Maximum Torque Specialists Cadillac Forums  

Go Back   Maximum Torque Specialists Cadillac Forums > Cadillac Tech > Engines

Engines All things technical about Cadillac engines.

Reply
 
Thread Tools Display Modes
Old 09-07-2005, 05:53 PM   #1
Chevcaddy41
Junior Member
 
Join Date: Sep 2005
Posts: 8
Default 700R4 fuel mileage

This is only my second post, first was over a year ago on the old forum. Just got finished with a summer long test of a 700R4 behind my 70-500. Results are very disappointing, Cadillacs are NOT Chevys. My car is a 41 Chevy coupe with a 70 ElDorado engine with an Edelbrock intake, Holley carb and headers, thru flowmaster mufflers, 9" Ford rear. Last year I drove the car to Cumberland Md. for the Western Maryland Street Rod Roundup and got 20 miles to the gallon with the old turbo 400 and 2:73 gears. This year when I really needed the mileage I got 15 with 700R4 and 3:00 gears, 129 miles one way. Mileage was even worse going to Hershey with the 700R4 and 3:73 gears, I think around 13.8, then went to Columbus with 3:50 gears, got 14.4 miles per gallon. Guess who just sold a rebuilt 700R4 to some Chevy nut for cheap? Got home from Cumberland Sunday night, the 700R4 was out Monday afternoon, Turbo 400 got put in Tuesday, just got back from test drive with the old 400. I won't be changing trannys again, 400's are the only way to go. Thanks for letting this old Mountaineer vent!!
Chevcaddy41 is offline   Reply With Quote
Old 09-08-2005, 09:06 PM   #2
Vern
Member
 
Join Date: May 2005
Location: Dayton, OH
Posts: 70
Default

Interesting. I'm not a fan of the 700R4 either but it is surprising. What stall converter did you run in each? Did you have a lock up converter with a manual lock up? How much does your car weigh?

I can get 17mpg on the interestate with a 3800lb including me Cutlass with a 2004R, lock up convereter, 3.42s, 28" tires, 8.5 rear, and q-jet on 89 octane. This is despite a 230@50 duration cam. It runs mid 12s at 109.

My buddy has a cab & half full size chevy truck with a 2004R tranny, lock up converter, q-jet and 230@50duration cam in a 454. His mileage sucked bad as in 10mpg in town barely 14 on the hwy. But his converter was never right. It would start to noticeably slip going up a grade if he gave it any gas. I think the truck was to heavy for his converter.
__________________
87 442, 509ci Cad, Q-jet, Ebrock, Street portd heads, 230@50 518lift, Headers, 200-4R, Electric fans/fuel pump, 17mpg hwy, 87 GN, TE-60 turbo, Stretch intercooler, 42.5lb injectors, 3" downpipe, Methanol injection, 22mpg, Both to do high 11s on pump gas
Vern is offline   Reply With Quote
Old 09-09-2005, 03:14 PM   #3
Chevcaddy41
Junior Member
 
Join Date: Sep 2005
Posts: 8
Default 700R4 fuel mileage

Vern, the converter and trans were a package from TCI. Tranny and converter were what they recomended for my car. The converter did have a manual lockup. The car is a 41 Chevy coupe, 1970 ElDorado 500 engine, 9" ford rear, 28 inch tall tires, weights about 3400 pounds. Now you got to remember when I'm coming out from home I'm on I-79 in WVA. and I-68 and there ain't many level spots, this is real mountains down here. Anyway the turbo 400 is back in and the 700R4 is sold.
Chevcaddy41 is offline   Reply With Quote
Old 09-11-2005, 12:34 PM   #4
Chevcaddy41
Junior Member
 
Join Date: Sep 2005
Posts: 8
Default 700R4 fuel mileage

Vern, 17mpg on the interstate isn't that great, I got 20 last year with the turbo 400. I can get as much as 23 going to Columbus once I get thru Pa and get on some flat roads and the rice burners stay out of my way. Mid 12s are kool for a street car tho.
Chevcaddy41 is offline   Reply With Quote
Old 09-11-2005, 01:44 PM   #5
Modly
Member
 
Join Date: May 2005
Posts: 43
Default

That is quite some fuel economy you are pulling out of that thing. I don't think I've ever heard anybody getting 20 out of a Cadillac engine, without it being a complete dog.

I'm trying to figure out what would be wrong with that 700r4. My best guess is that it never locked up, or it had too much throttle. I know with my old truck (Chevy powered, but had a 700r4), If I went over 75 or so MPH, it would downshift to third gear (Which 700r4s do, when you give it more than a certain amount of throttle). Without an aftermarket modulator, it would just up and downshift like nuts at a certain speed, which killed economy. Assuming it was doing this up/downshift process over and over, and with that higher (numerically) gear ratio, it is pretty reasonable to see why it got lower fuel economy.

Honestly with the torque I'd get out of a 500, I'd want a 4L80 if I wanted a 4 speed tranny.
Modly is offline   Reply With Quote
Old 09-11-2005, 03:33 PM   #6
Vern
Member
 
Join Date: May 2005
Location: Dayton, OH
Posts: 70
Default

No 17 is not great but I think its not bad considering the cam and that I can get it while doing 75mph. I think if I was useing a th400 with the same everything else it would have gotten maybe 12 and turned a lot more rpms. Your mileage with the th400 & 500 Cad is the best I have ever heard of. I am a fan of the th400 behind the big Cad for most applications and like I said not much of a fan of the 700r4. But I suspect something was wrong that it did worse than your th400.
__________________
87 442, 509ci Cad, Q-jet, Ebrock, Street portd heads, 230@50 518lift, Headers, 200-4R, Electric fans/fuel pump, 17mpg hwy, 87 GN, TE-60 turbo, Stretch intercooler, 42.5lb injectors, 3" downpipe, Methanol injection, 22mpg, Both to do high 11s on pump gas
Vern is offline   Reply With Quote
Old 09-12-2005, 10:43 AM   #7
CadillacPat
Member
 
Join Date: May 2005
Location: Oscoda, MI (200 mi N of Detroit on Lake Huron)
Posts: 91
Default 700R4 fuel mileage

Chevcaddy41,
This topic has been brought up before on the old board. According to Al, a 500 in a '76 Sedan DeVille with his MT3 cam (rebuilt of course) will get 22 mpg on the highway. You have to understand that this cam is more technologically advanced than the cam of the day. It is made for very low speed torque (not over 4000 rpm). His MT5 cam is a modern version of the old '72/'73 Caddy cam and makes more hp and torque, with slightly lower mileage (than the MT3; if you can still get about 20 mpg with this cam, the extra power is worth it if you are not for all out fuel economy).
As far as the 700, gearing is everything. The stock Caddy cam likes an engine speed of about 2600 rpm-it's torque peak. So, with a 400, you need about a 2.93 rear, which came stock with 472/500's in the day. On my car, with a stock '73 500 and 400 ('84 Coupe with a 2.41 rear), the car gets it's best mileage around 70 mph-about 2200 rpm. With a lower rear like a 2.93, the car is supposed to get better mileage. This is because the engine WOULD be running at a more efficient speed. Also, with the 2.41 rear, and running over 70 mph, the car has much more drag to overcome. This is why a slightly lower gear at 70 mph should net more mileage. Currently, I get about 15 mpg at 70, but, the engine is in serious need of a rebuild. I am in the process of rebuilding either a 425 or 472 before winter, and will rebuilt a 500 next spring, probably at tax time.
Consequenly, this is why you got your best mileage with the 400 and 2.73's. With the 700 and 3.00's, you had an effective rear-end ratio of about 2.10. With the 700 and 3.73's, about 2.61. While the effective ratio of 2.10 is way too low, especially with a 230-degree cam, the 2.61 should be close enough to the 400's with 2.73's effective ratio of 2.73. a 3.50 rear would also be bad. Since you are running a 230-degree cam, which raises the engine's torque peak, a ratio of about 3.00 should work well as a compromise. You also have to remember that for most of us, around town driving is the most common, and the higher engine speed should net a slightly higher city mileage. While it may seem a bit high, the engine would turn about 2500 rpm at 65 mph with these gears (my tires are about 28" tall; 235/70/15).
__________________
Stock '72 Coupe w/ upgraded HEI; '98 C3500 to be upgraded to a 500/TH400; '93 Blazer needing a 500 (bad 5.7); '84 Coupe (engineless).
CadillacPat is offline   Reply With Quote
Old 09-12-2005, 10:44 AM   #8
CadillacPat
Member
 
Join Date: May 2005
Location: Oscoda, MI (200 mi N of Detroit on Lake Huron)
Posts: 91
Default 700R4 fuel mileage

Chevcaddy41,
This topic has been brought up before on the old board. According to Al, a 500 in a '76 Sedan DeVille with his MT3 cam (rebuilt of course) will get 22 mpg on the highway. You have to understand that this cam is more technologically advanced than the cam of the day. It is made for very low speed torque (not over 4000 rpm). His MT5 cam is a modern version of the old '72/'73 Caddy cam and makes more hp and torque, with slightly lower mileage (than the MT3; if you can still get about 20 mpg with this cam, the extra power is worth it if you are not for all out fuel economy).
As far as the 700, gearing is everything. The stock Caddy cam likes an engine speed of about 2600 rpm-it's torque peak. So, with a 400, you need about a 2.93 rear, which came stock with 472/500's in the day. On my car, with a stock '73 500 and 400 ('84 Coupe with a 2.41 rear), the car gets it's best mileage around 70 mph-about 2200 rpm. With a lower rear like a 2.93, the car is supposed to get better mileage. This is because the engine WOULD be running at a more efficient speed. Also, with the 2.41 rear, and running over 70 mph, the car has much more drag to overcome. This is why a slightly lower gear at 70 mph should net more mileage. Currently, I get about 15 mpg at 70, but, the engine is in seriously need of a rebuild. I am in the process of rebuilding either a 425 or 472 before winter, and will rebuilt a 500 next spring, probably at tax time.
__________________
Stock '72 Coupe w/ upgraded HEI; '98 C3500 to be upgraded to a 500/TH400; '93 Blazer needing a 500 (bad 5.7); '84 Coupe (engineless).
CadillacPat is offline   Reply With Quote
Old 09-12-2005, 10:46 AM   #9
CadillacPat
Member
 
Join Date: May 2005
Location: Oscoda, MI (200 mi N of Detroit on Lake Huron)
Posts: 91
Default 700R4 fuel mileage

Chevcaddy41,
This topic has been brought up before on the old board. According to Al, a 500 in a '76 Sedan DeVille with his MT3 cam (rebuilt of course) will get 22 mpg on the highway. You have to understand that this cam is more technologically advanced than the cam of the day. It is made for very low speed torque (not over 4000 rpm). His MT5 cam is a modern version of the old '72/'73 Caddy cam and makes more hp and torque, with slightly lower mileage (than the MT3; if you can still get about 20 mpg with this cam, the extra power is worth it if you are not for all out fuel economy).
As far as the 700, gearing is everything. The stock Caddy cam likes an engine speed of about 2600 rpm-it's torque peak. So, with a 400, you need about a 2.93 rear, which came stock with 472/500's in the day. On my car, with a stock '73 500 and 400 ('84 Coupe with a 2.41 rear), the car gets it's best mileage around 70 mph-about 2200 rpm. With a lower rear like a 2.93, the car is supposed to get better mileage. This is because the engine WOULD be running at a more efficient speed. Also, with the 2.41 rear, and running over 70 mph, the car has much more drag to overcome. This is why a slightly lower gear at 70 mph should net more mileage. Currently, I get about 15 mpg at 70, but, the engine is in seriously need of a rebuild. I am in the process of rebuilding either a 425 or 472 before winter, and will rebuilt a 500 next spring, probably at tax time.
__________________
Stock '72 Coupe w/ upgraded HEI; '98 C3500 to be upgraded to a 500/TH400; '93 Blazer needing a 500 (bad 5.7); '84 Coupe (engineless).
CadillacPat is offline   Reply With Quote
Old 09-13-2005, 05:06 PM   #10
zenish
Member
 
Join Date: Sep 2005
Location: stallings.nc
Posts: 47
Default

chevcaddy.did you try leaving the 700r4 in drive and check the mileage?in drive it has the same gear ratio as the turbo 400.
__________________
1964 c10,1975 500/turbo 400 mostly stock.
zenish is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 11:32 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.