raced my LT1 regularly I still didn't crack 2500 / yr.
But I only took it out like once a week.
Once I retire(soon) I plan on finishing this one and driving it every day the weather is nice! Weekend trips too.
I'd say 5-10,000 / yr is possible.
That would hurt a little at 10mpg!
But it will be a blast either way.
The gas mileage is not a real concern, just more of a curiosity, or a technical challenge.
The other reason for the OD is comfortable cruising.
I may even try a power-tour!
Agreed. When I raced my LT1 regularly I still didn't crack 2500 / yr.
But I only took it out like once a week.
Once I retire(soon) I plan on finishing this one and driving it every day the weather is nice! Weekend trips too.
I'd say 5-10,000 / yr is possible.
That would hurt a little at 10mpg!
But it will be a blast either way.
The gas mileage is not a real concern, just more of a curiosity, or a technical challenge.
The other reason for the OD is comfortable cruising.
I may even try a power-tour!
You definitely want to do the power tour, that is for sure. I did 3500 miles in 10 days. Trip average was 11.8 mpg, running 3000-3100 rpms most of the time on the highway.
I may try to do the Power Tour in 2021.....just hard to plan anything right now the way stuff is these days.
I live in NE Ohio, from April to October I drive my toys as much as possible. Almost 5000 a year. I even drive to Nj when possible.
That is great that you use yours. My girlfriend (now wife of 37 years) bought our '69 in '79 and it turned 50,000 on the way home from the seller. It has 63,000 on it now. . Now that I am retired I was going to use different toy every day, but I usually don't drive for pleasure and I am concerned with parking lot damage or theft. I don't know if theft is an issue with these anymore.
I was presented with the gas mileage issue by a friend with a hot rod, when I started looking for a BB. I did the calcs and figured out that I would use less than $50/ year more in gas with the way we were running them. He started looking at BB too then.
If you guys put together a NE power tour contingent, I would be interested too. It is one of my bucket list items.
Right now my 73 BB has just over 108,000 miles and the tires are 6 yrs old.
She runs nice and smooth, but I don’t have enough trust in taking it for any long drives.
I’ve collected most of the parts for my body off restomod and hope to start tearing it down early next year.
I’ll be retiring in 2022 and plan to have the Vette completed before I retire.
Then I hope to start stacking up some miles.
I’ve always thought the Power Tour would be great to do starting from California.
2022 could be the perfect time.
I know some of you were following this and many of us were rooting for 550HP, but it just didn't happen.
Well the cause finally came to the surface.
It was the 50 year old GM Snowflake Cylinder heads, particularly the poor flowing round exhaust port.
There is not a lot of difference in the intake flow, but the exhaust on the AFRs is 32-42% better!!!
And the exhaust to intake ratio is a poor 65% on the snowflakes and it jumps to 82% on the AFRs.
The computer model showed that big 70cfm exhaust flow difference is directly related to HP.
Switch the heads in the model and bang...560HP.
INSTANT 80HP
The snowflakes are just that ..old.. and the AFRs are just that much better.
Neither of my builders or I were expecting that big of a difference, but yeah, they are 50 years old. I was guessing half that.
I am not changing the real engine now, and at least the difference is mostly above 5000rpm.
But, if I would have known 1-1/2 years ago, what I know now, ....hmmm.....
So now YOU know.... Do you want to run old OEM heads....or new ones?
This is a GREAT thread ! Thanks for sharing it OP ! I remember reading in a Vizard book that someone from back in the day used like 40 lbs of welding rods to modify 074 heads (I assume making a D shaped exhaust port to improve flow), and working the intake side to near 400cfm (lift not specified). I think the heads need the exhaust ports welded up and ported, a cam with more exhaust duration, maybe 1.8:1 rockers on the exhaust only, and some intake work. Can’t hurt to have the carb CFM increased too (slab milling the throttle shafts, K&N Stubstack, general de-burring massaging working over), and you’ll find the “missing” power. Was the compression ratio ever stated or did I miss it ? Thanks again OP ! Good luck with it.
EDIT: So I went and dug the book out, it was 22 lbs of welding rod and 470 cfm of airflow ! at unspecified lift...this was for a pro stock team back in the day, running a 394 ci big block (de-stroked)...
Last edited by c6silver; Dec 10, 2020 at 09:10 AM.
